Electrical Engineering Training.pdf

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Electrical Engineering Training Series.

Back • Home • Up • Next Click here to order Electronic Components Online Introduction to Matter, Energy, and Electricity Matter, Energy, and Electricity Batteries Direct Current Introduction to Alternating Current and Transformers Inductive and Capacitive Reactance Transformers Useful AC Formulas Introduction to Circuit Protection, Control, and Measuring Circuit Measurement Circuit Protection Devices Circuit Control Devices

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Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading Electrical Conductors Wiring Techniques Schematic Reading

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Introduction to Generators and Motors Direct Current Generators Direct Current Motors Alternating Current Generators Alternating Current Motors Introduction to Electronic Emission, Tubes, and Power Introduction to Electron Tubes Special Purpose Tubes Power Supplies Introduction to Solid-State Devices and Power Supplies Semiconductor Diodes Transistors Special Devices Solid-State Power Supplies Introduction to Amplifiers Amplifiers Video and RF Amplifiers Special Amplifiers Introduction to Wave-Generation and Wave-Shaping Circuits Tuned Circuits Oscillators Waveforms and Wave Generators Wave Shaping Introduction to Wave Propagation, Transmission Lines, and Antennas Wave Propagation Radio Wave Propagation Principles of Transmission Lines Antennas Microwave Principles

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Waveguide Theory and Application Microwave Components and Circuits Microwave Antennas Modulation Principles Amplitude Modulation Angle and Pulse Modulation Demodulation Introduction to Number Systems and Logic Circuits Number Systems Fundamental Logic Circuits Special Logic Circuits Introduction to Microelectronics Microelectronics Miniature/Microminiature repair program Miniature and microminiature repair procedures Principles of Synchros, Servos, and Gyros Synchros Servos Gyros Related Devices Introduction to Test Equipment Test Equipment and Administration Use Miscellaneous Measurements Basic Meters Common Test Equipment Special Application Test Equipment The Oscilloscope and spectrum analyzer Radio-Frequency Communications Principles Introduction to Radio Introduction to Communications Theory

Fundamental Systems Equipment Introduction to Satellite Communications Introduction to Miscellaneous Communications Radar Principles Radar Radar Radar Radar

Fundamentals Subsystems Indicators and Antennas System Maintenance

Test Methods and Practices Basic Measurements Component Testing Quantitative Measurements Qualitative Measurements Introduction to Waveform Interpretation Introduction to Digital Computers Electronic Computers Hardware Software Data Representation and Communication Magnetic Recording Introduction to Magnetic Recording Magnetic Tape Magnetic Tape Recorder Magnetic Tape Recording Specifications Digital Magnetic Tape Recording Magnetic Disk Recording Fiber Optics Background on fiber optics Optical fibers and cables Optical sources and fiber optic transmitters Order this information in Adobe PDF Printable Format

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Book1 Matter Energy and Electricity

Home • Up • Next Click here to order Electronic Components Online Matter, Energy, and Electricity Matter Energy Levels Valence Nature of Charges Magnetism Magnetic Poles Theories of magnetism, Webers Theory Lines of Force Magnetic Shielding Electrical Charges Voltage Produced by Friction Voltage Produced by Chemical Action Electric Current Measurement of Current Conductance Wattage Rating Chapter 1 Summary Chapter 1 Answers

Chapter 2 - Batteries

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Primary Cell Polarization of the cell Other Types of Cells Series-Connected Cells Battery Construction Safety Precautions With Batteries Chapter 2 Summary Chapter 2 Answers

Chapter 3 - Direct Current The basic electric circuit Ohm's law Application of ohm's law Graphical analysis of the basic circuit Power Power rating Power conversion and efficiency Series DC circuits Current in a Series Circuit Voltage in a Series Circuit Power in a Series Circuit Rules for Series DC Circuits Kirchhoff's voltage law Application of Kirchhoff's voltage law Series Aiding and Opposing Sources Circuit terms and characteristics Open circuit Short circuit Source resistance Power transfer and efficiency Parallel DC circuits Voltage in a Parallel Circuit Current in a Parallel Circuit Resistance in a Parallel Circuit Power in a Parallel Circuit Equivalent Circuits Rules for Parallel DC Circuits

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Series-parallel DC circuits Practice Circuit Problem Redrawing circuits for clarity Redrawing a Complex Circuit Effects of open and short circuits Voltage dividers Multiple-load voltage dividers Power in the voltage divider Voltage divider with positive and negative voltage requirements Practical application of voltage dividers Equivalent circuit techniques Danger signals Electrical fires Summary Rules for series DC circuits Rules for parallel DC circuits

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Matter, Energy, and Electricity

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CHAPTER 1 MATTER, ENERGY, AND ELECTRICITY LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.

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Upon completing this chapter, you will be able to: 1. State the meanings of and the relationship between matter, element, nucleus, compound, molecule, mixture, atom, electron, proton, neutron, energy, valence, valence shell, and ion. 2. State the meanings of and the relationship between kinetic energy, potential energy, photons, electron orbits, energy levels, and shells and subshells.

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3. State, in terms of valence, the differences between a conductor, an insulator, and a semiconductor, and list some materials which make the best conductors and insulators. 4. State the definition of static electricity and explain how static electricity is generated. 5. State the meanings of retentivity, reluctance, permeability, ferromagnetism, natural magnet, and artificial magnet as used to describe magnetic materials.

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6. State the Weber and domain theories of magnetism and list six characteristics of magnetic lines of force (magnetic flux), including their relation to magnetic induction, shielding, shape, and storage. 7. State, using the water analogy, how a difference of potential (a voltage or an electromotive force) can exist. Convert volts to microvolts, to millivolts, and to kilovolts. 8. List six methods for producing a voltage (emf) and state the operating principles of and the uses for each method. 9. State the meanings of electron current, random drift, directed drift, and ampere, and indicate the direction that an electric current flows. 10. State the relationship of current to voltage and convert amperes to milliamperes and microamperes. 11. State the definitions of and the terms and symbols for resistance and conductance, and how the temperature, contents, length and cross-sectional area of a conductor affect its resistance and conductance values. 12. List the physical and operating characteristics of and the symbols, ratings, and uses for various types of resistors; use the color code to identify resistor values.

INTRODUCTION The origin of the modern technical and electronic Navy stretches back to the beginning of naval history, when the first navies were no more than small fleets of wooden ships, using windfilled sails and manned oars. The need for technicians then was restricted to a navigator and semiskilled seamen who could handle the sails. As time passed, larger ships that carried more sail were built. These ships, encouraging exploration and commerce, helped to establish world trade routes. Soon strong navies were needed to guard these sea lanes. Countries established their own navies to protect their citizens, commercial ships, and shipping lanes against pirates and warring nations. With the addition of mounted armament, gunners joined the ship's company of skilled or semiskilled technicians. The advent of the steam engine signaled the rise of an energy source more practical than either wind and sails or manpower. With this technological advancement, the need for competent operators and technicians increased. However, the big call for operators and technicians in the U.S. Navy came in the early part of the 20th century, when power sources, means of communication, modes of detection, and armaments moved with amazing rapidity toward involved technical development. Electric motors and generators by then had become the most widely used sources of power. Telephone systems were well established on board ship, and radio was being used more and more to relay messages from ship to ship and from ship to shore. Listening devices were employed to detect submarines. Complex optical systems were used to aim large naval rifles. Mines and torpedoes became highly developed, effective weapons, and airplanes joined the Navy team. During the years after World War I, the Navy became more electricity and electronic minded. It

was recognized that a better system of communications was needed aboard each ship, and between the ships, planes, submarines, and shore installations; and that weaponry advances were needed to keep pace with worldwide developments in that field. This growing technology carried with it the awareness that an equally skilled force of technicians was needed for maintenance and service duties. World War II proved that all of the expense of providing equipment for the fleet and of training personnel to handle that equipment paid great dividends. The U. S. Navy had the modern equipment and highly trained personnel needed to defeat the powerful fleets of the enemy. Today there is scarcely anyone on board a Navy ship who does not use electrical or electronic equipment. This equipment is needed in systems of electric lighting and power, intercommunications, radio, radar, sonar, loran, remote metering, weapon aiming, and certain types of mines and torpedoes. The Navy needs trained operators and technicians in this challenging field of electronics and electricity. It is to achieve this end that this module, and others like it, are published.

MATTER, ENERGY, AND ELECTRICITY If there are roots to western science, they no doubt lie under the rubble that was once ancient Greece. With the exception of the Greeks, ancient people had little interest in the structure of materials. They accepted a solid as being just that a continuous, uninterrupted substance. One Greek school of thought believed that if a piece of matter, such as copper, were subdivided, it could be done indefinitely and still only that material would be found. Others reasoned that there must be a limit to the number of subdivisions that could be made and have the material still retain its original characteristics. They held fast to the idea that there must be a basic particle upon which all substances are built. Recent experiments have revealed that there are, indeed, several basic particles, or building blocks within all substances. The following paragraphs explain how substances are classified as elements and compounds, and are made up of molecules and atoms. This, then, will be a learning experience about protons, electrons, valence, energy levels, and the physics of electricity.

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Chapter 2 - Batteries

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CHAPTER 2 BATTERIES LEARNING OBJECTIVES Upon completing this chapter, you will be able to: 1. State the purpose of a cell. 2. State the purpose of the three parts of a cell. 3. State the difference between the two types of cells. 4. Explain the chemical process that takes place in the primary and secondary cells. 5. Recognize and define the terms electrochemical action, anode, cathode, and electrolyte. 6. State the causes of polarization and local action and describe methods of preventing these effects. 7. Identify the parts of a dry cell. 8. Identify the various dry cells in use today and some of their capabilities and limitations. 9. Identify the four basic secondary cells, their construction, capabilities, and limitations. 10. Define a battery, and identify the three ways of combining cells to form a battery. 11. Describe general maintenance procedures for batteries including the use of the hydrometer, battery capacity, and rating and battery charging. 12. Identify the five types of battery charges. 13. Observe the safety precautions for working with and around batteries.

INTRODUCTION

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The purpose of this chapter is to introduce and explain the basic theory and characteristics of batteries. The batteries which are discussed and illustrated have been selected as representative of many models and types which are used in the Navy today. No attempt has been made to cover every type of battery in use, however, after completing this chapter you will have a good working knowledge of the batteries which are in general use. First, you will learn about the building block of all batteries, the CELL. The explanation will explore the physical makeup of the cell and the methods used to combine cells to provide useful voltage, current, and power. The chemistry of the cell and how chemical action is used to convert chemical energy to electrical energy are also discussed. In addition, the care, maintenance, and operation of batteries, as well as some of the safety precautions that should be followed while working with and around batteries are discussed. Batteries are widely used as sources of direct-current electrical energy in automobiles, boats, aircraft, ships, portable electric/electronic equipment, and lighting equipment. In some instances, they are used as the only source of power; while in others, they are used as a secondary or standby power source. A battery consists of a number of cells assembled in a common container and connected together to function as a source of electrical power.

THE CELL A cell is a device that transforms chemical energy into electrical energy. The simplest cell, known as either a galvanic or voltaic cell, is shown in figure 2-1. It consists of a piece of carbon (C) and a piece of zinc (Zn) suspended in a jar that contains a solution of water (H20) and sulfuric acid (H2S04) called the electrolyte.

Figure 2-1. - Simple voltaic or galvanic cell.

The cell is the fundamental unit of the battery. A simple cell consists of two electrodes placed in a container that holds the electrolyte. In some cells the container acts as one of the electrodes and, in this case, is acted upon by the electrolyte. This will be covered in more detail later.

ELECTRODES The electrodes are the conductors by which the current leaves or returns to the electrolyte. In the simple cell, they are carbon and zinc strips that are placed in the electrolyte; while in the dry cell (fig. 2-2), they are the carbon rod in the center and zinc container in which the cell is assembled.

Figure 2-2. - Dry cell, cross-sectional view.

ELECTROLYTE The electrolyte is the solution that acts upon the electrodes. The electrolyte, which provides a path for electron flow, may be a salt, an acid, or an alkaline solution. In the simple galvanic cell, the electrolyte is in a liquid form. In the dry cell, the electrolyte is a paste.

CONTAINER The container which may be constructed of one of many different materials provides a means of holding (containing) the electrolyte. The container is also used to mount the electrodes. In the voltaic cell the container must be constructed of a material that will not be acted upon by the

electrolyte. Q1.What is the purpose of a cell? Q2.What are the three parts of a cell? Q3.What is the purpose of each of the three parts of a cell?

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Direct Current

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DIRECT CURRENT LEARNING OBJECTIVES Upon completing this chapter, you will be able to: Identify the term schematic diagram and identify the components in a circuit from a simple schematic diagram. State the equation for Ohm's law and describe the effects on current caused by changes in a circuit. Given simple graphs of current versus power and voltage versus power, determine the value of circuit power for a given current and voltage. Identify the term power, and state three formulas for computing power. Compute circuit and component power in series, parallel, and combination circuits. Compute the efficiency of an electrical device. Solve for unknown quantities of resistance, current, and voltage in a series circuit. Describe how voltage polarities are assigned to the voltage drops across resistors when Kirchhoff's voltage law is used. State the voltage at the reference point in a circuit. Define open and short circuits and describe their effects on a circuit.

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State the meaning of the term source resistance and describe its effect on a circuit. Describe in terms of circuit values the circuit condition needed for maximum power transfer. Compute efficiency of power transfer in a circuit. Solve for unknown quantities of resistance, current, and voltage in a parallel circuit. State the significance of the polarity assigned to a current when using Kirchhoff's current law. State the meaning of the term equivalent resistance. Compute resistance, current, voltage, and power in voltage dividers. Describe the method by which a single voltage divider can provide both positive and negative voltages. Recognize the safety precautions associated with the hazard of electrical shock. Identify the first aid procedures for a victim of electrical shock.

INTRODUCTION The material covered in this chapter contains many new terms that are explained as you progress through the material. The basic dc circuit is the easiest to understand, so the chapter begins with the basic circuit and from there works into the basic schematic diagram of that circuit. The schematic diagram is used in all your future work in electricity and electronics. It is very important that you become familiar with the symbols that are used. This chapter also explains how to determine the total resistance, current, voltage, and power in a series, parallel, or combination circuit through the use of Ohm's and Kirchhoff's laws. The voltage divider network, series, parallel, and series-parallel practice problem circuits will be used for practical examples of what you have learned.

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Book 2

Back • Home • Up • Next Click here to order Electronic Components Online CONCEPTS OF ALTERNATING CURRENT Voltage Waveform Magnetic Field of a Coil Basic AC Generation Frequency Alternating Current Values Effective Value of a Sine Wave Sine Waves in Phase Ohm's law in AC Circuits Summary Answers

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INDUCTANCE Self-Inductance Inductance Unit of Inductance L/R Time Constant Power Loss in an Inductor Series Inductors without Magnetic Coupling Summary Answers

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CAPACITANCE The Farad Charging and Discharging a Capacitor Charge and discharge of an RC Series Circuit RC Time Constant Capacitors in series and parallel Fixed Capacitor Color codes for Capacitors Summary Answers

Inductive and Capacitive Reactance Inductive Reactance Capacitors and Alternating Current Capacitive Reactance Reactance, Impedance, and Power Relationships in AC Circuits Impedance Ohm's Law for AC Power in AC Circuits Calculating Reactive Power in AC Circuits Calculating Apparent Power in AC Circuits Power Factor Power Factor Correction Series RLC Circuits Inductive and Capacitive Reactance Summary Inductive and Capacitive Reactance Answers

Transformers Basic Operation of a Transformer Hollow-Core Transformers Transformer Windings Schematic Symbols for Transformers

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Producing a Counter EMF Coefficient of a coupling Effect of a load Power Relationships between primary and secondary windings Transformer Ratings Safety Effects of Current on the body Transformers Summary Transformers Answers

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INDUCTIVE AND CAPACITIVE REACTANCE

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Click here to order Electronic Components Online INDUCTIVE AND CAPACITIVE REACTANCE LEARNING OBJECTIVES Upon completion of this chapter you will be able to:

State the effects an inductor has on a change in current and a capacitor has on a change in voltage. State the phase relationships between current and voltage in an inductor and in a capacitor. State the terms for the opposition an inductor and a capacitor offer to ac Write the formulas for inductive and capacitive reactances. State the effects of a change in frequency on X L and XC.

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State the effects of a change in inductance on X L and a change in capacitance on XC. Write the formula for determining total reactance (X); compute total reactance (X) in a series circuit; and indicate whether the total reactance is capacitive or inductive. State the term given to the total opposition (Z) in an ac circuit. Write the formula for impedance, and calculate the impedance in a series circuit when the values of XC, X L, and R are given. Write the Ohm's law formulas used to determine voltage and current in an ac circuit. Define true power, reactive power, and apparent power; state the unit of measurement for and the formula used to calculate each. State the definition of and write the formula for power factor. Given the power factor and values of X and R in an ac circuit, compute the value of reactance in the circuit, and state the type of reactance that must be connected in the circuit to correct the power factor to unity (1). State the difference between calculating impedance in a series ac circuit and in a parallel ac circuit.

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INDUCTIVE AND CAPACITIVE REACTANCE You have already learned how inductance and capacitance individually behave in a direct current circuit. In this chapter you will be shown how inductance, capacitance, and resistance affect alternating current. INDUCTANCE AND ALTERNATING CURRENT This might be a good place to recall what you learned about phase in chapter 1. When two things are in step, going through a cycle together, falling together and rising together, they are in phase. When they are out of phase, the angle of lead or lag-the number of electrical degrees by which one of the values leads or lags the other-is a measure of the amount they are out of step. The time it takes the current in an inductor to build up to maximum and to fall to zero is important for another reason. It helps illustrate a very useful characteristic of inductive circuits-the current through the inductor always lags the voltage across the inductor. A circuit having pure resistance (if such a thing were possible) would have the alternating current through it and the voltage across it rising and failing together. This is illustrated in figure 4-1(A),which shows the sine waves for current and voltage in a purely resistive circuit having an ac source. The current and voltage do not have the same amplitude, but they are in phase. In the case of a circuit having inductance, the opposing force of the counter emf would be enough to keep the current from remaining in phase with the applied voltage. You learned that in a dc circuit containing pure inductance the current took time to rise to maximum even though the full applied voltage was immediately at maximum. Figure 4-1(B) shows the wave forms for a purely inductive ac circuit in steps of quarter-cycles. Figure 4-1. - Voltage and current waveforms in an inductive circuit.

With an ac voltage, in the first quarter-cycle (0° to 90°) the applied ac voltage is continually increasing. If there was no inductance in the circuit, the current would also increase during this first quartercycle. You know this circuit does have inductance. Since inductance opposes any change in current flow, no current flows during the first quarter-cycle. In the next quarter-cycle (90° to 180°) the voltage decreases back to zero; current begins to flow in the circuit and reaches a maximum value at the same instant the voltage reaches zero. The applied voltage now begins to build up to maximum in the other direction, to be followed by the resulting current. When the voltage again reaches its maximum at the end of the third quarter-cycle (270°) all values are exactly opposite to what

they were during the first half-cycle. The applied voltage leads the resulting current by one quarter-cycle or 90 degrees. To complete the full 360° cycle of the voltage, the voltage again decreases to zero and the current builds to a maximum value. You must not get the idea that any of these values stops cold at a particular instant. Until the applied voltage is removed, both current and voltage are always changing in amplitude and direction. As you know the sine wave can be compared to a circle. Just as you mark off a circle into 360 degrees, you can mark off the time of one cycle of a sine wave into 360 electrical degrees. This relationship is shown in figure 4-2. By referring to this figure you can see why the current is said to lag the voltage, in a purely inductive circuit, by 90 degrees. Furthermore, by referring to figures 4-2 and 4-1(A) you can see why the current and voltage are said to be in phase in a purely resistive circuit. In a circuit having both resistance and inductance then, as you would expect, the current lags the voltage by an amount somewhere between 0 and 90 degrees. Figure 4-2. - Comparison of sine wave and circle in an inductive circuit.

A simple memory aid to help you remember the relationship of voltage and current in an inductive circuit is the word ELI. Since E is the symbol for voltage, L is the symbol for inductance, and I is the symbol for current; the word ELI demonstrates that current comes after (Lags) voltage in an inductor. Q.1 What effect does an inductor have on a change in current? Q.2 What is the phase relationship between current and voltage in an inductor?

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TRANSFORMERS

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Click here to order Electronic Components Online TRANSFORMERS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: State the meaning of "transformer action." State the physical characteristics of a transformer, including the basic parts, common core materials, and main core types. State the names given to the source and load windings of a transformer. State the difference in construction between a highand a low-voltage transformer.

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Identify transformer symbols as to the type of transformer each symbol represents and the method used to denote transformer phasing. State the meaning of a "noload condition" and "exciting current" relative to a transformer. State what causes voltage to be developed across the secondary of a transformer and the effect of cemf in a transformer. State the meaning of leakage flux and its effect on the coefficient of coupling. Identify a transformer as step up or step down and state the current ratio of a transformer when given the turns ratio. Solve for primary voltage, secondary voltage, primary current and number of turns in the secondary given various transformer values. State the mathematical relationship between the power in the primary and the power in the secondary of a transformer and compute efficiency of a transformer. State the three power losses in a transformer. State the reason a transformer should not be operated at a lower frequency than that specified for the transformer. List five different types of transformers according to their applications.

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State the standard color coding for a power transformer. State the general safety precautions you should observe when working with transformers and other electrical components. TRANSFORMERS The information in this chapter is on the construction, theory, operation, and the various uses of transformers. Safety precautions to be observed by a person working with transformers are also discussed. A TRANSFORMER is a device that transfers electrical energy from one circuit to another by electromagnetic induction (transformer action). The electrical energy is always transferred without a change in frequency, but may involve changes in magnitudes of voltage and current. Because a transformer works on the principle of electromagnetic induction, it must be used with an input source voltage that varies in amplitude. There are many types of power that fit this description; for ease of explanation and understanding, transformer action will be explained using an ac voltage as the input source. In a preceding chapter you learned that alternating current has certain advantages over direct current. One important advantage is that when ac is used, the voltage and current levels can be increased or decreased by means of a transformer. As you know, the amount of power used by the load of an electrical circuit is equal to the current in the load times the voltage across the load, or P = EI. If, for example, the load in an electrical circuit requires an input of 2 amperes at 10 volts (20 watts) and the source is capable of delivering only 1 ampere at 20 volts, the circuit could not normally be used with this particular source. However, if a transformer is connected between the source and the load, the voltage can be decreased (stepped down) to 10 volts and the current increased (stepped up) to 2 amperes. Notice in the above case that the power remains the same. That is, 20 volts times 1

ampere equals the same power as 10 volts times 2 amperes. Q.1 What is meant by "transformer action?"

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Useful AC Formulas

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Click here to order Electronic Components Online USEFUL AC FORMULAS PERIOD TIME (t)

FREQUENCY (f) Join Integrated Publishing's Discussion Group

AVERAGE VOLTAGE OR CURRENT

EFFECTIVE VALUE OF VOLTAGE OR CURRENT

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MAXIMUM VOLTAGE OR CURRENT

OHM'S LAW OF AC CIRCUIT CONTAINING ONLY RESISTANCE

L/R TIME CONSTANT (TC)

MUTUAL INDUCTANCE (M)

TOTAL INDUCTANCE (LT) Series without magnetic coupling

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TOTAL INDUCTANCE (LT) PARALLEL (No magnetic coupling)

CAPACITANCE (C)

RC TIME CONSTANT (t)

TOTAL CAPACITANCE (CT) SERIES

TOTAL CAPACITANCE (CT) PARALLEL

INDUCTIVE REACTANCE (XL)

CAPACITIVE REACTANCE (XC)

IMPEDANCE (Z)

OHM'S LAW FOR REACTIVE CIRCUITS

OHM'S LAW FOR CIRCUITS CONTAINING RESISTANCE AND REACTANCE

REACTIVE POWER

APPARENT POWER

POWER FACTOR (PF)

VOLTAGE ACROSS THE SECONDARY (Es)

VOLTAGE ACROSS THE PRIMARY (Ep)

CURRENT ACROSS THE SECONDARY (Is)

CURRENT ACROSS THE PRIMARY (Ip)

TRANSFORMER EFFICIENCY

TRIGONOMETRIC FUNCTIONS In a right triangle, there are several relationships which always hold

true. These relationships pertain to the length of the sides of a right triangle, and the way the lengths are affected by the angles between them. An understanding of these relationships, called trigonometric functions, is essential for solving problems in a-c circuits such as power factor, impedance, voltage drops, and so forth. To be a RIGHT triangle, a triangle must have a "square" corner; one in which there is exactly 90° between two of the sides. Trigonometric functions do not apply to any other type of triangle. This type of triangle is shown in figure V-1. By use of the trigonometric functions, it is possible to determine the UNKNOWN length of one or more sides of a triangle, or the number of degrees in UNKNOWN angles, depending on what is presently known about the triangle. For instance, if the lengths of any two sides are known, the third side and both angles &thetas; (theta) and Φ (phi) may be determined. The triangle may also be solved if the length of any one side and one of the angles (&thetas; or Φ in fig. V-1) are known. Figure V-1. - A right triangle.

The first basic fact of triangles is that IN ANY RIGHT TRIANGLE, THE SUM OF THE THREE ANGLES FORMED INSIDE THE TRIANGLE MUST ALWAYS EQUAL 180°. If one angle is always 90° (a right angle) then the sum of the other two angles must always be 90°.

thus, if angle &thetas; is known, Φ may be quickly determined. For instance, if &thetas; is 30°m what is Φ ?

Also, if &thetas; is known, Φ may be determined in the same manner. The second basic fact you must understand is that FOR EVERY DIFFERENT COMBINATION OF ANGLES IN A TRIANGLE, THERE IS A DEFINITE RATIO BETWEEN THE LENGTHS OF THE THREE SIDES. Consider the triangle in figure V-2, consisting of the base, side B; the altitude, side A; and the hypotenuse, side C. (The hypotenuse is always the longest side, and is always opposite the 90° angle.) Figure V-2. - A 30° - 60° - 90° triangle.

If angle &thetas; is 30°, Φ must be 60°. With &thetas; equal to 30°, the ratio of the length of side B to side C is 0.866 to 1. That is, if the hypotenuse is 1 inch long, the side adjacent to &thetas;, side B, is 0.866 inch long. Also, with &thetas; equal to 30°, the ratio of side A to side C is 0.5 to 1. That is, with the hypotenuse 1 inch long, the side opposite to &thetas; (side A) is 0.5 inch long. With &thetas; still at 30°, side A is 0.5774 of the length of B. With the combination of angles given (30°-60°-90°) these are the ONLY

ratios of lengths that will "fit" to form a right triangle. Note that three ratios are shown to exist for the given value of &thetas;: the ratio B\C which is always referred to as the COSINE ratio of &thetas;, the ratio A\C, which is always the SINE ratio of &thetas;, and the ratio A\B, which is always the TANGENT ratio of &thetas;. If &thetas; changes, all three ratios change, because the lengths of the sides (base and altitude) change. There is a set of ratios for every increment between 0° and 90°. These angular ratios, or sine, cosine, and tangent functions, are listed for each degree and tenth of degree in a table at the end of this appendix. In this table, the length of the hypotenuse of a triangle is considered fixed. Thus, the ratios of length given refer to the manner in which sides A and B vary with relation to each other and in relation to side C, as angle &thetas; is varied from 0° to 90°. The solution of problems in trigonometry (solution of triangles is much simpler when the table of trigonometric functions is used properly. The most common ways in which it is used will be shown by solving a series of exemplary problems. Problem 1: If the hypotenuse of the triangle (side C) in figure V-3 is 10 inches long, and angle &thetas; is 33°, how long are sides B and A? Figure V-3. - Problem 1.

Solution: The ratio B/C is the cosine function. By checking the table of functions, You will find that the cosine of 33° is 0.8387. This means that the length of B is 0.8387 the length of side C. If side C is 10 inches long, then side B must be 10 X 0.8387, or 8.387 inches in length. To determine the length of side A, use the sine function, the ratio A\C. Again consulting the table of functions, you will find that the sine of 33° is 0.5446. Thus, side A must be 10 X 0.5446, or 5.446 inches in length.

Problem 2: The triangle in figure V-4 has a base 74.2 feet long, and hypotenuse 100 feet long. What is &thetas;, and how long is side A? Figure V4. - Problem 2.

Solution: When no angles are given, you Must always solve for a known angle first. The ratio B\C is the cosine of the unknown angle &thetas;; therefore 74.2/100 or 0.742, is the cosine of the unknown angle. Locating 0.742 as a cosine value in the table, you find that it is the cosine of 42.1°. That is, &thetas; = 42.1°. With &thetas; known, side A is solved for by use of the sine ratio A/C. The sine of 42.1°, according to the table, is 0.6704. Therefore, side A is 100 X 0.6704, or 67.04 feet long. Problem 3: In the triangle in figure V-5, the base is 3 units long, and the altitude is 4 units. What is &thetas;, and how long is the hypotenuse? Solution: With the information given, the tangent of &thetas; may be determined. Tan &thgr; = A/B = 4/3 = 1.33. Figure V-5. - Problem 3.

Locating the value 1.33 as a tangent value in the table of functions, you find it to be the tangent of 53.1°. Therefore, &thetas; = 53.1°.

Once &thetas; is known, either the sine or cosine ratio may be used to determine the length of the hypotenuse. The cosine of 53.1° is 0.6004. This indicates that the base of 3 units is 0.6004, the length of the hypotenuse. Therefore, the hypotenuse is 3/0.6004, or 5 units in length. Using the sine ratio, the hypotenuse is 4/0.7997, or 5 units in length. In the foregoing explanations and problems, the sides of triangles were given in inches, feet, and units. In applying trigonometry to ac circuit problems, these units of measure will be replaced by such values given in ohms, amperes, volts, and watts. Angle &thetas; will be the phase angle between (source) voltage and circuit current. However, the solution of these a-c problems is accomplished in exactly the same manner as the foregoing problems. Only the units and some terminology are changed.

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Book 3

Back • Home • Up • Next Click here to order Electronic Components Online Circuit Measurement Basic Meter Movements Permanent-Magnet Moving-Coil movement Compass and alternating current D'Arsonval meter movement Indicating Alternating Current Ammeters Ammeter Sensitivity Range Selection Voltmeters Making a voltmeter from a current sensitive meter movement Electrostatic Meter Movement Ohmmeters Ohmmeter Ranges Shunt Ohmmeter Ohmmeter safety precautions Multimeter Multimeter Movements Other Meters Wattmeter Frequency Meters Meter Reognition

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Frequency Meter Reading Summary Answers

Circuit Protection Devices Introduction Circuit protection devices Schematic Symbols Fuse Recognition Identification of fuses Fuseholders Fuseholder Identification Replacement of fuses. Circuit Breakers Magnetic trip element Trip-Free/Nontrip-Free Circuit Breakers The thermal-magnetic trip element Summary Answers

Circuit Control Devices Schematic symbol recognition. Schematic symbols of switches Rotary switch in automobile ignition system Switch schematic symbols. Snap-Acting Switches Switch Rating Replacement Switches and Their Characteristics Relays Maintenance of Relays Summary Answers Order this information in Adobe PDF Printable Format

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CIRCUIT MEASUREMENT

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Click here to order Electronic Components Online CIRCUIT MEASUREMENT LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Upon completion of this chapter you will be able to:

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State two ways circuit measurement is used, why incircuit meters are used, and one advantage of out-ofcircuit meters. Order this information on CDRom

State the way in which a compass reacts to a conducting wire including the compass reaction to increasing and decreasing dc and ac high and low frequencies. State how a d'Arsonval meter movement reacts to dc. State the purpose of a rectifier as used in ac meters. State the meaning of the term "damping" as it applies to meter movements and describe two methods by which damping is accomplished. Identify average value as the value of ac measured and effective value (rms) as the ac value indicated on ac meter scales. Identify three meter movements that measure dc or ac without the use of a rectifier. State the electrical quantity measured by an ammeter, the way in which an ammeter is connected in a circuit, and the effect of an ammeter upon a circuit. Define ammeter sensitivity. State the method used to allow an ammeter to measure different ranges and the reason for using the highest range when connecting an ammeter to a circuit. List the safety precautions for ammeter use.

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State the electrical quantity measured by a voltmeter, the way in which a voltmeter is connected in a circuit, the way in which a voltmeter affects the circuit being measured, and the way in which a voltmeter is made from a current reacting meter movement. Define voltmeter sensitivity. State the method used to allow a voltmeter to measure different ranges and the reason for using the highest range when connecting a voltmeter to a circuit. Identify the type of meter movement that reacts to voltage and the most common use of this movement. List the safety precautions for voltmeter use. State the electrical quantity measured by an ohmmeter, the second use of an ohmmeter, and the way in which an ohmmeter is connected to a resistance being measured. State the method used to allow an ohmmeter to measure different ranges and the area of an ohmmeter scale that should be used when measuring resistance. State the two types of ohmmeters and the way in which each can be identified. List the safety precautions for ohmmeter use.

State the primary reason for using a megger and the method of using it. Identify normal and abnormal indications on a megger. List the safety precautions for megger use. State how a multimeter differs from other meters, the reason a multimeter is preferred over separate meters, and the way in which a multimeter is changed from a voltage measuring device to a current measuring device. State the reason the ac and dc scales of a multimeter differ, the reason for having a mirror on the scale of a multimeter, and the proper way of reading a multimeter using the mirror. List the safety precautions for multimeter use. State the purpose of a hookon type voltameter. State the electrical quantity measured by a wattmeter and a watt-hour meter. Identify the two types of frequency meters. Identify the type of meter and interpret the meter reading from scale presentations of an ammeter; a voltmeter; an ohmmeter; a megger; a multimeter (current, voltage, and resistance examples); a wattmeter; a watt-hour meter; and a frequency meter (vibrating reed and movingdisk types).

CIRCUIT MEASUREMENT This chapter will acquaint you with the basics of circuit measurement and some of the devices used to measure voltage, current, resistance, power, and frequency. There are other quantities involved in electrical circuits, such as capacitance, inductance, impedance, true power, and effective power. It is possible to measure any circuit quantity once you are able to select and use the proper circuit measuring device. You will NOT know all there is to know about circuit measuring devices (test equipment) when you finish this chapter. That is beyond the scope of this chapter and even beyond the scope of this training series. However, more information on test equipment is provided in another portion of this training series. A question which you might ask before starting this chapter is "Why do I need to know about circuit measurement?" If you intend to accomplish anything in the field of electricity and electronics, you must be aware of the forces acting inside the circuits with which you work. Modules 1 and 2 of this training series introduced you to the physics involved in the study of electricity and to the fundamental concepts of direct and alternating current. The terms voltage (volts), current (amperes), and resistance (ohms) were explained, as well as the various circuit elements; e.g., resistors, capacitors, inductors, transformers, and batteries. In explaining these terms and elements to you, schematic symbols and schematic diagrams were used. In many of these schematic diagrams, a meter was represented in the circuit, as shown in figure 1-1. As you recall, the current in a dc circuit with 6 volts across a 6-ohm resistor is 1 ampere. The @(UPPERCASE A) in figure 1-1 is the symbol for an ammeter. An ammeter is a device that measures current. The name "ammeter" comes from the fact that it is a meter used to measure current (in amperes), and thus is called an AMpere METER, or AMMETER.

The ammeter in figure 1-1 is measuring a current of 1 ampere with the voltage and resistance values given. Figure 1-1. - A simple representative circuit.

In the discussion and explanation of electrical and electronic circuits, the quantities in the circuit (voltage, current, and resistance) are important. If you can measure the electrical quantities in a circuit, it is easier to understand what is happening in that circuit. This is especially true when you are troubleshooting defective circuits. By measuring the voltage, current, capacitance, inductance, impedance, and resistance in a circuit, you can determine why the circuit is not doing what it is supposed to do. For instance, you can determine why a radio is not receiving or transmitting, why your automobile will not start, or why an electric oven is not working. Measurement will also assist you in determining why an electrical component (resistor, capacitor, inductor) is not doing its job. The measurement of the electrical parameters quantities in a circuit is an essential part of working on electrical and electronic equipment. INTRODUCTION TO CIRCUIT MEASUREMENT Circuit measurement is used to monitor the operation of an electrical or electronic device, or to determine the reason a device is not operating properly. Since electricity is invisible, you must use

some sort of device to determine what is happening in an electrical circuit. Various devices called test equipment are used to measure electrical quantities. The most common types of test equipment use some kind of metering device. IN-CIRCUIT METERS Some electrical and electronic devices have meters built into them. These meters are known as in-circuit meters. An in-circuit meter is used to monitor the operation of the device in which it is installed. Some examples of in-circuit meters are the generator or alternator meter on some automobiles; the voltage, current, and frequency meters on control panels at electrical power plants; and the electrical power meter that records the amount of electricity used in a building. It is not practical to install an in-circuit meter in every circuit. However, it is possible to install an in-circuit meter in each critical or representative circuit to monitor the operation of a piece of electrical equipment. A mere glance at or scan of the in-circuit meters on a control board is often sufficient to tell if the equipment is working properly. While an in-circuit meter will indicate that an electrical device is not functioning properly, the cause of the malfunction is determined by troubleshooting. Troubleshooting is the process of locating and repairing faults in equipment after they have occurred. Since troubleshooting is covered elsewhere in this training series, it will be mentioned here only as it applies to circuit measurement. OUT-OF-CIRCUIT METERS In troubleshooting, it is usually necessary to use a meter that can be connected to the electrical or electronic equipment at various testing points and may be moved from one piece of equipment to another. These meters are generally portable and self-contained, and are known as out-of-circuit meters. Out-of-circuit meters are more versatile than in-circuit meters in that the out-of-circuit meter can be used wherever you wish to

connect it. Therefore, the out-of-circuit meter is more valuable in locating the cause of a malfunction in a device. Q.1 What are two ways that circuit measurement is used?

Q.2 Why are in-circuit meters used? Q.3 What is one advantage of an out-of-circuit meter when it is compared with an in-circuit meter?

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CIRCUIT PROTECTION DEVICES

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Click here to order Electronic Components Online CIRCUIT PROTECTION DEVICES LEARNING OBJECTIVES Upon completion of this chapter you will be able to: State the reasons circuit protection is needed and three conditions requiring circuit protection. Define a direct short, an excessive current condition, and an excessive heat condition. State the way in which circuit protection devices are connected in a circuit. Identify two types of circuit protection devices and label the schematic symbols for each type. Identify a plug-type and a cartridge-type fuse (open and not open) from illustrations.

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List the three characteristics by which fuses are rated and state the meaning of each rating. Identify a plug-type and a cartridge-type fuse (open and not open) from illustrations. List the three categories of time delay rating for fuses and state a use for each type of time-delay rated fuse. List the three categories of time delay rating for fuses and state a use for each type of time-delay rated fuse. Identify fuses as to voltage, current, and time delay ratings using fuses marked with the old military, new military, old commercial, and new commercial systems. List the three categories of time delay rating for fuses and state a use for each type of timedelay rated fuse. Identify a clip-type and a posttype fuseholder from illustrations and identify the connections used on a posttype fuseholder for power source and load connections. List the methods of checking for an open fuse, the items to check when replacing a fuse, the safety precautions to be observed when checking and replacing fuses, and the conditions to be checked for when conducting preventive maintenance on fuses. Select a proper replacement and substitute fuse from a listing of fuses.

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List the five main components of a circuit breaker and the three types of circuit breaker trip elements. Describe the way in which each type of trip element reacts to excessive current. Define the circuit breaker terms trip-free and nontripfree and state one example for the use of each of these types of circuit breakers. List the three time delay ratings of circuit breakers. Define selective tripping, state why it is used, and state the way in which the time delay ratings of circuit breakers are used to design a selective tripping system. Identify the factors used in selecting circuit breakers. List the steps to follow before starting work on a circuit breaker and the items to be checked when maintaining circuit breakers. CIRCUIT PROTECTION DEVICES Electricity, like fire, can be either helpful or harmful to those who use it. A fire can keep people warm and comfortable when it is confined in a campfire or a furnace. It can be dangerous and destructive if it is on the loose and uncontrolled in the woods or in a building. Electricity can provide people with the light to read by or, in a blinding flash, destroy their eyesight. It can help save people's lives, or it can kill them. While we take advantage of the tremendous benefits electricity can provide, we must be careful to protect the people and systems that use it. It is necessary then, that the mighty force of electricity be kept under control at all times. If for some reason it should get out of

control, there must be a method of protecting people and equipment. Devices have been developed to protect people and electrical circuits from currents and voltages outside their normal operating ranges. Some examples of these devices are discussed in this chapter. While you study this chapter, it should be kept in mind that a circuit protection device is used to keep an undesirably large current, voltage, or power surge out of a given part of an electrical circuit.

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CIRCUIT CONTROL DEVICES

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Click here to order Electronic Components Online CIRCUIT CONTROL DEVICES LEARNING OBJECTIVES Upon completion of this chapter you will be able to: State three reasons circuit control devices are used and list three general types of circuit control devices. Identify the schematic symbols for a switch, a solenoid, and a relay. State the difference between a manual and an automatic switch and give an example of each. State the reason multicontact switches are used.

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Identify the schematic symbols for the following switches: Single-pole, doublethrow, Double-pole, singlethrow, Double-pole, doublethrow, Single-break, Doublebreak, Rotary, Wafer State the characteristics of a switch described as a rocker switch. State the possible number of positions for a single-pole, double-throw switch. Identify a type of momentary switch. State the type of switch used to prevent the accidental energizing or deenergizing of a circuit. State the common name for an accurate snap-acting switch. State the meaning of the current and voltage rating of a switch. State the two types of meters you can use to check a switch. Select the proper substitute switch from a list. State the conditions checked for in preventive maintenance of switches. State the operating principle and one example of a solenoid. State the ways in which a solenoid can be checked for proper operation. State the operating principle of a relay and how it differs from a solenoid.

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State the two types of relays according to use. State the ways in which a relay can be checked for proper operation and the procedure for servicing it. CIRCUIT CONTROL DEVICES Circuit control devices are used everywhere that electrical or electronic circuits are used. They are found in submarines, computers, aircraft, televisions, ships, space vehicles, medical instruments, and many other places. In this chapter you will learn what circuit control devices are, how they are used, and some of their characteristics. INTRODUCTION Electricity existed well before the beginning of recorded history. Lightning was a known and feared force to early man, but the practical uses of electricity were not recognized until the late 18th century. The early experimenters in electricity controlled power to their experiments by disconnecting a wire from a battery or by the use of a clutch between a generator and a steam engine. As practical uses were found for electricity, a convenient means for turning power on and off was needed. Telegraph systems, tried as early as the late 1700s and perfected by Morse in the 1830s, used a mechanically operated contact lever for opening and closing the signal circuit. This was later replaced by the hand-operated contact lever or "key." Early power switches were simple hinged beams, arranged to close or open a circuit. The blade-and-jaw knife switch with a wooden, slate, or porcelain base and an insulated handle, was developed a short time later. This was the beginning of circuit control devices. Modern circuit control devices can change their resistance from a few milliohms (when closed) to well over 100,000 megaohms (when open) in a couple of milliseconds. In some circuit control devices, the movement necessary to cause the device to open or close is only .001 inch (.025 millimeters).

NEED FOR CIRCUIT CONTROL Circuit control, in its simplest form, is the application and removal of power. This can also be expressed as turning a circuit on and off or opening and closing a circuit. Before you learn about the types of circuit control devices, you should know why circuit control is needed. If a circuit develops problems that could damage the equipment or endanger personnel, it should be possible to remove the power from that circuit. The circuit protection devices discussed in the last chapter will remove power automatically if current or temperature increase enough to cause the circuit protection device to act. Even with this protection, a manual means of control is needed to allow you to remove power from the circuit before the protection device acts. When you work on a circuit, you often need to remove power from it to connect test equipment or to remove and replace components. When you remove power from a circuit so that you can work on it, be sure to "tag out" the switch to ensure that power is not applied to the circuit while you are working. When work has been completed, power must be restored to the circuit. This will allow you to check the proper operation of the circuit and place it back in service. After the circuit has been checked for proper operation, remove the tag from the power switch. Many electrical devices are used some of the time and not needed at other times. Circuit control devices allow you to turn the device on when it is needed and off when it is not needed. Some devices, like multimeters or televisions, require the selection of a specific function or circuit. A circuit control device makes possible the selection of the particular circuit you wish to use. TYPES OF CIRCUIT CONTROL DEVICES Circuit control devices have many different shapes and sizes, but most circuit control devices are either SWITCHES, SOLENOIDS, or RELAYS.

Figure 3-1 shows an example of each of these types of circuit control devices and their schematic symbols. Figure 3-1. - Typical circuit control devices: RELAY COIL TERMINALS

Figure 3-1, view A, is a simple toggle switch and the schematic symbol for this switch is shown below it. Figure 3-1, view B, is a cutaway view of a solenoid. The schematic symbol below the solenoid is one of the schematic symbols used for this solenoid. Figure 3-1, view C, shows a simple relay. One of the schematic symbols for this relay is shown next to the relay.

Q.1 What are three reasons circuit control is needed? Q.2 What are the three types of circuit control devices? Q.3 Label the schematic symbols shown in figure 3-2 .

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Book 4

Back • Home • Up • Next Click here to order Electronic Components Online Electrical Conductors Circular Mil Circular Mil-Foot Wire Sizes Stranded Wires and Cables Copper-Versus-Aluminum Conductors Conductor Insulation Plastics Insulation Fluorinated Ethylene Propylene (FEP) Paper Insulation Mineral Insulated Woven Covers Coaxial Cable Summary Answers

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Wiring Techniques General Wire-Stripping Instructions Fixture Joint Terminal Lugs Noninsulated Terminal and Splice Insulation Aluminum Terminals and Splices

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Improper crimping procedures eventually cause terminal failure Preinsulated Splices Splice Insulation Soldering Process Alternative Dip-Tinning Procedure Soldering Tools Soldering Gun Resistance Soldering Set Solder Flux Lacing Conductors Single Lace Double Lace Spot Tying Summary Answers Schematic Reading Test Equipment Cable-Marking Systems Shipboard Electronic Equipment Wire-Marking Systems Electrical Diagrams Schematic Diagram Wiring Diagram Safety Summary Answers Order this information in Adobe PDF Printable Format

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ELECTRICAL CONDUCTORS

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Click here to order Electronic Components Online ELECTRICAL CONDUCTORS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC-ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.

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Upon completing this chapter, you should be able to: Recall the definitions of unit size, mil-foot, square mil, and circular mil and the mathematical equations and calculations for each. Define specific resistance and recall the three factors used to calculate it in ohms.

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Describe the proper use of the American Wire Gauge when making wire measurements. Recall the factors required in selecting proper size wire. State the advantages and disadvantages of copper or aluminum as conductors.

Define insulation resistance and dielectric strength including how the dielectric strength of an insulator is determined. Identify the safety precautions to be taken when working with insulating materials. Recall the most common insulators used for extremely high voltages. State the type of conductor protection normally used for shipboard wiring. Recall the design and use of coaxial cable.

ELECTRICAL CONDUCTORS In the previous modules of this training series, you have learned about various circuit components. These components provide the majority of the operating characteristics of any electrical circuit. They are useless, however, if they are not connected together. Conductors are the means used to tie these components together. Many factors determine the type of electrical conductor used to connect components. Some of these factors are the physical size of the conductor, its composition, and its electrical characteristics. Other factors that can determine the choice of a conductor are the weight, the cost, and the environment where the conductor will be used. CONDUCTOR SIZES To compare the resistance and size of one conductor with that of another, we need to establish a standard or unit size. A convenient unit of measurement of the diameter of a conductor is the mil

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(0.001, or one-thousandth of an inch). A convenient unit of conductor length is the foot. The standard unit of size in most cases is the MIL-FOOT. A wire will have a unit size if it has a diameter of 1 mil and a length of 1 foot. SQUARE MIL The square mil is a unit of measurement used to determine the cross-sectional area of a square or rectangular conductor (views A and B of figure 1-1). A square mil is defined as the area of a square, the sides of which are each 1 mil. To obtain the crosssectional area of a square conductor, multiply the dimension of any side of the square by itself. For example, assume that you have a square conductor with a side dimension of 3 mils. Multiply 3 mils by itself (3 mils X 3 mils). This gives you a cross-sectional area of 9 square mils. Figure 1-1. - Cross-sectional areas of conductors.

Q.1 State the reason for the establishment of a "unit size" for conductors. Q.2 Calculate the diameter in MILS of a conductor that has a diameter of 0.375 inch. Q.3 Define a mil-foot. To determine the cross-sectional area of a rectangular conductor,

multiply the length times the width of the end face of the conductor (side is expressed in mils). For example, assume that one side of the rectangular cross-sectional area is 6 mils and the other side is 3 mils. Multiply 6 mils X 3 mils, which equals 18 square mils. Here is another example. Assume that a conductor is 3/8 inch thick and 4 inches wide. The 3/8 inch can be expressed in decimal form as 0.375 inch. Since 1 mil equals 0.001 inch, the thickness of the conductor will be 0.001 X 0.375, or 375 mils. Since the width is 4 inches and there are 1,000 mils per inch, the width will be 4 X 1,000, or 4,000 mils. To determine the cross-sectional area, multiply the length by the width; or 375 mils X 4,000 mils. The area will be 1,500,000 square mils. Q.4 Define a square mil as it relates to a square conductor.

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WIRING TECHNIQUES

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Click here to order Electronic Components Online WIRING TECHNIQUES LEARNING OBJECTIVES Upon completing this chapter, you should be able to: State the basic requirements for any splice and terminal connection, including the preferred wire-stripping method. Join Integrated State the reason the ends of the wire Publishing's are clamped down after a Western Discussion Group Union splice has been made. Explain the major advantage of the crimped terminal over the soldered terminal. Name the two types of insulation commonly used for noninsulated splices and terminal lugs. State an advantage of using Order this preinsulated terminal lugs and the information on CDcolor code used for each. Rom Explain the procedures for crimping terminal lugs with a hand crimp tool.

Recall the physical description and operating procedures for the HT900B/920B compressed air/nitrogen heating tool. Recall the safety precautions for Order this using the compressed air/nitrogen information in heating tool. Print (Hardcopy). Recall the procedures, precautions, and tools associated with soldering. Explain the procedures and precautions for tinning wire. Recall the types of soldering irons and their uses. State the purposes and required properties of flux. State the purpose for lacing conductors. Recall when double lacing of wire bundles is required. Recall the requirements for using spot ties. WIRING TECHNIQUES This chapter will assist you in learning the basic skills of proper wiring techniques. It explains the different ways to terminate and splice electrical conductors. It also discusses various soldering techniques that will assist you in mastering the basic soldering skills. The chapter ends with a discussion of the procedure to be followed when you lace wire bundles within electrical and electronic equipment. CONDUCTOR SPLICES AND TERMINAL CONNECTIONS Conductor splices and connections are an essential part of any electrical circuit. When conductors join each other or connect to a load, splices or terminals must be used. Therefore, it is important that they be properly made. Any electrical circuit is only as good as its weakest link. The basic requirement of any splice or connection is that it be both mechanically and electrically as sound as the conductor or device with which it is used. Quality workmanship and materials must be used to ensure lasting electrical contact, physical strength, and insulation. The most common methods of making splices and connections in electrical cables is explained in the discussion that follows. INSULATION REMOVAL

The preferred method of removing insulation is with a wire-stripping tool, if available. A sharp knife may also be used. Other typical wire strippers in use in the Navy are illustrated in figure 2-1. The hot-blade, rotary, and bench wire strippers (views A, B, and C, respectively) are usually found in shops where large wire bundles are made. When using any of these automatic wire strippers, follow the manufacturer's instructions for adjusting the machine; this avoids nicking, cutting, or otherwise damaging the conductors. The hand wire strippers are common hand tools found throughout the Navy. The hand wire strippers (view D of figure 2-1) are the ones you will most likely be using. Wire strippers vary in size according to wire size and can be ordered for any size needed. Figure 2-1. - Typical wire-stripping tools.

Hand Wire Stripper

The procedure for stripping wire with the hand wire stripper is as follows (refer to figure 2-2): Figure 2-2. - Stripping wire with a hand stripper.

Insert the wire into the center of the correct cutting slot for the wire size to be stripped. The wire sizes are listed on the cutting jaws of the hand wire strippers beneath each slot. After inserting the wire into the proper slot, close the handles together as far as they will go. Slowly release the pressure on the handles so as not to allow the cutting blades to make contact with the stripped conductor. On some of the newer style hand wire strippers, the cutting jaws have a safety lock that helps prevent this from happening. Continue to release pressure until the gripper jaws release the stripped wire, then remove. Knife Stripping A sharp knife may be used to strip the insulation from a conductor. The procedure is much the same as for sharpening a pencil. The knife should be held at approximately a 60° angle to the conductor. Use extreme care when cutting through the insulation to avoid nicking or cutting the conductor. This procedure produces a taper on the cut insulation as shown in figure 2-3.

Figure 2-3. - Knife stripping.

Locally Made Hot-Blade Wire Stripper If you are required to strip a large number of wires, you can use a locally made hot-blade stripper (figure 2-4) as follows: Figure 2-4. - Locally made hot-blade stripper.

In the end of a piece of copper strip, cut a sharp-edged "V."

At the bottom of the "V," make a wire slot of suitable diameter for the size wire to be stripped. Fasten the copper strip around the heating element of an electric soldering iron as shown in figure 2-4. The iron must be rated at 100 watts or greater in order to transfer enough heat to the copper strip to melt the wire insulation. Lay the wire or cable to be stripped in the "V"; a clean channel will be melted in the insulation. Remove the insulation with a slight pull.

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SCHEMATIC READING

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Click here to order Electronic Components Online SCHEMATIC READING LEARNING OBJECTIVES Upon completing this chapter, you should be able to: Recognize the marking system for cables to include shipboard and test equipment systems. Recognize the marking system for wire to include aircraft and shipboard electronic equipment systems. Recall the seven types of electrical diagrams and the functional design of each. Recall basic safety practices and precautions for working around electrical and electronic systems. SCHEMATIC READING

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This chapter is divided into three subtopicss - (1) cable and wiremarling systems, (2) electrical and electronic diagrams, and (3) safety precautions. First, we will discuss the systems used for marking cables and wires. We will then explain each of the types of diagrams you will encounter when troubleshooting, testing, repairing, or learning about circuit or system operation. Finally, we will briefly discuss safety practices relating to working around electrical and electronic systems. CABLE- AND WIRE-MARKING SYSTEMS Cables and wires are marked to give the technician a means of tracing them when troubleshooting and repairing electrical and electronic systems. Numerous cable- and wire-marking systems are used in ships, aircraft, and equipment throughout the Navy. A few of these systems are briefly discussed here to acquaint you with how marking systems are used. For a specific system or equipment, you should refer to tile applicable technical manual. CABLE-MARKING SYSTEMS Two typical cable-marking systems you are likely to see are the (1) shipboard and (2) test equipment cable-marking systems. Shipboard Cable-Marking Systems Metal tags embossed with the cable markings are used to identify all permanently installed shipboard electrical cables. These cable tags (figure 3-1) are placed on cables close to each point of connection, and on both sides of decks, bulkheads, and other barriers to identify the cables. The markings on the cable tags identify cables for maintenance and circuit repairs. The tags show (1) the SERVICE LETTER, which identifies a particular electrical system, (2) the CIRCUIT LETTER or LETTERS, which identify a specific circuit within a particular system, and (3) the CABLE NUMBER, which identifies an individual cable in a specific circuit.

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Figure 3-1. - Cable tag.

In figure 3-1, note that the cable is marked "C-MB144." The letter C denotes the service; in this case, the IC (interior communication) system. The letters MB denote the circuit; in this case, the engineorder circuit. The number 144 denotes cable number 144 of the MB circuit. Q.1 Why must cables and wires be identified? Q.2 Where would you find the wire identification system for a specific piece of equipment? Q.3 What does the cable number identify?

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Book 5

Back • Home • Up • Next Click here to order Electronic Components Online Direct Current Generators The elementary dc generator Effects of adding additional coils and poles Electromagnetic Poles Armature Reaction Motor reaction in a generator Armature Losses Hysteresis Losses Field Excitation Generator Construction Voltage Control Amplidynes Safety Precautions Summary Answers

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Direct Current Motors Counter EMF Practical DC Motors Shunt Motor Direction of Rotation

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Armature Reaction Manual and Automatic Starters Summary Answers

Alternating Current Generators

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Practical Alternators Single-phase alternators Three-phase alternators Frequency Principles of AC voltage control Summary Answers

Alternating Current Motors Rotating magnetic fields Three-phase rotating fields Induction Motors Single-phase induction motors Shaded-pole induction motors Summary Answers Order this information in Adobe PDF Printable Format

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DIRECT CURRENT GENERATORS

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Click here to order Electronic Components Online DIRECT CURRENT GENERATORS LEARNING OBJECTIVES Upon completion of the chapter you will be able to: State the principle by which generators convert mechanical energy to electrical energy. State the rule to be applied when you Join Integrated determine the direction of induced emf Publishing's in a coil. Discussion Group State the purpose of slip rings. State the reason why no emf is induced in a rotating coil as it passes through a neutral plane. State what component causes a generator to produce direct current rather than alternating current. Identify the point at which the brush Order this contact should change from one information on CDcommutator segment to the next. Rom State how field strength can be varied in a dc generator. Describe the cause of sparking between brushes and commutator. State what is meant by "armature reaction." Order this State the purpose of interpoles. information in

Explain the effect of motor reaction in a Print (Hardcopy). dc generator. Explain the causes of armature losses. List the types of armatures used in dc generators. State the three classifications of dc generators. State the term that applies to voltage variation from no-load to full-load conditions and how it is expressed as a percentage. State the term that describes the use of two or more generators to supply a common load. State the purpose of a dc generator that has been modified to function as an amplidyne. INTRODUCTION A generator is a machine that converts mechanical energy into electrical energy by using the principle of magnetic induction. This principle is explained as follows: Whenever a conductor is moved within a magnetic field in such a way that the conductor cuts across magnetic lines of flux, voltage is generated in the conductor. The AMOUNT of voltage generated depends on (1) the strength of the magnetic field, (2) the angle at which the conductor cuts the magnetic field, (3) the speed at which the conductor is moved, and (4) the length of the conductor within the magnetic field. The POLARITY of the voltage depends on the direction of the magnetic lines of flux and the direction of movement of the conductor. To determine the direction of current in a given situation, the LEFT-HAND RULE FOR GENERATORS is used. This rule is explained in the following manner. Extend the thumb, forefinger, and middle finger of your left hand at right angles to one another, as shown in figure 1-1. Point your thumb in the direction the conductor is being moved. Point your forefinger in the direction of magnetic flux (from north to south). Your middle finger will then point in the direction of current flow in an external circuit to which the voltage is applied. Figure 1-1. - Left-hand rule for generators.

THE ELEMENTARY GENERATOR The simplest elementary generator that can be built is an ac generator. Basic generating principles are most easily explained through the use of the elementary ac generator. For this reason, the ac generator will be discussed first. The dc generator will be discussed later. An elementary generator (fig. 1-2) consists of a wire loop placed so that it can be rotated in a stationary magnetic field. This will produce an induced emf in the loop. Sliding contacts (brushes) connect the loop to an external circuit load in order to pick up or use the induced emf. Figure 1-2. - The elementary generator.

The pole pieces (marked N and S) provide the magnetic field. The pole pieces are shaped and positioned as shown to concentrate the magnetic field as close as possible to the wire loop. The loop of wire that rotates through the field is called the ARMATURE. The ends of the armature loop are connected to rings called SLIP RINGS. They rotate with the armature. The brushes, usually made of carbon, with wires attached to them, ride against the rings. The generated voltage appears across these brushes. The elementary generator produces a voltage in the following manner (fig. 1-3). The armature loop is rotated in a clockwise direction. The initial or starting point is shown at position A. (This will be considered the zero-degree position.) At 0° the armature loop is perpendicular to the magnetic field. The black and white conductors of the loop are moving parallel to the field. The instant the conductors are moving parallel to the magnetic field, they do not cut any lines of flux. Therefore, no emf is induced in the conductors, and the meter at position A indicates zero. This position is called the NEUTRAL PLANE. As the armature loop rotates from position A (0°) to position B (90°), the conductors cut through more and more lines of flux, at a continually increasing angle. At 90° they are cutting through a maximum number of lines of flux and at maximum angle. The result is that between 0° and 90°, the induced emf in the conductors builds up from zero to a maximum value. Observe that from 0° to 90°, the black conductor cuts DOWN through the field. At the same time the white conductor cuts UP through the field. The induced emfs in the conductors are series-adding. This means the resultant voltage across the brushes (the terminal voltage) is the sum of the two induced voltages. The meter at position B reads maximum value. As the armature loop continues rotating from 90° (position B) to 180° (position C), the conductors which were cutting through a maximum number of lines of flux at position B now cut through fewer lines. They are again moving parallel to the magnetic field at position C. They no longer cut through any lines of flux. As the armature rotates from 90° to 180°, the induced voltage will decrease to zero in the same manner that it increased during the

rotation from 0° to 90°. The meter again reads zero. From 0° to 180° the conductors of the armature loop have been moving in the same direction through the magnetic field. Therefore, the polarity of the induced voltage has remained the same. This is shown by points A through C on the graph. As the loop rotates beyond 180° (position C), through 270° (position D), and back to the initial or starting point (position A), the direction of the cutting action of the conductors through the magnetic field reverses. Now the black conductor cuts UP through the field while the white conductor cuts DOWN through the field. As a result, the polarity of the induced voltage reverses. Following the sequence shown by graph points C, D, and back to A, the voltage will be in the direction opposite to that shown from points A, B, and C. The terminal voltage will be the same as it was from A to C except that the polarity is reversed (as shown by the meter deflection at position D). The voltage output waveform for the complete revolution of the loop is shown on the graph in figure 1-3. Figure 1-3. - Output voltage of an elementary generator during one revolution.

Q.1 Generators convert mechanical motion to electrical energy using what principle? Q.2 What rule should you use to determine the direction of induced emf in a coil?

Q.3 What is the purpose of the slip rings? Q.4 Why is no emf induced in a rotating coil when it passes through the neutral plane?

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DIRECT CURRENT MOTORS

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Click here to order Electronic Components Online DIRECT CURRENT MOTORS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: State the factors that determine the direction of rotation in a dc motor. State the right-hand rule for motors. Describe the main differences and Join Integrated similarities between a dc generator Publishing's and a dc motor. Discussion Group Describe the cause and effect of counter emf in a dc motor. Explain the term "load" as it pertains to an electric motor. List the advantages and disadvantages of the different types of dc motors. Compare the types of armatures and Order this uses for each. information on CDDiscuss the means of controlling the Rom speed and direction of a dc motor. Describe the effect of armature reaction in a dc motor.

Explain the need for a starting resistor in a dc motor. INTRODUCTION The dc motor is a mechanical workhorse, that can be used in many different ways. Many large pieces of equipment depend on a dc motor for their power to move. The speed and direction of rotation of a dc motor are easily controlled. This makes it especially useful for operating equipment, such as winches, cranes, and missile launchers, which must move in different directions and at varying speeds. PRINCIPLES OF OPERATION The operation of a dc motor is based on the following principle: A current-carrying conductor placed in a magnetic field, perpendicular to the lines of flux, tends to move in a direction perpendicular to the magnetic lines of flux. There is a definite relationship between the direction of the magnetic field, the direction of current in the conductor, and the direction in which the conductor tends to move. This relationship is best explained by using the RIGHT-HAND RULE FOR MOTORS (fig. 2-1). Figure 2-1. - Right-hand rule for motors.

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To find the direction of motion of a conductor, extend the thumb, forefinger, and middle finger of your right hand so they are at right angles to each other. If the forefinger is pointed in the direction of magnetic flux (north to south) and the middle finger is pointed in the direction of current flow in the conductor, the thumb will point in the direction the conductor will move. Stated very simply, a dc motor rotates as a result of two magnetic fields interacting with each other. The armature of a dc motor acts like an electromagnet when current flows through its coils. Since the armature is located within the magnetic field of the field poles, these two magnetic fields interact. Like magnetic poles repel each other, and unlike magnetic poles attract each other. As in the dc generator, the dc motor has field poles that are stationary and an armature that turns on bearings in the space between the field poles. The armature of a dc motor has windings on it just like the armature of a dc generator. These windings are also connected to commutator segments. A dc motor consists of the same components as a dc generator. In fact, most dc

generators can be made to act as motors, and vice versa. Look at the simple dc motor shown in figure 2-2. It has two field poles, one a north pole and one a south pole. The magnetic lines of force extend across the opening between the poles from north to south. Figure 2-2. - Dc motor armature rotation.

The armature in this simple dc motor is a single loop of wire, just as in the simple armature you studied at the beginning of the chapter on dc generators. The loop of wire in the dc motor, however, has current flowing through it from an external source. This current causes a magnetic field to be produced. This field is indicated by the dotted line through the loops. The loop (armature) field is both attracted and repelled by the field from the field poles. Since the current through the loop goes around in the direction of the arrows, the north pole of the armature is at the upper left, and the south pole of the armature is at the lower right, as shown in figure 2-2, (view A). Of course, as the loop (armature) turns, these magnetic poles turn with it. Now, as shown in the illustrations, the north armature pole is repelled from the north field pole and attracted to the right by the south field pole. Likewise, the south armature pole is repelled from the south field pole and is attracted to the left by the north field pole. This action causes the armature to turn in a clockwise direction, as shown in figure 2-2 (view B). After the loop has turned far enough so that its north pole is exactly opposite the south field pole, the brushes advance to the next segments. This changes the direction of current flow through the armature loop. Also, it changes the polarity of the armature field, as shown in figure 2-2 (view C). The magnetic fields again repel and attract each other, and the armature continues to turn.

In this simple motor, the momentum of the rotating armature carries the armature past the position where the unlike poles are exactly lined up. However, if these fields are exactly lined up when the armature current is turned on, there is no momentum to start the armature moving. In this case, the motor would not rotate. It would be necessary to give a motor like this a spin to start it. This disadvantage does not exist when there are more turns on the armature, because there is more than one armature field. No two armature fields could be exactly aligned with the field from the field poles at the same time. Q.1 What factors determine the direction of rotation in a dc motor? Q.2 The right-hand rule for motors is used to find the relationship between what motor characteristics? Q.3 What are the differences between the components of a dc generator and a dc motor?

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ALTERNATING CURRENT GENERATORS

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Click here to order Electronic Components Online ALTERNATING CURRENT GENERATORS LEARNING OBJECTIVES Upon completion of this chapter, you will be able to: Describe the principle of magnetic induction as it applies to ac generators. Describe the differences between the two basic types of ac generators. List the advantages and disadvantages of the two types of ac generators. Describe exciter generators within alternators; discuss construction and purpose. Compare the types of rotors used in ac generators, and the applications of each type to different prime movers.

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Explain the factors that determine the maximum power output of an ac generator, and the effect of these factors in rating generators. Explain the operation of multiphase ac generators and compare with singlephase. Describe the relationships between the individual output and resultant vectorial sum voltages in multiphase generators. Explain, using diagrams, the different methods of connecting three-phase alternators and transformers. List the factors that determine the frequency and voltage of the alternator output. Explain the terms voltage control and voltage regulation in ac generators, and list the factors that affect each quantity. Describe the purpose and procedure of parallel generator operation. INTRODUCTION Most of the electrical power used aboard Navy ships and aircraft as well as in civilian applications is ac. As a result, the ac generator is the most important means of producing electrical power. Ac generators, generally called alternators, vary greatly in size depending upon the load to which they supply power. For example, the alternators in use at hydroelectric plants, such as Hoover Dam, are tremendous in size, generating thousands of kilowatts at very high voltage levels. Another example is the alternator in a typical automobile, which is very small by comparison. It weighs only a few pounds and produces between 100 and 200 watts of power, usually at a potential of 12 volts.

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Many of the terms and principles covered in this chapter will be familiar to you. They are the same as those covered in the chapter on dc generators. You are encouraged to refer back, as needed, and to refer to any other source that will help you master the subject of this chapter. No one source meets the complete needs of everyone. BASIC AC GENERATORS Regardless of size, all electrical generators, whether dc or ac, depend upon the principle of magnetic induction. An emf is induced in a coil as a result of (1) a coil cutting through a magnetic field, or (2) a magnetic field cutting through a coil. As long as there is relative motion between a conductor and a magnetic field, a voltage will be induced in the conductor. That part of a generator that produces the magnetic field is called the field. That part in which the voltage is induced is called the armature. For relative motion to take place between the conductor and the magnetic field, all generators must have two mechanical parts - a rotor and a stator. The ROTor is the part that ROTates; the STATor is the part that remains STATionary. In a dc generator, the armature is always the rotor. In alternators, the armature may be either the rotor or stator. Q.1 Magnetic induction occurs when there is relative motion between what two elements? ROTATING-ARMATURE ALTERNATORS The rotating-armature alternator is similar in construction to the dc generator in that the armature rotates in a stationary magnetic field as shown in figure 3-1, view A. In the dc generator, the emf generated in the armature windings is converted from ac to dc by means of the commutator. In the alternator, the generated ac is brought to the load unchanged by means of slip rings. The rotating armature is found only in alternators of low power rating and generally is not used to supply electric power in large quantities. Figure 3-1. - Types of ac generators.

ROTATING-FIELD ALTERNATORS The rotating-field alternator has a stationary armature winding and a rotating-field winding as shown in figure 31, view B The advantage of having a stationary armature winding is that the generated voltage can be connected directly to the load. A rotating armature requires slip rings and brushes to conduct the current from the armature to the load. The armature, brushes, and slip rings are difficult to insulate, and arc-overs and short circuits can result at high voltages. For this reason, high-voltage alternators are usually of the rotating-field type. Since the voltage

applied to the rotating field is low voltage dc, the problem of high voltage arc-over at the slip rings does not exist. The stationary armature, or stator, of this type of alternator holds the windings that are cut by the rotating magnetic field. The voltage generated in the armature as a result of this cutting action is the ac power that will be applied to the load. The stators of all rotating-field alternators are about the same. The stator consists of a laminated iron core with the armature windings embedded in this core as shown in figure 3-2. The core is secured to the stator frame. Figure 3-2. - Stationary armature windings.

Q.2 What is the part of an alternator in which the output voltage is generated? Q.3 What are the two basic types of alternators? Q.4 What is the main advantage of the rotating field alternator?

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ALTERNATING CURRENT MOTORS

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Click here to order Electronic Components Online ALTERNATING CURRENT MOTORS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: List three basic types of ac motors and describe the characteristics of each type. Describe the characteristics of a series motor that enable it to be used as a universal motor. Explain the relationships of the individual phases of multiphase voltages as they produce rotating magnetic fields in ac motors. Describe the placement of stator windings in two-phase, ac motors using rotating fields.

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List the similarities and differences between the stator windings of two-phase and three-phase ac motors. State the primary application of synchronous motors, and explain the characteristics that make them suitable for that application. Describe the features that make the ac induction motor the most widely used of electric motors. Describe the difference between the rotating field of multiphase motors and the "apparent" rotating field of single-phase motors. Explain the operation of splitphase windings in singlephase ac induction motors. Describe the effects of shaded poles in single-phase, ac induction motors. INTRODUCTION Most of the power-generating systems, ashore and afloat, produce ac. For this reason a majority of the motors used throughout the Navy are designed to operate on ac. There are other advantages in the use of ac motors besides the wide availability of ac power. In general, ac motors cost less than dc motors. Some types of ac motors do not use brushes and commutators. This eliminates many problems of maintenance and wear. It also eliminates the problem of dangerous sparking. An ac motor is particularly well suited for constant-speed applications. This is because its speed is determined by the frequency of the ac voltage applied to the motor terminals.

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The dc motor is better suited than an ac motor for some uses, such as those that require variable-speeds. An ac motor can also be made with variable speed characteristics but only within certain limits. Industry builds ac motors in different sizes, shapes, and ratings for many different types of jobs. These motors are designed for use with either polyphase or single-phase power systems. It is not possible here to cover all aspects of the subject of ac motors. Only the principles of the most commonly used types are dealt with in this chapter. In this chapter, ac motors will be divided into (1) series, (2) synchronous, and (3) induction motors. Single-phase and polyphase motors will be discussed. Synchronous motors, for purposes of this chapter, may be considered as polyphase motors, of constant speed, whose rotors are energized with dc voltage. Induction motors, single-phase or polyphase, whose rotors are energized by induction, are the most commonly used ac motor. The series ac motor, in a sense, is a familiar type of motor. It is very similar to the dc motor that was covered in chapter 2 and will serve as a bridge between the old and the new. Q.1 What are the three basic types of ac motors? SERIES AC MOTOR A series ac motor is the same electrically as a dc series motor. Refer to figure 4-1 and use the left-hand rule for the polarity of coils. You can see that the instantaneous magnetic polarities of the armature and field oppose each other, and motor action results. Now, reverse the current by reversing the polarity of the input. Note that the field magnetic polarity still opposes the armature magnetic polarity. This is because the reversal effects both the armature and the field. The ac input causes these reversals to take place continuously. Figure 4-1. - Series ac motor.

The construction of the ac series motor differs slightly from the dc series motor. Special metals, laminations, and windings are used. They reduce losses caused by eddy currents, hysteresis, and high reactance. Dc power can be used to drive an ac series motor efficiently, but the opposite is not true. The characteristics of a series ac motor are similar to those of a series dc motor. It is a varying-speed machine. It has low speeds for large loads and high speeds for light loads. The starting torque is very high. Series motors are used for driving fans, electric drills, and other small appliances. Since the series ac motor has the same general characteristics as the series dc motor, a series motor has been designed that can operate both on ac and dc. This ac/dc motor is called a universal motor. It finds wide use in small electric appliances. Universal motors operate at lower efficiency than either the ac or dc series motor. They are built in small sizes only. Universal motors do not

operate on polyphase ac power. Q.2 Series motors are generally used to operate what type of equipment? Q.3 Why are series motors sometimes called universal motors?

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Book 6

Back • Home • Up • Next Click here to order Electronic Components Online INTRODUCTION TO ELECTRON TUBES The diode tube Diode operation with alternating voltage Plates The Envelope Plate Dissipation Introduction to grid bias Factors affecting triode operation Types of biasing Shunt grid leak biasing Operating classifications of tube amplifiers Mu and transconductance Interelectrode capacitance The pentode Summary Answers

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SPECIAL Beam power and power pentode tubes Power amplifier Planar tubes

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Gas-filled tubes The cathode-ray tube (CRT) Electrostatic Deflection Summary of the CRT Safety Summary Answers

POWER SUPPLIES Rectifiers The Conventional Full-Wave Rectifier The Bridge Rectifier Filters The Capacitor Filter The LC choke input filter Half-wave rectifier with an LC choke-input filter. Resistor-Capacitor (RC) Filters LC Capacitor-Input Filter Voltage Regulation Regulators Basic VR Tube Regulator Circuit VR Tubes Connected in Parallel Current Regulation Troubleshooting power supplies Summary Answers

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INTRODUCTION TO ELECTRON TUBES

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Click here to order Electronic Components Online INTRODUCTION TO ELECTRON TUBES LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.

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Upon completion of this chapter, you will be able to: State the principle of thermionic emission and the Edison Effect and give the reasons for electron movement in vacuum tubes. Identify the schematic representation for the various electron tubes and their elements.

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Explain how the diode, triode, tetrode, and pentode electron tubes are constructed, the purpose of the various elements of the tube, and the theory of operation associated with each tube. State the advantages, disadvantages, and limitations of the various types of electron tubes. Describe amplification in the electron tube, the classes of amplification, and how amplification is obtained. Explain biasing and the effect of bias in the electron tube circuit. Describe the effects the physical structure of a tube has on electron tube operation and name the four most important tube constants that affect efficient tube operation. Describe, through the use of a characteristic curve, the operating parameters of the electron tube. INTRODUCTION TO ELECTRON TUBES In previous study you have learned that current flows in the conductor of a completed circuit when a voltage is present. You learned that current and voltage always obey certain laws. In electronics, the laws still apply. You will use them continuously in working with electronic circuits. One basic difference in electronic circuits that will at first seem to violate the basic laws is that electrons flow across a gap, a break in the circuit in which there appears to be no conductor. A large part of the field of electronics and the entire field of electron tubes are concerned with the flow and control of these electrons "across the

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gap." The following paragraphs will explain this interesting phenomenon. THERMIONIC EMISSION You will remember that metallic conductors contain many free electrons, which at any given instant are not bound to atoms. These free electrons are in continuous motion. The higher the temperature of the conductor, the more agitated are the free electrons, and the faster they move. A temperature can be reached where some of the free electrons become so agitated that they actually escape from the conductor. They "boil" from the conductor's surface. The process is similar to steam leaving the surface of boiling water. Heating a conductor to a temperature sufficiently high causing the conductor to give off electrons is called THERMIONIC EMISSION. The idea of electrons leaving the surface is shown in figure 11. Figure 1-1. - Thermionic emission.

Thomas Edison discovered the principle of thermionic emission as he looked for ways to keep soot from clouding his incandescent light bulb. Edison placed a metal plate inside his bulb along with the normal filament. He left a gap, a space, between the filament and the plate. He then placed a battery in series between the plate and the filament, with the positive side toward the plate and the negative side toward the filament. This circuit is shown in figure 12. Figure 1-2. - Edison's experimental circuit.

When Edison connected the filament battery and allowed the filament to heat until it glowed, he discovered that the ammeter in the filament-plate circuit had deflected and remained deflected. He reasoned that an electrical current must be flowing in the circuit EVEN ACROSS THE GAP between the filament and plate. Edison could not explain exactly what was happening. At that time, he probably knew less about what makes up an electric circuit than you do now. Because it did not eliminate the soot problem, he did little with this discovery. However, he did patent the incandescent light bulb and made it available to the scientific community. Let's analyze the circuit in figure 1-2. You probably already have a good idea of how the circuit works. The heated filament causes electrons to boil from its surface. The battery in the filament-plate circuit places a POSITIVE charge on the plate (because the plate is connected to the positive side of the battery). The electrons (negative charge) that boil from the filament are attracted to the

positively charged plate. They continue through the ammeter, the battery, and back to the filament. You can see that electron flow across the space between filament and plate is actually an application of a basic law you already know - UNLIKE CHARGES ATTRACT. Remember, Edison's bulb had a vacuum so the filament would glow without burning. Also, the space between the filament and plate was relatively small. The electrons emitted from the filament did not have far to go to reach the plate. Thus, the positive charge on the plate was able to attract the negative electrons. The key to this explanation is that the electrons were floating free of the hot filament. It would have taken hundreds of volts, probably, to move electrons across the space if they had to be forcibly pulled from a cold filament. Such an action would destroy the filament and the flow would cease. The application of thermionic emission that Edison made in causing electrons to flow across the space between the filament and the plate has become known as the EDISON EFFECT. It is fairly simple and extremely important. Practically everything that follows will be related in some way to the Edison effect. Be sure you have a good understanding of it before you go on. Q.1 How can a sheet of copper be made to emit electrons thermionically? Q.2 Why do electrons cross the gap in a vacuum tube?

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SPECIAL-Purpose Tubes

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Click here to order Electronic Components Online SPECIAL-PURPOSE TUBES LEARNING OBJECTIVES Upon completion of this chapter, you will be able to: Determine the number and type of individual tubes contained within the signal envelope of a multi-unit tube. Explain the function and operating principle of the beam power tube and the pentode tube. State the difference between the capabilities of conventional tubes and variable-mu tubes. Describe the construction of uhf tubes, and explain the effects that ultra-high frequencies have on conventional-tube operation. Explain the operation of gasfilled diodes, thyratrons, and cold-cathode tubes.

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Explain the operating principles behind cathode-ray tubes, and the manner in which these tubes present visual display of electronic signals. INTRODUCTION TO SPECIAL-PURPOSE TUBES Because of their great versatility, the four basic tube types (diode, triode, tetrode, and pentode) covered in chapter 1 have been used in the majority of electronic circuits. However, these types of tubes do have limits, size, frequency, and power handling capabilities. Special-purpose tubes are designed to operate or perform functions beyond the capabilities of the basic tube types discussed in chapter 1. The special-purpose tubes covered in this chapter will include multiunit, multi-electrode, beam power, power pentode, variable-mu, uhf, cold cathode, thyratrons, and cathode-ray tubes. MULTI-UNIT AND MULTI-ELECTRODE TUBES One of the problems associated with electron tubes is that they are bulky. The size of an electron tube circuit can be decreased by enclosing more than one tube within a single envelope, as mentioned in chapter 1. There is a large variety of tubes that can be combined into this grouping of "specialty tubes" called MULTI-UNIT tubes. Figure 2-1 illustrates the schematic symbols of a few of the possible combinations found in multi-unit tubes. Figure 2-1. - Typical multi-unit tube symbols.

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An important point to remember when dealing with multi-unit tubes is that each unit is capable of operating as a separate tube. But, how it operates, either as a single tube or as a multi-unit tube, is determined by the external circuit wiring. When you analyze the schematic of a circuit, simply treat each portion of a multi-unit tube as a single tube, as shown in figure 2-2. Figure 2-2. - Multi-unit tube Identification.

Another type of special-purpose tube is the MULTI-ELECTRODE tube. In some applications, tubes require more than the three grids found in conventional tubes. In some cases, up to seven grids may be used. These types of tubes are called multi-electrode tubes and are normally classified according to the number of grids they contain. An example of this is illustrated in figure 2-3. Here, you see a tube with five grids; hence, its name is "pentagrid." The application of these tube types is beyond the scope of this module, but because multi-electrode tubes have been commonly used you should be aware of their existence. Figure 2-3. - Pentagrid multi-electrode tube.

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POWER SUPPLIES

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Click here to order Electronic Components Online POWER SUPPLIES LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Identify the various sections of a power supply. State the purpose of each section of a power supply. Join Integrated Describe the operation of the Publishing's power supply from both the whole unit standpoint and from Discussion Group the subunit standpoint. Describe the purpose of the various types of rectifier circuits used in power supplies. Describe the purpose of the various types of filter circuits used in power supplies. Order this Describe the operation of the information on CDvarious voltage and current Rom regulators in a power supply. Trace the flow of ac and dc in a power supply, from the ac input to the dc output on a schematic diagram.

Identify faulty components through visual checks. Identify problems within specific areas of a power supply by using a logical isolation method of troubleshooting. Apply safety precautions when working with electronic power supplies. INTRODUCTION In the early part of this century when electronics was first introduced, most electronic equipment was powered by batteries. While the use of batteries allowed the equipment to be portable (to some degree), it also placed several limitations on how the equipment could be used. Because of their general inefficiency, batteries had to be either replaced frequently or, if they were rechargeable, kept near a battery charger. Thus, the advantage of having portable equipment was more than offset by the need to replace or recharge the batteries frequently. Users of electronic equipment needed a power supply that was reliable, convenient, and cost effective. Since batteries failed to satisfy these requirements, the "electronic power supply" was developed. In today's Navy, all electronic equipment, both ashore and on board ship, require some type of power supply. Therefore, this chapter is of extreme importance to you. We will discuss the sections and individual components of the power supply and their purposes within the power supply. We will also discuss troubleshooting of each section and its components. THE BASIC POWER SUPPLY Figure 3-1 shows the block diagram of the basic power supply. Most power supplies are made up of four basic sections: a <emphasis type="b">TRANSFORMER, a RECTIFIER, a FILTER, and a REGULATOR. Figure 3-1. - Block diagram of a basic power supply.

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As you can see, the first section is the TRANSFORMER. The transformer serves two primary purposes: (1) to step up or step down the input line voltage to the desired level and (2) to couple this voltage to the rectifier section. The RECTIFIER section converts the ac signal to a pulsating dc voltage. However, you will see later in this chapter that the pulsating dc voltage is not desirable. For this reason, a FILTER section is used to convert the pulsating dc voltage to filtered dc voltage. The final section, the REGULATOR, does just what the name implies. It maintains the output of the power supply at a constant level in spite of large changes in load current or in input line voltage. Depending upon the design of the equipment, the output of the regulator will maintain a constant dc voltage within certain limits. Now that you know what each section does, let's trace a signal through the power supply and see what changes are made to the input signal. In figure 3-2, the input signal of 120 volts ac is applied to the primary of the transformer, which has a turns ratio of 1:3. We can calculate the output by multiplying the input voltage by the ratio of turns in the secondary winding to turns in the primary winding. Therefore, the output voltage of our example is: 120 volts ac X 3, or 360 volts ac. Depending on the type of rectifier used (full-wave or half-wave), the output from the rectifier will be a portion of the input. Figure 3-2 shows the ripple waveform associated with a full-wave rectifier. The filter section contains a network of resistors, capacitors, or inductors that controls the rise and fall time of the varying signal so that the signal remains at a more constant dc level. You will see this more clearly in the discussion of the actual filter circuits. You can see that the output of the filter is at a 180-volt dc level with an ac RIPPLE voltage riding on it. (Ripple voltage is a small ac voltage riding at some dc voltage level. Normally, ripple voltage is an unwanted ac voltage created by the filter section of a power supply.) This signal now goes to the regulator where it will be maintained at approximately 180 volts dc to the load. Figure 3-2. - Block diagram of a power supply.

Q.1 What are the four basic sections to a power supply? Q.2 What is the purpose of the regulator? THE TRANSFORMER The transformer has several purposes: In addition to coupling the input ac signal to the power supply, it also isolates the electronic power supply from the external power source and either steps up or steps down the ac voltage to the desired level. Additionally, most input transformers have separate step-down windings to supply filament voltages to both power supply tubes and the tubes in the external equipment (load). Such a transformer is shown in figure 33. Because the input transformer is located in the power supply and is the ultimate source of power for both the load and the power supply, it is called the POWER TRANSFORMER. Notice that the transformer has the ability to deliver both 6.3 and 5 volts ac filament voltages to the electron tubes. The High-voltage winding is a 1:3 step-up winding and delivers 360 volts ac to the rectifier. This transformer also has what is called a center tap. This center tap provides the capability of developing two high-voltage outputs from one transformer. Figure 3-3. - Typical power transformer.

Q.3 What are the purposes of the transformer in a power supply? Q.4 For what are the low voltage windings in a transformer used?

Q.5 For what is the center tap on a transformer used?

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Book 7

Back • Home • Up • Next Click here to order Electronic Components Online SEMICONDUCTOR DIODES Semiconductor applications Semiconductor theory Energy bands Covalent bonding Doping process Semiconductor diode PN Junction operation Junction Barrier PN Junction application Diode characteristics Diode identification Diode maintenance Summary Answers

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TRANSISTORS Transistor theory PNP Transistor Operation The basic transistor amplifier Types of bias

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Amplifier classes of operation Transistor configurations Transistor specifications Precautions Microelectronics Summary Answers

SPECIAL DEVICES The tunnel diode Tunnel diode energy diagram Silicon Controlled Rectifier (SCR) SCR Structure TRIAC Optoelectronic Devices Photodiode Transistors Field Effect Transistors JFET symbols and bias voltages Effects of bias on N-channel depletion MOSFET Summary Answers

Solid-state power supplies The power transformer The conventional full-wave rectifier The bridge rectifier Filters The capacitor filter LC Choke-Input Filter Ac component in an LC choke-input filter. Resistor-Capacitor (RC) Filters FAILURE ANALYSIS OF THE RESISTORCAPACITOR (RC) FILTER Voltage regulation

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Series voltage regulator Current regulators Voltage multipliers Short Circuit Protection Summary Answers

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SEMICONDUCTOR DIODES

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Click here to order Electronic Components Online SEMICONDUCTOR DIODES LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. The learning objective are listed below. Upon completion of this chapter, you should be able to do the following: State, in terms of energy bands, the differences between a conductor, an insulator, and a semiconductor. Explain the electron and the hole flow theory in semiconductors and how the semiconductor is affected by doping.

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Define the term "diode" and give a brief description of its construction and operation. Explain how the diode can be used as a half-wave rectifier and as a switch. Identify the diode by its symbology, alphanumerical designation, and color code. List the precautions that must be taken when working with diodes and describe the different ways to test them. INTRODUCTION TO SOLID-STATE DEVICES As you recall from previous studies in this series, semiconductors have electrical properties somewhere between those of insulators and conductors. The use of semiconductor materials in electronic components is not new; some devices are as old as the electron tube. Two of the most widely known semiconductors in use today are the JUNCTION DIODE and TRANSISTOR. These semiconductors fall under a more general heading called solidstate devices. A SOLID-STATE DEVICE is nothing more than an electronic device, which operates by virtue of the movement of electrons within a solid piece of semiconductor material. Since the invention of the transistor, solid-state devices have been developed and improved at an unbelievable rate. Great strides have been made in the manufacturing techniques, and there is no foreseeable limit to the future of these devices. Solid-state devices made from semiconductor materials offer compactness, efficiency, ruggedness, and versatility. Consequently, these devices have invaded virtually every field of science and industry. In addition to the junction diode and transistor, a whole new family of related devices has been developed: the ZENER DIODE, LIGHTEMITTING DIODE, FIELD EFFECT TRANSISTOR, etc. One development that has dominated solid-state technology, and probably has had a greater impact on the electronics industry than either the electron tube or transistor, is the INTEGRATED CIRCUIT. The integrated circuit is a minute piece of semiconductor material that can produce complete electronic circuit functions.

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As the applications of solid-state devices mount, the need for knowledge of these devices becomes increasingly important. Personnel in the Navy today will have to understand solid-state devices if they are to become proficient in the repair and maintenance of electronic equipment. Therefore, our objective in this module is to provide a broad coverage of solid-state devices and, as a broad application, power supplies. We will begin our discussion with some background information on the development of the semiconductor. We will then proceed to the semiconductor diode, the transistor, special devices and, finally, solid-state power supplies. SEMICONDUCTOR DEVELOPMENT Although the semiconductor was late in reaching its present development, its story began long before the electron tube. Historically, we can go as far back as 1883 when Michael Faraday discovered that silver sulfide, a semiconductor, has a negative temperature coefficient. The term negative temperature coefficient is just another way of saying its resistance to electrical current flow decreases as temperature increases. The opposite is true of the conductor. It has a positive temperature coefficient. Because of this particular characteristic, semiconductors are used extensively in power-measuring equipment. Only 2 years later, another valuable characteristic was reported by Munk A. Rosenshold. He found that certain materials have rectifying properties. Strange as it may seem, his finding was given such little notice that it had to be rediscovered 39 years later by F. Braun. Toward the close of the 19th century, experimenters began to notice the peculiar characteristics of the chemical element SELENIUM. They discovered that in addition to its rectifying properties (the ability to convert ac into dc), selenium was also light sensitive-its resistance decreased with an increase in light intensity. This discovery eventually led to the invention of the photophone by Alexander Graham Bell. The photophone, which converted variations of light into sound, was a predecessor of the radio receiver; however, it wasn't until the actual birth of radio that selenium was used to any extent. Today, selenium is an important and widely used semiconductor.

Many other materials were tried and tested for use in communications. SILICON was found to be the most stable of the materials tested while GALENA, a crystalline form of lead sulfide, was found the most sensitive for use in early radio receivers. By 1915, Carl Beredicks discovered that GERMANIUM, another metallic element, also had rectifying capabilities. Later, it became widely used in electronics for low-power, low-frequency applications. Although the semiconductor was known long before the electron tube was invented, the semiconductor devices of that time could not match the performance of the tube. Radio needed a device that could not only handle power and amplify but rectify and detect a signal as well. Since tubes could do all these things, whereas semiconductor devices of that day could not, the semiconductor soon lost out. It wasn't until the beginning of World War II that interest was renewed in the semiconductor. There was a dire need for a device that could work within the ultra-high frequencies of radar. Electron tubes had interelectrode capacitances that were too high to do the job. The point-contact semiconductor diode, on the other hand, had a very low internal capacitance. Consequently, it filled the bill; it could be designed to work within the ultra-high frequencies used in radar, whereas the electron tube could not. As radar took on greater importance and communication-electronic equipment became more sophisticated, the demands for better solid-state devices mounted. The limitations of the electron tube made necessary a quest for something new and different. An amplifying device was needed that was smaller, lighter, more efficient, and capable of handling extremely high frequencies. This was asking a lot, but if progress was to be made, these requirements had to be met. A serious study of semiconductor materials began in the early 1940's and has continued since. In June 1948, a significant breakthrough took place in semiconductor development. This was the discovery of POINTCONTACT TRANSISTOR. Here at last was a semiconductor that could amplify. This discovery brought the semiconductor back into competition with the electron tube. A year later, JUNCTION DIODES and TRANSISTORS were developed. The junction

transistor was found superior to the point-contact type in many respects. By comparison, the junction transistor was more reliable, generated less noise, and had higher power-handling ability than its point-contact brother. The junction transistor became a rival of the electron tube in many uses previously uncontested. Semiconductor diodes were not to be slighted. The initial work of Dr. Carl Zener led to the development of ZENER DIODE, which is frequently used today to regulate power supply voltages at precise levels. Considerably more interest in the solid-state diode was generated when Dr. Leo Esaki, a Japanese scientist, fabricated a diode that could amplify. The device, named the TUNNEL DIODE, has amazing gain and fast switching capabilities. Although it is used in the conventional amplifying and oscillating circuits, its primary use is in computer logic circuits. Another breakthrough came in the late 1950's when it was discovered that semiconductor materials could be combined and treated so that they functioned as an entire circuit or subassembly rather than as a circuit component. Many names have been given to this solid-circuit concept, such as INTEGRATED CIRCUITS, MICROELECTRONICS, and MICROCIRCUITRY. So as we see, in looking back, that the semiconductor is not something new, but it has come a long way in a short time. Q.1 What is a solid-state device? Q.2 Define the term negative temperature coefficient.

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TRANSISTORS

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Click here to order Transistors Online TRANSISTORS LEARNING OBJECTIVES Upon completion of this chapter, you should be able to do the following: Define the term transistor and give a brief description of its construction and operation. Explain how the transistor can be used to Join Integrated Publishing's amplify a signal. Name the four classes of amplifiers and Discussion Group give an explanation for each. List the three different transistor circuit configurations and explain their operation. Identify the different types of transistors by their symbology and alphanumerical designations. Order this List the precautions to be information on CDtaken when working with Rom transistors and describe ways to test them. Explain the meaning of the expression "integrated circuits."

Give a brief description on how integrated circuits are constructed and the advantages they offer over conventional transistor circuits. Name the two types of circuit boards. State the purpose and function of modular circuitry. INTRODUCTION TO TRANSISTORS The discovery of the first transistor in 1948 by a team of physicists at the Bell Telephone Laboratories sparked an interest in solid-state research that spread rapidly. The transistor, which began as a simple laboratory oddity, was rapidly developed into a semiconductor device of major importance. The transistor demonstrated for the first time in history that amplification in solids was possible. Before the transistor, amplification was achieved only with electron tubes. Transistors now perform numerous electronic tasks with new and improved transistor designs being continually put on the market. In many cases, transistors are more desirable than tubes because they are small, rugged, require no filament power, and operate at low voltages with comparatively high efficiency. The development of a family of transistors has even made possible the miniaturization of electronic circuits. Figure 21 shows a sample of the many different types of transistors you may encounter when working with electronic equipment. Figure 2-1. - An assortment of different types of transistors.

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Transistors have infiltrated virtually every area of science and industry, from the family car to satellites. Even the military depends heavily on transistors. The ever increasing uses for transistors have created an urgent need for sound and basic information regarding their operation. From your study of the PN-junction diode in the preceding chapter, you now have the basic knowledge to grasp the principles of transistor operation. In this chapter you will first become acquainted with the basic types of transistors, their construction, and their theory of operation. You will also find out just how and why transistors amplify. Once this basic information is understood, transistor terminology, capabilities, limitations, and identification will be discussed. Last, we will talk about transistor maintenance, integrated circuits, circuit boards, and modular circuitry. TRANSISTOR FUNDAMENTALS The first solid-state device discussed was the two-element

semiconductor diode. The next device on our list is even more unique. It not only has one more element than the diode but it can amplify as well. Semiconductor devices that have-three or more elements are called TRANSISTORS. The term transistor was derived from the words TRANSfer and resISTOR. This term was adopted because it best describes the operation of the transistor - the transfer of an input signal current from a low-resistance circuit to a highresistance circuit. Basically, the transistor is a solid-state device that amplifies by controlling the flow of current carriers through its semiconductor materials. There are many different types of transistors, but their basic theory of operation is all the same. As a matter of fact, the theory we will be using to explain the operation of a transistor is the same theory used earlier with the PN-junction diode except that now two such junctions are required to form the three elements of a transistor. The three elements of the two-junction transistor are (1) the EMITTER, which gives off, or emits," current carriers (electrons or holes); (2) the BASE, which controls the flow of current carriers; and (3) the COLLECTOR, which collects the current carriers. CLASSIFICATION Transistors are classified as either NPN or PNP according to the arrangement of their N and P materials. Their basic construction and chemical treatment is implied by their names, "NPN" or "PNP." That is, an NPN transistor is formed by introducing a thin region of P-type material between two regions of N-type material. On the other hand, a PNP transistor is formed by introducing a thin region of N-type material between two regions of P-type material. Transistors constructed in this manner have two PN junctions, as shown in figure 2-2. One PN junction is between the emitter and the base; the other PN junction is between the collector and the base. The two junctions share one section of semiconductor material so that the transistor actually consists of three elements. Figure 2-2. - Transistor block diagrams.

Since the majority and minority current carriers are different for N and P materials, it stands to reason that the internal operation of the NPN and PNP transistors will also be different. The theory of operation of the NPN and PNP transistors will be discussed separately in the next few paragraphs. Any additional information about the PN junction will be given as the theory of transistor operation is developed. To prepare you for the forthcoming information, the two basic types of transistors along with their circuit symbols are shown in figure 2-3. It should be noted that the two symbols are different. The horizontal line represents the base, the angular line with the arrow on it represents the emitter, and the other angular line represents the collector. The direction of the arrow on the emitter distinguishes the NPN from the PNP transistor. If the arrow points in, (Points iN) the transistor is a PNP. On the other hand if the arrow points out, the transistor is an NPN (Not Pointing iN).

Figure 2-3. - Transistor representations.

Another point you should keep in mind is that the arrow always points in the direction of hole flow, or from the P to N sections, no matter whether the P section is the emitter or base. On the other hand, electron flow is always toward or against the arrow, just like in the junction diode. CONSTRUCTION The very first transistors were known as point-contact transistors.

Their construction is similar to the construction of the pointcontact diode covered in chapter 1. The difference, of course, is that the point-contact transistor has two P or N regions formed instead of one. Each of the two regions constitutes an electrode (element) of the transistor. One is named the emitter and the other is named the collector, as shown in figure 2-4, view A. Figure 2-4. - Transistor constructions.

Point-contact transistors are now practically obsolete. They have been replaced by junction transistors, which are superior to pointcontact transistors in nearly all respects. The junction transistor generates less noise, handles more power, provides higher current and voltage gains, and can be mass-produced more cheaply than the point-contact transistor. Junction transistors are manufactured in much the same manner as the PN junction diode discussed earlier. However, when the PNP or NPN material is grown (view B), the impurity mixing process must be reversed twice to obtain the two junctions required in a transistor. Likewise, when the alloyjunction (view C) or the diffused-junction (view D) process is used, two junctions must also be created within the crystal.

Although there are numerous ways to manufacture transistors, one of the most important parts of any manufacturing process is quality control. Without good quality control, many transistors would prove unreliable because the construction and processing of a transistor govern its thermal ratings, stability, and electrical characteristics. Even though there are many variations in the transistor manufacturing processes, certain structural techniques, which yield good reliability and long life , are common to all processes: (1) Wire leads are connected to each semiconductor electrode; (2) the crystal is specially mounted to protect it against mechanical damage; and (3) the unit is sealed to prevent harmful contamination of the crystal. Q.1 What is the name given to the semiconductor device that has three or more elements? Q.2 What electronic function made the transistor famous? Q.3 In which direction does the arrow point on an NPN transistor?

Q.4 What was the name of the very first transistor? Q.5 What is one of the most important parts of any transistor manufacturing process?

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SPECIAL DEVICES

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Click here to order Electronic Components Online SPECIAL DEVICES LEARNING OBJECTIVES Upon completion of this chapter, you will be able to: Explain the basic operation and the major applications of the Zener diode. Describe the basic operation of the tunnel diode and the varactor.

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Explain the basic operation of the silicon Publishing's controlled rectifier and the TRIAC, and Discussion Group compare the advantages and disadvantages of each. List the five most commonly used optoelectronic devices and explain the uses of each. Describe the basic operation, applications, and major advantages of the unijunction transistor. Order this Describe the basic operation, applications, information on CDand major advantages of the field effect Rom transistor and the metal oxide semiconductor field effect transistor. Explain the basic operation and the major applications of the Zener diode. Describe. the basic operation of the tunnel diode and the varactor.

Explain the basic operation of the silicon controlled rectifier and the TRIAC, and compare the advantages and disadvantages of each.

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List the five most commonly used optoelectronic devices and explain the uses of each. Describe the basic operation, applications, and major advantages of the unijunction transistor. Describe the basic operation, applications, and major advantages of the field-effect transistor and the metal-oxide semiconductor field-effect transistor. INTRODUCTION TO SPECIAL DEVICES If you consider the sensitive nature and the various interacting properties of semiconductors, it should not be surprising to you that solid state devices can be designed for many different purposes. In fact, devices with special features are so numerous and new designs are so frequently introduced that it would be beyond the scope of this chapter to describe all of the devices in use today. Therefore, this chapter will include a variety of representative devices that are used extensively in Navy equipment to give you an idea of the diversity and versatility that have been made possible. These devices have been grouped into three categories: diodes, optoelectronic devices, and transistors. In this chapter each device will be described and the basic operation of each one will be discussed. DIODES Diodes are two terminal semiconductors of various types that are used in seemingly endless applications. The operation of normal PN-junction diodes has already been discussed, but there are a number of diodes with special properties with which you should be familiar. A discussion of all of the developments in the diode field would be impossible so some of the more commonly used special diodes have been selected for explanation. These include Zener diodes, tunnel diodes, varactors, silicon controlled rectifiers (SCR), and TRIACs. Zener Diodes When a PN-junction diode is reverse biased, the majority carriers (holes in the P-material and electrons in the N-material) move away from the junction. The barrier or depletion region becomes wider, as illustrated in figure 3-1, (view A, view B, view C) and majority carrier current flow becomes very difficult across the high resistance of the wide depletion region. The presence of minority carriers causes a small leakage current that remains nearly constant for all reverse voltages up to a certain value. Once this value has been exceeded, there is a sudden increase in the reverse current. The voltage at which the sudden increase in current occurs is called the BREAKDOWN VOLTAGE. At breakdown, the reverse current increases very rapidly with a slight increase in the reverse voltage. Any diode can be reverse biased to the point of breakdown, but not every diode can safely dissipate the power associated with breakdown. A Zener diode is a PN junction designed to operate in the reverse-bias breakdown region. Figure 3-1A. - Effects of bias on the depletion region of a PN junction.

Figure 3-1B. - Effects of bias on the depletion region of a PN junction.

Figure 3-1C. - Effects of bias on the depletion region of a PN junction.

There are two distinct theories used to explain the behavior of PN junctions during breakdown: one is the ZENER EFFECT and the other is the AVALANCHE EFFECT. The ZENER EFFECT was first proposed by Dr. Carl Zener in 1934. According to Dr. Zener's theory, electrical breakdown in solid dielectrics occurs by a process called QUANTUM-MECHANICAL TUNNELING. The Zener effect accounts for the breakdown below 5 volts; whereas, above 5 volts the breakdown is caused by the avalanche effect. Although the avalanche effect is now accepted as an explanation of diode breakdown, the

term Zener diode is used to cover both types. The true Zener effect in semiconductors can be described in terms of energy bands; however, only the two upper energy bands are of interest. The two upper bands, illustrated in figure 3-2, view A, are called the conduction band and the valence band. Figure 3-2A. - Energy diagram for Zener diode.

The CONDUCTION BAND is a band in which the energy level of the electrons is high enough that the electrons will move easily under the influence of an external field. Since current flow is the movement of electrons, the readily mobile electrons in the conduction band are capable of maintaining a current flow when an external field in the form of a voltage is applied. Therefore, solid materials that have many electrons in the conduction band are called conductors. The VALENCE BAND is a band in which the energy level is the same as the valence electrons of the atoms. Since the electrons in these levels are attached to the atoms, the electrons are not free to move around as are the conduction band electrons. With the proper amount of energy added, however, the electrons in the valence band may be elevated to the conduction band energy level. To do this, the electrons must cross a gap that exists between the valence band energy level and the conduction band energy level. This gap is known as the FORBIDDEN ENERGY BAND or FORBIDDEN GAP. The energy difference across this gap determines whether a solid material will act as a conductor, a semiconductor, or an insulator. A conductor is a material in which the forbidden gap is so narrow that it can be considered nonexistent. A semiconductor is a solid that contains a forbidden gap, as shown in figure 32, view A. Normally, a semiconductor has no electrons at the conduction band energy level. The energy provided by room temperature heat, however, is enough energy to overcome the binding force of a few valence electrons and to elevate them to the conduction band energy level. The addition of impurities to the semiconductor material increases both the number of free electrons in the conduction band and the number of electrons in the valence band that can be elevated to the conduction band. Insulators are materials in which the forbidden gap is so large that practically no electrons can be given enough energy to cross the gap. Therefore, unless extremely large amounts of heat energy are available, these materials will not conduct electricity. View B of figure 3-2 is an energy diagram of a reverse-biased Zener diode. The energy bands of the P and N materials are naturally at different levels, but reverse bias causes the

valence band of the P material to overlap the energy level of the conduction band in the N material. Under this condition, the valence electrons of the P material can cross the extremely thin junction region at the overlap point without acquiring any additional energy. This action is called tunneling. When the breakdown point of the PN junction is reached, large numbers of minority carriers "tunnel" across the junction to form the current that occurs at breakdown. The tunneling phenomenon only takes place in heavily doped diodes such as Zener diodes. Figure 3-2B. - Energy diagram for Zener diode.

The second theory of reverse breakdown effect in diodes is known as AVALANCHE breakdown and occurs at reverse voltages beyond 5 volts. This type of breakdown diode has a depletion region that is deliberately made narrower than the depletion region in the normal PN-junction diode, but thicker than that in the Zener-effect diode. The thicker depletion region is achieved by decreasing the doping level from the level used in Zenereffect diodes. The breakdown is at a higher voltage because of the higher resistivity of the material. Controlling the doping level of the material during the manufacturing process can produce breakdown voltages ranging between about 2 and 200 volts. The mechanism of avalanche breakdown is different from that of the Zener effect. In the depletion region of a PN junction, thermal energy is responsible for the formation of electronhole pairs. The leakage current is caused by the movement of minority electrons, which is accelerated in the electric field across the barrier region. As the reverse voltage across the depletion region is increased, the reverse voltage eventually reaches a critical value. Once

the critical or breakdown voltage has been reached, sufficient energy is gained by the thermally released minority electrons to enable the electrons to rupture covalent bonds as they collide with lattice atoms. The released electrons are also accelerated by the electric field, resulting in the release of further electrons, and so on, in a chain or avalanche effect. This process is illustrated in figure 3-3. Figure 3-3. - Avalanche multiplication.

For reverse voltage slightly higher than breakdown, the avalanche effect releases an almost unlimited number of carriers so that the diode essentially becomes a short circuit. The current flow in this region is limited only by an external series current-limiting resistor. Operating a diode in the breakdown region does not damage it, as long as the maximum power dissipation rating of the diode is not exceeded. Removing the reverse voltage permits all carriers to return to their normal energy values and velocities. Some of the symbols used to represent Zener diodes are illustrated in figure 3-4 (view A, view B, view C, view D, and view E). Note that the polarity markings indicate electron flow is with the arrow symbol instead of against it as in a normal PN-junction diode. This is because breakdown diodes are operated in the reverse-bias mode, which means the current flow is by minority current carriers. Figure 3-4A. - Schematic symbols for Zener diodes.

Figure 3-4B. - Schematic symbols for Zener diodes.

Figure 3-4C. - Schematic symbols for Zener diodes.

Figure 3-4D. - Schematic symbols for Zener diodes.

Figure 3-4E. - Schematic symbols for Zener diodes.

Zener diodes of various sorts are used for many purposes, but their most widespread use is as voltage regulators. Once the breakdown voltage of a Zener diode is reached, the voltage across the diode remains almost constant regardless of the supply voltage. Therefore they hold the voltage across the load at a constant level. This characteristic makes Zener diodes ideal voltage regulators, and they are found in almost all solid-state circuits in this capacity. Q.1 In a reverse biased PN-junction, which current carriers cause leakage current? Q.2 The action of a PN-junction during breakdown can be explained by what two theories? Q.3 Which breakdown theory explains the action that takes place in a heavily doped PNjunction with a reverse bias of less than 5 volts? Q.4 What is the doping level of an avalanche effect diode when compared to the doping level of a Zener-effect diode? Q.5 During avalanche effect breakdown, what limits current flow through the diode? Q.6 Why is electron flow with the arrow in the symbol of a Zener diode instead of against the arrow as it is in a normal diode?

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Solid-state power supplies

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Click here to order Electronic Components Online SOLID-STATE POWER SUPPLIES LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Identify the various sections of a power supply. State the purpose of each section of a power supply. Describe the operation of the power supply from both a whole unit standpoint Join Integrated and from a subunit standpoint. Publishing's Describe the purpose of the various types of rectifier circuits used in Discussion Group power supplies. Describe the purpose of the various types of filter circuits used in power supplies. Describe the operation of the various voltage and current regulators in a power supply. Describe the operation of the various types of voltage multipliers. Order this Trace the flow of ac and dc in a power information on CDsupply, from the ac input to the dc Rom output on a schematic diagram. Identify faulty components through visual checks. Identify problems within specific areas of a power supply by using a logical isolation method of troubleshooting. Apply safety precautions when working with electronic power supplies. In today's Navy all electronic equipment, both ashore and on board ship, requires a power supply. The discovery of the silicon diode and other solid-state components made possible the reduction in size and the increase in reliability of electronic equipment. This is especially important on board ship where space and accessibility to spare parts are a major concern. In this chapter, you will read about the individual sections of the power supply, their components, and the purpose of each within the power supply.

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THE BASIC POWER SUPPLY View A of figure 4-1 shows the block diagram of a basic power supply. Most power supplies are made up of four basic sections: a TRANSFORMER, a RECTIFIER, a FILTER, and a REGULATOR. Figure 4-1A. - Block diagram of a basic power supply.

As illustrated in view B of figure 4-1, the first section is the TRANSFORMER. The transformer steps up or steps down the input line voltage and isolates the power supply from the power line. The RECTIFIER section converts the alternating current input signal to a pulsating direct current. However, as you proceed in this chapter you will learn that pulsating dc is not desirable. For this reason a FILTER section is used to convert pulsating dc to a purer, more desirable form of dc voltage. Figure 4-1B. - Block diagram of a basic power supply.

The final section, the REGULATOR, does just what the name implies. It maintains the output of the power supply at a constant level in spite of large changes in load current or input line voltages. Now that you know what each section does, let's trace an ac signal through the power supply. At this point you need to see how this signal is altered within each section of the power supply. Later on in the chapter you will see how these changes take place. In view B of figure 4-1, an input signal of 115 volts ac is applied to the primary of the transformer. The transformer is a step-up transformer with a turns ratio of 1:3. You can calculate the output for this transformer by multiplying the input voltage by the ratio of turns in the primary to the ratio of turns in the secondary; therefore, 115 volts ac X 3 = 345 volts ac (peak-to-peak) at the output. Because each diode in the rectifier section conducts for 180 degrees of the 360degree input, the output of the rectifier will be one-half, or approximately 173 volts of pulsating dc. The filter section, a network of resistors, capacitors, or inductors, controls the rise and fall time of the varying signal; consequently, the signal remains at a more constant dc level. You will see the filter process more clearly in the discussion of the actual filter circuits. The output of the filter is a signal of 110 volts dc, with ac ripple riding on the dc. The reason for the lower voltage (average voltage) will be explained later in this chapter. The regulator maintains its output at a constant 110-volt dc level, which is used by the electronic

equipment (more commonly called the load).

Q.1 What are the four basic sections of a power supply? Q.2 What is the purpose of the rectifier section? Q.3 What is the purpose of the filter section? Q.4 What is the purpose of the regulator section?

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Book 8

Back • Home • Up • Next Click here to order Electronic Components Online AMPLIFIERS Classification of amplifiers Transistor Amplifiers Amplifier coupling Impedance considerations for amplifiers Amplifier feedback Positive feedback Audio amplifiers Push-pull amplifiers Summary Answers

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VIDEO AND RF AMPLIFIERS Reading amplifier Frequency response curves Frequency-response curves Video amplifiers Low-frequency compensation for video amplifiers Radio-frequency amplifiers RF amplifier coupling Typical RF amplifier circuits Summary

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Answers

SPECIAL AMPLIFIERS Input signals in phase Single-input, single-output differential amplifier Operational amplifiers Operational amplifier Current flow in the operational circuit Bandwidth limitations Applications of operational amplifiers Scaling amplifier Difference amplifier Circuit for Q31 through Q33 Circuit for Q36 through Q38 Magnetic amplifiers Methods of changing inductance Flux paths in a saturable-core reactor. FLUX AIDING Simplified magnetic amplifier circuitry Summary Answers Order this information in Adobe PDF Printable Format

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AMPLIFIERS

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Click here to order Electronic Components Online AMPLIFIERS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Upon completion of this chapter, you will be able to: Define amplification and list several common uses; state two ways in which amplifiers are classified. List the four classes of operation of, four methods of coupling for, and the impedance characteristics of the three configurations of a transistor amplifier. Define feedback and list the two types of feedback. Describe and state one use for a phase splitter. State a common use for and one advantage of a push-pull amplifier.

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INTRODUCTION Order this

This chapter is a milestone in your study of electronics. Previous modules have been information in concerned more with individual components of circuits than with the complete circuits as the Print (Hardcopy). subject. This chapter and the other chapters of this module are concerned with the circuitry of amplifiers. While components are discussed, the discussion of the components is not an explanation of the working of the component itself (these have been covered in previous

modules) but an explanation of the component as it relates to the circuit. The circuits this chapter is concerned with are AMPLIFIERS. Amplifiers are devices that provide AMPLIFICATION. That doesn't explain much, but it does describe an amplifier if you know what amplification is and what it is used for. WHAT IS AMPLIFICATION? Just as an amplifier is a device that provides amplification, amplification is the process of providing an increase in AMPLITUDE. Amplitude is a term that describes the size of a signal. In terms of a.c., amplitude usually refers to the amount of voltage or current. A 5-volt peak-topeak a.c.signal would be larger in amplitude than a 4-volt peak-to-peak a.c. signal. "SIGNAL" is a general term used to refer to any a.c. or d.c. of interest in a circuit; e.g., input signal and output signal. A signal can be large or small, ac. or d.c., a sine wave or nonsinusoidal, or even nonelectrical such as sound or light. "Signal" is a very general term and, therefore, not very descriptive by itself, but it does sound more technical than the word "thing". It is not very impressive to refer to the "input thing" or the "thing that comes out of this circuit." Perhaps the concept of the relationship of amplifier-amplification-amplitude will be clearer if you consider a parallel situation (an analogy). A magnifying glass is a magnifier. As such, it provides magnification which is an increase in the magnitude (size) of an object. This relationship of magnifier-magnification-magnitude is the same as the relationship of amplifieramplification-amplitude. The analogy is true in one other aspect as well. The magnifier does not change the object that is being magnified; it is only the image that is larger, not the object itself. With the amplifier, the output signal differs in amplitude from the input signal, but the input signal still exists unchanged. So, the object (input signal) and the magnifier (amplifier) control the image (output signal). An amplifier can be defined as a device that enables an input signal to control an output signal. The output signal will have some (or all) of the characteristics of the input signal but will generally be larger than the input signal in terms of voltage, current, or power. USES OF AMPLIFICATION Most electronic devices use amplifiers to provide various amounts of signal amplification. Since most signals are originally too small to control or drive the desired device, some amplification is needed. For example, the audio signal taken from a record is too small to drive a speaker, so amplification is needed. The signal will be amplified several times between the needle of the record player and the speaker. Each time the signal is amplified it is said to go through a STAGE of amplification. The audio amplifier shown connected between the turntable and speaker system in figure 1-1 contains several stages of amplification. Figure 1-1. - Amplifier as used with turntable and speaker.

Notice the triangle used in figure 1-1 to represent the amplifier. This triangle is the standard block diagram symbol for an amplifier. Another example of the use of an amplifier is shown in figure 1-2. In a radio receiver, the signal picked up by the antenna is too weak (small) to be used as it is. This signal must be amplified before it is sent to the detector. (The detector separates the audio signal from the frequency that was sent by the transmitter. The way in which this is done will be discussed later in this training series.) Figure 1-2. - Amplifiers as used in radio receiver.

The audio signal from the detector will then be amplified to make it large enough to drive the speaker of the radio. Almost every electronic device contains at least one stage of amplification, so you will be seeing amplifiers in many devices that you work on. Amplifiers will also be used in most of the NEETS modules that follow this one. Q.1 What is amplification? Q.2 Does an amplifier actually change an input signal? Why or why not? Q.3 Why do electronic devices use amplifiers?

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VIDEO AND RF AMPLIFIERS

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Click here to order Amplifiers Online VIDEO AND RF AMPLIFIERS LEARNING OBJECTIVES Upon completion of this chapter, you will be able to: Define the term "bandwidth of an amplifier." Determine the upper and lower frequency limits of an amplifier from a frequency-response curve. List the factors that limit Frequency response in an amplifier. List two techniques used to increase the highFrequency response for a video amplifier. State one technique used to increase the lowfrequency response of a video amplifier.

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Identify the purpose of various components on a schematic of a complete typical video amplifier circuit. State the purpose of a frequency-determining network in an rf amplifier. State one method by which an rf amplifier can be neutralized. Identify the purpose of various components on a schematic of a complete typical rf amplifier. INTRODUCTION In this chapter you will be given information on the Frequency response of amplifiers as well as specific information on video and rf amplifiers. For all practical purposes, all the general information you studied in chapter 1 about audio amplifiers will apply to the video and rf amplifiers which you are about to study. You may be wondering why you need to learn about video and rf amplifiers. You need to understand these circuits because, as a technician, you will probably be involved in working on equipment in which these circuits are used. Many of the circuits shown in this and the next chapter are incomplete and would not be used in actual equipment. For example, the complete biasing network may not be shown. This is done so you can concentrate on the concepts being presented without being overwhelmed by an abundance of circuit elements. With this idea in mind, the information that is presented in this chapter is real, practical information about video and rf amplifiers. It is the sort of information that you will use in working with these circuits. Engineering information (such as design specifications) will not be presented because it is not needed to understand the concepts that a technician needs to perform the job of circuit analysis and repair. Before you are given the specific information on video and rf amplifiers, you may be wondering how these circuits are used.

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Video amplifiers are used to amplify signals that represent video information. (That's where the term "video" comes from.) Video is the "picture" portion of a television signal. The "sound" portion is audio. Although the Navy uses television in many ways, video signals are used for more than television. Radar systems (discussed later in this training series) use video signals and, therefore, video amplifiers. Video amplifiers are also used in video recorders and some communication and control devices. In addition to using video amplifiers, televisions use rf amplifiers. Many other devices also use rf amplifiers, such as radios, navigational devices, and communications systems. Almost any device that uses broadcast, or transmitted, information will use an rf amplifier. As you should recall, rf amplifiers are used to amplify signals between 10 kilohertz (10 kHz) and 100,000 megahertz (100,000 MHz) (not this entire band of frequencies, but any band of frequencies within these limits). Therefore, any device that uses frequencies between 10 kilohertz and 100,000 megahertz will most likely use an rf amplifier. Before you study the details of video and rf amplifiers, you need to learn a little more about the Frequency response of an amplifier and frequency-response curves. AMPLIFIER Frequency response In chapter 1 of this module you were shown the frequencyresponse curve of an audio amplifier. Every amplifier has a frequency-response curve associated with it. Technicians use frequency-response curves because they provide a "picture" of the performance of an amplifier at various frequencies. You will probably never have to draw a frequency-response curve, but, in order to use one, you should know how a frequency-response curve is created. The amplifier for which the frequency-response curve is created is tested at various frequencies. At each frequency, the input signal is set to some predetermined level of voltage (or current). This same voltage (or current) level for all of the input signals is used to provide a standard input and to allow evaluation of the output of the circuit at each of the frequencies tested. For each of these frequencies, the output is measured and marked on a graph. The graph is marked "frequency" along the horizontal axis and "voltage"

or "current" along the vertical axis. When points have been plotted for all of the frequencies tested, the points are connected to form the frequency-response curve. The shape of the curve represents the Frequency response of the amplifier. Some amplifiers should be "flat" across a band of frequencies. In other words, for every frequency within the band, the amplifier should have equal gain (equal response). For frequencies outside the band, the amplifier gain will be much lower. For other amplifiers, the desired Frequency response is different. For example, perhaps the amplifier should have high gain at two frequencies and low gain for all other frequencies. The frequency-response curve for this type of amplifier would show two "peaks." In other amplifiers the frequency-response curve will have one peak indicating high gain at one frequency and lower gain at all others. Note the frequency-response curve shown in figure 2-1. This is the frequency-response curve for an audio amplifier as described in chapter 1. It is "flat" from 15 hertz (15 Hz) to 20 kilohertz (20 kHz). Figure 2-1. - Frequency response curve of audio amplifier.

Notice in the figure that the lower frequency limit is labeled f1 and the upper frequency limit is labeled f2. Note also the portion inside the frequency-response curve marked "BANDWIDTH." You may be wondering just what a "bandwidth" is. BANDWIDTH OF AN AMPLIFIER The bandwidth represents the amount or "width" of frequencies, or the "band of frequencies," that the amplifier is MOST effective in amplifying. However, the bandwidth is NOT the same as the band of frequencies that is amplified. The bandwidth (BW) of an amplifier is the difference between the frequency limits of the amplifier. For example, the band of frequencies for an amplifier may be from 10 kilohertz (10 kHz) to 30 kilohertz (30 kHz). In this case, the bandwidth would be 20 kilohertz (20 kHz). As another example, if an amplifier is designed to amplify frequencies between 15 hertz (15 Hz) and 20 kilohertz (20 kHz), the bandwidth will be equal to 20

kilohertz minus 15 hertz or 19,985 hertz (19,985 Hz). This is shown in figure 2-1. Mathematically:

You should notice on the figure that the frequencyresponse curve shows output voltage (or current) against frequency. The lower and upper frequency limits (f1 and f2) are also known as HALF-POWER POINTS. The half-power points are the points at which the output voltage (or current) is 70.7 percent of the maximum output voltage (or current). Any frequency that produces less than 70.7 percent of the maximum output voltage (or current) is outside the bandwidth and, in most cases, is not considered a useable output of the amplifier. The reason these points are called "half-power points" is that the true output power will be half (50 percent) of the maximum true output power when the output voltage (or current) is 70.7 percent of the maximum output voltage (or current), as shown below. (All calculations are rounded off to two decimal places.) As you learned in NEETS, module 2, in an a.c. circuit true power is calculated using the resistance (R) of the circuit, NOT the impedance (Z). If the circuit produces a maximum output voltage of 10 volts across a 50-ohm load, then:

When the output voltage drops to 70.7 percent of the maximum voltage of 10 volts, then:

As you can see, the true power is 50 percent (half) of the maximum true power when the output voltage is 70.7 percent of the maximum output voltage. If, instead, you are using the output current of the above circuit, the maximum current is

The calculations are:

At 70.7 percent of the output current (.14 A):

On figure 2-1, the two points marked f1 and f2 will enable you to determine the frequency-response limits of the amplifier. In this case, the limits are 15 hertz (15 Hz) and 20 kilohertz (20 kHz). You should now see how a frequency-response curve can enable you to determine the frequency limits and the bandwidth of an amplifier.

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SPECIAL AMPLIFIERS

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Upon completion of this chapter, you will be able to: Describe the basic operation of a differential amplifier.

Describe the operation of a differential amplifier under the following conditions: Single Input, Single Output Single input, differential output Differential input, differential output List the characteristics of an operational amplifier. Identify the symbol for an operational amplifier. Label the blocks on a block diagram of an operational amplifier.

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Describe the operation of an operational amplifier with inverting and noninverting configurations. Describe the bandwidth of a typical operational amplifier and methods to modify the bandwidth. Identify the following applications of operational amplifiers: Adder Subtractor State the common usage for a magnetic amplifier. Describe the basic operation of a magnetic amplifier. Describe various methods of changing inductance. Identify the purpose of components in a simple magnetic amplifier. INTRODUCTION If you were to make a quick review of the subjects discussed in this module up to this point, you would see that you have been given a considerable amount of information about amplifiers. You have been shown what amplification is and how the different classes of amplifiers affect amplification. You also have been shown that many factors must be considered when working with amplifiers, such as impedance, feedback, Frequency response, and coupling. With all this information behind you, you might ask yourself "what more can there be to know about amplifiers?" There is a great deal more to learn about amplifiers. Even after you finish this chapter you will have only "scratched the surface" of the study of amplifiers. But, you will have prepared yourself for the remainder of the NEETS. This, in turn, should prepare you for further study and, perhaps, a career in electronics. As in chapter 2, the circuits shown in this chapter are intended to present particular concepts to you. Therefore, the circuits may be

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incomplete or not practical for use in an actual piece of electronic equipment. You should keep in mind the fact that this text is intended to teach certain facts about amplifiers, and in order to simplify the illustrations used, complete operational circuits are not always shown. In this chapter three types of special amplifiers are discussed. These are: DIFFERENTIAL AMPLIFIERS, OPERATIONAL AMPLIFIERS, and MAGNETIC AMPLIFIERS. These are called special amplifiers because they are used only in certain types of equipment. The names of each of these special amplifiers describe the operation of the amplifier, NOT what is amplified. For example, a magnetic amplifier does not amplify magnetism but uses magnetic effects to produce amplification of an electronic signal. A differential amplifier is an amplifier that can have two input signals and/or two output signals. This amplifier can amplify the difference between two input signals. A differential amplifier will also "cancel out" common signals at the two inputs. One of the more interesting aspects of an operational amplifier is that it can be used to perform mathematical operations electronically. Properly connected, an operational amplifier can add, subtract, multiply, divide, and even perform the calculus operations of integration and differentiation. These amplifiers were originally used in a type of computer known as the "analog computer" but are now used in many electronic applications. The magnetic amplifier uses a device called a "saturable core reactor" to control an a.c.output signal. The primary use of magnetic amplifiers is in power control systems. These brief descriptions of the three special amplifiers are intended to provide you with a general idea of what these amplifiers are and how they can be used. The remaining sections of this chapter will provide you with more detailed information on these special amplifiers. DIFFERENTIAL AMPLIFIERS

A differential amplifier has two possible inputs and two possible outputs. This arrangement means that the differential amplifier can be used in a variety of ways. Before examining the three basic configurations that are possible with a differential amplifier, you need to be familiar with the basic circuitry of a differential amplifier. BASIC DIFFERENTIAL AMPLIFIER CIRCUIT Before you are shown the operation of a differential amplifier, you will be shown how a simpler circuit works. This simpler circuit, known as the DIFFERENCE AMPLIFIER, has one thing in common with the differential amplifier: It operates on the difference between two inputs. However, the difference amplifier has only one output while the differential amplifier can have two outputs. By now, you should be familiar with some amplifier circuits, which should give you an idea of what a difference amplifier is like. In NEETS, module 7, you were shown the basic configurations for transistor amplifiers. Figure 3-1 shows two of these configurations: the common emitter and the common base. In view (A) of figure 31 a common-emitter amplifier is shown. The output signal is an amplified version of the input signal and is 180 degrees out of phase with the input signal. View (B) is a common-base amplifier. In this circuit the output signal is an amplified version of the input signal and is in phase with the input signal. In both of these circuits, the output signal is controlled by the base-to-emitter bias. As this bias changes (because of the input signal) the current through the transistor changes. This causes the output signal developed across the collector load (R2) to change. None of this information is new, it is just a review of what you have already been shown regarding transistor amplifiers. Figure 3-1A. - Common-emitter and common-base amplifiers.

Figure 3-1B. - Common-emitter and common-base amplifiers.

NOTE: Bias arrangements for the following explanations will be termed base-to-emitter. In other publications you will see the term emitter-to-base used to describe the same bias arrangement. THE TWO-INPUT, SINGLE-OUTPUT, DIFFERENCE AMPLIFIER If you combine the common-base and common-emitter configurations into a single transistor amplifier, you will have a circuit like the one shown in figure 3-2. This circuit is the two-input, single-output, difference amplifier.

Figure 3-2. - Two-input, single-output, difference amplifier.

In figure 3-2, the transistor has two inputs (the emitter and the base) and one output (the collector). Remember, the current through the transistor (and therefore the output signal) is controlled by the base-to-emitter bias. In the circuit shown in figure 3-2, the combination of the two input signals controls the output signal. In fact, the DIFFERENCE BETWEEN THE INPUT SIGNALS determines the base-to-emitter bias. For the purpose of examining the operation of the circuit shown in figure 3-2, assume that the circuit has a gain of -10. This means that for each 1-volt change in the base-to-emitter bias, there would be a 10-volt change in the output signal. Assume, also, that the input signals will peak at 1-volt levels (+1 volt for the positive peak and -1 volt for the negative peak). The secret to understanding this circuit (or any transistor amplifier circuit) is to realize that the collector current is controlled by the base-to-emitter bias. In other words, in this circuit the output signal (the voltage developed across R3) is determined by the difference between the voltage on

the base and the voltage on the emitter. Figure 3-3 shows this two-input, single-output amplifier with input signals that are equal in amplitude and 180 degrees out of phase. Input number one has a positive alternation when input number two has a negative alternation and vice versa. Figure 3-3. - Input signals 180° out of phase.

The circuit and the input and output signals are shown at the top of the figure. The lower portion of the figure is a comparison of the input signals and the output signal. Notice the vertical lines marked "T0" through "T8." These represent "time zero" through "time

eight." In other words, these lines provide a way to examine the two input signals and the output signal at various instants of time. In figure 3-3 at time zero (T0) both input signals are at 0 volts. The output signal is also at 0 volts. Between time zero (T0) and time one (T1), input signal number one goes positive and input signal number two goes negative. Each of these voltage changes causes an increase in the base-to-emitter bias which causes current through Q1 to increase. Increased current through Q1 results in a greater voltage drop across the collector load (R3) which causes the output signal to go negative. By time one (T1), input signal number one has reached +1 volt and input signal number two has reached -1 volt. This is an overall increase in base-to-emitter bias of 2 volts. Since the gain of the circuit is -10, the output signal has decreased by 20 volts. As you can see, the output signal has been determined by the difference between the two input signals. In fact, the base-to-emitter bias can be found by subtracting the value of input signal number two from the value of input signal number one.

Between time one (T1) and time two (T2), input signal number one goes from +1 volt to 0 volts and input signal number two goes from 1 volt to 0 volts. At time two (T2) both input signals are at 0 volts and the base-to-emitter bias has returned to 0 volts. The output signal is also 0 volts.

Between time two (T2) and time three (T3), input signal number one goes negative and input signal number two goes positive. At time three (T3), the value of the base-to-emitter bias is -2 volts.

This causes the output signal to be +20 volts at time three (T3). Between time three (T3) and time four (T4), input signal #1 goes from -1 volt to 0 volts and input signal #2 goes from +1 volt to 0 volts. At time four (T4) both input signals are 0 volts, the bias is 0 volts, and the output is 0 volts. During time four (T4) through time eight (T8), the circuit repeats the sequence of events that took place from time zero (T0) through time four (T4). You can see that when the input signals are equal in amplitude and 180 degrees out of phase, the output signal is twice as large (40 volts peak to peak) as it would be from either input signal alone (if the other input signal were held at 0 volts).

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Book 9

Back • Home • Up • Next Click here to order Electronic Components Online TUNED CIRCUITS Effect of Frequency on Inductive Reactance Resonance The ideal series-resonant circuit How the Parallel-LC Circuit Stores Energy Parallel resonance Resonant circuits as filter circuits Bandwidth Filters High-pass filter Multisection filters Summary Answers

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OSCILLATORS LC Network Solid-state LC Oscillators Oscillator circuits Tuned-base Armstrong oscillator Colpitts oscillator Crystal oscillators

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Pulsed oscillators Harmonics Summary Answer

WAVEFORMS AND WAVE GENERATORS Astable Multivibrator Monostable multivibrator block diagram Bistable Multivibrator Bistable multivibrator (flip-flop) Blocking oscillator Circuit damping Time-base generators Relationship of gate to linearity Improved unijunction sawtooth generator Series LR circuit. Summary Answers

WAVE SHAPING Series-positive limiter with positive bias Parallel Limiters Parallel-negative limiter with negative bias Dual-diode limiter Positive-diode clampers Negative diode clampers Common-base transistor clamper Nonsinusoidal Voltages Applied to an RC Circuit RL Integrators Integrator waveform analysis Differentiators Counters Negative counters Summary Answers

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TUNED CIRCUITS

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Click here to order Electronic Components Online TUNED CIRCUITS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Upon completion of this chapter, you will be able to:

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State the applications of a resonant circuit. Identify the conditions that exist in a resonant circuit. State and apply the formula for resonant frequency of an a.c. circuit. State the effect of changes in inductance (L) and capacitance (C) on resonant frequency (fr). Identify the characteristics peculiar to a series Order this resonant circuit. information on CDIdentify the characteristics peculiar to a parallel Rom resonant circuit. State and apply the formula for Q. State what is meant by the bandwidth of a resonant circuit and compute the bandwidth for a given circuit. Identify the four general types of filters. Identify how the series- and parallel-resonant Order this circuit can be used as a bandpass or a bandinformation in reject filter. Print (Hardcopy).

INTRODUCTION TO TUNED CIRCUITS When your radio or television set is turned on, many events take place within the "receiver" before you hear the sound or see the picture being sent by the transmitting station. Many different signals reach the antenna of a radio receiver at the same time. To select a station, the

listener adjusts the tuning dial on the radio receiver until the desired station is heard. Within the radio or TV receiver, the actual "selecting" of the desired signal and the rejecting of the unwanted signals are accomplished by what is called a TUNED CIRCUIT. A tuned circuit consists of a coil and a capacitor connected in series or parallel. Later in this chapter you will see the application and advantages of both series- and parallel-tuned circuits. Whenever the characteristics of inductance and capacitance are found in a tuned circuit, the phenomenon as RESONANCE takes place. You learned earlier in the Navy Electricity and Electronics Training Series, Module 2, chapter 4, that inductive reactance (XL) and capacitive reactance (XC) have opposite effects on circuit impedance (Z). You also learned that if the frequency applied to an LCR circuit causes XL and XC to be equal, the circuit is RESONANT. If you realize that XL and XC can be equal ONLY at ONE FREQUENCY (the resonant frequency), then you will have learned the most important single fact about resonant circuits. This fact is the principle that enables tuned circuits in the radio receiver to select one particular frequency and reject all others. This is the reason why so much emphasis is placed on XL and XC in the discussions that follow. Examine figure 1-1. Notice that a basic tuned circuit consists of a coil and a capacitor, connected either in series, view (A), or in parallel, view (B). The resistance (R) in the circuit is usually limited to the inherent resistance of the components (particularly the resistance of the coil). For our purposes we are going to disregard this small resistance in future diagrams and explanations. Figure 1-1A. - Basic tuned circuits.SERIES TUNED CIRCUIT

Figure 1-1B. - Basic tuned circuits.PARALLEL TUNED CIRCUIT

You have already learned how a coil and a capacitor in an a.c. circuit perform. This action will be the basis of the following discussion about tuned circuits. Why should you study tuned circuits? Because the tuned circuit that has been described above is used in just about every electronic device, from remote-controlled model airplanes to the most sophisticated space satellite. You can assume, if you are going to be involved in electricity or electronics, that you will need to have a good working knowledge of tuned circuits and how they are used in electronic and electrical circuits. REVIEW OF SERIES/PARALLEL A.C. CIRCUITS First we will review the effects of frequency on a circuit which contains resistance, inductance, and capacitance. This review recaps what you previously learned in the Inductive and Capacitive Reactance chapter in module 2 of the NEETS. FREQUENCY EFFECTS ON RLC CIRCUITS Perhaps the most often used control of a radio or television set is the station or channel selector. Of course, the volume, tone, and picture quality controls are adjusted to suit the individual's taste, but very

often they are not adjusted when the station is changed. What goes on behind this station selecting? In this chapter, you will learn the basic principles that account for the ability of circuits to "tune" to the desired station.

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OSCILLATORS

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Click here to order Oscillators Online OSCILLATORS LEARNING OBJECTIVES Upon completion of this chapter you will be able to:

List the two broad classifications of oscillators (wave generators). Identify the three frequencydetermining devices for sinewave oscillators. Describe the differences between series-fed and shuntfed oscillators. Explain how the crystal is equivalent to the series and parallel LC circuit. Identify the Armstrong oscillator. Identify the Hartley oscillator. Identify the Colpitts oscillator. Identify the resistivecapacitive oscillator.

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Determine the frequency of a resistive-capacitive oscillator. Explain the operation of a pulsed oscillator. Determine how many cycles are present in the output of a pulsed oscillator. Explain how frequency multiplication takes place. INTRODUCTION WAVE GENERATORS play a prominent role in the field of electronics. They generate signals from a few hertz to several gigahertz (109 hertz). Modern wave generators use many different circuits and generate such outputs as SINUSOIDAL, SQUARE, RECTANGULAR, SAWTOOTH, and TRAPEZOIDAL waveshapes. These waveshapes serve many useful purposes in the electronic circuits you will be studying. For example, they are used extensively throughout the television receiver to reproduce both picture and sound. One type of wave generator is known as an OSCILLATOR. An oscillator can be regarded as an amplifier which provides its own input signal. Oscillators are classified according to the waveshapes they produce and the requirements needed for them to produce oscillations. CLASSIFICATION OF OSCILLATORS (GENERATORS) Wave generators can be classified into two broad categories according to their output waveshapes, SINUSOIDAL and NONSINUSOIDAL. Sinusoidal Oscillators A sinusoidal oscillator produces a sine-wave output signal. Ideally, the output signal is of constant amplitude with no variation in frequency. Actually, something less than this is usually obtained. The degree to which the ideal is approached depends upon such factors as class of amplifier operation, amplifier characteristics, frequency stability, and amplitude stability.

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Sine-wave generators produce signals ranging from low audio frequencies to ultrahigh radio and microwave frequencies. Many low-frequency generators use resistors and capacitors to form their frequency-determining networks and are referred to as RC OSCILLATORS. They are widely used in the audio-frequency range. Another type of sine-wave generator uses inductors and capacitors for its frequency-determining network. This type is known as the LC OSCILLATOR. LC oscillators, which use tank circuits, are commonly used for the higher radio frequencies. They are not suitable for use as extremely low-frequency oscillators because the inductors and capacitors would be large in size, heavy, and costly to manufacture. A third type of sine-wave generator is the CRYSTALCONTROLLED OSCILLATOR. The crystal-controlled oscillator provides excellent frequency stability and is used from the middle of the audio range through the radio frequency range. Nonsinusoidal Oscillators Nonsinusoidal oscillators generate complex waveforms, such as square, rectangular, trigger, sawtooth, or trapezoidal. Because their outputs are generally characterized by a sudden change, or relaxation, they are often referred to as RELAXATION OSCILLATORS. The signal frequency of these oscillators is usually governed by the charge or discharge time of a capacitor in series with a resistor. Some types, however, contain inductors that affect the output frequency. Thus, like sinusoidal oscillators, both RC and LC networks are used for determining the frequency of oscillation. Within this category of nonsinusoidal oscillators are MULTIVIBRATORS, BLOCKING OSCILLATORS, SAWTOOTH GENERATORS, and TRAPEZOIDAL GENERATORS. THE BASIC OSCILLATOR An oscillator can be thought of as an amplifier that provides itself (through feedback) with an input signal. By definition, it is a nonrotating device for producing alternating current, the output

frequency of which is determined by the characteristics of the device. The primary purpose of an oscillator is to generate a given waveform at a constant peak amplitude and specific frequency and to maintain this waveform within certain limits of amplitude and frequency. An oscillator must provide amplification. Amplification of signal power occurs from input to output. In an oscillator, a portion of the output is fed back to sustain the input, as shown in figure 21.Enough power must be fed back to the input circuit for the oscillator to drive itself as does a signal generator. To cause the oscillator to be self-driven, the feedback signal must also be Figure 2-1. - Basic oscillator block diagram.

REGENERATIVE (positive). Regenerative signals must have enough power to compensate for circuit losses and to maintain oscillations. Since a practical oscillator must oscillate at a predetermined frequency, a FREQUENCY-DETERMINING DEVICE (fdd), sometimes referred to as a FREQUENCY-DETERMINING NETWORK (fdn), is needed. This device acts as a filter, allowing only the desired frequency to pass. Without a frequencydetermining device, the stage will oscillate in a random manner, and a constant frequency will not be maintained. Before discussing oscillators further, let's review the requirements for an oscillator. First, amplification is required to provide the necessary gain for the signal. Second, sufficient regenerative feedback is required to sustain oscillations. Third, a frequency-

determining device is needed to maintain the desired output frequency. The basic oscillator requirements, in addition to the application, determine the type of oscillator to be used. Let's consider some factors that account for the complexity and unique characteristics of oscillators. Virtually every piece of equipment that uses an oscillator has two stability requirements, AMPLITUDE STABILITY and FREQUENCY STABILITY. Amplitude stability refers to the ability of the oscillator to maintain a constant amplitude in the output waveform. The more constant the amplitude of the output waveform, the better the amplitude stability. Frequency stability refers to the ability of the oscillator to maintain its operating frequency. The less the oscillator varies from its operating frequency, the better the frequency stability. A constant frequency and amplitude can be achieved by taking extreme care to prevent variations in LOAD, BIAS, and COMPONENT CHARACTERISTICS. Load variations can greatly affect the amplitude and frequency stability of the output of an oscillator. Therefore, maintaining the load as constant as possible is necessary to ensure a stable output. As you should know from your study of transistor biasing, bias variations affect the operating point of the transistor. These variations may alter the amplification capabilities of the oscillator circuits as well. A well-regulated power supply and a biasstabilizing circuit are required to ensure a constant, uniform signal output. As a result of changing temperature and humidity conditions, the value or characteristics of components such as capacitors, resistors, and transistors can change. The changes in these components also cause changes in amplitude and frequency. Output power is another consideration in the use of oscillators. Generally speaking, high power is obtained at some sacrifice to stability. When both requirements are to be met, a low-power, stable oscillator can be followed by a higher-power BUFFER AMPLIFIER. The buffer provides isolation between the oscillator

and the load to prevent changes in the load from affecting the oscillator. If the oscillator stage must develop high power, efficiency becomes important. Many oscillators use class C bias to increase efficiency. Other types of oscillators may use class A bias when a high efficiency is not required but distortion must be kept at a minimum. Other classes of bias may also be used with certain oscillators. SINE-WAVE OSCILLATOR RC networks, LC tanks, and crystals may appear in sine-wave oscillator circuits. An amplifier can be made into a sine-wave oscillator by providing regenerative feedback through an RC network. RC Network Figure 2-2, view (A), shows the block diagram of an amplifier with an RC network through which regenerative feedback is provided. The RC network also acts as the frequency-determining device. View (B) shows a vector analysis of the signal E at various points in the circuit. Figure 2-2A. - RC oscillator. AMPLIFIER WITH AND RC FEEDBACK NETWORK

Figure 2-2B. - RC oscillator. VECTOR ANALYSIS

To analyze the operation of the circuit in view (A), assume that the amplifier is a common-emitter configuration. The signal on the collector (M) is 180 degrees out of phase with the signal (input) on the base (R). For the circuit to produce regenerative feedback, the RC network must provide a 180-degree phase shift of the collector signal. When power is applied to the circuit, a noise voltage (noise contains many different frequencies) will appear on the collector. This noise signal is represented by vector LM in view (B). As the signal couples through C1 and across R1 (view (A)), a phase shift occurs. The voltage across R1 (ER1), represented by vector LN, has been shifted in phase (about 60 degrees) and reduced in amplitude. The signal at point N (view (A)) is then coupled to the next RC section (R2 and C2). Using the same size resistor and capacitor as before will cause another 60-degree phase shift to take place. The signal at point P is the voltage across R2, represented by vector LP. Now the signal at point P has been shifted about 120 degrees and its amplitude is reduced still further. The same actions occur for the last section (R3 and C3). This signal experiences another 60-degree phase shift and has further amplitude reduction. The signal at point R (ER3) has been shifted 180 degrees and is represented by vector LR. Notice that point R is the input to the base of the common-emitter amplifier. Also, vector LR shows that the signal on the base is regenerative (aiding the circuit operation). This meets the regenerative feedback requirement. An exact 60-degree phase shift per stage is not required, but the sum of the three phase shifts must equal 180 degrees.

For a given RC network, only one frequency of the initial noise signal will be shifted exactly 180 degrees. In other words, the network is frequency selective. Therefore, the RC network is the frequency-determining device since the lengths of the vectors and their phase relationships depend on frequency. The frequency of oscillations is governed by the values of resistance and capacitance in these sections. Variable resistors and capacitors may be used to provide tuning in the feedback network to allow for minor variations in phase shift. For an RC phase-shift oscillator, the amplifier is biased for class A operation to minimize distortion of the wave or signal.

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WAVEFORMS AND WAVE GENERATORS

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Click here to order Electronic Components Online WAVEFORMS AND WAVE GENERATORS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Explain the operation of astable, monostable, and bistable multivibrators. Explain the operation of a blocking oscillator. Explain the operation of a sawtooth generator. Explain the operation of a trapezoidal wave generator. Explain how the jump voltage is produced in a trapezoidal wave generator. WAVEFORMS This chapter will present methods of generating waveforms. Before you begin to study how waveforms are generated, you need to know the basic characteristics of waveforms. This

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section will discuss basic periodic waveforms. PERIODIC WAVEFORMS A waveform which undergoes a pattern of changes, returns to its original pattern, and repeats the same pattern of changes is called a PERIODIC waveform. Periodic waveforms are nonsinusoidal except for the sine wave. Periodic waveforms which will be discussed are the sine wave, square wave, rectangular wave, sawtooth wave, trapezoidal wave, and trigger pulses. Sine Wave Each completed pattern of a periodic waveform is called a CYCLE, as shown by the SINE WAVE in figure 3-1, view (A).Sine waves were presented in NEETS, Module 2, Alternating Current and Transformers, Chapter 1. Figure 3-1. - Periodic waveforms.

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Square Wave A SQUARE WAVE is shown in figure 3-1, view (B). As shown, it has two alternations of equal duration and a square presentation for each complete cycle. Figure 3-2 shows a breakdown of the square wave and is the figure you should view throughout the square wave discussion. The amplitude is measured vertically. The time for a complete cycle is measured between corresponding points on the wave (T0 to T2, or T1 to T3). Figure 3-2. - Square wave.

One alternation is called a PULSE. The time for one complete cycle is called the PULSE-REPETITION TIME (prt). The number of times in 1 second that the cycle repeats itself is called the PULSE-REPETITION FREQUENCY (prf) or PULSE-REPETITION RATE (prr). If each alternation in figure 3-2 is 200 microseconds (µs), the prt will be 400 microseconds, and the prf will be 2,500 hertz. The following examples are provided to illustrate the mathematical relationship between prf and prt:

You should readily see that prt is just the inverse of prf. Therefore: Given:

The length of the pulse measured in time (T0 to T1) is referred to as the PULSE WIDTH (pw). The left side of the pulse is called the LEADING EDGE and the right side is called the TRAILING EDGE. Time is required for a voltage or current to change in amplitude. The interval of time needed for the voltage to go from 0 to 100 percent (or from 100 to 0 percent) of its maximum value is called the TRANSIENT INTERVAL. The two types of transient intervals are RISE TIME and FALL TIME. Rise time is more accurately defined as the time required for the voltage to build up from 10 percent to 90 percent of the maximum amplitude point. Fall time is the time required for the voltage to drop from 90 percent to 10 percent of the maximum amplitude point. In this text you will be presented with information in which waveforms appear to have instantaneous rise and fall times. This is done to simplify the presentation of the material. In reality these waveforms do have rise and fall times (transient intervals).

Rectangular Wave A rectangular wave is similar to the square wave. The difference is that in the rectangular waveform, the two alternations of the waveform are of unequal time duration. Figure 3-1, view (C), shows that the negative alternation (pulse) is shorter (in time) than the positive alternation. The negative alternation could be represented as the longer of the two alternations. Either way, the appearance is that of a rectangle. Sawtooth Wave The SAWTOOTH waveform is shown in figure 3-1 , view (D). A sawtooth wave resembles the teeth of a saw blade. There is a rapid vertical rise of voltage from T0 to T1, which is linear (straight). At T1 this voltage abruptly falls (essentially no time used) to its previous static value. The voltage remains at this value until T2 when it again has a linear rise. You can see this action in an oscilloscope where there are two voltage input locations, vertical and horizontal. If you apply a linear voltage to the vertical input, the electron beam will be forced to move in a vertical direction on the crt. A linear voltage applied to the horizontal input will cause the electron beam to move horizontally across the crt. The application of two linear voltages, one to the vertical input and one to the horizontal input at the same time, will cause the beam to move in both a vertical and horizontal (diagonal) direction at the same time. This then is how a sawtooth wave is made to appear on an oscilloscope. You should refer to NEETS, Module 6, Electronic Emission, Tubes, and Power Supplies, Chapter 2, for a review of oscilloscopes. Trapezoidal Wave A TRAPEZOIDAL wave looks like a sawtooth wave on top of a square or rectangular wave, as shown in figure 3-1 , view (E). The leading edge of a trapezoidal wave is called the JUMP voltage. The next portion of the wave is the linear rise or SLOPE. The trailing edge is called the FALL or DECAY. A trapezoidal wave is used to furnish deflection current in the electromagnetic cathode ray tube and is found in television and radar display systems. Electromagnetic cathode ray tubes use coils for the deflection system, and a linear rise in current is required for an accurate horizontal display. The square or rectangular wave portion provides the jump voltage for a

linear rise in current through the resistance of the coil. This will be explained further in a discussion of the trapezoidal sweep generator. Triggers A trigger is a very narrow pulse, as shown in figure 3-1 , view (F). Trigger pulses are normally used to turn other circuits on or off. WAVEFORM GENERATOR Nonsinusoidal oscillators generate complex waveforms such as those just discussed. Because the outputs of these oscillators are generally characterized by a sudden change, or relaxation, these oscillators are often called RELAXATION OSCILLATORS. The pulse repetition rate of these oscillators is usually governed by the charge and discharge timing of a capacitor in series with a resistor. However, some oscillators contain inductors that, along with circuit resistance, affect the output frequency. These RC and LC networks within oscillator circuits are used for frequency determination. Within this category of relaxation oscillators are MULTIVIBRATORS, BLOCKING OSCILLATORS, and SAWTOOTH- and TRAPEZOIDAL-WAVE GENERATORS. Many electronic circuits are not in an "on" condition all of the time. In computers, for example, waveforms must be turned on and off for specific lengths of time. The time intervals vary from tenths of microseconds to several thousand microseconds. Square and rectangular waveforms are normally used to turn such circuits on and off because the sharp leading and trailing edges make them ideal for timing purposes. MULTIVIBRATORS The type of circuit most often used to generate square or rectangular waves is the multivibrator. A multivibrator, as shown in figure 3-3, is basically two amplifier circuits arranged with regenerative feedback. One of the amplifiers is conducting while the other is cut off. Figure 3-3. - Astable Multivibrator.

When an input signal to one amplifier is large enough, the transistor can be driven into cutoff, and its collector voltage will be almost VCC. However, when the transistor is driven into saturation, its collector voltage will be about 0 volts. A circuit that is designed to go quickly from cutoff to saturation will produce a square or rectangular wave at its output. This principle is used in multivibrators. Multivibrators are classified according to the number of steady (stable) states of the circuit. A steady state exists when circuit operation is essentially constant; that is, one transistor remains in conduction and the other remains cut off until an external signal is applied. The three types of multivibrators are the ASTABLE, MONOSTABLE, and BISTABLE. The astable circuit has no stable state. With no external signal applied, the transistors alternately switch from cutoff to saturation at a frequency determined by the RC time constants of the coupling circuits. The monostable circuit has one stable state; one transistor conducts while the other is cut off. A signal must be applied to change this condition. After a period of time, determined by the internal RC components, the circuit will return to its original condition where it remains until the next signal arrives. The bistable multivibrator has two stable states. It

remains in one of the stable states until a trigger is applied. It then FLIPS to the other stable condition and remains there until another trigger is applied. The multivibrator then changes back (FLOPS) to its first stable state. Q.1 What type circuit is used to produce square or rectangular waves? Q.2 What type of multivibrator does not have a stable state? Q.3 What type of multvibrator has one stable state? Q.4 What type of multivibrator has two stable states?

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WAVE SHAPING

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Click here to order Electronic Components Online WAVE SHAPING LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Explain the operation of serieslimiter circuits. Explain the operation of parallel-limiter circuits. Describe the operation of a dual-diode limiter circuit. Explain the operation of clamper circuits. Explain the composition of nonsinusoidal waves. Explain how RC and RL circuits are used as integrators. Explain how RC and RL circuits are used as differentiators. Explain the operation of a counting circuit.

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Explain the operation of a step-by-step counter used as a frequency divider. LIMITERS As a technician, you will be confronted with many different types of LIMITING circuits. A LIMITER is defined as a device which limits some part of a waveform from exceeding a specified value. Limiting circuits are used primarily for wave shaping and circuit-protection applications. A limiter is little more than the half-wave rectifier you studied in NEETS, Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies. By using a diode, a resistor, and sometimes a dc bias voltage, you can build a limiter that will eliminate the positive or negative alternations of an input waveform. Such a circuit can also limit a portion of the alternations to a specific voltage level. In this chapter you will be introduced to five types of limiters: SERIES-POSITIVE, SERIES-NEGATIVE, PARALLEL-POSITIVE, PARALLEL-NEGATIVE, and DUAL-DIODE LIMITERS. Both series- and parallel-positive and negative limiters use biasing to obtain certain wave shapes. They will be discussed in this chapter. The diode in these circuits is the voltage-limiting component. Its polarity and location, with respect to ground, are the factors that determine circuit action. In series limiters, the diode is in series with the output. In parallel limiters, the diode is in parallel with the output. SERIES LIMITERS You should remember, from NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies, that a diode will conduct when the anode voltage is positive with respect to the cathode voltage. The diode will not conduct when the anode is negative in respect to the cathode. Keeping these two simple facts in mind as you study limiters will help you understand their operation. Your knowledge of voltage divider action from NEETS, Module 1, Introduction to Matter, Energy, and Direct Current will also help you understand limiters.

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In a SERIES LIMITER, a diode is connected in series with the output, as shown in view (A) of figure 4-1. The input signal is applied across the diode and resistor and the output is taken across the resistor. The series-limiter circuit can limit either the positive or negative alternation, depending on the polarity of the diode connection with respect to ground. The circuit shown in figure 4-1, view (B), is a SERIES-POSITIVE LIMITER. Reversing D1 would change the circuit to a SERIES-NEGATIVE LIMITER. Figure 4-1A. - Series-positive limiter.

Figure 4-1B. - Series-positive limiter.

Series-Positive Limiter Let's look at the series-positive limiter and its outputs in figure 4-1. Diode D1 is in series with the output and the output is taken across resistor R1. The input must be negative with respect to the anode of the diode to make the diode conduct. When the positive alternation of the input signal (T0 to T1) is applied to the circuit, the cathode is positive with respect to the anode. The diode is reverse biased and will not conduct. Since no current can flow, no output is developed across the resistor during the positive alternation of the input signal. During the negative half cycle of the input signal (T1 to T2), the cathode is negative with respect to the anode. This causes D1 to be forward biased. Current flows through R1 and an output is developed. The output during each negative alternation of the input is approximately the same as the input (-10 volts) because most of the voltage is developed across the resistor. Ideally, the output wave shape should be exactly the same as the input wave shape with only the limited portion removed. When the diode is reverse biased, the circuit has a small amount of reverse current flow, as shown just above the 0-volt reference line in figure 4-2.During the limiting portion of the input signal, the diode resistance should be high compared to the resistor. During the time the diode is conducting, the resistance of the diode

should be small as compared to that of the resistor. In other words, the diode should have a very high front-toback ratio (forward resistance compared to reverse resistance). This relationship can be better understood if you study the effects that a front-to-back resistance ratio has on circuit output. Figure 4-2. - Actual output of a series-positive limiter.

The following formula can be used to determine the output amplitude of the signal:

Let's use the formula to compare the front-to-back ratio of the diode in the forward- and reverse-biased conditions. Given:

You can readily see that the formula comparison of the forward- and reverse-bias resistance conditions shows that a small amount of reverse current will flow during the limited portion of the input waveform. This small amount of reverse current will develop as the small positive voltage (0.09 volt) shown in figure 4-2 (T0 to T1 and T2 to T3). The actual amount of voltage developed will depend on the type of diode used. For the remainder of this chapter, we will use only idealized waveforms and disregard this small voltage. SERIES-POSITIVE LIMITER WITH BIAS. - In the seriespositive limiter (figure 4-1, view (A)), the reference point at the bottom of resistor R1 is ground, or 0 volts. By placing a dc potential at point (1) in figure 4-3 (views (A) and (B)), you can change the reference point. The reference point changes by the amount of dc potential that is supplied by the battery. The battery can either aid or oppose the flow of current in the series-limiter circuit. POSITIVE BIAS (aiding) is shown in view (A) and NEGATIVE BIAS (opposing) is shown in view (B). Figure 4-3A. - Positive and negative bias. POSITIVE BIAS

Figure 4-3B. - Positive and negative bias. NEGATIVE BIAS

When the dc aids forward bias, as in view (A), the diode conducts even with no signal applied. An input signal sufficiently positive to overcome the dc bias potential is required to reverse bias and cut off the diode.

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Book 10

Back • Home • Up • Next Click here to order Electronic Components Online WAVE PROPAGATION Transverse waves Terms used in wave motion Characteristics of wave motion Refraction Sound waves Elasticity and density and velocity of transmission Light waves Speed of Light Electric Field Combined Electric and Magnetic Fields Summary Answers

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Radio wave propagation Radio Waves Polarization The effect of the earth's atmosphere on radio waves Sky Wave Refraction in the ionosphere Skip Distance/Skip Zone Transmission Losses

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Variations in the Ionosphere Frequency selection considerations Weather versus propagation Tropospheric propagation Summary Answers Principles of transmission lines Types of transmission mediums Losses in transmission lines Length of a transmission line Leakage Current Characteristic Impedance and the Infinite Line Voltage change along a transmission line Velocity of wave propagation Reflections on a transmission line Reflections of AC voltage from a short circuit Terminating a transmission line Standing waves on a transmission line Summary Answers Antennas Radiation of electromagnetic energy Antenna characteristics Polarization Requirements for Various Frequencies Radiation resistance Polar-coordinate graph for anisotropic radiator Methods of Feeding Energy to an Antenna Folded dipole Array antennas Directional arrays Broadside arrays End-Fire arrays Parasitic arrays Multielement Parasitic Array

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Special Antennas Rhombic antennas RF safety precautions RF Burns Summary Answers Order this information in Adobe PDF Printable Format

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WAVE PROPAGATION

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Click here to order Electronic Components Online WAVE PROPAGATION LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Upon completion of this chapter, you should be able to:

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State what wave motion is, define the terms reflection, refraction, and diffraction, and describe the Doppler effect. State what sound waves are and define a propagating medium.

List and define terms as applied to sound waves, such as cycle, frequency, wavelength, and velocity.

Order this information on CDDefine pitch, intensity, loudness, and quality Rom List the three requirements for sound.

and their application to sound waves. State the acoustical effects that echoes, reverberation, resonance, and noise have on sound waves. Define light waves and list their characteristics.

List the various colors of light and define the terms reflection, refraction, diffusion, and absorption as applied to light waves. State the difference between sound waves and light waves.

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State the electromagnetic wave theory and list the components of the electromagnetic wave. INTRODUCTION TO WAVE PROPAGATION Of the many technical subjects that naval personnel are expected to know, probably the one least susceptible to change is the theory of wave propagation. The basic principles that enable waves to be propagated (transmitted) through space are the same today as they were 70 years ago. One would think, then, that a thorough understanding of these principles is a relatively simple task. For the electrical engineer or the individual with a natural curiosity for the unknown, it is indeed a simple task. Most technicians, however, tend to view wave propagation as something complex and confusing, and would just as soon see this chapter completely disappear from training manuals. This attitude undoubtedly stems from the fact that wave propagation is an invisible force that cannot be detected by the sense of sight or touch. Understanding wave propagation requires the use of the imagination to visualize the associated concepts and how they are used in practical application. This manual was developed to help you visualize and understand those concepts. Through ample use of illustrations and a step-by-step transition from the simple to the complex, we will help you develop a better understanding of wave propagation. In this chapter, we will discuss propagation theory on an introductory level, without going into the technical details that concern the engineer. However, you must still use thought and imagination to understand the new ideas and concepts as they are presented. To understand radio wave propagation, you must first learn what wave propagation is and some of the basic physics or properties that affect propagation. Many of these properties are common everyday occurrences, with which you are already familiar. WHAT IS PROPAGATION? Early man was quick to recognize the need to communicate beyond the range of the human voice. To satisfy this need, he developed alternate methods of communication, such as hand gestures, beating on a hollow log, and smoke signals. Although these methods were effective, they were still greatly limited in range. Eventually, the range limitations were overcome by the development of courier and postal systems; but there was then a problem of speed. For centuries the time required for the delivery of a message depended on the speed of a horse. During the latter part of the 19th century, both distance and time limitations were largely overcome. The invention of the telegraph made possible instantaneous communication over long wires. Then a short time later, man discovered how to transmit messages in the form of RADIO WAVES. As you will learn in this chapter, radio waves are propagated. PROPAGATION means "movement through a medium." This is most easily illustrated by light rays. When a light is turned on in a darkened room, light rays travel from the light bulb throughout the room. When a flashlight is turned on, light rays also radiate from its bulb, but are focused into a narrow beam. You can use these examples to picture how radio waves propagate. Like the light in the room, radio waves may spread out in all directions. They can also be focused (concentrated) like the flashlight, depending upon the need. Radio waves are a form of radiant energy, similar to light and heat. Although they can neither be seen nor felt, their presence can be detected through the use of sensitive measuring devices. The speed at which both forms of waves travel is the same; they both travel at the speed of light.

You may wonder why you can see light but not radio waves, which consist of the same form of energy as light. The reason is that you can only "see" what your eyes can detect. Your eyes can detect radiant energy only within a fixed range of frequencies. Since the frequencies of radio waves are below the frequencies your eyes can detect, you cannot see radio waves. The theory of wave propagation that we discuss in this module applies to Navy electronic equipment, such as radar, navigation, detection, and communication equipment. We will not discuss these individual systems in this module, but we will explain them in future modules. Q.1 What is propagation? PRINCIPLES OF WAVE MOTION All things on the earth - on the land, or in the water - are showered continually with waves of energy. Some of these waves stimulate our senses and can be seen, felt, or heard. For instance, we can see light, hear sound, and feel heat. However, there are some waves that do not stimulate our senses. For example, radio waves, such as those received by our portable radio or television sets, cannot be seen, heard, or felt. A device must be used to convert radio waves into light (TV pictures) and sound (audio) for us to sense them. A WAVE can be defined as a DISTURBANCE (sound, light, radio waves) that moves through a MEDIUM (air, water, vacuum). To help you understand what is meant by "a disturbance which moves through a medium," picture the following illustration. You are standing in the middle of a wheat field. As the wind blows across the field toward you, you can see the wheat stalks bending and rising as the force of the wind moves into and across them. The wheat appears to be moving toward you, but it isn't. Instead, the stalks are actually moving back and forth. We can then say that the "medium "in this illustration is the wheat and the "disturbance " is the wind moving the stalks of wheat. WAVE MOTION can be defined as a recurring disturbance advancing through space with or without the use of a physical medium. Wave motion, therefore, is a means of moving or transferring energy from one point to another point. For example, when sound waves strike a microphone, sound energy is converted into electrical energy. When light waves strike a phototransistor or radio waves strike an antenna, they are likewise converted into electrical energy. Therefore, sound, light, and radio waves are all forms of energy that are moved by wave motion. We will discuss sound waves, light waves, and radio waves later. Q.2 How is a wave defined as it applies to wave propagation? Q.3 What is wave motion? Q.4 What are some examples of wave motion? WAVE MOTION IN WATER A type of wave motion familiar to almost everyone is the movement of waves in water. We will explain these waves first to help you understand wave motion and the terms used to describe it.

Basic wave motion can be shown by dropping a stone into a pool of water (see figure 1-1). As the stone enters the water, a surface disturbance is created, resulting in an expanding series of circular waves. Figure 1-2 is a diagram of this action. View A shows the falling stone just an instant before it strikes the water. View B shows the action taking place at the instant the stone strikes the surface, pushing the water that is around it upward and outward. In view C, the stone has sunk deeper into the water, which has closed violently over it causing some spray, while the leading wave has moved outward. An instant later, the stone has sunk out of sight, leaving the water disturbed as shown in view D. Here the leading wave has continued to move outward and is followed by a series of waves gradually diminishing in amplitude. Meanwhile, the disturbance at the original point of contact has gradually subsided. Figure 1-1. - Formation of waves in water.

Figure 1-2. - How a falling stone creates wave motion to the surface of water.

In this example, the water is not actually being moved outward by the motion of the waves, but up and down as the waves move outward. The up and down motion is transverse, or at right angles, to the outward motion of the waves. This type of wave motion is called TRANSVERSE WAVE MOTION. Q.5 What type of wave motion is represented by the motion of water?

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Radio wave propagation

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Click here to order Electronic Components Online RADIO WAVE PROPAGATION LEARNING OBJECTIVES Upon completion of this unit, you should be able to: State what the electromagnetic field is and what components make up the electromagnetic field. State the difference between the induction field and the radiation field. State what radio waves are.

List the components of a radio wave and define the terms cycle, frequency, harmonics, period, wavelength, and velocity as applied to radio wave propagation.

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Compute the wavelength of radio waves. State how radio waves are polarized, vertically and horizontally.

State what reflection, refraction, and Order this diffraction are as applied to radio waves. information on CDState what influence the Earth's atmosphere Rom has on radio waves and list the different layers of the Earth's atmosphere. Identify a ground wave, a sky wave, and state the effects of the ionosphere on the sky wave. Identify the structure of the ionosphere.

Define density of layer, frequency, angle of incidence, skip distance, and skip zone. Describe propagation paths.

Describe fading, multipath fading, and selective fading. Describe propagation paths. State how transmission losses affect radio wave propagation.

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State how electromagnetic interference, manmade/natural interference, and ionospheric disturbances affect radio wave propagation. State how transmission losses affect radio wave propagation. Identify variations in the ionosphere.

Identify the maximum, optimum, and lowest usable frequencies of radio waves. State what temperature inversion is, how frequency predictions are made, and how weather affects frequency. State what tropospheric scatter is and how it affects radio wave propagation.

ELECTROMAGNETIC FIELDS The way energy is propagated into free space is a source of great dispute among people concerned with it. Although many theories have been proposed, the following theory adequately explains the phenomena and has been widely accepted. There are two basic fields associated with every antenna; an INDUCTION FIELD and a RADIATION FIELD. The field associated with the energy stored in the antenna is the induction field. This field is said to provide no part in the transmission of electromagnetic energy through free space. However, without the presence of the induction field, there would be no energy radiated. INDUCTION FIELD Figure 2-1, a low-frequency generator connected to an antenna, will help you understand how the induction field is produced. Let's follow the generator through one cycle of operation. Figure 2-1. - Induction field about an antenna.

Initially, you can consider that the generator output is zero and that no fields exist about the antenna, as shown in view A. Now assume that the generator produces a slight potential and has the instantaneous polarity shown in view B. Because of this slight potential, the antenna capacitance acts as a short, allowing a large flow of current (I) through the antenna in the direction shown. This current flow, in turn, produces a large magnetic field about the antenna. Since the flow of current at each end of the antenna is minimum, the corresponding magnetic fields at each end of the antenna are also minimum. As time passes, charges, which oppose antenna current and produce an electrostatic field (E field), collect at each end of the antenna. Eventually, the antenna capacitance becomes fully charged and stops current flow through the antenna. Under this condition, the electrostatic field is maximum, and the magnetic field (H field) is fully collapsed, as shown in view C. As the generator potential decreases back to zero, the potential of the antenna begins to discharge. During the discharging process, the electrostatic field collapses and the direction of current flow reverses, as shown in view D. When the current again begins to flow, an associated magnetic field is generated. Eventually, the electrostatic field completely collapses, the generator potential reverses, and current is maximum, as shown in view E. As charges collect at each end of the antenna, an electrostatic field is produced and current flow decreases. This causes the magnetic field to begin collapsing. The collapsing magnetic field produces more current flow, a greater accumulation of charge, and a greater electrostatic field. The antenna gradually reaches the condition shown in view F, where current is zero and the collected charges are maximum. As the generator potential again decreases toward zero, the antenna begins to discharge and the electrostatic field begins to collapse. When the generator potential reaches zero, discharge current is maximum and the associated magnetic field is maximum. A brief time later, generator potential reverses, and the condition shown in view B recurs. NOTE: The electric field (E field) and the electrostatic field (E field) are the same. They will be used

interchangeably throughout this text. The graph shown in figure 2-2 shows the relationship between the magnetic (H) field and the electric (E) field plotted against time. Note that the two fields are 90 degrees out of phase with each other. If you compare the graph in figure 2-2 with figure 2-1, you will notice that the two fields around the antenna are displaced 90 degrees from each other in space. (The H field exists in a plane perpendicular to the antenna. The E field exists in a plane parallel with the antenna, as shown in figure 2-1.) Figure 2-2. - Phase relationship of induction field components.

All the energy supplied to the induction field is returned to the antenna by the collapsing E and H fields. No energy from the induction field is radiated from the antenna. Therefore, the induction field is considered a local field and plays no part in the transmission of electromagnetic energy. The induction field represents only the stored energy in the antenna and is responsible only for the resonant effects that the antenna reflects to the generator. RADIATION FIELDS The E and H fields that are set up in the transfer of energy through space are known collectively as the radiation field. This radiation field is responsible for electromagnetic radiation from the antenna. The radiation field decreases as the distance from the antenna is increased. Because the decrease is linear, the radiation field reaches great distances from the antenna. Let's look at a half-wave antenna to illustrate how this radiation actually takes place. Simply stated, a half-wave antenna is one that has an electrical length equal to half the wavelength of the signal being transmitted. Assume, for example, that a transmitter is operating at 30 megahertz. If a halfwave antenna is used with the transmitter, the antenna's electrical length would have to be at least

16 feet long. (The formula used to compute the electrical length of an antenna will be explained in chapter 4.) When power is delivered to the half-wave antenna, both an induction field and a radiation field are set up by the fluctuating energy. At the antenna, the intensities of these fields are proportional to the amount of power delivered to the antenna from a source such as a transmitter. At a short distance from the antenna and beyond, only the radiation field exists. This radiation field is made up of an electric component and a magnetic component at right angles to each other in space and varying together in intensity. With a high-frequency generator (a transmitter) connected to the antenna, the induction field is produced as described in the previous section. However, the generator potential reverses before the electrostatic field has had time to collapse completely. The reversed generator potential neutralizes the remaining antenna charges, leaving a resultant E field in space. Figure 2-3 is a simple picture of an E field detaching itself from an antenna. (The H field will not be considered, although it is present.) In view A the voltage is maximum and the electric field has maximum intensity. The lines of force begin at the end of the antenna that is positively charged and extend to the end of the antenna that is negatively charged. Note that the outer E lines are stretched away from the inner lines. This is because of the repelling force that takes place between lines of force in the same direction. As the voltage drops (view B), the separated charges come together, and the ends of the lines move toward the center of the antenna. But, since lines of force in the same direction repel each other, the centers of the lines are still being held out. Figure 2-3. - Radiation from an antenna.

As the voltage approaches zero (view B), some of the lines collapse back into the antenna. At the same time, the ends of other lines begin to come together to form a complete loop. Notice the direction of these lines of force next to the antenna in view C. At this point the voltage on the antenna is zero. As the charge starts to build up in the opposite direction (view D), electric lines of force again begin at the positive end of the antenna and stretch to the negative end of the antenna. These lines of force, being in the same direction as the sides of the closed loops next to the antenna, repel the closed loops and force them out into space at the speed of light. As these loops travel through space, they generate a magnetic field in phase with them. Since each successive E field is generated with a polarity that is opposite the preceding E field (that is, the lines of force are opposite), an oscillating electric field is produced along the path of travel. When an electric field oscillates, a magnetic field having an intensity that varies directly with

that of the E field is produced. The variations in magnetic field intensity, in turn, produce another E field. Thus, the two varying fields sustain each other, resulting in electromagnetic wave propagation. During this radiation process, the E and H fields are in phase in time but physically displaced 90 degrees in space. Thus, the varying magnetic field produces a varying electric field; and the varying electric field, in turn, sustains the varying magnetic field. Each field supports the other, and neither can be propagated by itself. Figure 2-4 shows a comparison between the induction field and the radiation field. Figure 2-4. - E and H components of induction and radiation fields.

Q.1 Which two composite fields (composed of E and H fields) are associated with every antenna?

Q.2 What composite field (composed of E and H fields) is found stored in the antenna? Q.3 What composite field (composed of E and H fields) is propagated into free space?

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Principles of transmission lines

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Click here to order Electronic Components Online PRINCIPLES OF TRANSMISSION LINES LEARNING OBJECTIVES Upon completion of this chapter, you will be able to: State what a transmission line is and how transmission lines are used. Explain the operating principles of transmission lines. Join Integrated Describe the five types of transmission Publishing's lines. State the length of a transmission Discussion Group line. Explain the theory of the transmission line. Define the term LUMPED CONSTANTS in relation to a transmission line. Define the term DISTRIBUTED CONSTANTS in relation to a transmission line. Define LEAKAGE CURRENT. Describe how the electromagnetic lines Order this of force around a transmission line are information on CDaffected by the distributed constants. Rom Define the term CHARACTERISTIC IMPEDANCE and explain how it affects the transfer of energy along a transmission line. State how the energy transfer along a transmission line is affected by characteristic impedance and the infinite line. Order this Identify the cause of and describe the information in characteristics of reflections on a Print (Hardcopy). transmission line. Define the term STANDING WAVES as applied to a transmission line. Describe how standing waves are produced on a transmission line and identify the types of terminations.

Describe the types of standing-wave ratios. INTRODUCTION TO TRANSMISSION LINES A TRANSMISSION LINE is a device designed to guide electrical energy from one point to another. It is used, for example, to transfer the output rf energy of a transmitter to an antenna. This energy will not travel through normal electrical wire without great losses. Although the antenna can be connected directly to the transmitter, the antenna is usually located some distance away from the transmitter. On board ship, the transmitter is located inside a radio room and its associated antenna is mounted on a mast. A transmission line is used to connect the transmitter and the antenna. The transmission line has a single purpose for both the transmitter and the antenna. This purpose is to transfer the energy output of the transmitter to the antenna with the least possible power loss. How well this is done depends on the special physical and electrical characteristics (impedance and resistance) of the transmission line. TERMINOLOGY All transmission lines have two ends (see figure 3-1). The end of a two-wire transmission line connected to a source is ordinarily called the INPUT END or the GENERATOR END. Other names given to this end are TRANSMITTER END, SENDING END, and SOURCE. The other end of the line is called the OUTPUT END or RECEIVING END. Other names given to the output end are LOAD END and SINK. Figure 3-1. - Basic transmission line.

You can describe a transmission line in terms of its impedance. The ratio of voltage to current (Ein/Iin) at the input end is known as the INPUT IMPEDANCE (Zin). This is the impedance presented to the transmitter by the transmission line and its load, the antenna. The ratio of voltage to current at the output (E out/Iout) end is known as the OUTPUT IMPEDANCE (Zout). This is the impedance presented to the load by the transmission line and its source. If an infinitely long transmission line could be used, the ratio of voltage to current at any point on that transmission line would be some particular value of impedance. This impedance is known as the CHARACTERISTIC IMPEDANCE. Q.1 What connecting link is used to transfer energy from a radio transmitter to its antenna located on the mast of a ship? Q.2 What term is used for the end of the transmission line that is connected to a

transmitter? Q.3 What term is used for the end of the transmission line that is connected to an antenna?

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Antennas

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Click here to order Electronic Components Online ANTENNAS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: State the basic principles of antenna radiation and list the parts of an antenna. Explain current and voltage distribution on an antenna. Describe how electromagnetic energy is radiated from an antenna.

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Explain polarization, gain, and radiation resistance characteristics of an antenna. Describe the theory of operation of half- wave and quarter-wave antennas. List the various array antennas.

Describe the directional array antennas presented and explain the basic operation of each.

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Identify various special antennas presented, such as long-wire, V, rhombic, turnstile, ground-plane, and corner-reflector; describe the operation of each. List safety precautions when working aloft and around antennas.

INTRODUCTION If you had been around in the early days of electronics, you would have considered an ANTENNA (AERIAL) to be little more than a piece of wire strung between two trees or upright poles. In those days, technicians assumed that longer antennas automatically provided better reception than shorter antennas. They also believed that a mysterious MEDIUM filled all space, and that an antenna used this medium to send and receive its energy. These two assumptions have since been discarded. Modern antennas have evolved to the point that highly directional, specially designed antennas are used to relay worldwide communications in space through the use of satellites and Earth station antennas (fig. 4-1). Present transmission theories are based on the assumption that space itself is the only medium necessary to propagate (transmit) radio energy. Figure 4-1. - Satellite/earth station communications system.

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A tremendous amount of knowledge and information has been gained about the design of antennas and radio-wave propagation. Still, many old-time technicians will tell you that when it comes to designing the length of an antenna, the best procedure is to perform all calculations and try out the antenna. If it doesn't work right, use a cut-and-try method until it does. Fortunately, enough information has been collected over the last few decades that it is now possible to predict the behavior of antennas. This chapter will discuss and explain the basic design and operation of antennas. PRINCIPLES OF ANTENNA RADIATION After an rf signal has been generated in a transmitter, some means

must be used to radiate this signal through space to a receiver. The device that does this job is the antenna. The transmitter signal energy is sent into space by a TRANSMITTING ANTENNA; the rf signal is then picked up from space by a RECEIVING ANTENNA. The rf energy is transmitted into space in the form of an electromagnetic field. As the traveling electromagnetic field arrives at the receiving antenna, a voltage is induced into the antenna (a conductor). The rf voltages induced into the receiving antenna are then passed into the receiver and converted back into the transmitted rf information. The design of the antenna system is very important in a transmitting station. The antenna must be able to radiate efficiently so the power supplied by the transmitter is not wasted. An efficient transmitting antenna must have exact dimensions. The dimensions are determined by the transmitting frequencies. The dimensions of the receiving antenna are not critical for relatively low radio frequencies. However, as the frequency of the signal being received increases, the design and installation of the receiving antenna become more critical. An example of this is a television receiving antenna. If you raise it a few more inches from the ground or give a slight turn in direction, you can change a snowy blur into a clear picture. The conventional antenna is a conductor, or system of conductors, that radiates or intercepts electromagnetic wave energy. An ideal antenna has a definite length and a uniform diameter, and is completely isolated in space. However, this ideal antenna is not realistic. Many factors make the design of an antenna for a communications system a more complex problem than you would expect. These factors include the height of the radiator above the earth, the conductivity of the earth below it, and the shape and dimensions of the antenna. All of these factors affect the radiatedfield pattern of the antenna in space. Another problem in antenna design is that the radiation pattern of the antenna must be directed between certain angles in a horizontal or vertical plane, or both. Most practical transmitting antennas are divided into two basic classifications, HERTZ (half-wave) ANTENNAS and MARCONI (quarter-wave) ANTENNAS. Hertz antennas are generally installed some distance above the ground and are positioned to radiate either vertically or horizontally. Marconi antennas operate with one

end grounded and are mounted perpendicular to the Earth or to a surface acting as a ground. Hertz antennas are generally used for frequencies above 2 megahertz. Marconi antennas are used for frequencies below 2 megahertz and may be used at higher frequencies in certain applications. A complete antenna system consists of three parts: (1) The COUPLING DEVICE, (2) the FEEDER, and (3) the ANTENNA, as shown in figure 4-2. The coupling device (coupling coil) connects the transmitter to the feeder. The feeder is a transmission line that carries energy to the antenna. The antenna radiates this energy into space. Figure 4-2. - Typical antenna system.

The factors that determine the type, size, and shape of the antenna are (1) the frequency of operation of the transmitter, (2) the amount of power to be radiated, and (3) the general direction of the receiving set. Typical antennas are shown in figure 4-3. Figure 4-3. - Typical antennas.

CURRENT AND VOLTAGE DISTRIBUTION ON AN ANTENNA A current flowing in a wire whose length is properly related to the rf produces an electro magnetic field. This field is radiated from the wire and is set free in space. We will discuss how these waves are set free later in this chapter. Remember, the principles of radiation of electromagnetic energy are based on two laws: 1. A MOVING ELECTRIC FIELD CREATES A MAGNETIC (H) FIELD. 2. A MOVING MAGNETIC FIELD CREATES AN ELECTRIC (E) FIELD. In space, these two fields will be in phase and perpendicular to each other at any given time. Although a conductor is usually considered present when a moving electric or magnetic field is mentioned, the laws that govern these fields say nothing about a

conductor. Therefore, these laws hold true whether a conductor is present or not. Figure 4-4 shows the current and voltage distribution on a halfwave (Hertz) antenna. In view A, a piece of wire is cut in half and attached to the terminals of a high-frequency ac generator. The frequency of the generator is set so that each half of the wire is 1/4 wavelength of the output. The result is a common type of antenna known as a DIPOLE. Figure 4-4. - Current and voltage distribution on an antenna.

At a given time the right side of the generator is positive and the left side negative. Remember that like charges repel. Because of this, electrons will flow away from the negative terminal as far as possible, but will be attracted to the positive terminal. View B

shows the direction and distribution of electron flow. The distribution curve shows that most current flows in the center and none flows at the ends. The current distribution over the antenna will always be the same no matter how much or how little current is flowing. However, current at any given point on the antenna will vary directly with the amount of voltage developed by the generator. One-quarter cycle after electrons have begun to flow, the generator will develop its maximum voltage and the current will decrease to 0. At that time the condition shown in view C will exist. No current will be flowing, but a maximum number of electrons will be at the left end of the line and a minimum number at the right end. The charge distribution view C along the wire will vary as the voltage of the generator varies. Therefore, you may draw the following conclusions: 1. A current flows in the antenna with an amplitude that varies with the generator voltage. 2. A sinusoidal distribution of charge exists on the antenna. Every 1/2 cycle, the charges reverse polarity. 3. The sinusoidal variation in charge magnitude lags the sinusoidal variation in current by 1/4 cycle. Q.1 What are the two basic classifications of antennas? Q.2 What are the three parts of a complete antenna system? Q.3 What three factors determine the type, size, and shape of an antenna?

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Book 11

Back • Home • Up • Next Click here to order Electronic Components Online Waveguide theory and application Waveguide theory Developing the Waveguide from Parallel Lines Energy Propagation in Waveguides Magnetic field pattern in a waveguide Radiation from probe placed in a waveguide Waveguide Modes of Operation Waveguide operation in other than dominant mode Waveguide Input/Output Methods Waveguide Impedance Matching Waveguide Terminations Waveguide Plumbing Waveguide Devices Cavity Resonators Several types of cavities Waveguide junctions Hybrid Rings Ferrite Devices Summary Answers

Microwave components and circuits

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Velocity Modulation Microwave tubes The Multicavity Power Klystron The Reflex Klystron The Decibel Measurement System The magnetron Split-anode magnetron Probable electron paths in an electron-resonance magnetron oscillator Magnetron coupling methods Solid-state microwave devices Varactor Devices Energy transfer from pump signal to input signal Bulk-Effect Semiconductors The Point-Contact Diode Microwave Transistors Summary Answers Microwave antennas Reflector antennas Horn radiators Antenna arrays Summary Answers

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Waveguide theory and application

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Click here to order Electronic Components Online WAVEGUIDE THEORY AND APPLICATION LEARNING OBJECTIVES Upon completion of this chapter the student will be able to: Describe the development of the various types of waveguides in terms of their advantages and disadvantages. Describe the physical dimensions of the various types of waveguides and explain the effects of those dimensions on power and frequency. Explain the propagation of energy in waveguides in terms of electromagnetic field theory. Identify the modes of operation in waveguides.

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Explain the basic input/output methods used in waveguides. Describe the basic principles of waveguide plumbing. Explain the reasons for and the methods of terminating waveguides.

Explain the basic theory of operation and applications of directional couplers. Describe the basic theory of operation, construction, and applications of cavity resonators. Describe the basic theory of operation of waveguide junctions. Explain the operation of ferrite devices in terms of their applications.

INTRODUCTION TO WAVEGUIDE THEORY AND APPLICATION That portion of the electromagnetic spectrum which falls between 1000 megahertz and 100,000 megahertz is referred to as the MICROWAVE region. Before discussing the principles and applications of microwave frequencies, the meaning of the term microwave as it is used in this module must be established. On the surface, the definition of a microwave would appear to be simple because, in electronics, the prefix "micro" normally means a millionth part of a unit. Micro also means small, which is a relative term, and it is used in that sense in this module. Microwave is a term loosely applied to identify electromagnetic waves above 1000 megahertz in frequency because of the short physical wavelengths of these frequencies. Short wavelength energy offers distinct advantages in many applications. For instance, excellent directivity can be obtained using relatively small antennas and low-power transmitters. These features are ideal for use in both military and civilian radar and communication applications. Small antennas and other small components are made possible by microwave frequency applications. This is an important consideration in shipboard equipment planning where space and weight are major problems. Microwave frequency usage is especially important in the design of shipboard radar because it makes possible the detection of smaller targets.

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Microwave frequencies present special problems in transmission, generation, and circuit design that are not encountered at lower frequencies. Conventional circuit theory is based on voltages and currents while microwave theory is based on electromagnetic fields. The concept of electromagnetic field interaction is not entirely new, since electromagnetic fields form the basis of all antenna theory. However, many students of electronics find electromagnetic field theory very difficult to visualize and understand. This module will present the principles of microwave theory in the simplest terms possible but many of the concepts are still somewhat difficult to thoroughly understand. Therefore, you must realize that this module will require very careful study for you to properly understand microwave theory. Antenna fundamentals were covered in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas. This module will show you the solutions to problems encountered at microwave frequencies, beginning with the transmission of microwave energy and continuing through to waveguides in chapter 1. Later chapters will cover the theory of operation of microwave components, circuits, and antennas. The application of these concepts will be discussed more thoroughly in later NEETS modules on radar and communications. Q.1 What is the region of the frequency spectrum from 1000 MHz to 100,000 MHz called? Q.2 Microwave theory is based upon what concept?

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Microwave components and circuits

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Click here to order Electronic Components Online MICROWAVE COMPONENTS AND CIRCUITS LEARNING OBJECTIVES Upon completion of this chapter the student will be able to: Explain the basic principles of microwave tubes and describe the limitations of conventional tubes. Describe the basic principles of velocity modulation. Outline the development of microwave tubes.

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Describe the basic theory of operation of klystrons including multicavity and reflex klystrons. Explain the basic theory of operation of traveling-wave tubes and backwardwave oscillators. Describe the construction, basic theories of operation, and typical Order this applications of magnetrons and information on CDamplitrons. Rom Describe the basic theory of operation of tunnel diodes when used in oscillator-, amplifier-, and frequencyconverter circuits. Explain the operation of varactors when used in parametric amplifiers and frequency converters. Order this

State the basic principles of operation of bulk-effect diodes and the gunn oscillator. Explain the basic operation of passive microwave diodes in terms of theory and application. Explain the basic operation of microwave transistors in terms of theory and application. MICROWAVE COMPONENTS The waveguides discussed in chapter 1 serve to transport microwave energy from one place to another. Energy is transported after it has been generated or amplified in a previous stage of the circuit. In this chapter you will be introduced to the special components used in those circuits. Microwave energy is used in both radar and communications applications. The fact that the frequencies are very high and the wavelengths very short presents special problems in circuit design. Components that were previously satisfactory for signal generation and amplification use are no longer useful in the microwave region. The theory of operation for these components is discussed in this chapter. Because the theory of operation is sometimes difficult to understand, you need to pay particular attention to detail as you study this chapter. It is written in the simplest manner possible while retaining the necessary technical complexity. MICROWAVE TUBE PRINCIPLES The efficiency of conventional tubes is largely independent of frequency up to a certain limit. When frequency increases beyond that limit, several factors combine to rapidly decrease tube efficiency. Tubes that are efficient in the microwave range usually operate on the theory of VELOCITY MODULATION, a concept that avoids the problems encountered in conventional tubes. Velocity modulation is more easily understood if the factors that limit the frequency range of a conventional tube are thoroughly understood. Therefore, the frequency limitations of conventional tubes will be discussed before the concepts and applications of velocity modulation are explained. You may want to review NEETS, Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, Chapters 1 and 2, for a refresher on vacuum tubes before proceeding. Frequency Limitations of Conventional Tubes Three characteristics of ordinary vacuum tubes become increasingly important as frequency rises. These characteristics are interelectrode capacitance, lead inductance, and electron transit time. The INTERELECTRODE CAPACITANCES in a vacuum tube, at low or medium

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radio frequencies, produce capacitive reactances that are so large that no serious effects upon tube operation are noticeable. However, as the frequency increases, the reactances become small enough to materially affect the performance of a circuit. For example, in figure 2-1, view (A), a 1-picofarad capacitor has a reactance of 159,000 ohms at 1 megahertz. If this capacitor was the interelectrode capacitance between the grid and plate of a tube, and the rf voltage between these electrodes was 500 volts, then 3.15 milliamperes of current would flow through the interelectrode capacitance. Current flow in this small amount would not seriously affect circuit performance. On the other hand, at a frequency of 100 megahertz the reactance would decrease to approximately 1,590 ohms and, with the same voltage applied, current would increase to 315 milliamperes (view (B)). Current in this amount would definitely affect circuit performance. Figure 2-1A. - Interelectrode capacitance in a vacuum tube. 1 MEGAHERTZ

Figure 2-1B. - Interelectrode capacitance in a vacuum tube. 100 MEGAHERTZ

Figure 2-1C. - Interelectrode capacitance in a vacuum tube. INTERELECTRODE CAPACITANCE IN A TUNED-PLATE TUNED-GRID OSCILLATOR

A good point to remember is that the higher the frequency, or the larger the

interelectrode capacitance, the higher will be the current through this capacitance. The circuit in figure 2-1, view (C), shows the interelectrode capacitance between the grid and the cathode (Cgk) in parallel with the signal source. As the frequency of the input signal increases, the effective grid-to-cathode impedance of the tube decreases because of a decrease in the reactance of the interelectrode capacitance. If the signal frequency is 100 megahertz or greater, the reactance of the grid-to-cathode capacitance is so small that much of the signal is short-circuited within the tube. Since the interelectrode capacitances are effectively in parallel with the tuned circuits, as shown in views (A), (B), and (C), they will also affect the frequency at which the tuned circuits resonate. Another frequency-limiting factor is the LEAD INDUCTANCE of the tube elements. Since the lead inductances within a tube are effectively in parallel with the interelectrode capacitance, the net effect is to raise the frequency limit. However, the inductance of the cathode lead is common to both the grid and plate circuits. This provides a path for degenerative feedback which reduces overall circuit efficiency. A third limitation caused by tube construction is TRANSIT TIME. Transit time is the time required for electrons to travel from the cathode to the plate. While some small amount of transit time is required for electrons to travel from the cathode to the plate, the time is insignificant at low frequencies. In fact, the transit time is so insignificant at low frequencies that it is generally not considered to be a hindering factor. However, at high frequencies, transit time becomes an appreciable portion of a signal cycle and begins to hinder efficiency. For example, a transit time of 1 nanosecond, which is not unusual, is only 0.001 cycle at a frequency of 1 megahertz. The same transit time becomes equal to the time required for an entire cycle at 1,000 megahertz. Transit time depends on electrode spacing and existing voltage potentials. Transit times in excess of 0.1 cycle cause a significant decrease in tube efficiency. This decrease in efficiency is caused, in part, by a phase shift between plate current and grid voltage. If the tube is to operate efficiently, the plate current must be in phase with the gridsignal voltage and 180 degrees out of phase with the plate voltage. When transit time approaches 1/4 cycle, this phase relationship between the elements does not hold true. A positive swing of a high-frequency grid signal causes electrons to leave the cathode and flow to the plate. Initially this current is in phase with the grid voltage. However, since transit time is an appreciable part of a cycle, the current arriving at the plate now lags the grid-signal voltage. As a result, the power output of the tube decreases and the plate power dissipation increases. Another loss of power occurs because of ELECTROSTATIC INDUCTION. The electrons forming the plate current also electrostatically induce potentials in the grid as they move past it. This electrostatic induction in the grid causes currents of positive charges to move back and forth in the grid structure. This back and forth action is similar to the action of hole current in semiconductor devices. When transittime effect is not a factor (as in low frequencies), the current induced in one side of the grid by the approaching electrons is equal to the current induced on the other

side by the receding electrons. The net effect is zero since the currents are in opposite directions and cancel each other. However, when transit time is an appreciable part of a cycle, the number of electrons approaching the grid is not always equal to the number going away. As a result, the induced currents do not cancel. This uncancelled current produces a power loss in the grid that is considered resistive in nature. In other words, the tube acts as if a resistor were connected between the grid and the cathode. The resistance of this imaginary resistor decreases rapidly as the frequency increases. The resistance may become so low that the grid is essentially short-circuited to the cathode, preventing proper operation of the tube. Several methods are available to reduce the limitations of conventional tubes, but none work well when frequency increases beyond 1,000 megahertz. Interelectrode capacitance can be reduced by moving the electrodes further apart or by reducing the size of the tube and its electrodes. Moving the electrodes apart increases the problems associated with transit time, and reducing the size of the tube lowers the power-handling capability. You can see that efforts to reduce certain limitations in conventional tubes are compromises that are often in direct opposition to each other. The net effect is an upper limit of approximately 1,000 megahertz, beyond which conventional tubes are not practical. Q.1 What happens to the impedance of interelectrode capacitance as frequency increases? Q.2 What undesirable effect is caused by the inductance of the cathode lead? Q.3 How does transit time affect the relationship of the grid voltage and the plate current at high frequencies? Q.4 Moving tube electrodes apart to decrease interelectrode capacitance causes an increase in the effect of what property?

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Microwave antennas

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Click here to order Electronic Components Online MICROWAVE ANTENNAS LEARNING OBJECTIVES Upon completion of this section the student will be able to: Explain the basic characteristics of coupling, directivity, reciprocity, and efficiency in microwave antennas. Describe the construction and basic Join Integrated theory of operation of reflector antennas Publishing's and horn radiators. Discussion Group Explain construction and operation of microwave lens antennas.

Describe the construction and theory of operation of driven and parasitic antenna arrays. Explain the basic operation and applications of frequency-sensitive antennas. INTRODUCTION In this chapter you will study the general characteristics of microwave antennas that are widely used in radar and communications applications. The basic principles of operation of microwave antennas are similar to those of antennas used at lower frequencies. You might want to review the principles presented in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas, at this time. Pay particular attention to basic antenna principles in chapter 4 for a review of microwave antennas.

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Print (Hardcopy). Antennas are devices used to radiate electromagnetic energy into space. The characteristics of transmitting and receiving antennas are similar, so a good transmitting antenna is often a good receiving antenna. A single antenna performs both functions in many modern applications.

ANTENNA CHARACTERISTICS Since the operating principles of low-frequency and microwave antennas are essentially the same, the electrical characteristics are also very similar. You will need a fundamental knowledge of radar and communications antenna electrical theory in your shipboard antenna maintenance work. Antenna theory is primarily a design consideration of antenna size and shape requirements that depend on the frequency used. A brief description of antenna electrical characteristics is sufficient for the needs of most students of electronics. Antenna Efficiency The effectiveness of an antenna depends upon its ability to couple or radiate energy into the air. An efficient antenna is one which wastes very little energy during the radiation process. The efficiency of an antenna is usually referred to as the POWER GAIN or POWER RATIO as compared to a standard reference antenna. The power gain of an antenna is a ratio of the radiated power to that of the reference antenna, which is usually a basic dipole. Both antennas must be fed rf energy in the same manner and must be in the same position when the energy is radiated. The power gain of a single dipole without a reflector is unity (one). An array of several dipoles in the same position as the single dipole, and fed with the same line, has a power gain of more than one. The effectiveness of an entire transmitting/ receiving system depends largely on impedance matching between the elements of the system. Impedance matching is particularly critical at the antenna connection. If a good impedance match is maintained between the system and the antenna throughout the operating frequency band, power transfer to and from the antenna is always maximum. The transmission line or waveguide used to transport energy to and from the antenna should have a characteristic impedance equal to that of the antenna. A proper impedance match allows all available power to be absorbed and radiated by the antenna without reflections back down the line. If you have a transmission line or waveguide with an impedance mismatch at the termination, standing waves are set up by the reflections. Standing waves cause losses in the form of unwanted radiations, heat losses in transmission lines, and arcing in waveguides. The STANDING-WAVE RATIO, abbreviated swr, is a way to measure the degree of mismatch between the transmission line and its load. The swr can be expressed as a ratio of the maximum and minimum values of the current or voltage in the standing waves that are set up on the lines as follows:

A transmission line or waveguide approaches a perfectly matched condition when the swr approaches a value of 1. A ratio that is a little higher than 1 is usually acceptable in practical applications. Measurement of swr is the only practical method of detecting an impedance mismatch between a transmitting/receiving system and its antenna. As such, the system swr is an important indication of the overall efficiency of the system during operation. The line impedance can usually be matched to the antenna at only one frequency. However, the swr will NOT become too high if the antenna is used over a small range of frequencies and the line is matched to the center frequency. Antenna Directivity You can divide antennas into two general classes based on directivity, omnidirectional and directional. OMNIDIRECTIONAL antennas radiate and receive energy from all directions at once (SPHERICAL WAVEFRONT). They are seldom used in modern radar systems as the primary antenna, but are commonly used in radio equipment and iff (identification friend or foe) receivers. DIRECTIONAL antennas radiate energy in LOBES (or BEAMS) that extend outward from the antenna in either one or two directions. The radiation pattern contains small minor lobes, but these lobes are weak and normally have little effect on the main radiation pattern. Directional antennas also receive energy efficiently from only one or two directions, depending upon whether it is unidirectional or bidirectional. Directional antennas have two characteristics that are important to you in radar and communications systems. One is DIRECTIVITY and the other is POWER GAIN. The directivity of an antenna refers to the NARROWNESS of the radiated beam. If the beam is NARROW in either the horizontal or vertical plane, the antenna has a high degree of directivity in that plane. An antenna may be designed for high directivity in one plane only or in both planes, depending on the application. The power gain of an antenna increases as the degree of directivity increases because the power is concentrated into a narrow beam and less power is required to cover the same distance. Since microwave antennas are predominantly unidirectional, the examples you will study in this chapter are all of the unidirectional type. Reciprocity

You read in this chapter that an antenna is able to both transmit and receive electromagnetic energy. This is known as RECIPROCITY. Antenna reciprocity is possible because antenna characteristics are essentially the same regardless of whether an antenna is transmitting or receiving electromagnetic energy. Reciprocity allows most radar and communications systems to operate with only one antenna. An automatic switch, called a DUPLEXER, connects either the transmitter or the receiver to the antenna at the proper time. Duplexer operation will be. explained in later NEETS modules dealing with radar and communications systems. Because of the reciprocity of antennas, this chapter will discuss antennas from the viewpoint of the transmitting cycle. However, you should understand that the same principles apply on the receiving cycle. Radar Fundamentals Radio, television, radar, and the human eye have much in common because they all process the same type of electromagnetic energy. The major difference between the light processed by the human eye and the radio-frequency energy processed by radio and radar is frequency. For example, radio transmitters send out signals in all directions. These signals can be detected by receivers tuned to the same frequency. Radar works somewhat differently because it uses reflected energy (echo) instead of directly transmitted energy. The echo, as it relates to sound, is a familiar concept to most of us. An experienced person can estimate the distance and general direction of an object causing a sound echo. Radar uses microwave electromagnetic energy in much the same way. Radar transmits microwave energy that reflects off an object and returns to the radar. The returned portion of the energy is called an ECHO, as it is in sound terminology. It is used to determine the direction and distance of the object causing the reflection. Determination of direction and distance to an object is the primary function of most radar systems. Telescopes and radars, in terms of locating objects in space, have many common problems. Both have a limited field of view and both require a geographic reference system to describe the position of an object (target). The position of an object viewed with a telescope is usually described by relating it to a familiar object with a known position. Radar uses a standard system of reference coordinates to describe the position of an object in relation to the position of the radar. Normally ANGULAR measurements are made from true north in an imaginary flat plane called the HORIZONTAL PLANE. All angles in the UP direction are measured in a second imaginary plane perpendicular to the horizontal plane called the VERTICAL PLANE. The center of the coordinate system is the radar location. As shown in figure 3-1, the target position with respect to the radar is defined as 60 degrees true, 10 degrees up, and 10 miles distant. The line directly from the radar to the target is called the LINE OF SIGHT. The distance from point 1 to point 2, measured along the line of sight, is called TARGET RANGE. The angle between the horizontal plane and the line of sight is known as the ELEVATION ANGLE. The angle measured in a clockwise direction in the horizontal plane between true north and the line of sight is known as BEARING (sometimes referred to as AZIMUTH). These three coordinates of range, bearing, and

elevation determine the location of the target with respect to the radar. Figure 3-1. - Radar target position.

Bearing and elevation angles are determined by measuring the angular position of the radar antenna (the transmitted beam) when it is pointing directly at the target. Range is more difficult to determine because it cannot be directly measured. The radar system is designed to measure range as a function of time. Since the speed of electromagnetic energy is the same as the speed of light, range is determined by measuring the time required for a pulse of energy to reach the target and return to the radar. Because the speed of the pulse is known, the two-way distance can be determined by multiplying the time by the speed of travel. The total must be divided by two to obtain the one-way range because the time value used initially is the time required for the pulse to travel to the target and return. The discussion of microwave antennas in this chapter requires only the most basic understanding of radar concepts! Radar fundamentals will be discussed in more detail in a later NEETS module. Q.1 Microwave antennas and low-frequency antennas are similar in what ways?

Q.2 What term is used to express the efficiency of an antenna? Q.3 What term is used to express the measurement of the degree of mismatch between a line and its load? Q.4 What type of antenna radiates in and receives energy from all directions at once? Q.5 What is the term that is used to describe narrowness in the radiated beam of an antenna? Q.6 What characteristic allows the same antenna to both transmit and receive?

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Book 12

Back • Home • Up • Next Click here to order Electronic Components Online Amplitude modulation Sine wave characteristics Amplitude Heterodyning Nonlinear impedance Two sine wave generators in linear circuits Spectrum Analysis Amplitude-modulated systems Blocked-grid keying Single-Stage Transmitters Amplitude modulation AM transmitter principles Analysis of an AM wave The amplitude of the audio-modulating voltage Modulation systems Control-Grid Modulator Summary Answers

Angle and pulse modulation Comparison of AM and fm receiver response to an AM

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signal Frequency Modulation Frequency spectra of fm waves under various conditions Methods of frequency modulation Phase modulation Basic Modulator Simulated phase-shift keying. TIMING Pulse Timing Radar modulation Communications pulse modulators Pulse-Time Modulation Pulse-Code Modulation Summary Answers

Demodulation Regenerative detector Shunt-Diode Detector FM Demodulation Ratio detector Gated-Beam detector Phase demodulation Low-pass filter Summary Answers Order this information in Adobe PDF Printable Format

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Amplitude modulation

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Click here to order Electronic Components Online AMPLITUDE MODULATION LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.

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Upon completion of this chapter, you will be able to: Discuss the generation of a sine wave by describing its three characteristics: amplitude, phase, and frequency. Describe the process of heterodyning. Discuss the development of continuous-wave (cw) modulation.

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Describe the two primary methods of cw communications keying. Discuss the radio frequency (rf) spectrum usage by cw transmissions. Discuss the advantages and disadvantages of cw transmissions. Explain the operation of typical cw transmitter circuitry. Discuss the method of changing sound waves into electrical impulses. Describe the rf usage of an AM signal. Calculate the percent of modulation for an AM signal. Discuss the difference between high- and low-level modulation. Describe the circuit description, operation, advantages, and disadvantages of the following common AM tube/transistor modulating circuits: plate/collector, control grid/base, and cathode/emitter. Discuss the advantages and disadvantages of AM communications. INTRODUCTION TO MODULATION PRINCIPLES People have always had the desire to communicate their ideas to others. Communications have not only been desired from a social point of view, but have been an essential element in the building of civilization. Through communications, people have been able to share ideas of mutual benefit to all mankind. Early attempts to maintain communications between distant points were limited by several factors. For example, the relatively short distance sound

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would carry and the difficulty of hand-carrying messages over great distances hampered effective communications. As the potential for the uses of electricity were explored, scientists in the United States and England worked to develop the telegraph. The first practical system was established in London, England, in 1838. Just 20 years later, the final link to connect the major countries with electrical communications was completed when a transatlantic submarine cable was connected. Commercial telegraphy was practically worldwide by 1890. The telegraph key, wire lines, and Morse code made possible almost instantaneous communications between points at great distances. Submarine cables solved the problems of transoceanic communications, but communications with ships at sea and mobile forces were still poor. In 1897 Marconi demonstrated the first practical wireless transmitter. He sent and received messages over a distance of 8 miles. By 1898 he had demonstrated the usefulness of wireless telegraph communications at sea. In 1899 he established a wireless telegraphic link across the English Channel. His company also established general usage of the wireless telegraph between coastal light ships (floating lighthouses) and land. The first successful transatlantic transmissions were achieved in 1902. From that time to the present, radio communication has grown at an extraordinary rate. Early systems transmitted a few words per minute with doubtful reliability. Today, communications systems reliably transmit information across millions of miles. The desire to communicate directly by voice, at a higher rate of speed than possible through basic telegraphy, led to further research. That research led to the development of MODULATION. Modulation is the ability to impress intelligence upon a TRANSMISSION MEDIUM, such as radio waves. A transmission medium can be described as light, smoke, sound, wire lines, or radio-frequency waves. In this module, you will study the basic principles of modulation and DEMODULATION (removing intelligence from the medium). In your studies, you will learn about modulation as it applies to radio-frequency communications. To modulate is to impress the characteristics (intelligence) of one waveform onto a second waveform by varying the amplitude, frequency, phase, or other characteristics of the second waveform. First, however, you will

review the characteristics and generation of a sine wave. This review will help you to better understand the principles of modulation. Then, an important principle called HETERODYNING (mixing two frequencies across a nonlinear impedance) will be studied and applied to modulation. Nonlinear impedance will be discussed in the heterodyning section. You will also study several methods of modulating a radio-frequency carrier. You will come to a better understanding of the demodulation principle by studying the various circuits used to demodulate a modulated carrier. Q.1 What is modulation? Q.2 What is a transmission medium? Q.3 What is heterodyning? Q.4 What is demodulation?

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Angle and pulse modulation

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Click here to order Electronic Components Online ANGLE AND PULSE MODULATION LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Describe frequency-shift keying (fsk) and methods of providing this type of modulation. Describe the development of frequency modulation (fm) and methods of frequency modulating a carrier. Discuss the development of phase modulation (pm) and methods of phase modulating a carrier. Describe phase-shift keying (psk), its generation, and application. Discuss the development and characteristics of pulse modulation.

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Describe the operation of the spark gap and thyratron modulators. Discuss the characteristics of a pulse train that may be varied to provide communications capability. Describe pulse-amplitude modulation (pam) and generation. Describe pulse-duration modulation (pdm) and generation. Describe pulse-position modulation (ppm) and generation. Describe pulse-frequency modulation (pfm) and generation. Describe pulse-code modulation (pcm) and generation. INTRODUCTION In chapter 1 you learned that modulation of a carrier frequency was necessary to allow fast communications between two points. As the volume of transmissions increased, a need for more reliable methods of communication was realized. In this chapter you will study angle modulation and pulse modulation. These two types of modulation have been developed to overcome one of the main disadvantages of amplitude modulation - susceptibility to noise interference. In addition, a special application of pulse type modulation for ranging and detection equipment will be discussed. ANGLE MODULATION ANGLE MODULATION is modulation in which the angle of a sinewave carrier is varied by a modulating wave. FREQUENCY MODULATION (fm) and PHASE MODULATION (pm) are two types of angle modulation. In frequency modulation the modulating signal causes the carrier frequency to vary. These variations are controlled by both the frequency and the amplitude of the modulating wave. In

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phase modulation the phase of the carrier is controlled by the modulating waveform. Let's study these modulation methods for an understanding of their similarities and differences. FREQUENCY-MODULATION SYSTEMS In frequency modulation an audio signal is used to shift the frequency of an oscillator at an audio rate. The simplest form of this is seen in FREQUENCY-SHIFT KEYING (fsk). Frequency-shift keying is somewhat similar to continuous-wave keying (cw) in AM transmissions. Frequency-Shift Keying Consider figure 2-1, views (A) through (D). View (A) is a radio frequency (rf) carrier which is actually several thousand or million hertz. View (B) represents the intelligence to be transmitted as MARKS and SPACES. Recall that in cw transmission, this intelligence was applied to the rf carrier by interrupting the signal, as shown in view (C). The amplitude of the rf alternated between maximum and 0 volts. By comparing views (B) and (C), you can see the mark/space intelligence of the Morse code character on the rf. The spacing of the waveform in view (D) is an example of the same intelligence as it is applied to the frequency instead of the amplitude of the rf. This is simple frequency-shift keying of the same Morse code character. Figure 2-1A. - Comparison of ON-OFF and frequency-shift keying. RF CARRIER (CW) (EACH CYCLE REPRESENTS SEVERAL THOUSAND OR SEVERAL MILLION CYCLES)

Figure 2-1B. - Comparison of ON-OFF and frequency-shift keying. AMPLITUDE VARYING (ON-OFF) MODULATING WAVE (MORSE CODE CHARACTER "N")

Figure 2-1C. - Comparison of ON-OFF and frequency-shift keying. TRANSMITTED ON-OFF KEYED CW SIGNAL

Figure 2-1D. - Comparison of ON-OFF and frequency-shift keying. TRANSMITTED FREQUENCY-SHIFT KEYED SIGNAL (FSK)

In fsk the output is abruptly changed between two differing frequencies by opening and closing the key. This is shown in view (D). For illustrative purposes, the spacing frequency in view (D) is shown as double the marking frequency. However, in practice the difference is usually less than 1,000 hertz, even when operating at several megahertz. You should also note that the limit of frequency shift is determined without reference to the amplitude of the keying signal in the fsk system. The frequency shift may be set at plus or minus 425 hertz from the allocated channel frequency. The total shift between mark and space would be 850 hertz. Either the mark or space may use the higher of the two frequencies. The upper frequency of the transmitted signal is usually the spacing interval and the lower frequency is the marking interval.

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Book 13

Back • Home • Up • Next Click here to order Electronic Components Online Number systems Carry and Borrow Principles Addition of Binary Numbers Subtraction of Binary Numbers Complementary Subtraction Octal number system Subtraction of Octal Numbers Hexadecmial (HEX) number system Subtraction of Hex Numbers Conversion of bases Decimal to Octal Decimal to Hex Binary conversion Binary to Hex Octal to Binary Octal to Hex Binary to Decimal Octal to Decimal Hex to Decimal Binary-coded decimal Summary Answers

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Fundamental logic circuits Logic Symbol The or gate The inverter The nand gate The nor gate Variations of fundamental gates Logic gates in combination Boolean algebra Summary Answers

Special logic circuits A quarter adder is a circuit Subtraction is accomplished in computers Flip-flops Toggle flip-flops J-K Flip-Flop Clocks and counters Counters Decade Counter Down Counters Shift registers Logic families Summary Answers Order this information in Adobe PDF Printable Format

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Number systems

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Click here to order Electronic Components Online NUMBER SYSTEMS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Upon completion of this chapter, you should be able to do the following: Recognize different types of number systems as they relate to computers. Identify and define unit, number, base/radix, positional notation, and most and least significant digits as they relate to decimal, binary, octal, and hexadecimal number systems.

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Add and subtract in binary, octal, and hexadecimal number systems. Convert values from decimal, binary, octal, hexadecimal, and binarycoded decimal number systems to each other and back to the other systems. Add in binary-coded decimal. INTRODUCTION How many money do what the or cows,

days' leave do you have on the books? How much you have to last until payday? It doesn't matter question is - if the answer is in dollars or days it will be represented by numbers.

Just try to imagine going through one day without using numbers. Some things can be easily described without using numbers, but others prove to be difficult. Look at the following examples: I am stationed on the aircraft carrier Nimitz. He owns a green Chevrolet. The use of numbers wasn't necessary in the preceding statements, but the following examples depend on the use of numbers: I have $25 to last until payday. I want to take 14 days' leave. You can see by these statements that numbers play an important part in our lives. BACKGROUND AND HISTORY Mans' earliest number or counting system was probably developed to help determine how many possessions a person had. As daily activities became more complex, numbers became more important in trade, time, distance, and all other phases of human life. As you have seen already, numbers are extremely important

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in your military and personal life. You realize that you need more than your fingers and toes to keep track of the numbers in your daily routine. Ever since people discovered that it was necessary to count objects, they have been looking for easier ways to count them. The abacus, developed by the Chinese, is one of the earliest known calculators. It is still in use in some parts of the world. The first adding machine was invented by Blaise Pascal (French) in 1642. Twenty years later, an Englishman, Sir Samuel Moreland, developed a more compact device that could multiply, add, and subtract. About 1672, Gottfried Wilhelm von Leibniz (German) perfected a machine that could perform all the basic operations (add, subtract, multiply, divide), as well as extract the square root. Modern electronic digital computers still use von Liebniz's principles. MODERN USE Computers are now employed wherever repeated calculations or the processing of huge amounts of data is needed. The greatest applications are found in the military, scientific, and commercial fields. They have applications that range from mail sorting, through engineering design, to the identification and destruction of enemy targets. The advantages of digital computers include speed, accuracy, and man-power savings. Often computers are able to take over routine jobs and release personnel for more important work - work that cannot be handled by a computer. People and computers do not normally speak the same language. Methods of translating information into forms that are understandable and usable to both are necessary. Humans generally speak in words and numbers expressed in the decimal number system, while computers only understand coded electronic pulses that represent digital information. In this chapter you will learn about number systems in general and about binary, octal, and hexadecimal (which we will refer to as hex) number systems specifically. Methods for converting numbers in the binary, octal, and hex systems to equivalent numbers in the decimal system (and vice versa) will also be described. You will see that

these number systems can be easily converted to the electronic signals necessary for digital equipment. TYPES OF NUMBER SYSTEMS Until now, you have probably used only one number system, the decimal system. You may also be familiar with the Roman numeral system, even though you seldom use it. THE DECIMAL NUMBER SYSTEM In this module you will be studying modern number systems. You should realize that these systems have certain things in common. These common terms will be defined using the decimal system as our base. Each term will be related to each number system as that number system is introduced. Each of the number systems you will study is built around the following components: the UNIT, NUMBER, and BASE (RADIX). Unit and Number The terms unit and number when used with the decimal system are almost self-explanatory. By definition the unit is a single object; that is, an apple, a dollar, a day. A number is a symbol representing a unit or a quantity. The figures 0, 1, 2, and 3 through 9 are the symbols used in the decimal system. These symbols are called Arabic numerals or figures. Other symbols may be used for different number systems. For example, the symbols used with the Roman numeral system are letters - V is the symbol for 5, X for 10, M for 1,000, and so forth. We will use Arabic numerals and letters in the number system discussions in this chapter. Base (Radix) The base, or radix, of a number system tells you the number of symbols used in that system. The base of any system is always expressed in decimal numbers. The base, or radix, of the decimal system is 10. This means there are 10 symbols - 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 - used in the system. A number system using three symbols - 0, 1, and 2 - would be base 3; four symbols would be base 4; and so forth. Remember to count the zero or the symbol used for zero when determining the number of symbols used in a

number system. The base of a number system is indicated by a subscript (decimal number) following the value of the number. The following are examples of numerical values in different bases with the subscript to indicate the base:

You should notice the highest value symbol used in a number system is always one less than the base of the system. In base 10 the largest value symbol possible is 9; in base 5 it is 4; in base 3 it is 2. Positional Notation and Zero You must observe two principles when counting or writing quantities or numerical values. They are the POSITIONAL NOTATION and the ZERO principles. Positional notation is a system where the value of a number is defined not only by the symbol but by the symbol's position. Let's examine the decimal (base 10) value of 427.5. You know from experience that this value is four hundred twenty-seven and one-half. Now examine the position of each number:

If 427.5 is the quantity you wish to express, then each number must be in the position shown. If you exchange the positions of the 2 and the 7, then you change the value. Each position in the positional notation system represents a power of the base, or radix. A POWER is the number of times a base is multiplied by itself. The power is written above and to the right of the base and is called an EXPONENT. Examine the following base 10 line graph:

Now let's look at the value of the base 10 number 427.5 with the positional notation line graph:

You can see that the power of the base is multiplied by the number in that position to determine the value for that position. The following graph illustrates the progression of powers of 10:

All numbers to the left of the decimal point are whole numbers, and all numbers to the right of the decimal point are fractional numbers. A whole number is a symbol that represents one, or more, complete objects, such as one apple or $5. A fractional number is a symbol that represents a portion of an object, such as half of an apple (.5 apples) or a quarter of a dollar ($0.25). A mixed number represents one, or more, complete objects, and some portion of an object, such as one and a half

apples (1.5 apples). When you use any base other than the decimal system, the division between whole numbers and fractional numbers is referred to as the RADIX POINT. The decimal point is actually the radix point of the decimal system, but the term radix point is normally not used with the base 10 number system. Just as important as positional notation is the use of the zero. The placement of the zero in a number can have quite an effect on the value being represented. Sometimes a position in a number does not have a value between 1 and 9. Consider how this would affect your next paycheck. If you were expecting a check for $605.47, you wouldn't want it to be $65.47. Leaving out the zero in this case means a difference of $540.00. In the number 605.47, the zero indicates that there are no tens. If you place this value on a bar graph, you will see that there are no multiples of 101.

Most Significant Digit and Least Significant Digit (MSD and LSD) Other important factors of number systems that you should recognize are the MOST SIGNIFICANT DIGIT (MSD) and the LEAST SIGNIFICANT DIGIT (LSD).

The MSD in a number is the digit that has the greatest effect on that number. The LSD in a number is the digit that has the least effect on that number. Look at the following examples:

You can easily see that a change in the MSD will increase or decrease the value of the number the greatest amount. Changes in the LSD will have the smallest effect on the value. The nonzero digit of a number that is the farthest LEFT is the MSD, and the nonzero digit farthest RIGHT is the LSD, as in the following example:

In a whole number the LSD will always be the digit immediately to the left of the radix point.

Q.1 What term describes a single object? Q.2 A symbol that represents one or more objects is called a _________. Q.3 The symbols 0, 1, 2, and 3 through 9 are what type of numerals? Q.4 What does the base, or radix, of a number system tell you about the system? Q.5 How would you write one hundred seventy-three base 10? Q.6 What power of 10 is equal to 1,000? 100? 10? 1? Q.7 The decimal point of the base 10 number system is also known as the _________. Q.8 What is the MSD and LSD of the following numbers? (a) 420. (b) 1045.06 (c) 0.0024 (d) 247.0001

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Fundamental logic circuits

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Click here to order Electronic Components Online FUNDAMENTAL LOGIC CIRCUITS LEARNING OBJECTIVES Upon completing this chapter, you should be able to do the following: Identify general logic conditions, logic states, logic levels, and positive and negative logic as these terms and characteristics apply to the inputs and outputs of fundamental logic circuits. Indentify the following logic circuit gates and interpret and solve the associated Truth Tables: AND OR Inverters (NOT circuits) NAND NOR Identify variations of the fundamental logic gates and interpret the associated Truth Tables. Determine the output expressions of logic gates in combination.

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Recognize the laws, theorems, and purposes of Boolean algebra. INTRODUCTION In chapter 1 you learned that the two digits of the binary number system can be represented by the state or condition of electrical or electronic devices. A binary 1 can be represented by a switch that is closed, a lamp that is lit, or a transistor that is conducting. Conversely, a binary 0 would be represented by the same devices in the opposite state: the switch open, the lamp off, or the transistor in cut-off. In this chapter you will study the four basic logic gates that make up the foundation for digital equipment. You will see the types of logic that are used in equipment to accomplish the desired results. This chapter includes an introduction to Boolean algebra, the logic mathematics system used with digital equipment. Certain Boolean expressions are used in explanation of the basic logic gates, and their expressions will be used as each logic gate is introduced. COMPUTER LOGIC Logic is defined as the science of reasoning. In other words, it is the development of a reasonable or logical conclusion based on known information. GENERAL LOGIC Consider the following example: If it is true that all Navy ships are gray and the USS Lincoln is a Navy ship, then you would reach the logical conclusion that the USS Lincoln is gray. To reach a logical conclusion, you must assume the qualifying statement is a condition of truth. For each statement there is also a corresponding false condition. The statement "USS Lincoln is a Navy ship" is true; therefore, the statement "USS Lincoln is not a Navy ship" is false. There are no in-between conditions. Computers operate on the principle of logic and use the TRUE and FALSE logic conditions of a logical statement to make a programmed decision.

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The conditions of a statement can be represented by symbols (variables); for instance, the statement "Today is payday" might be represented by the symbol P. If today actually is payday, then P is TRUE. If today is not payday, then P is FALSE. As you can see, a statement has two conditions. In computers, these two conditions are represented by electronic circuits operating in two LOGIC STATES. These logic states are 0 (zero) and 1 (one). Respectively, 0 and 1 represent the FALSE and TRUE conditions of a statement. When the TRUE and FALSE conditions are converted to electrical signals, they are referred to as LOGIC LEVELS called HIGH and LOW. The 1 state might be represented by the presence of an electrical signal (HIGH), while the 0 state might be represented by the absence of an electrical signal (LOW). If the statement "Today is payday" is FALSE, then the statement "Today is NOT payday" must be TRUE. This is called the COMPLEMENT of the original statement. In the case of computer math, complement is defined as the opposite or negative form of the original statement or variable. If today were payday, then the statement "Today is not payday" would be FALSE. The complement is shown by placing a bar, or VINCULUM, over the statement symbol (in this case, P). This variable is spoken as NOT P. Table 2-1 shows this concept and the relationship with logic states and logic levels. Table 2-1. - Relationship of Digital Logic Concepts and Terms Example 1: Assume today is payday

STATEMENT

SYMBOL CONDITION

LOGIC STATE

LOGIC LEVEL

Original: TODAY IS PAYDAY

P

TRUE

1

HIGH

Complement: TODAY IS NOT PAYDAY

P

FALSE

0

LOW

Example 2: Assume today is not payday Complement: TODAY IS NOT PAYDAY

P

FALSE

0

LOW

Complement: TODAY IS NOT PAYDAY

P

TRUE

1

HIGH

In some cases, more than one variable is used in a single expression. For example, the expression ABCD is spoken "A AND B AND NOT C AND D." POSITIVE AND NEGATIVE LOGIC To this point, we have been dealing with one type of LOGIC POLARITY, positive. Let's further define logic polarity and expand to cover in more detail the differences between positive and negative logic. Logic polarity is the type of voltage used to represent the logic 1 state of a statement. We have determined that the two logic states can be represented by electrical signals. Any two distinct voltages may be used. For instance, a positive voltage can represent the 1 state, and a negative voltage can represent the 0 state. The opposite is also true. Logic circuits are generally divided into two broad classes according to their polarity - positive logic and negative logic. The voltage levels used and a statement indicating the use of positive or negative logic will usually be specified on logic diagrams supplied by manufacturers. In practice, many variations of logic polarity are used; for example, from a high-positive to a low-positive voltage, or from positive to ground; or from a high-negative to a low-negative voltage, or from negative to ground. A brief discussion of the two general classes of logic polarity is presented in the following paragraphs.

Positive Logic Positive logic is defined as follows: If the signal that activates the circuit (the 1 state) has a voltage level that is more POSITIVE than the 0 state, then the logic polarity is considered to be POSITIVE. Table 2-2 shows the manner in which positive logic may be used. Table 2-2. - Examples of Positive Logic

As you can see, in positive logic the 1 state is at a more positive voltage level than the 0 state. Negative Logic As you might suspect, negative logic is the opposite of positive logic and is defined as follows: If the signal that activates the circuit (the 1 state) has a voltage level that is more NEGATIVE than the 0 state, then the logic polarity is considered to be NEGATIVE. Table 2-3 shows the manner in which negative logic may be used. Table 2-3. - Examples of Negative Logic

NOTE: The logic level LOW now represents the 1 state. This is because the 1 state voltage is more negative than the 0 state. In the examples shown for negative logic, you notice that the voltage for the logic 1 state is more negative with respect to the logic 0 state voltage. This holds true in example 1 where both voltages are positive. In this case, it may be easier for you to think of the TRUE condition as being less positive than the FALSE condition. Either way, the end result is negative logic. The use of positive or negative logic for digital equipment is a choice to be made by design engineers. The difficulty for the technician in this area is limited to understanding the type of logic being used and keeping it in mind when troubleshooting. NOTE: UNLESS OTHERWISE NOTED, THE REMAINDER OF THIS BOOK WILL DEAL ONLY WITH POSITIVE LOGIC. LOGIC INPUTS AND OUTPUTS As you study logic circuits, you will see a variety of symbols (variables) used to represent the inputs and outputs. The purpose of these symbols is to let you know what inputs are required for the desired output. If the symbol A is shown as an input to a logic device, then the logic level that represents A must be HIGH to activate the logic device. That is, it must satisfy the input requirements of the logic device before the logic device will issue the TRUE output.

Look at view A of figure 2-1. The symbol X represents the input. As long as the switch is open, the lamp is not lit. The open switch represents the logic 0 state of variable X. Figure 2-1. - Logic switch: A. Logic 0 state; B. Logic 1 state.

Closing the switch (view B), represents the logic 1 state of X. Closing the switch completes the circuit causing the lamp to light. The 1 state of X satisfied the input requirement and the circuit therefore produced the desired output (logic HIGH); current was applied to the lamp causing it to light. If you consider the lamp as the output of a logic device, then the same conditions exist. The TRUE (1 state) output of the logic device is to have the lamp lit. If the lamp is not lit, then the output of the logic device is FALSE (0 state). As you study logic circuits, it is important that you remember the state (1 or 0) of the inputs and outputs. So far in this chapter, we have discussed the two conditions of

logical statements, the logic states representing these two conditions, logic levels and associated electrical signals and positive and negative logic. We are now ready to proceed with individual logic device operations. These make up the majority of computer circuitry. As each of the logic devices are presented, a chart called a TRUTH TABLE will be used to illustrate all possible input and corresponding output combinations. Truth Tables are particularly helpful in understanding a logic device and for showing the differences between devices. The logic operations you will study in this chapter are the AND, OR, NOT, NAND, and NOR. The devices that accomplish these operations are called logic gates, or more informally, <emphasis type="i.GIF">gates. These gates are the foundation for all digital equipment. They are the "decision-making" circuits of computers and other types of digital equipment. By making decisions, we mean that certain conditions must exist to produce the desired output. In studying each gate, we will introduce various mathematical SYMBOLS known as BOOLEAN ALGEBRA expressions. These expressions are nothing more than descriptions of the input requirements necessary to activate the circuit and the resultant circuit output. THE AND GATE The AND gate is a logic circuit that requires all inputs to be TRUE at the same time in order for the output to be TRUE.

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Special logic circuits

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Click here to order Electronic Components Online SPECIAL LOGIC CIRCUITS LEARNING OBJECTIVES Upon completion of this chapter, you should be able to do the following: Recognize the types of special logic circuits used in digital equipment. Identify exclusive OR and exclusive NOR circuits and interpret their respective Truth Tables. Identify adder and subtracter circuits. Identify the types of flipflops used in digital equipment and their uses. Identify counters, registers, and clock circuits. Describe the elements that make up logic families - RTL, DTL, TTL, CMOS. INTRODUCTION

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Figure 3-1 is a portion of a typical logic diagram. It is similar to the diagrams you will encounter as your study of digital circuitry progresses. Figure 3-1. - Typical logic diagram. Order this information in Print (Hardcopy).

Look closely at the figure. You will see many familiar logic gates. You will also see several that you may not recognize. Digital equipment must be capable of many more operations than those described in chapter 2. Provisions must be made for accepting information; performing arithmetic or logic

operations; and transferring, storing, and outputting information. Timing circuits are included to ensure that all operations occur at the proper time. In this chapter you will become acquainted with the logic circuits used to perform the operations mentioned above. THE EXCLUSIVE OR GATE The exclusive OR gate is a modified OR gate that produces a HIGH output when only one of the inputs is HIGH. You will often see the abbreviation X-OR used to identify this gate. When both inputs are HIGH or when both inputs are LOW, the output is LOW. The standard symbol for an exclusive OR gate is shown in figure 3-2 along with the associated Truth Table. The operation function sign for the exclusive OR gate is ⊕. Figure 3-2. - Exclusive OR gate and Truth Table.

If you were to observe the input and output signals of an X-OR gate, the results would be similar to those shown in figure 3-3. At T0, both inputs are LOW and the output is LOW. At T1, A goes to HIGH and remains HIGH until T2. During this time the output is HIGH. At T3, B goes HIGH and remains HIGH through T5. At T4, A again goes HIGH and

remains HIGH through T5. Between T3and T4 , the output is HIGH. At T4, when both A and B are HIGH, the output goes LOW. Figure 3-3. - Exclusive OR gate timing diagram.

THE EXCLUSIVE NOR GATE The exclusive NOR (X-NOR) gate is nothing more than an XOR gate with an inverted output. It produces a HIGH output when the inputs are either all HIGH or all LOW. The standard symbol and the Truth Table are shown in figure 34. The operation function sign is ⊕ with a vinculum over the entire expression. Figure 3-4. - Exclusive NOR gate and Truth Table.

A timing diagram for the X-NOR gate is shown in figure 35. You can see that from T0 to T1, when both inputs are LOW, the output is HIGH. The output goes LOW when the inputs are opposite; one HIGH and the other LOW. At time T3, both inputs go HIGH causing the output to go HIGH. Figure 3-5. - Exclusive NOR gate timing diagram.

Q.1 What is the sign of operation for the X-OR gate? Q.2 What will be the output of an X-OR gate when both inputs are HIGH? Q.3 A two-input X-OR gate will produce a HIGH output when the inputs are at what logic levels? Q.4 What type of gate is represented by the output Boolean expression T ⊕ R? Q.5 What will be the output of an X-NOR gate when both inputs are LOW?

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Book 14

Back • Home • Up • Next Click here to order Electronic Components Online Microelectronics Solid-State devices Integrated Circuits Fabrication of microelectronic devices Fabrication of IC devices Thin Film Packaging Techniques Dual Inline Package Equivalent circuits Microelectronic system design concepts System packaging Interconnections in printed circuit boards Environmental considerations Summary Answers

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Miniature/microminiature (2M) repair program and high-reliability Test Equipment Repair Stations High-Intensity Light Safety Equipment

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Summary Answers

Miniature and microminature repair procedures Removal and replacement of discrete components Above-the-board termination Component Desoldering Installation and soldering of printed circuit components Soldering of PCB Components Removal and replacement of dips Repair of printed circuit boards and cards Safety Grounded Work Benches Summary Answers

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Microelectronics

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Click here to order Electronic Components Online MICROELECTRONICS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each topic. These learning objectives serve as a preview of the information you are expected to learn in the topic. The comprehensive check questions are based on the objectives. By successfully completing the OCC-ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Upon completion of this topic, you will be able to:

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Outline the progress made in the history of microelectronics. Describe the evolution of microelectronics from point-to-point wiring through high element density stateof-the-art microelectronics. List the advantages and disadvantages Order this of point-to-point wiring and high element information on CDdensity state-of-the-art microelectronics. Rom Identify printed circuit boards, diodes, transistors, and the various types of integrated circuits. Describe the fabrication techniques of these components. Define the terminology used in microelectronic technology including the Order this following terms used by the Naval information in Systems Commands: Print (Hardcopy). microelectronics

microcircuit microcircuit module miniature electronics system packaging levels of packaging (0 to IV) modular assemblies cordwood modules micromodules Describe typical packaging levels presently used for microelectronic systems. Describe typical interconnections used in microelectronic systems. Describe environmental considerations for microelectronics. INTRODUCTION In NEETS, Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, you learned that Thomas Edison's discovery of thermionic emission opened the door to electronic technology. Progress was slow in the beginning, but each year brought new and more amazing discoveries. The development of vacuum tubes soon led to the simple radio. Then came more complex systems of communications. Modern systems now allow us to communicate with other parts of the world via satellite. Data is now collected from space by probes without the presence of man because of microelectronic technology. Sophisticated control systems allow us to operate equipment by remote control in hazardous situations, such as the handling of radioactive materials. We can remotely pilot aircraft from takeoff to landing. We can make course corrections to spacecraft millions of miles from Earth. Space flight, computers, and even video games would not be possible except for the advances made in microelectronics. The most significant step in modern electronics was the development of the transistor by Bell Laboratories in 1948. This development was to solid-state electronics what the Edison Effect was to the vacuum tube. The solid-state diode and the transistor opened the door to microelectronics. MICROELECTRONICS is defined as that area of technology associated with and applied to the realization of electronic systems made of extremely small electronic parts or elements. As discussed in topic 2 of NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies, the term microelectronics is normally associated with integrated circuits (IC). Microelectronics is often thought to include only integrated circuits. However, many other types of circuits also fall into the microelectronics category. These will be discussed in greater detail under solid-state devices later in this topic. During World War II, the need to reduce the size, weight, and power of military electronic systems became important because of the increased use of these systems. As systems became more complex, their size, weight, and power requirements rapidly increased. The increases finally reached a point that was unacceptable, especially in aircraft and for

infantry personnel who carried equipment in combat. These unacceptable factors were the driving force in the development of smaller, lighter, and more efficient electronic circuit components. Such requirements continue to be important factors in the development of new systems, both for military and commercial markets. Military electronic systems, for example, continue to become more highly developed as their capability, reliability, and maintainability is increased. Progress in the development of military systems and steady advances in technology point to an ever-increasing need for increased technical knowledge of microelectronics in your Navy job. Q.1 What problems were evident about military electronic systems during World War II?

Q.2 What discovery opened the door to solid-state electronics? Q.3 What is microelectronics? EVOLUTION OF MICROELECTRONICS The earliest electronic circuits were fairly simple. They were composed of a few tubes, transformers, resistors, capacitors, and wiring. As more was learned by designers, they began to increase both the size and complexity of circuits. Component limitations were soon identified as this technology developed. VACUUM-TUBE EQUIPMENT Vacuum tubes were found to have several built-in problems. Although the tubes were lightweight, associated components and chassis were quite heavy. It was not uncommon for such chassis to weigh 40 to 50 pounds. In addition, the tubes generated a lot of heat, required a warm-up time from 1 to 2 minutes, and required hefty power supply voltages of 300 volts dc and more. No two tubes of the same type were exactly alike in output characteristics. Therefore, designers were required to produce circuits that could work with any tube of a particular type. This meant that additional components were often required to tune the circuit to the output characteristics required for the tube used. Figure 1-1 shows a typical vacuum-tube chassis. The actual size of the transformer is approximately 4 X 4 X 3 inches. Capacitors are approximately 1 X 3 inches. The components in the figure are very large when compared to modern microelectronics. Figure 1-1. - Typical vacuum tube circuit.

A circuit could be designed either as a complete system or as a functional part of a larger system. In complex systems, such as radar, many separate circuits were needed to accomplish the desired tasks. Multiple-function tubes, such as dual diodes, dual triodes, tetrodes, and others helped considerably to reduce the size of circuits. However, weight, heat, and power consumption continued to be problems that plagued designers. Another major problem with vacuum-tube circuits was the method of wiring components referred to as POINT-TO-POINT WIRING. Figure 1-2 is an excellent example of point-topoint wiring. Not only did this wiring look like a rat's nest, but it often caused unwanted interactions between components. For example, it was not at all unusual to have inductive or capacitive effects between wires. Also, point-to-point wiring posed a safety hazard when troubleshooting was performed on energized circuits because of exposed wiring and test points. Point-to-point wiring was usually repaired with general purpose test equipment and common hand tools. Figure 1-2. - Point-to-point wiring.

Vacuum-tube circuits proved to be reliable under many conditions. Still, the drawbacks of large size, heavy weight, and significant power consumption made them undesirable in most situations. For example, computer systems using tubes were extremely large and difficult to maintain. ENIAC, a completely electronic computer built in 1945, contained 18,000 tubes. It often required a full day just to locate and replace faulty tubes. In some applications, we are still limited to vacuum tubes. Cathode-ray tubes used in radar, television, and oscilloscopes do not, as yet, have solid-state counterparts. One concept that eased the technician's job was that of MODULAR PACKAGING. Instead of building a system on one large chassis, it was built of MODULES or blocks. Each module performed a necessary function of the system. Modules could easily be removed and replaced during troubleshooting and repair. For instance, a faulty power supply could be exchanged with a good one to keep the system operational. The faulty unit could then be repaired while out of the system. This is an example of how the module concept improved the efficiency of electronic systems. Even with these advantages, vacuum tube modules still had faults. Tubes and point-to-point wiring were still used and excessive size, weight, and power consumption remained as problems to be overcome. Vacuum tubes were the basis for electronic technology for many years and some are still with us. Still, emphasis in vacuum-tube technology is rapidly becoming a thing of the past. The emphasis of technology is in the field of microelectronics. Q.4 What discovery proved to be the foundation for the development of the vacuum tube?

Q.5 Name the components which greatly increase the weight of vacuum-tube circuitry.

Q.6 What are the disadvantages of point-to-point wiring? Q.7 What is a major advantage of modular construction? Q.8 When designing vacuum-tube circuits, what characteristics of tubes must be taken into consideration?

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Miniature/microminiature (2M) repair program and high-reliability

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Click here to order Electronic Components Online MINIATURE/MICROMINIATURE (2M) REPAIR PROGRAM AND HIGH-RELIABILITY SOLDERING LEARNING OBJECTIVES Upon completion of this topic, the student will be able to: State the purpose and need for training and certification of 2M repair technicians. Explain the maintenance levels at which maintenance is performed. Identify the specialized and general test equipment used in fault isolation. Recognize the specialized types of tools used and the importance of repair facilities.

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Explain the principles of highreliability soldering. INTRODUCTION As mentioned in topic 1, advances in the field of microelectronics are impressive. With every step forward in production development, a corresponding step forward must be made in maintenance and repair techniques. This topic will teach you how the Navy is coping with the new technology and how personnel are trained to carry out the maintenance and repair of complex equipment. The program discussed in this topic is up to date at this time, but as industry advances, so must the capabilities of the technician. MINIATURE AND MICROMINIATURE (2M) ELECTRONIC REPAIR PROGRAM Training requirements for miniature and microminiature repair personnel were developed under guidelines established by the Chief of Naval Operations. The Naval Sea Systems Command (NAVSEA) developed a program which provides for the proper training in miniature and microminiature repair. This program, NAVSEA Miniature/Microminiature (2M) Electronic Repair, authorizes and provides proper tools and equipment and establishes a personnel certification program to maintain quality repair. The Naval Air Systems Command has developed a similar program specifically for the aviation community. The two programs are patterned after the National Aeronautics and Space Administration (NASA) high-reliability soldering studies and have few differences other than the administrative chain of command. For purposes of this topic, we will use the NAVSEA manual for reference. The 2M program covers all phases of miniature and microminiature repair. It establishes the training curriculum for repair personnel, outlines standards of workmanship, and provides guidelines for specific repairs to equipment, including the types of tools to use. This part of the program ensures high-reliability repairs by qualified technicians.

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Upon satisfactory completion of a 2M training course, a technician will be CERTIFIED to perform repairs. The CERTIFICATION is issued at the level at which the technician qualifies and specifies what type of repairs the technician is permitted to perform. The two levels of qualification for technicians are MINIATURE COMPONENT REPAIR and MICROMINIATURE COMPONENT REPAIR. Miniature component repair is limited to discrete components and single- and double-sided printed circuit boards, including removal and installation of most integrated circuit devices. Microminiature component repair consists of repairs to highly complex, densely packaged, multilayer printed circuit boards. Sophisticated repair equipment is used that may include a binocular microscope. To ensure that a technician is maintaining the required qualification level, periodic evaluations are conducted. By inspecting and evaluating the technician's work, certification teams ensure that the minimum standards for the technician's level of qualification are met. If the standards are met, the technician is recertified; if not, the certification is withheld pending retraining and requalification. This portion of the program ensures the high-quality, high-reliability repairs needed to meet operational requirements. Q.1 Training requirements for (2M) repair personnel were developed under guidelines established by what organization? Q.2 What agencies provide training, tools, equipment, and certification of the 2M system? Q.3 To perform microminiature component repair, a 2M technician must be currently certified in what area? Q.4 Multilayer printed circuit board repair is the responsibility of what 2M repair technician? LEVELS OF MAINTENANCE Effective maintenance and repair of microelectronic devices require one of three levels of maintenance. Level-of-repair designations called SOURCE, MAINTENANCE, and RECOVERABILITY CODES (SM&R) have been developed and are assigned by the

Chief of Naval Material. These codes are D for DEPOT LEVEL, I for INTERMEDIATE LEVEL, and O for ORGANIZATIONAL LEVEL. DEPOT-LEVEL MAINTENANCE. SM&R Code D maintenance is the responsibility of maintenance activities designated by the systems command (NAVSEA, NAVAIR, NAVELEX). This code augments stocks of serviceable material. It also supports codes I and O activities by providing more extensive shop facilities and equipment and more highly skilled technicians. Code D maintenance includes repair, modification, alteration, modernization, and overhaul as well as reclamation or reconstruction of parts, assemblies, subassemblies, and components. Finally, it includes emergency manufacture of nonavailable parts. Code D maintenance also provides technical assistance to user activities and to code I maintenance organizations. Code D maintenance is performed in shops, located in shipyards and shore-based facilities, including contractor maintenance organizations. INTERMEDIATE-LEVEL MAINTENANCE SM&R code I maintenance, performed at mobile shops, tenders or shore-based repair facilities (SIMAS) provides direct support to user organizations. Code I maintenance includes calibration, repair, or replacement of damaged or unserviceable parts, components, or assemblies, and emergency manufacture of nonavailable parts. It also provides technical assistance to ships and stations. ORGANIZATIONAL-LEVEL MAINTENANCE SM&R code O maintenance is the responsibility of the activity who owns the equipment. Code O maintenance consists of inspecting, servicing, lubricating, adjusting, and replacing parts, minor assemblies, and subassemblies. An INTEGRATED LOGISTICS SUPPORT PLAN (ILSP) determines the maintenance level for electronic assemblies, modules, and boards for each equipment assigned to an activity. The ILSP codes the items according to the normal maintenance capabilities of that activity. This results in two additional repair-level categories - NORMAL and EMERGENCY.

Normal Repairs Generally, 2M repairs are performed at the level set forth in the maintenance plan and specified by the appropriate SM&R coding for each board or module. Therefore, normal repairs include all repairs except organizational-level repair of D- and I-coded items and intermediate-level repair of D-coded items. Emergent/Emergency Repairs In the NAVSEA 2M Electronic Repair Program, emergent/emergency repairs are those arising unexpectedly. They may require prompt repair action to restore a system or piece of equipment to operating condition where normal repairs are not authorized. These Code O repairs on boards or modules are normally SM&R-coded for Code D repairs. Emergent/emergency 2M repairs may be performed only to meet an urgent operational commitment as directed by the operational commander. SOURCE, MAINTENANCE, AND RECOVERABILITY (SM&R) CODES The Allowance Parts List (APL) is a technical document prepared by the Navy for specific equipment/system support. This document lists the repair parts requirements for a ship having the exact equipment/component. To determine the availability of repair parts, the 2M technician must be familiar with these documents. SM&R codes, found in APLs, determine where repair parts can be obtained, who is authorized to make the repair, and at what maintenance level the item may be recovered or condemned. Q.5 What are the three levels of maintenance? Q.6 Maintenance performed by the user activity is what maintenance level?

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Miniature and microminature repair procedures

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Click here to order Electronic Components Online MINIATURE AND MICROMINIATURE REPAIR PROCEDURES LEARNING OBJECTIVES Upon completion of this topic, the student will be able to: Explain the purpose of conformal coatings and the methods used for removal and replacement of these coatings. Explain the methods and practices for the removal and replacement of discrete components on printed circuit boards. Join Integrated Identify types of damage to printed circuit boards, and describe the repair Publishing's procedures for each type of repair. Discussion Group Describe the removal and replacement of the dual-in-line integrated circuit. Describe the removal and replacement of the TO-5 integrated circuit. Describe the removal and replacement of the flat-pack integrated circuit. Describe the types of damage to which many microelectronic components are susceptible and methods of preventing damage. Explain safety precautions as they relate to 2M repair. INTRODUCTION As you progress in your training as a technician, you will find that the skill and knowledge levels required to maintain electronic systems become more demanding. The increased use of miniature and microminiature electronic circuits, circuit complexity, and new manufacturing techniques will make your job more challenging. To maintain and repair equipment effectively, you will have to duplicate with limited facilities what was accomplished in the factory with extensive facilities. Printed circuit boards that were manufactured completely by machine will have to be repaired by hand. To meet the needs for repairing the full range of electronic equipment, you must be properly trained. You must be capable of performing high-quality, reliable repairs to the latest circuitry. MINIATURE AND MICROMINIATURE ELECTRONIC REPAIR PROCEDURES As mentioned at the beginning of topic 2, 2M repair personnel must undergo specialized training. They are trained for a particular level of repair and must be

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certified at that level. Also, recertification is required to ensure the continued high-quality repair ability of these technicians. THIS SECTION IS NOT, IN ANY WAY, TO BE USED BY YOU AS AUTHORIZATION TO ATTEMPT THESE TYPES OF REPAIRS WITHOUT OFFICIAL 2M CERTIFICATION. In the following sections, you will study the general procedures used in the repair, removal, and replacement of specific types of electronic components.By studying these procedures, you will become familiar with some of the more common types of repair work. Before repair work can be performed on a miniature or microminiature assembly, the technician must consider the type of specialized coating that usually covers the assembly. These coatings are referred to as CONFORMAL COATINGS. CONFORMAL COATINGS Conformal coatings are protective material applied to electronic assemblies to prevent damage from corrosion, moisture, and stress.These coatings include epoxy, parylene, silicone, polyurethane, varnish, and lacquer. Coatings are applied in a liquid form; when dry, they exhibit characteristics that improve reliability. These characteristics are: Heat conductivity to carry heat away from components Hardness and strength to support and protect components Low moisture absorption Electrical insulation Conformal Coating Removal Because of the characteristics that conformal coatings exhibit, they must be removed before any work can be done on printed circuit boards. The coating must be removed from all lead and pad/eyelet areas of the component. It should also be removed to or below the widest point of the component body. Complete removal of the coating from the board is not done. Methods of coating removal are thermal, mechanical, and chemical. The method of removal depends on the type of coating used. Table 3-1 shows suggested methods of removal of some types. Note that most of the methods are variations of mechanical removal. Table 3-1. - Conformal Coating Removal Techniques

The coating material can best be identified through proper documentation; for example, technical manuals and engineering drawings. If this information is not available, the experienced technician can usually determine the type of material by testing the, hardness, transparency, thickness, and solvent solubility of the coating. The thermal (heat) properties may also be tested to determine the ease of removal of the coating by heat. The methods of removal discussed here describe the basic concept, but not the step-by-step "how to" procedures. THERMAL REMOVAL. - Thermal removal consists of using controlled heat through specially shaped tips attached to a handpiece. Soldering irons should never be used for coating removal because the high temperatures will cause the coatings to char, possibly damaging the board materials. Modified tips or cutting blades heated by soldering irons also are not used; they may not have proper heat capacity or allow the hand control necessary for effective removal. Also, the thin plating of the circuit may be damaged by scraping. The thermal parting tool, used with the variable power supply, has interchangeable tips, as shown in figure 3-1, that allow for efficient coating removal. These thin, blade-like instruments act as heat generators and will maintain the heat levels necessary to accomplish the work. Tips can be changed easily to suit the configuration of the workpiece. These tips cool quickly after removal of power because their small thermal mass and special alloy material easily give up residual heat. Figure 3-1. - Thermal parting tips.

The softening or breakdown point of different coatings vary, which is a concern when you are using this method. Ideally, the softening, point is below the solder melting temperature. However, when the softening point is equal to or above the solder melting point, you must take care in applying heat at the solder joint or in component areas. The work must be performed rapidly to limit the heating of the area involved and to prevent damage to the board and other components. HOT-AIR JET REMOVAL. - In principle, the hot-air jet method of coating removal uses controlled, temperature-regulated air to soften or break down the coating, as shown in figure 3-2. By controlling the temperature, flow rate, and shape of the jet, you may remove coatings from almost any workpiece configuration without causing any damage. When you use the hot-air jet, you do not allow it to physically contact the workpiece surface. Delicate work handled in this manner permits you to observe the removal process. Figure 3-2. - Hot air jet conformal coating removal.

POWER-TOOL REMOVAL DESCRIPTION. - Power-tool removal is the use of abrasive grinding or cutting to mechanically remove coatings. Abrasive grinding/rubbing techniques are effective on thin coatings (less than 0.025 inch) while abrasive cutting methods are effective on coatings greater than 0.025 inch. This method permits consistent and precise removal of coatings without mechanical damage or dangerous heating to electronic components. A variable-speed mechanical drive handpiece permits fingertip-control and proper speed and torque to ease the handling of gum-type coatings. A variety of rotary abrasive materials and cutting tools is required for removal of the various coating types. These specially designed tools include BALL MILLS, BURRS, and ROTARY BRUSHES. The ball mill design places the most efficient cutting area on the side of the ball rather than at the end. Different mill sizes are used to enter small areas where thick coatings need to be removed (ROUTED). Rubberized abrasives of the proper grade and grit are ideally suited for removing thin, hard coatings from flat surfaces; soft coatings adhere to and coat the abrasive causing it to become ineffective. Rotary bristle brushes work better than rubberized abrasives on contoured or irregular surfaces, such as soldered connections, because the bristles conform to surface irregularities. Ball mill routing and abrasion removal are shown in figure 3-3. Figure 3-3. - Rotary tool conformal coating removal.

CUT AND PEEL. - Silicone coatings (also referred to as RTV) can easily be removed by cutting and peeling. As with all mechanical removal methods, care must be taken to prevent damage to either components or boards. CHEMICAL REMOVAL. - Chemical removal uses solvents to break down the coatings. General application is not recommended as the solvent may cause damage to the boards by dissolving the adhesive materials that bond the circuits to the boards. These solvents may also dissolve the POTTING COMPOUNDS (insulating material that completely seals a component or assembly) used on other parts or assemblies. Only thin acrylic coatings (less than 0.025 inch) are readily removable by solvents. Mild solvents, such as ISOPROPYL ALCOHOL, XYLENE, or TRICHLOROETHANE, may be used to remove soluble coatings on a spot basis. Evaluations show that many tool and technique combinations have proven to be reliable and effective in coating removal; no single method is the best in all situations. When the technician is determining the best method of coating removal to use, the first consideration is the effect that it will have on the equipment. Conformal Coating Replacement Once the required repairs have been completed the conformal coating must be replaced. To ensure the same protective characteristics, you should use the same type of replacement coating as that removed. Conformal coating application techniques vary widely. These techniques depend on material type, required thickness of application, and the effect of environmental conditions on curing. These procedures cannot be effectively discussed here. Q.1 What material is applied to electronic assemblies to prevent damage from corrosion, moisture, and stress? Q.2 What three methods are used to remove protective material?

Q.3 What chemicals are used to remove protective material? Q.4 Abrasion, cutting, and peeling are examples of what type of protective material removal? Q.5 Why should the coating material be replaced once the required repair has been completed?

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Book 15

Back • Home • Up • Next Click here to order Electronic Components Online Synchros Synchro classification Schematic Symbols Synchro Characteristics Operation of three electromagnets spaced 120° apart. Synchro Torque Transmitter Torque synchro system Torque differential synchro systems TX-TDX-TR system operation (subtraction). TX-TDR-TX System Operation (Subtraction) Control Synchro system operation Synchro capacitors Multispeed syschro systems Zeroing systems Electrical lock method Troubleshooting synchro systems Summary Answers

Servos Functional servo loops

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Velocity Servo Loop Friction Clutch Damping Servo components and circuits Rate Generator (Tachometer) Demodulators in the servo system Magnetic Amplifiers Summary Answers

Gyros Basic Gyro Elements Precession Degrees of freedom Establishing and Maintaining a Fixed Position Rate Gyros Accelerometers Summary Answers

Related Devices Step-transmission systems Resolvers Summary Answers

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Synchros

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Click here to order Electronic Components Online SYNCHROS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions placed throughout the chapters are based on the objectives. By successfully completing the Nonresident Training Course (NRTC), you indicate that you have met the objectives and have learned the information. The learning objectives for this chapter are listed below.

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Upon completing this chapter, you will be able to: Define the term "synchro." State the primary purpose of a synchro. Explain the importance of synchros in naval equipment. Name the two general classifications of synchros.

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Explain the differences between torque and control synchros. Name the seven functional classes of synchros and list all inputs and outputs. Name the two types of synchro identification codes. Interpret all synchro markings and identify the particular codes used. Draw the five standard schematic symbols for synchros and identify all connections. Describe the general construction and physical appearance of synchro rotors and stators. Name the two common types of synchro rotors, giving an application of each. List the different synchro characteristics and give a brief explanation of each. State the advantage of using 400-Hz synchros over 60-Hz synchros. Explain the operation of a basic synchro transmitter and receiver. State the difference between a synchro transmitter and a synchro receiver. List the basic components that compose a torque synchro system. Explain the operation of a simple synchro transmission system.

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Define the term "correspondence" and explain how it is used in a simple synchro system. Explain the principle behind reversing the S1 and S3 leads on a synchro receiver and how this action affects receiver operation. Explain what happens when the rotor leads on a synchro transmitter or receiver are reversed. State the purposes of differential synchros. Name the two types of differential synchros and give a brief explanation of each. Explain the difference between the torque differential transmitter and the torque differential receiver. Name the components that make up the TDX and the TDR synchro systems. Explain how the two differential synchro systems add and subtract. State the wiring changes required to convert the differential synchro systems from subtraction to addition. State the purposes and functions of control synchros. Name the different types of control synchros. Explain how the CX and CDX differ from the TX and TDX. Explain the theory and operation of a control transformer.

List the basic components that compose a control synchro system. Explain the operation of a control synchro system and how it is used to control a servo system. State the purpose and function of the synchro capacitor. Explain how synchro capacitors improve the accuracy of synchro systems. Explain the method used to connect synchro capacitors in a circuit. Define single and multispeed synchro systems. State the purposes and functions of multispeed synchro systems. Stale the purposes for zeroing synchros. Name three common synchro zeroing methods and give a brief explanation of each. Explain the different troubleshooting techniques used in isolating synchro malfunctions and breakdowns. SYNCHRO FUNDAMENTALS Synchros play a very important role in the operation of Navy equipment. Synchros are found in just about every weapon system, communication system, underwater detection system, and navigation system used in the Navy. The importance of synchros is sometimes taken lightly because of their low failure rate. However, the technician who understands the theory of operation and the alignment procedures for synchros is well ahead of the problem when a malfunction does occur. The term "synchro" is an abbreviation of the word "synchronous." It is the name given to a

variety of rotary, electromechanical, position-sensing devices. Figure 1-1 shows a phantom view of typical synchro. A synchro resembles a small electrical motor in size and appearance and operates like a variable transformer. The synchro, like the transformer, uses the principle of electromagnetic induction. Figure 1-1. - Phantom view of a synchro.

Synchros are used primarily for the rapid and accurate transmission of information between equipment and stations. Examples of such information are changes in course, speed, and range of targets or missiles; angular displacement (position) of the ship's rudder; and changes in the speed and depth of torpedoes. This information must be transmitted quickly and accurately. Synchros can provide this speed and accuracy. They are reliable, adaptable, and compact. Figure 1-2 shows a simple synchro system that can be used to transmit different as of data or information In this system, a single synchro transmitter furnishes information to two synchro receivers located in distant spaces. Operators put information into the system by turning the handwheel. As the handwheel turns, its attached gear rotates the

transmitter shaft (which has a dial attached to indicate the value of the transmitted information). As the synchro transmitter shaft turns, it converts the mechanical input into an electrical signal, which is sent through interconnecting wiring to the two synchro receivers. The receiver shafts rotate in response to the electrical signal from the transmitter. When these shafts turn, the dials attached to the shafts indicate the transmitted information. Figure 1-2. - Data transfer with synchros.

By studying the simple synchro system, you can see that information can be transmitted over long distances, from space to space, and from equipment to equipment. In addition to supplying data by positioning dials and pointers, synchros are also used as control devices in servo systems. When the synchro and the servo are combined, they work as a team to move and position heavy loads. The methods used to accomplish this are covered in detail in the next chapter. Q.1 What is the name given to a variety of rotary electromechanical, position sensing devices? Q.2 What is the primary purpose of a synchro system?

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Servos

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Click here to order Electronic Components Online SERVOS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Define the term "servo system" and the terms associated with servo systems, including openloop and closed-loop control Join Integrated systems. Publishing's Identify from schematics and block Discussion Group diagrams the various servo circuits; give short explanations of the components and their characteristics; and of each circuit and its characteristics. Trace the flow of data through the components of typical servo systems from input(s) to outputs(s) Order this (cause to effect). information on CDRom

SERVOS Servo mechanisms, also called SERVO SYSTEMS or SERVOS for short,

have countless applications in the operation of electrical and electronic equipment. In working with radar and antennas, directors, computing devices, ship's communications, aircraft control, and many other equipments, it is often necessary to operate a mechanical load that is remote from its source of control. To obtain smooth, continuous, and Order this accurate operation, these loads are normally best controlled by synchros. As information in you already know, the big problem here is that synchros are not powerful Print (Hardcopy). enough to do any great amount of work. This is where servos come into use. A servo system uses a weak control signal to move large loads to a desired position with great accuracy. The key words in this definition are move and great accuracy. Servos may be found in such varied applications as moving the rudder and elevators of a model airplane in radio-controlled flight, to controlling the diving planes and rudders of nuclear submarines. Servos are powerful. They can move heavy loads and be remotely controlled with great precision by synchro devices. They take many forms. Servo systems are either electromechanical, electrohydraulic, hydraulic, or pneumatic. Whatever the form, a relatively weak signal that represents a desired movement of the load is generated, controlled, amplified, and fed to a servo motor that does the work of moving the heavy load. Q.1 What is a servo? CATEGORIES OF CONTROL SYSTEMS A control system is a group of components that are linked together to perform a specific purpose. Generally, a control system has a large power gain between input and output. The components used in the system and the complexity of the system are directly related to the requirements of the system's application. Control systems are broadly classified as either CLOSED-LOOP or OPENLOOP. Closed-loop control systems are the type most commonly used in the Navy because they respond and move the loads they are controlling quicker and with greater accuracy than open-loop systems.

The reason for quicker response and greater accuracy is that an automatic feedback system informs the input that the desired movement has taken place. Upon receipt of this feedback information, the system stops the motor, and motion of the load ceases until another movement is ordered by the input. This is similar to the system that controls heat in many homes. The thermostat (input) calls for heat. The furnace (output) produces heat and distributes it. Some of the heat is "fed back" to the thermostat. When this "feedback" raises the temperature of the room to that of the thermostat setting, the thermostat responds by shutting the system down until heat is again required. In such a system, the feedback path, input to output and back to input, forms what is called a "closed loop." This is a term you will hear and use often in discussions of control systems. Because closed-loop control systems are automatic in nature, they are further classified by the function they serve (e.g., controlling the position, the velocity, or the acceleration of the load being driven). An open-loop control system is controlled directly, and only, by an input signal, without the benefit of feedback. The basic units of this system are an amplifier and a motor. The amplifier receives a low-level input signal and amplifies it enough to drive the motor to perform the desired job. Open-loop control systems are not as commonly used as closed-loop control systems because they are less accurate. OPEN-LOOP CONTROL SYSTEM As we stated previously, an open-loop control system is controlled directly, and only, by an input signal. The basic units of this type consist only of an amplifier and a motor. The amplifier receives a low-level input signal and amplifies it enough to drive the motor to perform the desired job. The open-loop control system is shown in basic block diagram form in figure 2-1. With this system, the input is a signal that is fed to the amplifier. The output of the amplifier is proportional to the amplitude of the input signal. The phase (ac system) and polarity (dc system) of the input signal determines the direction that the motor shaft will turn. After amplification, the input signal is fed to the motor, which moves the output shaft (load) in the direction that corresponds with the input signal. The motor will not stop driving the output shaft until the input signal is reduced to zero or removed. This system usually requires an operator who controls speed and direction of movement of the output by varying the input. The operator could be controlling the input by either a mechanical or an electrical linkage. Figure 2-1. - Open-loop control system basic block diagram.

THE CLOSED-LOOP CONTROL SYSTEM A closed-loop control system is another name for a servo system. To be classified as a servo, a control system must be capable of the following: Accepting an order that defines the desired result Determining the present conditions by some method of feedback Comparing the desired result with the present conditions and obtaining a difference or an error signal Issuing a correcting order (the error signal) that will properly change the existing conditions to the desired result Obeying the correcting order We have discussed the open- and closed-loop control systems and defined a servo system as a closed-loop control system. Although not technically accurate by definition, open-loop control systems are also often referred to in the Navy and many publications as servo systems even though they lack one of the five basic requirements, that of feedback. Q.2 In an open-loop control system, what action reduces the input to zero so the load is stopped at the desired position? Q.3 What basic requirement of a closed-loop system (not present in openloops) enables present load position to be sensed? OPERATION OF A BASIC SERVO SYSTEM For the following discussion of a servo system, refer to figure 2-2, view (A),

view (B), view (C) and view (D).This closed-loop servo system is the most common type in the Navy today. It is normally made up of electromechanical parts and consists basically of a synchro-control system, servo amplifier, servo motor, and some form of feedback (response). Figure 2-2A. - A basic servo system (closed-loop).

Figure 2-2B. - A basic servo system (closed-loop).

Figure 2-2C. - A basic servo system (closed-loop).

Figure 2-2D. - A basic servo system (closed-loop).

The synchro-control system provides a means of controlling the movement of the load, which may be located in a remote space. The servo amplifier and servo motor are the parts of the system in which power is actually developed (to move the load). As you remember, the controlling signal from a CT is relatively weak, too weak to drive an electric motor directly. In views A through D of figure 2-2, assume that the control signal will be initiated by a handcrank input connected to the synchro transmitter (CX). The dials located on the CX and the CT indicate the positions of the synchro's rotors, while the dial on the load indicates the position of the load. In view A, the dials of both the CX and the load indicate that the load is in the desired position. Because the load is where it should be, there will be no error signal present at the servo amplifier and no power to the servo motor. In view B, the rotor of the CX has been moved by the handcrank to 90°. (This indicates that it is ordered to move the load by 90°.) Notice that the rotor of the CT is still at 0°. The CT now develops a signal, called the ERROR SIGNAL, which is proportional in amplitude to the amount the CT rotor is out of correspondence with the CX rotor. The phase of the error signal indicates the direction the CT rotor must move to reduce the error signal to zero or to "null out." The error signal is sent to the servo amplifier. In view C, the error signal has been amplified by the servo amplifier and sent on to the servo motor. The motor starts to drive in the direction that will reduce the error signal and bring the CT rotor back to the point of correspondence. In this case the motor is turning clockwise. The mechanical linkage attached to the servo motor also moves the rotor of the CT. This feedback causes the amplitude of the error signal to decrease, slowing the speed at which the load is moving. In view D, the servo motor has driven both the load and the rotor of the CT, so that the CT is now in correspondence with the CX rotor. As a result, the error signal is reduced to zero (nulled). The load stops at its new position.

Note that in this servo system, we moved a heavy load to a predetermined position through the simple turning of a handcrank. In responding to the handcrank, the servo system performed a basic positioning function . Two key points for you to remember, thus far, about the operation of the closed-loop servo system are: The original error (movement of the CX rotor) was "detected" by the CT. For this reason the CT is called an ERROR DETECTOR. The servo motor, in addition to moving the load, also provides mechanical feedback to the CT to reduce the error signal. For this reason the servo motor is also called an ERROR REDUCER. Q.4 An error signal is the difference between what two quantities fed to the CT (error detector)? Q.5 What are the two functions of the servo motor in the system shown in figure 2-2?

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Gyros

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Click here to order Electronic Components Online GYROS LEARNING OBJECTIVES Upon completion of this chapter you should be able to: Describe the characteristics of a gyroscopes. List the two basic properties of gyroscopes and explain them. Describe the components of a universally mounted gyro. Describe the factors that determine rigidity in a gyro. List the factors that determine the direction of precession in a gyro. Explain the right-hand rule for gyro precession. Describe the term "Degree of Freedom" as it applies to gyros. Explain the effect of apparent precession (apparent rotation). Explain the purposes of erection systems. Describe the use of gyros with only one degree of freedom.

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Explain the purpose of an accelerometer. Explain the principle on which accelerometers operate. Explain the need for a pulsecounting accelerometer. GYROS The word gyroscope was first coined by a French scientist, Leon Foucault, in 1852. It is derived from the Greek words "gyro," meaning revolution, and "skopien," meaning to view. The gyroscope, commonly called a GYRO, has existed since the first electron was sent spinning on its axis. Electrons spin and show all the characteristics of a gyro; so does the Earth, which spins about its polar axis at over 1000 miles per hour at the Equator. The Earth's rotation about its axis provides the stabilizing effect that keeps the North Pole pointed within one degree of Polaris (the North Star). Any rapidly spinning object - a top, a wheel, an airplane propeller, or a spinning projectile - is fundamentally a gyroscope. Strictly speaking, however, a gyroscope is a mechanical device containing a spinning mass that is universally mounted; that is, mounted so it can assume any position in space. Figure 3-1 shows a model of a gyro. As you can see, a heavy wheel (rotor) is mounted so that its spin axis is free to turn in any direction. The wheel spins about axis X; it can turn about axis Y, and it can turn about axis Z. With this mechanical arrangement, the spinning wheel can assume any position in space. Figure 3-1. - Gyro model, universally mounted.

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BASIC PROPERTIES OF GYROSCOPES Gyroscopes have two basic properties: rigidity and precession. Those properties are defined as follows: RIGIDITY - The axis of rotation (spin axis) of the gyro wheel tends to remain in a fixed direction in space if no force is applied to it. PRECESSION - The axis of rotation has a tendency to turn at a right angle to the direction of an applied force. The idea of maintaining a fixed direction in space is simple to illustrate. When any object is spinning rapidly, it tends to keep its axis pointed always in the same direction. A toy top is a good example. As long as the top is spinning fast, it stays balanced on its point. Because of this gyro action, the spinning top resists the tendency of gravity to change the direction of its axis. You can think of many more examples. A bicycle is easier to

balance at high speed than when it is barely moving. At high speed, the bicycle wheels act as gyros, and tend to keep their axes (axles) parallel to the ground. Note that it is easy to move the gyro as long as you keep the axis POINTING in the SAME DIRECTION. The gyro resists only those forces that tend to change the direction of its axis. In a bicycle, since the axis of rotation (the wheel's axles) is horizontal, the wheels win resist any force that tends to tilt or turn them to the right or left. If you can obtain a gyroscope top, you can do some instructive experiments with it. Hold the gyro top with its axis vertical as shown in figure 3-2 and start it spinning. As long as it is spinning fast, it will stay balanced. You can balance it on a string or on the point of your finger; the axis will stay vertical as long as the top is spinning fast. As we mentioned before, this ability of a gyro to keep its axis fixed in space is called RIGIDITY. Figure 3-2. - A gyroscope top.

PRECESSION Now, if you stop the gyro top and turn its axis horizontal, and then start it spinning again, balancing

one end on a pivot, (fig. 3-3), it won't fall. The top's axis will stay horizontal, resisting the tendency of gravity to change its direction Although the gyro will RESIST the force that gravity applies to it, the gyro will still RESPOND to that force. The gyro responds by moving its axis at a RIGHT ANGLE to the APPLIED FORCE. Figure 3-3. - Gyro top with axis horizontal.

The axis will tilt in a direction 90° away from the applied force. This is called PRECESSION. Figure 3-4 is another view of the same gyroscope. Its far end is still balanced on the pivot. Gravity is pulling down on the gyro. If the gyro rotor is turning in the direction shown by the arrow, the near end of the frame (axis) will move to the left. If the rotor were turning in the opposite direction, the frame would move to the right. Note that in each of these examples the direction of movement was displaced from the applied force (gravity) by 90°. The axis stays horizontal, but the gyroscope responds to the force of gravity by rotating around the pivot. Figure 3-4. - Gyro precession.

Gyro action may be summarized as follows: A spinning gyro tends to keep its axis pointing in the same direction. This is called RIGIDITY. If you apply a force that tends to change the direction of the spin axis, the axis will move at a right angle to the direction of the applied force. The direction of precession will be 90° clockwise from the applied force if the rotor is spinning clockwise (when viewed from the "free" end of the rotor's axis); if the rotor is spinning counterclockwise, the precession will be 90° counterclockwise. If the axis is horizontal, and you try to tilt it, the axis will turn. If the axis is horizontal, and you try to turn it, the axis will tilt. This second characteristic of a gyro is called PRECESSION. Because of precession, we can control the direction that the spin axis points. This enables us to aim the spin axis where we want it to point. Without precession, the rigidity of the gyro would be useless. Q.1 Can any rapidly spinning object be considered a gyroscope? Q.2 In the drawing in figure 3-1, which axis is the gyro spin axis? Q.3 What gyro property causes the gyro to remain in a fixed position?

Q.4 What type(s) of force does a gyro resist? Q.5 In what direction will a gyro precess in response to an outside force?

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Related Devices

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Click here to order Electronic Components Online RELATED DEVICES LEARNING OBJECTIVES Upon completion of this chapter, you should be able to: Compare standard synchro system connections with IC synchro connections. Describe the operation of a step transmitter and receiver, and list the advantages and disadvantages of a steptransmission system. Compare the construction and operation of a resolver to those of a transformer, describe the solution of resolution and composition problems by a resolver. RELATED DEVICES Some other devices that logically should be included in

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this module are the IC synchros, step motors, and resolvers. These are all electromagnetic devices used in various shipboard and aircraft applications. They can be considered as second cousins of the synchro. IC SYNCHROS The engine order telegraph, steering telegraph, rudderangle indicator, and similar position-indicating systems used on naval ships are usually simple synchro systems. Some ships, however, use IC synchros to transfer such information. These units operate on the same general principle as the synchros we discussed in chapter 1. The interior communication synchro (IC synchro) is gradually being phased out and replaced by standard synchros when replacement is required. However, you will still find some IC synchros in use today. For that reason, you will find some background information on their purpose and theory to be beneficial. We will present these synchros in very basic form in the following paragraphs. Because of their construction, IC synchros are sometimes called reversed synchros. The primary winding, consisting of two series-connected coils, is mounted physically on the stator. The secondary, consisting of three Y-connected coils, is mounted physically on the rotor. This is shown schematically in figure 4-1. Figure 4-1. - IC synchro schematic diagrams.

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IC synchros operate on the same principles of interacting magnetic fields as other synchros, but differ in direction of shaft rotation and amount of torque obtainable. When an IC transmitter and IC receiver are connected in parallel as shown in view A of figure 4-2, the shaft of the IC receiver follows the rotation of the IC transmitter shaft. In view B, the IC transmitter is replaced by a synchro transmitter; the IC receiver shaft now turns in a direction opposite to that of the synchro transmitter. Voltages that cause counterclockwise rotation of a standard synchro shaft cause clockwise rotation of an IC synchro shaft. When it is desirable to have the IC synchro receiver turn in an opposite direction from that of the transmitter, the connections are as shown in view C. For a standard synchro receiver to follow the rotation of an IC transmitter, their connections must be made as shown in view D. Figure 4-2A. - IC versus standard synchro connections.

Figure 4-2B. - IC versus standard synchro connections.

Figure 4-2C. - IC versus standard synchro connections.

Figure 4-2D. - IC versus standard synchro connections.

The torque obtainable from either an IC synchro or a standard synchro is determined by the magnetizing power, which is limited by the allowable temperature rise. When the stator is energized, as in IC synchros, the magnetizing power can be increased with a resulting larger torque. The reason for this is that the losses are dissipated in the form of heat around the outer shell of the IC transmitter or receiver. In standard synchros, this heat loss is dissipated through the rotor, the air gap, and then the outer shell to the surrounding air. The electrical zero position for an IC synchro is the position where rotor coil R2 is aligned with the stator as shown in figure 4-1. To zero an IC synchro, apply the same general theory as we described for other synchros. For further information on IC synchro replacement, alignment, and theory, refer to Military Handbook, Synchros, Description and Operation, (MIL-HDBK-225A). Q.1 What two characteristics of IC synchros cause them to differ from standard synchros?

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Book 16

Back • Home • Up • Next Click here to order Electronic Components Online Test equipment administration and use Special Calibration Labels Measure TMDF Inventory report form. General test equipment information Working on de-energized circuits Resistance measurements Inductance bridge. Summary Answers

Miscellaneous Measurements Bolometer Frequency measurements Strobotac Absorption Wavemeter Use of the oscilloscope Testing Diodes with an Ohmmeter Voltage Checks Summary Answers

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Basic meters DC Ammeter Ammeter Connections Proper ammeter connection. Extending Voltmeter Ranges Voltmeter Sensitivity The megohmmeter Meter Accuracy Continuity tests Summary Answers

Common test equipment Measuring dc Voltages Measuring ac Voltages Overload Protection Meter design characteristics ICO Measurements Summary Answers

Special-application test equipment Signal Generators Controls and Indicators Period Measurement Huntron tracker 2000 Range Selection Control Logic CRT Display Min/Max Capacitance Values Summary Answers

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THE OSCILLOSCOPE AND SPECTRUM ANALYZER Differences of potential. Vertical deflection plates CRT Designation Trace Rotation control Attenuator Control Components used to provide a stable display Turning on the scope Components Used to Select Vertical-Deflection Operating Mode Accessories IF Section Normal indications upon power on Summary Answers

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Test equipment administration and use

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Click here to order Electronic Components Online TEST EQUIPMENT ADMINISTRATION AND USE LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions included are based on the objectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. Upon completing this chapter, you should be able to: Describe the Ship Configuration and Logistic Support Information System (SCLSIS). State the differences between calibration and repair. Explain the various calibration status labels used by the Navy. List the procedures for obtaining repairs to test equipment.

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Describe the Metrology Automated System for Uniform Recall and Reporting (MEASURE) System and the purpose of the Metrology Equipment Recall and Reporting (METER) card and recall schedule. Describe major test equipment References available to you. Explain the purposes and benefits of testing. State the safety precautions involved in working with test equipment. List three precautions you should observe to avoid damaging electric measuring instruments. State the correct procedures for using a safety shorting probe. Describe resistance, voltage, and current measurements in terms of purposes, methods, and instruments used. Describe how capacitance and inductance are measured. Explain the operation of bridges in the measurement of unknown resistances, capacitances, and inductances. One purpose of this chapter is to acquaint you with the practical use of test equipment. The presence of adequate test equipment in your shop is not in itself a "cure-all" for making repairs to complex electronic equipment. You must know how to best use the equipment available. First, however, you must understand the basis of electronic theory and be able to apply it to the system under repair. Another purpose of this chapter is to introduce you to calibration and repair procedures, and basic voltage and current measurements. You will also learn how ac bridges are used for precise measurements of resistance,

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capacitance, and inductance. Much of the theory of operation and practical applications of the basic types of test instruments used in electrical and electronic circuits are found in the instruction books and technical manuals that accompany various equipments. You should read and understand these books before you attempt to use any test instrument. You should also know the established safety precautions to ensure your safety and safe equipment operating procedures to protect equipment from damage. TEST EQUIPMENT IDENTIFICATION One of the first things you must learn as a maintenance technician is how to identify the various electronic equipment and components by their appropriate nomenclatures. You will find that several methods are used to identify test equipment used; this may be somewhat confusing to you at first. For example, a Tektronix Model 541A oscilloscope can also be identified as a CBTV-541A. The Joint Electronics Type Designation System (JETDS) is used by all branches of the military to identify equipment by a system of standardized nomenclatures. Q.1 What system is currently used by all branches of the military to identify test equipment? ELECTRONIC TEST EQUIPMENT CLASSIFICATION The Electronic Test Equipment Classification Board was established in 1973 to control the increased use of undesirable electronic test equipment (ETE) in fleet and shore activities. The board classifies electronic test equipments as GENERAL PURPOSE (GPETE) or SPECIAL PURPOSE (SPETE) and assigns responsibility for their management. Items classified as general purpose are managed by the Space and Warfare Systems Command (SPAWARSYSCOM). Items classified as special purpose are managed by the individual systems command that generates the requirement. GPETE is test equipment that has the capability, without modification, to generate, modify, or measure a range of parameters of electronic functions required to test two or more equipments or systems of basically different design. Special-purpose electronic test equipment (SPETE) is

specifically designed to generate, modify, or measure a range of parameters of electronic functions of a specific or peculiar nature required to test a single system or equipment. These special test equipments are procured by the systems command that has the responsibility for the system/equipment requiring the SPETE for maintenance.

Q.2 Name the two classes of test equipment. Q.3 What test equipment is designed to generate, modify, or measure a range of parameters of electronic functions of a specific nature required to test a single system or equipment? Until the ETE classification board was established, the uncontrolled increase in use of nonstandard GPETE had resulted in loss of inventory control and increased support costs. NESEA has the responsibility for evaluating requests to purchase nonstandard GPETE and for recommending its approval or disapproval to NAVSEA. NAVSEA will then forward its final decision to the originating command for such requests. SHIP CONFIGURATION AND LOGISTIC INFORMATION SYSTEM (SCLSIS) PROGRAM The Navy must maintain, update, and calibrate thousands of pieces of equipment. To do this, the SHIP CONFIGURATION AND LOGISTIC SUPPORT INFORMATION SYSTEM (SCLSIS) program was designed to keep track of all installed and portable equipment in the fleet. SCLSIS is used to keep up with the existence, location, and changes made to equipment. The SCLSIS program seeks to improve the quality of equipment reporting, provide information needed by other Navy management systems, and reduce record keeping. It is also designed to assist Navy supply systems that furnish spares, documentation, and training necessary to support installed and portable equipment. Therefore, the inventory of assigned test equipment on board ship is directly related to SCLSIS records. Properly maintained SCLSIS records also show the complete inventory of test equipment on board by quantity, serial number, and location. The SCLSIS program has two basic elements: (1) VALIDATION, to establish a baseline data inventory, and (2) INVENTORY UPDATING, to correct errors or omissions and to document configuration changes.

Q.4 Name the two basic elements of the SCLSIS program.

CALIBRATION AND REPAIR PROCEDURES The difference between the terms calibration and repair needs to be addressed before we proceed further. Calibration is little more than checking, adjusting, or systematically aligning a test instrument to a known standard. To do this, you must ensure that the equipment you send to the calibration lab is in working order. The calibration lab is where actual repair work becomes important. Obvious problems, such as open power cords, burned components, broken meters, and missing hardware, should be repaired or replaced before sending equipment to the calibration lab. Most calibration labs with which you will deal will be part of an intermediate maintenance activity (IMA) on board a tender. CALIBRATION STATUS You can determine the calibration status of any test equipment by checking the calibration label or tag located on the equipment. These calibration labels or tags advise you as to whether the item is usable and within its calibration interval. Tags and labels to be used in the METROLOGY CALIBRATION (METCAL) coordination program are listed in the following paragraphs. No other calibration labels or tags are authorized to be placed on test equipment. Calibrated Label The CALIBRATED label , shown in view A of figure 1-1, has black lettering and a white background and comes in two sizes. It is the most commonly used label in the METCAL program. This label indicates that the instrument to which it is attached is within its applicable tolerance on all parameters. If there are any qualifying conditions for use of the instrument, one of the other labels described in the next paragraphs should be used. Figure 1-1. - Calibration labels and tags.

Calibrated - Refer to Report Label

The CALIBRATED - REFER TO REPORT label, shown in view B of figure 1-1, has red lettering and a white back- ground. It comes in two sizes and is used when you must know the actual measurement values to use the instrument. Q.5 What calibration label is used when actual measurement values must be known to use the test equipment?

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Miscellaneous Measurements

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Click here to order Electronic Components Online MISCELLANEOUS MEASUREMENTS LEARNING OBJECTIVES Upon completing this chapter, you should be able to: Define and explain the use of the terms "dB" and "dBm" as they apply to power measurements. Describe the use of resistive loads, bolometers, and thermocouples in power measurements. Explain the measurement of mechanical rotation using the tachometer, stroboscope, and the strobotac.

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Explain the measurement of frequency in various ranges using vibrating reeds, tuned circuits, heterodyne frequency meters, absorption wavemeters, cavity wavemeters, and frequency counters. Describe the use of frequencymeasurement devices, oscilloscopes, and spectrum analyzers in waveform analysis and maintenance. Describe semiconductor testing and applicable terms in maintenance.

In chapter 1, you studied test equipment administration and the basic measurements that all technicians are responsible for performing. Topic 2 presents miscellaneous measurements that are fairly common; keep in mind, however, that you may not routinely perform these measurements in your particular job. This chapter introduces you to several test instruments and components found in those test instruments. It will also serve as a review of some of the basics of electronic theory related to test equipment. POWER MEASUREMENTS You may be required to check the power consumption and the input-signal power levels of electronic equipment. The determination of dc power is fairly simple; recall that the unit of power, the watt, is the product of the potential in volts and the current in amperes (P = E X I). As discussed in NEETS, Module 2, Introduction to Alternating Current and Transformers, the phase angle of the voltage and current must be considered for accurate ac power measurements. The measurement of ac power is further complicated by the frequency limitations of various power meters. If there is no phase angle difference, you can compute ac power in the same manner as dc power; that is, by determining the effective value of the product of the voltage and current.

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For equipments that operate in the audio-frequency (af) range, power levels have to be determined in the performance of routine checks and during corrective maintenance procedures. Power measurements for af circuits are usually indicated in terms of decibels (dB) or decibels referenced to 1 milliwatt (dBm). Because the actual calculation of decibel measurements is seldom required, the following explanation is somewhat simplified. Most test equipment is designed to measure and indicate decibels directly. This eliminates the need for you to perform complicated calculations. Nevertheless, a basic explanation of the decibel measurement system is necessary for you to understand the significance of dB readings and amplifier-gain ratings that are expressed in decibels. THE DECIBEL SYSTEM The basic unit of measurement in the system is not the decibel; it is the bel. The bel is a unit that expresses the logarithmic ratio between the input and the output of any given component, circuit, or system. It may be expressed in terms of voltage, current, or power. Most often, it is used to show the ratio between input and output power to figure gain. You can express the power gain of the amplifier (N) in bels by dividing the output (P1) by the input (P2) and taking the base 10 logarithm of the resulting quotient. The formula for determining this gain is:

If an amplifier doubles the input power, the quotient of P1to P2 will be 2. If you consult a logarithm table, you will find that the base 10 logarithm of 2 is 0.3, making the power gain of the amplifier 0.3 bel. Q.1 What is the logarithmic ratio between the input and output of a given circuit called?

Experience has shown that because the bel is a rather large unit, it is difficult to apply. A more practical unit, and one that can be used more easily, is the decibel (1/10 bel). You can convert any figure expressed in bels to decibels by multiplying that figure by 10 or simply by moving the decimal point one place to the right. Applying this rule, we find that the above ratio of 0.3 bel is equal to 3 decibels. The decibel (dB) cannot be used to represent actual power; only the ratio of one power compared to another. To say that an amplifier has a 3 dB gain means that the output power is twice the input power. This gives no indication of the actual power represented. You must be able to state the input power for it to be meaningful. In many applications, a mathematical expression represents the actual power, not a power ratio. One standard reference is the dBm. The dBm is an abbreviation used to represent power levels above or below 1 milliwatt. Negative dBm (-dBm) represents power levels below 1 milliwatt, and positive dBm (+dBm) represents power levels above 1 milliwatt. In other words, a dBm value is a specific amount of power; 0 dBm is equal to 1 milliwatt. Briefly stated, the amount of power in a given value of dBm is the power which results if 1 milliwatt is amplified or attenuated by that dB value. For example, 40 dBm represents an actual power level (watts or milliwatts) that is 40 dB above 1 milliwatt, whereas -10 dBm represents a power level that is 10 dB below 1 milliwatt. The formula for finding dBm is a variation of the dB power formula:

Q.2 What term is used to represent power levels above or below a 1-milliwatt reference? You do not need to use the formula in most applications. The following shows conversions of dBm to mW: +20dBm=100mW +10dBm=10mW

+7dBm=5mW +6dBm = 4mW +4dBm=2.5mW +3dBm=2mW 0dBm=1mW -3dBm=.5mW -10dBm=.1mW For a +10 dBm level, start with the 1 milliwatt reference and move the decimal point one place to the right (+10 dBm = 10 mW). Another 10 dB increment brings the power level to +20 dBm, thereby moving the decimal point another place to the right (+20 dBm = 100 mW). For a -10 dBm level, again start with 1 milliwatt, but this time move the decimal point one place to the left (-10 dBm = .1 mW). An additional 10 dB decrease results in another decimal point shift to the left (-20 dBm = .01 mW). For a 3 dB increase, you double the power. For a 3 dB decrease, you reduce the power by one-half (+3 dBm = 2 mW and -3 dBm = .5 mW). A +6 dBm level is an additional 3 dB change from +3 dBm. In this case, you just double the power level of the +3 dBm (+6 dBm = 4 mW). Q.3 What milliwatt value is equal to +6 dBm? The dB change can be made in either direction. For example, +7 dBm is a decrease from +10 dBm. Reducing the +10 dBm power by one-half, we have +7 dBm, or 5 mW. A +4 dBm power level is a 3 dB decrease from +7 dBm (+4 dBm - 2.5 mW). By using this simple method, you can quickly find any power level that corresponds to a given dBm. Some test instruments you will be using are calibrated in decibels and have a 1 milliwatt zero reference level. Figure 2-1 illustrates such an instrument. Notice that this is an ac voltmeter in which the upper scale of the meter indicates ac voltage and the lower scale indicates decibels. The zero power-level indicator on the decibel scale is located at, or near, center scale. If the power in the line

being measured is more than the reference value, the meter will indicate a value to the right of the zero mark (+dB). If the power is less than the reference value, the meter will indicate a value to the left of the zero mark (-dB). Such meters are useful when recording measurements where a direct indication in decibels is desired. However, you must remember that this meter is still a voltmeter and that power measurements are not meaningful unless the circuit impedance is known. If you feel the need to review how to calculate power in ac circuits, refer to NEETS, Module 2. Figure 2-1. - Ac voltmeter.

MEASUREMENT METHODS At radio frequencies below the UHF range, power is usually

determined by voltage, current, and impedance measurements. One common method used to determine the output power of radiofrequency (rf) oscillators and radio transmitters consists of connecting a known resistance to the equipment output terminals. Current flowing through this resistance is then measured and the power is calculated as the product of I2R. Because power is proportional to the current squared, the meter scale can be calibrated to indicate power units directly. A THERMOCOUPLE AMMETER can be used in this manner for measuring rf power. The resistor used to replace the normal load is specially designed to have low reactance and the ability to dissipate the required amount of power. Such resistors are commonly called DUMMY LOADS or DUMMY ANTENNAS. Q.4 What name is given to a resistor used to replace the normal load in a circuit?

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Basic meters

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Click here to order Electronic Components Online BASIC METERS LEARNING OBJECTIVES Upon completing this chapter, you should be able to: Describe the basic theory of the galvanometer. Describe the basic theory of the D'Arsonval meter movement. State the proper procedure for connecting Join Integrated Publishing's an ammeter to a circuit. Discussion Group Define ammeter sensitivity. State the proper procedure for connecting a voltmeter to a circuit. Describe possible effects on a circuit caused by the connection of a voltmeter. Define voltmeter sensitivity. Describe the internal operation of an ohmmeter with the use of a block diagram. Order this Describe the operating procedure for information on CDusing a megohmmeter. Rom Describe the use of the electrodynamometer-type meter as a voltmeter, ammeter, and wattmeter. Describe the factors that limit wattmeter capability.

Describe an open circuit, a ground, a short, and the tests used to check for these conditions. When troubleshooting, testing, or repairing electronic equipment, you will use various meters and other types of test equipment to check for proper circuit voltages, currents, resistances, and to determine if the wiring is defective. You may be able to connect these test instruments to a circuit and take readings without knowing just how the instruments operate. However, to be a competent technician, you need to be able to do more than merely read a test instrument. You need a basic knowledge of how test instruments operate. This chapter discusses the operating principles of some of the test instruments you will use in equipment troubleshooting. METERS The best and most expensive measuring instrument is of no use to you unless you know what you are measuring and what each reading indicates. Remember that the purpose of a meter is to measure quantities existing within a circuit. For this reason, when the meter is connected to the circuit, it must not change the condition of the circuit. METER POWER SOURCE Meters are either SELF-EXCITED or EXTERNALLY EXCITED. Self-excited meters operate from their own power sources. Externally excited meters get their power from the circuit to which they are connected. Most common meters (voltmeters, ammeters, and ohmmeters) that you use in your work operate on the electromagnetic principle. All measuring instruments must have some form of indicating device, usually a meter, to be of any use to you. The most basic indicating device used in instruments that measure current and voltage operates by using the interaction between the magnetic fields associated with current flow in the circuit. Before continuing, you might want to review the properties of magnetism and electromagnetism in NEETS, Module 1, Introduction to Matter, Energy, and Direct Current.

Q.1 What meters operate from their own power sources? BASIC METER MOVEMENT A stationary, permanent-magnet, moving-coil meter is the basic meter movement used in most measuring instruments used for servicing electrical equipment. When current flows through the coil, a resulting magnetic field reacts with the magnetic field of the permanent magnet and causes the movable coil to rotate. The greater

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the intensity of current flow through the coil, the stronger the magnetic field produced; the stronger the magnetic field produced, the greater the rotation of the coil. The GALVANOMETER is an example of one type of stationary, permanent-magnet, moving-coil measuring instrument. Galvanometer The galvanometer is used to measure very low currents, such as those in bridge circuits. In modified form, the galvanometer has the highest sensitivity of any of the various types of meters in use today. A simplified diagram of a galvanometer is shown in figure 31. It is different from other instruments used for the same purpose because its movable coil is suspended by means of metal ribbons instead of a shaft and jewel-bearing arrangement often used in other instruments. Figure 3-1. - Simplified galvanometer.

The movable coil is wrapped around the aluminum frame of the

galvanometer. The coil is suspended between the poles of the magnet by means of thin, flat ribbons of phosphor bronze. These ribbons provide a conduction path for the current between the circuit being tested and the movable coil. The ribbons allow the coil to twist in response to the interaction of the applied current through the coil and the magnetic field of the permanent magnet. They also provide the restoring force for the coil. Basically, the restoring force is that force necessary to return the movable frame to its resting position after a reading. The ribbons restrain or provide a counterforce to the magnetic force acting on the coil. When the driving force of the coil current is removed, the restoring force provided by the ribbons returns the coil to its zero position. Q.2 What physical component of a galvanometer provides the restoring force for the coil? To determine the amount of current flow, we must have a means to indicate the amount of coil rotation. Either of two methods may be used: (1) the POINTER arrangement or (2) the LIGHT AND MIRROR arrangement. Q.3 In a galvanometer, what two methods are used to indicate the amount of coil rotation? In the pointer arrangement, one end of the pointer is mechanically connected to the rotating coil; as the coil moves, the pointer also moves. The other end of the pointer moves across a graduated scale and indicates the amount of current flow. The overall simplicity of this arrangement is its main advantage. However, a disadvantage of this arrangement is that it introduces a mechanical coil balancing problem, especially if the pointer is long. Q.4 What is the primary disadvantage of the pointer arrangement for indicating coil rotation? In the light and mirror arrangement, the use of a mirror and a beam of light simplifies the problem of coil balance. When this arrangement is used to measure the turning of the coil, a small mirror is mounted on the supporting ribbon, as shown in figure 3-1. An internal light source is directed to the mirror and then reflected to the scale of the meter. As the movable coil turns, so does the mirror. This causes the light reflection to move across the graduated scale of the meter. The movement of the reflection is proportional to the movement of the coil; therefore, the intensity of the current being measured by the meter is accurately indicated. If the beam of light and mirror arrangement is used, the beam of light is swept to the right or left across a translucent screen

(scale). The translucent screen is divided uniformly with the zero reading located at center scale. If the pointer arrangement is used, the pointer is moved in a horizontal plane to the right or left across a scale that is divided uniformly with the zero reading at the center. The direction in which the beam of light or the pointer moves depends on the direction (polarity) of current through the coil. D'Arsonval Meter Movement Most dc instruments use meters based on some form of the D'Arsonval meter movement. In D'Arsonval-type meters, the length of the conductor and the strength of the field between the poles of the magnet are fixed. Therefore, any change in current causes a proportional change in the force acting on the coil. Figure 3-2 is a simplified diagram showing the principle of the D'Arsonval movement. Figure 3-2. - D'Arsonval meter movement.

In the figure, only one turn of wire is shown; however, in an actual meter movement, many turns of fine wire would be used, each turn adding more effective length to the coil. The coil is wound on an aluminum frame (bobbin) to which the pointer is attached. Oppositely wound hairsprings (only one is shown in the figure) are also attached to the bobbin, one at either end. The circuit to the coil is completed through the hairsprings. In addition to serving as conductors, the hairsprings serve as the restoring force that returns the pointer to the zero position when no current flows.

Q.5 What component of the D'Arsonval meter movement completes the circuit for current flow to the coil?

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Common test equipment

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Click here to order Electronic Components Online COMMON TEST EQUIPMENT LEARNING OBJECTIVES Upon completing this chapter, you should be able to: Describe the proper operating procedures for using the multimeter. Describe the proper operating procedures for using the digital multimeter. Describe the proper operating procedures for using the differential voltmeter. Describe the proper operation of the transistor tester. Describe the proper procedure for using the RCL bridge to measure resistance, capacitance, and inductance.

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In the previous chapters, you have learned how to use some basic and miscellaneous measuring instruments to perform required maintenance and Order this upkeep of electronic systems and components. You were also introduced to the information on CDconstruction and operation of basic meter movements in test equipment. This Rom chapter will introduce you to some of the testing instruments commonly used in the Navy today. MULTIMETERS During troubleshooting, you will often be required to measure voltage, current, and resistance. Rather than using three or more separate meters for these measurements, you can use the MULTIMETER. The multimeter contains circuitry that allows it to be used as a voltmeter, an ammeter, or an ohmmeter. A multimeter is often called a VOLT-OHM-MILLIAMMETER (VOM).

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One of the greatest advantages of a VOM is that no external power source is required for its operation; therefore, no warm-up is necessary. Other advantages are its portability, versatility, and freedom from calibration errors caused by aging tubes, line voltage variations, and so forth.

Q.1 What is one of the greatest advantages of a VOM? Two disadvantages are that (1) the VOM tends to "load" the circuit under test, and (2) the meter movement is easily damaged as a result of improper testing procedures. Never press down on or place any object on the glass face of any multimeter. This can disable the meter movement from operating properly or cause damage. MEASURING RESISTANCE, VOLTAGE, AND CURRENT WITH A NONELECTRONIC VOM In the discussion that follows, you will become familiar with the operation and use of the multimeter in measuring resistance, voltage, and current. The meter selected for this discussion is the Simpson 260 multimeter, as shown in figure 4-1. The Simpson 260 is a typical VOM used in the Navy today. Figure 4-1. - Simpson 260 Series 6XLP Volt-Ohm-Milliammeter (VOM)

The multimeter has two selector switches. The switch on the lower left is the function switch, and the one in the lower center is the range switch. The function switch selects the type of current you will be measuring (+dc, -dc, or ac). The range switch is a 12-position switch that selects the range of ohmmeter, voltmeter, or milliammeter measurements you will make. The multimeter is equipped with a pair of test leads; red is the positive lead and black is the negative, or common, lead. Eight jacks are located on the lower part of the front panel. To prepare the meter for use, simply insert the test leads into the proper jacks to obtain the circuit and range desired for each application. In most applications, the black lead will be inserted into the jack marked at the lower left with a negative sign (-) or with the word COMMON. Measuring Resistance Before proceeding, you should be aware of the following important safety precaution that must be observed when using the ohmmeter function of a VOM: Never connect an ohmmeter to a "hot" (energized) circuit. Be sure that no power is applied and that all capacitors are discharged. Q.2 Before you connect a VOM in a circuit for an ohmmeter reading, in what condition must the circuit be? The internal components of the multimeter use very little current and are protected from damage by an overload protection circuit (fuse or circuit breaker). However, damage may still occur if you neglect the safety precaution in the CAUTION instructions above. Because no external power is applied to the component being tested in a resistance check, a logical question you may ask is, Where does the power for deflection of the ohmmeter come from? The multimeter contains its own twobattery power supply inside the case. The resistive components inside the multimeter are of such values that when the leads are connected together (no resistance), the meter indicates a full-scale deflection. Because there is no resistance between the shorted leads, full-scale deflection represents zero resistance. Before making a measurement, you must zero the ohmmeter to ensure accurate readings. This is accomplished by shorting the leads together and adjusting the OHMS ADJ control so that the pointer is pointing directly at the zero mark on the OHMS scale. The ZERO OHMS control is continuously variable and is used to adjust the meter circuit sensitivity to compensate for battery aging in the ohmmeter circuits. An important point to remember when you are making an accurate resistance measurement is to "zero" the meter each time you select a new range. If this is not done, the readings you obtain will probably be incorrect. When making a resistance measurement on a resistor, you must give the following considerations to the resistor being tested: The resistor must be electrically isolated. In some instances, a soldered

connection will have to be disconnected to isolate the resistor. Generally, isolating one side of the resistor is satisfactory for you to make an accurate reading. The meter leads must make good electrical contact with the resistor leads. Points of contact should be checked for dirt, grease, varnish, paint or any other material that may affect current flow. Touch only the insulated portions of the test leads. Your body has a certain amount of resistance, which the ohmmeter will measure if you touch the uninsulated portions of the leads. Figure 4-2 is a functional block diagram of the ohmmeter circuit in a VOM. The proper method of checking a resistor is to connect the red lead to one end of the resistor and the black lead to the other end of the resistor. Figure 4-2. - Functional block diagram of an ohmmeter circuit.

Because zero resistance causes full-scale deflection, you should realize that the deflection of the meter is inversely proportional to the resistance being tested; that is, for a small resistance value, the deflection will be nearly full scale; and for a large resistance value, the deflection will be considerably less. This means that the left portion of the OHMS scale represents high resistance; the right side of the scale represents low resistance. Zero resistance (a short circuit) is indicated on the extreme right side of the scale; infinite resistance (an open circuit) is located on the extreme left side of the scale. Notice that you read the OHMS scale on the multimeter from RIGHT to LEFT. For example, the pointer of the multimeter in figure 4-3 indicates 8.0 ohms. To determine the actual value of a resistor, multiply the reading on the meter scale by the range switch setting (R X 1, R X 100, or R X 10,000). Figure 4-3. - Ohmmeter scale.

Notice that the scale marks are crowded on the left side of the OHMS scale, which makes them difficult to read. Therefore, the best range to select is one in which the pointer will fall in the space from midscale to slightly to the right side of midscale. The divisions in this area of the scale are evenly spaced and provide for easier reading and greater accuracy. Q.3 When taking resistance readings with a VOM, you will obtain the most accurate readings at or near what part of the scale?

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Special-application test equipment

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Click here to order Electronic Components Online SPECIAL-APPLICATION TEST EQUIPMENT LEARNING OBJECTIVES Upon completing this chapter, you should be able to: Explain the theory of operation of two types of power meters. Describe the purpose of the controls and indicators found on power meters. Join Integrated Describe the proper procedure for taking Publishing's power measurements for incident and reflected energy. Discussion Group Describe the uses and purposes of the controls and indicators found on the signal generator. Explain the theory of operation of a typical frequency counter. Describe the uses and purposes of the controls and indicators found on the frequency counter. Explain the uses and purposes of the Order this controls and indicators found on the information on CDTracker 2000. Rom Describe the proper procedures for troubleshooting with a logic probe. Describe the proper procedures for troubleshooting using the Tracker 2000. In chapters 3 and 4, you studied the more common pieces of test equipment. As a technician, you will routinely use this test equipment to troubleshoot and perform maintenance on electronic equipment. However, the equipments you will study in this chapter may or may not be found in your shop. This is because these equipments have specific or specialized uses. Unless your rating is involved with the equipment with which they are used, you may not have reason to use them. They are presented here so that you will be familiar with their overall function should the need arise. The equipments you will study in this chapter are power meters, signal generators, frequency counters, and integrated circuit-testing devices. POWER METERS

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As a technician, you will use a POWER METER to measure power. There are various types of power meters, some of which are called WATTMETERS. Figure 5-1 shows the AN/URM-120 wattmeter, which is one type of power meter commonly used in the Navy. This particular power meter measures power directly; that is, you connect it directly between the transmitter output (rf source) and the load, most likely an antenna. Figure 5-1. - Wattmeter (AN/URM-120).

Other types of power meters measure power indirectly; that is, they sample power in other ways - but not by being placed directly between the output of the transmitter and the load. Let's discuss the direct-measuring power meter first; then we'll talk about an indirect-measuring power meter. DIRECT-MEASURING POWER METERS The direct-measuring power meter is designed to measure incident (forward) and reflected (reverse) rf power from 50 to 1,000 watts at 2 MHz to 30 MHz and 10 to 500 watts at 30 MHz to 1,000 MHz. Three separate COUPLER-DETECTORS (sometimes called ATTENUATORS), each rated to cover a portion of the frequency and power ranges, are provided with the wattmeter. These devices couple the rf signal into the wattmeter and detect the signal. The coupler-detector knob projects through the top of the wattmeter case, as shown on the AN/URM-120 wattmeter in figure 5-1. A nameplate on the top of the POWER RANGE knob indicates the power range. The POWER RANGE knob can be rotated 360° to the desired power range. The coupler-detector rotates 180° inside the metal case for either forward or reverse power measurements. Also located inside the metal case are the indicating meter and cable for interconnecting the meter to the coupler-detector. The LOCKING knob locks the coupler-detector and POWER RANGE knobs in place. Two N-TYPE connectors (one male and one female) are located on either side of the wattmeter case to connect the instrument between the power source and the load. The

upper and lower parts of the wattmeter are held together with quick-action fasteners, which permit easy access to the inside of the wattmeter. Power measurements are made by inserting the proper coupler-detector and connecting the wattmeter in the transmission line between the load and the rf power source. To measure incident power with the wattmeter, rotate the arrow on the COUPLER-DETECTOR knob toward the load, and position the POWER RANGE knob for peak meter reading. To measure reflected power, position the arrow toward the rf power source. In effect, rotating the coupler-detector causes the coupler to respond only to a wave traveling in a particular direction, either to (incident) or from (reflected) the load. It will be unaffected by a wave traveling in the opposite direction. A diode rectifier in the coupler rectifies the energy detected by the coupler. This detected rf energy is measured across a known impedance to obtain either incident or reflected power. Operating the Wattmeter Always de-energize and tag the rf power source before measuring incident power. Insert the proper coupler-detector for the rf power being measured into the wattmeter case. Remove the wire shunt (not shown in figure 5-1) from the meter terminals, then connect the wattmeter into the transmission line, either at the load or the rf source. Ensure that all connections are tight. Position the POWER RANGE knob to a value higher than the rated power of the rf source. If the rated power to be measured is not known, place the POWER RANGE knob in the highest power position before turning on the power source. Rotate the coupler-detector so that the arrow indicating power flow points toward the load. Turn on the rf power source. Rotate the POWER RANGE knob to the proper range for measuring and observe the point at which the indicating meter peaks. Q.1 To measure incident power, you must rotate the coupler-detector of the wattmeter so that the arrow indicating power flow points toward which end of the transmission line?

Reflected power is measured in the same manner as described for incident power, except that the coupler-detector is rotated so that the arrow points toward the rf source. After completing power measurements, de-energize the rf source, disconnect the wattmeter from the transmission line, and place the wire shunt on the meter terminals. Interpreting Power Measurements Made by the Wattmeter The rf power measurements made by the wattmeter are used to determine the voltage standing wave ratio (VSWR) of the load and the power absorbed by the load. (VSWR is covered in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas.) The VSWR can be determined from a chart provided in the wattmeter technical manual, or it can be calculated (as shown in the following example for a UHF transmitter) by the formula below (Pi is the incident power, and Pr is the reflected power as measured by the wattmeter): Where: Pi = 30 watts Pr = 0.5 watts

The example above results in a standing wave ratio expressed as 1.3 to 1. In a perfectly matched transmission line where there is no reflected power (Pr = 0), the standing wave ratio would be 1 to 1. A standing wave ratio of 1.5 to 1 indicates a 5percent reflection of energy (loss) and is considered to be the maximum allowable loss. So, our example is within allowable limits. If the standing wave ratio is greater than 1.5 to 1, then the transmission line efficiency has decreased and troubleshooting is necessary. An excellent discussion of the reasons for standing wave ratio increases is presented in EIMB, Test Methods and Practices, NAVSEA 0967-LP-000-0130. You can determine the rf power absorbed by the load simply by subtracting the reflected power reading from the incident power reading made by the wattmeter (30 watts - 0.5 watts = 29.5 watts). The power meter just discussed is often described as an IN-LINE POWER METER because readings are taken while the power meter is connected in series with the transmission line. Another type of power meter used by the Navy measures power indirectly. An example of an indirect-measuring power meter is described in the next section. INDIRECT-MEASURING POWER METERS An example of an indirect-measuring power meter is the HP-431C, shown in figure 5-2. The controls, connectors, and indicators for the power meter are illustrated in figure 5-3. This power meter can be operated from either an ac or dc primary power source. The ac source can be either 115 or 230 volts at 50 to 400 hertz. The dc source is a 24-volt rechargeable battery. Overall circuit operation of the power meter is shown in the block diagram in figure 5-4. Figure 5-2. - Power meter (HP-431C).

Figure 5-3. - Power meter controls, indicators, and connectors.

Figure 5-4. - Power meter block diagram.

The HP-431C power meter indirectly measures microwave frequency power by using two bridge circuits - the detection bridge and the compensation and metering bridge. The detection bridge incorporates a 10-kilohertz (kHz) oscillator in which the amplitude is determined by the amount of heating of the thermistors in that bridge caused by microwave power. (Thermistors were covered in chapter 2 of this module.) The compensation and metering bridge contains thermistors that are affected by the same microwave power heating as those of the detection bridge. An unbalance in the metering bridge produces a 10-kHz error signal. This error signal, plus the 10-kHz bias that is taken directly from the 10-kHz OSCILLATOR-AMPLIFIER, is mixed in the SYNCHRONOUS DETECTOR. The synchronous detector produces a dc current (Idc) that is proportional to the 10-kHz error signal. The Idc error signal is fed back to the compensation and metering bridge, where it substitutes for the 10-kHz power in heating the thermistor and drives the bridge toward a state of balance. The dc output of the synchronous detector also operates the meter circuit for a visual indication of power. Q.2 What condition produces the 10-kHz error signal generated by the metering bridge in the HP-431C power meter?

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THE OSCILLOSCOPE AND SPECTRUM ANALYZER

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Click here to order Electronic Components Online THE OSCILLOSCOPE AND SPECTRUM ANALYZER LEARNING OBJECTIVES Upon completing this chapter, you should be able to: Describe the purpose of the CRT used in the oscilloscope. Explain the operation of an oscilloscope. Describe the purpose of the controls and Join Integrated indicators found on an oscilloscope. Publishing's Describe the proper procedure for using a dualDiscussion Group trace oscilloscope. Describe the accessory probes available for use with a dual-trace oscilloscope. Explain the operation of the spectrum analyzer. Describe the purpose of the controls and indicators found on the spectrum analyzer. One of the most widely used pieces of electronic test equipment is the OSCILLOSCOPE. An oscilloscope is used to show the shape of a video pulse Order this appearing at a selected equipment test point. Although some oscilloscopes information on CDare better than others in accurately showing video pulses, all function in Rom fundamentally the same way. If you learn how one oscilloscope operates, you will be able to learn others. As you will learn in this chapter, there are many different types of oscilloscopes - varying in complexity from the simple to the complex. Before we get into our discussion of the dual-trace oscilloscope, we will first present a general overview of basic single-trace oscilloscope operation. Shortly, we will see how oscilloscopes use a CATHODE-RAY TUBE (CRT) in which controlled electron beams are used to present a visible

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pattern of graphical data on a fluorescent screen. Another piece of test equipment used is the SPECTRUM ANALYZER. This test equipment is used to sweep over a band of frequencies to determine what frequencies are being produced by a specific circuit under test, and then the amplitude of each frequency component. An accurate interpretation of the display will allow you to determine the efficiency of the equipment being tested. CATHODE-RAY TUBES A detailed discussion of CATHODE-RAY TUBES (CRTs) is presented in NEETS, Module 6, Electronic Emission, Tubes, and Power Supplies. Before continuing with your study of CRTs in this section, you may want to review chapter 2 of that module. Cathode-ray tubes used in oscilloscopes consist of an ELECTRON GUN, a DEFLECTION SYSTEM, and a FLUORESCENT SCREEN. All of these elements are enclosed in the evacuated space inside the glass CRT. The electron gun generates electrons and focuses them into a narrow beam. The deflection system moves the beam horizontally and vertically across the screen. The screen is coated with a phosphorous material that glows when struck by the electrons. Figure 6-1 shows the construction of a CRT. Figure 6-1. - Construction of a CRT.

ELECTRON GUN The ELECTRON GUN consists of a HEATER and a CATHODE to generate electrons, a CONTROL GRID to control brightness by controlling electron flow, and two ANODES (FIRST and SECOND). The main purpose of the first (FOCUSING) anode is to focus the electrons into a narrow beam on the screen. The second (ACCELERATING) anode accelerates the electrons as they pass. The control grid is cylindrical and has a small opening in a baffle at one end. The anodes consist of two cylinders that contain baffles (or plates) with small holes in their centers.

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Q.1 What element controls the number of electrons striking the screen?

Q.2 What element is controlled to focus the beam? Cathode and Control Grid As in most conventional electron tubes, the cathode is indirectly heated and emits a cloud of electrons. The control grid is a hollow metal tube placed over the cathode. A small opening is located in the center of a baffle at the end opposite the cathode. The control grid is maintained at a negative potential with respect to the cathode to keep the electrons bunched together. A high positive potential on the anodes pulls electrons through the hole in the grid. Because the grid is near the cathode, it can control the number of electrons that are emitted. As in an ordinary electron tube, the negative voltage of the grid can be varied either to control electron flow or stop it completely. The brightness (intensity) of the image on the fluorescent screen is determined by the number of electrons striking the screen. This is controlled by the voltage on the control grid. Electrostatic Lenses and Focusing The electron beam is focused by two ELECTROSTATIC FIELDS that exist between the control grid and first anode and between the first and second anodes. Figure 6-2 shows you how electrons move through the electron gun. The electrostatic field areas are often referred to as LENSES because the fields bend electron streams in the same manner that optical lenses bend light rays. The first electrostatic lens cause the electrons to cross at the first focal point within the field. The second lens bend the spreading streams and return them to a new, second focal point at the CRT. Q.3 Why are the electrostatic fields between the electron gun elements called lenses? Figure 6-2. - Formation of an electron beam.

Figure 6-2 also shows the relative voltage relationships on the electrongun elements. The cathode (K) is at a fixed positive voltage with respect to ground. The grid is at a variable negative voltage with respect to the cathode. A fixed positive voltage of several thousand volts is connected to the second (accelerating) anode. The potential of the first (focusing) anode is less positive than the potential of the second anode. The first anode can be varied to place the focal point of the electron beam on the screen of the tube. Control-grid potential is established at the proper level to allow the correct number of electrons through the gun for the desired image intensity.

Q.4 What is the function of the second anode? ELECTRON BEAM-DEFLECTION SYSTEM The electron beam is developed, focused, and accelerated by the electron gun. The beam appears on the screen of the CRT as a small, bright dot. If the beam is left in one position, the electrons will soon burn away the illuminating coating in that one area. To be of any use, the beam must be able to move. As you have studied, an electrostatic field can bend the path of a moving electron. As you have seen in the previous illustrations, the beam of electrons passes through an electrostatic field between two plates. You should remember that electrons are negatively charged and that they will be deflected in the direction of the electric force (from negative to positive). This deflection causes the electrons to follow a curved path while in the electrostatic field. When the electrons leave the electrostatic field, they will take a straight

path to the screen at the angle at which they left the field. Because they were all deflected equally, the electrons will be traveling toward the same spot. Of course, the proper voltages must exist on the anodes to produce the electrostatic field. Changing these voltages changes the focal point of the beam and causes the electron beam to strike the CRT at a different point. Factors Influencing Deflection The ANGLE OF DEFLECTION (the angle the outgoing electron beam makes with the CRT center line axis between the plates) depends on the following factors: Length of the deflection field; Spacing between the deflection plates; The difference of potential between the plates; and The accelerating voltage on the second anode. LENGTH OF DEFLECTION FIELD. - As shown in figure 6-3, a long field (long deflection plates) has more time to exert its deflecting forces on an electron beam than does a shorter field (short deflection plates). Therefore, the longer deflection plates can bend the beam to a greater deflection angle. Figure 6-3. - Factors influencing length of field.

Q.5 What effect do longer deflection plates have on the electron beam?

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Book 17

Back • Home • Up • Next Click here to order Electronic Components Online Introduction to radio System introduction Navy frequency band use Communications fundamentals Summary Answers

Introduction to communications theory Frequency Multiplication Ship-to-ship ssb Single-Sideband Automatic Gain/Volume Control (agc/avc) Delayed Automatic Gain Control Audio Tone Audio reproduction devices Summary Answers

Fundamental systems equipment

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Transmitters Radio Transmitters Antenna distribution systems Manual Telegraphy Basic Systems Rfcs Send System Rfcs Receive System Afts System Facsimile Shipboard communications systems quality monitoring Electromagnetic radiation Summary Answers

Introduction to satellite communications Satellite Characteristics Earth terminal characteristics Standard receive-only equipment systems Role of satellite communications Future satellite communications Summary Answers

Introduction to miscellaneous communications systems and equipment Receive Equipment Naval tactical data system Portale equipment Lasers - Theory of operation Summary Answers

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Introduction to radio

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Click here to order Electronic Components Online INTRODUCTION TO RADIO-FREQUENCY COMMUNICATIONS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.

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Upon completion of this chapter, you will be able to: Define electrical telecommunications. Describe the use of radiotelegraph, radiotelephone, teletypewriter, and facsimile.

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Define and describe the interrelationships of the system, set, group, unit, assembly, subassembly, part, and reference designations. State the frequency ranges of the various frequency bands and describe the most common uses of those bands by the Navy. Describe a strategic communications link. Describe a tactical communications link. Describe the five basic communications modes of operation. Describe a switched communications network. Describe the purpose of the two Navy-only networks. INTRODUCTION TO NAVAL TELECOMMUNICATIONS When the wireless (radiotelegraph) was invented, the Navy saw a possible use for it. It could be used for communications from shore stations to ships along the coast. In 1899, the first official naval radio message was sent from ship to shore. It only traveled a distance of 20 miles but that was a start. The next advance was in 1916 when the Navy first used radiotelephone between ships. Three years later the first airborne radio was used to communicate with a ground station. In the early years, communications was not the best because of poor tuning techniques. Receivers often did not pick up the signal. This problem was almost eliminated in 1931 when the first superheterodyne receivers were installed in the fleet. In 1944, another important event took place. The first successful radio teletypewriter transmissions between ships were completed. The first successful use of radiophoto (facsimile) occurred in 1945 with the transmission of the surrender document signing that ended World War II. Naval communications has grown tremendously in size and complexity since then. The fleets of our modern Navy travel faster and are spread over

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greater areas of ocean than any seagoing force of the past. Commanders and their subordinates throughout the Department of the Navy use the facilities of naval communications as a primary method of communicating. Naval communications relies on top performance from all of its assigned personnel. Reliable, secure, and timely transmission and receipt of information, based on wartime requirements, is the ultimate goal. Previous modules have discussed electronic components or circuitry in individual units. In this chapter we will tie up some loose ends for you and discuss radio-frequency communications. We will cover the considerations involved in receiving or transmitting a radio-frequency signal between two or more geographic locations. Let's start by defining telecommunications. TELECOMMUNICATIONS refers to communications over a distance and includes any transmission, emission, or reception of signs, signals, writings, images, or sounds. Intelligence produced by visual means, oral means, wire, radio, or other electromagnetic systems are also included. Electrical, visual, and sound telecommunications are all used in the Navy. In this chapter we will talk only about electrical types of telecommunications. ELECTRICAL The types of electrical communications are radio and wire. Radio uses electromagnetic waves to transmit and receive intelligence. The waves are not guided by a physical path between sender and receiver. Wire uses conductors to carry these waves. Radio is the most important method the Navy has of communicating between widely separated forces. The transmission methods we will be discussing are radiotelegraph, radiotelephone, teletypewriter, and facsimile. Radiotelegraph Radiotelegraph transmissions are referred to as continuous wave (cw) telegraphy. Cw is a manual or automatic system of transmitting signals using a wave of radio-frequency (rf) energy.

The radio operator separates a continuously transmitted wave into dots and dashes based on the Morse code. This is accomplished by opening and closing a telegraphic hand key. Radiotelegraphy was the first means of radio communications that had military and commercial importance. Radiotelegraph still is used as a means of communication to, from, and among widely separated units of the Navy. Relative slow speed of transmission and the requirement for experienced operators are the major disadvantages of radiotelegraph. The main advantage is reliability. A thinking person at both sending and receiving stations provides a capability of being understood not present in automated systems. Radiotelephone Radiotelephone is one of the most useful military communications methods. Because of its directness, convenience, and ease of operation, radiotelephone is used by ships, aircraft, and shore stations. It has many applications and is used for ship-to-shore, shore-to-ship, ship-to-ship, air-to-ship, ship-to-air, air-to-ground, and ground-to-air communications. Modern means of operation make it possible to communicate around the world by radiotelephone. One of the most important uses of radiotelephone is short-range tactical communications. This method permits tactical commanders to communicate directly with other ships. Little delay results while a message is prepared for transmission, and acknowledgments can be returned instantly. Radiotelephone equipment for tactical use usually is operated on frequencies that are high enough to have line-of-sight characteristics; that is, the waves do not follow the curvature of the earth. As you know, these characteristics limit the usual range of radiotelephone from 20 to 25 miles. This is important because it reduces the chances of the enemy intercepting the message. Radiotelephone procedures can be learned easily by persons with no other training in communications. Radiotelephone has some disadvantages. You may find transmissions unreadable because of static, enemy interference, or high local noise level caused by shouts, gunfire, and bomb or shell bursts. Wave propagation characteristics of radiotelephone

frequencies sometimes are unpredictable, and tactical transmissions may be heard from great distances. Most radiotelephone messages are in plain language, and if information is to be kept from the enemy, users must keep their messages short, stick to the proper procedures, and be careful of what they say. Q.1 What are the two types of electrical communications? Q.2 What is the main advantage of radiotelegraph communications? Q.3 Why is radiotelephone one of the most useful methods of military communications? Q.4 What are the disadvantages of radiotelephone communications? Teletypewriter Teletypewriter (tty) signals may be transmitted by either landline (wire), cable, or radio. The landline tty is used both by the military services and by commercial communication companies. The Navy uses radio teletypewriter (rtty) mainly for high-speed automatic communications across ocean areas. The tty unit is equipped with a keyboard similar to a typewriter. When the operator presses a key, a sequence of signals is transmitted. At receiving stations, the signals are fed into terminal equipment that translates the sequences of signals into letters, figures, and symbols and types the messages automatically. The rtty mode of transmission and reception is rapidly becoming more efficient and reliable for communications between ships and from ship-to-shore. Ships copy what is known as "fleet broadcast" messages on rtty. The speed at which message traffic is transmitted on rtty circuits depends on the equipment in use. Normal speed of operation is 100 words per minute, but it may be faster or slower. You may find high-speed equipment, capable of printing a line or even a page at a time, in some communications centers. The use of rtty has brought about a considerable savings in manpower.

Facsimile Facsimile (fax) is the process used to transmit photographs, charts, and other graphic information electronically. The image to be transmitted is scanned by a photoelectric cell. Electrical changes in the cell output, corresponding to the light and dark areas being scanned, are transmitted to the receiver. At the receiver, the signal operates a recorder that reproduces the picture. The fax signals may be transmitted either by landline or radio. Facsimile transmissions suffer distortion from all of the common sources of interference experienced with ordinary radiotelegraph and radio teletypewriter. Certain characteristics of TIF transmission make it less susceptible to complete loss of intelligence. For example, picture quality will be downgraded by any noise bursts, since facsimile recording is a continuous recording of signals coming from a receiver. However, because the machine scans material at the rate of about 100 lines per inch, each line is only 1/100th of an inch high. So you can see, if a noise burst interfers with the signal, it will distort a line only 1/100th of an inch high, leaving the image still readable. Under similar circumstances on a conventional rtty circuit, such distortion could cause a portion of the page copy to be unreadable. Facsimile transmission is not intended to be a replacement for teletypewriter and other general methods of transmission. It is an important communications supplement and provides a means of handling certain types of graphic and pictorial intelligence by swift communications methods. It is widely used by the Navy weather information services and ship and station weather centers to obtain the latest weather maps. Chances are the photo you saw in the newspaper was transmitted by facsimile. Q.5 What is the main use of a radio teletypewriter? Q.6 What is facsimile?

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Introduction to communications theory

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Click here to order Electronic Components Online INTRODUCTION TO COMMUNICATIONS THEORY LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Describe the four basic types of transmitters. Describe the two basic types of singlesideband circuits. Describe the three basic types of Join Integrated teletypewriter circuits. Publishing's List the four primary functions of a basic Discussion Group receiver. Describe the four primary functions of a basic receiver. State the four characteristics of a basic receiver. Evaluate the four characteristics of a basic receiver. Describe the fundamental heterodyning Order this process. information on CDDescribe the basic difference between an Rom AM and an fm receiver. Describe single-sideband suppressed carrier communications. State the purpose of carrier reinsertion and how it is used in single-sideband communications. Order this Describe the basic theory and functions of information in receiver control circuits. Print (Hardcopy). Describe the basic frequency synthesis process. Describe the basic audio reproduction process.

INTRODUCTION In the previous chapter you learned the fundamentals of U.S. naval telecommunications and communications. Now, let's look at the equipment and systems that are used to communicate in the Navy. The fundamental equipment used to communicate are the transmitter and receiver. Transmitters and receivers must each perform two basic functions. The transmitter must generate a radio frequency signal of sufficient power at the desired frequency. It must have some means of varying (or modulating) the basic frequency so that it can carry an intelligible signal. The receiver must select the desired frequency you want to receive and reject all unwanted frequencies. In addition, receivers must be able to amplify the weak incoming signal to overcome the losses the signal suffers in its journey through space. Representative transmitters and their fundamental features are described for you in this module. TRANSMITTER FUNDAMENTALS Basic communication transmitters include continuous wave (cw), amplitude modulated (AM), frequency modulated (fm), and single sideband (ssb) types. A basic description of each of these transmitters is given in this chapter. CONTINUOUS WAVE TRANSMITTER The continuous wave is used principally for radiotelegraphy; that is, for the transmission of short or long pulses of rf energy to form the dots and dashes of the Morse code characters. This type of transmission is sometimes referred to as interrupted continuous wave. Cw transmission was the first type of radio communication used, and it is still used extensively for long-range communications. Two of the advantages of cw transmission are a narrow bandwidth, which requires less output power, and a degree of intelligibility that is high even under severe noise conditions. (For example, when the receiver is in the vicinity of rotating machinery or thunderstorms.) A cw transmitter requires four essential components. These are a generator, amplifier, keyer, and antenna. We have to generate rf oscillations and have a means of amplifying these oscillations. We also need a method of turning the rf output on and off (keying) in accordance with the intelligence to be transmitted and an antenna to radiate the keyed output of the transmitter. Let's take a look at the block diagram of a cw transmitter and its power supply in figure 2-1. The oscillator generates the rf carrier at a preset frequency and maintains it within close tolerances. The oscillator may be a self-excited type, such as an electron-coupled oscillator, or a quartz crystal type, which uses a crystal cut to vibrate at a certain frequency when electrically excited. In both types, voltage and current delivered by the oscillator are weak. The oscillator outputs must be amplified many times to be radiated any distance. Figure 2-1. - Cw transmitter block diagram.

The buffer stage or first intermediate power amplifier stage (referred to as the ipa) is a voltage amplifier that increases the amplitude of the oscillator signal to a level that drives the power amplifier (pa). You will find the signal delivered by the buffer varies with the type of transmitter and may be hundreds or thousands of volts. The buffer serves two other purposes. One is to isolate the oscillator from the amplifier stages. Without a buffer, changes in the amplifier caused by keying or variations in source voltage would vary the load of the oscillator and cause it to change frequency. It may also be used as a frequency multiplier, which is explained later in this text. As you can see in the figure, a key is used to turn the buffer on and off. When the key is closed, the rf carrier passes through the buffer stage; when the key is open (buffer is turned off), the rf carrier is prevented from getting through. The final stage of a transmitter is the power amplifier (referred to as the pa). In chapter 3 of NEETS, Module 1, Introduction to Matter, Energy, and Direct Current, you learned that power is the product of current and voltage (P = IE). In the power amplifier a large amount of rf current and voltage is made available for radiation by the antenna. The power amplifier of a high-power transmitter may require far more driving power than can be supplied by an oscillator and its buffer stage. One or more low-power intermediate amplifiers are used between the buffer and the final amplifier that feeds the antenna. The main difference between many low- and high-power transmitters is in the number of intermediate poweramplifier stages used. Figure 2-2 is a block diagram of the input and output powers for each stage of a typical mediumpower transmitter. You should be able to see that the power output of a transmitter can be increased by adding amplifier stages capable of delivering the power required. In our example, the .5 watt output of the buffer is amplified in the first intermediate amplifier by a factor of 10, (this is a times 10 [ X 10] amplifier) giving us an input of 5 watts to the second intermediate amplifier. You can see in this example the second intermediate amplifier multiplies the 5 watt input to it by a factor of 5 ( X 5) and gives us a 25 watt input to our power (final) amplifier. The final amplifier multiplies its input by a factor of 20 (X 20) and gives us 500 watts of power out to the antenna. Figure 2-2. - Intermediate amplifiers increase transmitter power.

Q.1 What are the four basic transmitter types? Q.2 What is the function of the oscillator in a cw transmitter? Q.3 What is the final stage of a transmitter? AMPLITUDE MODULATED TRANSMITTER In AM transmitters, the instantaneous amplitude of the rf output signal is varied in proportion to the modulating signal. The modulating signal may consist of many frequencies of various amplitudes and phases, such as the signals making up your own speech pattern. Figure 2-3 gives you an idea of what the block diagram of a simple AM transmitter looks like. The oscillator, buffer amplifier, and power amplifier serve the same purpose as those in the cw transmitter. The microphone converts the audio frequency (af) input (a person's voice) into corresponding electrical energy. The driver amplifies the audio, and the modulator further amplifies the audio signal to the amplitude necessary to fully modulate the carrier. The output of the modulator is applied to the power amplifier. The pa combines the rf carrier and the modulating signal in the power amplifier to produce the amplitude-modulated signal output for transmission. In the absence of a modulating signal, a continuous rf carrier is radiated by the antenna. Figure 2-3. - AM radiotelephone transmitter block diagram.

FREQUENCY MODULATED TRANSMITTER In frequency modulation (fm) the modulating signal combines with the carrier to cause the frequency of the resultant wave to vary with the instantaneous amplitude of the modulating signal. Figure 2-4 shows you the block diagram of a frequency-modulated transmitter. The modulating signal applied to a varicap causes the reactance to vary. The varicap is connected across the tank circuit of the oscillator. With no modulation, the oscillator generates a steady center frequency. With modulation applied, the varicap causes the frequency of the oscillator to vary around the center frequency in accordance with the modulating signal. The oscillator output is then fed to a frequency multiplier to increase the frequency and then to a power amplifier to increase the amplitude to the desired level for transmission. Figure 2-4. - Fm transmitter block diagram.

Harmonics True harmonics are always exact multiples of the basic or fundamental frequency generated by an oscillator and are created in amplifiers and their associated circuits. Even harmonics are 2, 4, 6, and so on, times the fundamental; odd harmonics are 3, 5, 7, and so on, times the fundamental. If an oscillator has a fundamental frequency of 2,500 kilohertz, the harmonically related frequencies are 5,000 second harmonic 7,500 third harmonic 10,000 fourth harmonic 12,500 fifth harmonic You should note that the basic frequency and the first harmonic are one and the same. The series ascends indefinitely until the intensity is too weak to be detected. In general, the energy in frequencies above the third harmonic is too weak to be significant.

In some electronics books, and later in this chapter, you will find the term SUBHARMONIC used. It refers to a sine wave quantity (for example, an oscillator output) that has a frequency that is a submultiple of the frequency of some other sine wave quantity it helped make. For example, a wave that is half the fundamental frequency of another wave is called the second subharmonic of that wave; one with a third of the fundamental frequency is called a third subharmonic; and so forth. Q.4 What purpose does a microphone perform in an AM transmitter? Q.5 In an fm transmitter, when does an oscillator generate only a steady frequency? Q.6 What is a harmonic? Q.7 If the fundamental frequency is 200 megahertz, what is the third harmonic?

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Fundamental systems equipment

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Click here to order Electronic Components Online FUNDAMENTAL SYSTEMS EQUIPMENT LEARNING OBJECTIVES Upon completion of this chapter you will be able to: State the function of a radio communications handset, a radio set control, and a transfer switchboard. Describe the functions and interrelationships of a radio transmitter. Describe the functions of receive and transmit multicouplers. Describe the differences between the codes used for manual telegraphy and teletypewriter transmissions. Describe the two basic modes of teletypewriter operation. Describe the two types of teletypewriter dc circuits.

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State the two types of radio teletypewriter shift systems and describe their basic differences. Describe the functions and interrelationships of radiofrequency-carrier shift send and receive systems. Describe the signal flow in an audio-frequency-tone shift system. State the function of the tone terminal set in an audiofrequency-tone shift system. Describe the basic multiplexing process. Describe the three operations performed by a facsimile system. Describe the functions and interrelationships of facsimile equipment. Describe the countermeasures that can be used to eliminate compromising emanations. EQUIPMENT PURPOSES A communications system is a collection of equipment used together to do a specific job. You may see this equipment used to send or receive voice communications, or both, or to send, receive, or send and receive teletypewriter information. Figure 3-1 is a basic block diagram of a voice system. You can see how this equipment is interconnected to form a basic communications system.We are going to look at several of the equipment blocks in detail. Figure 3-1. - Voice system.

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HANDSET The handset converts acoustical energy (your voice) to electrical energy for use in modulating a radio transmitter. It also converts electrical energy to acoustical energy for reproduction of a received signal. When the push-to-talk button is depressed on the handset, the dc keying circuit to the transmitter is closed, placing the transmitter on the air. Handsets are normally connected to a radio set control unit. RADIO SET CONTROL UNIT The radio set control unit shown in figure 3-2 provides a capability to remotely control some radiophone transmitter functions and the receiver output. Some of the controls are used for turning the transmitter on and off. Others are used for voice modulating the transmission (or keying when cw operation is desired). You can even

control the audio output level of the receiver and silence the receiver when transmitting. Figure 3-2. - Radio set control unit.

Under standard operating conditions up to four of these units can be used in parallel with a single transmitter and receiver group to provide additional operating positions. This setup is often found aboard ship where a transmitter and/or receiver is controlled and operated from several locations such as the bridge or the combat information center. TRANSFER SWITCHBOARDS A transmitter transfer switchboard provides the capability to transfer remote control station functions and signals to transmitters. Figure 3-3 is a representative transfer switchboard that provides the capability for selectively transferring any one, or all, of ten remote control station functions and signals to any one of six transmitters. The cabinet has ten rotary switches arranged in two vertical rows of five each. Each switch has eight positions. The circuitry is arranged so that you cannot parallel transmitter control circuits; that is, you cannot connect more than one transmitter to any remote control location. Figure 3-3. - Transmitter transfer switchboard.

Each switch operating knob corresponds to a remote control station. Each switch position (1 through 6) corresponds to a transmitter. One switch position, X, provides for transfer of all circuits to additional transmitter transfer switchboards when more than six transmitters are installed in the system. When the rotary switch is placed in the OFF position the remote control station is removed from the system. Let's look at an example of one transfer switchboard application. When remote control station number two is to have control of transmitter number three, the switch knob designated number two is rotated until its pointer indicates position three on its dial plate. The receiver transfer switchboard permits the operator to transfer the audio output from a receiver to a remote control station audio circuit. A representative receiver transfer switchboard is shown in figure 3-4. This switchboard contains ten seven-position switches. Each switch is connected to a remote control station, and each switch position (one through five) is connected to a receiver.

Figure 3-4. - Receiver transfer switchboard.

The X position on each switch allows transfer of circuits to additional switchboards just like with the transmitter transfer switchboard. Q.1 What are the basic functions of a handset? Q.2 What capability does a transmitter transfer switchboard provide? Q.3 What function does a receiver transfer switchboard perform?

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Introduction to satellite communications

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Click here to order Electronic Components Online INTRODUCTION TO SATELLITE COMMUNICATIONS LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Describe the basic operation of the two types of satellites. Describe the basic components of an operational satellite system. Describe the function of earth terminal equipment. Describe the basic signal flow of a typical shipboard receive-only system. Describe the basic signal flow of a typical shipboard transceiver system. Describe the advantages of satellite communications in terms of capacity, reliability, vulnerability, and flexibility. Describe the limitations of satellites in terms of power, receiver sensitivity, and availability.

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HISTORY OF SATELLITE COMMUNICATIONS The first artificial satellite was placed in orbit by the Russians in 1957. That satellite, called Sputnik, signaled the beginning of an era. The United States, who was behind the Russians, made an all-out effort to catch up, and launched Score in 1958. That was the first satellite with the primary purpose of communications.

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The first regular satellite communications service was used by the Navy in 1960. The moon was used to bounce teletypewriter signals between Hawaii and Washington, D.C. During the early 1960s, the Navy used the moon as a medium for passing messages between ships at sea and shore stations. This method of communications proved reliable when other methods failed. Military satellite communications technology was at a low level until 1965. At that time high quality voice transmissions were conducted between a satellite and two earth stations. That was the stepping stone to the Initial Defense Communications Satellite Program (IDCSP), which will be covered later in this chapter. Experience with satellite communications has demonstrated that satellite systems can satisfy many military requirements. They are reliable, survivable, secure, and a cost effective method of telecommunications. You can easily see that satellites are the ideal, if not often the only, solution to problems of communicating with highly mobile forces. Satellites, if properly used, provide much needed options to large, fixed-ground installations. For the past fifty years, the Navy has used high-frequency (hf) transmissions as the principal method of sending messages. In the 1970s, the hf spectrum was overcrowded and "free" frequencies were at a premium. Hf jamming and electronic countermeasures (ECM) techniques became highly sophisticated during that period. As a result the need for new and advanced long-range transmission methods became apparent. Communications via satellite is a natural outgrowth of modern technology and of the continuing demand for greater capacity and higher quality in communications. In the past, the various military branches have had the resources to support their communications needs. Predicted usage indicates that large-scale improvements will have to be made to satisfy future needs of the Department of Defense. These needs will require greater capacity for long-haul communications to previously inaccessible areas. Satellite communications has the most promise for satisfying these future requirements. DEFENSE COMMUNICATIONS SATELLITE PROGRAM (DCSP) The Defense Communications Satellite Program (DCSP) was initiated by the Secretary of Defense in 1962. Phase I of the program was given the title Initial Defense Communications Satellite Program (IDCSP). The first satellite launch occurred in June 1966 when seven experimental satellites were placed into orbit. The final launch of this program consisted of eight satellites and occurred in June 1968. DEFENSE SATELLITE COMMUNICATIONS SYSTEM (DSCS) PHASE II The Phase II Defense Satellite Communications System (DSCP Phase II) has changed from an all-analog communications system to an all-digital communications system. The performance capability provided by the Phase II DSCS is limited by equipment availability. Extensive digital traffic capability has become common. You can credit this to the availability of digital modems (modulator/demodulator) and broadband equipment. Overall performance of the Phase II DSCS is a great improvement over the capabilities provided by Phase I DSCS. The Phase II satellites provide a great increase in effective radiated power and rf bandwidths. You will find these satellite configurations use wide coverage and narrow beam antennas. They provide an extensive range of communications services and capabilities. (This will be

further discussed later, in this chapter.) FUNDAMENTAL SATELLITE COMMUNICATIONS SYSTEM A satellite communications system uses satellites to relay radio transmissions between earth terminals. The two types of communications satellites you will study are ACTIVE and PASSIVE. A passive satellite only reflects received radio signals back to earth. An active satellite acts as a REPEATER; it amplifies signals received and then retransmits them back to earth. This increases signal strength at the receiving terminal to a higher level than would be available from a passive satellite. A typical operational link involves an active satellite and two or more earth terminals. One station transmits to the satellite on a frequency called the UP-LINK frequency. The satellite then amplifies the signal, converts it to the DOWN-LINK frequency, and transmits it back to earth. The signal is next picked up by the receiving terminal. Figure 4-1 shows a satellite handling several combinations of links simultaneously. Figure 4-1. - Satellite communications system.

DESCRIPTION OF COMMUNICATIONS SATELLITE SYSTEM The basic design of a satellite communications system depends to a great degree upon the characteristics of the orbit of the satellite. In general terms, an orbit is either elliptical or circular in shape. A special type of orbit is a SYNCHRONOUS ORBIT. In this type you will find the period (time required for one revolution) of the orbit the same as that of the earth. An orbit that is not synchronous is called ASYNCHRONOUS. A period of orbit that approaches that of the earth is called NEAR SYNCHRONOUS (subsynchronous). Orbits are discussed in more detail later in this chapter.

In addition to the fundamental components shown in figure 4-1, the design of the overall system determines the complexity of the various components and the manner in which the system operates. Current satellites are capable of handling many teletypewriter (tty) and voice circuits at the same time. Orbit Descriptions Orbits generally are described according to the physical shape of the orbit and the angle of inclination of the plane of the orbit. These terms aye discussed in the following paragraphs: PHYSICAL SHAPE. - All satellites orbit the earth in elliptical orbits. (A circle is a special case of an ellipse.) The shape of the orbit is determined by the initial launch parameters and the later deployment techniques used. PERIGEE and APOGEE are two, of the three parameters used to describe orbital data of a satellite. These are shown on figure 4-2. Perigee is the point in the orbit nearest to the center of the earth. Apogee is the point in the orbit the greatest distance from the center of the earth. Both distances are expressed in nautical miles. Figure 4-2. - Elliptical satellite orbit.

ANGLE OF INCLINATION. - The ANGLE OF INCLINATION (angle between the equatorial plane of the earth and the orbital plane of the satellite) is the third parameter used to describe the orbit data of a satellite. Figure 4-3 depicts the angle of inclination between the equatorial plane and the orbital plane. Most satellites orbit the earth in orbital planes that do not coincide with the equatorial plane of the earth. A satellite orbiting in any plane not identical with the equatorial plane is in an INCLINED ORBIT. Figure 4-3. - Inclined satellite orbit.

The inclination of the orbit determines the area covered by the path of the satellite. As shown in figure 4-4, the greater the inclination, the greater the amount of surface area covered by the satellite. Figure 4-4. - Effect of orbit plane inclination on satellite coverage.

SPECIAL TYPES OF INCLINED ORBITS. - A satellite orbiting in a plane that coincides with the equatorial plane of the earth is in an EQUATORIAL ORBIT. A satellite orbiting in an inclined orbit with an angle of inclination of 90 degrees or near 90 degrees is in a POLAR ORBIT. SPECIAL TYPES OF CIRCULAR ORBITS. - We stated previously that a circular orbit is a special type of elliptical orbit. You should realize a circular orbit is one in which the major and

minor axis distances are equal or approximately equal. Mean height above earth, instead of perigee and apogee, is used in describing a circular orbit. While we are discussing circular orbits, you should look at some of the terms mentioned earlier in this chapter. A satellite in a circular orbit at a height of approximately 19,300 nautical miles above the earth is in a synchronous orbit. At this altitude the period of rotation of the satellite is 24 hours, the same as the rotation period of the earth. In other words, the orbit of the satellite is in sync with the rotational motion of the earth. Although inclined and polar synchronous orbits are possible, the term synchronous usually refers to a synchronous equatorial orbit. In this type of orbit, satellites appear to hover motionlessly in the sky. Figure 4-5 shows how one of these satellites can provide coverage to almost half the surface of the earth. Figure 4-5. - Illumination from a synchronous satellite.

Three of these satellites can provide coverage over most of the earth (except for the extreme north and south polar regions). A polar projection of the global coverage of a three-satellite system is shown in figure 4-6. Figure 4-6. - Worldwide synchronous satellite system viewed from above the North Pole.

A satellite in a circular orbit at other than 19,300 nautical miles above the earth is in a nearsynchronous orbit. If the orbit is lower than 19,300 nautical miles, the period of orbit of the satellite is less than the period of orbit of the earth. The satellite then appears to be moving slowly around the earth from west to east. (This type of orbit is also called subsynchronous.) If the orbit is higher than 19,300 nautical miles, the period of orbit of the satellite is greater than the period of orbit of the earth. The satellite then appears to be moving slowly around the earth from east to west. Although inclined and polar near-synchronous orbits are possible, near synchronous implies an equatorial orbit. A satellite in a circular orbit from approximately 2,000 miles to 12,000 miles above the earth is considered to be in a MEDIUM ALTITUDE ORBIT. The period of a medium altitude satellite is considerably less than that of the earth. When you look at this altitude satellite, it appears to move rather quickly across the sky from west to east. Q.1 What are the two types of communications satellites? Q.2 A typical satellite communications operational link consists of a satellite and what two other components? Q.3 A satellite in a synchronous orbit can cover how much of the surface of the earth?

Q.4 What areas of the earth are not normally covered by satellites?

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Introduction to miscellaneous communications systems and equipment

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Click here to order Electronic Components Online INTRODUCTION TO MISCELLANEOUS COMMUNICATIONS SYSTEMS AND EQUIPMENT LEARNING OBJECTIVES Upon completion of this chapter you will be able to: Describe the basic operation of communications systems that operate at medium frequencies and below. Describe the basic microwave line-of-sight Join Integrated communications system. Publishing's Describe the basic tropospheric scatter Discussion Group communications system. Describe the objective/purpose of the naval tactical data system (NTDS). Describe the naval tactical data system (NTDS) data transmission subsystems in terms of links. Explain the various applications of portable communications equipment. Order this Define the term laser. information on CDDescribe the basic theory of operation of lasers Rom Describe the possible applications of lasers in communications. INTRODUCTION In the previous four chapters we've looked at communications equipment and systems that were used Order this in several frequency ranges. Some have had many applications. In this chapter you will look at information in systems used in some portions of the rf spectrum that have not been covered in detail. We will also Print (Hardcopy). discuss the naval tactical data system (NTDS), which operates in the high-frequency and ultrahighfrequency regions. Various portable communications equipments used in the military and an introduction to the laser and its uses in communications are included. Some of the applications presented are fairly new to the military community. SYSTEMS

As discussed in chapter 1, the frequency range from elf to shf is from below 300 hertz up to 30 gigahertz. The first area we will cover is the lower frequency bands (medium frequency [mf] and below). You will then get a look at the microwave region and the high-frequency and ultrahighfrequency range as it pertains to the naval tactical data system (NTDS). MEDIUM FREQUENCY AND BELOW Most of the receivers and transmitters that you will see used in the mf portions of the rf spectrum and below are very similar in design. In chapter 1 we discussed the operational uses of the equipment; now let's look at the equipment itself. Equipment items covered in this and other chapters are meant to be merely representative of equipment that may be encountered in naval communications. No attempt will be made to include all of the possible equipment or equipment configurations. Transmit Equipment You should realize the transmitters used in bands of medium frequency and below are similar to those you studied in chapter 2. In other words, a transmitter used in one frequency range is basically the same as one used in another range. However, there are some differences. Two of the differences are component size and the use of a technique called DOUBLING UP. The components used in bands of medium frequency and below are much larger physically than the ones previously discussed. This is because of the higher operating voltage and current levels required to produce the very high-powered rf outputs needed for the uses covered in chapter 1. A given resistor used in an hf application may be rated at 1/2 watt, whereas the same resistor used in a lower frequency application would probably be rated in tens or even hundreds of watts. A block diagram of a doubled-up transmitter is shown in figure 5-1. Remember, bands of medium frequencies and below are used almost exclusively for broadcast and are on the air continuously. Doubling up increases reliability. As you can see, two transmitters are located in the same equipment cabinet. This allows you to quickly transfer circuits if one should fail. This dual installation also allows both amplifiers to be used together to double the output power. When you use this application, you sacrifice the doubling-up capability of only the power amplifier. All the other components are still available as backups. Let's go through figure 5-1 and describe the block functions. Figure 5-1. - Doubled-up transmitter block diagram.

The frequency generator part of the frequency generator and fsk block is an oscillator. It provides the carrier frequencies for the cw mode. The fsk part is a FREQUENCY SYNTHESIZER (a frequency source of high accuracy). It makes both the mark and space frequencies from a very stable clock oscillator. The keying pulses determine which fsk frequency the keyer chooses to transmit. This signal is then sent to the transmitter control console where it is distributed to the first rf amplifier. This amplifier is referred to as the preliminary intermediate-power amplifier (pre-ipa). The pre-ipa uses linear, untuned, push-pull, rf amplifiers to provide amplified rf to drive other rf amplifiers. The pre-ipa output goes to the intermediate power amplifier (ipa). The ipa receives the pre-ipa output, amplifies the signal, and drives other selected power amplifiers. The ipa is a single-stage, untuned, linear, push-pull, rf circuit that uses water and forced-air cooled tubes. Signals are then sent through the amplifier control, where they are used for signal monitoring purposes before being applied to the final rf amplifier (pa). The pa amplifies the signal to the final desired power level. The pa also contains variometers (variable inductors) for coupling. This coupled output is fed to the rf tuning unit. The rf tuning unit consists of variable oil-filled capacitors and a fixed inductor for frequency tuning. The signal is then sent to a knife switch. This switch simply routes the signal to the DUMMY LOAD or the antenna by way of the HELIX HOUSE. (A dummy load is a nonradiating device the absorbs the rf and has the impedance characteristics of the antenna.) The dummy load is impedance matched to the pa. It allows testing of the pa without putting a signal on the air. When the equipment is in an operating mode, the dummy load is not used. The helix house is a small building physically separated from the transmitter location. It contains antenna loading, coupling, and tuning circuits. The main components consist of a HELIX (large coil) and variable inductors. The signal is fed from the helix directly to the antenna. Sometimes two antennas are used.

Antenna designs vary with the amount and type of land available, desired signal coverage, and bandwidth requirements. Figure 5-2 shows a simplified transmit antenna. The Navy uses TOP-HAT (flat-top) capacitive loading with one or more radiating elements. Typical top hat antennas consist of two or more lengths of wire parallel to each other and to the ground, each fed at or near its mid point. The lengths of wire are usually supported by vertical towers. These antennas may take many shapes. The matching network shown is in the helix house. Figure 5-3 shows the installation at the naval communications unit in Cutler, Maine. The Navy has several of these types of installations. They are used primarily for fleet broadcasts and have power outputs in the .25- to 2-megahertz range. You should notice the transmitter, the location of the helix houses, and the dual antennas. You should also notice the transmission line tunnel. It is underground and over a half-mile long. Figure 5-4, view (A) and view (B), shows another antenna configuration. This array of monopoles (quarter-wave, vertically polarized stubs) is referred to as a TRIATIC antenna. A triatic antenna is a special form of a rhombicarranged monopole array. This type of array is designed to transmit from a particular location. Triatics are all basically the same but have some design differences at each site. The physical differences compensate for differences in terrain. Now that we have looked at the transmit side, let's look at the receive side. Figure 5-2. - Simplified vlf transmitting antenna.

Figure 5-3. - Cutler, Maine antenna installation.

Figure 5-4A. - Triatic type antenna.

Figure 5-4B. - Triatic type antenna.

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Book 18

Back • Home • Up • Next Click here to order Electronic Components Online Radar fundamentals Radar measurement range Pulse energy content Bearing Radar principles of operation Scanning Electronic scanning Frequency-modulation method Radar classification and use Air-Search Radar Tracking radar Summary Answers

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Radar subsystems Transmitters Modulator Switching Devices Power amplifier transmitter Duplexers ATR Tube Waveguide Duplexer

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Receivers Mixer Receiver special circuits Logarithmic Receiver Summary Answers

Radar indicators and antennas Plan position indicator Ranging circuits Radar antennas Corner reflectors Summary Answers

Radar system maintenance The Echo Box Receiver performance checks Standing wave measurements Dry-Air systems Cooling systems Summary Answers

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Radar fundamentals

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Click here to order Electronic Components Online RADAR FUNDAMENTALS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the objectives. By successfully completing the OCC/ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below. Define range, bearing, and altitude as they relate to a radar system. Discuss how pulse width, peak power, and beam width affect radar performance. Describe the factors that contribute to or detract from radar accuracy.

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Using a block diagram, describe the basic function, principles of operation, and interrelationships of the basic units of a radar system. Explain the various ways in which radar systems are classified, including the standard Army/Navy classification system. Explain the basic operation of cw, pulse, and Doppler radar systems. INTRODUCTION TO RADAR FUNDAMENTALS The term RADAR is common in today's everyday language. You probably use it yourself when referring to a method of recording the speed of a moving object. The term Radar is an acronym made up of the words radio detection and ranging. The term is used to refer to electronic equipment that detect the presence, direction, height, and distance of objects by using reflected electromagnetic energy. Electromagnetic energy of the frequency used for radar is unaffected by darkness and also penetrates weather to some degree, depending on frequency. It permits radar systems to determine the positions of ships, planes, and land masses that are invisible to the naked eye because of distance, darkness, or weather. The development of radar into the highly complex systems in use today represents the accumulated developments of many people and nations. The general principles of radar have been known for a long time, but many electronics discoveries were necessary before a useful radar system could be developed. World War II provided a strong incentive to develop practical radar, and early versions were in use soon after the war began. Radar technology has improved in the years since the war. We now have radar systems that are smaller, more efficient, and better than those early versions. Modern radar systems are used for early detection of surface or air objects and provide extremely accurate information on distance, direction, height, and speed of the objects. Radar is also used to guide missiles to targets and direct the firing of gun systems. Other

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types of radar provide long-distance surveillance and navigation information. BASIC RADAR CONCEPTS The electronics principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for a return echo can be roughly converted to distance if the speed of sound is known. Radar uses electromagnetic energy pulses in much the same way, as shown in figure 1-1. The radiofrequency (rf) energy is transmitted to and reflects from the reflecting object. A small portion of the energy is reflected and returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object. Figure 1-1. - Radar echo.

NOTE: The terms TARGET, RETURN, ECHO, CONTACT, OBJECT, and REFLECTING OBJECT are used interchangeably throughout this module to indicate a surface or airborne object that has been detected by a radar system. Radar systems also have some characteristics in common with telescopes. Both provide only a limited field of view and require reference coordinate systems to define the positions of detected objects. If you describe the location of an object as you see it through a telescope, you will most likely refer to prominent features of the landscape. Radar requires a more precise reference system. Radar surface angular measurements are normally made in a clockwise direction from TRUE NORTH, as shown in figure 1-2, or from the heading line of a ship or aircraft. The surface of the earth is represented by an imaginary flat plane, tangent (or parallel) to the earth's surface at that location. This plane is referred to as the HORIZONTAL PLANE. All angles in the up direction are measured in a second imaginary plane that is perpendicular to the horizontal plane. Figure 1-2. - Radar reference coordinates.

This second plane is called the VERTICAL PLANE. The radar location is the center of this coordinate system. The line from the radar set directly to the object is referred to as the LINE OF SIGHT (los). The length of this line is called RANGE. The angle between the horizontal plane and the los is the ELEVATION ANGLE. The angle measured clockwise from true north in the horizontal plane is called the TRUE BEARING or AZIMUTH angle. These three coordinates of range, bearing, and elevation describe the location of an object with respect to the antenna. Q.1 Radar surface-angular measurements are referenced to true north and measured in what plane? Q.2 The distance from a radar set to a target measured along the line of sight is identified by what term?

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Radar subsystems

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Click here to order Electronic Components Online RADAR SUBSYSTEMS LEARNING OBJECTIVES Upon completion of this chapter, the student will be able to: Describe, in general terms, the function of a radar synchronizer. State the basic requirements and types of master synchronizers. Describe the purpose, requirements, and operation of a radar modulator. Describe the basic operating sequence of a keyedoscillator transmitter. Describe the basic operating sequence of a power-amplifier transmitter. State the purpose of a duplexer.

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State the operational principles of tr and atr tubes. Describe the basic operating sequence of series and parallel connected duplexers. List the basic design requirements of an effective radar receiver. List the major sections of a typical radar receiver. Using a block diagram, describe the operational characteristics of a typical radar receiver. INTRODUCTION TO RADAR SUBSYSTEMS Any radar system has several major subsystems that perform standard functions. A typical radar system consists of a SYNCHRONIZER (also called the TIMER or TRIGGER GENERATOR), a TRANSMITTER, a DUPLEXER, a RECEIVER, and an INDICATOR. These major subsystems were briefly described in chapter 1. This chapter will describe the operation of the synchronizer, transmitter, duplexer, and receiver of a typical pulse radar system and briefly analyze the circuits used. Chapter 3 will describe typical indicator and antenna subsystems. Because radar systems vary widely in specific design, only a general description of representative circuits is presented in this chapter. SYNCHRONIZERS The synchronizer is often referred to as the "heart" of the radar system because it controls and provides timing for the operation of the entire system. Other names for the synchronizer are the TIMER and the KEYER. We will use the term synchronizer in our discussion. In some complex systems the synchronizer is part of a system computer that performs many functions other than system timing. SYNCHRONIZER FUNCTION The specific function of the synchronizer is to produce TRIGGER

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PULSES that start the transmitter, indicator sweep circuits, and ranging circuits. Timing or control is the function of the majority of circuits in radar. Circuits in a radar set accomplish control and timing functions by producing a variety of voltage waveforms, such as square waves, sawtooth waves, trapezoidal waves, rectangular waves, brief rectangular pulses, and sharp peaks. Although all of these circuits can be broadly classified as timing circuits, the specific function of any individual circuit could also be wave shaping or wave generation. The operation of many of these circuits and associated terms were described in detail in NEETS, Module 9, Introduction to Wave-Generation and Wave-Shaping Circuits. Q.1 What is the purpose of the synchronizer in a radar system? Q.2 What is the purpose of the majority of circuits in a radar system? SYNCHRONIZER OPERATION Radar systems may be classified as either SELF-SYNCHRONIZED or EXTERNALLY SYNCHRONIZED systems. In a selfsynchronized system, the timing trigger pulses are generated in the transmitter. In an externally synchronized system, the timing trigger pulses are generated by a MASTER OSCILLATOR, which is usually external to the transmitter. The master oscillator in an externally synchronized system may be a BLOCKING OSCILLATOR, a SINE-WAVE OSCILLATOR, or an ASTABLE (FREE-RUNNING) MULTI-VIBRATOR. When a blocking oscillator is used as a master oscillator, the timing trigger pulses are usually obtained directly from the oscillator. When a sine-wave oscillator or an astable multivibrator is used as a master oscillator, pulse-shaping circuits are required to form the necessary timing trigger pulses. In an externally synchronized radar system, the pulse repetition rate (prr) of the timing trigger pulses from the master oscillator determines the prr of the transmitter. In a self-synchronized radar system, the prr of the timing trigger pulses is determined by the prr of the modulator or transmitter.

Associated with every radar system is an indicator, such as a cathode-ray tube, and associated circuitry. The indicator can present range, bearing, and elevation data in visual form so that a detected object may be located. Trigger pulses from the synchronizer are frequently used to produce gate (or enabling) pulses. When applied to the indicator, gate pulses perform the following functions: Initiate and time the duration of the indicator sweep voltage Intensify the cathode-ray tube electron beam during the sweep period so that the echo pulses may be displayed Gate a range marker generator so that range marker signals may be superimposed on the indicator presentation Figure 2-1 shows the time relationships of the various waveforms in a typical radar set. The timing trigger pulses are applied to both the transmitter and the indicator. When a trigger pulse is applied to the transmitter, a short burst of transmitter pulses (rf energy) is generated. Figure 2-1. - Time relationship of waveforms.

This energy is conducted along a transmission line to the radar antenna. It is radiated by the antenna into space. When this transmitter energy strikes one or more reflecting objects in its path, some of the transmitted energy is reflected back to the antenna as echo pulses. Echo pulses from three reflecting targets at different ranges are illustrated in figure 2-1. These echoes are converted to the corresponding receiver output signals as shown in the figure. The larger initial and final pulses in the receiver output signal are caused by the energy that leaks through the duplexer when a pulse is being transmitted. The indicator sweep voltage shown in figure 2-1 is initiated at the same time the transmitter is triggered. In other applications, it may be more desirable to delay the timing trigger pulse that is to be fed to the indicator sweep circuit. Delaying the trigger pulse will initiate the indicator sweep after a pulse is transmitted. Note in figure 2-1 that the positive portion of the indicator intensity

gate pulse (applied to the cathode-ray tube control grid) occurs only during the indicator sweep time. As a result, the visible cathode-ray tube trace occurs only during sweep time and is eliminated during the flyback (retrace) time. The negative portion of the range-marker gate pulse also occurs during the indicator sweep time. This negative gate pulse is applied to a range-marker generator, which produces a series of range marks. The range marks are equally spaced and are produced only for the duration of the range-marker gate pulse. When the range marks are combined (mixed) with the receiver output signal, the resulting video signal applied to the indicator may appear as shown at the bottom of figure 2-1. Q.3 A self-synchronized radar system obtains timing trigger pulses from what source? Q.4 What type of multivibrator can be used as a radar master oscillator? Q.5 In an externally synchronized radar, what determines the prr of the transmitter? Q.6 In figure 2-1, what causes the initial and final pulses on the receiver output signal? BASIC SYNCHRONIZER CIRCUITS The basic synchronizer circuit should meet the following three basic requirements: It must be free running (astable). Because the synchronizer is the heart of the radar, it must establish the zero time reference and the prf (prr). It should be stable in frequency.

For accurate ranging, the prr and its reciprocal, pulserepetition time (prt), must not change between pulses. The frequency must be variable to enable the radar to operate at different ranges. Three basic synchronizer circuits can meet the above mentioned requirements. They are the SINE-WAVE OSCILLATOR, the SINGLE-SWING BLOCKING OSCILLATOR, and the MASTERTRIGGER (ASTABLE) MULTIVIBRATOR. Figure 2-2 shows the block diagrams and waveforms of these three synchronizers as they are used in externally synchronized radar systems. In each case, equally spaced timing trigger pulses are produced. The prr of each series of timing trigger pulses is determined by the operating frequency of the associated master oscillator. Figure 2-2. - Timers used in externally synchronized radar systems.

Sine-Wave Oscillator Synchronizer

In the sine-wave oscillator synchronizer (figure 2-2, view A), a sinewave oscillator is used for the basic timing device (master oscillator). The oscillator output is applied to both an overdriven amplifier and the radar indicator. The sine waves applied to the overdriven amplifier are shaped into square waves. These square waves are then converted into positive and negative timing trigger pulses by means of a short-time-constant RC differentiator. By means of a limiter, either the positive or negative trigger pulses from the RC differentiator are removed. This leaves trigger pulses of only one polarity. For example, the limiter in view A of figure 2-2 is a negative-lobe limiter; that is, the limiter removes the negative trigger pulses and passes only positive trigger pulses to the radar transmitter. A disadvantage of a sine-wave oscillator synchronizer is the large number of pulse-shaping circuits required to produce the necessary timing trigger pulses. Master Trigger (Astable) Multivibrator Synchronizer In a master trigger (astable) multivibrator synchronizer (view B, figure 2-2), the master oscillator generally is an astable multivibrator. The multivibrator is either ASYMMETRICAL or SYMMETRICAL. If the multivibrator is asymmetrical, it generates rectangular waves. If the multivibrator is symmetrical, it generates square waves. In either case, the timing trigger pulses are equally spaced after a limiter removes undesired positive or negative lobes. There are two transistors in an astable multivibrator. The two output voltages are equal in amplitude, but are 180 degrees out of phase. The output of the astable multivibrator consists of positive and negative rectangular waves. Positive rectangular waves are applied to an RC differentiator and converted into positive and negative trigger pulses. As in the sine-wave synchronizer, the negative trigger pulses are removed by means of a negative-lobe limiter, and the positive pulses are applied to the transmitter. Both positive and negative rectangular waves from the astable multivibrator are applied to the indicator. One set of waves is used to intensify the cathode-ray tube electron beam for the duration of

the sweep. The other set of waves is used to gate (turn on) the range marker generator. Single-Swing Blocking Oscillator Synchronizer In the single-swing, blocking-oscillator synchronizer, shown in view C of figure 2-2, a free-running, single-swing blocking oscillator is generally used as the master oscillator. The advantage of the single-swing blocking oscillator is that it generates sharp trigger pulses without additional shaping circuitry. Timing trigger pulses of only one polarity are obtained by means of a limiter. Gating pulses for the indicator circuits are produced by applying the output of the blocking oscillator to a one-shot multivibrator or another variable time delay circuit (not shown). Crystal-controlled oscillators may be used when very stable frequency operation is required. Q.7 What basic circuits meet the requirements of an externally synchronized master oscillator? Q.8 Name a disadvantage of sine-wave oscillator synchronizers. Q.9 Which of the basic timing circuits produces sharp trigger pulses directly?

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Radar indicators and antennas

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Click here to order Electronic Components Online RADAR INDICATORS AND ANTENNAS LEARNING OBJECTIVES Upon completion of this chapter, the student will be able to: Describe the purpose of the A scope, the range-height indicator (rhi), and the plan position indicator (ppi). State the relationship between range and sweep speed and length on a radar indicator. Explain the purpose of timing triggers, video, and antenna position inputs to a radar indicator. List the major units of a ppi and describe their functions. Describe the basic operation of sweep deflection and sweep rotation in a ppi.

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List and describe the operation of the three range measurement circuits. Describe antenna directivity and power gain characteristics. Describe the focusing action of a basic parabolic antenna. Describe the basic radiation patterns of the most common parabolic reflectors. Describe the basic characteristics of horn radiators. INTRODUCTION Radar systems require an antenna to both transmit and receive radar energy and an indicator system to display the video information generated. This chapter will briefly describe some commonly used indicators and antenna systems. Antenna systems are described in more detail in NEETS, Module 10, Introduction to Wave Generation, Transmission Lines, and Antennas, and Module 11, Microwave Principles. RADAR INDICATORS The information available from a radar receiver may contain as many as several million separate data bits per second. From these and other data, such as the orientation of the antenna, the indicator should present to the observer a continuous, easily understandable, graphic picture of the relative position of radar targets. It should provide size, shape, and insofar as possible, indications of the type of targets. A cathode-ray tube (crt) fulfills these requirements to an astonishing degree. The cathode-ray tube's principal shortcoming is that it cannot present a true threedimensional picture. The fundamental geometrical quantities involved in radar displays are the RANGE, AZIMUTH ANGLE (or BEARING), and ELEVATION ANGLE. These displays relate the position of a radar target to the origin at the antenna. Most radar displays include one

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or two of these quantities as coordinates of the crt face. The actual range of a target from the radar, whether on the ground, in the water, or in the air is known as SLANT RANGE. The majority of displays use as one coordinate the value of slant range, its horizontal projection (GROUND RANGE), or its vertical projection (ALTITUDE). Since slant range is involved in every radar situation, it inevitably appears in at least one display on every set. Slant range is the coordinate that is duplicated most often when more than one type of display is used. This is partly because displays presenting range have the highest signal-to-noise discrimination and partly for geometrical reasons. Range is displayed by means of a linear time-base sweep, starting from a given point or line at a definite time in each pulse cycle. Thus, distances along this range sweep actually measure slant range. The sweep speed determines the scale factor, which relates the distance on the tube to actual range. The sweep length is the total distance represented. Distances are expressed in miles (statute or nautical) or yards. The origin of the range sweep may be on or off the tube face. The angle at which the antenna is pointing, either in azimuth or elevation, may provide two-dimensional information in the display; that is, range and azimuth, or range and elevation. A radar indicator, sometimes called a radar repeater, acts as the master timing device in analyzing the return of the video in a radar system. It also provides that capability to various other locations physically remote from the radar system. Each indicator should have the ability to select the outputs from any desired radar system aboard the ship. This is usually accomplished by the use of a RADAR DISTRIBUTION SWITCHBOARD. The switchboard contains a switching arrangement that has inputs from each radar system aboard ship and provides outputs to each repeater. The radar desired is selected by means of a selector switch on the repeater. For the repeater to present correct target position data, the indicator must have the following three inputs from the selected radar: Trigger timing pulses.

These pulses ensure that the sweep on the repeater starts from its point of origin each time the radar transmits. As discussed earlier, the repeater displays all targets at their actual range from the ship based on the time lapse between the instant of transmission and the instant the target's echo is received. The returning echo. The echo, in rf form, is detected (converted to a video signal) by the radar receiver and applied to the repeater. Antenna information. The angular sweep position of a plan position indicator (ppi) repeater must be synchronized to the angular position of the radar antenna to display target bearing (azimuth) information. The three most common types of displays, called scopes, are the Ascope, the RANGE-HEIGHT INDICATOR (RHI) SCOPE, and the PLAN POSITION INDICATOR (PPI) SCOPE. The primary function of these displays will be discussed in this section. However, detailed descriptions will be limited to the ppi scope, which is the most common display. THE A SCOPE The A-scope display, shown in figure 3-1, presents only the range to the target and the relative strength of the echo. Such a display is normally used in weapons control radar systems. The bearing and elevation angles are presented as dial or digital readouts that correspond to the actual physical position of the antenna. Figure 3-1. - A scope.

The A-scope normally uses an electrostatic-deflection crt. The sweep is produced by applying a sawtooth voltage to the horizontal

deflection plates. The electrical length (time duration) of the sawtooth voltage determines the total amount of range displayed on the crt face. The ranges of individual targets on an A-scope are usually determined by using a movable range gate or step that is superimposed on the sweep. Ranging circuits will be discussed in more detail later in this section. RANGE-HEIGHT INDICATOR (RHI) The range-height indicator (rhi) scope, shown in figure 3-2, is used with height-finding search radars to obtain altitude information. The rhi is a two-dimensional presentation indicating target range and altitude. The sweep originates in the lower left side of the scope. It moves across the scope, to the right, at an angle that is the same as the angle of transmission of the height-finding radar. The line of sight to the horizon is indicated by the bottom horizontal line. The area directly overhead is straight up the left side of the scope. Target echoes are displayed on the scope as vertical PIPS or BLIPS (spots of increased intensity that indicate a target location). The operator determines altitude by adjusting a movable height line to the point where it bisects the center of the blip. Target height is then read directly from an altitude dial or digital readout. Vertical range markers are also provided to estimate target range. Figure 3-2. - RHI scope.

Q.1 What are the three fundamental quantities involved in radar displays? Q.2 What are the required radar inputs for proper indicator operation? Q.3 What coordinates are displayed on an rhi scope?

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Radar system maintenance

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Click here to order Electronic Components Online RADAR SYSTEM MAINTENANCE LEARNING OBJECTIVES Upon completion of this chapter, the student will be able to: Interpret the transmitter frequency spectrum in terms of frequency distribution, power output, receiver response, and an acceptable spectrum curve. Describe the methods for measuring the average and peak power outputs of a radar transmitter. Describe the methods of measuring receiver sensitivity. Define receiver bandwidth in terms of the receiver response curve and state the most common methods of measuring tr tube recovery time.

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List the support systems associated with a typical shipboard radar system and describe the basic function of each. State the general rules for the prevention of personnel exposure to rf radiation and Xray emissions. INTRODUCTION TO RADAR MAINTENANCE The effectiveness of your radar system depends largely upon the care and attention you give it. An improperly adjusted transmitter, for example, can reduce the accuracy of a perfectly aligned receiver; the entire system then becomes essentially useless. Maintenance, therefore, must encompass the entire system for best operation. Because of the complexity of most radar systems, trying to detail stepby-step procedures for specific maintenance actions in this chapter is impractical. However, the basic procedures for some maintenance actions that are common to most radar systems will be discussed. Also, an overview of support systems for radars will be presented. This will include electrical power, dry-air systems, and liquid cooling systems. Finally, safety precautions inherent to radars are listed. TRANSMITTER PERFORMANCE CHECKS The transmitter of a radar is designed to operate within a limited band of frequencies at an optimum power level. Operation at frequencies or power levels outside the assigned band greatly decreases the efficiency of the transmitter and may cause interference with other radars. Therefore, transmitter performance must be monitored closely for both frequency and output power. TRANSMITTER FREQUENCY Whether of the fixed-frequency or tunable type, the radar transmitter frequency should be checked periodically. If the transmitter is of the fixed-frequency type and found to be operating outside its normal operating band, the problem is probably a defective part. The defective component must be replaced. If the transmitter is tunable,

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the transmitter must again be tuned to the assigned frequency. Each time a radar transmitter generates an rf pulse, it produces electromagnetic energy. You should recall from your study of NEETS, Module 12, Modulation Principles, that the square wave used to modulate the transmitter carrier wave has (1) the fundamental squarewave frequency and (2) an infinite number of odd harmonics of the fundamental square wave frequency. When this square wave is used to modulate the transmitter carrier frequency, both the fundamental and odd harmonic frequencies of the square wave heterodyne with the transmitter carrier frequency. The heterodyning process produces in each transmitted rf pulse the following frequencies: The fundamental carrier frequency The sum and difference frequencies between the carrier and fundamental squarewave frequencies The sum and difference frequencies between the odd harmonics of the square wave and the carrier frequencies For a complete discussion of this process, you should review module 12. Actually, the radar energy is distributed more or less symmetrically over a band of frequencies. This frequency distribution of energy is known as the FREQUENCY SPECTRUM. An analysis of frequency spectrum characteristics may be made with a SPECTRUM ANALYZER. The spectrum analyzer presents a graphic display of energy versus frequency. An extensive explanation of spectrum analyzer use can be found in the Electronics Installation and Maintenance Book (EIMB), Test Methods and Practices, NAVSEA 0967-LP-000-0130. Spectrum Analysis When properly performed and interpreted, a spectrum analysis will reveal misadjustments and troubles that would otherwise be difficult to locate. Therefore, you should be able to perform a spectrum

analysis and understand the results. You may be wondering why we are so interested in the frequency spectrum of an rf pulse. To better understand why, look at the spectrum of a transmitter as compared to the response curve of a receiver in figure 4-1. The receiver's response curve has a broader bandwidth than the transmitted spectrum, which ensures complete coverage. But the receiver responds best to frequencies in the middle of the bandwidth. This causes the receiver response to taper off from both sides of the center frequency until the response passes through the half-power points, as shown on the curve. Usually the receiver response beyond these points is too low to be useful and is not considered. Notice that the spectrum of the transmitter is centered inside the response curve of the receiver, thus yielding maximum efficiency. Figure 4-1. - Transmitter spectrum compared with receiver response.

Any frequency, when modulated by another frequency, will produce a base frequency with sideband frequencies (sum and difference). In other words, the output of a pulsed radar will contain more than one frequency. The output frequency spectrum of the pulsed radar transmitter does not consist of just a single frequency that is turned on and off at the pulse-repetition frequency (prf). Consider the spectrum as a base frequency (carrier) that is modulated by short rectangular pulses occurring at the prf of the radar. Two distinct modulating components are present: One component consists of the prf and its associated harmonics; the other component consists of the

fundamental and odd-harmonic frequencies that make up the rectangular modulating pulse. The distribution of power over the radar frequency spectrum depends on the amount of modulation. A pulsed radar spectrum is illustrated in figure 4-2. The vertical lines represent the modulation frequencies produced by the prf and its associated harmonics; the lobes represent the modulation frequencies produced by the fundamental pulse frequency and its associated harmonics. The amplitude of the main lobe falls to zero on each side of the carrier. The side lobes are produced by the odd harmonics of the fundamental pulse frequency. The zero points are produced by the even harmonics of the fundamental pulse frequency. In an ideal spectrum each frequency above the carrier has its counterpart in another frequency below the carrier. These frequencies are equally spaced and have equal power. Therefore, the pattern is symmetrical about the carrier. The main lobe, of course, contains the major portion of the transmitted rf energy. Figure 4-2. - Spectrum of a pulse-modulated carrier.

A radar transmitter in good condition should produce a spectrum curve similar to the curves shown in view A or B in figure 4-3. Good curves are those in which the two halves are symmetrical and contain deep, well-defined minimum points (minima) on both sides of the main peak. Figure 4-3. - Comparison of radar spectra.

A curve without well-defined minima, as in the curve shown in view C, indicates that the transmitter output is being frequency modulated during the pulse. This condition may occur when a pulse without sufficiently steep sides or a flat peak is applied to the transmitter. It may also occur when a transmitter tube is unstable or is operated without proper voltage, current, or magnetic field. An extremely irregular spectrum, as in the curve in view D, is an indication of severe frequency modulation. This condition usually causes trouble with the receiver automatic frequency control (afc) as well as a general loss of signal strength. You can often improve a faulty spectrum by adjusting the transmission line stubs or by replacing the transmitter tube. When the spectrum has two large peaks that are quite far apart, it indicates that the transmitter tube is DOUBLE MODING (shifting from one frequency to another). This could be caused by standing waves in the transmission line or a faulty transmitter tube. Standing waves may be caused by a faulty line connection, a bad antenna rotating joint, or obstructions in the line. (Standing waves are described in NEETS, Module 10,

Introduction to Wave Propagation, Transmission Lines, and Antennas.) In the case of a good or fair spectrum curve with sharply defined minimum points on both sides of the main lobe, the distance between these two points is proportional to the duration of the transmitted pulse. The device most commonly used to check the frequency spectrum of a radar transmitter is the spectrum analyzer. Frequency-Measuring Devices Devices used to determine the basic carrier frequency of a radar transmitter are the ELECTRONIC FREQUENCY COUNTER, the WAVEMETER, and the ECHO BOX. One or more of these devices may be included in a special RADAR TEST SET designed for a specific system or type of radar. Radar test sets quite often consist of several types of test equipment. This combination of test equipments enables both transmitter and receiver performance checks to be carried out with one test instrument. Electronic frequency counters, frequency meters, and wavemeters are discussed in NEETS, Module 16, Introduction to Test Equipment. The echo box is discussed in the next section. The specific equipments and procedures required to measure the frequency of any radar system are found in the associated system technical manuals and related PMS documents. Q.1 The spectrum of a radar transmitter describes what characteristic of the output pulse? Q.2 Where should the transmitter spectrum be located with respect to the receiver response curve? Q.3 The ideal radar spectrum has what relationship to the carrier frequency? Q.4 The display screen of a spectrum analyzer presents a graphic plot of what two signal characteristics?

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Book 21

Back • Home • Up • Next Click here to order Electronic Components Online Basic measurements Oscilloscope Method Multimeter Method Oscilloscope method RCL Bridges Reactance-type measurements Summary Answers

Component testing Klystron Tube Tests Transistor Testers Metal oxide semiconductor Diode testers Silicon-controlled rectifiers (SCR) Unijunction transistors (UJTs) MOSFET (Depletion/Enhancement Type) Test Logic Probes Typical voltage Tolerances for Dry Cell Batteries Fiber-optic testing Testing Components by Comparison

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Summary Answers

Quantitative measurements Wheatstone Bridge Impedance testing of antennas and transmission lines Iron-core, composite-coil, and torsion-head wattmeters Bolometer Power Meter Frequency measurements Frequency Counter Methods Summary Answers

Qualitative measurements SWR Meters Intermodulation distortion measurements Summary Answers

Introduction to waveform interpretation Oscilloscope Measurement Methods Spectrum waveform analysis and measurements Spectrum analyzer applications Frequency Modulation Time-domain reflectometry Swept-frequency testing equipment Sweeping antennas Summary Answers

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Basic measurements

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Click here to order Electronic Components Online BASIC MEASUREMENTS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions and answers are based on the objectives and enable you to check your progress through the reading assignments. By successfully completing the OCC/ECC, you demonstrate that you have met the objectives and have learned the information. The learning objectives for this chapter are listed below.

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Upon completion of this chapter, you will be able to do the following: Explain the importance of performing basic electronic measurements. Explain the importance of voltage measurements in troubleshooting. Order this Identify the various methods of performing voltage measurements. information on CDRom Identify the various methods of performing current measurements.

Identify the various methods of performing resistance measurements. Identify the various methods of performing capacitance measurements. Identify the various methods of measuring inductance. INTRODUCTION TO MEASUREMENTS In today's modern Navy, a large part of a ship's, submarine's, or aircraft's ability to complete its mission depends on the efficiency of sophisticated electronic systems. As the technician responsible for these systems, you are the focal point in ensuring their reliability. In the event of a system failure, it is your responsibility to repair the system and to do so in a timely manner. Whether you are troubleshooting a faulty system or performing preventive maintenance, you are required to perform basic electronic measurements on a regular basis. This chapter will acquaint you with various alternative methods of performing measurements and discuss the relative merits and demerits of each method. No discussion of electronic test equipment or electronic measurements would be complete without mentioning the Navy's Metrology Calibration (METCAL) program. Figure 1-1 shows the METCAL structure. Basically, the METCAL program is an elaborate quality control system designed to compare your electronic test equipment with test equipment of much greater accuracy. When you submit your piece of test equipment for calibration, it is compared with the calibration laboratory's equipment (referred to as STANDARDS), which are generally at least four times more accurate than yours. If your equipment does not meet specifications, it is either repaired, adjusted, or rejected with an explanation of why the calibration laboratory was unable to calibrate it. The accuracy of equipment at your local calibration laboratory is ensured by calibration of the test equipment to the standards of the next higher echelon calibration laboratory. The accuracies of test equipment at each higher echelon is increased by a ratio of approximately 4 to 1. Figure 1-1. - Calibration laboratory structure.

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METCAL provides assurance that your test equipment is in top-notch shape. Remember, your measurements are only as accurate as your test equipment; be fully aware of the limitations of your test equipment and never use equipment that isn't properly calibrated when performing measurements or adjustments. Q.1 What assures the accuracy of your electronic test equipment? Now that we have discussed the advantages of calibrated test equipment, let's review the reason for all this concern. The fundamental electrical quantities of a circuit are voltage and current and are dependent on the circuit characteristics of resistance, capacitance, and inductance. In addition to these three individual characteristics, don't forget that many electronic components exhibit more than one circuit characteristic at the same time. An example would be a piece of coaxial cable that is engineered by its manufacturer to meet characteristic specifications for impedance, capacitance, and

inductance. But let's keep it simple and begin by covering voltage measurements. Operation and use of common test equipment was covered in NEETS Module 16, Introduction to Test Equipment, NAVEDTRA B72 - 16 - 00 - 95. It is recommended that you review this module before continuing. VOLTAGE MEASUREMENTS Most Navy technical manuals provide voltage charts that list correct voltages at all primary test points in a piece of equipment. Voltage measurements, when compared with these charts, provide a valuable aid in locating troubles quickly and easily. However, if the sensitivity of the test equipment differs from that of the test equipment used in preparing the chart, the voltage measurements may not reflect true circuit conditions. You must keep in mind that a voltmeter with low sensitivity used on a low range may disturb circuits under test or provide a false indication. Most technical manuals will tell you what type and model of test equipment was used to prepare the voltage charts. As a rule of thumb, the input impedance of the voltmeter should exceed the impedance of the circuit by a ratio of at least 10 to 1. Technicians have spent uncounted hours of wasted time because they have selected improper test equipment. Q.2 The input impedance of your test equipment should exceed the impedance of the circuit under test by what ratio? DC VOLTAGE MEASUREMENTS Direct current voltage may be steady, pulsating, or have ac superimposed on it. The average value of a dc waveform depends on the symmetry of the wave and other aspects of the wave shape. It can vary from 63.6% of peak value for a rectified full sine wave to 50% of peak value for a triangular wave. For a superimposed sine wave, the average value can be zero. Regardless of whether the dc is steady, pulsating, or the ac is superimposed on the dc, a rectifier form of measuring device will indicate its average value. Voltages are usually measured by placing the measuring device in parallel with the component or circuit (load) to be measured. The measuring device should have an infinite internal resistance (input impedance) so that it will absorb no energy from the circuit under test and, therefore, measure the true voltage. The accuracy of the voltage measurement depends on the total resistance of the measuring device compared to the load being measured. When the input impedance of the measuring device is 10 times greater than

the load being measured, the error usually can be tolerated. If this error cannot be tolerated, a high input impedance measuring device, such as a vacuum tube voltmeter (vtvm), should be used. Alternatively, using two voltmeters in series increases the voltage range and, because of the increase in total voltmeter resistance, provides a more accurate measurement of voltage across the load. If the voltage to be measured is sufficiently high, more than two similar voltmeters can be connected in series across the load to provide greater accuracy; the total voltage measurement is the sum of the individual meter indications. Q.3 What are the advantages of using two voltmeters in series? Multimeter Method A common piece of test equipment used in the Navy is the Simpson 260 analog multimeter, as shown in figure 1-2. It is capable of measuring both ac and dc voltages of up to 5,000 volts. Figure 1-2. - Simpson 260 multimeter.

Two obvious advantages of the Simpson 260 are its portability and ease of operation. Among its disadvantages are its low input impedance and the inherent low accuracy associated with D'Arsonval meter movements, which are used in the meter. When performing measurements with any analog multimeter, remember that the most accurate readings are taken with the pointer midscale. You should also be aware of inaccuracies introduced as a result of parallax. PARALLAX is defined as the apparent displacement of the position of an object because of the difference between two points of view. In the case of meters, this means the position of a meter's pointer will appear to be at different positions on the scale depending on the angle from which the meter is viewed. Some of the Simpson 260 and 270 series multimeters have effectively eliminated the problem of parallax by incorporating a mirror on the scale that accurately reflects the position of the pointer of the meter movement. Q.4 At what point on a meter movement are the most accurate readings taken?

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Component testing

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Click here to order Electronic Components Online COMPONENT TESTING LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Explain the importance of testing individual electronic components. Identify the various methods of testing electron tubes. Join Integrated Identify the various methods of testing Publishing's semiconductors. Discussion Group Identify the various methods of testing integrated circuits. Identify the various types of testing batteries and their characteristics. Identify the various methods of testing rf attenuators and resistive loads. Identify the various methods of testing fiberoptic devices. Order this INTRODUCTION TO COMPONENT TESTING

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It is imperative that you be able to troubleshoot an equipment failure to the component level. In the majority of cases, Navy technicians are expected to troubleshoot and identify faulty components. This chapter, "Component Testing," will acquaint you with alternative methods of testing various components and their parameters. A quick glance at the Navy's mission and concept of operation explains why we, in most cases, must be able to troubleshoot to Order this the faulty component level. A ship must be a self-sustaining unit when deployed. Storage information in space is a primary consideration on most ships and a limiting factor for storage of bulky Print (Hardcopy). items or electronic modules as ready spares. Therefore, it is practical to store only individual components common to a great number of equipment types. This of course, limits the larger

replacement modules available to you during troubleshooting. Q.1 Why are most ships limited in their ability to stock replacement modules for repair of electronic equipment? TESTING ELECTRON TUBES In equipment that uses vacuum tubes, faulty tubes are responsible for more than 50% of all electronic equipment failures. As a result, testing of electronic tubes is important to you. You can determine the condition of a tube by substituting an identical tube known to be good for the questionable one. However, indiscriminate substitution of tubes is to be avoided for at least the following two reasons: (1) detuning of circuits may result and (2) a tube may not operate properly in a high-frequency circuit even though it performs well in a low-frequency circuit. Therefore, your knowledge of tube-testing devices and their limitations, as well as correct interpretation of the test results obtained, is indispensable for accurate and rapid maintenance. Because the operating capabilities and design features of a tube are demonstrated by its electrical characteristics, a tube is tested by measuring those characteristics and comparing them with representative values established for that type of tube. Tubes that read abnormally high or low with respect to the standard are suspect. Practical considerations, which take into account the limitations of the tube test in predicting actual tube performance in a particular circuit, make it unnecessary to use complex and costly test equipment with laboratory accuracy. For most applications, testing of a single tube characteristic is good enough to determine tube performance. Some of the more important factors affecting the life expectancy of an electron tube are listed below: The circuit function of the tube Deterioration of the cathode coating A decrease in emission of impregnated emitters in aging filament-type tubes Defective seals that permit air to leak into the envelope and oxidize the emitting surface Internal short circuits and open circuits caused by vibration or excessive voltage If the average receiving tube is not overdriven or operated continuously at maximum rating, it can have a life of at least 2,000 hours before the filament opens. Because of the expansion and contraction of tube elements during the process of heating and cooling, electrodes may lean or sag, which causes excessive noise or microphonics to develop. Other electron-tube defects are cathode-to-heater leakage and nonuniform electron emission of the cathode. These common tube defects contribute to about 50% of all electronic equipment failures. For this reason you should immediately eliminate any tube known to be faulty. However, avoid blind or random replacement of good tubes with fresh spares. The most common cause of tube failure is open filaments. Evidence of a tube defect is often obvious when the filament is open in glass-envelope tubes. You will also notice the brighter-than-normal cherry-red glow of the plate when the plate current is excessive. Also, when the tube becomes gassy or when arcing occurs between electrodes, you will probably have visual indication. Metalencased tubes can be felt for warmth to determine if the heater is operating. You can tap a

tube while it is operating in a circuit to reveal an aural indication of loose elements within the tube or microphonics, which are produced by loose elements. Most tubes are extremely fragile and subject to damage during shipment. When you replace a tube, never make the assumption that the new tube is good because it's new. You should always test tubes before installing them. Q.2 What is the most common cause of electron tube failure? SUBSTITUTION METHODS Substituting with a tube known to be in good condition is a simple method of testing a questionable tube. However, in high-frequency circuits tube substitution should be carried out in a logical sequence. Replace tubes one at a time so that you can observe the effect of differences in interelectrode capacitance in the substituted tubes on tuned circuits. The tube substitution test method cannot be used to advantage in locating more than one faulty tube in a single circuit for two reasons: (1) If both an rf amplifier tube and IF amplifier tube are defective in a receiver, replacing either one will not correct the trouble; and (2) if all the tubes are replaced, there is no way for you to know what tubes were defective. Under these conditions, using test equipment designed for testing the quality of a tube saves you valuable time. Q.3 What is the most accurate method of determining the condition of an electron tube?

NOTE ON SYMBOLS USED IN THE FOLLOWING SECTIONS: IEEE and ANSI standards (see inside front cover) are used to define various terms, such as anode (plate) current, anode voltage, and anode resistance. This book uses Ea for anode voltage, Ia for anode current, and ra for anode resistance. These are the same as Ep, Ip, and rp that you will see elsewhere. This module uses the terms anode and plate interchangeably. ELECTRON TUBE TESTERS A representative field type of electron tube tester designed to test all common low-power tubes is shown in figure 2-1.The tube test conditions are as close as possible to actual tube operating conditions and are programmed on a prepunched card. The card switch (S101, fig. 2-1) automatically programs the tube test conditions when it is actuated by a card. A card compartment on the front panel of the tester provides storage for the most frequently used cards. The cover of the tester (not shown) contains the operating instructions, the brackets for storing the technical manual, the power cord, the calibration cell for checking the meter and short tests, the calibration cards, the blank cards, and a steel hand punch. Figure 2-1. - Electron tube tester.

Front Panel When a prepunched card is fully inserted into the card switch (S101), a microswitch is actuated that energizes a solenoid, causing the card switch contacts to complete the circuit. The card switch has 187 single-pole, single-throw switches arranged in 17 rows with 11 switches in each row. The card is used to push the switches closed; thus, the absence of a hole in the card is required to actuate a switch. The meter (M301) contains four scales. The upper scale is graduated from 0 to 100 for direct numerical readings. The three lower scales, numbered 1, 2, and 3, are read for LEAKAGE, QUALITY, and GAS, respectively. Each numbered scale includes green and red areas marked GOOD and REPLACE. Inside a shield directly in front of the meter are five neon lamps (DS301 through DS305), which indicate shorts between tube elements. The number 2 pushbutton (MP6) is used for transconductance, emission, and other quality tests (described later). The number 3 pushbutton (MP7) is used to test for the presence of gas in the tube envelope. The number 4 pushbutton (MP8) is used for tests on dual tubes. A neon lamp (DS203) lights when pushbutton number 4 is to be used. Eleven tube test sockets are located on the panel, plus tube pin straighteners for the 7- and 9-pin miniature tubes. The power ON-OFF spring-return toggle switch (S105) turns the tester on by energizing a line relay. The pilot light (DS107) lights when this relay closes. Above the power ON-OFF switch are five fuses. Fuses F101, F201, and F202 protect circuits in the tester not protected by other means and have neon lamps to indicate when they have blown. Fuses F102 and F103 protect both sides of the power line. Auxiliary Compartment

A group of auxiliary controls covered by a hinged panel is used for special tests and for calibration of the tester. Two of these controls, labeled SIGNAL CAL (R152 and R155, fig. 22), are used with special test cards for adjusting the regulation and amplitude of the signal voltage. A pushbutton labeled CATH ACT (S302D) is used for making cathode activity tests. When this button is pressed, DS106 on the front panel (fig. 2-1) lights, and the filament voltage of the tube under test is reduced by 10%. Results of the test are read as a change in reading on the numerical meter scale. Figure 2-2. - Auxiliary compartment.

Pushbutton S302E and potentiometers R401 and R405 (fig. 2-2) are used for balancing the transconductance (Gm) bridge circuit under actual tube operating current. Pressing S302E removes the grid signal and allows a zero balance to be made with one potentiometer or the other, depending upon whether the tube under test is passing high or low plate current. Lamp DS108 on the front panel lights when S302E is pressed. Pushbutton S302C is used for checking grid-to-cathode shorts at a sensitivity much higher than the normal tests. Results of this test are indicated by the short test lamps on the front panel. Certain special tests require the use of a continuously adjustable auxiliary power supply. By pressing pushbutton S302B, you may use meter M301 to read the voltage of the auxiliary power supply on meter M301. This voltage may be adjusted by the use of the potentiometer R142. The rest of the potentiometer controls are calibration controls and are adjusted by the use of special calibration cards and a calibration test cell. All circuits in the tester, except the filament supply, are electronically regulated to compensate for line voltage fluctuations. The filament supply voltage is adjusted by pressing pushbutton S302A and rotating the filament standardization adjustment switch S106 until

meter M301 reads midscale. Program Cards The circuits to be used in testing are selected by a prepunched card. These cards are made of tough vinyl plastic material. The tube numbers are printed in color on the tabs of the cards and also at the edge of the card for convenience in filing. A special card is provided to use as a marker when a card is removed for use. Blank cards are provided so that additional test cards may be punched for new tubes that are developed or to replace cards that have become unserviceable. Operation Before operating the tester for the first time, and periodically thereafter, you should calibrate it using the calibration test cards as described in the equipment technical manual. NORMAL TESTS. - The tester is equipped with a three-conductor power cord, one wire of which is chassis ground. It should be plugged into a grounded 105- to 125-volt, 50- to 400hertz outlet. Before operating the tester, open the auxiliary compartment (fig. 2-2) and ensure that the FILAMENT STD ADJ and the Gm BAL knobs are in the NOM position. The GRID SIG and CATH ACT buttons (S302E and S302D) should be up and lamps DS108 and DS106 on the front panel should be out. Turn on the tester and allow it to warm up for 5 to 10 minutes, then press the CARD REJECT KNOB (fig. 2-1) down until it locks. If a nontest card is installed in the card switch, remove it. This card is used to keep the switch pins in place during shipment and should be inserted before transporting the tester. Plug the tube to be tested into its proper socket. (Use the pin straighteners before plugging in 7- and 9-pin miniature tubes.) Select the proper card or cards for the tube to be tested. Insert the card selected into the slot in the card switch until the CARD REJECT KNOB pops up. The card will operate the tester only if it is fully inserted and the printing is up and toward the operator. Do not put paper or objects other than program cards into the card switch, because they will jam the switch contacts. If the overload shuts off the tester when the card is inserted in the switch, check to see that the proper card is being used for the tube under test and that the tube under test has a direct interelement short. As soon as the card switch is actuated, the tube under test is automatically subjected to an interelement short test and a heater-to-cathode leakage test. A blinking or steady glow of any of the short test lamps is an indication of an interelement short. If the short test lamps remain dark, no interelement shorts exist within the tube. If a short exists between two or more elements, the short test lamp or lamps connected between these elements remain dark, and the remaining lamps light. The abbreviations for the tube elements are located on the front panel just below the short test shield so that the neon lamps are between them. This enables the operator to tell which elements are shorted. Heater-to-cathode shorts are indicated as leakage currents on the #1 meter scale. If the meter reads above the green area, the tube should be replaced. A direct heater-to-cathode short causes the meter to read full scale.

To make the QUALITY test, push the number 2 button (fig. 2-1) and read the number 2 scale on meter M301 to determine if the tube is good. (This test may be one of various types, such as transconductance, emission, plate current, or voltage drop, depending upon the type of tube under test.) To test the tube for GAS, press the number 3 button and read the number 3 meter scale. The number 2 button also goes down when number 3 is pressed. If a dual tube having two identical sections is being tested, the neon lamp (DS203) will light, indicating that both sections of the tube may be tested with one card. To do this, check the tube for shorts, leakage, quality, and gas as described previously; then hold down button number 4 and repeat these tests to test the second section of the tube. Dual tubes with sections that are not identical require two cards for testing. A second card is also provided to make special tests on certain tubes. AUXILIARY TEST. - As mentioned previously, two special tests (cathode activity and sensitive grid shorts) may be made by use of controls located in the auxiliary compartment (fig. 2-2). The cathode activity test (CATH ACT) is used to indicate the amount of useful life remaining in the tube. By reducing the filament voltage by 10 percent and allowing the cathode to cool off slightly, the ability of the cathode as an emitter of electrons can be estimated. This test is made in conjunction with the normal quality test. To make the CATH ACT test, allow the tube under test to warm up, press button number 2 (fig. 2-1), and note the reading of scale number 2 on meter M301. Note also the numerical scale reading on M301. Next, lock down the CATH ACT button (fig. 2-2), wait for about 1.5 minutes, then press button number 2 (fig. 2-1) again and note the numerical and number 2 scale readings on meter M301. The tube should be replaced if the numerical reading on M301 differs from the first reading by more than 10 percent or if the reading is in the red area on the number 2 scale. It is sometimes desirable to check certain tubes for shorts at a sensitivity greater than normal. To make the SENSITIVE GRID SHORTS test, push S302C (fig. 2-2) and note if any short test lamps (fig. 2-1) light. HIGH-POWER HF AMPLIFIER TUBE TESTS You normally test high-power amplifier tubes, which operate in the low-to-high frequency range, in the transmitter in which they are to be used. When you operate the tube in a transmitter, its condition can be determined by using built-in meters to measure the grid current, plate current, and power output and comparing those values with those obtained when using tubes known to be good. Q.4 Normally, how are high-power rf tubes tested?

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Quantitative measurements

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Click here to order Electronic Components Online QUANTITATIVE MEASUREMENTS LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Explain the purposes and benefits of performing quantitative measurements. Identify the various methods of performing impedance measurements. Identify the various methods of performing power measurements. Identify the various methods of performing frequency measurements. INTRODUCTION TO QUANTITATIVE MEASUREMENTS You have already studied the basics of performing electronics measurements and how to determine if a component is or is not functioning properly. This chapter will cover techniques used in

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measurements of specific impedance, frequency, and power. These measurements are extremely important to you in evaluating the performance of a piece of electronic equipment. IMPEDANCE MEASUREMENTS Impedance measurements are often used during routine test procedures. Impedance-measuring equipment, such as impedance bridges, are mainly used in determining the capacitance and inductance of component parts. However, the values of combined circuit constants also may be obtained and used in direct calculations of impedance. An impedance measurement effectively totals the inductive and capacitive reactance together with the resistance in a circuit. In addition, impedance measurements are useful in testing and analyzing antenna and transmission line performance and for determining the figure of merit (Q) of electrical parts and resonant circuits. Q meters are impedance-measuring instruments that determine the ratio of reactance to resistance of capacitors or inductors and resistors. Details of Q meters and impedance bridges as well as a number of other methods of measuring circuit impedance are described in the following paragraphs. Also discussed are methods of measuring the impedance of antennas and transmission lines. BRIDGE METHODS Bridges are among the most accurate types of measuring devices used in the measurement of impedance. In addition, bridges are also used to measure dc resistance, capacitance, and inductance. Certain types of bridges are more suitable for measuring a specific characteristic, such as capacitance or inductance. Basic schematics for the various bridge circuits are shown in figure 3-1. The bridge circuits shown are similar in that they usually contain two branches in the measuring circuit, two branches in the comparing circuit, a detector circuit, and a power circuit, as shown in figure 3-2. The bridge shown in figure 3-2 is actually the dc Wheatstone bridge; however, the general principles of circuit operation for ac remain the same. Figure 3-1. - Basic bridge circuits.

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Figure 3-2. - Typical bridge circuit configuration.

The comparing circuit contains branches A and B and has provisions for changing the ratios of the branches with respect to each other, which enables various measuring ranges to be obtained. Comparison of figures 3-1 and 3-2 shows that either or both branches of the comparing circuit do not necessarily contain resistors alone. Branch B of the Hay bridge, containing CB and RB in series connection, provides a striking contrast with the parallel connection of CB and RB of the Maxwell bridge. The measuring circuit in figure 3-2 also contains two branches. The resistance, capacitance, or inductance to be measured is connected to branch X of the bridge-measuring circuit. The subscript X is also used in figure 3-1 to designate the circuit parameters involved in computing the values of various electronic parts. Branch S contains the variable control used to bring the bridge into a balanced condition. A potentiometer is used for this purpose in most bridge equipment, because it offers a wide range of smoothly variable current changes within the measuring circuit.

The third arm of the bridge is the detector circuit. The detector circuit may use a galvanometer for sensitive measurements that require high accuracy. In the case of bridges using ac as the power source, the galvanometer must be adapted for use in an ac circuit. In many practical bridge circuits using ac to operate the bridge, an electronray indicating tube is used to indicate the balanced condition by opening and closing the shadow area of the tube. Headsets are also used for audible balance detection, but this method reduces the accuracy obtainable with the bridge. Switches are used in bridge circuits to control the application of operating power to the bridge and to complete the detector circuit. Frequently, the two switching functions are combined into a single key, called a bridge key, so that the operating power is applied to the bridge prior to the detector circuit. This sequence reduces the effects of inductance and capacitance during the process of measurement. The most unfavorable condition for making a measurement occurs when the resistance, capacitance, or inductance to be measured is completely unknown. In these cases, the galvanometer cannot be protected by setting the bridge arms for approximate balance. To reduce the possibility of damage to the galvanometer, you should use an adjustable shunt circuit across the meter terminals. As the bridge is brought closer to the balanced condition, the resistance of the shunt can be increased; when the bridge is in balance, the meter shunt can be removed to obtain maximum detector sensitivity. Bridges designed specifically for capacitance measurements provide a dc source of potential for electrolytic capacitors. The electrolytic capacitors often require the application of dc polarizing voltages in order for them to exhibit the same capacitance values and dissipation factors that would be obtained in actual circuit operation. The dc power supply and meter circuits used for this purpose are connected so that there is no interference with the normal operation of the capacitance-measuring bridge circuit. The dissipation factor of the capacitor may be obtained while the capacitor is polarized. In figure 3-2, the signal voltage in the A and B branches of the bridge will be divided in proportion to the resistance ratios of its component members, RA and RB, for the range of values selected. The same signal voltage is impressed across the branches S and X of the bridge. The variable control, RS, is rotated to change the current flowing through the S and X branches of the bridge. When the

voltage drop across branch S is equal to the voltage drop across branch A, the voltage drop across branch X is equal to the voltage drop across branch B. At this time the potentials across the detector circuit are the same, resulting in no current flow through the detector circuit and an indication of zero-current flow. The bridge is balanced at these settings of its operating controls, and they cannot be placed at any other setting and still maintain this balanced condition. The ability of the bridge circuit to detect a balanced condition is not impaired by the length or the leads connecting the bridge to the electronic part to be measured. However, the accuracy of the measurement is not always acceptable, because the connecting leads exhibit capacitive and inductive characteristics, which must be subtracted from the total measurement. Hence, the most serious errors affecting accuracy of a measurement are because of the connecting leads. Stray wiring capacitance and inductance, called residuals, that exist between the branches of the bridge also cause errors. The resistance-ratio bridge, for example, is redrawn in figure 3-3 to show the interfering residuals that must be eliminated or taken into consideration. Fortunately, these residuals can be reduced to negligible proportions by shielding and grounding. A method of shielding and grounding a bridge circuit to reduce the effects of interfering residuals is through the use of a Wagner ground, as shown in figure 3-4. Observe that with switch S in position Y, the balanced condition can be obtained by adjusting Z1 and Z2. With switch S in position X, the normal method of balancing the bridge applies. You should be able to reach a point where there is no deflection of the meter movement for either switch position (X or Y) by alternately adjusting Z1 and Z2 when the switch is at position Y and by adjusting RS when the switch is at position X. Under these conditions, point 1 is at ground potential; and the residuals at points 2, 3, and 4 are effectively eliminated from the bridge. The main disadvantage of the Wagner ground is that two balances must be made for each measurement. One is to balance the bridge, and the other is to balance the Wagner ground. Both adjustments are interacting because RA and RB are common to both switch positions X and Y. Figure 3-3. - Resistance-ratio bridge residual elements.

Figure 3-4. - Wagner ground.

Many bridge instruments provide terminals for external excitation potentials; however, do not use a voltage in excess of that needed to

obtain reliable indicator deflection because the resistivity of electronic parts varies with heat, which is a function of the power applied. Q.1 What conditions must be met in order to balance a bridge circuit? Q.2 When you are measuring a component using a bridge, what is the most common cause of inaccurate measurements?

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Qualitative measurements

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Click here to order Electronic Components Online QUALITATIVE MEASUREMENTS LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Identify the various methods of measuring standing-wave ratios. Identify the various methods of determining electrical losses Join Integrated caused by deterioration of Publishing's transmission lines. Discussion Group Identify the methods of measuring intermodulation distortion. INTRODUCTION TO QUALITATIVE MEASUREMENTS As a technician, you are responsible for repairing and maintaining complex electronic systems. The basic ability to repair a specific piece of equipment is Order this only the first step in becoming a qualified technician. Your ultimate goal should be to become proficient at systems fault isolation - in other words, to information on CDRom know the entire system like the back of your hand. To reach this goal you will need to be familiar with all parts of the system and know how they are interconnected and interact with each other. There are numerous shortcuts or tricks of the trade that can only be learned through experience on any

system, but the most practical thing for you to remember is to approach all problems in a logical manner. Various combinations of electronic equipment are interconnected to form a system capable of performing specific functions. You must be able to apply Order this general test methods and practices to installation, tuning, maintenance, and information in repair of the system. This requires you to have a thorough knowledge of Print (Hardcopy). many types of electronic equipment. When radar, communication, and digital computers are interconnected, they require different maintenance procedures than when they are operated separately. Revised test procedures may be necessary. Detrimental interactions between equipment or facilities must be corrected and effective preventive maintenance procedures must be planned for all equipment within the system. System quality figures, such as sensitivity and coverage, must be determined and measured during equipment preventive maintenance checks to assure efficient operation. System monitoring at specific test points is often used to help localize a problem. System testing and monitoring are frequently accomplished by using an external piece of electronic equipment, which is designed specifically for testing a particular system. Some computers and computer systems build in their own monitoring and testing devices and will inform the operator when and where failure has occurred. You must realize that any equipment designed to test, monitor, or repair another system is itself subject to malfunction and will require periodic checks and preventive maintenance. This chapter will cover some of the basic test methods and practices associated with system-level troubleshooting. STANDING-WAVE RATIO (SWR) MEASUREMENTS Standing-wave ratio (swr) is the ratio of the maximum voltage or current to the minimum voltage or current at any point along a transmission line. Swr measurements are used to determine the matching quality of the termination of the line. A variety of methods and test equipments may be used to measure the voltage or current distribution along a transmission line. An open transmission line is accessible for coupling to many types of voltagemeasuring devices, such as a wavemeter or a grid-dip meter. However, at higher frequencies where coaxial cables or waveguides are used to minimize skin effect losses, (discussed in NEETS, module 10) access is more complicated. Access to the interior of the

waveguide or center conductor of the coaxial cable must be gained by using a unidirectional or bidirectional coupler, which is inserted into the transmission line. The coupler contains a slot into which an rf probe is inserted and positioned with respect to directivity. The conditions that produce standing waves and their adverse effects are discussed in detail in NEETS, module 10. The different methods of detecting and measuring standing waves are discussed in the following paragraphs. PROBES A magnetic or electric probe can be used to observe the standing wave on a short-circuited, terminated line. The wavelength is obtained by measuring the distance between alternate maximum or minimum current points along the line. A typical setup operating at 300 megahertz might use two 10-foot lengths of number 14 phosphor-bronze wires, which are spaced 1 inch apart and supported parallel to a set of probe guide rails. The line should be partially matched to the source generator by means of a parallel-wire shorting stub connected in parallel with the transmission line and the oscillator output line. Figure 4-1, view A and view B, illustrates the types of probes required for this method of measurement. Figure 4-1A. - Typical electromagnetic probe.

Figure 4-1B. - Typical electromagnetic probe.

NEON-LAMP AND MILLIAMMETER METHODS In this method of measurement, a neon bulb or milliammeter is moved along the two-wire parallel transmission line. Points of maximum voltage (standingwave voltage peaks) with the lamp or points of maximum current (standingwave current peaks) with the indicator will have maximum brilliance or indication, respectively. Q.1 At what points along a transmission line will a neon lamp glow the brightest? BRIDGE METHODS The bridge method permits measurement of the standing-wave ratio without actually measuring the standing waves. The bridge method is applicable because the input impedance of a line terminated in its characteristic impedance is a pure resistance equal to the characteristic impedance. A line terminated in this way can be used as the unknown resistance in a bridge circuit and a null can be obtained in the indicating device when the other resistance arms of the bridge are properly adjusted. Many types of bridges can be used. For example, an ac bridge that is independent of the applied frequency can be used. The bridge will become unbalanced when the line is no longer properly terminated. Improper termination will produce a reactive component as well as a resistive component in the input impedance of the line and result in a standing wave. The reading of the indicating device depends on the degree of imbalance, which becomes more severe as the mismatch caused by the termination becomes worse. The indicating device can be calibrated directly to indicate the standing-wave ratio. The most common indicator consists of a crystal

rectifier, a filtering circuit, and a sensitive dc meter movement in series with a high resistance. RESISTANCE-CAPACITANCE BRIDGE A resistance-capacitance bridge circuit is shown in view A of figure 4-2. The bridge is theoretically independent of the applied frequency. Figure 4-2A. - Resistance-capacitance bridge circuit for measuring standingwave ratio.

However, the applied frequency must be low enough to avoid skin effect, stray inductance, capacitance, and coupling between circuit elements and wiring. The leads must be kept short to eliminate stray reactance, which causes bridge imbalance. The rectifier circuit wiring must be isolated from other bridge component fields so that induced voltages do not cause an erroneous indication. You should only use resistors having negligible capacitance and inductance effects. Before you calibrate a newly constructed bridge, the following procedure must be followed if residual readings caused by stray effects are to be held to a minimum: Connect a noninductive resistor (RL in view B) that is equal to the characteristic impedance of the line to the output terminals of the bridge. Figure 4-2B. - Resistance-capacitance bridge circuit for measuring standingwave ratio.

Apply an rf voltage to the input terminals and adjust the variable capacitor for a minimum reading on the meter. Reconnect the resistor (RL) to the input terminals and connect the rf power source to the output terminals. Adjust the rf voltage amplitude applied to the bridge until a full-scale meter reading is obtained. Reconnect the bridge in the normal manner (resistor RL to the output terminals, etc.). If the meter reading is now more than 1% or 2% of the full-scale reading, different arrangements (lead dress) of the internal wiring must be tried until the null is reduced to 0 or as close as possible to the 0 point. The bridge can be calibrated after completion of the preceding check. Connect the transmission line under investigation to the output terminals of the bridge and connect a succession of noninductive resistors (RO in view C)to the load end of the transmission line until the bridge is balanced. Assuming that the bridge was originally balanced for the characteristic impedance of the line, the standing-wave ratio can be computed from the following equation:

Figure 4-2C. - Resistance-capacitance bridge circuit for measuring standingwave ratio.

Select the formula that yields a ratio greater than unity. The swr calibration can be recorded on the meter scale directly, recorded on a chart in terms of the meter deflection, or plotted on a graph against the meter deflection. The variable capacitor, in turn, can be calibrated for various characteristic impedances. This is accomplished by applying suitable resistors (RO) across the output terminals and noting the capacitor settings at the respective balance points. A range of 50 to 300 ohms should prove attainable. ACCURACY OF BRIDGE MEASUREMENTS To assure accurate measurements, the rf signal applied to the bridge must be properly adjusted each time a calibrated instrument is used. Essentially, this adjustment is a repetition of the previously described reversed-bridge procedure. The following steps are to be performed: Connect the line to the input terminals of the bridge and connect the transmitter to the output terminals. Adjust the transmitter coupling until fullscale deflection is obtained. From this point on, the coupling must be left untouched. Reconnect the bridge in the usual way and proceed with the measurement. POWER OUTPUT VERSUS IMPEDANCE MATCHING For maximum transfer of the power out of an rf source, with minimum heating from reflected power, the total output impedance sensed by the rf source must be equal to the internal impedance of that source. A perfect impedance match between transmitter and load would exist if the swr were 1 to 1. As

discussed in NEETS, module 10, test equipment designed to measure the instantaneous voltage of a standing wave will give you a voltage standingwave ratio (vswr). Test equipment designed to measure the instantaneous current component of a standing wave will give you the current standingwave ratio (iswr). Regardless of the type of test equipment selected, both ratios will be the same. Q.2 What vswr is a perfect match between a transmitter and its load?

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Introduction to waveform interpretation

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Click here to order Electronic Components Online INTRODUCTION TO WAVEFORM INTERPRETATION LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Explain the use of waveform interpretation in testing applications. Identify the different types of modulation and methods of measuring modulation. Explain the various uses of spectrum analyzers. Explain the various uses of time-domain reflectometers. Identify the various tests that can be performed with the swept-frequency technique. INTRODUCTION TO WAVEFORM INTERPRETATION Measurements performed with oscilloscopes, time-domain

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reflectometers, and spectrum analyzers enable you to view the signal produced by the equipment or circuit under test. However, a visual display is of no value unless you are able to interpret the signal characteristics. A displayed waveform is a representation of a varying signal related to time. You can graphically plot an unknown waveform by using a system of coordinates in which the amplitude of the unknown signal is plotted linearly against time. An analysis of the resultant waveform provides you with valuable information in determining the characteristics of many electronic (and some mechanical) devices. For example, the waveform of a signal may indicate the presence of harmonics or parasitic oscillations, or it may indicate how closely a device is following a desired cycle of operation. As the parts in an amplifier begin to shift in value or deteriorate, waveform distortion often occurs and indicates abnormal operation of a circuit and often precedes circuit breakdown. Malfunctioning of electrical or electronic circuits within equipment can usually be traced, by waveform inspection, to a specific part or parts of the circuit responsible for the distorted signal. On the basis of these facts, it is apparent that there is an important need for test equipment that can provide a visual presentation of a waveform at the instant of its occurrence in a circuit. DISTORTION is a term used by technicians and engineers alike that generally signifies dissatisfaction with the shape of the wave processed by an amplifier. Distortion of a waveform is the undesired change or deviation in the shape of the observed signal with respect to a reference waveform. Classifying any waveform as a distorted wave without reference to the electronic circuitry involved is meaningless. A waveform that can be validly termed distorted with respect to a specific amplifier circuit may be the normal waveform to be expected from another amplifier circuit. One of the most important steps in waveform analysis, the one that usually proves the most difficult for the maintenance personnel, is the interpretation of patterns viewed on the test equipment. This chapter will cover some of the basic test methods and practices associated with waveform interpretation. MODULATION MEASUREMENTS

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Modulation measurements are sometimes required during tuning procedures to adjust transmitting equipment for the proper amount of modulation. During maintenance tests of modulated transmitter equipment, you should determine the amount of distortion in the output signal and the modulation level or index. The modulation level in multiplexing equipment is usually set at the factory or during corrective maintenance procedures. Proper adjustment of the input signal level and automatic signal-level regulation circuits provides the correct amount of modulation. Defects in modulation circuits of a transmitter can be detected by measurements of the quality of the received signals at the receiver. Corrective maintenance analysis of multiplex equipment modulation circuits can usually be made by signal-level measurements. Some radio transmitters, when operating in the AM mode, must be adjusted for correct modulation during normal tuning procedures. If the modulation level is low, the transmitter is not operating at its maximum efficiency. On the other hand, modulation in excess of 100% produces serious distortion. Since neither of these conditions is desirable, amplitude modulation should be maintained between 60% and 95% when possible. The modulation level or index of AM and fm radio transmitters that operate in the vhf range is initially adjusted by the manufacturer or during corrective maintenance. The amplifier gain of the modulator can be initially adjusted by reference to the modulation meter provided on the front panel of the equipment. Pulse modulation of radar and radio beacon signals can be measured by waveform displays presented on a standard oscilloscope. The amount of usable energy in a pulsed waveform, as measured by a spectrum analyzer, is also an indication of the pulse modulation quality. Attaining 100% amplitude modulation of an rf carrier with a sine wave requires a modulating power equal to one-half of the rf carrier power. Under this condition, the average power of the modulated carrier is equal to 1.5 times the average unmodulated carrier power. The added power is divided equally between the upper and lower sidebands. During the peaks of 100% modulation, the amplitude of the carrier is doubled. This will cause the instantaneous peak power to be four times the instantaneous unmodulated peak power P = E2/R. When voice modulation is

employed, only the highest amplitude peaks can be allowed to modulate the carrier 100%. Since many speech components do not modulate the carrier 100%, the average power required for voice modulation is less than that required for modulation with a sine wave. Voice peaks usually modulate a carrier 100% when the modulation increases the average carrier output power 25% over its normal value. Q.1 What is the result of overmodulating an AM signal? Q.2 For AM transmissions, the carrier is normally modulated within what range? AMPLITUDE-MODULATION MEASUREMENTS An increase in the power output of an AM transmitter is indicated by an increase in antenna current. The increase can be taken as a measure of the degree of modulation and can be expressed as a percentage, as shown in figure 5-1. The graph for this figure was developed from the relationship existing between the carrier power and the increased power resulting from the added modulation power. The formula for calculating the PERCENTAGE of MODULATION is as follows:

Figure 5-1. - Antenna current increase with amplitude modulation.

The use of this formula is based on the assumption that the modulating voltage is a pure sine wave. Normal broadcasting, however, is characterized by complex envelope patterns, as illustrated in figure 5-2. In this light, the previous formula is not so clear. Consequently, the preceding formula should be viewed more correctly as the PERCENTAGE OF POSITIVE PEAK MODULATION. When the minimum voltage (E min) rather than the peak voltage (Emax) is used to compute percentage of modulation, the computed percentage (shown below) is the PERCENTAGE OF NEGATIVE PEAK MODULATION:

Figure 5-2. - Rf carrier amplitude-modulated by a complex wave envelope.

Since the preceding two modulation percentages often differ, you should define the AVERAGE PERCENTAGE OF MODULATION, as shown below (refer to fig. 5-3):

Figure 5-3. - Rf amplitude percentage modulation wave envelope.

From the preceding definitions of percentage of modulation, you should note that methods of measuring all three types of modulation percentages must be devised. When differing values are obtained, however, the cause may not necessarily be directly related to unequal positive and negative peaks of a complex modulation wave. Another possibility is distortion caused by carrier shift. Distortion may also be produced by effects other than the

modulation process - for example, parasitic oscillation, nonlinear radio-frequency amplification of modulated signals, and distortion present in the audio amplifiers. Unfortunately, continuous variations in the percentage of modulation create a number of additional problems. For example, damping is necessary so that a meter can provide an average reading despite fluctuations. An average reading, on the other hand, will not disclose the presence of transient overmodulation. This shortcoming is serious because of the large number of sideband frequencies produced in addition to the normal ones whenever overmodulation occurs. Not only do these extra frequencies interfere drastically with other transmissions, but they also may significantly distort the modulation signal. These considerations account for the importance of using a meter that responds to modulation peak; specifically, both positive-peak and negative-peak overmodulation must be indicated. Positive-peak overmodulation occurs when the positive modulation exceeds 100%; negative-peak overmodulation occurs when the negative modulation exceeds 100%.

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Book 22

Back • Home • Up • Next Click here to order Electronic Components Online Operational concepts Electronic computers Digital computer generations Uses of a digital computer Using a desktop computer Summary Answers

Hardware Types of internal storage Classifications of internal storage Physical organization of data on a disk. Magnetic drum Input/Output devices (external) Floppy disk drive units (Input/Output) Display Devices Summary Answers

Software

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Utility programs Programming Tools of Flowcharting Program coding Packaged software Summary Answers

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Data representation and communications Computer coding systems Data storage concepts Storage access methods Summary Answers

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Operational concepts

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Click here to order Electronic Components Online OPERATIONAL CONCEPTS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions placed throughout the chapters are based on the objectives. By successfully completing the Nonresident Training Course (NRTC), you indicate that you have met the objectives and have learned the information. The learning objectives for this chapter are listed below.

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Upon completion of this chapter, you will be able to do the following: Describe the history of computers. Describe how computers are classified. Explain how digital computers have changed during each generation.

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Describe the practical applications of digital computers in the Navy. Describe the initial steps needed to use a microcomputer. Explain storage media handling, backups, and the threats to storage media. INTRODUCTION Digital computers are used in many facets of today's Navy. It would be impossible for one NEETS module to cover all the ways they are used in any depth. A few of these ways are covered later in this chapter. The purpose of this module is to acquaint you, the trainee, with the basic principles, techniques, and procedures associated with digital computers. We will use a desktop (personal) computer for most of the examples. Personal computers should be more familiar to you than the large mainframes, and the operating principles of personal computers relate directly to the operating principles of mainframe computers. You will learn the basic terminology used in the digitalcomputer world. When you have completed these chapters satisfactorily, you will have a better understanding of how computers are able to perform the demanding tasks assigned to them. If we were to define the word computer, we would say a computer is an instrument for performing mathematical operations, such as addition, multiplication, division, subtraction, integration, vector resolution, coordinate conversion, and special function generation at very high speeds. But the usage of computers goes well beyond the mathematical-operations level. Computers have made possible military, scientific, and commercial advances that before were considered impossible. The mathematics involved in orbiting a satellite around the earth, for example, would require several teams of mathematicians for a lifetime. Now, with the aid of electronic digital computers, the conquest of space has become reality. Computers are employed when repetitious calculations or the

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processing of large amounts of data are necessary. The most frequent applications are found in the military, scientific, and commercial fields. They are used in many varied projects, ranging from mail sorting, through engineering design, to the identification and destruction of enemy targets. The advantages of digital computers include speed, accuracy, reliability, and man-power savings. Frequently computers are able to take over routine jobs, releasing people for more important work; work that cannot be handled by a computer. HISTORY OF COMPUTERS The ever increasing need for faster and more efficient computers has created technological advances that can be considered amazing. Ever since humans discovered that it was necessary to count objects, we have been looking for easier ways to do it. Contrary to popular belief, digital computers are not a new idea. The abacus is a manually operated digital computer used in ancient civilizations and used to this day in the Orient (see fig. 1-1). For those who consider the abacus outdated, in a contest between a person using a modern calculator and a person using an abacus, the person using the abacus won. Figure 1-1. - Abacus.

The first mechanical adding machine (calculator) was invented by Blaise Pascal (French) in 1642. Twenty years later, an Englishman, Sir Samuel Morland, developed a more compact device that could multiply, add, and subtract. In 1682, Wilhelm Liebnitz (German) perfected a machine that could perform all the basic operations (addition, subtraction, division, and multiplication), as well as extract the square root. Liebnitz's principles are still in use today in our modern electronic digital computers.

As early as 1919, electronics entered the scene. An article by W. H. Eccles and F. W. Jordan described an electronic "trigger circuit" that could be used for automatic counting. It was the ECCLES-JORDAN multivibrator which was a little ahead of its time because a trigger circuit is one of many components required to make an electronic digital computer. Modern digital computers use these circuits, known as flip-flops, to store information, perform arithmetic operations, and control the timing sequences within the computer. Under the pressure of military needs in World War II, the science of electronic data processing made giant strides forward. In 1944, Harvard University developed a computing system known as the Automatic Sequence Controlled Calculator. After the initial design and construction, several improved models were built. Meanwhile, at the University of Pennsylvania, a second system was being developed. This system, completed in 1946, was named ENIAC (Electronic Numerical Integrator and Computer). ENIAC employed 18,000 vacuum tubes in its circuitry; and in spite of these bulky, hot tubes, it worked quite successfully. The first problem assigned to ENIAC was a calculation in nuclear physics that would have taken 100 human-years to solve by conventional methods. The ENIAC solved the problem in 2 weeks, only 2 hours of which were actually spent on the calculation. The remainder of the time was spent checking the results and operational details. All modern computers have their basics in these two early developments conducted at Harvard University and University of Pennsylvania. In 1950, the UNIVAC I was developed. This machine was usually regarded as the most successful electronic data processor of its day. An outstanding feature of the UNIVAC I was that it checked its own results in each step of a problem; thus eliminating the need to run the problems more than once to ensure accuracy. During the first outbreak of publicity about computers (especially when the UNIVAC predicted the outcome of the 1952 presidential election), the term "giant brain" caused much confusion and uneasiness. Many people assumed that science had created a thinking device superior to the human mind. Currently most people know better. By human standards the giant brain is nothing more than a talented idiot that is wholly dependent upon human instructions to perform even the simplest job. A computer is only a machine and definitely cannot think

for itself. The field of artificial intelligence, however, is developing computer systems that can "think"; that is, mimic human thought in a specific area and improve performance with experience and operation. The field of digital computers is still in the growing stages. New types of circuitry and new ways of accomplishing things are continuing to be developed at a rapid rate. In the military field, the accomplishments of digital computers are many and varied. One outstanding example is in weapons systems. Most of the controlling is done by digital computers. CLASSIFICATIONS OF COMPUTERS Computers can be classified in many different ways. They can be classified by the type of technology they use (mechanical, electromechanical, or electronic), the purpose for which they were designed (general purpose or special purpose), by the type of data they can handle (digital or analog), by the amount they cost (from $50 to $10 million and up), and even by their physical size (handheld to room size). We will briefly explain mechanical, electromechanical, and electronic computers; special-purpose and general-purpose computers; and analog and digital computers. MECHANICAL COMPUTERS Mechanical or analog computers are devices used for the computation of mathematical problems. They are made up of components, such as integrators, sliding racks, cams, gears, springs, and driveshafts. Figure 1-2 shows a typical mechanical computer used by the Navy. These computers are analog in nature, and their physical size depends on the number of functions the computer has to perform. In an analog computer, a continuing input will give a constantly updated output. This being perfect for target information, the Navy uses these analog computers primarily for gun fire control. As systems for naval weapons became more and more complex, the need for a different computer was apparent. The functions that had to be performed had increased the size of the computer to an unreasonable scale. Figure 1-2. - Bulkhead-type mechanical computer

ELECTROMECHANICAL COMPUTERS Electromechanical computers came next and differ from mechanical computers in that they use electrical components to perform some of the calculations and to increase the accuracy. Because the electrical components are smaller than their mechanical counterparts, the size of the computer was reduced, even though it performs more functions. The components used to perform the calculations are devices such as synchros, servos, resolvers, amplifiers, servo amplifiers, summing networks, potentiometers, and linear potentiometers. Figure 1-3 shows one of the Navy's electromechanical computers. These computers are used in gun fire control and missile fire control. Even though they are better than the mechanical computer, they still have their drawbacks. Of prime importance is that they are special-purpose computers. This means they can only be used for one job, dependent on their design characteristics. By today's Navy standards they are still too large, and the maintenance time on them is excessive. The need for a more accurate, reliable, versatile, and smaller computer was recognized. Figure 1-3. - Electromechanical computer.

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Hardware

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Click here to order Electronic Components Online HARDWARE LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Explain the cpu and describe the functions of the different sections. Categorize the types of storage and their functions. Join Integrated Describe how storage is classified. Publishing's Analyze and compare the Discussion Group input/output devices and explain their functions. INTRODUCTION Components or tools of a computer system are grouped into one of two categories, hardware or software. We refer to the machines that compose a Order this computer system as hardware. This hardware includes all the mechanical, information on CDelectrical, electronic, and magnetic devices within the computer itself (the Rom central processing unit) and all related peripheral devices (printers, magnetic tape units, magnetic disk drive units, and so on). These devices will be covered in this chapter to show you how they function and how they relate to one another. Take a few minutes to study figure 2-1. It shows the functional

units of a computer system: the inputs, the central processing unit (cpu), and the outputs. The inputs can be on any storage medium from punched cards, paper tape, or magnetic ink to magnetic tape, disk, or drum; or they can be entries from a console keyboard or a cathode-ray tube (crt) terminal. The data from one or more of these inputs will be processed by the central Order this processing unit to produce output. The output may be in punched cards or information in paper tape, on magnetic tape, disk, or drum, or it may be printed reports or Print (Hardcopy). information displayed on a console typewriter or crt terminal. The figure also shows the data flow, instruction flow, and flow of control. We'll start our hardware discussion with the cpu and then move into storage media (disk, tape, and drum). We'll end the chapter with a discussion of input/output devices and how they work. CENTRAL PROCESSING UNIT (CPU) The brain of a computer system is the central processing unit, which we generally refer to as the cpu or mainframe. The central processing unit IS THE COMPUTER. It is the cpu that processes the data transferred to it from one of the various input devices, and then transfers either the intermediate or final results of the processing to one of many output devices. A central control section and work areas are required to perform calculations or manipulate data. The cpu is the computing center of the system. It consists of a control section, internal storage section (main or primary memory), and arithmeticlogic section (fig. 2-1). Each of the sections within the cpu serves a specific function and has a particular relationship to the other sections within the cpu. Figure 2-1. - Functional units of a computer system.

CONTROL SECTION The control section may be compared to a telephone exchange because it uses the instructions contained in the program in much the same manner as the telephone exchange uses telephone numbers. When a telephone number is dialed, it causes the telephone exchange to energize certain switches and control lines to connect the dialing phone with the phone having the number dialed. In a similar manner, each programmed instruction, when executed, causes the control section to energize certain control lines, enabling the computer to perform the function or operation indicated by the instruction. The program may be stored in the internal circuits of the computer (computer memory), or it may be read instruction-by-instruction from external media. The internally stored program type of computer, generally referred to only as a stored-program computer, is the most practical type to use when speed and fully automatic operation are desired. Computer programs may be so complex that the number of instructions plus

the parameters necessary for program execution will exceed the memory capacity of a stored-program computer. When this occurs, the program may be sectionalized; that is, broken down into modules. One or more modules are then stored in computer memory and the rest in an easily accessible auxiliary memory. Then as each module is executed producing the desired results, it is swapped out of internal memory and the next succeeding module read in. In addition to the commands that tell the computer what to do, the control unit also dictates how and when each specific operation is to be performed. It is also active in initiating circuits that locate any information stored within the computer or in an auxiliary storage device and in moving this information to the point where the actual manipulation or modification is to be accomplished. The four major types of instructions are (1) transfer, (2) arithmetic, (3) logic, and (4) control. Transfer instructions are those whose basic function is to transfer (move) data from one location to another. Arithmetic instructions are those that combine two pieces of data to form a single piece of data using one of the arithmetic operations. Logic instructions transform the digital computer into a system that is more than a high-speed adding machine. Using logic instructions, the programmer may construct a program with any number of alternate sequences. For example, through the use of logic instructions, a computer being used for maintenance inventory will have one sequence to follow if the number of a given item on hand is greater than the order amount and another sequence if it is smaller. The choice of which sequence to use will be made by the control section under the influence of the logic instruction. Logic instructions, thereby, provide the computer with the ability to make decisions based on the results of previously generated data. That is, the logic instructions permit the computer to select the proper program sequence to be executed from among the alternatives provided by the programmer. Control instructions are used to send commands to devices not under direct command of the control section, such as input/output units or devices. ARITHMETIC-LOGIC SECTION The arithmetic-logic section performs all arithmetic operations-adding, subtracting, multiplying, and dividing. Through its logic capability, it tests various conditions encountered during processing and takes action based on the result. As indicated by the solid arrows in figure 2-1, data flows between the arithmetic-logic section and the internal storage section during processing. Specifically, data is transferred as needed from the internal storage section to the arithmetic-logic section, processed, and returned to the internal storage

section. At no time does processing take place in the storage section. Data may be transferred back and forth between these two sections several times before processing is completed. The results are then transferred from internal storage to an output unit, as indicated by the solid arrow (fig. 2-1). MEMORY (INTERNAL STORAGE) SECTION All memory (internal storage) sections must contain facilities to store computer data or instructions (that are intelligible to the computer) until these instructions or data are needed in the performance of the computer calculations. Before the stored-program computer can begin to process input data, it is first necessary to store in its memory a sequence of instructions, and tables of constants and other data it will use in its computations. The process by which these instructions and data are read into the computer is called loading. Actually, the first step in loading instructions and data into a computer is to manually place enough instructions into memory using the keyboard or electronically using an operating system (discussed in chapter 1), so that these instructions can be used to bring in more instructions as desired. In this manner a few instructions are used to bootstrap more instructions. Some computers make use of an auxiliary (wired) memory that permanently stores the bootstrap program, thereby making manual loading unnecessary. The memory (internal storage) section of a computer is essentially an electronically operated file cabinet. It has a large number (usually several hundred thousand) of storage locations; each referred to as a storage address or register. Every item of data and program instruction read into the computer during the loading process is stored or filed in a specific storage address and is almost instantly accessible. Q.1 What is the brain of a computer system? Q.2 How many sections make up the central processing unit? Q.3 What are the names of the sections that make up the cpu? Q.4 The control section can be compared to what? Q.5 What are the four major types of instructions in the control section? Q.6 What capability allows the arithmetic/logic section to test various conditions encountered during processing and take action based on the result?

Q.7 In the arithmetic/logic section, data is returned to what section after processing? Q.8 What is the process by which instructions and data are read into a computer?

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Software

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Click here to order Electronic Components Online SOFTWARE LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Recognize and compare the different types and functions of operating systems. Identify the types of utilities and explain their functions. Describe the different types and functions of programming languages. Explain the steps necessary to develop a program and describe the tools used. Compare and describe the types and functions of applications packages. INTRODUCTION

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Up to now we have been discussing computer OPERATIONAL CONCEPTS and HARDWARE (the computer and its peripheral devices), and how these devices work and communicate with each other. What about this thing called SOFTWARE? Do we really need it? We most certainly do! Software plays a major role in computer data processing. For example, without software, the computer could not perform simple addition. It's the software that makes everything happen. Or putting it another way, software brings the computer to life. You already know it takes a program to make the computer function. You load an operating system into the computer to manage the computer's resources and operations. You give job information to the operating system to tell it what you want the computer to do. You may tell it to assemble or compile a COBOL program. You may tell it to run the payroll or print inventory reports. You may tell it to copy a tape using a utility program. You may tell it to print the data from a disk file, also using a utility program. You may tell it to test a program. This job information may be entered through the console or read into the computer from tape or disk. It also may be entered by the programmer or user from a remote computer terminal. The operating system receives and processes the job information and executes the programs according to that job information. Software can be defined as all the stored programs and routines (operating aids) needed to fully use the capabilities of a computer. Generally speaking, we say, "If it is not hardware then it must be software." OPERATING SYSTEMS The operating system is the heart of any computer system. Through it, everything else is done. Basically, operating systems are designed to provide the operator with the most efficient way of executing many user programs. An operating system is a collection of many programs used by the computer to manage its own resources and operations. These programs control the execution of other programs. They schedule, assign resources, monitor, and control the work of the computer. There are several types.

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TYPES OF OPERATING SYSTEMS Operating systems are designed to provide various operating modes. Some systems can only do one task at a time, while others can perform several at a time. Some systems allow only one person to use the system, and others allow multiple users. Single user/single tasking operating systems are the simplest and most common on microcomputers. CP/M-801, CP/M-861, and MSDOS(1,2)2 are examples. Single user/multitasking operating systems allow you to do more than one task as long as the tasks don't use the same type of resources. For example, you can print one job while you run another, as long as the second job does not require the printer. Examples are Concurrent CP/M-863, Concurrent DOS3, and MS-DOS (3.0 and above). Multiuser/multitasking operating systems let more than one user access the same resources at the same time. This is especially useful for sharing common data. These are only feasible on processors (the functional unit in a computer that interprets and executes instructions) of 16 bits or more and with large memories. UNIX4 is an example. There are also multiprocessor systems, shared resource systems. This means each user (or operator) has a dedicated microprocessor (cpu), which shares common resources (disks, printers, etc.). 1CP/M

and CP/M-86 are registered trademarks of Digital Research

Inc. 2MS-DOS

is a registered trademark of Microsoft Corporation.

3Concurrent

CP/M and Concurrent DOS are trademarks of Digital Research Inc. 4UNIX

is a trademark of AT & T.

COMPATIBILITY WITH APPLICATIONS SOFTWARE To use an applications program, it must be compatible with the operating system. Therefore, the availability of application software for a particular operating system is critical. Because of this, several operating systems have become the most popular. For 8-bit microcomputers, CP/M (Control Program for Microprocessors) is

widely used because many hardware manufacturers have adopted it. MS-DOS (MicroSoft Disk Operating System) designed from CP/M dominates in lower performance 16-bit systems. UNIX, an operating system for larger computers, is being used on the more powerful 16-bit and 32-bit microcomputers. Other operating systems are offered by microcomputer manufacturers. To overcome the applications software compatibility problem, some software comes in several versions so it can be run under several different operating systems. The point to remember is that not all applications software will run on all systems. You have to check to see that compatibility exists. You need the right version. OPERATING SYSTEM FUNCTIONS To give you a better idea of what you can expect to see on your microcomputer display screen, we will show a few fundamental disk operating system commands and messages. Again, the functions of each operating system are about the same, but each may use a different command to do about the same thing. For example, try not to get confused because CP/M uses the command PIP (peripheral interchange program) to copy a file, while MS-DOS uses the command COPY. Remember, the first thing you need to do is boot (initial program load) the system. There are many ways this can be done. Here is an example. When you turn on the power, a prompt may appear on the screen. You then insert the operating system floppy disk into the drive A. Type a B (for boot) and press the RETURN key. The operating system will load from the disk. If you are using a system set up for automatic booting, you won't have to type the B. The system automatically loads the operating system when you insert the disk that contains it. Some systems will then ask for date and time. Enter these. You will next see a prompt, usually A> (or A:). The system is ready and drive A is assigned as your primary drive. One thing you might want to do is to display the disk directory to see what is on the disk. To do this, enter DIR following the A>. This will list your files. COMMAND.COM CONFIGUR.COM

DATDBL.BAK DATDBL.DOC FINANCE.BAS MASTER.DOC It may also give you file size and the date and time of the file. Let's take an example. Let's say you are to copy the file "MASTER.DOC" from the floppy disk in drive A to the floppy disk in drive B and then delete the file on the floppy disk in drive A. You have just displayed the directory of the floppy disk in drive A. Check to see that the file you want is on the floppy disk in drive A. It is. You then insert the floppy disk on which you want the copy into drive B. Be sure it is formatted with the track and sector information so it is ready to receive data. Also, be sure the disk is not write-protected. On a 51/4 inch floppy disk that means the write protect notch is uncovered. Following the A> type COPY MASTER.DOC B: and press RETURN. The system will copy the file and give it the same name. Next you might want to display the directory on drive B to see that the file was copied. You can do this by entering DIR B: following the A> prompt. To delete the file on the floppy disk in drive A, type DEL MASTER.DOC following the A> prompt on the screen and press RETURN. You probably noticed each entry in the directory is followed by three characters. These are called extensions, and we use them to tell us the type of file we are working with. For example, .BAK means backup file. .BAS means BASIC source program. .TMP means temporary file. .DOC means ASCII document file. .BIN means binary file, and so on. Other typical built-in operating system commands you can use might include:

RENAME

to change the name of a file

DISKCOPY to copy a whole floppy disk FORMAT

to initialize a floppy disk, get it ready to receive data and programs from the system

TIME

to display or set the time

You will learn to use these and many other system commands as you operate a specific computer. We won't go into any more detail here. You will have documentation and reference manuals for the specific version of the operating system you will be using. Q.1 What is the heart of any computer system? Q.2 Which types of operating systems are the simplest and most common on microcomputers? Q.3 What types of operating systems let more than one user access the same resources at the same time? Q.4 Why is the availability of applications software for a particular operating system critical? Q.5 How is the applications software compatibility problem overcome?

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Data representation and communications

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Click here to order Electronic Components Online DATA REPRESENTATION AND COMMUNICATIONS LEARNING OBJECTIVES Upon completion of this chapter, you will be able to do the following: Explain data and how it is represented. Explain computer coding systems. Define a parity bit and what it is used for. Explain data storage concepts. Describe three storage access methods. Describe networks and data communications.

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INTRODUCTION One of the major problems we face in using a digital computer is communicating with it. We must have one or more ways of getting data into the computer to be processed. You learned in chapter 2 that there are several types of input devices that read data into a computer. But how does one prepare the data to be used as input? How do we convert human-readable documents into a computer-readable Order this form, and what type of input media do we use? If the data is to be used by another computer some information on CDdistance away, how do we transmit it? Well, as you probably suspect, there are several ways to Rom perform this conversion and transmission process, and that is the chapter of our discussion. DATA Data is a general term used to describe raw facts. To put it simply, data is nothing more than a collection of related elements or items, that when properly coded into some type of input medium, can be processed by a computer. Data items might include your service number, your name, your Order this paygrade, or any other fact. Until some meaning has been given to the data, nothing can really be information in determined about it; therefore, it remains data. When this data has been processed together with Print (Hardcopy). other facts, it then has meaning and it becomes information we can understand and properly use. DATA REPRESENTATION Data is represented by symbols. Symbols convey meaning only when understood. The symbol itself is not the information, but merely a representation of it. Symbol meaning is one of convention (fig. 4-

1).Symbols may convey one meaning to you and me, another meaning to others, and no meaning at all to those that do not know their significance. Data must be reduced to a set of symbols that the computer can read and interpret before there can be any communication with the computer. The first computers were designed to manipulate numbers to solve arithmetic problems. But as you can see in figure 4-1, we create, use, and manipulate many other symbols to represent facts in the world in which we live. We are fortunate that early computer experts soon realized the need to manipulate nonnumerical symbols as well. Manipulating these symbols is possible if an identifying code or coded number is assigned to the symbol to be stored and processed. Thus, the letters in a name such as ALBERT or CAROL can be represented by different codes, as can all special characters, such as #, (,), &, $, @, and yes, even the comma. The data to be represented is called source data. Figure 4-1. - Communications symbols.

SOURCE DATA Source data or raw data is typically written on some type of paper document, which we refer to as a source document. The data contained on the source document must be converted into a machinereadable form for processing either by direct or indirect means. The data may be entered directly into the computer in its original form; namely right from the source document on which it is recorded by way of magnetic ink characters, optically recognizable characters, or bar code recognition. Or the data on the documents may be entered indirectly on input media, such as punched cards, paper tape, magnetic tape, or magnetic disk. It may also be keyed directly into a computer from a keyboard. If you look at figure 4-2, you see a list of SERVMART items that have been typed on a preprinted form. To most people this is just another piece of paper; however, to the Storekeeper (SK) it is a source document to be used to provide input data to the computer. In this example, the SERVMART form deals with requisitioning supplies. The form could be sent to the data-entry department to be used as a source document. There the data-entry operator can key the data into or on whatever computer medium is to be used, according to a prescribed format. The data elements are numbered in the order they are to be keyed: (1) document identification, (2) stock number, (3) unit of issue, (4) quantity, and so on. You'll notice we need more than numbers, and that is where coding systems

come into play. Figure 4-2. - SERVMART shopping list (source document).

Q.1 What is a general term used to describe raw facts? Q.2 How is data represented? Q.3 What were the first computers designed to manipulate in order to solve arithmetic problems? Q.4 By what two means can the data contained on a source document be converted into a machinereadable form for processing? Q.5 What are some of the types of input media on which data may be indirectly entered?

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Book 23

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Click here to order Electronic Components Online Introduction to magnetic recording Prerequisites for magnetic recording Summary Answers

Magnetic tape Causes of magnetic tape failure Tape Reels and Tape Cartridges Handling, Storing, and packaging magnetic tape Summary Answers

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Magnetic tape recorder record and reproduce electronics Summary Answers

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Magnetic tape recording specifications Harmonic Distortion Flutter Summary Answers

Digital magnetic tape recording Digital magnetic tape recording encoding methods Summary Answers

Magnetic disk recording Fixed magnetic recording disks Recording digital data on magnetic disks Magnetic disk drive preventive maintenance Summary Answers

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Introduction to magnetic recording

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Click here to order Electronic Components Online INTRODUCTION TO MAGNETIC RECORDING LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. They serve as a preview of the information you are expected to learn in the chapter. The comprehension check questions placed within the text are based on the objectives. By successfully completing those questions and the associated NRTC, you show that you have met the objectives and have learned the information. The learning objectives for this chapter are listed below.

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After completing this chapter, you will be able to do the following: Describe the history and purpose of magnetic recording. State the prerequisites for magnetic recording. Describe a magnetic recording head, how it's constructed, and how it operates.

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INTRODUCTION Have you ever wondered how a whole album of your favorite music got onto one of those little cassette tapes? Or, what about computer floppy disks; have you ever wondered how they can hold 180 or more pages of typed text? The answer to both of these questions is magnetic recording. Magnetic recording devices seldom get much attention until they fail to work. But without magnetic recording, recording your favorite television show on a video cassette recorder would be impossible, portable tape players wouldn't exist, and you wouldn't be able to get money from an automated bank teller machine at two o'clock in the morning. Now what about the Navy? Could it operate without magnetic recording? The answer is definitely no. Without it: Computer programs and data would have to be stored on either paper cards or on rolls of paper tape. Both of these methods need a lot of storage space, and they take much longer to load into and out of the computer. There wouldn't be any movies to show or music to play on the ship's entertainment system when the ship is at sea and is out of range for television and radio reception. Intelligence-collection missions would be impossible since you couldn't store the collected signals for later analysis. As you can see, magnetic recording plays a very important part both in our Navy life and in our civilian life. HISTORY OF MAGNETIC RECORDERS

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In 1888, Oberlin Smith originated the idea of using permanent magnetic impressions to record sounds. Then in 1900, Vladeniar Poulsen brought Mr. Smith's dream to reality. At the Paris Exposition, he demonstrated a Telegraphone. It was a device that recorded sounds onto a steel wire. Although everyone thought it was a great idea, they didn't think it would succeed since you had to use an earphone to hear what was recorded. It wasn't until 1925, when electronic amplifiers were developed, that magnetic recording started to receive the attention it deserved. The best magnetic recording is the one that produces an output signal identical to the input signal. It didn't take long to realize that the magnetism generated during the recording process didn't vary directly to the current which caused it. This is because there's a step in the magnetism curve where it crosses the zero point and changes polarity. This step causes the output signal to be distorted when compared with the input signal. Figure 1-1 shows this step. Figure 1-1. - Magnetic recording without bias voltage.

In 1907, Mr. Poulsen discovered a solution to this problem. He discovered dc bias. He found that if a fixed dc voltage were added to the input signal, it moved the input signal away from the step in the magnetism curve. This prevented the input signal from crossing the zero-point of the magnetism curve. The result is an output signal exactly like the input signal. Figure 1-2 shows this process. Figure 1-2. - Magnetic recording with dc bias voltage.

Unfortunately, dc bias had its problems. Since only a small portion of the magnetism curve was straight enough to use, the output signal was weak compared with the natural hiss of the unmagnetized tape passing the playback head. This is commonly called poor signal-to-noise ratio (SNR). We'll explain SNR in more detail later. From the beginning, the U.S. Naval Research Laboratories (NRL) saw great potential in magnetic recording. They were especially interested in using it to transmit telegraph signals at high speed. After electronic amplifiers were invented around 1925, W.L. Carlson and G.W. Carpenter at the NRL made the next important magnetic recording discovery. They found that adding an ac bias voltage to the input signal instead of a fixed dc bias voltage would reproduce a stronger output signal greatly improve the signal-tonoise ratio

greatly reduce the natural tape hiss that was so common with dc bias To make ac bias work, they used an ac frequency for the bias voltage that was well above what could be heard, and a level that placed the original input signal away from both steps in the magnetism curve. This resulted in two undistorted output signals that could be combined into one strong output. See figure 1-3. Figure 1-3. - Magnetic recording with ac bias voltage.

Until 1935, all magnetic recording was on steel wire. Then, at the 1935 German Annual Radio Exposition in Berlin, Fritz Pfleumer demonstrated his Magnetophone. It used a cellulose acetate tape coated with soft iron powder. The Magnetophone and its "paper" tapes were used until 1947 when the 3M Company introduced the first plastic-based magnetic tape.

In 1956, IBM introduced the next major contribution to magnetic recording - the hard disk drive. The disk was a 24-inch solid metal platter and stored 4.4 megabytes of information. Later, in 1963, IBM reduced the platter size and introduced a 14-inch hard disk drive. Until 1966, all hard disk drives were "fixed" drives. Their platters couldn't be removed. Then in 1966, IBM introduced the first removable-pack hard disk drive. It also used a 14-inch solid metal platter. In 1971, magnetic tape became popular again when the 3M Company introduced the first 1/4-inch magnetic tape cartridge and tape drive. In that same year, IBM invented the 8-inch floppy disk and disk drive. It used a flexible 8-inch platter of the same material as magnetic tape. Its main goal was to replace punched cards as a program-loading device. The next contribution to magnetic recording literally started the personal computer (PC) revolution. In 1980, a little-known company named Seagate Technology invented the 5-1/4-inch floppy disk drive. Without it, PCs as we know them today would not exist. From then on, it was all downhill. Magnetic tape became more sophisticated. Floppy disks and disk drives became smaller, while their capacities grew bigger. And hard disk capacities just went through the roof. All of the major hurdles affecting magnetic recording had been successfully cleared, and it was just a matter of refining both its methods and materials. Q.1 Why did the early inventors of magnetic recording find it necessary to add a fixed dc bias to the input signal? Q.2 How does dc bias added to the input signal correct the distortion in the output signal? Q.3 Why does adding dc vice ac bias voltage to the input signal result in a poor signal-to-noise ratio (SNR)? Q.4 What are three advantages of adding an ac bias voltage to the input signal instead of adding a fixed dc bias voltage? Q.5 Why does using ac vice dc bias voltage result in a stronger

output signal?

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Magnetic tape

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Click here to order Electronic Components Online MAGNETIC TAPE LEARNING OBJECTIVES After completing this chapter, you'll be able to do the following: Describe the physical properties of magnetic tape in terms of: The Three Basic Materials Used To Make magnetic Tape. The function of the magnetic tape's base material, oxide coating, and binder glue. Describe the two types of magnetic recording tape. Describe the following types of tape errors and their effects on magnetic tape recording: signal dropout, noise, skew, and level.

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Describe the following causes of magnetic tape failure: normal wear, accidental damage, environmental damage, and winding errors. Describe the purpose and makeup of tape reels and tape cartridges. Describe the two methods for erasing magnetic tape, the characteristics of automatic and manual tape degaussers, and the procedures for degaussing magnetic tape. Describe the proper procedures for handling, storing, and packaging magnetic tape, tape reels, and tape cartridges. PHYSICAL PROPERTIES OF MAGNETIC TAPE The three basic materials used to make magnetic tape are (1) the base material, (2) the coating of magnetic oxide particles, and (3) the glue to bind the oxide particles onto the base material. See figure 2-1. Figure 2-1. - Magnetic tape construction.

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BASE MATERIAL The base material for magnetic tape is made of either plastic or metal. Plastic tape is used more than metal tape because it's very flexible, it resists mildew and fungus, and it's very stable at high temperatures and humidity. OXIDE COATING Oxide particles that can be magnetized are coated onto the base material. The most common magnetic particles used are either gamma ferric oxide or chromium dioxide. It's very important that these magnetic particles are uniform in size. If they're not, the tape's surface will be abrasive and will reduce the life of the recorder's magnetic heads. An ideal magnetic particle is needle-shaped. It's actual size depends on the frequency of the signal to be recorded. Generally, long particles are used to record long wavelength signals (lowfrequency signals), and short particles are used to record short wavelength signals (high-frequency signals). GLUE

The glue used to bond the oxide particles to the base material is usually an organic resin. It must be strong enough to hold the oxide particles to the base material, yet be flexible enough not to peel or crack. TYPES OF MAGNETIC RECORDING TAPE There are two basic types of magnetic recording tape in common use: analog and digital. Analog magnetic tape is used to record, store, and reproduce audio and instrumentation type signals. These signals are usually in a frequency band from very-low frequency (VLF) to 2.5 MHz. Digital magnetic tape is used to record, store, and reproduce computer programs and data. It's base material thickness is about 50 percent thicker than analog magnetic tape. This allows the digital tape to withstand the more strenuous starts and stops associated with digital magnetic recorder search, read, and write functions. Digital magnetic tape is also held to much stricter quality control standards. It's important not to have any blemishes or coating flaws on the tape's surface. Because, if you lost one digital data bit, your computer program or data would be bad. In contrast, losing one microsecond of an analog signal is not nearly as critical. Q.1 Magnetic tape is made of what three basic materials? Q.2 Why is plastic magnetic tape used more than metal tape? Q.3 Which of the two types of magnetic tape is used to record audio and instrumentation type signals in the VLF to 2.5MHz frequency range? Q.4 What type of magnetic tape is used to record computer programs and data, and what are the additional thickness and quality standards for this type of tape? TAPE ERRORS AND THEIR EFFECTS Four types of tape errors that will degrade the performance of a

magnetic recording system are signal dropout, noise, skew, and level (signal amplitude changes). DROPOUT ERRORS Signal dropout is the most common and the most serious type of tape error. It's a temporary, sharp drop (50% or more) in signal strength caused by either contaminates on the magnetic tape or by missing oxide coating on part of the tape. During recording and playback, the oxide particles on the tape can flake off and stick to the recorder's guides, rollers, and heads. After collecting for awhile, the oxide deposits (now oxide lumps) break loose and stick to the magnetic tape. As the tape with the lumps passes over the head, the lumps get between the tape and the head and lift the tape away from the head. This causes the signal dropouts. Although oxide lumps cause most signal dropouts, remember that any contaminate (such as dust, lint or oil) that gets between the tape and the head can cause signal dropouts. NOISE ERRORS Noise errors are unwanted signals that appear when no signal should appear. They're usually caused by a cut or a scratch on the magnetic tape. It's the lack of oxide particles at the cut or the scratch that causes the noise error. SKEW ERRORS Skew errors only occur on multi-track magnetic tape recorders. The term skew describes the time differences that occur between individual tracks of a single magnetic head when the multi-track tape isn't properly aligned with the magnetic head. There are two types of skew errors: fixed and dynamic. Fixed skew happens when properly aligned magnetic tape passes an improperly aligned magnetic head. Dynamic skew happens when misaligned tape passes a properly aligned head. This type of skew is usually caused by one or more of the following: A misaligned or worn-out tape transport system.

A stretched or warped magnetic tape. A magnetic tape that is improperly wound on a reel. LEVEL ERRORS Magnetic tape is manufactured to have a specified output signal level (plus or minus some degree of error). Level errors happen when the actual output signal level either drops or rises to a level outside the expected range. For example, if a magnetic tape is rated for 10 volts ( +/-10%), any output signal level below 9 volts or above 11 volts is a level error. Level errors are caused by an uneven oxide coating on the magnetic tape. This can come from either the original manufacturing process or from normal wear and tear. Some causes of level errors are permanent and cannot be removed by any means. For example, a crease in the tape, a hole in the oxide, or a damaged edge. Other causes of level errors are removable and may be cleaned off the tape. For example, oxide flakes or clumps, metallic particles, or dirt are removable. Q.5 What are four types of tape errors that can degrade a magnetic recording system's performance? Q.6 What are signal dropouts, and what are two tape defects that can cause signal dropouts? Q.7 What is the most common and most serious type of signal dropout? Q.8 You see a build-up of dust and lint on the take-up reel of a tape recorder. This can cause which of the four types of tape errors? Q.9 What type of tape error causes noise to appear on the tape when no signal should appear? What causes this type of tape error? Q.10 The multi-track tape recorder in your computer system has a fixed skew error. What does this mean and what is the probable cause? Q.11 Some tapes you are using may have level errors. What does

this mean and what is the cause?

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Magnetic tape recorder record and reproduce electronics

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Click here to order Electronic Components Online MAGNETIC TAPE RECORDER RECORD AND REPRODUCE ELECTRONICS LEARNING OBJECTIVES After completing this chapter, you'll be able to do the following: State the two types of record and reproduce electronics used on magnetic tape recorders. Describe the purpose and function of direct Join Integrated record electronics and the four main parts of a Publishing's recorder's direct record component. Discussion Group Describe the purpose and function of direct reproduce electronics and the three main parts of a recorder's direct reproduce component. Describe the purpose and function of frequency modulation (FM) record electronics and the three main parts of a recorder's FM record component. Describe the purpose and function of FM Order this reproduce electronics and the four main parts of information on CDa recorder's FM record component. Rom

RECORD AND REPRODUCE ELECTRONICS There are two ways to record and reproduce analog signals. The first way is direct record. It's also called amplitude modulation (AM) electronics. The second way is frequency modulation (FM). Even though direct record and reproduce circuits are much different from FM record and reproduce electronics, they both share the same two very important jobs. They both must: Take an input signal, process it as needed, and then send it to the record magnetic head for reproduction. Take the reproduced signal from the reproduce magnetic head, process it as needed, and output it for listening or analysis. DIRECT RECORD ELECTRONICS

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Direct record electronics record input signals onto magnetic media just as the signals appeared at the recorder's input. The only processing an input signal receives is the adding of a bias signal. The added bias signal makes sure the signal stays away from the steps of the magnetism curve. Figure 5-1 shows a basic block diagram of a recorder's direct record electronics. Figure 5-1. - Direct record electronics.

Direct record electronics has four main parts: Input pre-amplifier circuit. This circuit takes the input signal, amplifies it, and sends it to the summing network. It also matches the impedance between the source of the input signal and the magnetic tape recorder. Bias source. This circuit generates the high-frequency bias signal and sends it to the summing network. Normally, the frequency of the bias signal will be five to ten times higher than the highest frequency the tape recorder can record. Summing network. This network takes the input signal and the bias signal, mixes them, and sends the resulting signal to the head driver circuit. Head driver circuit. This circuit takes the signal from the summing network, amplifies it, and sends it to the record head for recording. DIRECT REPRODUCE ELECTRONICS Direct reproduce electronics amplify the very weak input signals from the reproduce head, and send them out for listening or analysis, as needed. Figure 5-2 shows a basic block diagram of direct reproduce electronics. Figure 5-2. - Direct reproduce electronics.

Direct reproduce electronics consists of three main parts: Pre-amplifier circuit.

This circuit takes the very weak reproduced signal from the reproduce head and (a) amplifies the signal, (b) removes any bias signal that was used during the recording process, and (c) sends the signal to the equalization and phase correction circuit. Equalization and phase correction circuit. This circuit takes the pre-amplified signal and fixes any Frequency response problems that the reproduce magnetic head may have caused. To better understand this, look at the voltage versus Frequency response graph in figure 5-3. The top of the graph shows the input signal that comes from the pre-amplifier and the bottom shows the equalization signal generated by the equalization circuit. In the top part of the graph, note how the output voltage level varies as the frequency of the signal varies. This isn't good. A good output voltage level is one that remains constant as the frequency changes. The equalization signal corrects this problem. Notice that when the input signal and the equalization signal are combined they cancel each other out. This allows a nice flat (voltage versus frequency) output signal to go to the output amplifier circuit. Figure 5-3. - Equalization process.

Output amplifier circuit. This circuit takes the signal from the equalization and phase correction circuit and amplifies it for output. It also matches the magnetic recorder's impedance to the output device that is used for listening or recording. FM RECORD ELECTRONICS FM record electronics process signals to be recorded differently than direct record electronics. Instead of recording the input signal just as it appears at the recorder's input, FM record electronics use the

input signal to vary (modulate) the carrier frequency of a record oscillator. The frequency modulated output signal of the record oscillator then becomes the signal that's actually recorded onto the magnetic media. Figure 5-4 shows a block diagram of the FM record electronics. Figure 5-4. - FM record electronics.

FM record electronics consist of three main parts: Input pre-amplifier circuit. This circuit does two things: (a) it serves as an impedance matcher between the signal source and the magnetic recorder, and (b) it pre-amplifies the input signal. Record oscillator circuit. This circuit generates a carrier signal onto which the input signal will be modulated. The input signal is used to vary (frequency modulate) the carrier signal. This is how the input signal gets frequency modulated onto the carrier signal. The output of this circuit is the frequency-modulated carrier signal. The center frequency of the carrier depends on two things: (a) the bandwidth of the signal you're recording, and (b) the media onto which you're recording. For magnetic tape, the carrier frequency can be as low as 1.688 kHz for an operating tape speed of 17/8 inches per second, and as high as 900 kHz for 120 inches per second. Head driver circuit. This circuit takes the frequency-modulated output from the record oscillator circuit, amplifies it, and sends it to the magnetic head for recording. The output level of this circuit is set to be just below the magnetic saturation point of the magnetic media. FM REPRODUCE ELECTRONICS The FM reproduce electronics work just like direct reproduce electronics, with one exception. FM reproduce electronics must first demodulate the original input signal from the carrier frequency before the intelligence can be sent to the output device for listening or analysis. Figure 5-5 shows a block diagram of the FM reproduce electronics. Figure 5-5. - FM reproduce electronics.

FM reproduce electronics consist of four main parts: Pre-amplifier circuit. This circuit takes the frequency modulated carrier frequency from the reproduce head and amplifies it.

Limiter/demodulator circuit. This circuit takes the output of the preamplifier, stabilizes the amplitude level, and demodulates the signal intelligence from the carrier frequency. Low-pass filter circuit. This circuit takes the signal intelligence from the limiter/demodulator circuit and cleans up any noise or left over carrier signal. Output amplifier circuit. This circuit takes the output from the low-pass filter and amplifies it for output. It also matches the impedance of the magnetic recorder to the output device. Q.1 What two types of record and reproduce electronics are used by magnetic tape recorders? Q.2 The head driver circuit in a tape recorder's direct record electronics component (figure 5-1) performs what function? Q.3 The equalization and phase correction circuit in a tape recorder's direct reproduce electronics (figure 5-2) performs what function? Q.4 How do FM record electronics differ from AM (direct record) electronics? Q.5 The head driver circuit of a tape recorder's FM record electronics (figure 5-4)performs what function? Q.6 What is the major difference between direct reproduce electronics and FM reproduce electronics?

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Magnetic tape recording specifications

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MAGNETIC TAPE RECORDING SPECIFICATIONS LEARNING OBJECTIVES After completing this chapter, you'll be able to do the following: Define the seven most common magnetic tape recording specifications. Describe a magnetic tape recorder's signal-tonoise ratio (SNR) specification, how it's measured, and why a high SNR is important. Describe a tape recorder/reproducer's Join Integrated frequency-response specification, how it's Publishing's measured, and the three factors that can limit or Discussion Group degrade a recorder's Frequency response. Describe a tape recorder's harmonic-distortion specification, how it's measured, and how a recorder produces harmonic distortion. Describe a recorder's phase-response specification, how it's measured, and why good phase response is important. Describe a recorder's flutter specification, how Order this it's measured, and why minimal flutter is information on CDimportant. Rom Describe a recorder's time-base error (TBE) specification, how it's measured, and why minimal TBE is important. Describe a multi-track magnetic tape recorder's skew specification, how it's measured, and why minimal skew is important. INTRODUCTION Have you ever gone to a store to buy a magnetic tape recorder? Were you able to decide which of the displayed models was the good one to buy? Or, did you instead end up confused when the salesperson started spouting words like SNR, flutter, and bandwidth. If so, you weren't alone.

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This chapter (1) defines the seven most common magnetic tape recording specifications, (2) describes their effect on the magnetic recording process, and (3) tells how to measure each specification. The remaining paragraphs in this chapter describe each of the following magnetic tape recorder specifications: Signal-to-noise ratio Frequency response Harmonic distortion Phase response Flutter Time-base error Skew SIGNAL-TO-NOISE RATIO Signal-to-noise ratio (SNR) is the first magnetic tape recorder specification we'll describe. It's one of the most important specifications of a magnetic tape recorder. SIGNAL-TO-NOISE RATIO DEFINITION The SNR is the ratio of the normal signal level to the magnetic tape recorder's own noise level. It's measured in decibels (dB). In other words, the higher the SNR of a magnetic tape recorder, the wider the range of input signals it can properly record and reproduce. The noise part of the signal-to-noise ratio is generated in the magnetic tape recorder itself. Although noise can be generated by almost any part of the magnetic tape recorder, it's usually generated by either the magnetic heads or the magnetic tape. SIGNAL-TO-NOISE RATIO MEASUREMENT You can measure the SNR with a vacuum tube voltmeter (VTVM) and a signal generator. The equipment set up for measuring the SNR is shown in figure 6-1. After equipment setup, measure the SNR as follows: Figure 6-1. - Test equipment setup for measuring signal-to-noise ratio.

Set the signal generator to inject a test signal into the tape recorder. The technical manual for the tape recorder you're testing will tell you how to set up the signal generator. While recording and reproducing, set the output level of the tape recorder's reproduce electronics to a level that displays 0-dB reference on the VTVM. Disconnect the signal generator. The voltage displayed on the VTVM will drop from 0-dB to some negative dB level. This level is the magnetic tape recorder's SNR. There are two things you should know when reading SNR specifications in technical manuals, equipment brochures, etc.

First, the SNR is stated in three ways. You'll see it as (1) root-mean-square (RMS) signal-to-RMS noise, (2) peak-to-peak signal-to-RMS noise, or (3) peak signal-to-RMS noise. If the SNR specification doesn't state which way it was measured, you could be mislead. For example, a 25-dB RMS SNR is equal to a 34-dB peak-to-peak signal-to-RMS noise ratio, or a 28-dB peak signal-to-RMS noise ratio. Second, all SNR specifications should include the record level that was used. Since the SNR varies directly to the record level, you could be mislead by a SNR that doesn't include the record level of the test signal used when the SNR was measured. Frequency response The frequency-response specification of a magnetic tape recorder is sometimes called the bandwidth. A typical frequency-response specification might read within + / - 3 db from 100 Hz to 100 kHz at 60 ips. This means the magnetic tape recorder is capable of recording all frequencies between 100 Hz and 100 kHz at 60 inches per second (ips) without varying the output amplitude more than 3 dB. FREQUENCY-RESPONSE DEFINITION Frequency response is the amplitude variation with frequency over a specified bandwidth. Let's convert this to plain English. The frequency-response specification of a magnetic tape recorder tells you the range of frequencies the recorder can effectively record and reproduce. What exactly does the word effectively mean? That's hard to say because Frequency response varies from recorder to recorder, and from manufacturer to manufacturer. But a good rule of thumb is that an effective frequencyresponse specification tells the lowest and highest frequencies that the recorder can record and reproduce with no more than + / - 3-dB difference in output amplitude. FREQUENCY-RESPONSE MEASUREMENT The equipment setup for measuring the Frequency response of a magnetic tape recorder is the same as for measuring the signal-to-noise ratio. It's shown in figure 6-1. After equipment setup, measure a recorder's Frequency response as follows: Set the signal generator to output a test signal. The technical manual for the tape recorder will tell you how. Set the recorder's reproduce electronics output level to a 0-dB reference on the VTVM. While recording at a set speed, vary the frequency of the signal generator from the lowest to highest frequency you're checking. Make sure that the output level of the signal generator stays the same. As you sweep through the frequencies, look at the VTVM. You'll see the amplitude rise and fall as you vary the output frequency of the signal generator. As you approach the lowest and the highest frequencies that the magnetic tape recorder can effectively record, you'll see the VTVM drop to less than - 3 dB. This determines the lower and upper limits of the frequency-response specification for that magnetic tape recorder. FREQUENCY-RESPONSE LIMITING FACTORS

Four factors that can limit or degrade the Frequency response of magnetic tape recorders are: A too-high or too-low bias signal level setting for the record head. An improper reproduce head. An improper tape transport speed. A poor magnetic tape-to-head contact. The magnetic record head transforms the electrical signal into a magnetic field for recording onto magnetic tape. If the bias signal level is set to high, you might erase the higher frequencies. If it's too low, you'll get excessive tape distortion. The reproduce head transforms the magnetic field from the magnetic tape back into an electrical signal. As explained in chapters 3 and 5, the head gap of a recorder's reproduce head and the operating speed of the magnetic tape transport determine the wavelength of the reproduce head. The wavelength determines the center frequency of a recorder's frequency-response specification. Once you pass this center frequency, both below and above, the output voltage level of the recorder's reproduce head will decrease. Figure 6-2 shows this. This is why the equalization circuits described in chapter 5, figure 53,are used. Figure 6-2. - Frequency response of a reproduce head.

Poor tape-to-head contact can seriously degrade the record and reproduce process. Magnetic heads are designed to reduce tape-to-head gap as much as possible. A tape-to-head gap is extremely degrading at the higher frequencies. Figure 6-3 shows this. Note how a .1-mil gap causes only a small loss at 10 kHz. But, at 1 MHz, it causes a 46-dB loss! You must maintain tape-to-head contact. Keeping the magnetic tape recorder heads and tape transport clean is the best way to do this. Figure 6-3. - Effects of poor tape-to-head contact.

Q.1 Two tape recorders have signal-to-noise ratios (SNRs) of 25-dB RMS and 35-dB RMS respectively. Which of the SNRs can record and reproduce the widest range of input signals and why? Q.2 You plan to measure your tape recorder's SNR. What test equipment will you need? Q.3 Technical manuals for tape recorders can state the SNR in what three different ways? Q.4 The frequency-response specification of your tape recorder reads within +/- 3 dB from 150 Hz to 150 kHz at 60 ips. What does this mean? Q.5 While measuring Frequency response, as the signal generator approaches the lowest and highest frequency the recorder can effectively record, the VTVM reading drops to less than - 3 dB. What does this indicate? Q.6 List four factors that can degrade the Frequency response of magnetic tape recorders.

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Digital magnetic tape recording

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Click here to order Electronic Components Online DIGITAL MAGNETIC TAPE RECORDING LEARNING OBJECTIVES After completing this chapter, you'll be able to do the following: Describe the characteristics of digital magnetic tape recording and the difference between analog and digital recording. Describe each of the three formats for digital Join Integrated magnetic tape recording (serial, parallel, and Publishing's serial-parallel). Discussion Group Define the following terms as they apply to digital magnetic tape recording: mark, space, bitcell period, packing density, and bit-error rate (BER). Describe the eight most common methods for encoding digital data onto magnetic tape. Describe the characteristics and use of the following categories of digital magnetic tape Order this recorders: (1) computer-compatible, (2) information on CDtelemetry, and (3) instrumentation. Rom INTRODUCTION TO DIGITAL MAGNETIC TAPE RECORDING This chapter introduces you to digital magnetic tape recording. It describes (1) the three formats for digital magnetic tape recording, (2) the eight methods of encoding digital data onto magnetic tape, and (3) the configuration differences between the three types of digital tape recorders. Until now, you've learned about magnetic tape recording from an analog point-of-view. That is, the signal you record and reproduce is the actual analog input signal waveform. In digital magnetic tape recording, the signal you record and reproduce is, instead, a series of digital pulses. These pulses are called binary ones and zeros. These ones and zeros can represent one of three types of data: (1) data used by digital computers, (2) pulsed square-wave signals, or (3) digitized analog waveforms. The digital magnetic tape recording process stores data onto tape by magnetizing the tape to its saturation point in one of two possible polarities: positive (+) or negative (-). The saturation point of

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magnetic tape is the point where the magnetic tape is magnetized as much as it can be. DIGITAL MAGNETIC TAPE RECORDING FORMATS There are three digital magnetic tape recording formats: serial, parallel, and serial-parallel. Each of these is described below. Figure 7-1 shows each of the three formats as they apply to recording an eight-bit binary data stream. SERIAL DIGITAL MAGNETIC TAPE RECORDING FORMAT This is the simplest of the three digital magnetic tape recording formats. It's usually used when recording instrumentation or telemetry data. In this format, the incoming data pulses are recorded onto a single recorder track of the magnetic tape in a single, continuous stream. Figure 7-1A shows how this looks. Figure 7-1A. - Digital magnetic tape recording formats.

PARALLEL DIGITAL MAGNETIC TAPE RECORDING FORMAT In this format, the incoming data pulses come in on more than one input channel and are recorded sideby-side onto more than one tape track. The data pulses across the width of the magnetic tape are related to each other. Figure 7-1B shows how this looks. This format is usually used to store computer data. Figure 7-1B. - Digital magnetic tape recording formats.

SERIAL-PARALLEL DIGITAL MAGNETIC TAPE RECORDING FORMAT This format is more complex. It takes a serial input stream of data pulses, breaks them up, and records them on more than one recorder track. When the tape is reproduced, the recorder recombines the broken-apart data into its original form. Figure 7-1C shows how this looks. The serial-parallel format is usually used in instrumentation recording when the input data rate is high. Figure 7-1C. - Digital magnetic tape recording formats.

DIGITAL MAGNETIC TAPE RECORDING DEFINITIONS Before we describe the methods for encoding digital data onto magnetic tape, let's define the following terms: Mark: The voltage state of a digital one (1) data bit. It's also sometimes called true. Space: The voltage state of a digital zero (0) data bit. It's also sometimes called false.

Bit-cell period: The time occupied by a single digital bit. Packing density: The number of bits per fixed length of magnetic tape per track. There are three categories of packing density: Low density - 200 to 1,000 bits per inch (bpi). Medium density - 1,000 to 8,000 bpi. High density - 8,000 to 33,000 bpi. Bit-error rate: The number of bits within a finite series of bits that will be reproduced incorrectly. Q.1 In digital magnetic tape recording, the series of recorded digital pulses can represent what three types of data? Q.2 What three formats are used for digital magnetic tape recording? Q.3 What format of digital tape recording is normally used to store computer data? Q.4 What format of digital tape recording takes a serial input stream of data pulses, breaks them up, and records them on more than one data track? Q.5 What format of digital tape recording is normally used to record instrumentation or telemetry data?

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Magnetic disk recording

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Click here to order Electronic Components Online MAGNETIC DISK RECORDING LEARNING OBJECTIVES After completing this chapter, you'll be able to do the following: Describe how flexible (floppy) disks are constructed; how data is organized on them; how they are handled, stored, and shipped; and how they are erased. Join Integrated Describe how fixed (hard) disks are Publishing's constructed; how data is organized on Discussion Group them; how they are handled, stored, and shipped; and how they are erased. Describe each of the following methods for recording (encoding) digital data onto magnetic disks: frequency-modulation encoding, modified frequencymodulation encoding, and run lengthlimited encoding. Order this Describe the characteristics of floppy information on CDdisk drive transports and hard disk drive Rom transports and describe the preventive maintenance requirements of each type. Describe the following parts of the electronics component of a magnetic disk drive: control electronics, write/read electronics, and interface electronics. Order this Describe the five most common types of information in disk drive interface electronics.

Define the following magnetic disk recording specifications: seek time, latency period, access time, interleave factor, transfer rate, and recording density. INTRODUCTION Magnetic disk recording was invented by International Business Machines (IBM) in 1956. It was developed to allow mainframe computers to store large amounts of computer programs and data. This new technology eventually led to what's now known as the computer revolution. This chapter introduces you to the following aspects of magnetic disk recording: Disk recording mediums Disk recording methods Disk drive transports Disk drive electronics Disk recording specifications MAGNETIC DISK RECORDING MEDIUMS There are two types of disk recording mediums: flexible diskettes and fixed (hard) disks. The following paragraphs describe (1) how flexible and fixed disks are made; (2) how data is organized on them; (3) how to handle, store, and ship them; (4) and how to erase them. FLEXIBLE MAGNETIC RECORDING DISKETTES Flexible diskettes, or floppy disks as they're more commonly called, are inexpensive, flexible, and portable magnetic storage mediums. They have the following characteristics. Floppy Disk Construction Floppy disks are made of round plastic disks coated with magnetic oxide particles. The disks are enclosed in a plastic jacket which protects the magnetic recording surface from damage. Floppy disks come in three sizes: 8 inch, 5 1/4 inch, and 3 1/2 inch. Figure 8-1 shows each size. All disk sizes can either be single-sided or double-sided. Single-sided disks store data on only one side of the disk; double-sided disks store data on both sides. Figure 8-1. - Floppy disk construction.

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When floppy disks are manufactured, the magnetic oxide coating is applied to both sides. Each disk is then checked for errors. Disks certified as single-sided, are checked on only one side; disks certified as double-sided are checked on both sides. Floppy disks are also classified by how much data they can store. This is called a disk's density. There are three levels of floppy disk density: singledensity, double-density , and high-density. Some of the more common types of floppy disks and their storage capacity are listed below: TYPE OF FLOPPY DISK

STORAGE CAPACITY

5-1/4" double-sided, double-density 360,000 bytes 5-1/4" double-sided, high-density

1,200,000 bytes

3-1/2" double-sided, double-density 720,000 bytes 3-1/2" double-sided, high-density

1,400,000 bytes

Floppy Disk Data Organization Data is stored on a floppy disk in circular tracks. Figure 8-2 shows a circular track on a floppy disk. The total number of tracks on a floppy disk is permanently set by (1) the

number of steps the disk drive's magnetic head stepper motor can make, and (2) whether the disk drive has a magnetic head for one or both surfaces of the floppy disk. These two things will also determine the type of floppy disk that's needed. Each type of disk is rated with a number that represents how many tracks per inch (TPI) it can hold. Some common track capacities are 40, 48, 80, and 96 TPI. Figure 8-2. - Tracks and sectors of a magnetic disk.

Each track of a floppy disk is broken up into arcs called sectors. A disk is sectored just as you'd slice an apple pie. Figure 8-2 shows the sectors of a floppy disk. How many slices are made? That depends on who made the disk and in what host computer the disk is used. There are two methods for sectoring a floppy disk: Hard Sectoring: This method sectors the disk physically. The disk itself will have marks or sensor holes on it that the floppy disk drive hardware can detect. This method is seldom used today. Soft sectoring: This method sectors the disk logically. The computer software determines the sector size and placement, and then slices the disk into sectors by writing codes on the disk. This is called formatting or initializing a floppy disk. During formatting, if the computer software locates a bad spot on the disk, it locks it out to prevent the bad spot from being used. Soft sectoring is by far the most popular method of sectoring a floppy disk.

Once a floppy disk is formatted, the computer uses the disk's side number, a track number, and a sector number (together) as an address. It's this address that locates where on the disk the computer will store the data. Floppy Disk Handling, Storage, and Shipping Floppy disks hold a lot of data. Even disks with only a 360,000-byte storage capacity can hold 180 pages of data! That's why it's important to handle, store, and ship floppy disks properly. One hundred and eighty pages of data is a lot of data to retype just because of carelessness. Before we get into disk handling and storage procedures, let's first learn about head-todisk contact. Do you remember reading in chapter 2 that the quality of magnetic tape recording is seriously degraded when dust, dirt, or other contaminates get between the magnetic head and the tape? Well, the same is true for magnetic disk recording. In fact, head-to-disk contact is extremely important with floppy disks. This is because floppy disk drives, unlike magnetic tape drives, spin at very high speeds - 300 to 600 revolutions-per-minute (RPM). If anything gets between the head and the recording surface, you can lose data, or even worse, you can damage the magnetic head and the disk's recording surface. Figure 8-3 shows the size relationship between a disk drive's magnetic head, the disk recording surface, and some common contaminants. Figure 8-3. - Size relationship of distance between head and disk to contaminants.

You must handle, store, and ship floppy disks with great care if you want them to stay in good condition. Here's some specific precautions you should take:

DO always store 8" and 5-1/4" floppy disks in their envelopes when not in use. Dirt, dust, etc., can get on the recording surface through the magnetic head read/write access hole if you leave it exposed for any length of time. DO always write on a floppy disk label first, and then place the label on the disk. NEVER write directly on a floppy disk. If you absolutely must write on a disk, use a felt-tip marker. DO hold floppy disks by their outside corners only. DO NOT bend them. And NEVER, NEVER paper clip them to anything, or anything to them. DO always store floppy disks in an upright position. Laying them on their side can cause them to warp. DO always keep floppy disks away from food, liquids, and cigarette smoke. All of these can easily damage floppy disks. DO always ship floppy disks in appropriate shipping containers. When shipping only a few disks, use the specially designed cardboard shipping envelopes. If you must ship a large number of disks, make sure the box you use is sturdy enough to protect the disks from damage. A good rule of thumb is to use a shipping box that allows you to place 2 inches of packing material around the disks. DO NOT touch any exposed recording surfaces. Something as simple as a fingerprint can destroy the data on a floppy disk. DO NOT expose a floppy disk to magnetic fields. Telephones, magnetic copy holders, printers, and other electronic equipment generate magnetic fields that can destroy the data on a floppy disk. DO NOT expose floppy disks to extreme heat or cold. Floppy disks will last longer if they're stored in an environment that stays around 70-80 degrees Farenheit and 30-60 percent relative humidity.

Floppy Disk Erasing There are two ways to erase a floppy disk: (1) degauss it and then reformat it, or (2) just reformat it. The process for degaussing floppy disks is the same as for degaussing magnetic tape. Refer back to chapter 2 for the details on this. If the floppy disks were used to store classified, or unclassified but sensitive information, they can't be de-classified by erasing them. This is because, with the right equipment and software, the data that was on the disk can be reconstructed. Floppy disks are cheap and easy to replace. If you can't re-use the floppy disks to store other classified data, just destroy them, using the procedures in OPNAVINST 5510.1, DON Information and Personnel Security Program Regulation. Q.1 Floppy disks are manufactured in what three sizes? Q.2 What type of floppy disk is made to store data on both sides of the disk? Q.3 What are the three levels of floppy disk density? Q.4 What is the storage capacity of a 5-1/4" double-sided, high-density floppy disk? Q.5 The floppy disks you are using have a rating of 96 TPI. What does this mean?

Q.6 The process of formatting a floppy disk is called what type of sectoring? Q.7 What three components determine the address that locates where on a floppy disk the computer will store the data? Q.8 Why should you always store floppy disks in their envelopes? Q.9 Why should you never place floppy disks near telephones or other electronic equipments that generate magnetic fields? Q.10 What are the two ways to erase floppy disks?

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Click here to order Fiber Optic Products Online Background on fiber optics Fiber optic data links History of fiber optic technology Fiber optic systems Advantages and disadvantages of fiber optics Summary Answers Fiber optic concepts Propagation of light Properties of light Reflection of light Refraction of light Diffusion of light Absorption of light Basic optical-material properties Basic structure of an optical fiber Propagation of light along a fiber Mode Theory Optical fiber types Multimode Fibers Properties of optical transmission Attenuation Dispersion Summary Answers

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Optical fibers and cables Multimode step-index fiber Multimode graded-index fiber Single mode step-index fibers Single mode graded-index fibers Fabrication of optical fibers Optic cables Cable strength and support members Cable designs Summary Answers Optic splice, connector, and coupler Optical fiber coupling loss Reflection losses Fiber end preparation Fiber mismatches Fiber optic splices Mechanical splices Fusion splicing Multifiber splicing Fiber optic connectors Military connectors Fiber optic couplers Summary Answers Fiber optic measurement techniques Laboratory measurements Cutoff Wavelength Bandwidth Chromatic Dispersion Fiber Geometry Core Diameter Numerical Aperture Return Loss and Reflectance Field measurements Optical Time-Domain Reflectometry Power Meter Summary Answers

Optical sources and fiber optic transmitters Optical source properties Semiconductor light-emitting diodes and laser diodes Semiconductor material and device operating principles Light-emitting diodes Laser diodes Superluminescent diodes Fiber optic transmitters Fiber optic transmitter packages Summary Answers Optical detectors and fiber optic receivers Optical detectors Semiconductor material and device properties Response Time Avalanche photodiodes Fiber optic receivers Receiver noise Receiver design Fiber optic receiver packages Summary Answers Fiber optic links Link classification Digital transmission Analog transmission System design System installation Summary Answers

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Background on fiber optics

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Click here to order Fiber Optic Products Online BACKGROUND ON FIBER OPTICS LEARNING OBJECTIVES Learning objectives are stated at the beginning of each chapter. These learning objectives serve as a preview of the information you are expected to learn in the chapter. The comprehensive check questions are based on the ob jectives. By successfully completing the NRTC, you indicate that you have met the objectives and have learned the information. The learning objec tives are listed below. Upon completing this chapter, you should be able to do the following: Describe the term fiber optics. List the parts of a fiber optic data link. Understand the function of each fiber optic data link part. Outline the progress made in the history of fiber optic technology.

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Describe the trade-offs in fiber properties and component selection in the design of fiber optic systems. List the advantages and the disadvantages of fiber optic systems compared to electrical commu nications systems. DEFINITION OF FIBER OPTICS In the other Navy Electricity and Electronics Training Series (NEETS) modules, you learn the basic concepts used in electrical systems. Electrical systems include telephone, radio, cable tele vision (CATV), radar, and satellite links. In the past 30 years, researchers have developed a new technology that offers greater data rates over longer distances at costs lower than copper wire systems. This new technology is fiber optics. Fiber optics uses light to send information (data). More formally, fiber optics is the branch of optical technology concerned with the transmission of radiant power (light energy) through fibers. Q.1 Define fiber optics.

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Optical fibers and cables

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Click here to order Fiber Optic Products Online OPTICAL FIBERS AND CABLES LEARNING OBJECTIVES Upon completion of this chapter, you should be able to do the following: Describe multimode and single mode step-index and gradedindex fibers. Explain the terms refractive index profile, relative refractive index difference, and profile parameter. List the performance advantages of 62.5/125 μm multimode graded-index fibers.

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Identify the two basic types of single mode step-index fibers. Describe the vapor phase oxidation and direct-melt optical fiber fabrication procedures.

Describe the fiber drawing process.

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List the benefits of cabled optical fibers over bare fibers. Identify the basic cable components, such as buffers, strength members, and jacket materials. Order this Describe the material and information in design requirements imposed Print (Hardcopy). on military fiber optic cable designs. Describe the advantages and disadvantages of OFCC cable, stranded cable, and ribbon cable designs. OPTICAL FIBER AND CABLE DESIGN Optical fibers are thin cylindrical dielectric (non-conductive) waveguides used to send light energy for communication. Optical fibers consist of three parts: the core, the cladding, and the coating or buffer. The choice of optical fiber materials and fiber design depends on operating conditions and intended application. Optical fibers are protected from the environment by incorporating the fiber into some type of cable structure. Cable strength members and outer jackets protect the fiber. Optical cable structure and material composition depend on the conditions of operation and the intended application. OPTICAL FIBERS Chapter 2 classified optical fibers as either single mode or multimode fibers. Fibers are classified according to the number of modes that they can propagate. Single mode fibers can propagate only the fundamental mode. Multimode fibers can propagate hundreds of modes. However, the classification of an optical fiber depends on more than the number of modes that a fiber can propagate. An optical fiber's refractive index profile and core size further distinguish single mode and multimode fibers. The refractive index profile describes the value of refractive index as a function of radial distance at any fiber diameter. Fiber refractive index profiles classify single mode and multimode fibers as follows:

Multimode step-index fibers Multimode graded-index fibers

Single mode step-index fibers Single mode graded-index fibers In a step-index fiber, the refractive index of the core is uniform and undergoes an abrupt change at the core-cladding boundary. Step-index fibers obtain their name from this abrupt change called the step change in refractive index. In gradedindex fibers, the refractive index of the core varies gradually as a function of radial distance from the fiber center. Single mode and multimode fibers can have a step-index or gradedindex refractive index profile. The performance of multimode graded-index fibers is usually superior to multimode step-index fibers. However, each type of multimode fiber can improve system design and operation depending on the intended application. Performance advantages for single mode graded-index fibers compared to single mode step-index fibers are relatively small. Therefore, single mode fiber production is almost exclusively step-index. Figure 3-1 shows the refractive index profile for a multimode step-index fiber and a multimode graded-index fiber. Figure 3-1 also shows the refractive index profile for a single mode step-index fiber. Since light propagates differently in each fiber type, figure 3-1 shows the propagation of light along each fiber. Figure 3-1. - The refractive index profiles and light propagation in multimode step-index, multimode graded-index, and single mode step-index fibers.

In chapter 2, you learned that fiber core size and material composition can affect system performance. A small change in core size and material composition affects fiber transmission properties, such as attenuation and dispersion. When selecting an optical fiber, the system designer decides which fiber core size and material composition is appropriate. Standard core sizes for multimode step-index fibers are 50 μm and 100 μm. Standard core sizes for multimode graded-index fibers are 50 μm, 62.5 μm, 85 μm, and 100 μm. Standard core sizes for single mode fibers are between 8 μm and 10 μm. In most cases, the material used in the preparation of optical fibers is high-quality glass (SiO2). This glass contains very low amounts of impurities, such as water or elements other than silica and oxygen. Using highquality glass produces fibers with low losses. Small amounts of

some elements other than silica and oxygen are added to the glass material to change its index of refraction. These elements are called material dopants. Silica doped with various materials forms the refractive index profile of the fiber core and material dopants are discussed in more detail later in this chapter. Glass is not the only material used in fabrication of optical fibers. Plastics are also used for core and cladding materials in some applications. A particular optical fiber design can improve fiber optic system performance. Each single mode or multimode, step-index or graded-index, glass or plastic, or large or small core fiber has an intended application. The system designer must choose an appropriate fiber design that optimizes system performance in his application. Q.1 Describe the term "refractive index profile." Q.2 The refractive index of a fiber core is uniform and undergoes an abrupt change at the core-cladding boundary. Is this fiber a step-index or graded-index fiber? Q.3 Multimode optical fibers can have a step-index or gradedindex refractive index profile. Which fiber, multimode stepindex or multimode graded-index fiber, usually performs better? Q.4 List the standard core sizes for multimode step-index, multimode graded-index, and single mode fibers.

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Optical sources and fiber optic transmitters

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Click here to order Fiber Optic Products Online OPTICAL SOURCES AND FIBER OPTIC TRANSMITTERS LEARNING OBJECTIVES Upon completion of this chapter, you should be able to do the following: Explain the principal properties of an optical source and fiber optic transmitter. Discuss the optical emission properties of semiconductor light-emitting diodes (LEDs) and laser diodes (LDs). Describe the operational differences between surfaceemitting LEDs (SLEDs), edgeemitting LEDs (ELEDs), superluminescent diodes (SLDs), and laser diodes. Describe typical fiber optic transmitter packages. INTRODUCTION TO OPTICAL SOURCES AND FIBER OPTIC

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TRANSMITTERS Chapter 1 taught you that a fiber optic data link has three basic functions. One function is that a fiber optic data link must convert an electrical signal to an optical signal permitting the transfer of data along an optical fiber. The fiber optic device responsible for that signal conversion is a fiber optic transmitter. A fiber optic transmitter is a hybrid device. It converts electrical signals into optical signals and launches the optical signals into an optical fiber. A fiber optic transmitter consists of an interface circuit, a source drive circuit, and an optical source. The interface circuit accepts the incoming electrical signal and processes it to make it compatible with the source drive circuit. The source drive circuit intensity modulates the optical source by varying the current through the source. An optical source converts electrical energy (current) into optical energy (light). Light emitted by an optical source is launched, or coupled, into an optical fiber for transmission. Fiber optic data link performance depends on the amount of optical power (light) launched into the optical fiber. This chapter attempts to provide an understanding of light-generating mechanisms within the main types of optical sources used in fiber optics. Q.1 What are the three parts of a fiber optic transmitter? Q.2 Which part of a fiber optic transmitter converts the processed electrical signal to an optical signal?

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