Electronics Engineering Communications

COMMUNICATIONS ENGINEERING

Periodic Evaluation Test 1

1. A diode noise generator is required to produce 10 uV of noise in a receiver with an input impedance of 75 ohms and a noise power bandwidth of 200 KHz. What is the expected current through the diode be in mA? a. 0.276 b. 0.000133 c. 276 d. 12.34 2. Which of the following operations can be directly performed? a. dBm+dBm b. dBμ-dB c. (dB)(dB) d. dBf - dBμ 3. Wire gauge commonly employ in telephone wires. a. AWG 17 b. AWG 5 c. AWG 19 d. AWG 18 4. A 2 dBW signal is fed to a three-output port power splitter. Find the power level at each output port a. 0.67 dBW b. -1.74 dBW c. 1. dBW d. -2.77 dBw

 5. What is the result if a balanced modulator is not perfectly balanced? a. SB filtered b. Low sideband transmitted c. Carrier transmitted d. Both sideband transmitted 6. Calculate the output signal-to-noise ratio (SNR) for four identical links if the SNR for any one link is 40 dB a. 34 dB b. 36 dB c. Still 40 dB d.46 dB 7. The noise figure of an amplifier is 4 dB. Find the output SNR when the input SNR is 42 dB a. 36 dB b. 38 dB c. 40 dB d. 46 dB 8.Find the noise factor for an attenuator pad having an insertion loss of 12 dB a. 14.8 b. 15.8 c. 12 d. 18.5

9. A superheterodyne is tuned to 2738 KHz. The IF is 475 KHz and the Q-factor is 30. What is the image frequency? a. 3.09 MHz b. 4385 KHz c. 4.5 KHz d. 3688 KHz 10. The pre-emphasis network in Europe has a time constant of _________. a. 75 us b. 300 us c. 150 us d. 100 us 11. The long term cycle of solar disturbance is ..... a. 20 days b. 8 years c. 11 years d. 17 years 12. Thermal agitation noise is..... a. Deterministic b. Immeasurable c. Predictable d. Random

13. Balanced modulators generate..... a. DSBFC b. DSBSC c. SSBFC d. SSBSC 14. Which of the following is not considered part of the super heterodyne front-end? a. IF amplifier b. Local oscillator c. Mixer d. RF amplifier 15. The AM envelope detector is essentially a ..... a. Half wave rectifier with a capacitor filter b. Network of diodes, resistors and capacitors c. Plain diode d. Purely resistive network 16. In FM, 100% modulation means a. Actual deviation reaches 75 kHz b. Actual deviation equals the maximum allowed deviation c. A modulation index of 1 d. Intelligence amplitude equals carrier amplitude

 17. Single sideband full carrier, single channel, AM broadcast is..... a. A3E b. H3E c. J3E d. R3E 18. In AM, the carrier component contains _____ intelligence a. No b. The same c. A distorted d. All of the 19. Using TDR,a transmission line impairment is located 3000 meter from the source. For a velocity of propagation ofn0.8c, determine the time elapsed from the beginning of the pulse to the reception of the echo. a. 5 usec b. 15 usec c. 25 usec d. 35 usec 20. A 50-ohm coaxial cable has a load connected at its end with an impedance of 50 ohms as well. What is the impedance of the cable at a point quarter wavelength from the load? a. 50 ohms b. j50 ohms c. 1 ohms d. 50 + j50 ohms

  21. The guardband for each FM broadcast channel is..... a. 20 kHz on each side b. 25 kHz on each side c. 25 kHz on one side only d. 20 Hz on one side only Which determines the number of sideband components in FM? a. Modulation index b. Modulation frequency c. Carrier frequency d. All of the above Envelope detectors perform a. Companding b. Heterodyning c. Mixing d. Rectification An AM transmitter is rated 1 kW at 100% modulation. What must be its rating at no modulation? a. 600 Watts b. 660 Watts c. 667 Watts d. 767 Watts

  25. Increasing the FM modulation index will most likely result in a. An increase in transmitter output power b. A decrease in transmitter output power c. An increase in the required bandwidth d. A fixed bandwidth operation 26. The Costas loop is a a. Clock recovery circuit b. Carrier recovery circuit c. Phase recovery circuit d. Transmitter circuit 27. A carrier signal ec = 120sin500,000t is fed to a 50Ω antenna. Find the carrier power desired. a. 144 watts b. 288 watts c. 414 watts d. 72 watts 28. A resonant half-wave dipole in free space has a feed line current of 1A. How much power appears at the input to the feed point? a. 73 W b. 146 W c. 219 W d. 292 W

   29. The “wolf number” in communications tells about…… a. The number of sunspots b. The depth of the F-layer in the atmosphere c. The critical angle of ionospheric propagation d. The number of big bad wolves 30. A communications tower has a UHF radio antenna mounted 120 feet above the earth’s surface. Calculate the radio horizon for this set-up. a. 15.49 miles b. 14.95 miles c. 15.94 miles d. 18.49 miles 31. It is the highest frequency that can be reflected when a signal strikes the ionosphere with vertical incident wave. a. Optimum working frequency b. Frequency at optimum level c. Maximum usable frequency d. Critical frequency 32. A signal propagated via sky-wave propagation follows a path 50 degrees from the normal at a critical frequency of 4 MHz. What is the maximum usable frequency? a. 6.22 MHz b. 7.22 MHz c. 5.22 MHz d. 6.58 MHz

  33. ” Each point on a primary wavefront can be considered to be new sources of secondary spherical wave and that a secondary wavefront can be constructed as the envelope of these secondary waves” a. Superposition principle b. Huygens principle c. Jams principle d. Maxwells reflection advocate 34. A 100 Kohm resistor is connected in parallel with a 100pF capacitor. Determine the effective noise bandwidth a. 25KHz b. 400KHz c. 100 KHz d. 45 KHz 35. When the magnetic field is parallel to the surface of the earth, what is the polarization of the electromagnetic signal? a. horizontal b. circular c. vertical d. elliptical 36. A 10 kilo-ohm resistor is connected in parallel with a 0.01 pF capacitor. Determine the rms noise voltage at 17 degree C. a. 633 uV b. 25.75 uV c. 363 uV d. 524 uV

37. The signal in a particular channel is measured to be 25 dBm while the noise in that same channel is 6dBm. Find the signal to noise ratio. a. 4.1333 dB b. 19 dBm c. 31 dBm d. 19 dB 38.. This is the noise occurring in the presence of a signal resulting from a mismatch between the exact value of an analog signal and the closest available level in a digital coder. a. Idle channel noise b. Estimation noise c. Quantizing noise d. Impulse noise 39. What is the gain of an isotropic antenna? a. 0 b. 1 c. 100 d. 10 40. If an amplifier has a noise figure of 10 dB, find the equivalent amplifier input capacitance for a bandwidth of 2 MHz a. 0.08 pF b. 332 uF c. 0.072 pF d. 234 pF

41. ITU purposely divided the world in 3 regions for geopolitical spectrum allocation, what region Philippines falls in? a. Region 1 b. Region 2 c. Region 3 d. Region 4 42. It is a device that detects both vertically and horizontally polarized signals simultaneously. a. Horiver transducer b. Spectrum analyzer c. Orthomode transducer d. Smith chart 43. If 4 KW antenna produces 50 uV/m of electric field in the receiving antenna, a 16 KW will produce what field intensity in same receiving antenna. a. 200 uV/m b. 150 uV/m c. 100 uV/m d. 50 uV/m 44. How high must a receiving antenna be to receive a signal directly from an over the horizon transmitter whose antenna is 30 ft high? The distance between the antennas is 15 miles. a. 26.3 meters b. 26.3 miles c. 26.3 feet d. 16.3 feet

45. What propagation condition is usually indicated when the VHF signal is received from a station over 5 000 miles away? a. D-layer absorption b. Faraday rotation c. Tropospheric ducting d. Thermal inversion 46. A coaxial cable having an inner diameter of 0.025 mm and using insulator with the dielectric constant of 2.56 is to have a Zo of 2000. What must be the outer conductor diameter? a. 50 m b. 500 m c. 386 km d. 3.86E15 km 47. A quarter-wave stub could be used to a. Increase the SWR b. Decreased the SWR c. Act as aninsulator or short circuit d. All of the above

48. A technique that can be used to locate impairment in a metallic cable is______. a. Peak detection b. HRC c. LRC d. TDR

49. A form of transmission line used at high UHF and microwave frequencies sandwiched between to ground planes and separated from each by a dielectric a. Strip line b. microstrip c. Coaxial line d. Twin lead transmission line 50. A shorted transmission line less than quarter wavelength will exhibit____ reactance a. inductive b. capacitive c. Maximum d. minimum

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