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. 0.276b. 0.000133c. 276d. 12.342. Which of the following operations can be directly performed?a. dBm+dBmb. dB-dBc. (dB)(dB)d. dBf - dB3. Wire gauge commonly employ in telephone wires.a. AWG 17b. AWG 5c. AWG 19d. AWG 184. A 2 dBW signal is fed to a three-output port power splitter. Find the power level at each output port a. 0.67 dBWb. -1.74 dBWc. 1. dBWd. -2.77 dBw

5. What is the result if a balanced modulator is not perfectly balanced? a. SB filteredb. Low sideband transmittedc. Carrier transmittedd. Both sideband transmitted6. Calculate the output signal-to-noise ratio (SNR) for four identical links if the SNR for any one link is 40 dBa. 34 dBb. 36 dBc. Still 40 dBd.46 dB7. The noise figure of an amplifier is 4 dB. Find the output SNR when the input SNR is 42 dBa. 36 dBb. 38 dBc. 40 dBd. 46 dB8.Find the noise factor for an attenuator pad having an insertion loss of 12 dBa. 14.8b. 15.8c. 12d. 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 MHzb. 4385 KHzc. 4.5 KHzd. 3688 KHz10. The pre-emphasis network in Europe has a time constant of _________.a. 75 usb. 300 usc. 150 usd. 100 us11. The long term cycle of solar disturbance is .....a. 20 days b. 8 yearsc. 11 yearsd. 17 years12. Thermal agitation noise is.....a. Deterministic b. Immeasurable c. Predictable d. Random

13.Balanced modulators generate..... a. DSBFCb. DSBSCc. SSBFCd. SSBSC14. Which of the following is not considered part of the super heterodyne front-end?a. IF amplifierb. Local oscillator c. Mixer d. RF amplifier 15. The AM envelope detector is essentially a .....a. Half wave rectifier with a capacitor filterb. Network of diodes, resistors and capacitorsc. Plain diode d. Purely resistive network16. In FM, 100% modulation meansa. Actual deviation reaches 75 kHzb. Actual deviation equals the maximum allowed deviation c. A modulation index of 1d. Intelligence amplitude equals carrier amplitude

17. Single sideband full carrier, single channel, AM broadcast is.....a. A3Eb. H3Ec. J3Ed. R3E18. In AM, the carrier component contains _____ intelligencea. No b. The samec. A distorted d. All of the19. 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 usecb. 15 usecc. 25 usecd. 35 usec20. 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 ohmsb. j50 ohmsc. 1 ohmsd. 50 + j50 ohms

21. The guardband for each FM broadcast channel is.....a. 20 kHz on each sideb. 25 kHz on each sidec. 25 kHz on one side onlyd. 20 Hz on one side onlyWhich determines the number of sideband components in FM?a. Modulation indexb. Modulation frequencyc. Carrier frequency d. All of the aboveEnvelope detectors performa. 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 Wattsb. 660 Wattsc. 667 Wattsd. 767 Watts

25. Increasing the FM modulation index will most likely result ina. An increase in transmitter output powerb. A decrease in transmitter output powerc. An increase in the required bandwidthd. A fixed bandwidth operation26. The Costas loop is aa. Clock recovery circuitb. Carrier recovery circuitc. Phase recovery circuitd. Transmitter circuit27. A carrier signal ec = 120sin500,000t is fed to a 50 antenna. Find the carrier power desired.a. 144 wattsb. 288 wattsc. 414 wattsd. 72 watts28. 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 Wb. 146 Wc. 219 Wd. 292 W

29. The wolf number in communications tells abouta. The number of sunspotsb. The depth of the F-layer in the atmospherec. The critical angle of ionospheric propagationd. The number of big bad wolves30. A communications tower has a UHF radio antenna mounted 120 feet above the earths surface. Calculate the radio horizon for this set-up.a. 15.49 milesb. 14.95 milesc. 15.94 milesd. 18.49 miles31. It is the highest frequency that can be reflected when a signal strikes the ionosphere with vertical incident wave.a. Optimum working frequencyb. Frequency at optimum levelc. Maximum usable frequencyd. Critical frequency32. 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 MHzb. 7.22 MHzc. 5.22 MHzd. 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 wavesa. Superposition principleb. Huygens principlec. Jams principled. Maxwells reflection advocate34. A 100 Kohm resistor is connected in parallel with a 100pF capacitor. Determine the effective noise bandwidtha. 25KHzb. 400KHzc. 100 KHzd. 45 KHz35. When the magnetic field is parallel to the surface of the earth, what is the polarization of the electromagnetic signal?a. horizontalb. circularc. verticald. elliptical36. 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 uVb. 25.75 uVc. 363 uVd. 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 dBb. 19 dBmc. 31 dBmd. 19 dB38.. 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 noiseb. Estimation noisec. Quantizing noised. Impulse noise39. What is the gain of an isotropic antenna? a. 0 b. 1 c. 100 d. 1040. If an amplifier has a noise figure of 10 dB, find the equivalent amplifier input capacitance for a bandwidth of 2 MHza. 0.08 pFb. 332 uFc. 0.072 pFd. 234 pF

41. ITU purposely divided the world in 3 regions for geopolitical spectrum allocation, what region Philippines falls in?a. Region 1b. Region 2c. Region 3d. Region 442. It is a device that detects both vertically and horizontally polarized signals simultaneously.a. Horiver transducerb. Spectrum analyzerc. Orthomode transducerd. 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/mb. 150 uV/mc. 100 uV/md. 50 uV/m44. 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 metersb. 26.3 milesc. 26.3 feetd. 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 absorptionb. Faraday rotationc. Tropospheric ductingd. Thermal inversion46. 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 mb. 500 mc. 386 kmd. 3.86E15 km47. A quarter-wave stub could be used toa. Increase the SWRb. Decreased the SWRc. Act as aninsulator or short circuitd. All of the above

48. A technique that can be used to locate impairment in a metallic cable is______.a. Peak detectionb. HRCc. LRCd. 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 dielectrica. Strip lineb. microstripc. Coaxial lined. Twin lead transmission line50. A shorted transmission line less than quarter wavelength will exhibit____ reactancea. inductiveb. capacitivec. Maximum d. minimum

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