Amplitude Modulation MCQ

21. How much power will an AM transmitter, rated at 50 kW, radiate if it is modulated to 100%?

  1. 50 kW
  2. 25 kW
  3. 100 kW
  4. 75 kW
Answer
Answer. a

22. An AM modulator has output

S(t) = 20 cos(300πt) + 6 cos(320πt) + 6 cos (280πt)

Then what is the modulation index of the wave?

  1. More than 100%
  2. 0.93
  3. 0.6
  4. 0.3
Answer
Answer. c

23. Which one of the following is considered as an A.M. signal?

  1. Binary phase-shift keying (BPSK)
  2. Differential phase-shift keying (DPSK)
  3. Differential encoded PSK
  4. Quadrature PSK
Answer
Answer. d

24. The antenna current of an A.M. transmitter is 8 A when only carrier is sent, but it increases to 8.93 A when the carrier is modulated. Then what is the percentage modulation of the wave?

  1. 43.00%
  2. 70.14%
  3. 100.00%
  4. 57.00%
Answer
Answer. b

25. For an AM signal, the bandwidth is 10 kHz and the highest frequency component present is 705 kHz. What is the carrier frequency used for this AM signal?

  1. 695 kHz
  2. 700 kHz
  3. 705 kHz
  4. 710 kHz
Answer
Answer. b

26. In an AM system, for satisfactory operation, carrier frequency must be n times the bandwidth of message-signal. What is the value of n?

  1. > 2
  2. > 5
  3. > 10
  4. > 50
Answer
Answer. d

27. Consider the following statements about analog communication and multiplexing:

  1. Noise problem for analog communication has the greatest effect on TDM system.
  2. Noise problem for analog communication has the least effect on SDM system.

Which of these statements is/are correct?

  1. i only
  2. ii only
  3. Both i and ii
  4. Neither i nor ii
Answer
Answer. c

28. A carrier is amplitude modulated by 4 signals of frequency 10 kHz, 15 kHz, 20 kHz and 25 kHz. What is the bandwidth of the modulated signal?

  1. 25 kHz
  2. 50 kHz
  3. 140 kHz
  4. 70 kHz
Answer
Answer. b

29. What is the power contained in SSB transmission when the carrier power is 1 kW and the modulation index is 0.3?

  1. 22.5 W
  2. 90 W
  3. 300 W
  4. 1 kW
Answer
Answer. a

30. If two signals modulate the same carrier with different modulation depths of 0.3 and 0.9, the resulting modulation signal will

  1. be over-modulated
  2. have the resultant modulation limited to 1.0
  3. have the resultant modulation index around 0.82
  4. have the resultant modulation index around 0.95
Answer
Answer. d
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