Amplitude Modulation MCQ

1. The modulating index of an AM-signal is reduced from 0.8 to 0.5. The ratio of the total power in the new modulated signal to that of the original signal will nearly be

  1. 0.39
  2. 0.63
  3. 0.85
  4. 1.25
Answer
Answer. c

2. Consider the following features of FM vis-a-vis AM:

  1. Better noise immunity is provided
  2. Lower bandwidth is required
  3. The transmitted power is better utilized
  4. Less modulating power is required

Which of the above are advantages of FM over AM?

  1. i, ii and iii only
  2. i,iii and iv only
  3. i and iv only
  4. i, ii, iii and iv
Answer
Answer. b

3. Modulation is used to

  1. Separate different transmission
  2. Reduce the bandwidth requirement
  3. Allow the use of practicable antennas
  4. Ensure that intelligence may be transmitted over a long distance

Which of the above statements are correct

  1. i, ii and iii only
  2. i,iii and iv only
  3. i and iv only
  4. i, ii, iii and iv
Answer
Answer. b

4. If a carrier of 100% modulated AM is suppressed before transmission, the power saving is nearly

  1. 50%
  2. 67%
  3. 100%
  4. 125%
Answer
Answer. b

5. Consider the following types of modulation:

  1. Amplitude modulation
  2. Frequency modulation
  3. Pulse modulation
  4. Phase modulation

Which of the above modulation are used for telecasting TV programs?

  1. ii and iii
  2. iii and iv
  3. i and ii
  4. i and iv
Answer
Answer. c

6. In TV, video signals are transmitted through

  1. amplitude modulation
  2. frequency modulation
  3. either amplitude or frequency modulation
  4. neither amplitude nor frequency modulation
Answer
Answer. a

7. Multiplexing scheme which uses carrier phase shifting and synchronous detection to permit two DSB signals to occupy the same frequency band is called

  1. NBFM
  2. CDMA
  3. QAM
  4. FDMA
Answer
Answer. c

8. In a typical AM receiver circuit, the oscillator frequency is

  1. same as signal frequency
  2. always equal to 455 Hz
  3. lower than the signal frequency by 455 Hz
  4. higher than the signal frequency by 455 kHz
Answer
Answer. d

9. A broadcast AM transmitter radiates 50 kW of carrier power. The radiation power at 85% of modulation is

  1. 68.1 kW
  2. 60.8 kW
  3. 61.8 kW
  4. 62.0 kW
Answer
Answer. a

10. A 100 V carrier peak changes from 160 V to 40 V by a modulating signal. The modulation factor is

  1. 0.3
  2. 0.5
  3. 0.6
  4. 0.7
Answer
Answer. c

11. A 1000 W carrier is amplitude-modulated and has a side-band power of 300 W. The depth of modulation is

  1. 0.545
  2. 0.255
  3. 0.95
  4. 0.775
Answer
Answer. d

12. In an Amplitude Modulated (AM) wave with 100% modulation (ma), the carrier is suppressed. The percentage of power-saving will be

  1. 50%
  2. 100%
  3. 66.7%
  4. 25%
Answer
Answer. c

13. A carrier wave of frequency 2.5 GHz amplitude is modulated with two modulating frequencies equal to 1 kHz and 2 kHz. The modulated wave will have the total bandwidth

  1. 2 kHz
  2. 6 kHz
  3. 3 kHz
  4. 4 kHz
Answer
Answer. d

14. RF carrier 10 kV at 1 MHz is amplitude modulated and modulation index is 0.6. The peak voltage of the signal is

  1. 600 kV
  2. 1200 kV
  3. 10 kV
  4. 6 kV
Answer
Answer. d

15. Bandwidth occupied by 100 MHz carrier, AM modulated by the signal frequency of 10 kHz is

  1. 100 MHz
  2. 20 kHz
  3. 10 kHz
  4. 110 MHz
Answer
Answer. b

16.  In double sideband suppressed carrier modulation, the modulated wave undergoes phase reversal, whenever

  1. modulating signal’s amplitude decreases
  2. modulating signal’s amplitude increases
  3. modulating signal crosses zero
  4. carrier signal crosses zero
Answer
Answer. c

17. Diode demodulator will ignore

  1. the amplitude modulation
  2. the frequency modulation
  3. PCM
  4. PWM
Answer
Answer. b

18. Which one of the following modulation techniques has got maximum SNR?

  1. AM-JSB
  2. AM-SSB
  3. FM
  4. AM-SC
Answer
Answer. c

19. What is the assigned bandwidth of each of the channels in the AM broadcast band?

  1. 5 kHz
  2. 10 kHz
  3. 15 kHz
  4. 200 kHz
Answer
Answer. b

20. For which one of the following modulated signals, the original message, up to a scaling factor can be recovered using envelope detection?

  1. 20 cos(200πt) + 30 m(t) cos(200πt)
  2. 20 cos(200πt) + 16 m(t) cos(200πt)
  3. 10 m(t) cos(400πt)
  4. 10 cos(m(t)) cos(400πt)
Answer
Answer. b
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