Angle Modulation MCQ

1. Carson’s rule is (with symbols having their standard meaning)

  1. B = 2 DW
  2. B = 2(D+1)W
  3. B=\sqrt{2} (D+1)W
  4. B = \sqrt{2} DW
Answer. b

2. In a frequency modulated (FM) system, when the audio frequency is 500 Hz and audio frequency voltage is 2.4 V, The frequency deviation δ is 4.8 kHz. If the audio frequency voltage is now increased to 7.2 V then what is the new value of deviation?

  1. 3.6 kHz
  2. 0.6 kHz
  3. 14.4 kHz
  4. 12.4 kHz
Answer. c

3. The four basic elements in a PLL are loop filter loop amplifier, VCO and

  1. Up converter
  2. Down converter
  3. Phase detector
  4. Frequency multiplier
Answer. c

4. V = A sin (ωct+ m sin ωmt) is the expression for

  1. Amplitude modulated signal
  2. Frequency modulated signal
  3. Phase modulated signal
  4. Carrier signal used for modulation
Answer. b or c

5. When the modulation frequency is doubled the modulation index is halved and the modulating index is halved and the modulation voltage remains constant. This happens when the modulating system is

  1. AM
  2. PM
  3. FM
  4. Delta Modulation
Answer. c

6. An FM signal is represented by

V = 12 sin (6 x 108t + 5 sin 1250t)

The carrier frequency f and frequency deviation δ, respectively, are

  1. 191 MHz and 665 Hz
  2. 95.5 MHz and 995 Hz
  3. 191 MHz and 995 Hz
  4. 95.5 MHz and 665 Hz
Answer. b

7. In FM modulation, when the modulation index increases, the transmitted power is

  1. decreased
  2. increased
  3. non-related
  4. unchanged
Answer. d

8. In a frequency division multiplexed (FDM) system, cross talk occurs due to

  1. imperfect time synchronization between transmitter and receiver
  2. imperfect filtering at the receiver front-end
  3. imperfect carrier recovery at the receiver
  4. channel noise
Answer. b

9. Which of the following are the advantages of FM over AM?

  1. Better noise immunity is provided
  2. Lower bandwidth is required
  3. Transmitted power is more useful
  4. Less modulating power is required
  1. i, ii and iv
  2. i, ii and iii
  3. i, iii and iv
  4. ii, iii and iv
Answer. c

10. In phase modulation, the frequency deviation is

  1. independent of the modulating signal frequency
  2. increasingly proportional to the modulating signal frequency
  3. directly proportional to the modulating signal frequency
  4. inversely proportional to the square root of the modulating signal frequency
Answer. c

11. Modulation has a number of advantages. Which of one of the following is not correct?

  1. Efficient transmission
  2. Reduction in noise and interference
  3. Overcomes hardware limitations
  4. Requires higher power transmitter
Answer. c

12. Which one of the following statement is not correct?

  1. FM has an infinite number of side-bands
  2. Modulation index for FM is always greater than one
  3. As modulation depth increases the BW increases
  4. As modulation depth increases the sideband power increases
Answer. b

13. In a frequency modulation system, maximum frequency deviation allowed is 1000 and modulating frequency is 1 kHz. Determine the modulation index β.

  1. 2000
  2. 2
  3. 1000
  4. 1
Answer. d

14. The maximum deviation allowed in a frequency modulation system is 100 kHz; the modulating signal frequency is 10 kHz. The bandwidth requirement as per Carson’s rule will be

  1. 110 kHz
  2. 220 kHz
  3. 210 kHz
  4. 120 kHz
Answer. b

15. Which of the following component blocks is not required in the FDM transmitter block diagram?

  1. Filter cutting off lower and higher frequencies
  2. Filter cutting off higher frequencies
  3. Single side band modulator
  4. Double side band modulator
Answer. d