Angle Modulation MCQ

16. The main advantage of the pre-emphasis circuit in FM transmitter is

  1. To increase the carrier power
  2. To improve the signal to noise ratio at low audio frequencies
  3. To increase the bandwidth of side band
  4. To improve the signal to noise ratio at high audio frequencies
Answer. d

17. In phase modulation, phase deviation is proportional to

  1. Carrier amplitude
  2. Carrier phase
  3. Message signal
  4. Message signal frequencies
Answer. c

18. An indirect way of generating FM, is

  1. The Armstrong modulator
  2. The reactance FET modulator
  3. The varactor diode modulator
  4. The reactance bipolar transistor modulator
Answer. a

19. The de-emphasis filter in an FM receiver comes

  1. Before FM demodulator
  2. After FM demodulator and before baseband filter
  3. After baseband filter
  4. Before RF amplifier
Answer. b

20. Consider the following statements about FM

  1. Modulation index determines the number of significant sideband components.
  2. Theoretical bandwidth is infinite.
  3. Carrier suppression is not possible
  4. Sidebands are not symmetric about carrier

Which of these statements is/are correct?

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

21. If an FM wave is represented by the equation e = 10 sin (9 x 108t + 4 sin 1500t), then what is the carrier frequency?

  1. 127.32 MHz
  2. 150.00 MHz
  3. 143.31 MHz
  4. 208.00 MHz
Answer. c

22. Which one of the following factors is limited in case of F.M.?

  1. Maximum frequency deviation
  2. Maximum permissible modulation index
  3. Signal to noise voltage ratio
  4. Minimum permissible modulation index
Answer. a

23. An F.M. signal which is modulated by a 4 kHz sine wave reaches a maximum frequency of 100.01 MHz and minimum frequency of 99.97 MHz, then what is the one side frequency deviation of the signal?

  1. 6.67
  2. 5
  3. 10
  4. 20
Answer. d

24. An angle modulated signal is described by the equation

xc(t) = 10 cos[2πfct + 10 sin(4000πt) + 5 sin 2000πt]

What is the bandwidth of this modulated signal?

  1. 6 kHz
  2. 45 kHz
  3. 54 kHz
  4. 63 kHz
Answer. c

25. With the increase in the transmission bandwidth, received signal-power in AM and FM will respectively

  1. increase, increase
  2. remain same, increase
  3. increase, remain same
  4. remain same, remain same
Answer. b

26. What is the automatic frequency control voltage of the FM transmitter VCO?

  1. dc voltage
  2. Sine wave voltage
  3. Square wave voltage
  4. Ramp voltage
Answer. a

27. PLL demodulators are now used in commercial receivers because of which of the following

  1. PLL demodulators do not exhibit threshold in S/N performance.
  2. No requirement of pre-emphasis and de-emphasis.
  3. Cheap PLL ICs are available.

Select the correct answer using the code given below.

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

28. Which of the following are the advantages of FM broadcasting over AM broadcasting

  1. Better S/N ratio
  2. Not subject to signal fading
  3. Power efficiency is superior
  4. Demodulation is simpler

Select the correct answer from the code given below.

  1. i and ii
  2. ii and iii
  3. i, ii and iii
  4. i and iii
Answer. d

29. Which one of the following signals can be applied to a delta modulator whose step size is 0.1 V and sampling frequency is 20π kHz so that no slope overload occurs?

  1. 2 sin (1200πt)
  2. 1 sin (2600πt)
  3. 3 sin (1000πt)
  4. 4 sin (400πt)
Answer. d

30. Which of the following is not a component of PLL?

  1. Frequency multiplier
  2. Phase detector
  3. VCO
  4. Loop filter
Answer. a
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