MCQ on Pulse Code Modulation (PCM)

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MCQ on Pulse Code Modulation (PCM)

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Multiple Choice Questions of PCM

1. Companding is used

  • to overcome quantizing noise in PCM
  • in PCM transmitters, to allow amplitude limiting in the receivers
  • to protect small signals in PCM from quantizing distortion.
  • in PCM receivers, to overcome impulse noise.

Answer: to overcome quantizing noise in PCM

2. The biggest disadvantages of PCM is

  • its inability to handle analog signals
  • the high error rate which its quantizing noise introduces
  • its incompatibility with TDM
  • the large bandwidths that are required for it.

Answer: the large bandwidths that are required for it.

3. Indicate which of the following pulse modulation systems is analog

  • PCM
  • Differential PCM
  • PWM
  • Delta modulation

Answer: PWM

4. Quantizing noise occurs in

  • time-division multiplexing
  • FDM
  • PCM
  • PWM

Answer: PCM

5. Quantizing noise can be reduced by increasing the number of samples per second. It is true,

  • yes, it is
  • no, it is not
  • not necessarily
  • none of these

Answer: none of these

6. In PCM a system, the quantization noise depends upon

  • the number of quantization levels only
  • the sampling rate only
  • both the sampling rate and the number of quantization levels
  • none of the above is correct

Answer: both the sampling rate and the number of quantization levels

7. The signal-to quantization noise ratio in PCM system depends upon

  • sampling rate
  • number of quantization levels
  • message signal bandwidth
  • none of the above

Answer: number of quantization levels

8. Indicate which of the following systems is digital?

  • Pulse-position modulation
  • Pulse-code modulation
  • Pulse-width modulation
  • Pulse-frequency modulation

Answer: Pulse-code modulation

9. Quantizing noise occurs in

  • time-division multiplex
  • frequency-division multiplex
  • pulse-code modulation
  • pulse-width modulation

Answer: Pulse-code modulation

10. In order to reduce quantizing noise, one must

  • increase the number of standard amplitudes
  • send pulses whose sides are more nearly vertical
  • use an R.F. amplifier in the receiver
  • increase the number of samples per second

Answer: increase the number of standard amplitudes

11. The biggest disadvantages of PCM is

  • its inability to handle analog signals
  • the high error rate which its quantizing noise reduces
  • its incompatibility with TDM
  • the large bandwidth that are required for it

Answer: the large bandwidth that are required for it

12. The main advantage of PCM system is

  • a lower bandwidth
  • a lower power
  • lower noise
  • None of the above

Answer: lower noise

13. Quantization noise is produced in

  • all pulse modulation system
  • PCM
  • all modulation system
  • none of the above

Answer: PCM

14. One of the following systems is analog –

  • PCM
  • delta
  • differential PCM
  • PAM

Answer: PAM

15. For an efficient communication in PCM system number of samples per second must at least be equal to twice the highest modulating frequency. Comment

  • Not necessary
  • A very important consideration
  • Who cares
  • 80- 50, true

Answer: A very important consideration

16. In PCM system, output S/N increases

  • linearly with bandwidth
  • exponentially with bandwidth
  • inversely with bandwidth
  • none of these

Answer: linearly with bandwidth

17. The transmitted pulse in PCM system usually occur at a uniform rate for minimum bandwidth

  • true
  • false

Answer: true

18. In a DM system, the granular (idling) noise occurs when the modulating signal

  • increase rapidly
  • remains constant
  • decreases rapidly
  • the nature of modulating signal has nothing to do with this noise

Answer: remains constant

19. Quantization noise is produced in

  • all pulse modulation system
  • PCM
  • all modulation system
  • none of these

Answer: PCM

20. The main advantage of PCM signal is

  • lower bandwidth
  • higher bandwidth
  • lower noise
  • none of these

Answer: lower noise

21.  For transmission of normal speech signal the PCM channel needs a bandwidth of

  • 64 kHz
  • 8 kHz
  • 4 kHz
  • none of these

Answer: 64 kHz

22. The non-uniform quantization leads to

  • reduction in transmission bandwidth
  • increase in maximum SNR
  • increase in SNR for low level signals
  • simplification of quantization process

Answer: increase in SNR for low level signals

23. The equipment needed either at the transmitter or at the receiver is

  • simpler
  • more complicated
  • of simple complexity, when delta modulation is used in the case of PCM
  • none of these

Answer: of simple complexity, when delta modulation is used in the case of PCM

24. PCM systems use non-uniform quantization in order to

  • raise SNR for low level signals
  • cut down the required bandwidth of transmission
  • increases the maximum SNR
  • none of these

Answer: raise SNR for low level signals

25. The use of non-uniform quantization leads to

  • reduction in transmission bandwidth
  • increase in maximum SNR
  • Increase in SNR for low level signals
  • Simplification of quantizations process

Answer: Increase in SNR for low level signals

26. In QAM, both identities are varied.

  • amplitude and phase
  • frequency and phase
  • bit rate and phase
  • baud rate and phase

Answer: amplitude and phase

27. Signal-to-quantization noise ratio of a PCM system using 8-bit words for the analog signal that does not exceed its quantization boundary is

  • 48 dB
  • 54 dB
  • 52.7 dB
  • 64 dB

Answer: 48 dB

28. Granular noise is associated with

  • PCM
  • DPCM
  • DM
  • QAM

Answer: DM

29. The signal to quantization noise ratio in a PCM system depends upon

  1. sampling rate
  2. number of quantization levels
  3. message signal bandwidth
  • 1, 2 and 3
  • 2 and 3 only
  • 2 only
  • 3 only

Answer: 2 only

30. In PCM, if the transmission path is very long

  • repeater stations are used
  • the pulse width may be increased
  • pulse amplitude is increased
  • pulse spacing is reduced

Answer: repeater stations are used

31. A signal having uniformly distributed amplitude in the interval (-V, + V) is to be encoded using PCM with uniform quanti-zation. The (SNR)q is determined by

  • dynamic range of the signal
  • sampling rate
  • no. of quantizing levels
  • power spectrum of a signal

Answer: no. of quantizing levels

32. In PCM the biggest disadvantage compared to analog modulation is

  • large bandwidth
  • larger noise
  • inability to handle analog signals
  • incompatibility with TDM system

Answer: large bandwidth

33. In an ADM system, the output signal amplitudes for l’s and 0’s are

  • fixed and the repetition rate is also fixed
  • fixed but the repetition rate is variable
  • variable and the repetition rates is also variable
  • variable but the repetition rate is fixed

Answer: fixed and the repetition rate is also fixed

34. The use of non-uniform quantization leads to

  • reduction in transmission BW
  • increase in max. SNR
  • increase in SNR for low-level signals
  • simplification of the quantization process

Answer: increase in SNR for low level signals

35. Consider the following statements comparing DM and PCM systems, DM requires

  1. a lower sampling rate
  2. a higher sampling rate
  3. a larger BW
  4. simple harware

Which of these statements are correct?

  • 1, 2 and 4
  • 1, 2 and 3
  • 1, 3 and 4
  • 2, 3 and 4

Answer: 1, 2 and 4

36. For uniform quantization with 32 levels, the qunantized output can be represented by n binary digits where n is

  • 5
  • 8
  • 6
  • 4

Answer: 5

37. In a PCM system, the number of quantization levels are 16 and the maximum signal frequency is 4 kHz, the bit transmission rate is

  • 64 bps
  • 16 kbps
  • 32 kpbs
  • 32 bps

Answer: 32 kpbs

38. PCM systems require regenerative repeaters over long distances. The correct sequence of the operations which such a repeater performs is

  • Timing, equalization, and decision making
  • Equalization timing and decision making
  • Timing, thresholding, and equalization
  • Thresholding, timing, and equalization

Answer: Equalization timing and decision making

39. In a DM system, the granular noise occurs when the

  • modulating signal increases rapidly
  • pulse rate decreases,
  • modulating signal remains constant
  • pulse amplitude increases

Answer: pulse amplitude increases

40. In a PCM system, the amplitude levels are transmitted in a 7 unit code. The sampling is done at the rate of 10 kHz. The BW should be

  • 5 kHz
  • 35 kHz
  • 70 kHz
  • 5 MHz

Answer: 35 kHz

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