Pulse Modulation MCQ

1. The main units in a pulse code modulator are

  1. Sampler
  2. Quantizer
  3. Encoder
  4. Comparator
  1. i and ii only
  2. ii and iii only
  3. ii and iv
  4. i, ii and iii
Answer. d

2. In a PCM system, a five bit-encoder is used. If the difference between two consecutive levels is 1V, then the range of the encoder is

  1. 0 – 30 V
  2. 0 – 31 V
  3. 1 – 30 V
  4. 1 – 32 V
Answer. a

3. If the number of bits per sample in a PCM system is increased from 8 to 16, then the bandwidth will be increased

  1. 4 times
  2. 2 times
  3. 16 times
  4. 8 times
Answer. b

4. Which one of the following systems gives the highest figure-of-merit (a measure of the noise performance)?

  1. WBFM
  2. NBFM
  3. SSB
  4. AM
Answer. a

5. Consider the following statements comparing delta modulation (DM) with PCM system:

DM requires

  1. A lower sampling rate
  2. A higher sampling rate
  3. A higher bandwidth
  4. Simple hardware

Which of the above statements are correct?

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

6. The main advantage of time-division multiplexing (TDM) over frequency division multiplexing (FDM) is that it

  1. requires less bandwidth
  2. requires less power
  3. requires simple circuitry
  4. provide a better signal-to-noise ratio
Answer. d

7. A signal is passed through an LPF with cut-off frequency 10 kHz. The minimum sampling frequency is

  1. 10 kHz
  2. 5 kHz
  3. 30 kHz
  4. 20 kHz
Answer. d

8. 24 voice channels are sampled uniformly at a rate of 8 kHz and then time division multiplexed. The sampling process uses flat-top samples with 1 μs duration. The multiplexing operation includes the provision of synchronization by adding an extra pulse of 1 μs duration. The spacing between successive pulses of the multiplexed signal is

  1. 6 μs
  2. 4 μs
  3. 8.4 μs
  4. 7.2 μs
Answer. b

9. Output data ratio of a 8-bit PCM-TDM system sampling 24 voice channels, comparing these using μ-law at the rate of 8 kHz and with a I frame alignment word, is

  1. 1.2 x 106 bits/sec
  2. 1.4 x 106 bits/sec
  3. 1.6 x 106 bits/sec
  4. 1.8 x 106 bits/sec
Answer. c

10. A binary channel with a capacity of 36 kbits/sec is available for PCM voice transmission. If signal is band-limited to 3.2 kHz, then the appropriate values of quantizing level L and the sampling frequency respectively are

  1. 64 and 7.2 kHz
  2. 32 and 3.6 kHz
  3. 64 and 3.6 kHz
  4. 32 and 7.2 kHz
Answer. d

11. In time-division multiplexing cross talk may be avoided by

  1. proper base band filtering.
  2. proper selection of time of sampling.
  3. increasing the amplitude of signal
  4. proper quantization.
Answer. a

12. A comparison of FDM and TDM systems shows that

  1. FDM requires lower bandwidth, but TDM has greater noise immunity.
  2. FDM has greater noise immunity and requires lower bandwidth the TDM.
  3. FDM requires channel synchronization while TDM has greater noise immunity.
  4. FDM requires more multiplexing, while TDM requires band-pass filter.
Answer. c

13. DPCM is particularly suited for

  1. Radar signals transmission
  2. Radio signals transmission
  3. Speech signals transmission
  4. Seismic signals transmission
Answer. c

14. The following events will not happen when quantizing noise is decreased in PCM.

  1. Increase in the number of standard levels.
  2. Increase in bandwidth.
  3. Decrease in channel noise.
  4. Decrease in randomness due to difference in digit sent and actual signal at an instant.
Answer. d

15. A binary channel with capacity 36 kbps is available for PCM transmission. If signal is band-limited to 3.2 kHz, then approximate values of quantizing levels (L) and sampling frequency (fs) respectively are

  1. 32 and 3.6 kHz
  2. 64 and 7.2 kHz
  3. 64 and 3.6 kHz
  4. 32 and 7.2 kHz
Answer. d

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