Digital Communication MCQ Questions and Answers for Practice

1. Two binary values are represented by two different frequencies in :

1. frequency-shift-keying
2. phase-shift-keying
3. amplitude-shift-keying
4. none of these above

2. Codec uses

1. Delta modulation only
2. PCM and Delta modulation
3. Pulse code modulation technique only
4. None of these

3. ASK is a result of combination of Shift keying and

1. Analog modulation
2. Amplitude modulation
3. Digital modulation
4. None of these above

4. ASK is rarely used in modems because

1. it is highly susceptible to noise
2. it takes care of amplitude only
3. it shifts only between ON and OFF states
4. none of the above

5. The qualifier differential to PSK means that

1. it uses phase shifts of 180 degree
2. phase shift is with reference to the previous bit transmitted
3. it uses phase shifts of multiple of 90 degree
4. none of these above

6. In PCM

1. Pulse Amplitude modulation samples are quantized
2. Non-linear coding scheme is undertaken
3. Digital signal is converted into analog signal
4. None of these

7. In modems

1. A digital signal changes some characteristics of a carrier wave
2. Digital signal is amplified
3. Several digital signal are multiplexed
4. None of these above

8. Modulation is used to

1. Separate differing transmission
2. Ensure that information may be transmitted over long distances
3. Reduce the bandwidth
4. Allow the use of practicable antennas

9. One factor in the accuracy of a reconstructed PCM signal is the

1. Carrier frequency
2. Number of bits used for quantization
3. Signal bandwidth
4. Baud rate

10. The modulation techniques used to convert analog signal into digital signal are

1. Delta modulation
2. Adaptive delta modulation
3. Pulse code modulation
4. All of the above

11. In PCM, the parameter varied in accordance with the amplitude of the modulating signal is

1. Frequency
2. Phase
3. Amplitude
4. None of the above

12. The error probability of a PCM is

1. Gaussian noise + error component due to inter symbol interference
2. Calculated using power spectral density
3. Calculated using noise and inter symbol interference
4. All of the above

13. In Delta Modulation, the bit rate is

1. N times the modulating frequency
2. N times the nyquist criteria
3. N times the sampling frequency
4. None of the above

14. DPCM is a technique

1. Where difference between successive samples of the analog signals are encoded into n-bit data streams
2. Where digital codes are the quantized values of the predicted value
3. To convert analog signal into digital signal
4. All of the above

15. Granular noise occurs when

1. Step size is too large
2. There is interference from the adjacent channel
3. Step size is too small
4. Bandwidth is too large