Coherent Detection MCQ [Free PDF] – Objective Question Answer for Coherent Detection Quiz

1. The correlating detector is also known as

A. Maximum likelihood detector
B. Minimum likelihood detector
C. Maximum & Minimum likelihood detector
D. None of the mentioned

Answer: A

A coherent detector considers phase as the most important parameter. This coherent detector is also known as the maximum likelihood detector.

 

2. The minimum Nyquist sampling rate is given as, fs =

A. 1/T
B. T
C. 2/T
D. 2T

Answer: A

The input signal comprises a prototype signal plus noise and the bandwidth is 1/2T where T is the symbol time and the minimum Nyquist sampling rate can be given as 2W or 1/T.

 

3. Phase-locked loop circuitry is used for

A. Carrier wave recovery
B. Phase estimation
C. Carrier wave recovery & Phase estimation
D. None of the mentioned

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Answer: C

The phase-locked loop circuitry locks on the arriving carrier wave and estimates its phase.

 

4. In differential PSK the date is

A. Encoded differentially
B. Decoded differentially
C. Encoded & Decoded differentially
D. None of the mentioned

Answer: A

In this method, the data is encoded deferentially that is the presence of binary zero, or one is manifested by the symbol’s similarity or difference when compared to that of the previous symbol.

 

5. Envelope detector consists of

A. Rectifier and high pass filter
B. Rectifier and low pass filter
C. Amplifier and low pass filter
D. Amplifier and high pass filter

Answer: B

An envelope detector consists of a rectifier and a low pass filter. The detectors are matched to the envelopes and not to the signal themselves.

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6. The minimum required spacing is the difference between the

A. Center of the spectral main lobe and first zero crossing
B. First and second zero crossing
C. First and last zero crossing
D. None of the mentioned

Answer: A

The frequency difference between the centre of the spectral main lobe and the first zero crossing is called the minimum required spacing in non-coherent detection.

 

7. The minimum tone separation corresponds to

A. T
B. 1/T
C. 2T
D. T/2

Answer: B

In non-coherent detection, the minimum tone separation corresponds to 1/T.

 

8. Matched filter is used for

A. Coherent detection
B. Non-coherent detection
C. Coherent & Non-coherent detection
D. None of the mentioned

Answer: A

The matched filter is used for coherent detection. It cannot be used for non-coherent detection because matched filter output is a function of unknown angle α.

 

9. In differential encoding the _________ different between two waveforms is measured.

A. Magnitude
B. Frequency
C. Phase
D. Time period

Answer: C

In differential encoding, the phase of the present signal waveform is compared with the phase of the previous signal.

 

10. The error probability of DPSK is ________ worse than PSK.

A. Twice
B. 3 dB
C. Twice (3dB.
D. None of the mentioned

Answer: C

DPSK has twice as much as noise than in PSK. The error probability in DPSK is twice (3dB. worse than PSK.

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