This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Coherent detection”.
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
View Answer
Explanation: Coherent detector considers phase as the most important parameter. This coherent detector is also known as maximum likelihood detector.
2. The minimum nyquist sampling rate is given as, fs =
a) 1/T
b) T
c) 2/T
d) 2T
View Answer
Explanation: The input signal comprises of a prototype signal plus noise and the bandwidth is 1/2T where T is the symbol time and 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
View Answer
Explanation: 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
View Answer
Explanation: In this method, the data is encode deferentially that is the presence of binary zero or one is manifested by 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
View Answer
Explanation: 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.
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
View Answer
Explanation: The frequency difference between the center of the spectral main lobe and the first zero crossing is called as 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
View Answer
Explanation: 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
View Answer
Explanation: 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 wave forms is measured.
a) Magnitude
b) Frequency
c) Phase
d) Time period
View Answer
Explanation: 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
View Answer
Explanation: DPSK has twice as much as noise than in PSK. The error probability in DPSK is twice (3db) worse than PSK.
Sanfoundry Global Education & Learning Series – Digital Communications.
To practice all areas of Digital Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.
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