Signals and Noises

Digital Communications Systems

This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Signals and Noises”.

1. The term heterodyning refers to
a) Frequency conversion
b) Frequency mixing
c) Frequency conversion & mixing
d) None of the mentioned

2. The causes for error performance degradation in communication systems are
a) Interference
b) Electrical noise
c) Effect of filtering
d) All of the mentioned

3. Thermal noise in the communication system due to thermal electrons
a) Can be eliminated
b) Cannot be eliminated
c) Can be avoided upto some extent
d) None of the mentioned
.

4. White noise has _______ power spectral density.
a) Constant
b) Variable
c) Constant & Variable
d) None of the mentioned

5. Which are called as hard decisions?
a) Estimates of message symbol with error correcting codes
b) Estimates of message symbol without error correcting codes
c) All of the mentioned
d) None of the mentioned

6. The filter which is used to recover the pulse with less ISI is called as
a) Matched filter
b) Correlator
c) Matched filter & Correlator
d) None of the mentioned

7. The composite equalizing filter is the combination of
a) Receiving and equalizing filter
b) Transmitting and equalizing filter
c) Amplifier and equalizing filter
d) None of the mentioned
View AnswerAnswer: a

8. The sample from the demodulation process consists of sample which is _______ to energy of the received symbol and _____ to noise.
a) Directly and inversely proportional
b) Inversely and directly proportional
c) Both directly proportional
d) Both inversely proportional

9. The average noise power of white noise is
a) 0
b) Infinity
c) 1
d) None of the mentioned

10. The channel may be affected by
a) Thermal noise
b) Interference from other signals
c) Thermal noise & Interference from other signals
d) None of the mentioned

11. Channels display multi-path due to
a) Scattering
b) Time delayed reflections
c) Diffraction
d) All of the mentioned

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