# Signal and Noise MCQ [Free PDF] – Objective Question Answer for Signal and Noise Quiz

1. The term heterodyning refers to

A. Frequency conversion
B. Frequency mixing
C. Frequency conversion & mixing
D. None of the mentioned

The method heterodyning means frequency conversion and mixing and this result in a spectral shift.

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

The main causes of error performance degradation are interference electrical noise effect of filtering and also due to the surroundings.

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

Thermal noise which cannot be eliminated is caused by the motion of thermal electrons and causes degradation in the system.

4. White noise has _______ power spectral density.

A. Constant
B. Variable
C. Constant & Variable
D. None of the mentioned

The AWGN has constant power spectral density.

5. Which are called hard decisions?

A. Estimates of message symbols with error-correcting codes
B. Estimates of message symbols without error-correcting codes
C. All of the mentioned
D. None of the mentioned

If error-correcting codes are not present, the detector output consists of estimates of the message symbol

which is also called hard decisions.

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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

The optimum filter used to recover the pulse with the best possible signal-to-noise ratio and less or no ISI is called a correlator or matched filter.

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

The functions of both receiving and equalizing filters can be performed by only the equalizing filter alone. Thus equalizing filter is the combination of equalizing and receiving filter.

8. The sample from the demodulation process consists of the sample which is _______ to the 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

The output symbol of the sampler consists of the sample which is directly proportional to the energy of the received signal and inversely proportional to the noise.

9. The average noise power of white noise is

A. 0
B. Infinity
C. 1
D. None of the mentioned

White noise is an idealized process with a two-sided spectral density equal to constant N0/2 and frequencies varying from minus infinity to plus infinity. Thus the average noise power is infinity.

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