This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Noise in FM”.

1. What is the probability density function of thermal noise?

a) Poisson

b) Gaussian

c) Binomial

d) Armstrong

View Answer

Explanation: Thermal noise is approximately white, it means that its power spectral density is nearly equal throughout the frequency spectrum. The amplitude of the signal has a Gaussian probability density function.

2. Neutralization cancels unwanted feedback by bypassing the feedback to the neutral or ground plane.

a) True

b) False

View Answer

Explanation: Neutralization cancels unwanted feedback by adding feedback out of phase with the unwanted feedback.

3. What is the spectral density of white noise?

a) varies with bandwidth

b) varies with frequency

c) constant

d) infinite

View Answer

Explanation: Random signals are considered as white noise if they are observed to have a flat spectrum. Its spectral density remains constant.

4. Which is the true statement about noise performance of wideband FM system?

a) it is independent of modulation index

b) it is generally poorer than that of an AM system

c) it is independent of signal to noise ratio

d) it exhibits a threshold

View Answer

Explanation: Noise performance of wideband FM system exhibits a threshold.

5. What is the power ratio of one decibel?

a) 10:1

b) 1.26:1

c) 3:1

d) 2.5:1

View Answer

Explanation: Power ratio is a method used by media companies to measure revenue performance compared to the audience share it controls. Power ratio of one decibel is close to 1.26:1.

6. Bit is a unit of ________

a) Channel Capacity

b) Entropy

c) Information

d) Rate of information

View Answer

Explanation: Bit is a unit of information. It is used in computing and digital communications.

7. What is the maximum possible value of entropy?

a) 1

b) ∞

c) 1000

d) 18

View Answer

Explanation: Entropy is the measure of disorder. Higher the disorder, higher is the entropy of the system. The maximum possible value of entropy is 1.

8. If we double the value of resistor then how it affects the thermal noise power?

a) gets doubled

b) gets halved

c) gets quadrupled

d) remains unchanged

View Answer

Explanation: The thermal noise power remains unchanged, if we double the values of given resistors.

9. What is the auto correction function of white noise?

a) Impulse Function

b) Step Function

c) Constant

d) Linear Function

View Answer

Explanation: White noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. Its auto correlation function is an impulse function.

10. Pick odd one about:

a) Cosmic noise

b) Galactic noise

c) Atmospheric noise

d) Polar noise

View Answer

Explanation: Galactic noise is a random noise that originates from outside the earth’s atmosphere.

**Sanfoundry Global Education & Learning Series – Analog Communications.**

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