# Analog Communications Questions and Answers – Noise in FM

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) Bessel

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. What is the spectral density of white noise?
a) varies with bandwidth
b) varies with frequency
c) constant
d) infinite

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

3. Which is the true statement about noise performance of wideband FM system?
a) it is independent of modulation index
b) more prone to noise interference
c) it is independent of signal to noise ratio
d) it exhibits a threshold

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

4. What is the power ratio of one decibel?
a) 2:1
b) 1.26:1
c) 3:1
d) 2.5:1

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.

5. Bit is a unit of ________
a) Channel Capacity
b) Entropy
c) Information
d) Rate of information

Explanation: Bit is a unit of information. Information is the message to be transmitted. It is used in computing and digital communications.
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6. What is the maximum possible value of entropy?
a) 1
b) ∞
c) 100
d) 50

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.

7. If we double the value of resistor then how it affects the thermal noise power?
a) gets doubled
b) gets halved
d) remains unchanged

Explanation: The thermal noise power remains unchanged if we double the values of given resistors as both are independent of each other.

8. What is the auto correction function of white noise?
a) Impulse Function
b) Step Function
c) Ramp Function
d) Parabolic Function

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.

9. Pick the odd one out.
a) Cosmic noise
b) Galactic noise
c) Atmospheric noise
d) Polar noise

Explanation: Galactic noise is a random noise that originates from outside the earth’s atmosphere, whereas others are present in the Earth’s atmosphere.

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