Noise in Communication Systems MCQs

Practice Noise in Communication Systems MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Communication SystemsNoise in Communication Systems

A receiver has a noise figure of 6 dB. Its noise factor is approximately?

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Correct Answer: B. 4

Explanation: Noise factor F=10^(NF/10)=10^0.6≈3.98, approximately 4.

Reference: Standard communication systems: noise figure numerical

Question 2

Communication SystemsNoise in Communication Systems

If a system has input SNR of 30 dB and output SNR of 24 dB, its noise figure is?

A3 dB
B6 dB
C24 dB
D54 dB

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Correct Answer: B. 6 dB

Explanation: Noise figure in dB is SNRin(dB)-SNRout(dB)=30-24=6 dB.

Reference: Standard communication systems: noise figure from SNR

Question 3

Communication SystemsNoise in Communication Systems

The equivalent noise temperature Te of a device with noise factor F is related to standard reference temperature T0 by?

ATe=T0/F
BTe=T0(F-1)
CTe=T0F^2
DTe=(F-1)/T0

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Correct Answer: B. Te=T0(F-1)

Explanation: Equivalent noise temperature is Te=T0(F-1), commonly using T0=290 K.

Reference: Standard communication systems: equivalent noise temperature

Question 4

Communication SystemsNoise in Communication Systems

A device has noise factor F=2 at reference temperature 290 K. Its equivalent noise temperature is?

A145 K
B290 K
C580 K
D870 K

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Correct Answer: B. 290 K

Explanation: Te=T0(F-1)=290(2-1)=290 K.

Reference: Standard communication systems: equivalent noise temperature numerical

Question 5

Communication SystemsNoise in Communication Systems

For cascaded stages, Friis’ formula shows that the overall receiver noise performance is strongly influenced by?

AThe noise factor and gain of the first stage
BOnly the last-stage output power
CAntenna color
DAudio-frequency volume setting

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Correct Answer: A. The noise factor and gain of the first stage

Explanation: In Friis' cascade formula, noise contributions of later stages are divided by preceding gains, making a low-noise high-gain first stage especially important.

Reference: Standard communication systems: Friis formula

Question 6

Communication SystemsNoise in Communication Systems

Two cascaded stages have F1=2, G1=10 and F2=5, where gain is a linear power ratio. The total noise factor is?

A2.0
B2.4
C2.5
D7.0

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Correct Answer: B. 2.4

Explanation: Friis' formula for two stages is F=F1+(F2-1)/G1=2+(5-1)/10=2.4.

Reference: Standard communication systems: Friis formula numerical

Question 7

Communication SystemsNoise in Communication Systems

Thermal-noise power available from a resistor over bandwidth B at absolute temperature T is ideally?

AkTB
BkT/B
CTB/k
DkB/T

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Correct Answer: A. kTB

Explanation: The available thermal-noise power is N=kTB, where k is Boltzmann's constant.

Reference: Standard communication systems: thermal noise power

Question 8

Communication SystemsNoise in Communication Systems

At T=290 K and bandwidth B=1 MHz, thermal-noise power kTB is approximately?

A4.0×10^-21 W
B4.0×10^-15 W
C2.9×10^-7 W
D1.38×10^-23 W

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Correct Answer: B. 4.0×10^-15 W

Explanation: N=kTB≈1.38×10^-23×290×10^6≈4.0×10^-15 W.

Reference: Standard communication systems: thermal noise numerical

Question 9

Communication SystemsNoise in Communication Systems

If receiver bandwidth is doubled while temperature remains constant, the available thermal-noise power ideally?

AHalves
BRemains unchanged
CDoubles
DQuadruples

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Correct Answer: C. Doubles

Explanation: From N=kTB, noise power is directly proportional to bandwidth, so doubling B doubles N.

Reference: Standard communication systems: noise bandwidth relationship