Microwave Engineering Questions and Answers – Noise Characteristics of Receivers

This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Noise Characteristics of Receivers”.

1. The noise power will determine the maximum detectable signal level for a receiver.
a) True
b) False
View Answer

Answer: b
Explanation: The noise power will determine the minimum detectable signal level of the receiver for a given transmitter power, maximum range of a communication link. There is a limit on the maximum noise that can be associated with a signal in spite of which the signal can be recovered from the noise.

2. Equivalent noise temperature of a transmission line connecting the antenna to the receiver is:
a) TP (LP-1)
b) TP (LP + 1)
c) TP/ (LP-1)
d) TP / (LP + 1)
View Answer

Answer: a
Explanation: The transmission line connecting the antenna to the receiver has a loss of LT and is at a physical temperature TP. its noise equivalent temperature is given by TP (LP-1).

3. In a receiver, if the noise figure of the mixer stage in the receiver is 7 dB, then the equivalent noise temperature is given that the receiver is operating at 290 K:
a) 1163 K
b) 1789 K
c) 1000 K
d) 1234 K
View Answer

Answer: a
Explanation: Equivalent noise temperature for a given noise figure is given by To (FM-1). FM is the noise figure in dB. Substituting the given values for noise figure and temperature, noise equivalent temperature is 1163 K.
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4. If a transmission line connecting the antennas to the receiver has a loss of 1.5 dB, given the physical temperature is 270C, noise equivalent temperature is:
a) 123 K
b) 145 K
c) 345 K
d) 234 K
View Answer

Answer: a
Explanation: The noise equivalent temperature of the transmission line is given by TP(LP-1). Converting the value from dB scale and substituting, noise equivalent temperature is 123 K.

5. Given that the antenna efficiency is 0.9, equivalent brightness temperature is 200 K; physical temperature is 300 K, noise temperature of an antenna is:
a) 220 K
b) 210 K
c) 240 K
d) None of the mentioned
View Answer

Answer: b
Explanation: Noise temperature of an antenna is given by rad Tb + (1- rad) TP. Tb is the equivalent brightness temperature and TP is the physical temperature. Substituting the given values, noise temperature of the antenna is 210 K.
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6. If a receiver is operating at a bandwidth of 1 MHz and has antenna noise temperature of 210 K, then the input noise power is:
a) -90 dBm
b) -115 dBm
c) -56 dBm
d) -120 dBm
View Answer

Answer: b
Explanation: Input noise power is given the expression kBTa) Here k is the Boltzmann’s constant, B is the operational bandwidth of the antenna and TA is the antenna noise temperature. Substituting in the above expression, input noise power is -115 dBm.

7. Antenna noise temperature of a system is 210 K, noise temperature of transmission line is 123 K, loss of a transmission line connecting the antenna to receiver is 1.41 and noise temperature of the receiver cascade is 304 K. then the total system noise temperature is:
a) 840 K
b) 762 K
c) 678 K
d) 1236 K
View Answer

Answer: b
Explanation: The total system noise temperature is given by the expression TA+TTL+LTTREc) TA is the antenna noise temperature, TTL is the transmission line noise temperature, TREC is the noise temperature of receiver cascade. Substituting the given values, total system noise temperature is 762 K.
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8. If the received power at antenna terminals is -80dBm, and if the input noise power is -115 dBm, then the input SNR is:
a) 45 dB
b) -195 dB
c) -35 dB
d) 35 dB
View Answer

Answer: d
Explanation: Input SNR of a system is (Si-Ni) in dB. Substituting the given signal power and noise power in dB, input SNR of the system is 35 dB.

9. A receiver system is operating at a bandwidth of 1 MHz and has a total system noise temperature of 762 K. then the output noise power is:
a) -110 dBm
b) -234 dBm
c) -145 dBm
d) -124 dBm
View Answer

Answer: a
Explanation: Output noise power of a receiver system is kBTsys. B is the operating bandwidth and Tsys is the total system noise temperature. Substituting the given values in the given equation, output noise power is -110 dBm.
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10. If the received power at the antenna terminals is Si=-80 dBm and the output noise power is -110 dBm then the output signal to noise ratio is given by:
a) 30 dB
b) -30 dB
c) 35 dB
d) -35 dB
View Answer

Answer: a
Explanation: Output signal to noise ratio in dB is given by (So-No). Substituting the given values in the above equation, the output SNR is 30 dB.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
To practice all areas of Microwave Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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