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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

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)

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

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

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

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.

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

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

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.

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

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

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.

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

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.
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