15. The noise equivalent temperature of a circuit having a noise figure of 11 with a reference temperature of 300?K is oK

A.3000

B.3300

C.30

D.3

16. The noise figure of a circuit whose noise equivalent temperature and noise reference temperature are the same is

A.1

B.0

C.2

D. infinity

17. The input signal-to-noise ratio for an envelope detector is90. If the modulation index for the incoming AM waves is 0.5, the output signal-to-noise ratio is

A.20

B.45

C.18

D.180

18. If input signal-to-noise ratio of a synchronous detector is 100, the output signal-to-noise ratio is

A.50

B.25

C.200

D.400

19. If maximum frequency deviation of a transmission system is 75 kHz and modulating frequency is 15 kHz, the improvement in the output S/N ratio due to FM over a comparable AM system with m = 1 is

A.25

B.75

C.90

D.225

20. The minimum value of ms for an FM system required to produce a noticeable improvement in S/N ratio over a comparable AM system with m =1 is

A. ji

B.

C. it

D.1/./3

21. The major source of thermal noise in a microwave system is

A. waveguide feeder

B. receiver mixer

C. TWT amplifier transmitter

D. FM demodulator

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