Exercise: Communication Systems

Questions for: Communication Systems

In the television system in India, the odd and even fields are scanned
A:
25 times each
B:
25 times each but alternately
C:
50 times each
D:
50 times each but alternately
Answer: B

Each field is scanned 25 times but alternately.

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In a system an input resistance of 20 kÎĐ causes a noise voltage of 15ΞV. If two such input resistances each of 20 kÎĐ are used in parallel, the total noise voltage will be about
A:
15 ΞV
B:
30 ΞV
C:
7.5 ΞV
D:
10.6 ΞV
Answer: D

Overall resistance = 10 kW. Noise voltage = (15) = 10.6 ΞV.

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Dolby system of noise reduction divides the total audio spectrum into
A:
8 frequency bands
B:
4 frequency bands
C:
2 frequency bands
D:
none of the above
Answer: B

Dolby A system divides the frequency in 4 bands viz.f < 80 Hz, 80 Hz < f < 2999 Hz, f > 3000 Hz, f > 9000 Hz.

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For a system to be designated as hi-fi, the signal to noise ratio should be at least
A:
25 dB
B:
50 dB
C:
75 dB
D:
100 dB
Answer: B

Hi-Fi system has a ratio at least equal to 50 dB.

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In a two tone AM system the two modulating frequencies are 2000 p and 4000 p rad/sec. If carrier frequency is 2p x 106 rad/sec the frequencies of upper sidebands are
A:
1.002 MHz and 1.004 MHz
B:
1.001 MHz and 1.002 MHz
C:
1.001 MHz and 1.004 MHz
D:
1.002 MHz and 1.008 MHz
Answer: B

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