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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 5
21.
The time required for horizontal blanking is 16% of that for each horizontal line. If horizontal time is 63.5 μs, the horizontal blanking time for each line is about
1 μs
10 μs
100 μs
none of the above
Answer: Option
Explanation:

.

22.
When the number of quantising levels is 16 in PCM, the number of pulses in a code group will be
3
4
8
16
Answer: Option
Explanation:

2n = L n = 4.

23.
A message signal with bandwidth 10 kHz is lower sideband SSB modulated with carrier frequency fc1 = 106 Hz. The resulting signal is then passed though a narrow band frequency modulator with carrier frequency fc2 = 109 Hz. The bandwidth of the output would be
4 x 104 Hz
2 x 106 Hz
2 x 109 Hz
2 x 1010 Hz
Answer: Option
Explanation:

Bandwidth = 2Δf + 2B

But for NBFM, B < 1

BW ≈ 2fm 2fc1 2 x 106 Hz.

24.
In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to quantization noise ratio improves by the factor.
8/6
12
16
8
Answer: Option
Explanation:

Given n1 = 6, n2 = 8,

then (SNR)Q = 22(n2 - n1) 16.

25.
For 10 bit PCM system, the signal to quantization noise ratio is 62 dB. If the number of bits is increased by 2, then the signal to quantization noise ratio will
increased by 6 dB
increased by 12 dB
decreased by 6 dB
decreased by 12 dB
Answer: Option
Explanation:

= (SNR)Q + 6.02 x 2 (SNE)Q + 12 dB.

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