Exercise: Communication Systems

Questions for: Communication Systems

A remote control of TV uses a 10 bit word. The maximum number of total commands it can transmit is
A:
64
B:
256
C:
512
D:
1024
Answer: D

210 = 1024.

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Generally a VCR has
A:
four stationary video heads
B:
two stationary video heads
C:
four rotating video heads
D:
two rotating video heads
Answer: D

VCR has two rotating leads about 180° apart.

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A signal is sampled at 8 kHz and is quantized using 8 bit uniform quantizer. Assuming SNRq for a sinusoidal signal, the correct statement for PCM signal with a bit rate of R is
A:
R = 32 KbPs, SNRq = 25.8 dB
B:
R = 64 KbPs, SNRq = 49.8 dB
C:
R = 64 KbPs, SNRq = 58.8 dB
D:
R = 32 KbPs, SNRq = 49.8 dB
Answer: B

where n is no. of bit, fs is sampling frequency.

SNR = 1.76 + 6.02n

= 1.76 + 6.02 x 8 49.8 dB.

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24 telephone channels, each band limited to 3.4 kHz, are to be time division multiplexed by using PCM, calculate the bandwidth of PCM system for 128 quantization levels and an 8 KHz sampling frequency
A:
192 kHz
B:
2 MHz
C:
1.299 MHz
D:
1.54 MHz
Answer: D

Given, n = 24, fm = 3.4 kHz

M = 128,

2N = 128 n = 7

But fs = 2fm, here we will consider fs (sampling) frequency

instead at 2fm 2 x 3.4 kHz 6.8 KHz.

B.W. = [24(7 + 1)] 8 kHz = 1.54 MHz.

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In a TV, the output from RF tuner is about
A:
1 ΞV
B:
1000 ΞV
C:
100 ΞV
D:
0.5 ΞV
Answer: B

It is about 1 mV.

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