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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 5
31.
If a line is terminated in characteristic impedance Z0, the input impedance measured at the input will be
Z0
Z0/2
Zero
infinite
Answer: Option
Explanation:

If line is terminated in Z0, the input impedance is Z0.

32.
In a TV, the output from RF tuner is about
1 μV
1000 μV
100 μV
0.5 μV
Answer: Option
Explanation:

It is about 1 mV.

33.
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
192 kHz
2 MHz
1.299 MHz
1.54 MHz
Answer: Option
Explanation:

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.

34.
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
R = 32 KbPs, SNRq = 25.8 dB
R = 64 KbPs, SNRq = 49.8 dB
R = 64 KbPs, SNRq = 58.8 dB
R = 32 KbPs, SNRq = 49.8 dB
Answer: Option
Explanation:

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

SNR = 1.76 + 6.02n

= 1.76 + 6.02 x 8 49.8 dB.

35.
Generally a VCR has
four stationary video heads
two stationary video heads
four rotating video heads
two rotating video heads
Answer: Option
Explanation:

VCR has two rotating leads about 180° apart.

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