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Communication Systems problems

1. If C is capacity of noisy channel, (bits/s), ?f is bandwidth Hz and S/N is signal to noise ratio, then
Options
A.
B.
C.
D.

2. Which of the following cannot be the Fourier series expansion of a periodic signal?
Options
A. x(t) = 2 cos t + 3 cos 3t
B. x(t) = 2 cos pt + 7 cos t
C. x(t) = cos t + 0.5
D. x(t) = 2 cos 1.5pt + sin 3.5 pt

3. In colour TV receiver, varactor diode is used for
Options
A. detection
B. rectification
C. tuning
D. both (a) and (b)

4. Frequency shift keying is used mostly in
Options
A. telegraphy
B. telephony
C. satellite communication
D. radio transmission

5. Which of the following has the highest input impedance?
Options
A. CE
B. CB
C. CC
D. Push pull

6. Degaussing in a picture tube means
Options
A. Adding magnetism in mask and mounting frame
B. Removing residual magnetism in mask, shield etc...
C. Increasing resistance of coils to decrease time constant
D. Decreasing resistance of coils to increase time constant.

8. If the bandwidth is increased by 2, the ?_FM ?_AM (where ? is the ratio of SNR of output to SNR at input, FM is frequency modulation and AM is amplitude modulation) is increased by a factor of
Options
A. 2
B. 3
C. 4
D. 6

9. When the channel is noisy, producing a conditional probability of error p = 0.5; the channel capacity and entropy function would be, respectively,
Options
A. 1 and 1
B. 1 and 0.5
C. 0.5 and 1
D. 0 and 1

10. c(t) and m(t) are used to generate an FM signal. If the peak frequency deviation of the generated FM signal is three times the transmission bandwidth of the AM signal, then the coefficient of the term cos [2p(1008 x 10³t)] in the FM signal (in terms of the Bessel Coefficients) is
Options
A. 5 J₄(3)
B. J₈(3)
C. J₈(4)
D. 5 J₄(6)

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