Digital Communications Laboratory Viva Questions - Part 2

Theory_Questions:

    Two Signals x1(t) = sink(200t) and x2(t)=sinc(400t) then find the Nyquist rate of [x1(t)* x2(t)]

(A).200Hz.

(B).400Hz.

(C).100Hz.

(D).300Hz.

    A signal represents by x (t) = 5cos (400πt) is sampled at a rate of 300 samples/sec. The resulting samples are passed through an ideal LPF with cut-off frequency of 150Hz.which of the following will be contained in the output of LPF?

(A).100Hz.

(b).100Hz, 150Hz.

(C).50Hz, 100Hz.

(d).20Hz, 100Hz, 150Hz.

    If a continuous time signal x (t) = 4cos (200 πt) is sampled with a periodic pulse function, aliasing will not occur when the sampling period is.

(A).6msec.

(B).8msec.

(C).4msec.

(D).10msec.

    Find the Nyquist Rate of Sinc2(100t)

(A).100Hz.

(B).200Hz.

(C).50Hz.

(D).400Hz.

5. A message Signal m (t) = 4cos (2π *103t)) is sampled and transmitted through as channel using 4-bit PCM. Determine the Maximum possible Quantization error.

(A).0125V.

(B).0.5V.

(C).0.25V.

(D).1V.

6. In the above problem if signal is sampled at 60% higher than the Nyquist rate determine the sampling rate.

(A).1 KHz.

(B).2Khz.

(C).1.6Khz.

(D).3.2Khz.

7. A signal x(t)= 5cos(20πt) is sampled at a rate of 25Hz to recover the original signal what should be the range of Cut-off frequency of the Low pass filter?

(A).5Hz-10Hz.

(B).10Hz-15Hz.

(C).10Hz-25Hz.

(D).15Hz-25Hz.

8. An analog message sampled at regular time intervals and sampled values rounded up to the nearest of a pre-selected quantized level is

(A).still analog.

(B).digital.

(C).analog in amplitude but discrete in time.

(D).quantized in amplitude and discrete in time.





9. Designing of any communication system is aimed at improving the —--of the system.

(A).Fidelity of signal.

(B).Noise.

(C). signal to noise ratio

(D).Signal detection.

10. Fourier Transform of

(a).

(b).

(c).

(d). Both B and C

Key:

1.A

2.A

3.C

4.B

5.C

6.D

7.B

8.C

9.C

10. D