Analog and Digital Communication June 2008

(Common for CS, EC, EE &EI, IT Engg.)

Note:   Attempt any five questions. All question carry equal marks.

1. (a)     State and prove time shifting and time differentiation property of Fourier transform.

(b)         Explain signal distortion in transmission.

2. (a)    A single tone modulating signal em = Em cos ωm t amplitude modulates a carrier ee = Ec cos  ωc t:

(i)     Derive an expression for the AM wave e(t)

(ii)    Derive an expression for modulating index.

(b)       How the PM signal can be generated with the FM signal? Discuss in detail.

3. (a)   Explain parameter variation method of FM generation.

(b)       A modulating signal 5 cos 2π 15 × 103 t, angle modulates a carrier A cos ωc t.

(i)     Find the modulating index and bandwidth for FM and PM system.

(ii)       Determine the change in the in the bandwidth and the modulation index for both FM and PM is

Reduced to 7kHz.

4. (a)   Explain PCM technique . Explain why PCM technique is noise resistant than other forms of pulse

Modulation.

(b)        Explain with neat diagram working working of superhetrodyne receivers for AM wave.

5. (a)    State sampling theorem.

(ii)    24 Telephone channel all band limited to 3.4 kHz are time division multiplexed and sampled at the

Rate 8000 samples per second, find the bandwidth of the PCM system if 256 quantization levels

Are used .

(b)   Draw the schematic diagram of a delta modulation system and explain its working. What is its

Limitation and how are they overcome?

6. (a)  Briefly explain BFSK technique. Specify the bandwidth requirement?

(b)    Discuss the properties of matched filter. What is the need of using the same?

7. (a)  Define the following terms:

(i) Unit of information and information

(ii)  Entropy (iii) Channel capacity (iv) Rate of information

(b)     Apply the Shannon-fano Coding procedure to find the coding efficiency for the following message

Ensemble:

[X] = [ XX2  X3  X X5  XXx8 ]

[P] = [1/4  1/8 1/16  1/16  1/16 1/4  1/16 1/80]

8.  Write short notes on any three of the following:

(i)  Generation of AM

(ii)  Pre- emphases and De-emphases

(iii) Quantization

(iv)  Companding