**B.E. (fourth semester) EXAMINATION, Dec, 2004**

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

**ANALOG AND DIGITAL COMMUNICATION**

**(404)**

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

1. (a) Define convolution State the prove time convolution theorem in Fourier transform.

(b) Find Fourier transform of the following function and sketch them.

(i) Sgn (t)

(ii) Cos ω_{0}t u (t)

2. (a) Explain the working of envelope detector . What is the upper limit of the RC to ensure capacitor

Follows the envelope?

(b) A multiple tone modulating signal f(t) consisting of three frequency is given by :

f (t) = E1 cos ω_{1}t + E_{2} cos ω_{2}t + E_{3} cos ω_{3}t

ω_{3} > ω_{2} > ω_{1} > and E1>E2>E_{3}

_{ }The signal F (t) modulates a carrier e_{c} = E_{c} dos w_{c }t.

(i) Derive the expression for AM wave

(ii) Draw the signal sided spectrum and find the bandwidth of the AM wave

3. (a) How the FM signal can be generated with PM signal discuss in detail

(b) A 25 MHz carrier is modulated by 400 Hz audio sine wave. If the carrier voltage is 4volt and the

Maximum deviation is 10 kHz, write the equation of this modulated wave for (i) FM (ii) PM. If

the modulating frequency is now changed to 2 kHz, Write new equation FM and PM

4. (a) Draw the block diagram superhetrodyne receiver and explain its working in detail .

(b) (i) State sampling theorem

(ii) 24 Telephone channels each band limited to 3.4 kHz are to betimes division multiplexed by

Using PCM. Calculate the bandwidth of the PCM system for 128 quantization levels and 8 kHz

Sapling frequency .5. (a) Draw the schematic diagram of a delta modulation system and explain

its working. What are its limitation and how are they over come?

(b) Explain PCM technique. Explain why PCM is noise resistant and then other forms of pulse

Modulation.

6. (a) Draw and explain with block diagram of QPSK transmitter .

(b) Compare various digital carrier modulation schemes.

7. (a) Find te channel capacity in the channel shown in fig. bellow

(b) Apply Shannon- fano coding producer to find the coding efficiency for the following message ensemble:

[X] = [ X_{1 }X_{2} X_{3} X_{4 } X_{5} X_{6 }X_{7 } ]

[P] = [0.4 0.2. 0.12 0.08 0.08 0.08 0.04]

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

(i) Companding

(ii) Quantization

(iii) Matched filter

(iv) SN performance of PCM