# Analog and Digital Communication Dec 2003

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

ANALOG AND DIGITAL COMMUNICATION

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

1. (a)    State the prove time shifting property and frequency shifting property in Fourier transform.

(b)     Evaluate the Fourier transform of a trapezoidal function f(t) shown in fig. 1.

2. (a)    Explain the synchronous detection method of DSB –SC  signal . Explain the effect of phase and frequency errors in synchronous detection.

(b)   The antenna current of a AM broadcast transmitter modulated to a death of a 40 % by an audio sine wave as 11A. it increase to 12 a as a result of simultaneous modulation by author audio sine wave . What is the modulation index due to the second wave?

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

(b)    When the modulating frequency in an FM system is 400 Hz and the modulating voltage is 2.4 V,  the modulation index is 60. Calculate the maximum deviation. What is the modulation index  when the modulation frequency is reduce to 250 Hz and the modulating voltage is  simultaneously raised to 3.2 V?

4. (a) (i)    State and prove sampling theorem.

(ii)     Write merits and demerits of DM.

(b)     8 channels each band limited to 5 kHz are to be time division multiplexed. Each sample Is coded into a 6-bit word. Find the output rate in bitssec, and the required bandwidth.

5  (a)      Draw the schematic diagram of QPSK generating system and explain its working . Give the merits and demerits over BPSK.

(b)     Discuss the principle of matched filter

6.  (a)      Find the channel capacity for the channel shown in fig. 2.

(b)        Apply the Shannon fano coding procedure to find the coding efficiency for the following message insemble:

[X] = [ X1 X2 X3 X4  X5 X6 X7 X8  ]

[P] = [11  18  116  116  116  14  116  116]

7.  (a)    Discuss the block diagram of AM radio transmitter and explain the working of each stage .

(b)         Distinguish between the following:

(i)      Analog, discrete and digital signals:

(ii)     DPCM and delta modulation

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

(i)      Envelope detector

(ii)      BW consideration of FM

(iii)     DPCM

(iv)     Quantization

(v)     SN performance of PCM