Andhra University 2005 B.Tech Information Technology - Analog Communications - Question Paper

MODEL PAPER

B.Tech (IT) Degree exam

Second Year - 1st Semester

ANALOG COMMUNICATIONS

Time: three hrs
Max Marks: 70

First ques. is Compulsory

ans any 4 from the remaining ques.

All ques. carry equal marks

ans all parts of any ques. at 1 place

1. (a) describe Fourier series and Fourier transforms?
(b) discuss the properties of Fourier transforms?
(c) Differentiate ranging from Wideband FM and Narrowband FM?
(d) Show a scheme to convert PM to FM?
(e) describe the terms Sensitivity and Fidelity as applied to receivers?
(f) In a broadcast Super heterodyne receivers with no RF amplifiers, if the IF used is 455KHz, obtain image frequency at 1000KHz?
(g) describe the terms Amplitude modulation?

2. (a) an AM wave form has the subsequent form, x(t) = 10(1+0.5 cos2000 pt) cos two x 108 pt volts. Consider one ohm load and obtain (i) the avg. power content of every spectral component of x(t), (ii) the side band power and (iii) modulation index. (8)
(b) discuss SSB generation using phase shift method. explain relative merits and demerits of SSB modulation over DSB modulation. (6)

3. (a) Determine the Fourier transform of (5)

x(t) = {cosp t -1/2 = t = +1/2
0 otherwise
(b) Prove that an Autocorrelation function is an Even function? (5)
(c) A carrier wave vc(t) = A sin wct is amplitude-modulated by an audio wave vm(t) = B sin 3wmt. Sketch the complete spectrum of the modulated wave and compute the total power in the side bands in (B/A) = 0.5. (4)

4.(a) provide the PM and FM equations. Show that FM can be generated using PM modulator. (4)
(b) discuss with neat block schematic diagram the Armstrong method of FM generation. Draw the phasor diagram illustrating the principle. (4)
(c) discuss the operation of Foster silly discriminator using Block diagram ? (6)

5. (a) what is the significance of VSB signal and where does it obtain its application? Show that a VSB wave plus carrier retains the base band info in its envelope. (8)
(b) an angle modulated wave is defined by F(t) = 10cos[1X108pt +10cos 2000 pt]. compute (i) power of the modulated signal, (ii) the maximum frequency deviation and (iii) band width of a signal. (6)

6. Classify radio transmitters and discuss any 1 AM and FM transmitters with block diagram? (14)

7. (a) discuss major factors that influence the option of intermediate frequency in any particular system. (6)
(b) Draw a neat block diagram of Super heterodyne Receiver and discuss its operation? (8)

8. (a) Draw a neat block diagram of Communication Receiver and Explain? (8)
(b) discuss the working of delayed AGC circuit and compare the above with No, Ideal and simple AGC circuits using AGC characteristics? (6)

Earning:   Approval pending.