Jawaharlal Nehru Technological University Anantapur 2011-2nd Year B.Tech Electronics and Communications Engineering Analog Communications s, - Question Paper

JAWAHARlAL NEHRU TECHNOLOGICAL UNIVERSITY, Anantapur
ans any 5 ques.
All ques. carry equal marks Max Marks:80

1. (a) discuss the collector modulation method for generating AM wave with a neat circuit diagram and waveforms.
(b) An AM amplifier provides an output of 106 W at 100% modulation. The internal loss is 20 W
i. What is un-modulated carrier power?
ii. What is the side band power? [10+6]

2. (a) What is the need to suppress the carrier in AM wave? Write the expressions of the DSB-SC wave in time and frequency domain. Draw its waveform and spectrum.
(b) When the modulation percentage is 75, an AM transmitter produces 10 KW.How much of this is carrier power? What would be the percentage of power saving if the carrier is suppressed before transmission took place. [8+8]

3. (a) discuss VSB. What is the need for VSB transmission? What is the transmission bandwidth of VSB?
(b) A 400Wcarrier is modulated on depth of 75 percent compute the total power in the modulated wave in the subsequent forms of AM:
i. A3E
ii. DSB-SC
iii. J3E. [8+8]

4. (a) How do you distinguish the 2 cases of frequency modulation (FM) namely,the narrow-band FM and the wideband FM?
(b) FM is called a Constant Band Width system-Justify with suitable illustrations.
(c) In a FM system if modulation index is doubled by halving modulating frequency, what will be the effect on the maximum deviation? [6+6+4]

5. discuss the noise performance of SSB - SC receiver and prove its S/N Ratio is unity. [16]

6. (a) What is frequency drift? elaborate the factors that influence the frequency drift How is it avoided?
(b) discuss about radio broadcast transmitters with the help of block diagram. [9+7]

7. (a) define the circuit of an FET amplitude limiter, and with the aid of the transfer characteristic discuss the operation of the circuit.
(b) What can be done to improve the overall limiting performance of an FM receiver ? discuss the operation of the double limiter and also AGC in addition to a limier. [8+8]

8. (a) describe and define pulse position modulation, and discuss with waveforms how it is derived from PWM.
(b) discuss clearly the generation and demodulation of PWM with the help of necessary diagram. [8+8]

Earning:   Approval pending.