December 17, 2011

ANALOG COMMUNICATIONS JNTU ECE previous years question papers

( Common to Electronics & Communication Engineering and Electronics & Telematics)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. (a) Explain 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) Explain 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; calculate the total power in the modulated wave in the following forms of AM:
i. A3E
ii. DSB-SC
iii. J3E. [8+8]
4. (a) How do you distinguish the two 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. Explain the noise performance of SSB - SC receiver and prove its S/N Ratio is unity. [16]
6. (a) What is frequency drift? What are the factors that influence the frequency drift How is it avoided?
(b) Explain about radio broadcast transmitters with the help of block diagram.7. (a) Describe the circuit of an FET amplitude limiter, and with the aid of the transfer characteristic explain the operation of the circuit.
(b) What can be done to improve the overall limiting performance of an FM receiver ? Explain the operation of the double limiter and also AGC in addition to a limier. [16]
8. (a) Define and describe pulse position modulation, and explain with waveforms how it is derived from PWM.
(b) Explain clearly the generation and demodulation of PWM with the help of necessary diagram.



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