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Posted By: Sra1 Member Level: Diamond Posted Date: 28 May 2008
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2007 Jawaharlal Nehru Technological University B.Tech Electronics COMMUNICATION ENGINEERING (Supplimentary Examinations, November 2007) Question paper
Set No 4
---------------
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. (a) An AM transmitter has antenna current of 2A with modulation index of 60 percent. What will be the total antenna current if one more identical antenna is connected in parallel with the previous one, keeping the transmitter output same? Will it affect the modulation index?
(b) An audio frequency signal 10 sin(2p × 500t) is used to amplitude modulate a
carrier of 50 sin 2p105t. Calculate
i. Modulation index
ii. Side band frequencies
iii. Amplitude of each side band frequencies
iv. Bandwidth required
v. Total power delivered to the load of 600 ohms
vi. Transmission efficiency. [8+8]
2. (a) A sinusoidal modulating wave of amplitude 5V, and frequency 1kHz is applied to a frequency modulator. The frequency sensitivity of the modulator is 45Hz/V the carrier frequency is 100kHz. Calculate its frequency deviation and modulation index.
(b) Explain analytically how do the AM and narrow-band FM differ each other. Show that the average power of FM is constant. [6+10]
3. (a) Explain the operation of ISB transmitter with block diagram. Where it is used?
(b) What is the function of crystal filters in SSB transmitter?
(c) State and explain with respect to ‘Q’, various types of filters used to separate side bands? [4+6+6]
4. (a) Distinguish between simple AGC and delayed AGC.
(b) Draw a block diagram of a superheterodyne receiver and explain the function of each stage.
(c) What is meant by the term “tracking error”? Explain. [5+6+5]
5. (a) Explain why inductunce and capacitance do not generate noise.
(b) Define noise factor, in terms of input and output signal to noise ratios of a network.
(c) The noise factor of an amplifier is given as 5:1. If the input S/N is 50 db.
Calculate the output S/N ratio in decibels. [5+6+5]
6. (a) Explain the generation and demodulation of pulse-position modulation.
(b) What is meant by Cross-talk? Explain in detail. [10+6]
7. Draw the block diagram of DPSK transmitter and receiver and explain the operation. [16]
8. (a) Which is more efficient, circuit switching or virtual circuits switching? Why?
(b) What are the three switching methods? Explain [8+8]
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