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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 3
-------------------
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) Distinguish between phase and frequency modulation. Show that FM can be
derived using PM and vice versa with the help of differentiator or integrator
networks.
(b) Compute the bandwidth requirement for the transmission of FM signal having
a frequency deviation 75 KHz and an audio bandwidth of 10KHz.
(c) In a FM system the frequency deviation constant is 1KHz/V. A sinusoidal
modulating signal of amplitude 15 V and frequency 3 MHz is applied, Calculate
i. Peak frequency deviation
ii. Modulating index. [6+4+6]
3. (a) Explain the requirements of carrier frequency for a radio transmitter.
(b) Explain the working of broadcast transmitter? [8+8]
4. (a) Explain the necessity for AGC in a radio receiver.
(b) Discuss the consideration that governs the choice of IF in a receiver.
(c) Explain the operation of superheterodyne receiver. [5+5+6]
5. (a) Define noise figure and derive the expression for the overall noise figure of Cascaded linear networks, in terms of network parameters F1,
N
n1,
G1; F2,
N
n2,
G2,
etc.,
(b) Draw an experimental set up to measure the Noise figure of a system and explain. [10+6]
6. (a) Explain the generation and demodulation of pulse-position modulation.
(b) What is meant by Cross-talk? Explain in detail. [10+6]
7. (a) Discuss the bandwidth efficiency of M-ary digital modulation techniques.
(b) Draw the signal space diagram of coherent QPSK system and explain. [8+8]
8. (a) Explain the common - channel-signaling modes?
(b) Consider a simple telephone network consisting of two end offices and one intermediate switch with a 1-MHz full-duplex trunk between each end office and the intermediate switch. The average telephone is used to make four calls per 8-hour workday, with a mean call duration of six minutes. Ten percent of the calls are long distance, what is the maximum number of telephones an end office can support? [8+8]
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