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Posted By: Sree.... Member Level: Diamond Posted Date: 21 May 2008
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2007 Andhra Pradesh State Jawaharlal Nehru Technological University B.Tech COMMUNICATION ENGINEERING Set No. 4 Question paper
Code No: RR321001 Set No. 4
III B.Tech II Semester Regular Examinations, Apr/May 2007
COMMUNICATION ENGINEERING
(Electronics & Instrumentation Engineering)
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 to 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) The sinusoidal modulating wave m(t) = Am cos(2pfmt) is applied to a phase
modulation with phase sensitivity Kp . The unmodulated carrier wave has
frequency fc and amlititude Ac . Determine the spectrum of the resulting
phase modulated wave, assuming that the maximum phase deviation ßp =
KpAm does not exceed 0.5 radians.
(b) A carrier wave of frequency 100 MHz is frequency modulated by sine wave of
amplitude 20 volts and frequency 100 KHz. The frequency sensitivity of the
modulation is 25 KHz per volt. Determine the approximate bandwidth of FM
wave using Carson’s rule. [10+6]
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) Briefly explain the function of each of the block in the superheterodyne re-
ceiver.
(b) Calculate the image rejection of a receiver having an RF amplifier and an IF
of 450 Hz, if the Q’s of the relevant coils are 65 at an incoming frequency of
i. 1200 Hz
ii. 20 MHz [8+8]
1 of 2
Code No: RR321001 Set No. 4
5. (a) Derive Noise figure formula for cascaded network
(b) A mixer circuits has a noise figure of 12 dB. It is preceded by an amplifier
that has an equivalent noise temperature of 200 K and a power gain of 30 dB.
Calculate the equivalent noise temperature of the combination referred to the
amplifier input. [8+8]
6. (a) Draw the conceptual diagram of multiplexing-demultiplexing and explain.
(b) Distinguish between sampling and quantization. [8+8]
7. Draw the block diagram of DPSK transmitter and receiver and explain the opera-
tion. [16]
8. (a) Compare RS-423 with RS-422.
(b) How is X.21 able to eliminate most of the control circuits of the EIA standard?
(c) What is the difference between balanced and unbalanced circuits. [6+4+6]
? ? ? ? ?
2 of 2
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