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Reg No.:_ Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
FOURTH SEMESTER B.TECH DEGREE EXAMINATION(S), DECEMBER 2019
Course Code: EC208
Course Name: ANALOG COMMUNICATION ENGINEERING
Max. Marks: 100 Duration: 3 Hours

PARTA
Answer any two full questions, each carries 15 marks. Marks
1 a) Explain thermal noise in amplifiers. Write down the expression for the noise (8)
power and derive the expression for noise voltage.
b) Derive the spectrum for sinusoidally modulated AM wave and draw the spectrum. (7)
2 a) A receiver consists of an amplifier which has a noise temperature of 100 K anda (6)
gain of 30 dB. The output of the amplifier is connected to a mixer which has a
noise figure of 15dB. Calculate the noise temperature of the mixer and the overall
noise temperature of the receiver referred to the input.
b) Draw the circuit diagram of a BJT collector modulator for AM and explain its (9)
working with waveforms.
3 a) Define noise factor and derive the expression for the output noise power of an (6)
amplifier in terms of noise factor.
b) The antenna current of an AM transmitter, 30% modulated by a sine wave is 10 A. (6)
It increases to 10.75 A while modulated by another sine wave simultaneously.
What is the modulation index due to the second wave?

c) Mention the need for modulating a signal before transmission. (3)

PART 13
Answer any two full questions, each carries 15 marks.

4 a) Derive the expression for the output of a sinusoidally modulated FM wave. Define (8)

various parameters in the expression.
b) Explain the operation of a doubly balanced diode ring modulator with the help ‏آہ‎ (7)

diagram.

5 a) A sinusoidal modulating waveform of maximum amplitude 4 ५ and ೩ frequency (6)
of 1 KHz is applied to an FM generator, which has a frequency deviation constant
of 5000 Hz/volt. Calculate the maximum frequency deviation, modulation index,

and bandwidth.