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Posted Date: 30 May 2019      Posted By:: Tushar Pathak    Member Level: Bronze  Points: 3 (₹ 2)

2019 Dayanand Sagar University B.E Electronics & Communication Engineering AC, 4th semester, ECE,2019 Question paper

Course: B.E Electronics & Communication Engineering   University/board: Dayanand Sagar University

Analog communication final paper, containing amplitude modulation,angle modulation,random process,noise,its also include one marks questions.

1 Each Question carries 1 Mark 1 x 20
a) In amplitude modulation, bandwidth is ……………. the audio signal frequency
b) If Amin = 40 and Amax = 60, what is the percentage modulation?
c) In amplitude modulation, the ………… of carrier is varied according to the strength of the signal.
d) Over-modulation results in …………..
e) Define Coherent Detection
f) Define Hilbert transform
g) An SSB modulator can be implemented with a Product modulator followed by a…. filter.
h) SSB is a standard form for radio communication.
a) True b) False
i) A system with a differentiator followed by an FM modulator is called …………
j) An FM transmitter has a maximum deviation of 12 kHz and a maximum modulating frequency
of 12 kHz. The bandwidth by Carson's rule is ………..
k) When the modulating signal controls the Phase of the carrier, we get……….modulation
l) The amount of data transmitted for a given amount of time is called……….
m) A continuous random variable X is uniformly distributed over the interval [10, 16]. The Expected
value of X is
n) What is the value of an area under the conditional PDF ?
o) Define probability density function
p) The sum of the product of each value of a discrete random variable X times its probability is
referred to as its……
q) The noise due to random behavior of charge carriers is……..Noise
r) For a three-stage cascade amplifier, calculate the overall noise figure when each stage has a
gain of 12 DB and noise figure of 8dB.
s) Define Noise Factor
t) Thermal noise is also known as………Noise
2 a Explain the terms mean, correlation and covariance functions 8
b Let X be a continuous random variable having uniform probability distribution defined in the
range 2=X=4. Let Y be 3X+2. Determine the means mx and my and mean square value of X
and Y 8
3 a Explain the generation of AM wave using square law modulator with equivalent equation,
Illustrate the spectrum before and after filtering process 10
b An Amplitude modulated signal is given S(t) = 10 cos (2p×10 6t) + 5 cos (2p×10 6t) cos
(2p×103t) + 2 cos (2p×10 6t) cos (4p×10 3t) Determine the i) Total modulated power ii) Side
band power and iii) Net modulation index 4
c With time domain and frequency domain description, Illustrate the significance of double side
band suppressed carrier modulation 2
4 a Develop an expression for representing SSB containing upper side band in time domain 8

b Analyze the errors caused by the change in frequency and phase in coherent detection method
of DSBSC by first deriving perfect synchronization expression 8
5 a Illustrate with the help of the spectrum that FM contains infinite number of sidebands 10
b An FM generator with 2 multipliers is used to transmit audio signals in the range 50 Hz to
15kHz. A narrow band phase modulator is supplied with a carrier wave of frequency f1=200kHz.
The desired FM at the output has a carrier frequency of 108 MHz and frequency deviation is
75kHz. Design multiplier and mixer oscillator frequencies. Assume ß = 0.2 6
6 a Define PLL. Develop the nonlinear model of PLL and draw the block diagram 10
b Investigate the effects of nonlinearity on FM systems 6
7 a Develop Friiss formula for cascade connection of noisy networks 10
b Two port devices are connected in cascade. For the first stage the noise figure and available
power gain are 5 dB and 12 dB respectively. For the second stage the noise figure and power
gain are 15 dB and 10 dB. Determine overall noise figure in dB. Also find equivalent noise
temperature 6
8 a Analyze the technique used for the transmission of a number of independent signals over a
single communication channel by modulating different carrier 10
b The incoming signal has the mid band frequency that may lie in the range of 530 K Hz
to1650KHz and associated bandwidth of 10KHz .This signal has to be translated to a fixed
frequency band centered at 450KHz Determine the tuning range provided by the Local
Oscillator. 6

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