Hall Ticket No:
Question Paper Code: A3412
VARDHAMAN COLLEGE OF ENGINEERING
(AUTONOMOUS) B. Tech IV Semester Regular/Supplementary Examinations, May 2018
(Regulations: VCE-R15) ANALOG COMMUNICATIONS
(Electronics and Communication Engineering) Date: 18 May, 2018 FN
Time: 3 hours
Max Marks: 75
Answer ONE question from each Unit
All Questions Carry Equal Marks
Unit I
1.
With a neat circuit diagram explain the generation of AM wave using switching modulator.
8M
With a neat diagram explain detection of AM wave using envelop detector.
7M
2.
With a neat diagram explain generation of DSBSC using Ring Modulator.
7M
Consider the message signal Cos Volts and the carrier wave Cos(100πt) volts:
i. Give the time time-domain expression for the resulting conventional AM wave for 75% modulation
ii. Find the power developed across a load of 100Ω due to this AM wave
8M
Unit II
3.
Explain the concept of frequency division multiplexing with relevant block diagram.
7M
Consider the message signal containing the frequency components 100, 200 and 400Hz. This message signal is applied to an SSB modulator together with a carrier at 100kHz with only USB retained. The coherent detector employed at the receiver uses a local oscillator that gives a sine wave of frequency 100.02kHz:
i. Determine the frequency components of the detector output
ii. Repeat your analysis assuming only LSB is transmitted
8M
4.
Derive a time domain expression for SSB modulated wave in which only the upper sideband is retained.
8M
Why VSB modulation is used in the transmission of video signal and how it can be demodulated in the receiver.
7M
Unit III
5.
Derive a mathematical equation for the WBFM wave with sinusoidal modulating signal and show that the bandwidth required for an ideal WBFM is infinity.
7M
An angle modulated signal with carrier frequency fc 106Hz is described by the equation 20cos[2fct 10 5 volts. Find the following:
i. The power in the modulated signal
ii. The maximum frequency deviation
iii. The deviation ratio
iv. The approximate transmission bandwidth
8M
6.
Explain demodulation of an FM wave using PLL with the help of neat sketch.
8M
Explain with the help of block diagram and relevant mathematical equation the generation of NBFM and also show that how it can be used in generating WBFM.
7M
Unit IV
7.
Derive an expression for figure of merit of an AM receiver that uses a non-coherent detector and show that it reduces to for a single tone modulation .
8M
Average noise power per unit bandwidth measured at front end of the AM receiver is 10-3w/Hz. The modulating wave is sinusoidal with carrier power of 80kw and sideband power of 10kw/sideband. The message bandwidth is 5KHz. Assuming the use of an envelope detector in the receiver; determine the output signal to noise ratio of the receiver. By how many dB is system inferior to a DSBSC modulation system?
7M
Cont…2

8.
Explain the generation and de-modulation of pulse width modulation with waveforms.
7M
Derive an expression for figure of merit of a DSBSC receiver using synchronous detector.
8M
Unit V
9.
Explain with suitable block diagram and necessary waveforms the working of superhetrodyne receiver with its characteristics.
8M
Find the tuning range necessary for the oscillator capacitor in a medium wave superhetrodyne receiver which tunes over the range of signals from 530kHz to 1650kHz and uses an IF of 455 kHz if the oscillator frequency is:
i. Higher than the signal frequency
ii. Lower than the signal frequency
7M
10.
Draw the block diagram of AM transmitter using high level modulation and explain the various blocks.
8M
In a broadcast superhetrodyne receiver having no RF amplifier, the loaded Q of the antenna coupling circuit(at the input to the mixer) is 80. If the intermediate frequency is 455 kHz, calculate:
i. The image frequency and its rejection ratio at 1000kHz
ii. The image frequency and its rejection ratio at 50MHz
7M