Analog Communication - Dec 2011

Electronics & Telecomm. (Semester 5)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) Explain White Gaussian Noise and Determine thermal noise power at room temperature for a B.W. of 5MHz, Also calculate noise volt for R=50?(10 marks) 1 (b) Draw the block diagram of Superheterodyne Radion Receiver and explain Selective & Sensitivity of radion receiver, wha is tracking error?(10 marks) 2 (a) Distriguish between High level and low level modulation by six points(6 marks) 2 (b) An AM transmitter radiates 5 MHz carrier with 80 kw power, carrier is modulated by 500 Hz & 1 KHz signals
1. What will be the total modulation index if each signal modulates at 60% of modulation?
2. Determine the transmitted power.
3. Draw the frequency spectrum of modulated signal.
4. What is % of power saving if one of sideband and carrier is suppressed?(8 marks) 2 (c) Explain VSB transmission & State its two advantages(6 marks) 3 (a) State necessity of pre emphasis & de-emphasis. Draw 75 usec circuit and explain them(6 marks) 3 (b) Distriguish between :-
(i) Narrowband & wideband FM
(ii) FM & PM(8 marks) 3 (c) The modulating frequency in FM system is 600Hz and the modulating voltage is 2V, with depth of modulation of 70. Calculate the maximum deviation. What will be-the modulation index if the modulating frequency is reduced to 400Hz & modulating voltage is simultaneously raised to 3.5v?(6 marks) 4 (a) What is double spotting? How does it arise and how it can be reduce?(6 marks) 4 (b) A receiver is tuned to 3-30 MHz frequency range with IF frequency of 40525 MHz.
(i) Find the range of local oscillator frequency and image frequency od AM receiver having channel bandwidth of 10 KHz
(ii) Draw the frequency response of IF & AF amplifire(8 marks) 4 (c) Compare delayed AGC & simple AGC. Eplain working of delayed AGC circuit(6 marks) 5 (a) With bock diagram explain working of Radion detector, how amplitude limiting is achieved in it? Explain(6 marks) 5 (b) (i) What is aliasing error? How it can be eliminated?(4 marks) 5 (b) (ii) Find the Nyquist rate interval for the signal x(t)= Sin 200πt/πt(4 marks) 5 (c) State advantages and drawbacks of pulse modulation over continuous wave modulation(6 marks) 6 (a) With the help of block diagram, explain how AFC system stabilize the local oscillator frequency(6 marks) 6 (b) Explain generation of Flat top sampling with neat circuit diagram(6 marks) 6 (c) With neat block diagram and waveforms, explain working of Adaptive delta modulation. State its advantages.(8 marks)

Write short note on (Any Four ):-

7 (a) Non Uniform Quantizations(5 marks) 7 (b) μ-law & A-law of companding(5 marks) 7 (c) Generation of PWM & advantages of PWM(5 marks) 7 (d) Fidelity and image frequency of AM receiver (5 marks) 7 (e) Delta modulation(5 marks) 7 (f) Phase Modulation(5 marks)