Principles of Analog & Digital Comm. - May 2012

Information Technology (Semester 3)

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) What is the effect of Gaussian noise on digital communication?(5 marks) 1(b) A 4kHz bandlimited signal is sampled at Nyquist rate and quantized to 4 levels Q1, Q2, Q3, Q4. The respective probabilities are P₁=P₂=1/8 and P₃=P₄=3/8. Find the rate of information.(5 marks) 1(c) Prove time convolution property of Fourier transform. (5 marks) 1(d) Explain Electronic Communication System with block diagram. (5 marks) 2(a) Draw circuit diagram of Foster Seeley discriminator and explain its working with phasor diagram.(10 marks) 2(b) Explain overload and hunting error in Delta Modulation. Find the condition to avoid slope overload error. (10 marks) 3(a) Draw the circuit diagram for ring modulator for generating DSB-SC AM signal and explain its working. (10 marks) 3(b) Explain the working of envelope detector. An audio signal of bandwidth 5 kHz is modulated on carrier frequency 1MHz using conventional AM. Determine range of values of RC for successful demodulation of this signal using an envelope detector.(10 marks) 4(a) What is multiplexing in communication systems? Draw the block diagram of frequency division multiplexing to transmit five signals.(10 marks) 4(b) A carrier C(t)=Acos 2?t is angle modulated(PM or FM) by a sinusoidal signal m(t)=2cos2000?t. The deviation constants are k_p=1.5 rad/V and k_f= 3000 Hz/V.
i. Determine modulation index in each case
ii. Determine the bandwidth in each case using Carson's rule
iii. If amplitude of m(t) is decreased by a factor of two, how would bandwidth change.(10 marks) 5(a) Explain the concept of image frequency and its rejection. Discuss double spotting.(10 marks) 5(b) Prove sampling theorem for low pass signals. What is use of anti-aliasing filter? (10 marks) 6(a) Draw the ASK, PSK and FSK waveforms for digital data 10100110. (10 marks) 6(b) What is need of pre-emphasis and de-emphasis in FM? Explain the standards used for the same with circuits. (10 marks) 7(a) Define Noise factor and Noise temperature.(5 marks) 7(b) Compare TDM and FDM. (5 marks) 7(c) Explain Friss Transmission formula. (5 marks) 7(d) Discuss Third Method of SSB generation (5 marks)