Principles of Analog & Digital Comm. - Dec 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) Find Fourier transform of unit impulse signal ?(t). (5 marks) 1(b) Draw and explain the basic block diagram of Communication system. (5 marks) 1(c) Explain A-law and ?-law companding.(5 marks) 1(d) Compare Frequency modulation and Phase modulation. (5 marks) 2(a) Define Amplitude Modulation. Derive the equation of AM wave. Draw envelope of AM for m< 1, m = 1 and m > 1.(10 marks) 2(b) A 400 W carrier is modulated to depth of 75%. Calculate total power in following forms of AM:
i. DSB - FC
ii. DSB - SC
iii. SSB - FC
iv. SSB - SC.(10 marks) 3(a) Explain working of Foster Seeley discriminator with phasor diagram (10 marks) 3(b) In an FM system,when the Audio Frequency (AF) is 500 Hz and the AF voltage is 2.4 V, the deviation is 4.8 kHz. If the AF voltage is now increased to 7.2 V,what is new deviation? If the AF voltage is raised to 10V while the AF is droppedto 200 Hz, what is new deviation? Find modulation index in each case.(10 marks) 4(a) Explain the sideband generation in SSB using phase shift method.(10 marks) 4(b) Explain satellite communication system. List applications in various fields.(10 marks) 5(a) Draw and explain block diagram of four channel FDM system. (10 marks) 5(b) Explain double conversion superheterodyne receiver with neat block diagram. (10 marks) 6(a) Explain the terms sensitivity, image frequency, double spotting, automatic gain control and three point tracking in radio receivers. (10 marks) 6(b) How adaptive DM is improvement of linear DM? Draw block diagram of adaptive DM and explain its working. (10 marks) 7(a) State sampling theorem for low pass signals. What is Nyquist rate? (5 marks) 7(b) Explain working of balanced modulator. (5 marks) 7(c) Define Noise temperature and Noise Bandwidth. (5 marks) 7(d) Find Fourier transform of x(t) = e^-at, t?0. (5 marks)