Fundamentals of Communication Engg - Dec 2012
Electronics Engineering (Semester 4)
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.
Answer any four of the following:-
1 (a) Compare and contrast between AM and FM.(5 marks)
1 (b) In a broadcast superheterodyne receiver having no RF amplifier, the loaded Q of the antenna coupling circuit is 150. If the IF is 455 kHz, calculate the image frequency and its rejection ratio at 1400 kHz.(5 marks)
1 (c) Explain noise triangle in FM.(5 marks)
1 (d) Explain the following terms:-
i) Signal-to-noise ratio
ii) Noise figure
iii) Noise factor
iv) Equivalent noise temperature(5 marks) 2 (a) When the modulation percentage is 75 an AM transmitter produces 10 kW. How much of this is carrier power? What would be the percentage power saving if the carrier and one of its side-bands were suppressed before transmission took place?(6 marks) 2 (b) Explain VSB transmission.(8 marks) 2 (c) Explain the phase shift method for SSB generation giving voltage equations at each stage.(6 marks) 3 (a) Compare FM and PM.(4 marks) 3 (b) Explain Armstrong method of FM generation with the help of a neat block diagram and phasor diagrams.(10 marks) 3 (c) In an FM system, when the audio frequency is 1000 Hz and AF voltage is 2 V, the frequency deviation is 4.8 kHz. If the AF voltage is raised to 10 V while the AF is dropped to 500 Hz, find the modulation index in each case.(6 marks) 4 (a) With the help of a neat block diagram and waveform explain superheterodyne AM radio receiver.(10 marks) 4 (b) Explain the working of a phase discriminator FM detector with the help of a neat circuit diagram and phasor diagrams.(10 marks) 5 (a) State sampling theorem. Explain flat-top sampling. Draw its spectrum and explain aperture effect.(10 marks) 5 (b) Explain generation and demodulation of PAM, PPM and PWM with waveforms.(10 marks) 6 (a) Explain delta modulation with a neat block diagram and waveforms. Also explain slope overload error and granular noise. Suggest the remedy for both.(10 marks) 6 (b) Draw the following line codes for 10010:
ii) Polar NRZ
iii) Polar RZ
iv) Unipolar RZ
V) AMI(5 marks) 6 (c) Draw and explain the block diagram of PCM transmitter and receiver.(5 marks)
Write short notes on:-
7 (a) Companding in PCM(5 marks) 7 (b) AGC in radio receiver(5 marks) 7 (c) Choice of IF in radio receivers(5 marks) 7 (d) Practical diode detector.(5 marks)