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) List frequency band and communication application of usable frequency spectrum shown below
(i) Voice frequency
(ii) Very low frequency
(iii) Medium frequency
(iv) High frequency
(v) Ultra high frequency(5 marks)
1 (b) A three stage amplifire has the following power gains and noise figure (as ratios, not in dB) for each stage. Calculate the power gain, noise figure and noise temperature for the cascaded amplifier, assuming method condition
| Stage | Power Gain | Noise Figure |
| 1 | 10 | 2 |
| 2 | 20 | 4 |
| 3 | 30 | 5 |
(5 marks)
1 (c) Compare High level and Low level modulation in terms of power level types of amplifier used, efficiency, limitation and application(5 marks)
1 (d) Explain effect to change in modulating frequency for Amplitude, Frequency and Phase modulation(5 marks)
2 (a) Explain Amplitude Modulation (AM) for more that one modulating signal in following terms:
(i) Mathematical equation
(ii) AM Waveform
(iii) AM amplitude and power spectrum
(iv) Modulation coefficeint
(v) Transmission power(10 marks)
2 (b) Draw block diagram of superheterodync receiver. Write frequency component present at the output of each block if modulating frequency is 2 kHz, carrier frequency 550 KHz and Intermediate frequency (IF) of 455 KHz also sketch waveforms at the output of IF and detector stage.(10 marks)
3 (a) With help of a neat block diagram explain the principle and generation of indirect method of FM generation(10 marks)
3 (b) Explain with block diagram how AFC will counteract a downward drift in frequency oscillator being stabilized(6 marks)
3 (c) A 20 MHz carrier is modulated by a 400 Hz audio sine wave. If the carrier voltage is 5 volts and maximum deviation is 10 KHz, write an equation for FM wave and calculate the power dissipated across 100 Ω resistor.(4 marks)
4 (a) State and prove sampling theorem for low pass band limited signal(10 marks)
4 (b) With the help of neat circuit diagram explain the generation and detection of Pulse Position Modulation (PPM) siganl(10 marks)
5 (a) Draw block diagram of Adaptive Delta Modulator and explain its working(10 marks)
5 (b) How is Adaptive Delta Modulation (AMD) an improvement over Linear Delta Modulation(DM) in following terms :
(i) slop overload
(ii) distortion
(iii) SNR
(iv) BW
(5 marks)
5 (c) Compare DM, ADM, PCM and DPCM in following terms :
(i) Number of bits sample
(ii) Step Size
(iii) Distortion
(iv) Complexity
(v) Appliction (5 marks)
6 (a) Draw a block diagram of PCM system and explain the function of each bolck.
(b) Draw block diagram of phase cancellation SSB generator and explain how carrier and unwanted sidebands are suppressed(10 marks)
Write short note on (any four) :-
7 (a) Independent sideband system(5 marks)
7 (b) Tracking in AM receiver (5 marks)
7 (c) Phase Modulation(5 marks)
7 (d) Noise in communication system(5 marks)
7 (e) Quantization error(5 marks)
7 (f) Ratio Detector(5 marks)
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