COMMUNICATION ENGINEERING

COMMUNICATION ENGINEERING
SEM-IV, 2012
B.TECH EXAMINATION
UTTARAKHAND TECHNICAL UNIVERSITY
(UTU)

Time: 2 Hours

Total Marks: 50

Attempt any four:

3×4=12

1. What is amplitude modulation and explain the low level and high level A. M. modulation method with the help of block diagram?
2. A modulation signal 10sin (2 Ω×10³t) is used to modulate a carrier signal 20sin (2Ω×10⁴t).Determine the modulation index, percentage modulation, frequencies of the sideband components. What will be the bandwidth of the modulated signal?
3. What is single sideband suppressed carrier modulation? Write one method of SSB generation and why is SSB not used for broadcasting?
4. What is DSB-SC? Explain the generation of DSB-SC with proper waveform and diagram.
5. What is VSB-SC? Explain the generation and detection of VSB-SC with suitable waveforms and diagram.
6. Calculate the percentage power saving when the carrier and one of the side bands are suppressed in an AM wave modulated to a depth of (1)100% (2)50%.

Attempt any four:

3×4=12

1. An FM transmission has a frequency deviation of 20 kHz. (i)Determine the percentage modulation of this signal if it is broadcasted in the 88-108MHz band (ii) Calculate the percentage modulation if this signal is broadcasted as the audio portion of a television broadcast.
2. In an FM system a 7 kHz modulating signal modulates 107.6 MHz carrier wave so that the frequency deviation is 50 kHz. Find (i) Carrier swing in the FM signal and modulating index m_f   (ii) The highest and lowest frequencies attained by the FM signal.
3. What is phase lock loop and explain the operating principle of PLL? Explain the advantage and disadvantages of FM over AM.
4. With the help of block diagram discuss Armstrong method of generating FM signal.
5. Explain the operation of balanced slope detector using a circuit diagram and describe noise in AM system.
6. Write a short note on external and internal noise. 

Attempt any two:

6.5×2=13

1. Describe the generation and detection of differential phase shift keying.
2. Explain adaptive delta modulation? How this modulation is advantageous over delta modulation.
3. Explain sampling theorem in detail. A PCM system uses a uniform quantizer followed by a v bit encoder, so that RMS signal to quantization noise ratio is approximately given as (1.8+6v) dB.

Attempt any two:

6.5×2=13

Write short on any two parts of the following: 

1. Satellite communication.
2. Sky wave propagation and tropospheric propagation.
3. Personal communication system.

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