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Code No: 134AC R16


B.Tech II Year II Semester Examinations, December - 2018
(Electronics and Communication Engineering)
Time: 3 Hours Max. Marks: 75

Note: This question paper contains two parts A and B.

Part A is compulsory which carries 25 marks. Answer all questions in Part A.
Part B consists of 5 Units. Answer any one full question from each unit. Each question
carries 10 marks and may have a, b, c as sub questions.

(25 Marks)
1.a) Define analog Modulation and also, list different types of analog modulations. [2]
b) Define Modulating Signal, Carrier and Modulated Signals. [3]
c) What is Guard band? [2]
d) Compare SSB and VSB. [3]
e) List the disadvantages of FM over AM. [2]
f) In an FM system, if mf is doubled by halving the modulating frequency, what will be the
effect on the maximum deviation? [3]
g) What is threshold effect? [2]
h) What is pre-emphasis? Why is it used? [3]
i) Illustrate Single and double polarity PAM wave. [2]
j) Define Sensitivity, Selectivity and image frequency. [3]

(50 Marks)
2.a) With the help of waveforms and spectrum, describe the concept of Amplitude modulation
both in time domain and frequency domain.
b) Describe the coherent detection of DSB-SB modulated waves. [5+5]
3.a) With necessary circuit diagram and waveforms, explain how DSB-SC wave is generated
i) Balance Modulators and
ii) Ring Modulator.
b) When a broadcast AM transmitter is 50 percent modulated, its antenna current is 12 A.
What will be current when the modulation depth is increased to 0.9? [8+2]

4. Describe the SSB in frequency domain and then explain how to generate SSB modulated
wave using frequency discrimination method. Also, list the advantages of SSB. [10]
5.a) Describe the VSB in time domain and then explain any one method of generating VSB
modulated wave.
b) Give the applications of AM-FC and VSB modulation schemes. [6+4]

6.a) Discuss the detection of FM wave using zero crossing detector.
b) Discuss the generation of FM wave using direct method. [5+5]
7.a) Analyze Sinusoidal FM wave with the help of its spectrum.
b) Explain how FM signal is detected with the help of PLLs. [5+5]

8.a) Derive the Noise Figure for cascade stages.

b) What is thermal noise? Derive the expression for the thermal noise voltage across a
resistor. [6+4]
9.a) Discuss the noise performance of AM system using envelope detection.
b) Draw the Phasor representation of FM noise. [5+5]

10.a) Of all the frequencies that must be rejected by a superheterodyne receiver, why is the
image frequency so important? What is the image frequency and how does it arise? If the
image-frequency rejection of a receiver is insufficient, what steps could be taken to
improve it?
b) Define and distinguish between PTM and PAM schemes. [6+4]
11.a) Describe the generation and demodulation of PPM with the help of block diagram.
b) Draw the block diagram of FM receiver and explain each block, briefly. [5+5]