Categories: Second Year Second Semester (2-2)

II B. Tech II Semester Supplementary Examinations, April-2018

ANALOG COMMUNICATIONS

(Electronics and communication Engineering)Time: 3 hours Max. Marks: 70

Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answer ALL the question in Part-A

3. Answer any THREE Questions from Part-B

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PART ?A

1. a) What are the basic constituents of a communication system? (4M)

b) How can you obtain a DSB-SC signal? What is the Band-width of DSB-SC

signal? (4M)

c) What do you mean by angle modulation? What are the types of angle modulation? (4M)

d) Write down the expression for the signal to noise ratio at the output of angle

modulation systems. (4M)

e) Define the term distributor or de-commutator? (2M)

f) Write the main functions of a radio receiver? (4M)

PART -B

2. a) With suitable diagram explain the square-law diode modulation method for AM

generation? (8M)

b) An amplitude modulated voltage is given by V = 50 (1 + 0.2 cos 100 t + 0.001 cos

3500t) cos 10

6

t. State all frequency components present in the voltage, and find

modulation index for each modulating voltage term. What is the effective

modulation index of V? (8M)

3. a) List out the methods for generation of SSB-SC signal and explain any one of the

method in detail. (8M)

b) Find the various frequency components and their amplitudes in the voltage given

by v (t) = 50 (1+ 0.7 Cos 5000t- 0.3 Cos 1000t) sin 5×10

6

t. Draw the single sided

spectrum. Also evaluate the modulated and sideband power. (8M)

4. a) Explain in detail about NBFM and WBFM. Derive the expression for bandwidth

of wideband FM. (8M)

b) An angle modulated signal is represented in time domain as s (t) = 10 Cos (2p.10

6

t

+ 3 Sin 2p.10

3

t). Assuming the given signal as PM,

i) Calculate the frequency deviation, modulation index, B.W and power.

ii) Repeat the above calculations when the message frequency is doubled. (8M)

5. a) Derive the expression and explain how pre-emphasis/de-emphasis filtering

improves the signal to noise ratio? (8M)

b) Find Figure of merit and signal to noise ratio for the Ring modulator. (8M)

6. a) With neat sketch explain the generation of PWM and PPM? (8M)

b) Three signals m

1

, m

2

and m

3

are to be multiplexed, m

1

and m

2

have a 50 kHz

bandwidth, and m

3

has a 10 KHz bandwidth. Design a commutator switching

system so that each signal is sampled at its Nyquist rate. (8M)

7. a) Draw the block diagram of amplitude modulated transmitter and explain functions

of various blocks. (8M)

b) Briefly discuss about the frequency stability in FM Transmitter? (8M)

1 of 1

SET – 1

R13

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