ANALOG COMMUNICATION SYSTEM PAPER 2

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ANALOG COMMUNICATION SYSTEM (New) EC 301 5th Sem May 2k5

Note: Section A is compulsory. Attempt any Four questions from Section B and two from Section C. Assume any missing data.

Section A Marks 2 each

1.

1. Describe the differences between low and high level modulation.
2. For a modulation coefficient of 0.4 and carrier power of 400 W, determine total side-band and transmitted power.
3. Describe three point tracking.
4. What is the purpose of a squelch circuit?
5. What is the difference between coherent and non-coherent receiver?
6. Define modulation index for FM and PM.
7. Describe the significance of FM noise triangle.
8. Describe basic difference between AM and FM services.
9. What is the purpose of 19 kHz plot in FM stereo-broadcasting?
10. Describe sampling theorem.

Section B Marks 5 each

2. What is the difference between low and level modulation? Draw circuit diagram of low level modulator and explain its function.

3. Describe the operation of a filter type SSB transmitter with the help of block diagram.

4. One output to an AM DSFBC modulator is an 800 kHz carrier with an amplitude of 40 Vp. The second input is a 25 kHz modulating signal whose amplitude is sufficient to produce a + 10 V change in the amplitude of the envelope. Calculate:

1. Upper and lower side band frequencies.
2. Modulation coefficient and percentage modulation.
3. Maximum and minimum positive amplitude of the envelope.
4. Draw output frequency spectrum
5. Draw the envelope and label it .

5. The mutual conductance of an FET varies linearly with gate voltage between the limits 0 to 9 ms. The FET is used as a capacitive reactance modulator with Xcgd =10. Rgs is placed across an oscillator circuit which is tuned to 50 MHz by a 50 pF capacitor. What will be the total frequency variation when trans-conductance of FET is varied from zero to maximum by modulating voltage?

6. Draw the circuit diagram of Foster Seeley discriminator.

Section C Marks 10 each

7. (a) What is difference between pulse modulation, frequency modulation and amplitude modulation.
(b) Define and describe pulse position modulation and explain wit the help of waveforms how it is derived from PWM?
(c) Explain pulse position demodulator. 3,4,3

8. (a) Explain the working of product demodulator with the help of diagram.
(b) With the help of block diagram explain the working of SSB Pilot Carrier Receiver.

9 (a) A 25 MHz carrier is modulated by 400 Hz audio sine wave. If the carrier voltage is 4 and the maximum duration is 10 kHz, write the equation of this modulated wave for: (i) FM (ii) PM
If the modulating frequency is now changed to 2 kHz, all else remaining constant write new equation for (i) FM (ii) PM
(b) Describe the FM generation using PLL (Phase Locked Loop)