Punjab Engineering College 2005 B.Tech Analog Communication System - Question Paper

EC 301 fifth Sem May 2005
ANALOG COMMUNICATION SYSTEM
Note: part A is compulsory. Attempt any 4 ques. from part B and 2 from part C. presume any missing data.

part A Marks two every

1.

1. define the differences ranging from 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. define 3 point tracking.
4. What is the purpose of a squelch circuit?
5. What is the difference ranging from coherent and non-coherent receiver?
6. describe modulation index for FM and PM.
7. define the significance of FM noise triangle.
8. define basic difference ranging from AM and FM services.
9. What is the purpose of 19 kHz plot in FM stereo-broadcasting?
10. define sampling theorem.

part B Marks five every

2. What is the difference ranging from low and level modulation? Draw circuit diagram of low level modulator and discuss its function.

3. define the operation of a filter kind SSB transmitter with the help of block diagram.

4. 1 output to an AM DSFBC modulator is an 800 kHz carrier with an amplitude of 40 Vp. The 2nd 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 tag it .

5. The mutual conductance of an FET varies linearly with gate voltage ranging from the limits 0 to nine 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.

part C Marks 10 every

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

8. (a) discuss the working of product demodulator with the help of diagram.
(b) With the help of block diagram discuss 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 four and the maximum duration is 10 kHz, write the formula of this modulated wave for: (i) FM (ii) PM
If the modulating frequency is now changed to two kHz, all else remaining constant write new formula for (i) FM (ii) PM
(b) define the FM generation using PLL (Phase Locked Loop)

Earning:   Approval pending.