Kurukshetra University 2007 B.Tech Electronics and Communications Engineering Analog Communications - Question Paper

Analog Communications
Paper-ECE-203E
Maximum Marks : 100

Note:—Attempt 5 ques. in all, selecting at lowest 1 ques. from every part.

SECTION-I

1.(a) A receiver having overall voltage gain A, output resistance RL & bandwidth B operates at temperature T oK. The receiver input resistance is Rr and it is fed from an antenna having resistance Ra. Derive a formula for noise power No. Also obtain the value of noise figure F in terms of Ra, Rt and Req, where Req is the equivalent noise resistance excluding RT [10]

(b) The noise output of a resistor is amplified by a noiseless amplifier having gain of 60 and bandwidth of 90 kHz. A meter connected to the output of the amplifier reads 1.2 mV rms. (i) If the resistor is operated at 17 oC what is its resistance ? (ii) If the bandwidth of the amplifier is decreased to 10 kHz, its gain remaining constant, what will the meter learn now ? [10]

2. (a) elaborate the different sources of noise ? [5]

(b) describe noise bandwidth. What is the relation ranging from noise bandwidth BN and noise power PO at the output of a system ? [7]

(c) provide the mathematical Presentation of noise. [8]

part - II

3.(a) What is modulation ? Why is it needed to modulate a signal before transmission ? [5]

(b) obtain an expression for the instantaneous voltage of an amplitude modulated signal. Draw the waveforms for amplitude modulated signal; also define the power relations involved in AM. [10]

(c) Compare DSBSC-AM and SSB-AM. [5]

4.(a) With the help of suitable diagrams and waveforms define the square legal regulations diode modulation system. [10]

(b) discuss the working of a linear diode detector. [5]

(c)The rms value of a carrier voltage after amplitude modulation to a depth of 40% by a sinusoidal modulating voltage is 55 V. compute the rms value of can ier voltage when it is modulated to a depth of 80%. [5]

SECTION—III

5.(a) In a FM system if mf is doubled by halving the modulating frequency, what will be the effect on maximum deviation ? [5]

(b) discuss the spectrum of a frequency modulated signal and compare it with that of amplitude modulated signal. [15]

6.(a) What is the principle of operation of slope detectors ? discuss in detail the working of a balanced slope detector. [10]

(b) What is pre-emphasis and why is it needed ? [5]

(c) Differenaate ranging from WBFM and NBFM. [5]

part IV

7.(a) Draw and discuss the complete block diagram of Armstrong frequency modulation system in what circumstances can we dispense with the mixer ? [10]

(b) discuss radio telephone transmitter highlighting its special features like quantity compressors, VODAS and privacy devices. [10]

8.(a) explain the merits of delayed AGC as compared to simple AGC. Show AGC curves to illustrate the comparison and discuss how delayed AGC may be found an applied.[10]

(b) discuss with block diagram the functioning of a TRF receiver. [10]

Earning:   Approval pending.