West Bengal Institute of Technology (WBIT) 2011-4th Sem B.Tech Electronics and Communications Engineering B-TECH ,Analog Communication,,ester,WBUT - Question Paper

c) 1/T
d) T3
xv) Companding is used
a) in PCM transmitter, to allow amplitudes limiting in the receivers
b) to protect small signal in PCM
c) to overcome quantization noise in PCM
d) in PCM receiver, to overcome impulse noise.


GROUP-B
( Short ans kind Questions)
ans any 3 of the following: 3*5=15
2. obtain the Fourier transform of the following:
5

3. A modulating signal is provided by Vm = two sin ( 2p*500t) amplitude modulates a carrier signal provided by Vc = 10 sin ( 2p*10^6t). Determine
i) Modulating index
ii) Frequency current in the modulating signal
iii) Total transmission power. 5

4. State and prove Parsevel's theorem for power. 5

5. discuss the direct method of generation of FM signal using a varactor diode. elaborate the issues of this method? 3+2

6. Compare PAM,PWM and PPM signals. 5



GROUP-C
(Long ans kind Questions)
ans any 3 of the following: 3*15=45

7. a) Draw a the block diagram of a superheterodyne receiver. discuss the function of every block. 5
b)Explain the significance of the name superheterodyne. 2
c) How RF parts suppress the image channel? 3
d) Why is up-conversion used in superheterodyne receiver ? 3
e) describe image frequency Rejection Ratio. 2

8. a) "FM and PM are various but inseparable."--Justify the statement. 3
b) How is a Phase Locked Loop (PLL) used for demodulation of FM signal? Mention the
advantages of PLL demodulator. 5
c) An angle modulated signal with carrier frequency ?c = 2p*10^5 is defined by the
formula
?FM(t)= 10 cos ( ?ct + 10 sin 2000 pt)
i) obtain the power of the modulated signal.
ii) obtain the frequency deviation ?f
iii) obtain the modulation index.
iv) Estimate the bandwidth needed fir transmitting this signal. 7

9. a) discuss with proper block diagram the generation of FM signal using Armstrong
method. 5
b) What is Narrowband FM and Wideband FM ? 2
c) discuss with proper expression
i) modulation index
ii) bandwidth needed for transmission of FM. 4
d) The maximum deviation allowed in an FM broadcast system is 75kHz. If the
modulating frequency is a single tone sinusoid of 10kHz, obtain the bandwidth
of the FM signal. What will be the change in the bandwidth, if the modulating
frequency is doubled? Determine the bandwidth when modulating signal amplitude
is also doubled. 4

10. a) State sampling theorem. What is Nyquist rate of sampling? 2+2
b) What is pulse amplitude modulation? 2
c) What is meant by flat top sampling? Why is it more preferred than natural sampling?
2+1
d) discuss the demodulation of PAM signal using a hold circuit. 4
e) What is bandwidth needed for transmission of PAM signal? 2

11. a) State Channel capacity theorem. 3
b) What is meant by entropy of a source? 3
c) Apply Shannon-Fano algorithm to the source with M=8 emitting messages A, B, C, D, E,
F, G, H having probabilities P(A)= 1/2, P(B)= 1/8, P(C)= 1/8, P(D)= 1/16, P(E)= 1/16,
P(F)= 1/16, P(G)= 1/32, P(H)= 1/32,calculate entropy,average code length and
efficiency of coding. 9

12. Write short notes on any 3 of the following; 3*5
a) Foster-Seeley detector
b) VCO
c) Ring modulator
d) PCM
e) TDM.

Earning:   Approval pending.