Institute of Chartered Financial Analysts of India %28ICFAI%29 University 2008-2nd Sem B.Tech Electronics and Communications Engineering First semester -2009 - Question Paper

1) ans the subsequent : [4* 0.5=2 marks]

a) 400W carrier is modulated to a depth of 75%. compute the total power in the modulated wave.

b) Draw the frequency spectrum of the signal m(t)=Am cos Wmt

c) describe modulation index for FM.

d) You want to frequency modulate a 10 KHz signal with a modulation index of 2. What is the FM signal bandwidht ?

2) A multitone modulating signal m(t) consisting of 3 frequency components, is provided
m(t)= A1cosw1t + A2cosw2t + A3cosw3t, w3>w2>w1 and A1>A2>A3.
This signal modulates a carrier c(t)=Ac Coswc t.

a) Derive an expression for AM wave.

b) Draw a single sided spectrum and obtain the bandwidht of the AM wave. [marks=3]

3) The antenna current of an AM transmitter is 8A. When only the carrier is sent, but increases to 8.9A when the carrier is modulated by a single sine wave. obtain the
percentage modulation, determine the antenna current when the percentage modulation modifications to 0.8. [marks=2]

4) The modulating signal m(t) is an AM- sc system is single tone signal provided by M(t)=Am cos Wm t the signal m(t) modulates a carrier Ac cos wc t. Plot the single sided
trigonometric spectrum and obtain the bandwidth of the modulated signal. [marks=2]

5) For an FM modulator provided that : [marks=2]

change in frequency = 10 KHz
fm = 10 KHz
Vc = 10 V
fc = 500 KHz

a) Draw the spectrum

b) What is the bandwidth using Bessel table ?

c) What is the bandwidth using Carson's rule ?

6) A carrier Ac cos wc tis frquency modulated by a single tone modulating signal M(t)=Amcoswm t. obtain : [marks=3]

a) An expression for FM wave.

b) An expression for narrow band FM.

7) The maximum deviation allowed in a FM broadcast system is 75 KHz. If the modulating signal is a single tone sinusoid of 10 KHz, obtain the bandwidth of the FM signal. What will be the change in the bandwidth, if modulating frequency is doubled ? Determine the bandwidth when modulating signals amplitude is also doubled. [marks=2]

Earning:   Approval pending.