Analog Communication Laboratory Viva Questions 3

Theory_Questions:

1) What are the amplitude response H(f) and phase response β(f) of a distortion less system respectively?

a) H(f) =f, β(f) =-2∏ft0+n∏

b) H(f) =f, β(f) =-2∏ft0+n∏/2

c) H (f) =K, β(f) =-2∏ft0+n∏

d) H(f) =K, β(f) =-2∏ft0+n∏/2

Answer: [C] H (f) =K, β(f) =-2∏ft0+n∏

2) consider the signal g(t) =A rect(t/T) cos(2∏fct) ,what is the pre-envelope gp(t) of the signal g(t) ?

a) gp(t) = A rect(t/T) exp(j2∏fct)

b) gp(t) = A rect(t/T) exp(-j2∏fct)

c) gp(t) = -A rect(t/T) exp(j2∏fct)

d ) gp(t) = -A rect(t/T) exp(-j2∏fct)

Answer: [A] gp(t) = A rect(t/T) exp(-j2∏fct)

3) In the above problem, what is the complex envelope?

a) A rect(2t/T)

b) -A rect(t/T)

c) -A rect(2t/T)

d) A rect(t/T)

Answer: [D] A rect(t/T)

4) Efficiency of DSB-SC is?

a) 80%

b) 20%

c) 60 %

d) 100%

e) None

Answer: [D]100%

5) Band width of DSB-SC is

a) fm

b) 2 fm

c) fm/2

d) fm/4

Answer: [B] 2 fm

6) A carrier is modulated according to the message signal to generate an DSB-SC signal.If the message

signal has power of 20W and carrier has 40W,then what is the power in the total sidebands?

a) 800W

b) 20W

c) 60 W

d) 2400 W

e) None

Answer: [A] 800W

7) Consider an AM signal 2(2+0.5cos(2∏(3*103) t) ) cos(2∏(6*106) t,then what is the modulation index of

AM signal?

a) 0.5

b) 0.25

c) 0.99

d) 1

Answer: [B] b) 0.25

8) In the above problem what is the bandwidth of AM signal?

a) 3KHz

b) 1.5KHz

c) 6 KHz

d) 2 Khz

Answer: [C] 6 KHz

9) The Maximum amplitude value of the AM signal is 8 volts and Minimum value is 2volts.then what is the modulation index of the AM wave?

a) 2/3

b) 3/5

c) 1/4

d) 5/8

Answer: [B] 3/5

10) In the above problem, what is the total power of the AM wave?

a) 14.75 W

b) 15.25 W

c) 14.25 W

d) 15.75 W

Answer: [A] 14.75 W