Analog Communication Laboratory Viva Questions 9

Theory_Questions:

A SSB signal plus noise is demodulated by synchronous detection. Find the SNR at the output in dB. Given that the transmitted signal power is 1mW and is passed through a cable that has loss of 60 dB, message signal bandwidth is 1 MHz and the two sided noise spectral density is 10-20/2 W/Hz

a) 10 dB

b) 30 dB

c) 50 dB

d) 70 dB

Answer: [C] 50 dB

2. In the above problem, if the modulation scheme is replaced by DSB-SC. Find the SNR at the output

a) 10 dB

b) 30 dB

c) 50 dB

d) 70 dB

Answer: [C] 50 dB

3. In the above problem , if we use a tone modulated AM signal with μ=1. Find the output SNR

a) 45.2 dB

b) 50 dB

c) 55.2 dB

d) 40 dB

Answer: [A] 45.2 dB

4. If the message signal m(t) has a power of 10 mW, then what is the power of signal 2*m(t) cos(wct+Ø) where Ø is a random variable which is uniformly distributed in the interval 0 to 2π

a)10 mW

b) 20 mW

c) 40 mW

d) 30 mW

Answer: [B] 20 mW

5. A white noise with one sided spectral density of 2*10^(-6) W/Hz is applied to a simple RC low pass filter whose 3 dB cutoff frequency is 4 kHz. Determine the mean square value of the noise output

a) 8π*10^(-3) W

b) 2π*10^(-3) W

c) 16π*10^(-3) W

d) 4π*10^(-3) W

Answer: [D] 4π*10^(-3) W

6. A white noise with two sided power spectral density 10-6 W/Hz is passed through an SSB modulated circuit(LSB/USB) having side band bandwidth of 2 MHz. What is the noise power at the output of SSB modulator?

a) 2 W

b) 1 W

c) 4 W

d) 8 W

Answer: [C] 4 W

7. In the above problem if the output noise n(t) is represented by ni(t) cos wct ± nq(t) sinwct then what is the power of quadrature component nq(t) of noise is

a)2 W

b) 1 W

c) 4 W

d) 8 W

Answer: [C] 4 W

8. In the above 6th problem if the white noise is passed through DSB modulated circuit what is noise power at output of the DSB modulator

a)2W

b)1W

c)4W

d)8W

Answer: [D] 8W

9. What is the output noise power of phase detector and frequency discriminator if received signal power is 10nW, message signal bandwidth is 15KHz and power is 0.5W, and noise spectral density is 10ିଶ଴ W/Hz

a) 56nW and 1.5W

b) 56nW and 4.5W

c) 30nW and 4.5W

d) 30nW and 1.5W

Answer: [C] 30nW and 4.5W

10. For the same data in the above question, what is the SNR at phase detector and frequency discriminator outputs if phase deviation is 2 radians and frequency deviation is 75KHz.

a. 78.23 dB and 87.96 dB

b. 78.23 dB and 102.36 dB

c. 57.89 dB and 87.96 dB

d. 57.89 dB and 102.36 dB

Answer: [A] 78.23 dB and 87.96 dB