Analog Communications Interview Questions and Answers focuses on “Modulation Using Non-Linear Devices (Balanced Modulator)”.
1. The approximate aspect ratio for television is ________
a) 2 : 1
b) 3 : 2
c) 4 : 3
d) 3 : 4
Answer: c
Clarification: Aspect ratio is an image projection attribute that describes the proportional relationship between the width of an image and its height. The most common video-graphic aspect ratio is 4:3.
2. Signal to Noise ratio for a hi-fi system is equal to ________
a) 50 dB
b) 100 dB
c) 75 dB
d) 10 dB
Answer: a
Clarification: Signal to Noise ratio compares signal power to noise power. It determines how much signal is present in a transmitted wave compared to presence of noise. It is generally expressed in decibels(dB). For a hi-fi system, it should be equal to 50dB.
3. What is the use of SSB?
a) It has lesser bandwidth
b) It has large bandwidth
c) It has infinite bandwidth
d) It has zero bandwidth
Answer: a
Clarification: In SSB-SC(Single Side Band Suppressed Carrier), the carrier is suppressed and either of the upper side-band and lower-sideband, are transmitted. This reduces it’s bandwidth to the frequency of the message signal.
4. Approximate how many times odd and even fields of television system are scanned?
a) 25 times each
b) 50 times each
c) 50 times each but alternately
d) 25 times each but alternately
Answer: d
Clarification: In television system in India, each of odd and even fields are scanned 25 times but alternately.
5. Any signal and its Hilbert transform have same energy density spectrum.
a) True
b) False
Answer: a
Clarification: Hilbert transform of a signal results in a signal with same amplitude but a phase shift of -90 degrees. Thus, a signal and it’s Hilbert transform have same amplitude spectrum i.e. they have same energy density spectrum and also correlation spectrum.
6. If the spectrum of a narrow band noise is symmetrical and it has a power density spectrum 4×10-6. Power density of quadrature component is ________
a) 2 x 10-6
b) 5 x 10-6
c) 3 x 10-6
d) 4 x 10-6
Answer: a
Clarification: Power density is the amount of power per unit volume. Quadrature component is a amplitude modulated sinusoid which is offset in phase by one quarter cycle.
Power density of quadrature component is