This set of Analog Communications Interview Questions and Answers for freshers focuses on “Representation of SSB-SC in Time & Frequency Domain”.
1. Which device is has more chance to be found in SSB transmitter?
a) balanced modulator
b) class A RF amplifier
c) class C audio amplifier
d) class B RF amplifier
Explanation: In SSB-SC transmitter, a balanced modulator is more likely to be found in order to suppress the carrier, after which the result is passed through a band-pass filter in order to transmit the selected sideband.
2. The RF section of radio consists both oscillator and buffer stage.
Explanation: RF is an electromagnetic wave frequencies in the range 3 KHz to 300 GHz. RF section of radio consists of oscillator so as to provide the necessary frequency for mixing and it consists of a buffer stage for preventing the damage of signal source.
3. What is the frequency of audio modulation?
a) 10 Hz
b) 20 KHz
c) 30 KHz
d) 40 KHz
Explanation: Audio spectrum ranges from 20Hz to 20KHz and the frequency band for audio modulation ranges from 88MHz to 108 MHZ.
4. In telegraphy we generally use __________
a) Amplitude modulation
b) Frequency modulation
c) Frequency Shift Keying
d) Pulse Code modulation
Explanation: FSK (Frequency Shift Keying) is a method used to transmit binary data in form of digital signals. It is mainly used for telegraphy. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for the communication between computers and over telephone lines.
5. In FM both the frequency and amplitude of carrier signal is varied in accordance with the instantaneous value of modulating signal.
Explanation: In FM, the frequency of the carrier wave is varied with respect to the instantaneous amplitude of the message signal. The general expression for FM is as follows:
FM (t) = Ac sin (2πfct + βsin(2πfmt)), where symbols have their usual meaning.
6. In the equation, 20cos(108 t + 3 sin109 t) the modulation index is ________
Explanation: The general expression for FM is as follows:
FM (t) = Ac sin (2πfct + βsin(2πfmt)), where β is the modulation index.
Thus β = 3.
7. Antenna can also be used as a receiver.
Explanation: All antennas can be used as transmitter and receiver both. Antenna transmits or receives electromagnetic waves only. Transmitter antenna modulates the message signals and transmits the modulated waves and Receiver antenna receives the modulated wave and demodulates it.
8. What is the advantage of IF modulation?
a) it uses SSB which further reduces its bandwidth
b) modular section and visual exciter can be of any state
c) it cannot be tuned
d) modular section and visual exciter can be solid state devices
Explanation: Advantages of IF modulation is that the modular section and visual exciter can be solid state devices. Its other advantages are it can use VSB filter that can be introduced at low power level. Moreover it is economical.
9. We can use either cone type or horn type loudspeakers in tape recorders.
Explanation: In tape recorders, only cone type loudspeakers can be used. It does not work well with horn type loudspeakers.
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