# Analog Communications Questions and Answers – Generation of VSB

This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Generation of VSB”.

a) Hartley Oscillator
b) Crystal Oscillator
c) Armstrong Oscillator
d) Dynatron Oscillator

Explanation: In frequency modulation, frequency of the carrier wave is varied with the instantaneous amplitude of message signal. Crystal oscillator is used to generate a carrier signal with a precise or fixed frequency. But it has no use in frequency modulation.

2. What is the approximated range of audio frequencies?
a) 20Hz to 20KHz
b) 20Hz to 200KHz
c) 10Hz to 10KHz
d) 20Hz to 20MHz

Explanation: The standard fixed range of audio frequencies is from 20HZ to 20 KHz.

3. What is duty cycle?
a) ratio of time on to time off
b) ratio of time off to time on
c) 12 × (ratio of time on to time off)
d) 12 × (ratio of time off to time on)

Explanation: Duty cycle is the fraction of time in which the system is active. It can also be defined as the ratio of time on to time off of a system. At times, duty cycle, expressed as percentage, is the ratio of time on to sum of time on and time off.

4. Which of the following is used for demodulation of PAM signal?
a) a band reject filter
b) a band pass filter
c) a low pass filter
d) a high pass filter

Explanation: Pulse Amplitude Modulation is the transmission of data by varying the amplitude of different pulses. A low pass filter is always used to demodulate a PAM as it attenuates high frequencies and allows only low frequencies to pass.

5. Which of the following is not a part of analogue communication?
a) PPM
b) AM
c) PCM
d) PWM

Explanation: Pulse code modulation (PCM) is a digital form of communication. It has no relation with analog communication. Pulse Code Modulation is a technique in which the amplitude of an analogue signal is converted to a binary value represented as a series of pulses.
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6. For demodulation of PCM, it is first converted into ________
a) PAM
b) PWM
c) PPM
d) FM

Explanation: Pulse Code Modulation deals with converting an analog signal to a digital signal. During it’s demodulation, the wave to be treated is to be parallel. The series pulse wave signal is then converted into a parallel digital signal using a serial to parallel converter, after which it is further converted into the original analog signal with the help of a decoder or detector.

7. Inherently most noise resistant modulating system is _________
a) PCM
b) DSB
c) SSB
d) VSB

Explanation: In PCM, the amplitude of the analog signal is discritised and converted into digital form for transmission of binary data. PCM is least prone to noise and can travel long distances.

a) Pulse Modulation
b) Amplitude Modulation
c) Phase Modulation
d) Frequency Modulation

Explanation: In pulse modulation, message signal in the form of pulses are varied with respect to width, amplitude or position. It is mostly used for radio navigation and for many others.

9. Frequency modulated broadcast band generally lies in ________
a) VHF
b) HF
c) SHF
d) LF

Explanation: VHF (very high frequency) is the ITU designation for the range of radio frequency from 30MHz to 300MHz. Frequency modulated broadcast band generally lies in it only. HF ranges from 3MHz to 30MHz while SHF ranges from 3GHz to 30GHz. And LF ranges from 30KHz to 300KHz.

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