# Analog Communications Questions and Answers – Modulation of VSB Modulated Wave

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

1. Quantization noise occurs in ________
a) Frequency Division Multiplexing
b) Time Division Multiplexing
c) Delta Modulation
d) Amplitude Modulation

Explanation: Quantisation is the process through which a range of continuous analog values are quantized or rounded off to a single value, thereby forming samples of a discrete digital signal. Quantisation Error occurs when there is a difference between an input value and it’s quantized value. Quantisation occurs when an analog signal is converted into it’s digital form, thus it occurs in Pulse Code modulation (PCM).

2. Which is the greatest disadvantage of Pulse Code Modulation?
a) highly prone to noise
b) cannot travel long distances
c) its inability to handle analog signals
d) large bandwidth is required for it

Explanation: Pulse code modulation (PCM) is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only. Its greatest disadvantage is its requirement for large bandwidth.

3. Inductance and capacitance of a line is 0.8 μHm and 32 pFm. Find Z0?
a) 158
b) 166
c) 143
d) 127

Explanation:
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4. Pulse communication system that is inherently highly immune to noise is ________
a) PCM
b) PPM
c) PAM
d) PWM

Explanation: 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. It is less prone to noise and can travel through long distances without loss of data.

5. What the main advantage of PCM?
a) can travel small distances
b) higher bandwidth
c) lower noise
d) good reception

Explanation: 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. It is less prone to noise and can travel through long distances without loss of data.
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6. In AM pilot carrier, transmission has ________
a) carrier and part of one side band
b) two side bands and a carrier
c) two side bands
d) carrier, one side band and part of other side band

Explanation: In amplitude modulated wave, the transmitted wave has two side bands and a carrier. Thus it’s bandwidth is twice the maximum modulating frequency.

7. Quantization noise depends upon both sampling rate and number of quantization levels.
a) True
b) False

Explanation: Quantization noise in pulse code modulation (PCM) depends upon only on number of quantization levels.

8. Which of the following frequency is not transmitted in AM transmission?
a) Upper side band frequency
b) Carrier frequency
c) Lower side band frequency
d) Audio frequency

Explanation: Audio frequency is the frequency that is not transmitted in AM transmission.

9. Companding is used in PCM transmitters to allow amplitude limiting in the receivers.
a) True
b) False

Explanation: Companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio.

10. What is the use of Companding?
a) in PCM transmitters to allow amplitude limiting in the receivers
b) in PCM receiver to overcome impulse noise
c) to overcome quantizing noise in PCM
d) to protect small signals in PCM from quantizing distortion

Explanation: Companding is the process through which the signal to noise ratio of a wave is reduced by compressing and expanding the signal. It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio. It is mainly used to protect small signals in PCM from quantizing distortion.

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