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Chapter: Analog and Digital Communication

Important Short Questions and Answers: Analog Communication

Analog and Digital Communication - Important Short Questions and Answers: Analog Communication

ANALOG COMMUNICATION

 

1. Define modulation.

 

Modulation is defined as changing the characteristics of the carrier signal with respect to the instantaneous change in message signal.

 

 

2. What are the needs for modulation.

 

In order to carry the low frequency message signal to a longer distance, the high frequency carrier signal is combined with it.

 

a) Reduction in antenna height

 

b) Long distance communication c) Ease of radiation

 

d) Multiplexing

 

e) Improve the quality of reception f) Avoid mixing up of other signals

 

 

3. Define Frequency modulation.

 

Frequency Modulation is defined as changing the frequency of the carrier signal with respect to the instantaneous change in message signal.

 

 

4. Define Phase modulation.

 

Phase Modulation is defined as changing the phase of the carrier signal with respect to the instantaneous change in message signal.

 

5. Define noise

 

Noise is an unwanted electrical signal which gets added tom a transmitted signal when it is travelling towards the receiver

 

 

6. Define noise figure

 

Noise figure is a figure of merit and used to indicate how much the signal to noise ratio gets degraded as a signal passes through a series of circuits

 

7. Define Deviation ratio.

 

Deviation ratio is the worst case modulation index and is equal to the maximum peak frequency deviation divided by the maximum modulating signal frequency. Mathematically the deviation ratio is DR= f (max)/fm(max).

 

 

8. Define Amplitude modulation.

 

Amplitude Modulation is defined as changing the amplitude of the carrier signal with respect to the instantaneous change in message signal.

 

 

9. State Carson’s rule.

 

Carson‘s rule states that the bandwidth required to transmit an angle modulated wave as twice the sum of the peak frequency deviation and the highest modulating signal frequency.

 

Mathematically carson‘s rule is B=2( f +fm) Hz.

 

 

10. Define modulation index

 

It is defined as ratio of amplitude of the message signal to the amplitude of the carrier signal. m=Em/Ec.

 

 

11. What is meant by analog communication system?

 

The modulation systems or techniques in which one of the characteristics of the carrier is changed in proportion with the instantaneous value of modulating signal is called analog communication system.

 

 

12. What are the advantages of Analog communications

 

Transmitters and Receivers are simple

 

Low bandwidth requirement

 

FDM can be used

 

 

 

13. What are the disadvantages of analog communication?

 

Noise affects the signal quality

 

It is not possible to separate noise and signal

 

Repeaters can‘t be used between transmitters and receivers

 

Coding is not possible

 

It is not suitable for the transmission of secret information

 

14. Define percentage modulation

 

It s defined as the percentage change in the amplitude of the output wave whn the carrier is acted on by a modulating signal. M=(Em/Ec)*100



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