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
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