Modulation, Types, Need for Modulation

Modulation, Types, Need for Modulation:

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

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

Frequency modulation: Frequency Modulation is the changing frequency of the carrier signal with respect to the instantaneous change in message signal

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

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).

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

Carson’s rule : 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.

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

Percentage modulation: It is the percentage change in the amplitude of the output wave when the carrier is acted on by a modulating signal. M=(Em/Ec)*100