MODULATION:-

It is defined the superstition of low frequency base band signal (modulating signal) on a high frequency carrier wave. The  resultant wave is known as modulated wave.

A carrier wave can be represented as:-

c(t)=A_c  sin (ω_ct ± ɸ_c)

where , c(t)=signal strength(I or Vat any time)

A_c=Amplitude of carrier wave.

ω_c =Angular frequency(ω_c= 2πh_c).

ɸ_c = Initial phase.

So, during the modulation process any one of the parameters A_c, ω _c, ɸ_c  of carrier wave is varied in accordance with the modulating signal(message signal). Hence, modulation is of three types.

1. Amplitude Modulation  (A_c)
2. Frequency Modulation (ω_c)
3. Phase Modulation (ɸ_c)

 

In amplitude modulation degree of modulation is he ratio of amplitude of modulating signal to the amplitude of the carrier wave.

The modulation index determines the quality of the transmitted system. If modulation index is small variation of carrier amplitude will be small. So, audio signal transmitted will be weak. If modulation index increases audio signal on reception becomes more clear.