The process of varying one of the characteristics of a high frequency wave (carrier) in accordance with the instantaneous value of a modulating wave (low frequency signal) is known as modulation.
the audio frequency signal is also called modulating wave and resultant wave produced is called modulated wave.
let the carrier wave expressed as
e = Emsin(wt+Ø)
here, e is the instantaneous value of carrier wave
Em is the maximum value of the carrier wave
Ω is the angular frequency
Ø is the phase relation with respect to some reference.
Since there are three variables in the equation, therefore three types of modulation possible which are described below.
TYPES OF MODULATION : Different types of modulation are as follows:
(a) AMPLITUDE MODULATION
The process in which the amplitude of sinusoidal carrier wave is varied in accordance with the modulating signal, keeping the frequency and phase of the carrier wave constant, is known as amplitude modulation.
(b) FREQUENCY MODULATION
The process in which the frequency of carrier wave is varied in accordance with the modulating, signal, keeping amplitude & phase of the carrier wave constant is known as frequency modulation.
(c) PHASE MODULATION
the process in which the phase (Ø) of carrier wave is varied in accordance with the modulating signal, keeping the frequency & amplitude of carrier wave constant is known as phase modulation.
In India, in T.V. transmission, frequency modulation is used for sound signal and amplitude modulation for picture signal. However, amplitude modulation is used in radio transmission.
