Modulation and its Necessity

Modulation is the method of changing the carrier signal in according to the message signal.The high-frequency sin wave signal is known as carrier signal in the process of modulation.That output signal is called as modulating signal.Modulation is a process which making a change of shift at the range with frequencies of signal.

Types of modulation

A sinusoidal carrier wave can be expressed as

Its three distinct characteristics are :
i)   Amplitude (Ec)
(ii)   angular frequency (ωc)
(iii)   phase angle (θ).

Either of these three characteristics can be varied in accordance with the modulating signal. These result in three types of modulation.
(i)   Amplitude modulation (AM)
(ii)   Frequency modulation (FM)
(iii)   Phase modulation (PM)