Modulation is the process of varying some characteristic of a periodic wave with external signals.
Modulation is utilized to send an information bearing signal over long distances.
Radio communication superimposes this information bearing signal onto a carrier signal.
These high frequency carrier signals can be transmitted over the air easily and are capable of traveling long distances.
The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal.
In the field of communication engineering, the information bearing signal is also known as the modulating signal.
The modulating signal is a slowly varying signal, as opposed to the rapidly varying carrier frequency.
Types of Modulation
Types of modulation include: