What is modulation? Explain its necessity.

Explanation

Modulation. The process by which some characteristics of a relatively high frequency wave ( called carrier wave ) is varied in accordance with the instantaneous value of a low frequency wave ( called modulating wave ) is called modulation.
Reasons for modulation `(i)` For transmission of signal, the height of transmitting antenna should be comparable to wavelength of signal. For audio frequency having range of frequency from `20Hz` to `20,000Hz,` the height of antenna should be from `15km` to `15000km` which is not possible, hence modulation of signal is required.
`(ii)` The effective power radiated by an antenna is inversely proportional to square of length of antenna height. So for more power to be radiated, the height of the antenna should be small, hence modulation is needed.
`(iii)` If large number of signals are to be transmitted in the audio range `(20Hz` to `20kHz)` these signals get mixed and it becomes almost impossible to distinguish them. To remove this difficulty we communicate at higher frequencies and allotting a band of frequencies to each user. Hence modulation of the signal of low frequency to high frequency is required.