what is need of modulation & de-modulation in communication?

Answer Posted / syncopator

In a communication system, other than at audio frequencies,
a so-called carrier is used.

The carrier may be an r.f. transmission or it may be light
transmission.

It is usually said that the carrier itself does not contain
any information. *

Information may be imposed upon a transmitted carrier by
means of a system called modulation.

The information may be recovered at a receiving point by a
system called demodulation.

* Although it is said that an unmodulated carrier conveys
no information, this is not strictly true. It conveys the
informtaion that the transmitter is working.

An unmodulated r.f. carrier could also be use as a beacon,
although this would be most unusual.

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