Telecommunication is communication at a distance by technological means, particularly through electrical signals or electromagnetic waves
A basic telecommunication system consists of three primary units that are always present in some form:
A transmitter that takes information and converts it to a signal.
A transmission medium, also called the "physical channel" that carries the signal. An example of this is the "free space channel".
A receiver that takes the signal from the channel and converts it back into usable information.
For example, in a radio broadcasting station the station's large power amplifier is the transmitter; and the broadcasting antenna is the interface between the power amplifier and the "free space channel". The free space channel is the transmission medium; and the receiver's antenna is the interface between the free space channel and the receiver. Next, the radio receiver is the destination of the radio signal, and this is where it is converted from electricity to sound for people to listen to.