Telecommunication is the extension of communication over a distance. In practice it also recognizes that something may be lost in the process; hence the term 'telecommunication' covers all forms of distance and/or conversion of the original communications, including radio, telegraphy, television, telephony, data communication and computer networking.
The elements of a telecommunication system are a transmitter, a medium and possibly a channel imposed upon the medium  and a receiver. The transmitter is a device that transforms or encodes the message into a physical phenomenon; the signal. The transmission medium, by its physical nature, is likely to modify or degrade the signal on its path from the transmitter to the receiver. 
The receiver has a decoding mechanism capable of recovering the message within certain limits of signal degradation. In some cases, the final "receiver" is the human eye and/or ear and the recovery of the message is done by the brain.
Most simply, an antenna is an electronic component designed to send or receive radio waves.
More specifically, an antenna is an arrangement of conductors designed to radiate (transmit) an electromagnetic field in response to an applied alternating electromotive force (EMF) and the associated alternating electric current.

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