The sub-system that takes the information signal and processes it prior to transmission. The medium which transports the modulated signal to the receiver.
Air acts as the channel for broadcasts like radio.
May also be a wiring system like cable TV or the Internet. The sub-system that takes in the transmitted signal from the channel and processes it to retrieve the information signal. The information signal can rarely be transmitted as is, it must be processed. In order to use electromagnetic transmission, it must first be converted from audio into an electric signal. The conversion is accomplished by a transducer .