The function of information source is to produce required message which has to be transmitted, for example text, voice, video etc.
A transducer is a device which converts one form of energy into another form.
The message from the information source may or may not be electrical in nature. In a case when the message produced by the information source is not electrical in nature, an input transducer is used to convert it into a time-varying electrical signal
The function of the transmitter is to process the electrical signal from different aspects. Modulation is the main function of the transmitter.
In modulation, the message signal is superimposed upon the high- frequency carrier signal. Other functions of transmitter are restriction of range of audio frequencies, amplification.
The term channel means the medium through which the message travels from the transmitter to the receiver
The main function of the receiver is to reproduce the message signal in electrical form from the distorted received signal. This reproduction of the original signal is accomplished by a process known as the demodulation or detection.
Demodulation is the reverse process of modulation carried out in transmitter.
Output transducer is the final stage which is used to convert an electrical message signal into its original form.