Block diagram of electronic communication system.
Transducer: A transducer is usually required to convert the output of a source into an electrical signal that is suitable for transmission. For example, a microphone serves as the transducer that converts an acoustic speech signal into an electrical signal.
Transmitter: The transmitter converts the electrical signal into a form that is suitable for transmission through the physical channel or transmission medium. For example, in radio and TV broadcast, the transmitter must translate the information signal to be transmitted into the appropriate frequency range that matches the frequency allocation assigned to the transmitter. There is some internal noise available inside the transmitter section due to the electronic circuits used which is called thermal noise due to heat dissipation and other noises etc.
Channel: The communications channel is the physical medium that is used to send the signal from the transmitter to the receiver. In wireless transmission, the channel is usually the atmosphere (free space).
Receiver: The function of the receiver is to recover the message signal contained in the received signal. If the message signal is transmitted by carrier modulation, the receiver performs carrier demodulation in order to extract the message from the sinusoidal carrier. There is some internal noise available inside the receiver section due to the electronic circuits used which is called thermal noise due to heat dissipation and other noises etc.
Output Transducer: The output transducer converts electrical signal in to sound signal.