(i) Transducer: A device which converts energy from one form to another form.
(ii) Repeater: It is a combination of a receiver and a transmitter.
(iii) Transmitter: A device which processes the incoming message signal so as to make it suitable for transmission through a channel and for its subsequent reception.
(iv) Bandpass filter: A bandpass filter blocks lower and higher frequencies and allows only a band of frequencies to pass through.
