Any two of the following :
(i) Transducer—A device which converts energy from one form to another form.
(ii) Repeater—A repeater is a combination "of a receiver and a transmitter.
(iii) Transmitter—A transmitter processes the
incoming message signal so as to make it suitable for transmission through a channel and for its
. subsequent reception.
[Alternatively : A transmitter is a device used for sending the information in a communication system.]
(iv) Bandpass filter—A bandpass filter blocks lower
and higher frequencies and allows only a selective band of frequencies to pass through.