(i) Transducer : Any device that converts one form of energy into another can be termed as a transducer. An electrical transducer may be defined as a device that converts some physical variable in the electrical signals.
(ii) Repeater : A repeater is a combination of a receiver and a transmitter. A repeater picks up the signal from the transmitter, amplifies and retransmits it to the receivers sometimes with a change in carrier frequency.
(iii) Amplification : It is the process of increasing the amplitude of a signal using an electronic circuit called the amplifier. Amplification is done at a place between the source and the destination.