ABSTRACT
The word “telephony” is derived from the greek word “tele” meaning distant and “phone” meaning sound. The telephony is a branch of line communication, which deals with transmission of spoken messages. The speech from one person is converted into electrical signal in the microphone of his telephone instrument, the electrical signal then travels through wires to the telephone exchange and conveyed to loud speaker of the instrument of the “called person”, in which the electrical signal is converted back into sound. The hand telephone set described above makes use of electro magnetic devices and some electro-mechanical devices. A telephone exchange is the centre from where calls are made with the desired subscriber. Speech produces much more complex modulation pattern as compared to other signals but the principle of amplitude modulation in telephony remains the same. The ordinary telephone system remains almost engaged, therefore, that cannot be used.
