a. The telephone set is the device supplied the telephone user to initiate and receive telephone calls. It has two
principal circuits: the talking circuit, which provides an electrical path for the voice current, and the signaling circuit,
which provides an electrical path for the signaling current. In the local-battery telephone set the components of the
talking circuit are the transmitter, receiver, handset switch, battery, induction coil, and capacitor. The components of the
signaling circuit are the hand generator and ringer.
b. The electrical energy for the voice current comes from the battery. A handset switch controls the battery
current to the transmitter and thus increases the useful life of the battery. The handset switch, together with the
transmitter and receiver, usually is mounted in a handset.
c. The induction coil, which is essentially a transformer, extends the range of the telephone set and improves its
efficiency and performance. This it does by--
(1) Separating the transmitter and receiver current so that direct current from the transmitter does not pass
through the receiver.
(2) Inducing a higher voice-current voltage in the secondary winding as a result of its step-up action as a
(3) Increasing the percent change in the resistance of the transmitter circuit.