c. Circuit of handset. The
broken lines of figure 34 show the
wiring of the local-battery telephone
handset. The receiver terminals and the
handset switch are connected to
terminals in the transmitter end of the
A three-conductor cord
connects the handset to the telephone
In practice, the individual
conductors of the cord usually are
identified by the color of the conductor
leads; here (and in most circuit
diagrams) they are designated T for
transmitter, C for common, and R for
FIGURE 34. Wiring Diagram of Handset
with Hand Switch.
The circuits of the telephone sets of figure 28, using dry cells alone, can be used to provide voice conversation
only between telephone sets separated by short distances. The range may be extended, however, and performance and
efficiency may be improved, by including an induction coil in the circuit.
a. Functions. The induction coil performs two functions in this particular telephone set. First, it increases the
voltage of the voice current generated by the transmitter. Second, it separates the transmitter and receiver currents so that
the direct current of the transmitter circuit does not pass through the receiver (secondary) circuit.
The circuit of a local-battery telephone set with an induction coil is shown in A
and B, figure 35.
The induction coil consists of two separate coils which have a common connection
and are wound on an iron core.
One coil, the primary winding, receives the electrical energy; the