Current Paths in Simplex Circuit.
The function of the repeating coils which permit a metallic circuit to be simplexed without interference
between the two circuits can be explained by reference to figure 68, in which the paths of the metallic-line currents, or
side-circuit currents, are indicated by solid-line arrows and those of the simplex circuit by broken-line arrows.
a. Path of side-circuit current. Assume that a conversation is taking place between telephones T1 and T2 (fig.
68). Also assume an instant of time when the pulsating current in the primary of the induction coil of transmitter T1 flows
in the direction indicated by the solid-line arrows. This current induces an emf in the secondary of RC1 and causes a
corresponding current to flow in the secondary of repeating coils RC1 and RC2, as shown by the solidline arrow. Note
that the secondary windings of the two repeating coils are connected by the two wires of the metallic line, thus furnishing
a closed current path. The current flowing through the secondary winding of RC2 induces a corresponding emf in the
primary which produces a current in the primary winding. Since telephone T2 is connected to the primary of RC2, this
current flows through the receiver of T2, and results in the reproduction of the sound which originated in the transmitter of
FIGURE 68. Current Paths in Simplex