GENERAL ARRANGEMENT OF A TELEPHONE CIRCUIT.
In many forms of subscriber's instruments both receiver and transmitter are mounted on a single handle in such a way as to be conveniently placed for ear and mouth. For the sake of clearness the diagrammatic sketch of a complete installation (Fig. 64) shows them separated. The transmitters, it will be noticed, are located in battery circuits, including the primary windings P P2 of induction coils. The transmitters are in the line circuit, which includes the secondary windings S S2 of the coils.
We will assume that the transmitters are, in the first instance, both hung on the hooks of the metallic switches, which their weight depresses to the position indicated by the dotted lines. The handle of the magneto-generator at the left-end station is turned, and current passes through the closed circuit:—Line A, E B2, contact 10, the switch 9; line B, 4, the other switch, contact 5, and E B. Both bells ring. Both parties now lift their receivers from the switch hooks. The switches rise against contacts 1, 2, 3 and 6, 7, 8 respectively. Both primary and both secondary circuits are now completed, while the bells are disconnected from the line wires. The pulsations set up by transmitter T in primary coil P are magnified by secondary coil S for transmission through the line circuit, and affect both receivers. The same thing happens when T2 is used. At the end of the conversation the receivers are hung on their hooks again, and the bell circuit is remade, ready for the next call.