1-9. OPERATIONAL MODES AND CONTROLS. (CONT)
OUTGOING CALL WITH MODE SELECTOR SWITCH IN AC SUPV POSITION
When the telephone set is installed for operation with a switching facility and the MODE SELECTOR SWITCH is in AC SUPV position,
a request for service is transmitted to the switching facility by the hookswitch contacts when the handset is lifted from its cradle. The
hookswitch performs the following functions in the order given below:
Applies negative battery dc current to the send amplifier, preparing it for sending the seize tone to the switching facility.
Changes the input impedance of the telephone set to about 600 ohms.
Energizes the receiver element in the receive amplifier circuit.
Applies positive battery dc current to the dual tone multifrequency (DTMF) oscillator.
Opens the path to the latch circuit when the handset is lifted from its cradle.