Coupling system for pay-as-you-go telephone, pay-as-you-go telephone or pay-as-you-go telephone sets

摘要

This communication system has each station equipped with a repeater loudspeaker amplifier, microphone amplifier, call keys and tally-lamps. These stations are connected to a central unit that contains the matrix and gates. Each gate consists of a pair of back-to-back diodes in each of the two communication lines. The centre points of the diode pairs are connected together by a centre-tapped inductance so that the gates may be biased on or off. Transistor amplifiers are used to unlatch called-stations and initiate engaged-tally indications to other stations. Flashing call tallies are provided for alerting the called station.