GB770937A - Improvements in or relating to loudspeaker intercommunicating systems - Google Patents

Abstract

770,937. Intercommunication systems. STANDARD TELEPHONES & CABLES, Ltd. April 27, 1955, No. 12185/55. Class 40(4). In a loud-speaker intercommunication system in which each station may call one or more others by means of a calling key or keys, operation of a calling key at any station renders all other stations incapable of originating a call and thereafter makes a connection to the called station, a common one-way amplifier being included in the connection between stations each of which have a talk/listen key which at a station originating a call controls the direction of amplification. Fig. 2 shows the connections between the common amplifier and transmit/ receive loud-speakers at each station, together with a calling tone generator which can be connected to the amplifier input. Fig. 4 shows the arrangement for the keys for a system having stations A, B and C, each of which has two relays H and E and all of which have relays CR and TL in common. Assuming the system is clear of calls station A calls station B by making key B to actuate relay HA, which connects up relay EB, isolates the keys of all other stations leaving station A in complete control of the system, brings the calling tone relay CR and amplifier reversing relay TL into circuit with the talk/listen key of station A, and (see Fig. 2) connects the transmit/receive loud-speaker of station A to the output of the amplifier. Relay EB connects the loud-speaker of station B to the input of the amplifier. To call B the talk/ listen key at A has a third position in which it energizes relays CR and TL to apply calling tone. In the talk position of the key relay TL is energized to reverse the amplifier. Each station has an engaged lamp and a lamp for each of the other stations, the circuits being controlled by relays such as HA, EB (see Fig. 5, not shown).