GB993268A - Intercommunication systems - Google Patents

Abstract

993,268. Intercommunication systems. STANDARD TELEPHONES & CABLES Ltd. (Standard Elektrik LORENZ A.G.). April 25, 1962, No. 15730/62. Heading H4K. In an intercommunication system comprising master stations and substations, amplifiers and selective switching means are located only in the master stations but the direction of the amplifiers, i.e. for incoming or outgoing speech, is controllable by the substations and on initiation of a call by a substation an electronic oscillator at the master applies ringing signals to a ringing circuit extending between the two stations so as to actuate sound transducers thereat. A substation comprising a microphone-loudspeaker SW and a talk-listen key Spt is depicted in Fig. 5 and a diagram of a master station is shown in Fig. 4. In the latter, jumpers I associated with banks LT(n)I, LT(n)II of a line selection switch LT are dispensed with if the corresponding line ab extends to another master, while jumpers II are removed for lines to the substations. When a master is called (closing Spt in a substation or the appropriate line key in another master) an identification lamp AL lights and a transistorized ringing generator G oscillates since the loop on the calling line completes the path for a battery U (local or central). The master operates the appropriate line key to remove the ringing and identification circuits and actuates his speech key SpT whereby the amplifier Vr (outgoing) is put in the speech path and lamp BL lights. This lamp serves to indicate whether or not the speech key of the distant station (assuming that this is a master) is operated since if it is communication cannot take place. If the caller is a substation however and the master station speech key SpT is operated then lamp BL lights (in a circuit via Wi2) irrespective of the position of the speech key Spt in the substation and thus the master station can speak to, and without interruption from, this substation. However, if the master station speech key SpT is not actuated then amplifier Vr comes under the control of a relay R which energizes whenever the substation key Spt is operated and thus causes Vr to act as an incoming amplifier. A. master can communicate directly with his substations since the latter have no ringing facilities and conference calls can be set up by the simultaneous operation of more than one line key.