GB806222A - Disconnectible selective call receiver - Google Patents

Abstract

806,222. Electric selective signalling. STANDARD TELEPHONES & CABLES Ltd. (Lorenz A.G., C.). July 1, 1955, No. 19075/55. Class 40 (1). [Also in Group XL (c)] In a selective calling system for calling one of a plurality of radio receivers the call indicating parts S of the receivers are connected to and operated by the main receiver H only after operation of auxiliary receiver parts K operated by a signal transmitted to all the main receivers H. By this means the selectively energized parts S need hot have filters protecting them against speech frequencies and may operate with a reduction in their time of response, so enabling calling by dialling frequencies to be speeded up. The common signal may be a line clear signal which energizes a relay N of the permanently ready to receive portions K of all the receivers and therefore a relay Z to prepare all the call selecting parts S for possible reception of a call. Provided then within a predetermined time after cessation of a line clear signal, determined by the charge on a condenser C shunting the coil of the relay Z, selective circuits 10, 11 of one receiver are energized to operate relays X, Y, a further relay O pulls up to close contact O1 and signal an alarm and contact 02 so that relay Z and the call selector S remain responsive throughout the duration of the selective calling. Only then after the selective calling ceases is the selector S disconnected from the main receiver H at contact Z. Alternatively a call signal, other than the cessation of " line clear " common to all the receivers, may initiate a switching process disconnecting all the selectors S after a certain time except the one called. In a modification (Fig. 1, not shown), a call is begun by a frequency operating a relay which, through a holding circuit, connects up the main receiver H to the selectively called part S. Also a call is made'to end with a further frequency which interrupts the holding circuit and first operated relay and therefore disconnects the selectively called part S.