Patent GB-1433969-A (GB)
Title: Frequency multiplex switching system
IPC: H04Q11/02
Filed: 1974-05-21
Abstract: 1433969 Automatic exchange INTERNATIONAL STANDARD ELECTRIC CORP 21 May 1974 [22 May 1973] 22546/74 Addition to 1418447 Heading H4K In the switching system of the parent in which required interconnections are established by selecting corresponding frequencies of RF equipments coupled to respective antennae in a magnetically isolated space, the line terminal equipments each comprise detecting means for controlling switching operations in response to the receipt over the RF channel of one or several signalling frequencies, and sending means to transmit over the RF channel one or several signalling frequencies for switching purposes in a coupled terminal equipment, certain of the switching operations in the terminal units being effected by direct signalling from one to the other when a direct connection is established. The exchange apparatus, Fig. 2, comprises subscribers line circuits LA, incoming trunk circuits JA outgoing trunk circuits JD and auxiliary devices such as subscribers dialling junctors JN, outgoing senders EVD, incoming receivers RA and service line circuits LS all provided with an RF transmitter E and all except LS being provided with an RF receiver. Slow scanners EXL are DL in an interface unit for common control unit UCC determine conditions of subscribers lines and trunk lines respectively, and a fast scanner is supplied for alternative use in scanning the trunk lines. Markers MR set the frequencies of receivers R associated with the respective circuit units under the control of computer UCC. All the units of computer and interface are duplicated. A callers off-hook condition is indicated to common control UT by scanner EXL in response to the operation of relays L and A and after the class of the caller has been checked the controller selects an idle dialling junctor JN and supplies its number together with that of the caller to register RG of marker MR. The junctor sends modulated 450 Hz dialling tone over antennae 23 to the callers line circuit receiver which has been appropriately tuned and it is sent to the subscriber by DT1 over windings E 5 , E 4  of a hybrid transformer. Dialled pulses are sent to the controller by relays DT2 and N and when relay FN operates to indicate that dialling is completed, the controller ascertains that the called line is idle, cancels junctor number from register RG replaces it with that of the calling line circuit and at the same time writes the called number into the called-subscribers receiver-frequencyadjusting register. A 450 Hz calling signal operates DT 1 to send ringing current pulsed by cam CM to line over relays S and T and a ringing of busy tone is returned to the caller. The ringing tone is formed by alternate bursts of 450 Hz and 1575 Hz and is terminated by the called sub going off-hook by relays AS T and S whereupon relay C is operated in the calling line to establish the speech connection over windings E 3  and Eg and to cut-off the 450 Hz signal to the called subscriber to operate his relay C and complete for two-way transmission. At the conclusion of speech relay C is released over relays L and A indicating the "blocking" condition to the control UCC which resets the line circuit register of the cleared subscriber and sends a 450 Hz, 1575 Hz mix to the uncleared party. When he goes on-hook the new condition is detected and his line circuit is cleared. Operation for called subscriber busy and too slow dialling is also described together with an alternative arrangement using pushbutton V.F. dialling. Inter exchange calls using junctors are outlined and the transmission to subscribers of vocal messages are transferred and/or disabled lines by special service lines is proposed.