Patent GB-665746-A (GB)
Title: Improvements relating to telephone systems
Inventor: HUMPHRIES HORACE EDGAR
IPC: H04M1/715
Filed: 1949-01-14
Abstract: 665,746. Automatic exchange systems. SIEMENS BROS. & CO., Ltd. Jan. 13, 1950 [Jan. 14, 1949], No. 1105/49. Class 40 (iv). An unanswered incoming call to a substation comprising main and extension telephones gives a calling signal at one telephone for a certain period and then at the other telephone for a further period, the two periods being measured by the substation's impulse sender which is of the kind wherein the operation of a single key determines the transmission of all the digits of a multi-digit number.' A subscriber at a substation of this type at a P.A.B.X. is enabled to route an outgoing call to the main exchange by the operation of a single key and to complete the connection by means of a further key corresponding to the wanted number, all the digits of this number being sent before it is necessary for the caller to lift his receiver. As shown, the exchange line is connected to terminals LX, the main telephone to terminals LM, and the extension telephone to terminals LE. In this Abridgment the users of the main and extension telephones will be referred to as " main " and " extension " respectively. The impulse sender operates as described in Specification 646,439. P.A.B.X. with dialling-out facility. Main first operates a " send " key SK corresponding to the digits required to route the call to the main exchange, the marking terminal ZA, ..., ZG following those signifying the main exchange being connected to terminal OST. Then on the release of relay K at the beginning of the corresponding digit period, relay OS operates and brings up relay T, which releases all other relays and connects the exchange line to a loudspeaker MLS in which main hears dialling tone whereupon he operates a second " send " key SK corresponding to the wanted number. Incoming call. Ringing current rings main's bell CBM and energizes winding (i) of relay RR which operates and holds on its winding (ii), bringing up relays RC, K to start an impulsing sequence. If main answers, the ringing stops and the opening of switch-hook contact MSA releases relays RR, RC, K and any operated relays in the impulse sender. If main fails to answer, then on the release of relay K at the end of the 7th " pause " period, relay H being energized, relay CE operates on its winding (i) and holds on (ii), releasing all operated relays in the impulse sender and bringing up relay EX to disconnect main's bell CBM. Relay SW operates on its winding (i) and holds on (ii), lighting an indicator lamp LEL for main, while relay RC releases slowly to bring up relay K and start a further impulsing sequence. Contact p2 sends impulses to relay RE which repeatedly reverses the polarity of the wires of the extension telephone, causing distinctive ringing at the extension. If main answers at this time, switch-hook contact MSA releases CE and all other operated relays and main is in conversational connection with the caller. If, however, extension answers, switch-hook contact ESH is closed to hold EX and bring up relay SH which releases RR, CE and all other operated relays except SW and EX. Extension is now connected to the caller. Should the call remain unanswered, resetting relay CO returns the apparatus to normal at the end of the 7th "pause" period. If ringing current is still being applied, the sequence of operations starts again. Transfer of calls. By closing a key SCE so that relay EX is permanently energized, main can direct all incoming calls to extension who may offer a call to main by closing a key OK. This operates relays RR, SP, CO to hold the exchange line while completing a local conversational circuit for main and extension. Relay SH releases slowly, followed by CO, and meanwhile relay BZ by self-interruption produces a signal in main's loud-speaker MLS. When main lifts his receiver, extension can transfer the call to him by releasing key OK and momentarily operating a key SWK to release relays RR, SP, SW. Main may give the exchange line to extension, whom he first calls as described below. When extension lifts his receiver, the brief operation of a key TRK by main or of a key ETK by extension brings up relays BZ, SW to switch the exchange line to extension who may return the circuit to its previous condition by operating key SWK or may offer a call to main as above. Local loudspeaking telephone system. This comprises main's loud-speaker MLS and transmitter MTR, and a receiver EXR and transmitter EXTR for the use of extension. Main calls extension by closing a switch LSW and a " call " key MCK. Relay M buzzes by selfinterruption in extension's receiver EXR which extension then lifts from its switch-hook having contacts LSHA, LSHB, so that relay ES operates to complete the local speech circuits and light a lamp SEL. Extension calls main by operating his " call " key EXCK, whereupon relay M buzzes in loud-speaker MLS, and then lifting his receiver EXR. Main responds by closing switch LSW and relay ES completes the connection as before.