Patent GB-559016-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04M3/40
Filed: 1942-07-28
Abstract: 559,016. Automatic and semi-automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS, C., and BEALE, C. E. July 28, 1942, No. 10524. [Class 40 (iv)] Each train of numerical impulses is converted at the outgoing end of a long repeatered junction into a single impulse comprising one, two or three out of four voicefrequencies, and each such impulse is preceded by a preparatory impulse comprising all four voice-frequencies. The pause that follows a code impulse is lengthened when the corresponding impulse train consists of more than 5 impulses. A system for "demand" working is described in which calls are set up automatically by an operator. A timing switch TS is started by sleeve relay M when the junction is seized and an impulse of frequency X is sent for 100 milliseconds by relay FXY until the switch reaches position 3. At the distant end of the junction, the response of the corresponding relay XR brings about the operation of relay AR to seize the incoming selector and relays IR, NN pull up. The switch TS continues to position 6. Actuation of the dialling key operates RR which connects relay AM to the tip and ring of the jack. Relay B energizes and extinguishes the supervisory lamp which has so far been flashing over lead 10. The dialled digits set registers DSA .. DSD which are connected up in succession by a distributer DD under the control of dialling relay C, and corresponding relays CNA .. CND operate in series with CNR as the registrations are completed. Relay CNR starts a sending switch SC which connects up relay ST to send an impulse of all four frequencies W .. Z and then relay S to send an impulse of one, two or three of  those frequencies according to the setting of the relevant register. Finally, relay ZR operates to terminate the code impulse and the register and SC go home in turn in readiness for the sending of the next digit. If however the digit registered is greater than 5, relay EP energises in series with CNA .. CND and causes the register to make an additional cycle before SC goes home, thus increasing the inter-digital pause. On the return of the dialling key, relay KR energises over the sleeve and relays AM, B fall back, relighting the supervisory lamp. At the incoming end, the response of all four relays XR .. WR connects up CA, CC so that relay CB energizes at the end of the preparatory impulse and starts a sending switch SS which is marked by the relays operated by the code impulse and controls the transmission of impulses at springs IMPI in the usual manner. Backward tone signals reach the operator by way of transformer T1 and a "stopper" valve SV which prevents the possible operation of the echo-suppressors by noise from the cord circuit. Upon reply, relay I energizes in place of IR, bringing up FY momentarily to send an impulse of frequency Y and releasing CK which hitherto has been slowly pulsing. At the outgoing end, relay RS responds and connects up relay SA and switching relay CT which dims the supervisory lamp. The relapse of I when the called party hangs up re-operates CK and causes FY to pulse slowly and send frequency Y intermittently, two "on" periods being necessary to release switching relay CT and relight the supervisory lamp. When the operator takes down the relapse of M restarts the timing switch TS which advances by self-stepping to position 15, slowly to position 19 and finally by self-stepping home, relays B, FXY being operative to send a disconnect signal consisting of frequency X for 1¢ sec. followed by frequency Y for 300 milliseconds. Frequency X changes over the echo-suppressors, disconnects FY and brings up CC so that the following frequency Y connects up CR to initiate release of the incoming selector. In the event of a busy condition, the pulsing of I by busy flash causes the release of CK to provide a path for busy tone. If the operator clears before a reply signal is received, SA is back and the switch TS steps slowly to position 15 and extends the period of frequency X to 6 seconds in order to ensure the change-over of the echo-suppressors in the face of NU tone. If the first two or more digits received at the distant end select on outgoing voice-frequency junction, battery is returned over the test wire from the relay set associated therewith to operate relay DCO which locks and disconnects CB, CK, so that subsequent code impulses pass directly to the outgoing junction. In this case it will be seen that the outgoing junction is seized by ground on both legs through relays I, IR. If it is accessible from an ordinary selector train, however, the numerical impulse trains will require conversion to code form, as in the originating exchange, and in this case the seizure is by means of a direct current loop.