Patent GB-513552-A (GB)
Title: Improvements relating to telephone and like signalling systems
IPC: H04Q1/36
Filed: 1938-04-13
Abstract: 513,552. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and CHRISTIAN, D. A. April 13, 1938, No. 11342. [Class 40 (iv)] An impulse repeater including a feeding bridge has the following features: (a) the coupling between the incoming and outgoing sides of the bridge is solely by transformer action, (b) the impulse receiving relay and an auxiliary repeating relay, if used, are of the high-speed low impedance type described, for example, in Specification 405,436, [Group XXXVII], (c) the outgoing side of the bridge is short-circuited on the commencement of the first impulse (break) by the back contact of the receiving or repeating relay, the short circuit being maintained subsequently by the " dialling" relay, which also inserts a compensating resistance to maintain a constant load on the bridge. These arrangements aim at reducing distortion of the make-to-break ratio and at enabling the distortion readily to be determined since it is then due mainly to line characteristics. Special arrangements of back bridge relays are described for providing the low-impedance outgoing loop necessitated by the use of a low impedance receiving relay. In Fig. 1, a high-speed low impedance non-polarized relay and a polarized relay in parallel are employed, the polarization of the relay being effected by a metal rectifier presenting a low impedance to current flow in the normal direction so that it operates on seizure of the repeater and is released by the reply signal. This arrangement minimizes distortion of busy flash signals. In Fig. 2 (not shown), a single relay is used, polarized by a rectifier so that it responds in normal manner to the reply signal, the low impedance to normal flow being obtained by shunting the series circuit by an oppositely-poled rectifier. On seizure of the repeater, high-speed relay A operates its single contact, followed by a repeating relay AA of similar type, relay B and switching relay HA. The outgoing loop includes the single contact of AA which normally short-circuits the bridge, and relays D and I pull up, the former being connected in series with a rectifier MRC presenting a low impedance to normal current flow, and the latter being of low impedance high speed type. Relays J and IA follow D and I, the circuit being then in condition for repeating impulses. The operating winding (i) of AA is connected in series with rectifier MRB to prevent it from being slow-to-release due to the shunting effect of the winding of B. All four windings of repeating coil RC are in aiding relationship as regards D.C. magnetization of the core. On relapse of A and AA on the first impulse, AA again short-circuits the bridge, the shortcircuit being thereafter maintained by dialling relay C so that D, I and IA relapse during impulse trains, change of load on the repeating coil being minimized by resistance YA. The contact of AA is provided with a sparkquenching circuit QC which also improves impulse transmission. Relay C also operates BB followed by MD and when the bridge relays pull up again at the end of the train, BB and MD remain held. On reply, current reversal releases D followed by MD slowly, whereupon if the exchange is an intermediate one DD reverses the current feed at the incoming side of the bridge, repetition of a temporary reversal being prevented by MD, or, if the exchange is the calling exchange, booster metering is effected during the release of J by DD, the holding relays being maintained over metal rectifier MRA. Release. When the calling party replaces his receiver, A and AA fall back and B releases slowly, the opening of the outgoing loop causing the relapse of the bridge relay I, followed by that of relays IA and DD. Relays C and MD pull up, the latter connecting a further holding ground to the c-wire. When B ultimately releases, BB and MD fall back and removal of holding ground releases the preceding selectors and also the switching relay HA which is slower. The c-wire is again grounded during the release period of C to guard the repeater against seizure while apparatus at the distant end of the junction is releasing. If the called party clears first, current reversal operates the bridge relay D which releases DD to repeat the signal if necessary. When the calling party now clears, A, AA, D and I relapse and release occurs as previously described. Busy signalling and release. On receipt of busy tone and flash, D, I and IA release during the flash periods and BB is unlocked so that on the re-operation of IA after the first flash period, busy relay BR pulls up and prepares a delayed alarm over lamp LP and wire ALW. Relay BR also changes the feed connections on the incoming side so that on subsequent releases of IA the flash signal is repeated backwards. Relays A and B release during flash periods, but without effect since AA is held by BR which holds itself during these periods and maintains MD operated. Metering relay J is released. Rectifier MRB prevents B being held over the holding circuit of AA. The flash periods are repeated with minimum distortion since I is a high-speed relay and auxiliary relay IA being locally controlled can be designed to have equal operating and release lags. When the calling party clears, A and B are no longer energized during the tone periods, BR releases followed by AA and MD and the operation of C. Release is then completed as previously described.