Patent GB-483025-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M7/10
Filed: 1936-10-09
Abstract: 483,025. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., McCLEW, J. W., and WILLIAMS, A. H. Oct. 9,1936, No. 27473. [Class 40 (iv)] In an impulse repeater, the impedance bridge on the outgoing side comprises two relays in series each arranged, when energized, to connect a rectifier across the other, the rectifiers being oppositely poled. Each relay normally short-circuits its high resistance winding to avoid the possibility of the line relay at the incoming selector releasing when the relays become effectively connected in the loop, e.g. between impulse trains. The repeater is described for an A.C. impulsing system, speech transmission being improved by connecting the signal responsive relay across the line in series with a low-pass filter. Also, the above mentioned rectifiers are never directly across the line so that they do not interfere with speech. As the first impulse of a train is shortened by the sluggish action of the responsive relay before the line is cleared for impulsing, succeeding impulses are similarly shortened by interposing a series resistance in the relay circuit. Switch-setting, toll break-in, and release signals are differentiated by length, and, in case of a call from an operator, switchhook flicks by the calling party are repeated back as equalized A.C. impulses. A bridge in which the two relays are directly shunted by oppositely poled rectifiers is referred to. The A.C. relay AO, which has two windings each in series with a rectifier MRC, MRD and is connected in series with filter LPF, on operation by the seizing impulse operates impulse relay A followed by B which prepares the outgoing loop and extends a holding ground to the selector. Relays PF and HS pull up without effect at present. When the seizing impulse terminates, the relapse of AO releases A but B holds so that the loop is completed and bridge relays D, I both operate at first and each connects a rectifier MRA, MRB across the other and opens the short-circuit on its own high impedance winding. The direction of current feed from the selector is such that MRA shunts D leaving I operated alone. DX pulls up. The switch setting impulses are repeated by AO and A and immediately AO commences to operate it removes a shortcircuit from C which pulls up in series with DX, operates CR, opens the line beyond the A.C. relay and short-circuits the bridge D, I. Relay C holds in series with CR throughout the train and CR introduces resistance BY in series with the A.C. relay. On relapse of C, CR at the end of the train, D and I operate over the loop as before and I remains operated. Subsequent trains are similarly repeated and on battery reversal consequent to the reply of the called party, I falls back and D operates whereupon E (lower) pulls up and sends back an A.C. pulse from 10, 11 for metering or supervisory purposes, the pulse being terminated by slow-to-operate relay DR which releases E. The full impedance of D is connected across the line during conversation. Repetition of switch-hook flicks. The current reversals operate I and release D. Relays E (middle) and ER pull up and the backward A.C. pulse sent by E is terminated by slow releasing relay DR, DX also being operated and held. On re-operation of D and release of I, E (lower) operates and sends back an A.C. pulse as previously described, the reoperation of DR to terminate the pulse releasing DX. Subsequent flicks are similarly repeated, the A.C. pulses being independent of the speed of switch-hook manipulation. Release by called party. The re-operation of I sends back an A.C. pulse as described in the preceding paragraph and when the operator unplugs, a long A.C. pulse is -sent forward to operate AO, A, C and CR so that B is shorted for a sufficient length of time to release and open the outgoing loop. When the incoming selector has released, battery on the P wire energizes E (upper) to send back an A.C. pulse terminated by slow-to-operate relay JC. This pulse releases the equipment at the originating exchange. Toll break-in. This is effected by an A.C. pulse longer than switch-setting impulses but shorter than the release signal. Relays AO, A, C, CR operate long enough to release PF which is maintained by KS during switchsetting impulses. Relay PF re-makes the holding loop opened by A and when HS releases at the end of the pulse, it connects ground over the negative wire to operate a differential relay at the controlling switch. Break-down and re-ringing are effected by further pulses of the same length.