Patent GB-551419-A (GB)
Title: Improvements relating to telephone and like impulsing systems
IPC: H04Q1/32
Filed: 1941-10-31
Abstract: 551,419. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., CHRISTIAN, D. A., and VOSPER, W. T. Oct. 31, 1941, No. 14045. [Class 40 (iv)] In a direct current impulsing arrangement which corrects for the distortion produced by transmission over a junction, the correction is made in two steps by a main correcting circuit which provides a fixed change in the lengths of the makes and breaks appropriate to a certain impulsing speed and by an auxiliary correcting circuit which provides a further variable change in accordance with the departure of the actual impulsing speed from the aforesaid speed. Both correcting circuits are adjustable, and the main circuit is preferably set to give the proper correction at the maximum impulsing speed, the auxiliary circuit having no effect at that speed and being set to give the proper modification of the fixed correction at the minimum speed. As shown, the correction is applied at the receiving end of the junction, but the circuits may also be used to pre-distort the impulses at the sending end so that they arrive in correct form at the receiving end. In Fig. 1, incoming impulses are repeated by a sequence of relays AI, AA, AB. To obtain the fixed correction, the operation of AA is retarded by an impedance RA1 shunted by a resistance R1 and its release is retarded by a condenser QA pre-charged during breaks and a resistance R2, the resistances being adjustable to give a desired lengthening or shortening of the make period with a corresponding change in the break period. A second coil of RA1 serves to cancel the remanent flux during breaks. The auxiliary correction is obtained by variation of the operating lag of AB, which for zero correction is equal to its release lag, in accordance with the excess of the actual break period over that at the maximum impulsing speed. With the key K normal, relay AY which has an operating lag equal to the break period as delivered by AA at the maximum speed enables a pre-charged condenser QB to be partially discharged during the excess break period, so that when AA again pulls up the operation of AB is retarded by the recharging of QB, and the break period is extended. With the key K operated, in a similar way an impedance coil RA2 is premagnetized during the excess break period to hasten the operation of AB and shorten the break period. For the initial adjustment, an impulse generator TEO is connected to the junction at the ending end and the repeated impulses are applied over jack TJ2 to a ratiomeasuring instrument YM, a link L being transferred from jack TJ5 to jack TJ4 to operate CI but not BI. Impulses are sent at the maximum speed, e.g. 12 per second, for the adjustment of R1 and R2, and then at the minimum speed, e.g. 7 per second, for the. adjustment of R5. For a local test, a generator TEI is connected to jack BJ to send impulses simulating those received over the junction and the repeated impulses are observed on the instrument YM as before. Busy tone is applied to the junction over jack TJ1. In the modification shown in Fig. 2, the condenser QB is partially charged during the excess break period, and its subsequent discharge retards or hastens the operation of AB according to the position of the key K. In Fig. 3, both relays AA, AB take part in the fixed correction, the operation of AA being retarded by an impedance RA1 shunted by an adjustable resistance R1, and the release of AB being retarded when necessary bv the continued discharge of a condenser QC through an adjustable resistance R3 after AA has fallen back. For the auxiliary correction, with the key AK operated, a condenser QA is variably charged during the break period and its subsequent discharge retards the operation of AA and thus extends the break period. With the key BK operated, a condenser QB serves in a similar way to extend the make period by retarding the release of AB.