GB563504A - Improvements in telephone or like systems - Google Patents

Abstract

563,504. Automatic and semi-automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS, C., and BEALE, C. E. Feb. 13, 1943, No. 2401. [Class 40 (iv)] In a mixed system, of the kind described in Specifications 560,794 and 561,155 in which some junctions are equipped for voice frequency signalling and some for direct current signalling, the VF junctions being provided at either end with converting relay sets, in order to reduce the number of conversions in a connection over several junctions in tandem, each incoming relay set sends forward after each train of direct current impulses a voice frequency testing signal to determine whether continued conversion is necessary, and each outgoing relay set on receiving such a signal immediately after seizure sends back a direct current signal, the effect of the two signals being to provide a straightthrough path for subsequent voice frequency signals. In the system shown in Fig. 1, in which a call between exchanges A and D is set up from a manual board MB over two V.F. junctions VFT1, VFT2 with an intermediate D.C. junction DCT, the first digit sent in V.F. form from ORS1 is converted at 1RS1 to D.C. form to the selector 1S1 at exchange B and the second digit is similarly converted and repeated over DCT to set the selector 1S2 at exchange C. The testing signal following the first digit is without effect, but that following the second digit is received at OPS2, where switch-through takes place and a signal comprising a reversal of line current is returned to bring about switch-through at 1RS1. Subsequent dialling and supervisory signals therefore pass directly between ORS1 and IRS2. The operator's clearing signal, which consists of frequency X for at least 2 seconds followed by frequency Y, takes effect at both IRS1 and IRS2. It will be noted that if the outgoing repeater of the junction DCT includes an impulse regenerator, the testing signal will not reach ORS2 and the switch-through mentioned above will not take place. In this case, the supervisory signals are transmitted in cascade, passing between ORS2 and IRS1 in D.C. form, and the V.F. signals arriving at ORS2 are prevented from reaching the junction DCT. The outgoing and incoming relay sets described with reference to Figs. 2-5 and 7, 8 (not shown) are similar to those of the prior Specifications apart from modifications concerned with the features stated above. In a further modification, Figs. 9, 10 (not shown), the reply signal is transmitted in cascade when an impulse regenerator has been used in setting up the connection, but the X frequency acknowledgment signal from ORS1 takes effect in succession at 1RS1 and ORS2 to condition the circuits for end-to-end transmission, so that the release signal may pass directly without conversion.