Conversion from direct current to double voice frequency impulsing

摘要

641,888. Voice-frequency signalling. STANDARD TELEPHONES & CABLES, Ltd. Feb. 7, 1947, No. 3711. [Class 40 (iv)] In a system for repeating D.C. impulse trains as V.F. trains, the V.F. impulse corresponding to each " break " is transmitted in the subsequent " make " period, the first break period being utilized to send a V.F. digital prefix. Line and release relays A, B operate on seizure. During the first break period A connects frequency fx and also operates C which holds during impulsing so that during the subsequent make period frequency fy is connected to line. CO operates and locks at the first make to prevent further transmission of frequency fx. The duration of the final fy pulse is determined by the release time of C. In the receiver the initial fn impulse operates X to bring up dialling relay CC. The subsequent fy impulses are repeated by Y and YA (which increases their duration) via the dialling relay to the impulse receiving equipment. The normally operated relay SP is released by X and remains so while CC is operated to disconnect the outgoing line during impulsing. On release a long fn pulse is sent during the slow release of B so that normally operated relay R drops back to give a release signal.