GB693613A - Improvements relating to circuit arrangements for telephone installations employing s - Google Patents

Abstract

693,613. Voice frequency signalling. SIEMENS & HALSKE AKT.-GES. Sept. 27, 1949 [Oct. 1, 1948], No. 24822/49. Class 40 (iv). In a voice frequency signalling system voice immunity is attained by arranging that on reception by the receiver of the signal frequency, and when the transmitter is transmitting, the line is blocked to voice frequency signals at a point on the far side of the transmitter from the receiver, thus preventing signals the source of which precedes the transmitter from operating the receiver. The embodiment shown is a 4-wire system equipped for signalling in the W-E direction only but similar arrangements may be provided for E-W signalling. Normal operation. Initiation of a signal at the West terminal results in the closure of contact x in response to each impulse, whereupon S follows and brings up T which shortcircuits the W-E pair on the incoming side of the transmitter and inserts resistances W1 and W2 to maintain the impedance looking back into the pair at 600 ohms. Relay S also repeats the signal as impulses of voice frequency current over the W-E pair and in the receiver TE relay J1 responds. Relays V, VI, and T are thus operated, the former short-circuiting its winding II to render it slow-to-release so that it remains up between impulses. Relay T1 shortcircuits the incoming E-W pair and inserts resistances W3 and W4, while V and V1 bring up F which then interacts with A. A series of impulses of voice frequency current are thus transmitted over the E-W pair. Relay J in the receiver TE1 responds and brings up Ve for the duration of the series. Relay Ve completes an alternative circuit for T. At the end of the W-E signal V relapses, followed by VI, T1, F, and A. The consequent relapse of Ve releases T which restores the circuit to normal. Prevention of operation of receiver by signals from sources preceding the transmitter. A current of signal frequency incoming from the West initially brings up relay J1 and the reversion of impulses over the E-W pair results in the operation of T by Ve. The incoming W-E pair is thus short-circuited to prevent the current from reaching the receiver TE. Means other than short-circuiting the incoming pair may be used for blocking the line to signal frequency currents. If the signalling system is of the type in which the signal proper is preceded by a prefix signal it is arranged that the reverted impulses commence shortly after the termination of the prefix signal or on the reception of the signal proper.