Patent GB-499133-A (GB)
Title: Improvements in and relating to telephone installations
IPC: H04Q3/00
Filed: 1937-05-10
Abstract: 499,133. Automatic exchange systems. LEHNER, C., GADESMANN, M., LEICHTHAMMER, K., and LEICHTHAMMER, H., (trading as TELEFONBAU UND NORMALZEIT LEHNER & CO.). May 10, 1937, No. 13332. Convention date, May 8, 1936. [Class 40 (iv)] In an inter-exchange system employing alternating-current for impulsing and signalling, a backward signal transmitted when the wanted line is busy and when the called party hangs up first brings about the release of the connection back to the calling party's line circuit, busy tone being applied therefrom. The backward signal referred to consists of a long impulse over the junction, whereas the reply signal consists of a short impulse. Within the exchanges, the alternative signals may comprise battery and A.C. or strong and weak battery on one speech wire. First arrangement, Figs. 1, 2. Upon the initiation of a call, two-step line and cut-off relay T operates contacts t1, t2, and causes the finder AS to rotate into engagement with the calling line. Relay T energizes fully and connects up R, while line relay A energizes over the loop. The group selector GW is set in the usual way, and, should there be no idle outlet in the wanted group, M energizes and disconnects A, which in turn opens the test wire. Relav T reverts to its condition of partial energization over the loop, which now, however, includes R, so that busy tone is transmitted inductively over the windings of T. Assuming that an idle junction is found, switching relay P energizes in series with 2C in the outgoing repeater, and the latter connects up impulse relay 2A during the slow operating period of U, with the result that an impulse is sent over the junction. This is received bv impulse relay 3A and connects up 3C which seizes the final selector LW. Numerical impulses are repeated by A, 2A, 3A to line relay 4A, 4V being up during each train, and, after the last train, 4R pulls up and the wanted line is tested during the slow release period of 4U, If the line is idle, switching relay 4P energizes, ringing takes place and upon reply 4Y pulls up and returns battery on the b wire to operate 3K in the incoming repeater. A short impulse is sent back over the junction by 3S during the slow operating period of 3L and is received by W, which connects up 2H, Y. Relay Y locks and applies battery on the b wire to operate ZB, ZH in preparation for metering. If the calling party hangs up first, A, C fall back and 2A operates during the release period of C and sends a long impulse over the junction to which 3A responds, so that 3C is short-circuited and releases the final selector. If the called party hangs up first, on the relapse of 4Y, A.C. is returned on the b wire to operate 3M and a long impulse is sent back over the junction by 3S during the release period of 3N. Relay W responds and connects up 2H which short-circuits 2N and an A.C. impulse is sent back over the b wire to operate M which brings about release as described above. If the wanted line is busy, 3M is operated by A.C. on the b wire upon the relapse of 4U, with similar results, and the calling party receives busy tone from the individual line circuit. When zone-metering equipment MW is associated with the outgoing repeater, 2H may be operated therefrom when a non-existent exchange number is dialled, sending back A.C. on the b wire as before. Second arrangement, Figs. 3, 4. This differs from the first arrangement in that the busy and release signals from the fmal selector are sent by the connection of battery through a resistance W2 to the b wire. Relays 3M, K are in series, K being marginal, so that only 3M responds to such a signal and a long impulse is sent back over the junction by S during the release period of 3N. Relay W responds and connects up Y which locks and connects battery through a resistance W1 to the b wire. In the group selector GW, relays M, ZB are in series, ZB being marginal, so that only M responds and short-circuits N which disconnects line relay A. Busy tone is sent as in the first arrangement. If the wanted line is idle, the operation of 4Y when the called party replies connects direct battery to the b wire, so that K pulls up and at once short-circuits 3M, and a short impulse is sent back over the junction during the operating period of L. Relay W responds and connects up Y, and at the end of the impulse, X also energizes and connects direct battery to the b wire to operate ZB, which locks and disconnects M before N has time to relapse. If it is desired to prevent release when the called party hangs up, relays 2T, 3T are provided as shown in the outgoing and incoming repeaters. These relays are connected up by X, K respectively when the reply signal is sent and short-circuit resistance W1 and relay 3M, so that the backward release signal is suppressed.