Patent GB-348574-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H04B3/20
Filed: 1930-02-12
Abstract: 348,574. Two - way transmission. STANDARD TELEPHONES & CABLES, Ltd., SANDEMAN, E. K., and FILBY, F. G., Columbia House, Aldwych, London. Feb. 12, 1930, No. 4739. [Class 40 (iv).] In a two-way signalling system with a number of stations, means are provided for sending a preliminary pulse or signal for conditioning for reception the apparatus of the station to which the transmitted signal is to be sent, and a following pulse or signal for restoring the apparatus to normal, the auxiliary signals being sent entirely under the influence of the main signals. Fig. 1 shows terminal equipment for use in connection with a radio link. A detector amplifier R1 actuated by speech over the line W-E causes energization of relays E, F, the relay E being adapted to operate and release quickly and the relay F to operate and release slowly. A circuit is therefore closed for relay G until relay F operates its contacts. Relay 6 at contacts 9, 10, connects an oscillator O1 to the line, whereby a preliminary pulse is sent into a radio transmitter. A delay network D1 holds up speech while the preliminary pulse is being sent out. When speech has ended the output from R1 ceases, causing the relays E, F to be de-energized. A circuit is then closed for relay H until relay F releases. Relay H causes oscillator 2 to be connected to the line so that a following pulse is transmitted after speech has ended. Network D2 is provided to delay transmission of the following pulse until the last of the speech has passed through D1. The oscillators O1, 02 are adapted to generate coded signals, which are received, respectively, by tuned detectors R2, R3. The output from R2 causes relays J, K to operate, relay J opening the output circuit of R3, and relay K initiating the operation of a chain of relays K .. N. These relays which have predetermined times for operation and release, have a cycle of operations which is repeated so long as the preliminary pulse continues. Relay N is maintained operated since at no time is the current cut off for a period as long as the time necessary for its release. Relay N opens contacts 25, 26, and 27, 28, thereby removing earth from slow-release relays P, S. Unless the pulse is of a predetermined length these relays do not release. If, however, relay P releases, contacts 17, 18 close, completing a circuit through relay X which operates to switch the line into position for reception. Relay X locks up at contacts 19, 20. If the pulse is of greater length than the predetermined value relay S also releases and at contacts 15, 16 opens the locking circuit of relay X. When speech has ceased the following pulse causes the output from R3 to operate relay Q which, as one of a chain of relays Q, U, W, Y, operates in accordance with the code of the pulse, causing contacts 29, 30 and 31, 32 to open. If, again, the pulse is of sufficient length, slow-release relay T releases, opening contacts 21, 22 and allowing the contacts of relay X to fall back into the position for transmission. If the pulse is too long, relay V releases to close contacts 23, 24, and short-circuit contacts 21, 22, and since the difference between the release times of T and V is less than the release time of X, relay X is prevented from releasing. The switching may be carried out by using one code only with pulses of different lengths, in which case the amplifier R3 and relays Q, U, W, Y would be dispensed with, contacts 29, 30 and 31, 32, being operated by relay N. In the case of an intermediate station, the relay X is placed in series with two relays similar to E, F, so that the effect of the pulse for switching the line into the "receive" position continues to the end of the circuit. The relay X in this case operates quickly and releases slowly to allow the following pulse to pass the switch before the line returns to the " transmitting " position. In the construction shown in Fig. 4, which represents a submarine cable terminating in a four-wire line and having at each end generating and receiving apparatus, if signals are originated simultaneously at both ends, switching will only be effected at the E-W end, the pulse reeciving apparatus PRA at the W-E end being disconnected by the operation of relay 2.