Patent GB-170584-A (GB)
IPC: H04L5/06
Filed: 1921-10-20
Abstract: 170,584. Western Electric Co., Ltd., (Assignees of Hamilton, B. P.). Oct..21, 1920, [Convention date]. Wired wireless systems; combined transmitting and receiving arrangements; keying systems and apparatus.-In a system in which telegraph signals are transmitted by means of carrier waves, a low-frequency telegraph loop circuit being associated with separate transmitting and receiving branches of the carrier transmission line at one end thereof, in such a manner that signals originating in the low-frequency loop are reproduced in the transmitting branch, and signals received in the receiving branch are reproduced in the low-frequency loop, a normally-energized relay in the transmitting branch de-energizes in response to signals originating in the loop, thereby short-circuiting the input circuit of a carrieroscillation amplifier and so interrupting the normal flow of carrier waves in the line. Means are provided for preventing signals received over the receiving branch from being reproduced in the transmitting branch; and the system also comprises means whereby a break signal may be sent, for the purpose of interrupting the reception of signals in order to transmit in the opposite direction. The Figure shows an arrangement for multiplex working by carrier waves of different frequencies. A subscriber's loop L comprising a key K and sounder S is associated with a transmission line ML through a tranmitting branch comprising a carrier-wave generator G, amplifier TA, and tuned circuit TF, and through a receiving branch comprising tuned circuit RF, detector D, receiving relay R, and repeating relay 11; the transmitting and receiving branches being coupled with the line ML through a balanced transformer 10 provided with a balancing network MN. The subscriber's loop, which is controlled by the repeating relay 11, also comprises a relay 12 controlling a monitoring sounder S<11> at the central office, a central-office key K<1>, and a transmitting relay T. When no signals are being transmitted, continuous carrier waves are impressed by the generator G upon the line ML, and, being detected at the receiving station, cause the normal energization of the relays R, 11, and 12. When a signal is transmitted by opening either of the keys K, K<1>, the de-energization of relay T causes the short-circuiting of the input side of amplifier TA over the circuit 13 through a condenser, thus withdrawing the carrier waves from the line. At the same time, the de-energization of the relay 12 causes the sounder S<11> to short-circuit the contacts of the relay R. At the distant receiving station, the interruption in the carrier wave deenergizes relays R and 11, thus operating sounder S<1> at the central station and sounder S in the subscriber's loop. In order to prevent the deenergization of the relay 11 from also de-energizing relays 12 and T and thus sending a signal back to line, a capacity C is inserted as shown, which charges up during the movement of the armature of relay 11 between its front and back contacts and thus holds the relays 12, T energized. In order to interrupt the reception of signals for the purpose of transmitting in the opposite direction, a break signal may be given by holding open one of the keys K, K' at the receiving end. This short-circuits the contacts of receiving relay R through the back-contact of the sounder S<11>, thus preventing the received signals from being transferred to the loop. At the distant sending station, the normal incoming carrier wave having been withdrawn, the relay R is held open, so that when the sending operator has his key closed, relay 11 is de-energized, and the loop L is permanently opened, the relay 12 being locked energized over the back-contact of relay 11 and thus preventing the sounder S<11> from short-circuiting the contacts of relay R. The operator recognizes that a break signal is being transmitted, owing to his sounder S no longer responding to the movements of the key K. In an alternative arrangement, the condenser-discharge arrangement for holding the relays 12, T is replaced by a magnetic locking-device in which the relay 12 is provided with an auxiliary holding coil controlled by the repeating relay 11. In this case, the relay T is arranged in a local circuit controlled by the relay 12. The auxiliary coil is only energized when the repeating relay is de-energized, thus holding the armature of relay 12 and preventing the circuit of the relay T from being broken during the reception of signals.