Patent GB-191419045-A (GB)
Title: Improvements relating to Telegraphy.
IPC: H04L25/49
Filed: 1914-08-25
Granted: 1915-11-25
Abstract: 19,045. Bruce, W. M., and United Telegraph and Cable Co. Aug. 25. Transmitting and receiving systems; duplex telegraphs.-In systems in which each signal element consists of a positive and a negative impulse separated by an interval of shorter or longer duration, the cable is directly earthed after each impulse, and a controlling - means is provided for determining the duration of each impulse irrespective of the movement of the signalling-key. The key a and the polarized relays c, e are shown in normal positions. When the key a is depressed, a circuit is completed from ground g<1> over contact e<2> of relay e, battery B, contact a<2> of key a, and relay c. Part of this current may pass to line over resistance r, but this connexion may be omitted, the normal signalling-current passing over the lead 13 and contact c<3> of relay c. The relay e is connected in parallel with the cable and is made slowacting by the inductance r<2> in its circuit, so that after a certain interval of time, the relay c disconnects the ground from the contact e<2>, thus breaking the line circuit. When the key returns to the contact a<1>, similar circuits are closed to send a negative impulse to line. Various modifications of the apparatus are described to prevent distortion due to the signals being sent rapidly. In the arrangement shown in Fig. 1, when impulses are being sent rapidly, the slowacting relays b, b', which are inserted in the leads 3, 6, remain energized and complete a circuit for the relay d, which, by short-circuiting the resistance r<1>, causes the relay e to work more rapidly. In the form shown in Fig. 3, the solenoid s s is connected in parallel with the controlling-relay e and, by means of the contacts t ... t<3> co-operating with the mercury cup m, short-circuits a greater or lesser part of the inductance r<2>, according to the speed of signalling. In another form, the solenoid s actuates similar contacts to control short circuits for parts of a resistance placed in series with the battery. As the potential of the cable is zero for the first of a series of impulses, but is not quite zero for the succeeding impulses, means are provided at the transmitter or receiver to prevent distortions owing to this cause. In the transmitter shown in Fig. 4, a resistance r<4> in the cable circuit is shortcircuited by a slow-acting relay f immediately after the first impulse, so that the current sent into the cable for the first impulse is slightly less than for the succeeding impulses. In a modification, the relay f normally short-circuits part of the inductance in series with the controlling-relay e, the short circuit being removed by the first impulse, so that the relay e acts more quickly for the first than for the succeeding impulses. Fig. 6 shows a receiving-arrangement with means for preventing distortion due to the first impulse of a series being of slightly higher potential than the succeeding ones. The polarized relay h controls the circuit of a relay k, which controls the circuit of the sounder l. In parallel with the sounder is a slow-acting relay f which, after the first signal has been received, short-circuits the resistance r<4> in series with the relay h. The slow-acting relay may also be arranged to control the sounder circuit directly.