Patent GB-139259-A (GB)
Title: Improvements in and relating to electric telegraphs
IPC: H04L9/00
Filed: 1919-01-22
Abstract: 139,259. Roberts, W. H., and Matson, F. J. Jan. 22, 1919 Telephonic telegraphs.-In a telegraph system, more particularly adapted for military use in the field, the signals are transmitted over the line by direct currents of varying duration, as in plain Morse signalling, but are received on the telephone through the intervention of a buzzer controlled by a polarized relay. Provision is also made for supplying " jamming " currents from the receiving- station to line for the purpose of preventing tapping or other interception of the messages sent. When the sending-key 61 at station A is depressed, current from the battery 71 flows in the following circuit : Contact 2, line 72, relay coil CD at station B, relay coil DJ (in direction assisting CD), galvanometer coil lk, resistance 70, and earth, returning at station A through relay coil CD, galvanometer coil e, f, and contact 3. At the same time, current flows at the sending-station through resistance 70, coil kl, relay coil JD, and coil ef, to contact 3. The currents in the coils CD, JD neutralize one another, but, at the receiving-station, the armature of the relay 62 closes the buzzer circuit at 22. The buzzer circuit comprises the battery 64, buzzer winding 43, contacts 65, r (shunted by condenser 42), and contact 22. The telephone T shunts the buzzer winding and condenser as shown. The closing of the relay contact 22 at station B permits current from the battery 64 to energize the windings of the jamming pendulums 68, 69 in paraliel, over the circuit 64, 12, 11, 66, 22. As each pendulum in its oscillations makes contact at 10, the positive terminal of the battery 71 is applied to line through 10, D, C, the negative terminal being to earth at 7. The battery 71 at station B thus momentarily opposes the sending-battery 71, and the line current at these moments ceases. These intermissions of the line current will be visible on the " line-jamming indicator " 60 at the sending- station. when the sending-key 61 is released, a momentary current flows from the battery 71 at station A over the circuit 5, 4, f, e, DC, and earth, returning by earth at station B, resistance 70, windings JD, DC, and line 72. This current flows in the windings JD, DC at station B in the opposite direction to the current which was flowing while the transmitting-key 61 at station A was depressed, and as the relay 62 is polarized, the said momentary current opens the buzzer circuit at 22. Owing to the continued swinging by acquired momentum of the jamming-pendulums 68, 69 at station B, current from the battery 71 at that station still passes intermittently over the line, the circuit being as follows : battery 71, contacts 10, coil DC, line 72, resistance 70, coil @. windings JD, DC, and earth. At the same time, at station B, a neutralizing-current flows through contacts 10, coil DJ, coil lk, and resistance 70. If a contact at 10 at station B happens to synchronize with a momentary current at 5, 4 at station A, a double current flows over the line, the circuit being as follows : battery 71 at station B, 10, DC, line 72, 7 (at station A), battery 71 (which is thus in series with the distant battery), 5, 4. fe, DC, earth, and contact 7 at station B. These jamming-currents are in a direction that renders them incapable of closing the contact 22 of the polarized relay 62 at the receiving-station, and cannot therefore bring about any false signals at that station.