Patent GB-125434-A (GB)
Title: Improvements in or relating to Telegraph Systems.
IPC: H04K1/02
Filed: 1916-07-21
Abstract: 125,434. Automatic Telephone Manufacturing Co., Woodland, R., and Smith, S. R. July 21, 1916. Receiving systems and apparatus; transmitting systems and apparatus.- A telegraph system having a telephonic receiving apparatus is arranged for secret working by causing " jamming " impulses to be sent over the line from the receiving station during the intervals in which the receiver is not connected to the line. The " jamming " impulses emitted from a station have a particular tone in order that they may serve as an indication at the sending station that the correct station is receiving the message. Each station is provided with a transmitting key, a telephonic receiver, a main rotary switch for rendering the signalling impulses audible in the receiver, a rotary switch for giving a particular tone to the " jamming " impulses, an induction coil, a telephone transmitter, circuitchanging switches, and a battery. The main rotary switch and the induction coil may be employed for signalling, non - secretly, with alternating current; while the telephone transmitter and induction coil are employed for telephonic communication between the stations. In the arrangement shown in Figs. 1 and 2, the sending station shown in Fig. 1 is connected to the receiving station shown in Fig. 2 by a line 1 and earthreturn 2. To signal secretly between the stations the switches 9, 10 at the sending station and the switches 7, 8 at the receiving station are closed and the rotary switch 25 at the receiving station started. the sending station is then operated and the current impulses pass over the line 1 and the back contact of the key 4 at the receiving station to the rotary member 27 of the switch 25. Each time the member 27 engages a contact 13 it sends an impulse through the winding 34 of an induction coil and through the telephonic receivers 32, 33 thereby breaking up the signal impulses into impulses audible in the receivers 32, 33. Each time the member 27 engages a contact 14, a " jamming " impulse is sent from the battery at the receiving station over the line 1 to the transmitting station where is divides, one part passing to earth through a resistance 36, switch 10, and the receivers 32, 33, and the other part passing by way of the key 4, when the latter is in its normal position, contact members 27, 15 of the switch 25, winding 34 of the induction coil and the receivers 33, 32. Any other receiver on the line 1 will receive both the signalling impulses and the " jamming " impulses. A particular tone is given to the " jamming " impulses by means of a switch 17, 18 and an ohmic or inductive resistance 35. When it is desired to signal, non- secretly, by means of alternating-current impulses, the switch 25 is operated and the switches 5, 6 closed at the transmitting station; while to establish telephonic communication between the two stations, a switch 39 in the circuit of the microphone 38 is closed. Alternating current generated by the rotary switch 25 and the induction coil mav be employed for calling purposes. The rotary switch 25, Figs. 4 and 5, is operated by a motor through gearing 19, 20, 21, and 22 and is normally held against rotation by a stop 30 on a cam and spring-controlled arm 29. In the position shown, the contact arms 27 engage the contact 15, but when the switch is released by the operation of the cam 28 a governor 24 causes the disengagement of the contacts 15, 27 and the engagement of the contact 27 with the stationary contacts 13, 14. The switches 5, 6, 7, 8, 9, 10, Figs. 1, and 2, may be combined to form a single switch comprising two sets of concentric contacts 48, 49, Figs. 7, and two contact arms 43, 44 insulated from each other. The contacts 48 are higher than the contacts 49 and the short ends 46, 47 of the arms 43, 44 are lower than the other ends of these arms in order that they may engage the low contacts 49 as the arms are rotated. The cam 28, Fig. 4, is mounted on the spindle of the arms 43, 44.