Patent GB-130679-A (GB)
Title: An Inductively Untappable Telegraph.
Inventor: MORSE ARTHUR HYATT
IPC: H04L1/06
Filed: 1918-03-12
Abstract: 130,679. Morse, A. H. March 12, 1918. Alternating or pulsating current code telegraphy.-To prevent inductive tapping of a code telegraph system employing alternating or pulsating current, the system is provided with two adjacent and electrically identical lines over one of which the marking currents are sent, and over the second of which current is sent during the spacing periods. In a modification, pulsating current of one polarity is sent over a single line during the marking periods, and a pulsating current of opposite polarity is sent over the line during the spacing periods. With the first arrangement, two receivers may be employed, one of which is muffled; and, with the second arrangement, a polarized relay is employed to control the circuit of the receiver, or the relay itself may operate as a sounder. The transmitter contact-arm is held electro-magnetically in its operated position until the current in the line reaches its minimum value. In the arrangement shown in Fig. 1, the station A is provided with a battery B, an interrupter I, a tapping-key K, a two-position switch S, a sounder M, and a muffled sounder M'. The station A<1> is provided with similar apparatus. The key K consists of a pivoted member 3 actuating a contact member 1 through a spring 5. The member 1 is provided with the armature 8, 9 of two electromagnets 6, 7. To send at the station A and to receive at the station A<1>, the switches S at the stations are placed in the position shown. With the tapping-key K in its inoperative position as shown, interrupted current from the battery B passes through the back contacts of the key K, the magnet 6, contact member 11 of switch S, line L', contact member 12 of switch S at station A<1>, muffled receiver M<1>, battery B<1>, to earth. When the key K is depressed, the back contacts of the key are separated, and the front contacts are engaged to send an interrupted marking current over the line L to actuate the unmuffled receiver M<1>. The function of the magnets 6, 7 is to hold the contact member 1 in its operated position until the current passing through them is reduced to its minimum value. In the modification shown in Fig. 2, a condenser C, a resistance, or an impedance is connected in series with the receivers, while the magnets 6, 7 are placed in shunt circuits across the battery B. In the modification shown in Fig. 3, the battery B<2> at the station A is connected to the middle point of a resistance R, and the ends of this resistance are connected respectively to the windings of the magnets 32, 3. The lines L<2>, L<3> are connected to intermediate points 39, 40 of the resistance R. Each station is provided with a polarized relay 34 which may operate as a sounder or control a receiver 37. With the key K<2> in the position shown, the magnet 32 is energized with intermittent current from the battery B<2>, and an intermittent current of one polarity is sent to line. When the hey K<2> is operated, the magnet 33 is energized and an intermittent current of opposite polarity is sent to line to effect signalling. The contact member 31, Fig. 4, is operated by a lever 30 through springs 56, 57 and is provided with armatures 60, 61 of magnets 33, 34 so that the contact 58 or. 59 in the circuits of the magnets 33, 34 and the controlled circuit is not broken, upon the release of the lever 30, until the current through the magnet 33 or 34 falls to a predetermined value.