Patent GB-158200-A (GB)
Title: Improvements in and relating to wireless signalling systems
IPC: H04B14/08
Filed: 1918-03-08
Abstract: 158,200. Hammond, J. H. March 17, 1917, [Convention date]. Keying and modulating systems and apparatus; heterodyne receiving systems; spark-gap oscillation generators; controlling torpedoes.-A selective wireless system for telegraphy, telephony, or control consists of a transmitting system emitting waves and wave-groups and a receiving system comprising circuits tuned to the wave and wave-group frequencies respectively, circuits tuned to a beat ' frequency derived from the wave-group frequency and from a locally generated oscillation frequency, and a mercuryvapour detector the circuit of which contains a high-frequency alternator and a telephone receiver or the control relay of a torpedo or the like. When the system is employed for telegraphy, a 'beat' frequency of about 500 is employed; but when employed for telephony, the beat ' frequency is above the range of audibility or very high. Transmitter systems. In the arrangement shown in Fig. 1, the antenna 10 is inductively coupled to a condenser-discharge circuit 16, 17 by a transformer 15. The condenser-discharge circuit is connected to a high-potential directcurrent source 30 through choke coils 25, 26, and contains two stationary quenched spark-gaps 18, 19 and a rotary spark-gap 20 giving a group frequency to the emitted waves of about 30,000. In the modification shown in Fig. 2, the group frequency is obtained by an oscillation circuit 50, 51 placed across the condenser 17. In a further modification, the group frequency oscillation circuit is placed across a stationary quenched sparkgap. To effect signalling with the arrangement shown in Fig. 1, a transmitter key 31 is operated or a telephone transmitter is placed in the antenna circuit or in the condenser discharge circuit 16, 17; while to effect signalling in the arrangement shown in Fig. 2 or in its modification, a telephone transmitter 55 or a signalling key is placed in circuit with a coil 57 inductively coupled to the coil 51. Receiving system. A circuit 101, 103, Fig. 4, tuned to the wave frequency, is connected to the antenna 100 and coupled to a similarly tuned circuit 105, 106 by a transformer 104. The circuit 105, 106 is connected by leads 107, 108 to the grid 109 and the filament 110 of a gaseous detector 115. A circuit 117, 125, tuned to the group frequency of the received waves, is connected in the plate circuit of the detector 115 and coupled to a similarly tuned circuit 131, 132 and 133 by a transformer 130. The circuit 131, 132, 133 is coupled to a high frequency generator 139 by a transformer 135, and is connected to the grid 147 and the filament 148 of a gaseous detector 150 by leads 145, 146. A circuit 149,.152, tuned to the beat ' frequency of the circuit 131, 132, 133 and the generator 139, is connected to the plate circuit of the detector 150 and coupled to a similarly tuned circuit 156, 157 'by a transformer 162. The circuit 156, 157 is connected to the grid 162 of a mercury vapour detector 165 by a lead 158 and to the lower terminal 163 of the detector 185 by a lead 159, high resistance 160 and a variable resistance 161. An annular metal anode 169 is connected to the positive terminal of a battery 172 through a choke coil 170 and a variable resistance 171. A circuit 166, containing a high frequency alternator 167 and a telephone receiver 168, is connected across the upper and lower terminals of the detector 165. In a modification shown in Fig. 4<a>, the circuit 166 contains the control relay 175 of a solenoid 177 which operates a valve stem 179 through a rack 178 and pawl and ratchet mechanism.