Patent GB-157206-A (GB)
Title: Improvements in and relating to the transmission of radiant energy
IPC: H04J1/00
Filed: 1921-01-08
Abstract: 157,206. Hammond, J. H. March 22, 1917, [Convention date]. Secret and selective signalling systems; multiplex signalling; spark-gap apparatus; controlling boats &c.-Relates to multiplex systems of wireless telegraphy or telephony in which the transmitted waves of radio-frequency are subjected to a number of periodic modifications having different supersonic frequencies, to which the receiving apparatus is tuned to respond selectively. The invention may also be adapted to provide a system whereby a number of operators located at different distant points may separately or simultaneously control a number of boats or other movable bodies through a single transmitting station, each boat carrying a receiving station tuned to select and respond to a particular supersonic group frequency. Fig. 1 shows a system arranged for multiplex wireless telegraphy. An alternator 35 supplies alternating current to the intermediate circuit 18, 38, across which are bridged two circuits 45, 46 and 50, 51, tuned to different supersonic frequencies, and normally held open by the switches 47 and 52. The latter may be controlled from a distance by keys 57, 62. Upon depressing a key 57 or 62 the supersonic group frequency is varied and oscillations are produced in the circuit 16, 13, having a predetermined oscillation frequency and a supersonic group frequency determined by the frequency of the circuit 45, 46 or 50, 51 in operation. These are further divided into groups of audible frequency by an interrupter spark gap 21, comprising a casing 22 inside which rotates a copper disc 20 having around its periphery radial projections which are brought opposite a stationary terminal 23 as the disc is rotated. An alcohol container 30 supplies hydrogen to the interior of the casing 22 to assist in quenching the spark. A direct current generator may be used in place of the alternator 35. In a modification shown in Fig. 5, the aerial 200 is caused to radiate at its natural frequency by energy supplied by the alternator 206. A point of high potential in the aerial is connected to earth through a valve 212, the grid circuit of which is coupled to two circuits 235, 236, normally held open, but on the depression of signalling keys 249, 250, arranged to be energized by two alternators 239, 240 of different supersonic frequencies. When a key is operated a periodic variation in the conductivity of the valve, and hence a periodic variation in the amplitude of radiated waves, occurs. If both keys are closed, twoseries of periodic variations in amplitude are produced, the frequencies of the variations corresponding to the frequencies of the alternators 239, 240. Fig. 6 shows an arrangement for multiplex telephony, the antenna 300 being excited to radiate substantially undamped waves. The arrangement for multiplexing is similar to that shown in Fig. 5, the selective periodic variations applied to the grid 334 by the alternators 370, 371, 372 being further modified in accordance with speech by the microphones 373, 374, 375. In all the arrangements described the wave frequency is also periodically varied since the periodic modification of the high frequency waves varies the constant of the open aerial circuit. Transmitted signals may be received by a single receiving station having a number of co-operating circuits tuned to respond selectively to the supersonic group frequencies, or by a number of separate receiving stations tuned to respond respectively to the different group frequencies. A receiving system of the first kind for use with the telephone transmitter, Fig. 6, is shown in Fig. 7. The anode circuit of the amplifying valve 410 is coupled to three separate valvedetector circuits, the grid circuits 425, 426, 427 of which are tuned respectively to the supersonic group frequencies, i.e. the frequencies of the alternators 370, 371, 372, Fig. 6.