GB261847A - Improvements in or relating to means for wireless communication - Google Patents

Abstract

261,847. Secret Wireless, Ltd., and Chisholm, J. D. Aug. 27, 1925. Secret signalling systems; thermionic modulating systems.-In a secret signalling system of the kind in which a sequence of wave-lengths is used at the transmitter, and the receiver is responsive to all the wave-lengths used, the distributor switch by which the wave - length changes are effected is arranged to start transmission on one wave-length before the transmission on the preceding wave-length is cut off. The distributor is arranged in the grid circuit of the transmitting valves. Fig. 2 shows a transmitter employing two separate aerials 28, 128 energized by separate oscillators 31, 131 of different frequency. The plate supply circuit for the oscillator 31 includes a high-frequency choke 36 and a low-frequency choke. 39, the latter being included in the plate circuit of a modulating vale 41. The transmitting microphone 49 is coupled to the grid circuit of an amplifier 43, which has a choke 48 and resistance 79 in its plate circuit, and is coupled through a condenser 44 and resistance 45 to the grid of the modulator 41. Milliammeters 38, 40, 42, 47 are connected in the circuits. The oscillator 131 is similarly controlled by a modulator 141 and speech amplifier 143, and a rotary distributor 52 connects the microphone circuit to the amplifiers 43, 143 in turn. Fig. 3 shows the distributor, comprising three insulated arms 54 - - 56 rotated by a worm 59 and worm-wheel 58. Each arm extends in both directions from the centre, the shorter arms making contact with three concentric rings 80, .and the longer arms with intermittent contacts 60 arranged in groups of three. As the distribu. tor arm rotates, the emitted wave-length is varied in regular or irregular sequence, the contacts being so arranged that transmission on one wavelength overlaps that on the succeeding wavelength. The receiving station comprises a number of aerials or aerial branches corresponding to the number of wavelengths to be received. As shown in Fig. 1, each branch is coupled to a regenerative detector valve 19, 21, with its plate circuit tuned to the corresponding frequency. The low-frequency rectifier currents in the transformers 22, 23 are applied jointly to the speech amplifiers 24, 26. Between the aerial 10 and the receiving circuits an atmospheric eliminating device 11 is interposed, of the kind described in Specification 264,251. Specification 235,275 also is referred to.