Patent GB-176491-A (GB)
Title: Improvements in and relating to the generation of continuous waves for wireless telegraphy and telephony by thermionic valves supplied direct from a low-frequency polyphase circuit
IPC: H03B5/10
Filed: 1920-12-06
Abstract: 176,491. Preston, L. G., Fortesque, C. L., Airey, H. Morris-, and Shearing, G. Dec. 6, 1920. Thermionic oscillation generators; drying-out aerials; keying systems and apparatus.-A number of thermionic valves are fed from a lowfrequency polyphase supply so as to generate continuous oscillations for transmission, as described in Specification 163,725, the arrangement being such that whilst any one valve is feeding the aerial, the remainder act as insulators, and thereby prevent any wasteful damping of the aerial current. The high-frequency potential variations in the aerial act at the filaments of the valve, and not at the anodes as described in the above mentioned Specification. The separate anodes of the triode valves V1 - - V6, Fig. 1, are fed from a six-phase supply A, B, C, the windings of which are earthed as shown. High-frequency coils D - - K, together with condensers S, protect the supply windings from high-frequency currents. The filaments are fed from an alternating current supply T and are adjustably connected at L to the aerial. The grids are coupled to the aerial at W. For the one-sixth period during which the anode of the valve V1 is at maximum positive potential, relatively to the earth, it will feed highfrequency pulses to the aerial, the remaining valves acting meanwhile to insulate the aerial from earth, irrespective of their grid potentials. As the next phase of the supply is applied to say valve V3, the aerial is fed from that valve exclusively, and so on. Polyphase supply of any number of cycles may be similarly utilized by a corresponding number of valves. As shown in Fig. 3, the high-frequency oscillations are fed directly to the aerial when the switches S1, S2 close the contacts n and b respectively; but when the points c and d are closed the valves feed a local circuit Q1, S coupled at R to the aerial. The local circuit may be used to dry-out the aerial when this is affected by moisture. Various methods of signalling bv grid control are described, in which either a diode or driode valve, or both, are included in the grid circuit. In Fig. 5, the grid-leak resistance P is shunted by a diode H, F, to the anode H of which a. large negative potential is applied from a battery Q through a switch X. High-frequency oscillations are fed to the aerial as long as the switch X is open, but when this is closed through an electromagnet controlled by the sending-key 1, radiation ceases. As shown in Fig. 1 (Complete), the grid control is effected by means of an alternating-current supply W1 which feed the filaments of the valves H, and G. F, and also the plate of the diode rectifier H, through a transformed W2. So long as the sending-key is open, the rectifier H1 functions to charge a condenser S1, which maintains the grid G of the triode negative and prevents the passage of high-frequency oscillations. When the sending-key is closed, the condenser S, is shortcircuited and oscillations are fed to the aerial. The different alternating supplies to the filaments and plates of the valves are maintained in proper phase-relationship. Multi-anode valve-generators. may be used in place of the triodes shown.