GB555825A - Improvements in high frequency apparatus embodying electron discharge tubes - Google Patents

Abstract

555,825. Discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. April 25, 1941, No. 5344. Convention date, April 25, 1940. [Classes 39 (i) and 40 (v)] A transmission line 23, 24, Fig. 1, is partly formed by the electrodes 30, 32 of a discharge tube 29. The magnetic field of coil 39 causes electrons emitted from cathode 32 to rotate within the anode 30. It is shown that this rotating but non-oscillating space charge reduces the effective dielectric constant between the electrodes and thus alters the wave-propagating characteristics of of this section of the line ; by varying the current through coil 39 or the voltage of anode 30 the wave-propagating characteristics of the line may be altered. The line may be a short length terminated by a magnetron 10 and its resonant frequency may be altered by tube 29, the resultant frequency being taken off by loop 45 and line 46, 47. If the effective dielectric constant is reduced to zero, the effect of a short-circuiting piston is simulated. Alternatively, the tube may be placed between a source of oscillations, such as a generator or antenna, and a line to enable the coupling between them to be adjusted, or varied for amplitude modulation. The electrodes may be two wires or plates forming part of a Lecher line. The rotating space charge may be formed by a helically moving beam of electrons. In this case the outer cylinder 94, Fig. 5, is provided with a recess at one end within which is housed the cathode 97 and a modulating ring 107 which are maintained at negative potential relative to the earthed electrode 94 so as to direct a beam through aperture 103. A plate electrode, not shown, gives the beam an axial component, so that it travels in a helical path around an extension of the central line conductor ; or the beam may move round one wire of a Lecher line. In a modification, the resonant wave-length of a hollow resonator 153, Fig. 10, is varied by varying the capacity of a tube 137 placed in an extension 136 of the resonator. If the resonator is coupled to a source of oscillations, it enables the frequency generated to be modulated ; or the coupling between an ingoing line 150 and an outgoing line 151 and hence the amplitude of the transmitted frequency may be modulated. Specification 465,650 is referred to.