GB457704A - Improvements in and relating to gaseous electric discharge tubes applicable as high frequency oscillators - Google Patents

Abstract

457,704. Discharge apparatus ; generating circuits &c. BRITISH THOMSONHOUSTON CO., Ltd., Crown House, Aldwych, London. March 28, 1935, No. 9698. Convention date, March 28, 1934. [Classes 39 (i) and 40 (v)] High-frequency apparatus such as generators of oscillations of frequency of 300,000 kilocycles or more include an electric gas or vapour discharge device with a grid separating its envelope into two compartments which contain respectively the anode and cathode and which intercommunicate only through the grid openings, the device operating with anode and cathode plasmas separated by a continuous positive ion sheath on the grid. Variations of potential on the grid control the flow of electrons between the plasmas whilst leaving the degree of ionization constant. The device is filled with gas or vapour at a pressure sufficient to allow the formation of a plasma but insufficient to impede seriously the movement of electrons, mercury vapour at À1-2 microns or helium or neon at 1 mm. or other rare gas such as argon may be used. The grid 13, Fig. 1, of uniform mesh extends across the envelope 10 between the anode 11 and cathode 12 and is maintained negative. Coils 18, 23 in the anode and grid circuits are coupled together to generate oscillations at a frequency controlled by the tuning of the circuit by a condenser 24. The ionic sheath moves back and forth as the grid voltage oscillates and provides an on-and-off control allowing electrons to pass for a small portion of each cycle, the intensity of the electron flow when thus allowed being mainly limited by the cathode emission. Oscillations are efficiently generated with the duration of each cycle much less than the deionization time of the device. The auxiliary anode 11<1> to maintain the cathode plasma may be omitted. The supporting edge of the grid may be protected from sputtering by a glass shield. In modifications, the grid is a cylinder closed at one end and surrounding the cathode or anode. In another oscillator which can also be modified for use with input and output circuits, metal bands 27, 28, Fig. 4, partially or wholly surrounding the envelope form capacity couplings with the cathode and anode plasmas. The circuits between the parts 13, 27 and 27, 28 are coupled together, for example, by an inductor 37 tuned by a condenser 41. The potential of the grid 13 is positive before the plasmas are formed and drops when ionization starts, a resistance being connected for this purpose in the bias circuit of the grid or a positive starting voltage being supplied by a switch 44. The band 28 may be about the anode or as shown near the grid and a further band 26 about the anode plasma may be connected in the latter case to the band 28 through a circuit 39, 40 tuned to a harmonic of the frequency of the circuit 37, 41 to feed very high frequency oscillations to an output circuit 42 connected to a dipole antenna.