GB849490A - Improvements in or relating to coupling devices for coupling a coaxial transmission line to an electrical device - Google Patents

Abstract

849,490. Impedance matching. GENERAL ELECTRIC CO. Ltd. Dec. 23, 1958 [Sept. 24, 1957], No. 30007/57. Class 40(8). [Also in Group XL(c)] Coupling between a coaxial transmission line and an electrical device which may, for example be a second coaxial line, is varied by movement of a member of insulating material which bears against a probe connected to the end of the inner conductor of the line and lies in a space in the electrical device. The invention is described in connection with a valve amplifier in which one coaxial line forms the output connection and another length at coaxial line forms the anode circuit. The amplifier comprises a triode valve 1 the grid-cathode circuit of which is formed by a non-resonant length of ridged waveguide 2 formed by a recessed lower member 4 and an upper member 5 secured together by screws 6. A metal part 8 connected to the grid electrode of the valve is screwed into the member 5 to provide for grounded-grid operation, a metal part 9 connected to the cathode being spaced from the member 4 by an insulating sleeve 10. An input coaxial line 11: has a probe 12 projecting into the waveguide 2 opposite an adjustable screw 15 which in conjunction with a further adjustable screw 18 enables the coupling to be varied and matching achieved over a range of frequencies in the region of 200 mc/s./sec. The anode circuit is formed by a resonant quarter-wave section of coaxial line 3 loaded by a metal ring 21. Connection to the anode is effected through a rod 24 and a metal member 27 insulated from a metal member 26 by a layer of mica 25 and provided with fingers 30 engaging an anode disc 28. Metal fingers 23 extending from the rod 24 engage an anode cap 22 for cooling purposes. The outer conductor 32 (Fig. 2) of an output coaxial line 31 is integral with or connected to the member 5, and the inner conductor 33 carries a probe 34 of resilient material such as phosphor bronze or beryllium copper projecting into the resonant line 3. Coupling is adjustable by rotating a screw 35 of insulating material such as polytetrafluorethylene which bears against the probe 34, and tuning is effected by metal screws 36 and 37. The coaxial lines 11 and 31 may be terminated by coaxial sockets.