GB652758A - Improvements in or relating to tuning devices for electron-discharge tubes - Google Patents

Abstract

652,758. Velocity-modulated tubes. SPERRY CORPORATION. March 19, 1948, No. 8239. Convention date, April 3, 1947. [Class 39 (i)] [Also in Group XL (b)] In a tuning device for an electron discharge tube having one or more substantially cylindrical resonant-space resonators, one or all of which are adapted to be tuned by a plunger mounted for movement along its longitudinal axis in the interior of the resonator, the plunger comprises a rod of dielectric material provided with a conducting sleeve around it at the region where the rod is located within the resonator. A velocity-modulation tube, Fig. 1, comprises three cavity resonators 3, 4 and 5. The walls 11, 12 and 13 of the tube casing are provided with axially aligned bores or guides 14, 15 and 16 located eccentrically with respect to the drift spaces 9 and 10 and within which slides a dielectric rod 17 for example of quartz or glass. The bores 14, 15 and 16 and the rod 17 are so proportioned as to act as a wave-guide having a critical cut-off frequency above the operating frequencies of the resonators 3, 4 and 5, thus preventing undesired feed-back. The rod 17 is provided with sleeves or slugs 18, 19 and 20 of any conducting material such as silver or electro-deposited copper, and has a thin stem 22, Fig. 3, for example of tungsten, which projects into a sleeve 23 to which it is secured at its outer-end portion 24. The sleeve 23 is fixed at its inner end to a cylindrical cupshaped member 25 having an outer flange portion 26 sealed to one end of a bellows 27, the other end of which bellows is sealed to a cylindrical sleeve member 28. A cover 29 is attached to the sleeve 28 and carries a bushing 30 within which is rotatably mounted a hollow shaft 31, the inner end 34 of which is threaded to co-operate with a nut 35 fixed within the cup-shaped member 25. The outer end of the shaft 31 has a knob 32 secured thereon by a set-screw 33, so that turning the knob has the effect of moving the rod 17 and altering the tuning of the resonators. The sleeve 23 is made of a material such as copper having a co-efficient of expansion different from that of the stem 22, thus compensating for expansion and contraction of the resonator walls due to operating temperature changes and so preventing frequency drift. Gang tuning of resonators operating at different frequencies may be effected in a similar way, the diameters of the bores, rod and sleeves being varied to suit the various frequencies involved. The invention may be applied to reflex type tubes and the tuning rod may project chordwise or tangentially into the resonator.