Patent GB-567637-A (GB)
Title: Improvements in or relating to electrical apparatus for use with high frequency oscillations
IPC: G01R27/02
Filed: 1940-12-17
Abstract: 567,637. Artificial lines. HOLMAN, H. E., and CORK, E. C. Dec. 17, 1940, No. 17793. [Class 40 (iii)] [Also in Group XXXVI] Apparatus for use with high-frequency oscillations comprises a cylindrical conductor with a conducting piston slidable within it and an external clamp which, when tightened, establishes a low-impedance contact between the piston and the inner surface of the cylindrical conductor. A cylindrical conductor 1, Fig. 2, has a conductor 2 centrally supported within it. A piston 3, shown in detail in Fig. 4, is arranged to slide on the conductor 2 within the conductor 1, and a clamp 4 embracing the conductor 1 and shown in detail in Fig. 5 is mechanically coupled so as to slide with the piston. The piston 3 is attached to a tube 12 sliding on the conductor 2 and attached to a knob 13, which is attached to rods 14 passing through a fixed block 15 and attached to the clamp 4. As shown in Fig. 4, the piston 3 has a slot into which fits a semicircular segment 16. This is temporarily fixed in position 'by a pin passed through holes 16a so that the assembly can be machined to fit the bore of the cylinder 1. The periphery of the piston adjacent to the segment 16 is then further machined away so as to allow the segment to project as shown at band c to ensure that when inward radial pressure is applied, the segment will be pressed into firm contact with the conductor 2. The clamp 4 may consist of two members each having a semicircular face of the same curvature as the external surface of the conductor 1 and arranged to apply inward radial pressure to the conductor 1, which is thereby slightly distorted. The conductor 1 may be provided with a slot parallel to its axis so as to reduce the tendency to elliptical distortion. An alternative form of piston is shown in Fig. 6 and is divided into two parts, a spigot 17 on one part fitting into a recess in the other part so as to leave a space between the two parts. Two square-section D-shaped brass springs 19 are fitted between the two parts of the piston and are bent so that their central portions press on the conductor 2 and the outer limbs slide on the inner surface of the cylinder 1, the halves of the piston being held together by screws or rivets passing through the spigot 17. The piston flanges or body may be made of insulating material. In another form, Fig. 7, a short conducting cylinder is turned to fit the bore of the cylindrical conductor 1 and has a central hole to fit the conductor 2. It is provided with a tubular extension which may be a part of the actuating tube 12. The piston is divided by a .number of radial slots extending through part of the extension in order to afford radial elasticity. For tubes of larger bore the construction shown in Fig. 8 may be employed. The piston 3 consists of a flat metal disc slotted as shown at its periphery and round the central aperture. Cover-plates 20 are provided on each side of the piston and clear both the tube bore and the central rod. The conductors 1, 2 may have rectangular or other non-circular sections. The central conductor 2 may be omitted so as to form a wave-guide comprising a cylindrical conductor having one or more conducting pistons therein. The Provisional Specification describes also the application of the apparatus for the mixing of two high-frequency oscillations, shown in Fig. 9, and as an output coupling for a high-frequency generator, shown in Fig. 10. For mixing oscillations of different frequency, as in superheterodyne reception, the side tube 6, Fig. 1, is omitted and a screened feeder 10a, 10b, Fig. 9, is led in through pistons 3a, 3b and the inner conductors 11a, 11b are arranged to effect a sliding contact on the central wire 2. The two oscillations to be mixed are fed along the screened feeders 10a, 10b, the spacing between the pistons 3a, 3b and the points of contacts between the central wire and the inner conductors 11a, 11b being chosen to avoid reflections. The position of the pistons 3a, 3b in relation to the position of the capacity 9 feeding the detector 8 is adjusted so that a high impedance is presented to the detector 8. A circuit tuned to the difference of frequency between the oscillations to be mixed.is connected to the output of the detector 8 and currents are set up in this circuit. In the apparatus shown in Fig. 10, for coupling a source of high-frequency oscillations to an output circuit, high - frequency oscillations developed in the resonant cavity 20 of a velocity-modulation electron-discharge device induce currents in a loop 21 connected between the cylinder 1 and the inner conductor 2. The piston 3 is adjusted to tune the system to resonance, as indicated by the detector 8. The side tube 6 forms the outer conductor of an output feeder, the inner conductor of which is connected to the inner conductor 1. The side tube 6 joins the cylinder 1 at a point such that the feeder is matched to the resonant system.