Patent GB-305600-A (GB)
Title: Tuning system for electric circuits carrying high frequency currents
Filed: 1927-08-06
Abstract: 305,600. Elliott, H. F. Aug. 6, 1927. Condensers.-Relates to the tuning of electrical circuits carrying high frequency currents, such as radio circuits, and to means whereby a number of circuits can be simultaneously tuned as by means of condensers and inductances, and at the same time compensating for minute variations &c. in the parts constituting the tuning means. The invention comprises the use of an adjustable cam for controlling the tuning, and means for adjusting the cam surface at a plurality of points, the surface beng free to assume a substantially smooth and continuous curvature between the adjusting points. The invention is described with reference to a receiving set of known type, employing five variable con densers to be simultaneously tuned, the parts of the set being housed in a box containing a support 59 which is flanged at 112, 113 to receive certain parts and carries a number of sectorshaped cans 60 for other parts (Fig. 3). Each condenser comprises a pair of sets of movable plates 61, 62 each spring-biased to the all-out position and mounted on a sleeve 63, 64 which is rotatable about a stem 65, 66, respectively. Each sleeve carries an arm as 71, 72 connected by a link as 73, 74 to an actuator 75 which is rotated clockwise (Fig. 3) to bring the plates into mesh, the particular arrangements shown giving a straight-line frequency relation between the movement of the actuator and that of the plates. The actuator 75 is secured on the hub 83 of a larger wheel 87 which is rotated by links 89, 90 connected to a lever 99 which is provided with a stop 100. The means for ensuring that the condensers remain in step throughout the range comprise means for rotating the stem 65 and hence the insulator 67 so that the set 61<1> is moved with respect to its co-operating set, the stem carrying a lever 105 carrying a roller 106 spring-biassed into engagement with a cam surface on the wheel 87. The cam comprises a continuous flexible strip 108 the ends of which are connected by a spring 110, and adjustment of the cam surface is effected by a number of sets of screws 111. By proper adjustment of those screws 111 which are immediately under the rollers 106 at any point of the range of the wheel 87, the tuned circuits can be brought into resonance, the screws being close enough together to ensure complete accuracy over the entire range. The condensers are adjusted with each screw in tura under the follower so that their associated circuits resonate to a suitable frequency. A terminal block 116 on an extension of support 59 enables a connection to be made to external elements. The dial plate 119 has an arcuate aperture through which can be read a scale of wavelengths or kilocycles, mounted on a plate 124, by means of a pointer 127 carried by the arm 99. Pivoted at 135 on a boss on the arm 99 is a shaft 133 on which is journaled a sleeve carrying a knob 132 and having teeth 137 engaging a. rack on the plate 119. For coarse adjustment the knob is pushed away from the rack against the action of a spring 141 and then moved to rotate the arm 99. On release the knob is urged to reengage the rack and can then be rotated for fine adjustment. Instead of a rack, a friction drive may be used and the pivot 135 dispensed with. In a modification. the support 59 and cans 60 are reversed and the dial plate is at the side of the box. In another form, only one set of plates of each condenser is movable by the common operating means, the other set of each being movable by the cam.