Patent GB-502172-A (GB)
Title: Improvements in or relating to variable-inductance tuning devices for radio apparatus
IPC: H01F21/00
Filed: 1937-08-09
Abstract: 502,172. Variable resistances ; combination of resistances ; resistance. casings ; supplying current to moving conductors. MALLORY & CO., Inc., P. R. Aug. 9, 1937, Nos. 21913 and 21914. Convention dates, Aug. 8, 1936 and Aug. 11, 1936. [Classes 37 and 38 (i)] [Also in Group XXXV] A variable inductance comprises a coil formed of a bare conductor 210, Fig. 2, which is supported for rotation about the coil axis and a contactor 252 which travels along the conductor of the coil whenever the coil is rotated to vary the inductance. The contactor comprises a frame provided with non-resilient spacing means engaging the coil conductor or the periphery of-the form supporting this conductor for spacing the frame at a constant distance from the adjacent portion of the coil conductor during the rotation of the coil, a resilient contact member carried by the frame and. engaging the adjacent portion of the coil conductor, and spring means for urging the frame towards the coil whereby any eccentricities of the coil conductor or its form with respect to its axis of rotation are absorbed by the said spring means and the engaging pressure of the resilient contact member upon the coil conductor is thereby maintained constant. The shaft 212 is of hard copper, mounted in ball bearings, and insulated at 212a to prevent electrical noise, the inner end of the wire is connected at 247 to a three-legged slip-ring 239 and so through a bifurcated contact spring 275 to a fixed end inductance 280, which has a low Q ratio and can be adjusted in magnitude by means of a screw 284 ; the outer end of the wire is grounded to the casing through the shaft 212. The wire 210, which may be of hard copper plated with silver, lies in a V-shaped groove whose sides are at right-angles. The right-hand portion of the coil has a wider pitch than the left-hand portion, so that the adjustment becomes finer when the inductance in circuit is small. The left-hand portion of the coil is short-circuited by the phosphor-bronze spring contact 252 which is bifurcated and hooked at its end like a nib. Each half of the nib exerts a pressure of 15 grams. The contact is mounted on a carriage 250, Fig. 4, having insulating trolley wheels 253 which engage the wire 210 or the surface of the form so as to move the carriage parallel to the axis of the coil. The contact 252 communicates with a cross-wise phosphorbronze contact spring 251 which slides on the grounded bar 249 and has contact ears 255, Fig. 2. In a modification, two such inductance units are mounted in a single partitioned casing ; and one of the fixed end inductances is mounted coaxially inside the corresponding variable inductance. In a further modification, two guide bars like 249 are used, with the object of eliminating any turning moment that might act upon the contact carriage 257. In a further modification, designed to prevent coupling between the coils used for different ranges of frequency, each tuner comprises a pair of parallel and unequal coils, Fig. 12, geared by sprung split gears to rotate in opposite directions and connected by travelling contactors on a common carriage 433 to a common bar 432. The large coil 416 and small coil 420 are used for different ranges of frequency. Two such units in the same casing are shown, one being for tuning the antenna circuit and the other for tuning the oscillator. In a further modification, Fig. 16, two contactors 480, 481, spaced apart, are provided for the same high-frequency coil 420, in order that its unused part may not interfere, for ultra-high frequencies, with the part that is in circuit. For ultra-high frequencies both contactors are in contact with the wire and act to raise the natural frequency of that part of the coil which is out of circuit. For lower frequencies, however, one contactor 481 is raised off the wire 420 by turning an eccentric rod 483 which acts upon a post 482. In a further modification, the coils 416, 420 have uneqnal pitches and the latter is geared down from the former. In a further modification, the coil is tapped by means of a wire welded to or wound with the wire and brought through a hole in the form to a ring on the axis of the coil ; the tapping may be grounded for ultra-high frequencies in order to eliminate the effect of the out-of-circuit part of the. inductance. A trolley wheel for guiding the contactor carriage 250 comprises a knurled metal portion 332, Fig. 11, turned down to form trunnions at 333, and having insulating material 331 moulded or pressed upon it. A groove for embracing the spiral wire is cut in the periphery. Specifications 491,222, [Group XXXV], and 502,251 are referred to.