GB1223386A - Improvements in variable inductors - Google Patents

Abstract

1,223,386. Inductors. G. & E. BRADLEY Ltd. 18 March, 1969, No. 14235/69. Heading H1T. A variable inductor comprises two interfitting, coaxial coils 11, 12 which are relatively movable along their common axis, each coil having a tapping point and end connections which may be connected to those of the other coil in selected combinations to provide a range of inductance including at least one continuous range of at least one and a half to one. The coil 11 is wound on an insulating cylindrical former 13, which may be of vinyl resin, mounted between support boards 23, 24 which slide along a pair of brass rods 25. The coil 11 is driven between end stops 27, 28 by means of a rack 29, pinion 30, gearing 31, 32 and a knob. The coil 12 is held stationary between supports 33, 34 by rods 37, 38 fastened to end plates 35, 36. The coils are wound with a double layer of Silk-covered Litz wire with the odd-numbered turns (with the exception of the second) next is the former and the even-numbered turns outermost (Fig. 5, not shown), thus reducing self-capacitance. The ends and tappings of the coils are soldered to terminals on the insulating support members. The coils may be connected together in series to provide either positive mutual inductance (Fig. 1, not shown) to give a continuous range of 1¢ to 1, or negative mutual inductance (Fig. 2, not shown) giving a continuous range of more than 4 to 1. Alternatively, one half of each coil may be connected in series to provide negative mutual inductance over a continuous range of 2¢ to 1 (Fig. 3, not shown).