Permeability tuner

959,438. Inductors; magnetic compositions. PLESSEY CO. Ltd. Jan. 26, 1961 [Jan. 28, 1960], No. 3068/60. Headings H1H and HIT. A variable inductor for tunable circuits at high frequencies, e.g. television frequencies, comprises a coil 3 (Fig. 1), wound on a ferro- or ferri-magnetic core disc 2 situated in a magnetic field produced by two barium ferrite magnets 1 which are rotatable as shown by the arrows by means of a support 4 so as to vary the angle # between the coil axis and the saturating magnetic field which traverses the core 2. The effective permeability of the core in relation to the coil is stated to be 1+A Sin2# where A is a constant. By selectively switching to vary the effective number of coil turns continuous tuning over a wide frequency band is possible. The magnets may be stationary and the coil and disc core may be rotated. The disc core may be horizontal or turned angularly with respect to the plane of rotation of the magnets. The composition of ferrites suitable for the core are specified including Zn, Ni, Mg, Mn and Ba.