GB1007791A - Improvements in or relating to ferromagnetic rod aerials - Google Patents

Abstract

1,007,791. Frequency changing arrangements; aerials; controlled non-linear inductors. PLESSEY CO. Ltd. Feb. 20, 1962 [Nov. 21, 1960], No. 39927/60. Headings H3B, H3F and H4A. A ferrite rod aerial is adapted to act as a frequency changer. It is formed by two parts 1, 2, Figs. 1-4, connected by four identical bridge portions 3-6, whose identical magnetic reluctance is lower than that of the end parts 1, 2. The bridge portions 3-6 carry a number of windings, including serially-connected output windings 7-10, Fig. 2, on individual limbs, the output windings on adjacent limbs being wound in opposite directions. Each bridge portion also carries one of four serially-connected local oscillation windings 11-14, Fig. 4; the assembly also includes a pair of seriallyconnected biasing windings 15, 16, Fig. 3, to which a D.C. biasing current is applied, each of which embraces an adjacent pair of bridge portions. The last windings may alternatively be replaced by a pair of permanent magnets. The amplitude of local oscillations and current applied to the biasing windings are such, and the windings so arranged, that on each halfcycle of local oscillations two of the bridge members are swept to a point at which non- linearity of the magnetic characteristics occurs; in the one member the signal flux assists the other two fluxes and saturation will occur, so that the signal flux will divide unequally between these two members, flowing through the other member, in which it carries the material away from saturation. Sum and difference frequencies thereby appear in the output windings 7-10; these windings are, however, so arranged that the local oscillations do not appear in the output. The difference frequency is used, the output circuit being resonated at this frequency by means of series inductance 22, Fig. 2, and adjustable capacitor 23; the difference frequency is made several times the input frequency, a power gain being thereby obtained from the device. As a protection against the image frequency winding 17, 18 are located on the parts 1, 2 of the aerial rod, being resonated at this frequency by means of capacitor 19 so as to reduce the effectiveness of the aerial at this frequency. In an alternative embodiment the aerial comprises two separated ferrite rods 25, 26, Fig. 6, with four octagonal ferrite plates 27-30 located in the gap between them. The plates carry local oscillator windings 34 wound at an angle of 45 degrees to the axis of the aerial, and output windings 33 wound at right-angles to this axis. Bias is provided by two permanent magnets 31, 32 with their axes parallel to the windings 34.