GB493574A - Improvements in or relating to radio direction finding - Google Patents

Abstract

493,574. Directive wireless signalling. JAEGER - AVIATION. July 28, 1937, No. 20941. Convention date, July 29, 1936. [Class 40(v)] The currents in angularly displaced directional receiving aerials are separately modulated at the same low frequency by variation of the coupling between the loops and the receiving circuit at phases corresponding to the angular positions of the aerials, the receiver comprising a phasemeter which indicates the direction of incoming signals. In one embodiment, Fig. 3, two mutually perpendicular loop aerials 1, 2 feed a common transformer TR through couplings S1, S2 and S<1>1, S<1>2 respectively which are provided with magnetic cores N the permeability of which is varied at a low frequency by electromagnets F, E respectively, the coils S3 and S<1>3 of which are supplied with currents having a phase difference of 90‹. The phase of the resultant low frequency currents in the transformer TR is indicated by the receiver R and is a measure of the angle of incidence of the incoming wave energizing the aerials 1, 2. In a modification, Fig. 2 (not shown), the two couplings are associated with a common' circular magnetic core, means being provided to produce therein a rotating field. In systems in which the aerial and secondary circuits are tuned, in order to avoid detuning due to the variation of permeability of the coupling means, each coupling, e.g. between an aerial circuit Lo, Co, Fig. 5, and a secondary circuit L4, C4, comprises a pair of inductances L1, L<11>1, coupled respectively to a further pair L2, L<11>2, the permeability of the cores N, N<11> being varied with a phase difference of 180‹ by magnetizing currents in the coils S3, S<11>3, which are supplied from a common source A, B. The couplings may be matched by adjustable steady magnetizing currents from a source D. In a further embodiment, Fig. 6, the currents in the aerials 1, 2 are modulated by low frequency currents which are 90‹ out of phase, by the inclusion in their circuits of transformers T1, T2 respectively supplied with the modulating currents, and rectifiers d1, d2 respectively. The aerials 1, 2, Fig. 7, of another embodiment are coupled to circuits S2, S<1>2, respectively, which are variably damped by the shunt connected valves V1, V<1>1 to the grids of which are applied the out-ofphase modulating potentials. The modulation may alternatively be produced by variation of the capacity of condensers with a dielectric the ionization of which is caused to vary, Fig. 8 (not shown). These condensers comprise tubes of rarefied gas containing electrodes and controlled by external solenoids carrying high frequency currents of variable amplitude. The phasemeter of the receiver R is preferably constituted by a cathode-ray tube.