GB474972A - Improvements in radio compasses and direction finders - Google Patents

Abstract

474,972. Directive wireless signalling. KRUESI, G. G. Feb. 7, 1936, No. 3767. Convention date, Feb. 8, 1935. [Class 40 (v)] Relates to radio compasses of the type described in British Specification 452,651* and U.S.A. Specification 1,868,945, in which the pick-up on a directional and non-directional aerial is combined with a locally-produced oscillation, through a balanced modulator to produce a cardioid field-curve, which is then periodically reversed in polarity so as to indicate the desired direction. According to the invention, the inductance-capacity ratio of the two branch circuits of the modulator is first made constant substantially throughout the working range of frequencies, and the necessary balancing of the two circuits is then effected by varying only the inductive coupling between them. As shown in Fig. 1, the grids of the balanced modulator B are coupled in phase to a non-directive aerial A, and the plate circuits are coupled to the input 18 of the receiver D. The pick-up from the directive aerial C is simultaneously fed to the receiver through a transmission line 24 coupled to a mixing transformer 26 comprising three primary coils 28, 30 and 32, and a secondary coil 34 arranged as shown in Fig. 2. The plate coils 28, 30 and the frame aerial coil 32 are arranged substantially as described in Specification 452,651*, but each coil is mounted upon a former slidable upon a support 36 and the secondary coil 34 is mounted on an inner slidable former 40. An electrostatic shield 42 separates the former 40 and support 36. The desired balance to produce a symmetrical field pattern is secured by moving the frame aerial coil 32 towards one or other of the plate coils 28, 30. In addition, the plate coils may be moved relatively to each other. Alternatively, the frame aerial coil 34 may be adjusted alone, relatively to the other coils. The moving coil 44, Fig. 1, of the phase-meter indicator E is connected to the output of the receiver D, whilst the field-coil 46 is fed from tappings on the secondary winding 56 of the low-frequency local oscillator B1 feeding the balanced modulator. A wave-change switch 82 for the frame aerial is ganged to a corresponding switch 80 for the mixing transformer. In a modified arrangement in which the directional aerial is connected in push-pull to a balanced modulator, and the non-directional aerial is coupled to the output, so that the carrier-wave is present in the branch circuits of the modulator, the coupling coils between the modulator and the detector are wound in opposition and are adjustable so as to prevent the transfer of the carrier and undesired sideband frequencies, owing, for instance, to the different amplification effects of the valves in circuit. The Specification as open to inspection under Sect. 91 also comprises the subject-matter contained in Specification 475,090, some of which, however, does not appear in the Specification as accepted.