Patent GB-581807-A (GB)
Title: Improvements in radio direction finding apparatus
IPC: G01S19/48
Filed: 1942-03-03
Abstract: 581,807. Wireless direction - finding systems. STANDARD TELEPHONES & CABLES, Ltd. March 3, 1942, No. 2809. Convention date, March 5, 1941. [Class 40 (v)] In a wireless direction-finding system employing a pair of antenna systems with mutuallyperpendicular directional characteristics and a cathode-ray tube indicator, the beam of which is given a circular movement by a rotary field provided by oscillations in phase quadrature supplied to the deflecting systems from a lowfrequency local oscillator and phase-splitter, each of these oscillations together with the waves received by one of the directional aerials is fed to the corresponding one of a pair of push-pull amplifiers, the combined output from which is rectified to obtain the low-frequency wave resulting from the modulation by the local oscillations of the received signals, which low-frequency wave is applied directly to the oscillograph to indicate the maxima or minima occurring during the cycle of rotation of the beam. The system shown comprises a directional antenna system formed by crossed pairs of dipoles 1, 2 which are coupled respectively to circuits 3, 5 connected in push-pull relation to valves 4, 6. A phase-splitting circuit 12 connected to a source 10 of alternating current supplies, through amplifiers 13, 14, currents in phase quadrature to circuits 15, 16 coupled respectively to the grids of the valves 4, 5. This results in a modulation of the energy in the output line 7 connected to the valve anodes corresponding to that produced by rotation of the directional reception patterns. The indicator comprises a cathode-ray tube 20, the beam of which is rotated synchronously with the reception pattern by two pairs of deflecting plates connected to the circuits 15, 16. The antenna output circuit 7 is coupled through a valve 30 to a receiver-detector circuit 40 and a coupling circuit 41, in which the signals may be combined with a fixed intermediate frequency, the output from 41 being applied through a detector valve 42 to points on a potential divider 43 which supplies the operating potentials to the cathode-ray tube 20. This results in variation of the potential of the accelerating anode 24 of the tube, which produces velocity modulation of the beam and corresponding variations in the radial deflection, resulting in a pattern on the screen indicating the direction of the received signals. Sense ambiguity may be avoided by the use of a sensing antenna 26. The production of a continuous trace on the cathode-ray tube screen may be avoided by a rectifier valve 45 coupled to the output of the circuit 41, which through an amplifier 46 supplies energy to a resistance unit 47 in the biassing circuit of a grid 22 in the tube. By a switch 49 this output may be caused to increase or decrease the negative potential on the grid 22, so that the positions of maximum signal reception are indicated either by bright or dark portions of the trace. Modified circuits are illustrated for controlling the grid 22, for replacing the circuit shown between the coupling circuit 41 and the potentiometer, and for controlling the accelerating anode 24 by a relaxation generator to cause the beam to trace a spiral pattern, the grid 22 being normally biassed so that only the parts of this pattern lying on the radial line corresponding to peak signals are visible.