GB593568A - Improvements in or relating to radio direction finders - Google Patents

Abstract

593,568. Radio direction-finding; valve circuits. O'BRIEN, W. J., and DECCA RADIO & TELEVISION, Ltd. May 13, 1943, No. 7670. [Class 40 (v)] In a direction-finding system in which the pickups of fixed angularlydisposed directive aerials are modulated at low frequencies which are displaced in phase by an amount corresponding to the angular displacement of the aerials, the direction of received signals is indicated on a stroboscopic indicator driven in synchronism with the low-frequency source and operated by pulses derived from the modulated currents. In the arrangement shown in Fig. 1, the pick-ups from the aerials 40, 41 are applied respectively in parallel to the grids of push-pull modulators 1, 2 and 6, 7, the screens of which are fed with phase-displaced low-frequency currents from source 44 via transformer 9 and circuit 8, 10 so designed that the potentials applied to the valves 1, 2 are in phase quadrature with those applied to valves 6, 7. The outputs from the valves 1, 2 and 6, 7 are combined in the circuit 3, amplified in the superheterodyne receiver 12 and rectified at 13, giving rise to a current E1, Fig. 3, whose phase depends upon the direction of the received waves and having a frequency equal to that of the L.F. supply. In order to derive sharp pulses for controlling the stroboscopic indicator, the output E1 from the detector 13 is led to amplifier 15 and tuned transformer 17, giving the waveform E2 having a frequency double that of the L.F. supply. This is rectified at 18 to give waveform E3 which is passed through transformer 20 giving waveform E4, which in turn is fed through a biassed valve 21 to give waveform I and through transformer 14 to give sharp surges E5, which are applied to the lower grid of the gas-discharge tube 48 illuminating. the stroboscopic indicator 50 driven from the source 44. Two surges E5 are produced in each cycle of the low-frequency current, and in order to indicate sense, as well as direction, alternate surges are eliminated by utilizing the output of a non-directional aerial 22. This is led to one grid of a dual-control valve 26, another grid of which is fed with part of the combined output from the modulators 1, 2 and 6, 7. The output of valve 26 passes through amplifier 27, rectifier 28, amplifier 29 and tuned transformer 30 to give a waveform E6, Fig. 5, of the modulating frequency. This is passed through an over-biassed valve 31 to give a waveform Eg2, Fig. 5, which is applied to the upper grid of the discharge tube 48. This tube flashes only when it receives both the potential Eg2 on one grid and Eg1 (#E5 of Fig. 2) on the other, thereby preventing alternate pulses E5 from affecting the stroboscope. A test oscillator 51 and various switches 32, 35, 36, &c. are provided for synchronizing and balancing the system.