Patent GB-589809-A (GB)
Title: An arrangement for indicating the position of a movable subject
IPC: G01S1/02
Filed: 1944-08-31
Abstract: 589,809. Radio direction finding. HAZELTINE CORPORATION. Aug. 31, 1944, No. 16630. Convention date, Sept. 20, 1943. [Class 40 (v)] [Also in Group XXXVI] In a system for indicating on a cathode-ray tube the variations of a rotation or other movement-dependent quantity, a scale is marked electronically on the screen of the cathode-ray tube by pulses generated by phase comparison of a reference oscillation and an oscillation of the same frequency, the phase of which is contrclled by the original rotation or other movement. The radio direction finding system of Fig. 1 comprises a directive aerial 10, 11, 12 which is continuously rotated by a motor 13 and feeds the receiver 20, 21, 22 and 23 through the rotating coupling 18, 19, while a non- directional aerial 45 feeds a second receiver 48-53 which provides A.V.C. voltage for the directional receiver. A twophase generator 26,27,28 driven in synchronism with the directive aerial feeds the deflecting coils 24, 25 of the cathode-ray tube indicator 15 through radius modulators 29, 29<1> and amplifiers 30; 30<1>, the rectified signal from the directive receiver being fed to the radius modulators through contacts 97 of switch 93 which is driven through the 2 : 1 reduction gearing 69, 95, so that during alternate rotations of the directive aerial its directive pattern is traced on the long-after-glow screen of the C.R. tube 15. In order to facilitate the determination of the direction of the received signal, the line traced by the beam of the cathode-ray tube is cyclically displaced to produce overlapping patterns H, H<1>, Fig. 7, by means of a sine wave oscillator 61, which is of frequency high compared with the aerial rotation and is operative on alternate rotations due to the contacts 97<1> of switch 93 in the H.T. supply, and which feeds a coil 60 disposed about the neck of the tube. A beam control voltage supply 65 controlled by the oscillator 61 feeds a voltage to the grid of the tube through switch 94 to remove the cut-off bias when the beam displacement is a maximum. In order to produce on the screen of the C.R. tube, the scale for determining the bearing of the received signal with respect to a predetermined reference position of the rotating directional reception pattern, a series of marker signals' are generated by phase comparison between a reference oscillation and phase shifted oscillations produced by a phase shifter coupled to the rotating aerial system, the marker signals being displayed on the C.R. tube during alternate revolutions of the aerial. The phase shifter, which is driven at 24 times the speed of the aerial through gearing 69, 70, and is fed from a reference oscillator 75 of frequency high with respect to the rotation frequency, comprises stator coils 66, 67, coil 67 being coupled to the oscillator 75 through a 90 degrees phase shifter 76. The output from the secondary coil 68, which has a phase relation with respect to the output from oscillator 75 which varies continuously in accordance with the aerial position, is fed together with the reference oscillation to a pulse detector 78 which produces an output pulse corresponding to every 15 degrees of aerial rotation. The reference oscillation multiplied by three in the frequency multiplier 86 is fed together with the phase variable oscillations to a second pulse detector 79 which thus produces pulses corresponding to 5 degree rotations. The reference oscillations further multiplied by 5 in multiplier 87 are then fed together with the variable phase oscillations multiplied by 3 and 5 in multipliers 86<1>, 87<1> to the third pulse detector 80 which thus produces output pulses corresponding to 1 degree rotations. Detectors 78-80 which produce pulse outputs when the input oscillations have a predetermined phase relation, comprise, Fig. 2 (not shown), limiters producing square waves from the applied waves which are then added and differentiated so that the resultant pulses only exceed a clipping level when the input waves are phase coincident, the train of pulses produced during phase coincidence being passed to a peak rectifier and low-pass filter which produce the marker pulse. In order to produce the scale divisions on the screen of the C.R. tube during the alternate aerial rotations when the received signal is not applied to control the radial deflection system, the 5 and 15 degree pulses are fed to a modulator 90 together with high-frequency oscillations from an oscillator 91, the resultant highfrequency pulses being fed together with a D.C. bias from source 92, to control the radius modulator via switch 93. The 15 and 5 degree scale divisions thus appear as radial deflections near the periphery of the C.R. tube screen as indicated in Fig. 7, the 15 degree marks being of greater length due'to the addition of the 5 and 15 degree pulses in modulator 90. The one degree pulses from detector 80 are simultaneously fed via switch 94 to overcome the cut-off bias of the C.R. tube and thus appear as bright spots between the 5 degree marks in addition to brightening up the trace for the 5 and 15 degree marks. The gear train 69, 70 may be omitted and the secondary winding 68 driven at the aerial rotation speed in which case a. single marker signal will be derived. Vernier indications may, however, still be produced by stages of frequency multiplication. An adjustment of the orientation of the phase shifting coupling 66-68 with reference to the aerial system is desirable to permit orienting the scale divisions with known positions of the aerial. An auxiliary oscillator of the same frequency and phase as the reference oscillator 75 may be employed as the source of comparison signals for the pulse detector circuits and also the 15 and 5 degree scale divisions may be produced by causing the appropriate pulses to modulate the second anode voltage of the cathode-ray tube and thus vary the deflection sensitivity. Specifications 530,227, 537,878, 541,006 and 552,499 are referred to.