Patent GB-594534-A (GB)
Title: Improvements in radio position finding
IPC: G01S7/10
Filed: 1944-08-18
Abstract: 594,534. Radiolocation; valve generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 18, 1944, No. 15858. Convention date, Nov. 14, 1942. [Class 40 (v)] In an airborne pulse radar system in which the position of the aircraft with respect to responder beacons of known location is indicated on a multi-beam cathode-ray tube by the intersection of brilliant portions of the multiple traces, each cathode-ray is scanned spirally in synchronism with the pulse transmission, the origins of the traces are adjusted to represent the positions of the beacons and arcuate portions of the traces are brightened by the received pulses either by intensity modulation or by stopping the radial component of the spiral scan. In Fig. 1, the pulse generator 7 initiates the transmission of pulses from the transmitter 1 to the responders 39 and 41, and the reradiated pulses which may have different carrier frequencies are picked up by the receivers 3 and 5 and applied to intensity modulate the grids 31 and 33 of the double beam cathode-ray tube 21. Each cathode-ray beam is scanned spirally by modulating at 13 a sinusoidal oscillation from the generator 11 with a saw-tooth voltage from the generator 9 which is synchronized by the pulse generator 7, deriving phase-quadrature components by the phase-shift circuit 23 and applying these components to the two sets of X and Y plates of the tube. The origins of the two traces are initially set by means of the shift control circuits 17, 19, 25 and 27 to points 43 and 45 corresponding to the known location of the responders, so that one of the intersections 51, 53 of the intensified arcuate portions of trace 47, 49 gives the position of the mobile system. The ambiguity may be removed by using a third responder and a three-gun tube. In a modification, Fig. 2 (not shown), the cathode-ray beam is not intensity modulated, but the spiral scan is initiated by the received pulse and swept inwards from a maximum radius until the next transmitted pulse when the radius is held constant until the succeeding received pulse repeats the cycle. The repented scanning at a constant radius corresponding to the range of the responder produces an intensified trace similar to that obtained in the system of Fig. 1. The scanning wave is produced by feeding a sinusoidal oscillation to a modulator biassed by a voltage wave initiated by a received pulse which increases linearly until the next transmission occurs when the amplitude remains constant ; the modulator is biassed so that its output is inversely proportional to the amplitude of this waveform. In Fig. 4, the biassing voltage for the modulator 13 is taken from across the condenser 115 which is discharged when a positive pulse from the receiver triggers the gas-discharge valve 117. The positive pulse developed across the cathode resistance 119 triggers the valve 109 of the direct coupled multivibrator pair 109, 111 making valve 109 conductive and cutting off valve 111. The condenser 115 then charges linearly through the diode 114 and resistance 113 until a positive trigger pulse from the transmitter' pulse generator is applied to the grid of valve 111 to make it conductive and reduce its anode voltage and so stop charging condenser 115, the voltage across which remains constant until it is discharged by the next receiver pulse.