GB504293A - Improvements in and relating to radio direction or position finding - Google Patents

Abstract

504,293. Directive wireless systems. THOMAS, H. A. Oct. 22, 1937, No. 28921. [Class 40 (v)] To ascertain both the direction and elevation of an aeroplane in flight, or of a meteorological balloon, two vertical aerials, such as 1, 1a of an Adcock pair, are spaced apart by more than the work ing wavelength, and are continuously rotated on bearings 9, 10. The aerial voltage is fed to a common receiver 5 through transmis. sion lines 2, 2a of equal length, and the critical minima readings are recorded by a relay and stylus 15 on a synchronously-rotated scale 14. The aerial voltages are either added or subtracted, according to the position of a reversing switch 3. The arrangement gives several minima, both in azimuth and elevation, and the relative angular positions of these are used to determine the elevation of the craft. For a four-metre wave, the aerial spacing is 20 feet, and the whole structure can be mounted around one central shaft, though for longer waves up to 10 metres a turntable is used. The speed of rotation is 30 revolutions per minute or less. In a typical case, six minima are obtained : two in azimuth, when the plane of the aerials is normal to that containing the incident wave ; and four in elevation, when the projection of the aerial-spacing along the direction of the wave is equal to one wavelength. An aerial spacing of 1¢ wavelengths gives the best allround results, because. although the accuracy in elevation is somewhat less than that given by a wavelength spacing, the minima are sharper, and the range of elevation is increased Voltage subtraction is used for angles of elevation up to 40‹, and voltage addition beyond that angle up to 70‹. A typical record taken on a flat-paper scale by a spirally-moving marker is shown in Fig. 8 (Prov.). It is assumed that the azimuth angle is 243‹ and the elevation 35‹. The numbered ticks represent timing marks. The cluster of ticks between 242 and 260‹, and between 62 and 85‹ represents azimuth bearings, with voltage subtraction, from time 1 ... 4, the corresponding elevation ticks lying between 298 and 332‹; 8 to 12‹ ; 118 to 152‹ ; and 188 to 192‹. The reversing switch is operated, to add the aerial voltages, for the higher angles of elevation shown. The aerial system should be sited over an earth of homogeneous conductivity, preferably above a large screen. The Provisional Specification also includes graphs showing the variation of signal intensity with angular rotation as given by voltage addition and subtraction respectively; graphs indicating the accuracy of elevational readings and the effect of frequency changes upon them ; and a detailed description of the theory underlying the invention.