Patent GB-581920-A (GB)
Title: Improvements in or relating to methods and apparatus for determining the direction or position of sources or reflectors of radiant energy
IPC: G01S1/02
Filed: 1939-07-20
Abstract: 581,920. Radiolocation. BLUMLEIN, A. D., and WHITE. E. L. C. July 20, 1939, Nos. 21108 and 29283. [Class 40 (v)] To determine the direction and distance of a mobile or stationary transmitter (or reflector) a modulated wave is received by two pick-up devices, separated by a large multiple of the wave-length, the difference between the two rectified signals being compared with their sum to give a bearing, the indication of which is independent of the exact wave-form of the modulation. The invention is applicable to electro - magnetic and super - sonic pressure waves, and can be used to determine the altitude of an aeroplane, or the presence of submarines and icebergs. For ascertaining distance, the signals are emitted in the form of impulses, so as to allow a sufficient timeinterval between the outgoing and reflected wave. The indicating device may be a cathode ray tube or a dynamometer. As shown, modulated signals received on the widely spaced aerials 1, 2 are rectified at 3, 4, and the out-of-phase currents are fed through transmission lines 5, 6 to amplifiers 7, 8. The outputs are combined by the transformers 9, 10 so as to give sum and difference components, which are then applied to the deflecting plates of a cathode ray indicator. The " difference " component is integrated by a condenser 12 and resistance 11, so as to give it substantially the same form as tho "sum" component in the branch S. Alternatively the " sum " component may be differentiated for the same purpose. The two waves will then have the same shape and phase, but will differ in amplitude in accordance with the position of the distant transmitter. The amplitudes of the two currents are balanced by a variable attenuator 14 so as to give a straightline indication, say a 45‹ reflection for a transmitter situated on the line joining the two aerials 1, 2. The 180‹ ambiguity can be resolved by using, a second pair of aerials at right-angles to the first. Instead of rotating the aerial system, signals representing the " difference " currents between one pair of aerials are fed to one fixed coil of a radiogoniometer, and similar signals from the second pair of aerials are fed to the other fixed coil, output signals being taken from a pair of moving coils set at right-angles to each other, so as to give a form of frequency modulation, which, when compared with an " average " signal, will show the elevation of an aeroplane on the cathode ray indicator. Three aerials may be used instead of four, and a circular resistance potentiometer, suitably tapped, may take the place of the radiogoniometer. For " spotting " an aeroplane, a four-aerial system forming a 70-metre square is used with a central transmitter and two cathode-raytube indicators, one of which gives the azimuth and the other elevation. Both tubes are supplied with a saw-toothed scanning-frequency. Pulses of modulated current are radiated from the transmitter, and the timeinterval between the outgoing and reflected pulse is shown by the location of the trace of the reflected signal along the scanning track of one of the cathode ray tubes. This gives the required distance, and the orientation of the trace gives the elevation. The bearing in azimuth is given by setting the goniometer coil so as to keep the trace of the reflected signal on the second cathode ray tube say at rightangles to the scanning track. The two cathode ray tubes can then be manipulated to give a continual indication of azimuth, altitude, and distance. In a modified arrangement for obtaining direction in azimuth, a variable proportion of the maximum energy applied to the vertical deflecting plates of the cathode ray tube is added to the signal energy applied to the horizontal deflectors, so as to cancel the original signal in the horizontal direction and give only a vertical or altitude direction. This arrangement can be used for search-light control. Also the time-delay of a reflected signal in " spotting " can be measured by adding a steady potential to the scanning voltage, so as to keep the " echo " at a fixed reference point. The additional steady potential required is then calibrated to indicate distance. Phase or or frequency modulated signals can be used with an appropriate form of detector to give the same results as amplitude modulated signals. Specifications 451,019, 482,740, 543,602, 578,729 and 581,921 are referred to.