GB588851A - Improvements in or relating to object-locating and -detecting systems - Google Patents

Abstract

588,851. Radiolocation. WATSON, D. S., and WRIGHT, C. S. Jan. 11, 1945, No. 1969. [Class 40 (v)] In a radiolocation system in which an exploring beam oscillates, in elevation, e.g. at relatively high speed, whilst rotating or oscillating in azimuth, e.g. at relatively low speed, and in which indications of range and bearing are given in a cathode-ray plan-position-indicator, the signal input to the indicator is blocked during periods when the radial displacement of the cathode ray and the angular elevation of the exploring beam correspond to heights above, or alternatively below, a selected height, or above and below a selected height-band. By this means a considerable amount of unwanted energy is eliminated which would otherwise be fed to the indicator and give rise to background. Fig. 1 is a diagram showing ranger against height h for various elevational angles # of an exploring beam emanating from A in one direction in azimuth, and illustrates a case where the indicator response is limited to targets below 50,000 feet. The magnitude AD, AH, AF represents the complete period of each timebase sweep. The ratio ED/AE represents the ratio of the time during which the input to the P.P.1 is blocked to the time that it is open during each time-base sweep when the elevation of the beam is 10‹. Similarly the ratios JH/AJ and GF/AG represent this time ratio for elevations of 15‹ and 20‹ respectively, the time ratio increasing as the elevation increases. Referring to Fig. 3., elevational movement of the transmitter aerial is conveyed mechanically to a generator A producing a voltage V sin # which is fed to another voltage generator B comprising a linear time-base circuit triggered by the transmitter and which provides an output voltage Kr sin #. This voltage, which is proportional to the height corresponding to the elevation # and the instantaneous range r is fed to a unit C in which it is compared with a fixed voltage corresponding to a selected height and which provides an output when the rising voltage from the generator B exceeds the fixed value. The output of the unit C is fed to.a blanking generator D which in turn blocks the input of the indicator. Two voltage comparison units such as C may be provided, one for opening the indicator when h exceeds a selected minimum value and the other for closing it when h exceeds a selected maximum value. The invention may be applied also to object-locating systems employing for example, infra-red radiations or sonic or super-sonic radiations.