GB577276A - Improvements in radio blind-landing arrangements - Google Patents

Abstract

577,276. Directive wireless signalling. STANDARD TELEPHONES & CABLES, Ltd., EARP, C. W., and SAMSON, G. G. Feb. 23,1940, No. 3432. [Class 40 (v)] In a blind-landing system in which the glide path is determined by the field strength ratio between two overlapping beams, the respective aerials are so spaced apart that the glide path reaches the ground in front of them. For instance, the usual landing-line L1, Fig. 1, between two overlapping beams E and A is displaced by offsetting one aerial P, shown in plan in Fig. 3, by a distance S3 from the position O of the other aerial and by giving the beam from P an horizontal inclination to the glide path. The locus of the intersection of points of equal field-strength along the two beams will then be along the line L2 shown in elevation in Fig. 4, and will reach the ground well in front of both aerials so as to avoid any danger of collision. Alternatively one of the aerials may be set back from the other along the line of the glide path. The slope of the landing line can be adjusted, say from L1 to L4 or L5, Fig. 1, to suit different types of aircraft, by adjusting the relative fieldstrengths of the radiated beams ; or the same effect can be secured by regulating the gain of the amplifiers, or the zero of the indicator, used in reception. The two fields may be radiated at different frequencies, or one carrier may be modulated with different signals. To avoid phase interference, the carrier is preferably eliminated, the side-bands only being radiated. The landing- line may be combined with an approach path formed by overlapping beams ; one of these may be used for both purposes, a single carrier-wave transmitter supplying the whole system. Modulation may be effected in the way described in Specification 567,967.