Improvements in or relating to radio navigational aid systems

摘要

644,367. Radio navigation. PHILIPS LAMPS, Ltd. Feb. 6, 1947, No. 3643. Convention date, Feb. 5, 1944. Addition to 642,094. [Class 40 (vii)] Relates to omni-directional phase beacon systems as described in the parent Specification for enabling a mobile receiver to determine its bearing relative to the beacon in which the beacon radiates two fields on a common carrier amplitude modulated respectively with harmonically-related frequencies w and nw so that the modulation phase of the two fields at a distant point is directly proportional to the bearing # of that point and means being provided at the receiver for comparing the phases of the demodulated signals to obtain a quantity which is indicative of the bearing # and which is a function of (nŒ1)#. The accuracy of such a system is increased by making n large, e.g. n=8, but this results in (nŒ1) ambiguities in the 360 degree range of bearings and according to the present invention the ambiguities are resolved by radiating a third field having a modulation which is either proportional to the bearing or independent of bearing ; in the former case the modulation frequency may be ¢w, 2w, ¢nw or 2nw and in the latter case the modulation frequency may be w/m or nw/m where m is an integer differing from n and in either case at the receiver the modulation of the third field is compared in phase with that of the first or second fields to give an unambiguous but less accurate indication of the bearing #. In one embodiment of the parent Specification two cardioid directive patterns of the same carrier frequency are rotated in the same direction at angular speeds of wand nw and in one embodiment of the present invention, Fig. 1 (not shown), a further cardioid of the same carrier frequency is rotated in the same direction at a speed of 2w. At the receiver the signals obtained on demodulation having respective frequencies w, nw and 2w are separated by filters 25, 26, 27 and the 2w and nw signals are applied respectively to phasemeters 30 and 29 together with further signals of the same frequencies obtained by frequency multiplying the w signal at 31 and 28 by 2 and n respectively so that the meter 29 gives an accurate but ambiguous indication of # as in the parent Specification and meter 30 give a less accurate but unambiguous indication of #; if required a single phasemeter may be alternately connected to the two pairs of outputs from 26, 28 and 27, 31. Alternatively the phase difference may be measured by a cathode-ray tube as in the parent Specification. When the modulation phase of the third field is independent of bearing, the angle # may be determined unambiguously as in Specification 642,182. Specification 642,183 also is referred to.