GB608220A - Improvements in radio navigational aids - Google Patents

Abstract

608,220. Radio navigation. PHILIPS BALHAM WORKS, Ltd., (formerly RADIO TRANSMISSION EQUIPMENT, Ltd.), and BAILEY, C. E. G. Oct. 25, 1944, No. 20806. [Class 40 (vii)] The course line in a radio navigation system is defined by the overlapping of two radiation patterns of carrier frequency radiation', each pattern being modulated by different periodic waves, the sign of one of which is reversed about the course and the period of one of which is an integral multiple of the period of the other. In a first embodiment, the modulation waves are sinusoidal and the period of the wave which is not reversed about the course is three times that of the wave which is (a and b, Fig. 1). On one side of the course, the waves add to form a combined waveform as indicated at 1c and on the other side the combined waveform is such as at 1d; on the course only the modulation 1a can be received. In a suitable receiver the modulation signals are applied to a peak rectifier 3 followed by a 2/# attenuator 4 and also to a mean rectifier 6. The outputs of the attenuator 4 and rectifier 6 are applied in opposition to centre zero meter 5 which reads zero on the course and indicates deviations to either side thereof. In a second embodiment, the modulations are of rectangular waveform and that which is not reversed about the course is maintained alternately for equal times in each period at two different amplitudes (Fig. 2a) and that which is reversed is maintained alternately at two amplitudes, each substantially different from half the period of the first modulation, and has a period half that of the first modulation (Fig. 2b). The resultant of the two signals on the two sides of the beacon axis are shown in Figs. 2c and 2d. In a suitable receiver, the modulation signals are passed through a filter 7 to eliminate the steady components thereof and then applied to two halfwave peak rectifiers 8 and 9 with their inputs and outputs in opposition. The opposed outputs are fed to a central zero meter 10 providing the same indications as are provided by meter 5 of the first embodiment. The course defined by the system may be fixed or may be rotated in azimuth to form a rotary beacon and a modification of the waveform described in Specification 580,985 to give a system similar to the second embodiment above would enable the receiver indicating means described therein to be combined with automatic steering means for which the present system is particularly suitable. It is stated that the phase relationship between the modulations may be important.