Patent GB-774781-A (GB)
Title: Omnirange radio beacon system
IPC: G01S1/02
Filed: 1955-07-04
Abstract: 774,781. Radio navigation. STANDARD TELEPHONES &. CABLES, Ltd. (International & Telegraph Corporation). July 4, 1955, No. 19325/55. Class 40(7) In a phase beacon having a directional radiation pattern comprising n equally spaced radial lobes, the amplitude of (n - 1) of the lobes being equal and the amplitude of the n th lobe being different from the others, the pattern is rotated at f r.p.s. so that the envelope of amplitude variation of the signal received at a mobile receiver comprises the first and n th harmonics of the rotation frequency f and the R.F. energy applied to the directional beacon aerial 1, Fig. 1, is amplitude modulated by two subcarriers of frequency f1 and f2 respectively, the f1 subcarrier being frequency modulated by a burst of oscillations from a low frequency oscillator 14 when the n the different lobe is directed in a datum direction, e.g. north, and the f2 subcarrier being frequency modulated by a burst of oscillations from said oscillator when each of the other (n-1) lobes is directed in the datum direction. At the mobile receiver reference signals of frequency f and nf are derived from the subcarrier signals and compared in phase with the fundamental and harmonic components of the envelope waveform respectively to give an unambiguous coarse and ambiguous fine indication of the bearing of the receiver from the beacon. In the embodiment described n=3. The beacon radiation pattern Fig. 1B is produced by the aerial system 1 shown in plan and elevation in Figs. 1A and 1 respectively and comprising a fixed aerial 4 energized from an R.F. sound 2 and surrounded by three parasitic elements 6, 7 mounted on a disc 5 driven by a motor 8 at a speed of f = 30 c/s, elements 6 being nearer aerial 4 than elements 7. According to Specification 774,782 elements 6 may be wider than elements 7, the elements 6 and 7 being then equi-distant from aerial 4. The output from L.F. oscillator 14. is applied to frequency modulate the f1 subcarrier at 17 through a gate 15 which is opened when the lobe 16a is in the datum direction by a pulse from a pick-up 12 cooperating with a non-magnetic disc 10 driven by motor 8 and having a single iron slug 10a and the f2 subcarrier is modulated at 18 when each of the lobes 16b and 16c is in the datum direction by a similar arrangement comprising gate 15a, pick-up 13 and disc 11 which has two slugs 11a. At the mobile receiver, Fig. 2, the first and third. harmonic components of the bearing envelope waveform output from detector 25 are selected by filters 26, 27 and applied through ganged phase shifters 28, 29 to discriminators 36, 37. The subcarriers f1 and f2 from detector 25 are separated by filters 30, 33 and a reference pulse train of recurrence frequency f is produced by a limiter 31 and discriminator 32 and applied to discriminator 36, similar pulses produced by limiter 34 and discriminator 35 but corresponding to lobes 16b and 16c being combined with the output from discriminator 32 to give a reference pulse train of recurrence frequency 3f which is applied to discriminator 37. The settings of phase shifters 28 and 29 required to produce a zero output from discriminators 36 and 37 gives the required coarse and fine bearing indications.