Patent GB-1278275-A (GB)
Title: Radio hyperbolic navigation
IPC: G01S1/30
Filed: 1969-07-04
Abstract: 1278275 Radio navigation SOC D'ETUDES & D'APPLICATION DES TECHNIQUES NOUVELLES NEO-TEC 4 July 1969 [5 July 1968] 33922/69 Heading H4D Relates to a radio hyperbolic position-finding method, and corresponding receiving apparatus, in which families of hyperbole are defined by audio-frequency beats of different sensitivities the " partial " (i.e. within 2 II) phases E i  of which are given by K i  + K i X where K i  represents phase at a known location, K i  is the sensitivity (i.e. related to the characteristic frequency e.g. 300 kHz and a beat frequency of f 0  80 Hz), and x represents the hyperbola on which the receiver is located. According to the invention local signals of phases k i  + K i x<SP>1</SP> are generated, where x<SP>1</SP> represents an estimate of x, difference signals # i  representing the differences between phases k i <SP>1</SP> + K i x<SP>1</SP> and k i  + K i x are produced and linear combinations of difference signals are utilized to control x<SP>1</SP> so that it tends to x. The purpose of the invention is to remove ambiguity in position determination. Transmitting systems of the embodiments are of the types named " single-signal " or " twosignal " with reference signal and in both types spaced stations B, C radiate on frequencies F, F + f 0  respectively, and a third station A radiates a carrier of frequency F 0  modulated at frequency f 0 . In the " single-signal " type, a known point D receives all the transmissions and controls the frequency at station B (or C) such that the beat frequency f 0  at D is in phase with the demodulated f 0  at D; in the " twosignal " type the point D compares the transmissions from B and C to give the frequency f 0  which is then sent to A for modulation on to F 0 . Thus in the "single-signal" type the audio frequency (AF) signals produced at a receiver are stable in frequency and phase and are processed successively whereas in the "two-signal" type the A.F. Signals are processed in pairs. Transmissions from the stations may be simultaneous or sequential and the reference signal may be omitted, a second pair of stations B, C being utilized. " Single-signal " receiver, with reference signal, Fig. 3.-In the case considered there are produced successively at the receiver a reference- A.F. of phase #-=k 0 , a first position-A.F. of phase # 1  = k 1  + K 1 x (characteristic frequency (C.F.) corresponding to K 1  of 300 kHz) and a second position-A.F. of phase # 2  = k 2  + K 2 x (C.F. 310 kHz). Assuming that x is fixed, a memory 4 stores a quantity k 0 <SP>1</SP> representing a phase # 0 , a detector 3 compares the phase 90 with # 0  and controls memory 4 until k 0 <SP>1</SP> = k 0 ; and similarly for # 1  = k 1 <SP>1</SP> + K 1 x<SP>1</SP> to correct k 1 <SP>1</SP> in memory 5 such that k 1  + K 1 x = k 1 <SP>1</SP> + K 1 x<SP>1</SP> and for memory 6 such that k 2  + K 2 x = k 2 <SP>1</SP> + K 2 x<SP>1</SP>. If there are defined quantities: further quantities, e.g. are formed since a # 2  may be > 2#, and # 1  controls x<SP>1</SP> such that # 1 #O 1  and the " sensitivity " of the correction corresponds to 10 kHz, the resulting magnitude of x being not highly accurate but substantially unambiguous. To improve accuracy another quantity #, e.g. # 2  = # 1 - # 0  (of sensitivity # 300 kHz) may be utilized. Other signals, e.g. corresponding to a C.F. of 50 kHz may be processed. It is stated that similar considerations may be applied without reference signal transmission. If the receiver is moving a velocity memory 12 is added and varies the content x<SP>1</SP> of store À7; magnitude # 2  provides correction. Detector 3 comprises a phase comparator 14, Fig. 4, producing a rectangular waveform 15, Fig. 4a, of mark/space ratio dependent on phase difference of signals on lines 2, 9, the mark/space ratio being 1 : 1 when the phase difference is zero. The waveform is applied directly to a gate 21 and after inversion 24, Fig. 4a, to a gate 18, both gates being fed with clock pulses and such that outputs 26, 27, Fig. 4a, ensue. Integrating counter-dividers 19, 22 (which are reset after each signal processing) are provided and converters 20, 23 produce pulses which define the phase in magnitude and sign and are sent to an appropriate processing circuit via a selector 28. Such a processing circuit 5 comprises a " +/- " unit 29, fed additionally with clock pulses, and a counter-divider 30 together forming the memory 5 (see also Fig. 3) for k<SP>1</SP> 1 . Pulses applied to the " + " input of unit 29 add to clock pulses and vice-versa. Phase comaprator 14 comprises gates forming a NOT-EXCLUSIVE-OR logic circuit, Figs. 6, 6a (neither shown) including a preferred variant to ensure that the output waveform mark/space ratio is 1 : 1 when the inputs are in phase, Fig. 6b (not shown). The local signals from unit 8, Fig. 3, are produced from x<SP>1</SP> and k i <SP>1</SP> magnitudes by a counter arrange. ment, Fig. 5 (not shown). Further details include: (i) when the phase difference is not small (e.g. on initial operation) the above arrangement, Fig. 4, may be too slow and an alternative arrangement producing waveforms for the " +/- " unit 29 of Fig. 4 such that when the input signals are in phase two zero-level outputs ensue for application to the " +1- " unit, Figs. 7a ... 7d (none shown); (ii) a circuit for producing signals representing the difference # 1  = k 2 <SP>1</SP> - k 1 <SP>1</SP> (it being contrived that k 1  = k 2 ) incorporates " JK " bistables, Figs. 8a ... 8d (none shown) or Figs. 9a, 9b (neither shown), the latter not requiring symmetrical input signals; (iii) a " +/- " circuit incorporating " JK " bi-stables and an adder, Fig. 11 or Fig. 13 (neither shown); and (iv) a variant of the Fig. 3 embodiment, Fig. 14 (not shown). " Two-signal " receiver, Fig. 16.-In the " two-signal " case each of a pair of A.F. signals from receiver 90 are produced simultaneously on lines 91, 92 respectively and applied to phase comparators 101, 102 of the kind corresponding to Fig. 6 (see above) and their outputs are applied to a unit 103, e.g. as described above with reference to Fig. 4. The circuit of Fig. 14 (see above) is varied to yield simultaneous processing Fig. 15 (not shown). Three pairs of A.F. signals are utilized, each pair comprising a reference and a position-finding signal.