Patent GB-1056179-A (GB)
Title: Radio navigation system
Inventor: EARP CHARLES WILLIAM
IPC: G01S5/00
Filed: 1963-11-04
Abstract: 1,056,179. Radio navigation systems. STANDARD TELEPHONES & CABLES Ltd. Oct. 30, 1964 [Nov. 4, 1963], No. 43410/63. Heading H4D. A radio-navigation system comprises a plurality of fixed stations, each radiating a pair of sidebands of a carrier suppressed transmission, the modulation frequencies being different for each station and the suppressed carriers being phase interlocked, and a mobile station, receiving the pairs of sidebands and generating the suppressed carrier by local means whereby the pairs of aide bands may be demodulated to produce corresponding pairs of modulation signals, the phase difference between the signals of any pair of modulation signals representing the distance of the mobile station to the corresponding fixed station. Each fixed station 1 or 2, Fig. 1, comprises a carrier signal generator 5 or 7 and a modulation signal generator 6 or 9 feeding a balanced modulator 4 or 10 to produce the pairs of sidebands. The carrier signal generators which may operate at 20,000 c/s. are accurately phase locked, and the modulation frequencies of the two stations are different, for example 15 c/s. and 25 c/s. The mobile station 3 comprises an aerial 12 for receiving the pairs of sidebands and feeding them via pre detector stages 13 to a demodulator 14. The demodulator is also supplied with a signal at the carrier frequency from generator 15. The generator is highly stable and the signal remains substantially locked to the suppressed carrier signals. The modulation products of the upper sidebands appear at one output of the demodulator, and the modulation products of the lower sidebands appear at the other output. The modulation signals at 15 c/s. are separated out by filters 16 and 17 and the phase difference therebetween determined by phase measurer 20. This phase difference represents the distance from the mobile station to fixed station 1. Similarly the output of phase measurer 22, working on the signals at frequency 25 c/s., represents the distance from the mobile station to fixed station 2. The outputs of the phase measurers may be in the form of rotations of shafts 21 and 23. whereby, by coupling these shafts to a differential gear assembly 24, the gear assembly will give an output representing the difference in the distances of the two fixed stations which output can be used in a hyperbolic lattice navigation system. If a third fixed station is provided, a second hyperbolic lattice may be used enabling a fix to be made of the mobile station's position. In a second embodiment, Fig. 3 (not shown). three fixed stations are used having modulation frequencies of f 1 , f 2  and f 3 . The modulatoin signals at frequency f 3  in the output of the demodulator are fed to a phase-sensitive detector 28, the output signal of which is used to control a phase shifter in the path of the carrier signals from generator 15 to demodulator 14. A predetermined phase relationship is thus set up between the carrier signal and the sideband signals giving frequency f 3 . The output of phase measurer 20, thus represents the difference in the distance of the mobile station from station I and the third station, and the output of phase measurer 22 represents the difference in the distances of the mobile station from station 2 and the third station.