GB890497A - Improvements in or relating to systems for determining the positions of aircraft - Google Patents

Abstract

890,497. Radio navigation. GENERAL ELECTRIC CO. Ltd., and KIRKNESS, R. H. June 18, 1958 [June 27, 1957], No. 20398/57. Drawings to Specification. Class 40(7). In an aircraft position finding system signals emitted from a ground station, and from the aircraft in response to those signals, are detected by at least two spaced ground receiving stations. The times at which the signals from the ground transmitter and the aircraft arrive at pairs of receiving stations define ellipses which intersect at the aircraft position. To correlate the arrival times a digital computor is provided at the ground transmitter station, which may comprise a further receiving station defining a circle on which the aircraft lies, and radio links transfer information from the receiving stations to the computer. Many aircraft may be detected by this system, thus a first aircraft may respond to the transmitted or master pulse after a delay t1, a second aircraft after a delay tl + t2, a third after t1 + 2t 2 &c. Alternatively the ground transmitter may emit a series of pulses between the master pulses, and the aircraft transponders be arranged to count a certain number of pulses after each master pulse before responding. The transponder pulse may contain information concerning the aircraft. The computer may switch to hyperbolic position finding when the range of an aircraft falls below a certain value (see Specification 890,498). Aircraft coming within the useful range of the apparatus may lock on to the system by being allocated a position in time between the master pulses at which to respond, this lock may be made manually or may occur automatically by transmission of an allocating pulse from the ground station.