GB642368A - Improvements in or relating to radio navigation systems - Google Patents

Abstract

642,368. Radio navigation. O'BRIEN, W. J. Aug. 21, 1946, No. 24987. [A Specification was laid open to inspection under Sect. 91 of the Acts, Feb. 28, 1947.] [Class 40 (vii)] In an equi-phase difference contour radio navigation system, having three spaced transmitters, two of the transmitters radiate signals of different but harmonically related frequencies in fixed phase relation and the third radiates two other different frequencies harmonically related and in fixed phase relation to each other and to the signals from the other transmitters. At the receiver two signals of like frequency, one from the signals from the third transmitter and the other from the other two signals, are derived and compared in phase. Neglecting one of the signals from the third transmitter the system becomes similar to that described in Specification 620,479 and a receiver for such a system may be used to give an accurate position determination. However, by using all four signals a less accurate but less ambiguous determination of a single positional co-ordinate may be made at a phase comparison frequency lower than in the prior system. The transmitter radiating two frequencies may, in one embodiment, be placed on the line joining the other two and operated as a master transmitter having two oscillators of, say, 60 and 70 kc. feeding the antenna, the oscillators being interlocked to provide a fixed frequency ratio and phase relationship. The other two stations may be slave stations such as described in the above-mentioned Specification radiating respectively 80 kc. and 90 kc. signals, frequency and phase locked to the 60 kc. signals which they receive from the master station. At the receiver all the signals are received on a common antenna 8 and separated into four different channels 9, 10, 11 and 12 tuned to the individual frequencies. The two signals of 60 and 70 kc. received from the master transmitter are derived at 13 from channels 9 and 10 and the 10 kc. beat frequency applied to phase discriminator 14. The other input to the discriminator is the beat frequency of the 80 and 90 kc. received signals derived at 15 and the discriminator output drives phase indicator 16. Specifications 25491/46 (as open to inspection under Sect. 91), 620,480, 620,481, 620,507, and 642,398 also are referred to.