GB755886A - Improvements in or relating to direction finding systems - Google Patents

Abstract

755,886. Radio navigation. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. May 7, 1954 [May 7, 1953], No. 13449/54. Class 40 (7). In a system for determining the direction of a body M shown in a plan view in Fig. 1 with respect to a fixed point O, a directive transmitter beam located at the point executes a conical scan whilst the transmitter is controlled so as to emit a constant frequency carrier pulse modulated at F1, F2, F3 and F4 as the beam scans in succession each of four zones defined by two planes OP1, OP2 cutting at right angles along the axis of the cone. In a receiver carried by the body the signals D1, D2, D3 and D4 received respectively at each of said frequencies are integrated and then compared to derive the differences D1-D3 and D2-D4. These differences are proportional respectively to the rectangular co-ordinates of the displacement OM of the body from the core axis O in terms of axis OX, OY, bisecting to four zones. Fig. 4 shows one embodiment of the transmitter in which an offset aerial 10 is rotated in the focal plane of a paraboloid 11 under the control of motor 13 and is energized by a transmitter 14 operating at a constant radio frequency. The transmitter is pulse modulated by a modulator 16 under the control of a switching device 17 synchronized with the aerial scan by a drive from motor 13. Switching device 17 comprises a disc 18, Fig. 6, which is rotated between a light source and photo-cell and is formed around its periphery with serrations 25 of constant width but different spacing in the four quadrants whereby the transmitter is modulated with a different frequency in each of the four zones successively scanned by aerial 10. In the receiver, Fig. 7, the four frequencies are separated by filters 43-46 and applied to rectifiers 47-50 which integrate the corresponding signals D1-D4 and apply them to comparison devices 51. and 52. to derive the differences D1-D3 and D2-D4. The input of the receiver is a crystal rectifier 39 which feeds an amplifier 40 provided with an A.V.C. system 12, 41.