Patent GB-601976-A (GB)
Title: Radio guiding system
IPC: G01S7/04
Filed: 1945-03-09
Abstract: 601,976. Radio navigation. STANDARD TELEPHONES & CABLES, Ltd. March 9, 1945, No. 6008. Convention date, March 13, 1944. [Class 40 (vii)] A radio navigation system for guiding a craft over an area provided with spaced radio transmitters comprises an antenna arranged to scan a predetermined area in front of the craft, a receiver for receiving energy from the transmitters as they are scanned by the antenna, a semi-transparent viewing screen located so that the craft's pilot may obtain a direct view of the area in front therethrough, and means for reproducing on said screen a pattern substantially simulating the distribution of the transmitters in the scanned area. At an airport, in an instrument landing system, the hangers and runways are marked out by low-power transmitters working on centimetre waves. Preferably these transmitters are mounted on the same posts as the lights and radiate in all directions from which the lights are visible. On the aircraft a dipole receiving aerial 42 in a reflector 40 is made to scan an area ahead of the craft by means of mechanism 46 driven by motor 44. The line scan may be vertical as normally the angle to be covered is less in the vertical direction. A cathode-ray tube indicator is used on the screen 50 of which an area 64 is scanned by means of vertical scanning circuit 60 and horizontal scan circuit 58, synchronized with the antenna by control unit 62 driven by motor 44. A source of variable potential 61, whereby the size of the area 64 may be adjusted, is connected to scan units 58 and 60. As the landing ground is scanned by the antenna system, pulses of energy are received corresponding in time to the position of the transmitters. These pulses pass to receiver 66 and may then be applied direct to the control grid of the cathode-ray tube to produce indications on the tube which will simulate the pattern of the transmitters on the ground. The width of the indication pulses depends on the angle of reception of the 'scanning aerial and the distance to the transmitter, and the brightness will also vary with distance, thus a picture such as is shown would be produced by radiators down each side of a runway with a marker pattern 16AD near one end. In order to sharpen the indication, the pulses from the receiver may be passed through a differentiating circuit 68 and a clipper circuit 10 used to select a portion of either of the two short pulses produced. So that the pilot may see the indicator while at the same time having a direct view ahead, a semi-transparent plate 92, which may be a halfsilvered mirror or projection screen, is mounted in the line of vision of the pilot and on it is projected an image of the indications on tube 50 by means of an optical system 97. The oscillograph is preferably arranged so that the image of the pattern on the screen not only simulates the landing lights but is substantially coincident with them viewed directly. The screen may have a different fluorescent colour to that of the lights themselves in order to distinguish between them. Equations relating to the mean distance d2, between the pilot's eyes and the plate 92, and the distance d1 between the focus and the screen of the tube for a given magnification in the optical system and for real or virtual images are given. A pivoted frame for the aerial reflector, enabling it to perform the necessary scanning movements, is described with reference to Fig. 6 (not shown), and a horn shaped radiator for use on the ground with reference to Fig. 5 (not shown). The Specification as open to inspection under Sect, 91 (4) states that the viewing system of Fig. 7 may be used with other types of instruments. Specification 483,437 is referred to.