Patent GB-650942-A (GB)
Title: Improvements in and relating to radio vision apparatus
IPC: G01S1/02
Filed: 1947-07-11
Abstract: 650,942. Radio navigation. BRITISH THOMSON-HOUSTON CO., Ltd. July 11, 1947, No. 18523. Convention date, May 22, 1943. [Class 40 (vii)] The invention relates to aircraft radio navigation systems wherein beacons at known positions on the ground radiate or reflect radio waves and receiving equipment mounted on the aircraft presents indications on a screen corresponding to the positions of the beacons as viewed from the craft. According to the invention receiving equipment for such a system includes means for producing on the screen an indication of the position of the horizontal plane through the craft. A further line indicating the deviation of the direction of motion of the craft from a prescribed vertical plane may also be provided. The scanning equipment. The receiver is fed from an aerial 34 backed by a reflector 35 which is swept in one plane and nodded in a perpendicular plane to scan a field of view centred about the direction of travel of the craft. Scanning is performed by motor 39 coupled by means of linkages 38, 40, and 41 to a fork supporting the aerial system which is pivoted about a vertical axis on plane 28. Plane 28 is nodded by means of a second motor actuating arm 43. The instantaneous position of the scanning aerial in a plane parallel to plane 28 determines the position of slider 46 over potentiometer 45 and the nod angle of plane 28 the position of slider 49 over potentiometer 47, these potentiometers being included in circuits controlling the screen scanning. Also provided are potentiometer 104 whose slider 105 is set according to the deviation of the heading of the craft from a direction preset on compass control 106 and potentiometer 89 whose slider is set by vertical control 91, which may be gyroscopic, according to the deviation of the longitudinal axis of the craft from the horizontal. The receiver and indicator. The aerial 34 feeds converter stage 63 and intermediatefrequency amplifier and detector 64 applying signals as each object is scanned to an amplifier comprising valve stages 65, 66 and 67. The output from the amplifier feeds an automatic volume control circuit having diode 69 in shunt with resistor 70. Increase in the amplifier output increases the negative voltage across resistor 70 which is fed back through resistors 71, 72, 73, in relatively long time constant circuits to the grids 74, 75 and 76 of valves 65, 66 and 67, so decreasing the amplification. It is stated that variations of signal strength of 10,000: 1 can be brought to a constant output level by this circuit. The signals from valve 67 are also fed through condenser 80 to clipper and square law amplifier 81, which has the effect of sharpening the indications, phase inverter 82, and switches 83, to intensity-modulate cathoderay tube 18. Cathode-ray tube 18 is normally scanned horizontally by the movement of slider 46 over potentiometer 45 and vertically in accordance with the movement of slider 49 over potentiometer 47 to reproduce on the screen the scan performed by the aerial system so that images of the beacons scanned appear in their correct positions. At one end of the travel of linkage 38, Fig. 1, projection 86 closes contacts 85. These contacts are in the circuit of relay 84 which operates to disconnect the indicator from its usual scanning and intensity modulation voltages and instead causes a bright spot, due to the potential applied from battery 92a, to trace a horizontal line across the screen under the control of a scanning circuit including valve 94 at a vertical position dependent on the setting of vertical control potentiometer 89. At the other end of the travel of linkage 38 contacts 99 are made, operating relay 100 which alters the indicator connections so that a bright spot is scanned vertically across the tube screen at a horizontal position determined by the course error potentiometer 104. Airport ground layout. It is suggested that the airport runway be indicated by two pairs of beacons spaced along the runway, the members of each pair being equidistant on opposite sides of it (Fig. 3, not shown). Each beacon preferably radiates a modulated carrier, the modulating signals of the beacons to one side of the course line being in opposite phase to those of the beacons on the other side. This serves to emphasize the discrimination between beacons on opposite sides of the course line as explained by reference to Figs. 12 and 13 (not shown). If the angle swept by the scanning beam is known the distance to the end of the runway can be determined at the point where the indications from the pair of beacons at the end of the runway just vanish. At this point, too, the distance between the indications and the horizontal plane line on the screen can be used to calculate the altitude of the craft.