Patent GB-1120295-A (GB)
Title: Improvements in or relating to chart position indicating apparatus
Inventor: THOMPSON EDWARD ERNEST
IPC: G01S1/02
Filed: 1966-04-21
Abstract: 1,120,295. Indicating apparatus. DECCA Ltd. Feb. 9, 1967 [April 21, 1966], No.17560/66. Heading G1J. Apparatus for indicating on a chart a geographical location represented by the intersection of two position lines which are members of two families of position lines of a radio navigation system, comprises a chart 63 of a geographical area embracing the location, the position lines being representable on the chart by families of straight lines defined by the equations y = mx + c and x = ny + k, a computer 52 being provided for solving the equations and an index movable relative to the chart in the x, y co-ordinate directions in accordance with the values of x and y determined by the computer. The position of the geographical location is determined by measuring at a mobile receiver at the location, the phase relationship between signals received from a master transmitting station and three slave stations disposed around the master station. Thus for each slave station a hyperbolic position line through the position of the receiver is determined, the position line being one of a family of confocal hyperbolae having the master and slave stations as foci. The families of position lines are approximated to straight lines over the area of the chart which covers the position of the receiver and its surroundings. The intersection of one line from one family with a line from another family is taken as the origin of the coordinate system defined by the axes x, y which are parallel to the chart edges. The slopes and intercepts on the areas of the lines through the receiver position are then calculated as follows to determine the position of the receiver. The signals radiated from the radio navigation system are picked up by an aerial 41 and fed to a phase comparison system 42 which provides signals representing the three hyperbolic co-ordinates (i. e. the phase angles between the signals from the master and each of the three slave stations) in a manner fully described in Specification 620, 479. The outputs from the system 42 are fed to digitisers 43-45, the digital outputs of which represent the three hyperbolic co-ordinates used for driving the chart position indicating apparatus. Two of the three co-ordinates are selected by a pattern selector 46 which selects in accordance with an appropriately coded signal on a line 47. The selected signals are fed by gates 50, 51 to the computer 52 which converts the hyperbolic co-ordinates into x, y cartesian co-ordinates. The signals from the computer are fed to servomotors 56, 57 which produce error signals to drive motors 58, 67, this type of drive being fully described in Specification 914, 185. The motor 58 drives a lead screw 59 on which is mounted a carriage 60 to move the carriage across the chart to determine the y co-ordinate given by the position of an index line 61 on a transparent cursor 62. The motor 67 moves the chart with respect to an index 61a to indicate the x co-ordinate. A chart member 72 on which several charts 63 are marked is mounted on spools 70, 71. Opaque markings 73 are provided for determining the position of the chart by a method fully described in Specification 914, 185 and also for supplying to the computer the appropriate chart constants for each chart. Wipers 64 co-operate with conductive tracks 65 to provide signals representing the position of the index 61a in the y direction which signals are fed to the servo 56. Reference has been directed by the Comptroller to Specification 914, 185.