Patent GB-760528-A (GB)
Title: Improvements in or relating to computers for use in connection with radio navigationsystems
Inventor: HAWKER HAROLD GEORGE
IPC: G06G1/14
Filed: 1954-06-21
Abstract: 760,528. Calculating-apparatus. DECCA RECORD CO., Ltd. June 21, 1955 [June 21, 1954], No. 18192/54. Class 106 (1). ). Calculating-apparatus for use in connection with a hyperbolic radio navigation system, comprises a pair of superposed charts, each bearing a similar family of curves but one being laterally inverted with respect to the other, the charts being mounted for relative movement in the two co-ordinate directions. In a hyperbolic navigation system, a mobile receiver indicates the difference between its distances from two transmitting stations. The locus of points with the same difference value is a hyperbola. By determining the difference values with respect to two pairs of stations, the position of the receiver may be obtained as an intersection of the corresponding hyperbolae, In the present system, a master station and two slave stations are employed. The difference value is first found with respect to the master station and one of the slave stations and is converted, by simple calculation or by means of a table into a value x which represents the distance from the master station along the line towards the corresponding slave station of its intersection with the associated hyperbola. The value x is then determined with respect to the master station and the other slave station. In one embodiment, the curves on each of the two charts, Fig. 3, show the relationships between x and #, which is the bearing of the receiver from the master station with respect to the line joining the master station and the appropriate slave station, for different values of m, the range from the master station. All values of x and m are given in terms of the corresponding base-length separating the master station from the respective slave station. In use, the charts are so moved relative to one another that the two x values are aligned and the sum of aligned values of # is equal to the known angle at the master station between the two slave stations. The locus of points a having equal values of m on the two charts (where the two baselengths are arranged to be equal) may then be constructed, the intersection of this locus with the common ordinate representing the observed difference values corresponding to the position of the receiver. The values of m and 0 (with respect to either slave station) of this point may then be read. If the base-lengths are unequal, a locus of points b having m values in a corresponding proportion is drawn and the value of m with respect to either base-length may be read. In another embodiment (not shown), each chart bears curves, drawn for different values x, of m (plotted on a logarithmic scale) against #. In this case, when the baselengths are unequal, it is only necessary to shift the charts relatively in the direction of the axis of ordinates by an amount corresponding to the ratio between the base-lengths (which setting may be facilitated by a scale on one of the charts) and to read the values of m and # for the intersection of the two appropriate x curves. Preferably both charts are drawn on transparent paper and are movable on perpendicular sets of rollers over a rigid transparent or translucent screen.