GB1063214A - Improvements in or relating to radio navigation aids - Google Patents

Abstract

1,063,214. Radio navigation aids. MARCONI CO. Ltd. Jan. 17, 1964 [March 28, 1963], No. 12216/63. Heading H4D. A radio navigation system for guiding ships etc. in the vicinity of a harbour, includes, on the ship, a television receiver R3, Fig. 3, adapted to receive and display a transmitted television picture of a PPI display produced by a pulse harbour radar (A), Fig. 1 (not shown), the transmitted picture being radiated from a point T remote from the radar A, in the form of modulated television lines, the line excursions of which occur in predetermined time relation to the pulses transmitted by the radar, means R6 to indicate the passage of the radar beam AB through the ship, and means for including received radar pulses in the television display. The invention enables the ships own response in the television display to be identified, with the aid of a hyperbolic lattice corresponding to the loci of points within the surveyed area having the distance from said point to the radar (A) and the distance from said point to the transmitting point T differing by a fixed amount. As the radar beam sweeps through the ship, a pulse receiver actuated lamp R6 brightens up, and the radar pulses are displayed on the television display R3 in the form of a vertically aligned row of brightened up parts of spaced (or adjacent) television lines. The relative timing of the radar pulse and television line transmissions, is preferably such that with the ship on a line equi-distant from points (A) and T, the brightened up row is exactly halfway across the screen. The hyperbolic lattice may be provided on a separate graticule on board the ship, or may be transmitted to the ship as part of the television display. The horizontal position of the brightened up row is referred to the hyperbolic lattice by means of a horizontal scale, numbered in correspondence with the lattice lines, and provided on a graticule or as part of the television transmission. Video mapping techniques may be used to produce the lattice and scale in the television transmission. In the display shown it can be seen that the display carrying ship is on the hyperbolic line numbered 6. A marker AB is also provided in the television display to indicate the position of the radar beam. The position of the intersection of this marker with the selected hyperbolic line at the moment the indicator R6 lights gives a fix of the ships position. Where the hyperbolic lattice is on a movable graticule the transmitting point T may be identified in the display by the provision thereat of a large radar reflector. The radar transmission may be designed to have a distinguishing characteristic, such as its frequency, which may be recognized by the display receiver, e.g. by a frequency selective receiver R2. The indicator receiver R5 may be selectively responsive to the pulse repetition frequency of the radar transmission, to activate a relay, which in turn activates the lamp. A movable cursor may be provided on the television display pivoted at the representation of the point (A), and movable to follow the marker AB.