GB680594A - Improvements in and relating to electronic mapping systems - Google Patents

Abstract

680,594. Radiolocation. BRITISH THOMSON-HOUSTON CO., Ltd. (General Electric Co.). Sept. 26, 1950, No. 23567/50. Class 40 (vii). [Also in Group XL (b)] A system for providing an electronic map presentation, for example on the screen of a cathode-ray tube, comprises a cathode-ray tube, the screen of which is scanned in a predetermined manner, means for projecting the light emitted thereby through a map transparency having opaque markings on to a photo-electric cell, and a feedback path between the cell and the scanned cathode-ray tube, whereby variations in light intensity, as seen by the cell, due to screen irregularities are reduced. The cell output may be used to provide a presentation of the map on a cathode-ray tube which is also the plan position indicator of a radar system, the map scale and P.P.I. scale being the same and being readily variable in synchronism by a variation of the radial sweep rate. The map transparency 5 may be placed immediately in front of the screen 1a of the cathode-ray tube 1 which is scanned by a spot of normally constant intensity under the control of sweep signals applied to deflection yoke 2. The light passed by the map representation falls on photoelectric cell 6 whose output is amplified by amplifiers 7, 8 and 9. The main output of amplifier 9 may be fed to a radar P.P.I. display as mentioned above, but a portion of it is fed back to the cathode 3 of tube 1, a D.C. clamp circuit 10 being provided to maintain the cathode potential at its proper level. The feedback signal maintains a constant video signal output in the absence of map lines.