Cathode-tay-tube screens for radar

In radar displays of the intensity-modulated type, luminescent screens with afterglow are used to produce traces which persist for a time comparable with the interval between successive frames of the picture, which in the Plan Position Indicator is the time of rotation of the directive aerial. Theoretical and experimental studies show that the afterglow is a complex function of the excitation conditions. Two types of screen-testing apparatus are described which simulate the operational behaviour to the extent of using cyclic excitation at the aerial-rotation frequency in the application being considered. One particular case, H2S, is an airborne equipment with fairly high aerial-rotation frequency and low screen-excitation density. Some results for conditions simulating this are given. When measured by the methods described in this paper, afterglow intensity has been found to correlate reasonably well with operators´ assessment of the usefulness of the screen in the equipment. The quantitative relations between excitation density, afterglow, and derived functions are shown graphically and discussed. Some factors which may affect the operator´s response are considered, and some details given of the various screen materials used.