Information Cells on Intensity-Modulated CRT Screens

The distribution of current within the beam of a cathode-ray tube has a Gaussian variation. Consequently, if the wave form of a pulse of beam current is known, it is possible to determine the excitation of an intensity-modulated screen surface. In this report the nature of the excitation is discussed for an intensity-modulated sweep for both rectangular and triangular current waveforms. The results are extended to indicate what may be expected of an actual mapping radar set. The theoretical constants which arise in the development are evaluated from data obtained by the shrinking raster method of measuring spot size, which is termed line width in this paper for purposes of clarity. This permits determination of the size of an information cell on the screen as a function of pulse duration, sweep speed and line width. Then the number of information cells available on a tube may be determined. As a consequence, we find that there is no significant difference in the number of information cells available on the standard 5FP7, 7BP7, or 12DP7. Furthermore, the reduction of the over-all receiving-system frequency response by some radar displays may be estimated. In such a case the video bandwidth may be reduced.