Supermodel_Evelynn wrote: ↑26 Jan 2024, 09:50
wow so radars after image was natural CRT?
I always thought it was purposely made to do that using a software to delay the image to more easily see it.
It was 100% analog in the 1940s.
CRT radar back in those days did not even have a computer.
The radar spun at roughly 1 spin per second, and the CRT tube refreshed at only 1 Hz (one-sixtieth the refresh rate of NTSC). It can be higher or lower, depending on how fast the radar antenna spun in revolutions per second. To allow the CRT tubes to refresh at such a low refresh rate without flickering too much, they used really slow "glow in dark" phosphors that faded slower. Like your glow-in-dark toy.
Eventually when they added a computer, they still relied on the CRT's slowness to keep the afterimages running. The computer buffered the data and the CRT tubes did refresh faster, and some of the software based after images did occur -- but that did not happen originally. It was originally done by glow-in-dark on the CRT tubes themselves.
Remember your childhood glow-in-dark toys? Same phosphor! You shine a fluorescent light on them (or a light with lots of ultraviolet), they glow brightly for a second or two after you suddenly turn off the light, and continue fading and fading (but slower and slower fade).
Supermodel_Evelynn wrote: ↑26 Jan 2024, 09:50
Are they still using CRT for Radars today? or they upgraded to OLED etc?
Today, now the CRT afterimage effect on a digital panel, is simulated.
But the original CRT radar scope after images definitely was not software -- there was not even a computer at all!