Tony Duell ard at p850ug1.demon.co.uk
Fri Oct 8 13:15:14 CDT 2010

> It is amazing how many people have overlooked the 120 Hz refresh rate
> aspect of this thread. Making a big frame buffer with very fine
> resolution is the easy part - getting the video circuits and the tube
> to play along is where things get tough.

I am going to assuime that the scan lines are in the horizontal direction 
as they usually are (but no always, I have worked on at least one display 
system that scanned vertically!). So the vertical deflection is the 
slower one.

Yhe vertical rate, horizontal rate and number of lines are all related.
The main problems are (a) the video bandwidth (determines, essentially,
the total number of pixels displayable in a given time) and the horizontal
scan rate. 

Increasing the vertical rate from 60Hz to 120Hz is fairly easy if you
don't mind halving the number of lines. This keeps the horizontal scan
rate and the video bandwidth essentially unchanged. So as there are 1024
line 60Hz systems around 30 or more years ago, there couild easily have
been 512 line 120Hz units. 

I wonder about electrostaticeally-deflected CRTs. The main disadvantage 
is that you gnerally have a much smaller deflection angle than with 
electromagnetic ones, leading to long CRT (base to sreen) for a given 
screen size. But driving them fast is considerably easier than driving 
deflection coils fast. Doesn't help with the video bandwidth, I guess.


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