Re: IIgs RGB to VGA continued

["Vince Briel" <vbriel@removethisspamcamcast.net>]

J, Any more pics like vga5 and vga4? I think you have found the answer. I 
would have gone for the phase adjustment but it looks like you are correct 
with the filter. Can you do more pics with both resolutions again. Good work 
going with your gut, ha, you were right, we were wrong. This should make gs 
owners happy.

Vince
-- 
Making computers fun again
See the new AltairPC
http://www.brielcomputers.com

"jsnospam@cimmeri.com" <js@cimmeri.com> wrote in message 
1156961086.884620.271390@e3g2000cwe.googlegroups.com">news:1156961086.884620.271390@e3g2000cwe.googlegroups.com...
>
> The basic setup is:
> AL875 ADC
> AL250 scan doubler
> ICS1523 clock generator in a PLL
>
> We tried changing the dot clock sampling rate.   We noted many
> interesting effects, but no overall image improvement.
>
> Also considered phasing: it's done by the ICS clock generator chip.
> The phasing is adjustable and we tried changing it throughout its range
> and it made no difference.   Not during dot clock adjustment.
>
> Now look at:
> http://members.aol.com/mdnttrain/vga6.jpg
>
> In this latest photo, a first order low pass filter was added on each
> of the 3 color inputs.  This reproduces the lower bandwidth of the
> older monitors and makes the modulation bars disappear.   We are
> beginning to believe that the modulation bars are really coming out of
> the machine like that and not a defect of the converter itself.    A
> supporting observation is that the beat bars are quite "solid" looking
> (real beat bars we've seen are soft).
>
> Another is that they don't show up on the black and white portions of
> the image as Vince noted.   That means that if the bars ARE present,
> they are always white bars on white backround, and black bars on black
> backround .. which seems inconsistent with the other bars we're seeing.
>
> Do you all agree with our theory, or think something is still wrong in
> the converter's phasing circuit / dot clock rate?
>
> ~ J
>