Re: IIgs RGB to VGA continued

["Bill Garber" <willy46pa@comcast.net>]

"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


I will agree that the picture is much better now.  :o)

Bill Garber
Owner - Garberstreet Enterprizez
Co-owner - GSE-Reactive.com
(610)935-7676 (610)329-8996