Re: Analog NTSC to RGB converter?

[Linards Ticmanis <ticmanis@gmx.de>]

On 10/22/2012 05:18 PM, Linards Ticmanis wrote:

> I'll report on my results as soon as I have some - in case anybody is
> interested.

OK, the main part is done. It even does auto-detection of PAL or NTSC
mode, which I didn't know was even possible until Alex Freed rightly
suggested that I read the data sheet more attentively. All in all it's
working really well.

There are two remaining issues: First, the filter that removes the
chroma info from that signal which goes down the luma path still has to
be re-tuned by hand for either PAL or NTSC. Not too convenient as it is
deep inside this beast. As Alex has suggested, this needs to be switched
between two differently tuned filters just like the two quartzes are
switched; but currently I'm having a hard time finding out what exactly
to get for the second filter. According to the schematic the filter is a
tunable inductor and a capacitor in series (inside a grounded metal can,
as a single component), but no pF or �H values are given and I don't
understand the inscription on the component itself either.

Second, no matter how you tune the filter, the Apple II signal seems to
be a bit too "violent" for it. With the beam moving from white or black
into a colored area, it takes about 2-3 chroma cycles until the
filtering really gets going. No such problem when watching DVB TV, a DVD
or VHS through it, so I guess the fact that an Apple color signal is
more or less "pure" color carrier, highly saturated and instant-onset,
defeats the circuit until it's had time to adjust. I guess it's a trade
off with the fact that the monitor has a much higher bandwidth than a
normal video monitor - 80 char text is quite legible on it.

I'll stop replying to myself now.

-- 
Linards Ticmanis