Re: IGS Monitor from Composite Source?

mdj wrote:
On May 6, 2:39 pm, demp...@xxxxxxxxxxxxx (David Empson) wrote:

Steve ][ <s...@xxxxxxxxxxx> wrote:

Just wondering if anyone knows of a way to take a "composite RCA"
video signal and convert it into something that would display on the
IIGS Analog RGC monitor.

I assume you meant Analog RGB and that was just a typo.

In theory, yes. You would need a fancy video conversion box which
decoded the composite signal and produced an RGB signal for the monitor.
This would be an analog process and the signal quality would be much
lower than a genuine Analog RGB source, and probably worse than looking
at the same signal on a good quality composite colour monitor.


How so? A composite colour monitor has to decode the composite signal
to RGB to display it so I don't see how it would look any worse, other
than the higher-fidelity of most RGB displays.

Just because the adapter boxes that cost less than $500 are not
"Sony quality" chroma demodulators.

Of course, the *big* drop in quality comes from doing the chroma
separation inherent in composite video, with the consequent bandwidth
limitation.

I don't know if any such box exists. It would be simpler than a
hypothetical "composite to VGA" converter, because it doesn't need to do
a frequency conversion as well.


There are plenty of chips out there that'll decode NTSC into component
forms. I doubt you'd need a lot in the way of support circuitry to
drive it.

No, it's a mess. There are filters and delay lines involved, so any
chip you find will have lots of pins and lots of external components.
Chroma separation and demodulation is either an analog process or a
pretty complex DSP process, so there's no free lunch.

If your intention is to convert Apple II composite to RGB that might
be a little trickier, as some modern decoders tend to be confused by
the quasi-NTSC nature of the Apple II video signal.

That might be an issue for a "modern" digital/DSP solution--it might
not lock to the Apple II signal. An analog solution would not have
a problem with that.

-michael

NadaNet file server for Apple II computers!
Home page: http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."
.

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