Re: How I got interested in the Apple ][...

[ferdimh@gmx.de]

On Dec 18, 10:28 am, Linards Ticmanis <ticma...@gmx.de> wrote:
> heuser.mar...@freenet.de wrote:
> >> The picture is always shaky and unstable. With today's
> >> multisystem TVs, I converted all my Apples to NTSC.)
>
> > I have a PAL IIe connected via composite and it doesn't
> > shake or is unstable at all. Maybe the TV plays a heavy
> > part in this, too.
>
> Well, maybe "shake" is not the right word. I get this vertically moving
> moire effect on the left and right border of colored areas, caused (as I
> assume) by a beating wave ("Schwebung" in German, I'm not sure this
> translation is correct) created from the superposition of the frequency
> of the two quartzes.

This is called "dot crawl" and is a feature of both the PAL and the
NTSC systems!
By deliberately tuning the Color subcarrier frequency a little off
these dots shall move so fast that they will not be seen. This
mimimizes cross-color artifacts in pictures of the real world, but
makes the problem way worse if one attempts to display graphics.
Because the Apple doesn't generate a correct NTSC signal, the dots
dont form a crosshatch pattern, but a line. And because the color
subcarrier is locked to the other frequencies there is no movement.
There is a bright line between lo-res colors 3 and 4, and a black line
between 9 and 10, for example.
These artifacts are called cross-color, because the color information
is misenterpreted as brightness information.
Making an S-Video connection to the TV solves this issue. One would
then need to tap out the chroma and luma signals, which exist
separately on a PAL board.
Modern 100Hz CRT TVs and LCD TVs contain a DSP which shall elliminate
these problems. For normal video signals this is a cure worse than the
disease but it might help on the Apple ][.
BTW: Many modern TVs refuse to sync to an Apple because they don't
like the timing which is not perfectly accurate (e.g. there is no
interlacing). IMO the best viewing device for an Apple ][ would be a
CGA monitor. If I can get one, I'll try to make an adapter board.

--
Ferdinand Meyer-Hermann