[Coco] Re: [Color Computer] CoCo 2 and a PC VGA

[KnudsenMJ at aol.com]

In a message dated 9/10/04 8:13:50 PM Eastern Daylight Time, 
kevdig at hypersurf.com writes:

>   I don't believe this is quite correct. The VDG outputs a luminance 
>  signal and two color signals , phase a and b. I believe this amounts to 
>  describing a color space with 3 components. I am confident these could 
>  be converted into RGB with little or no signal loss.

You are right.  I, and maybe others, forgot that the Coco 1/2's VDG chip does 
not output RGB at all, but only composite.  The phase A and B signals are 
intended to modulate the I and Q phases of the 3.58 MHz color subcarrier, thus 
producing the NTSC color composite signal.  (Gene H. can jump in here and 
correct me -- hi, Gene, staying dry?).

You may be able to feed these A and B into a stock TV chroma demodulator 
chip, bypassing the 3.58 stuff completely, and maintain the original high 
bandwidth -- but I'd have to think about it.

I think it was Commodore that fed the luminance to their monitors separately 
from the color subcarrier, thus preserving the high luminance bandwidth.  In 
converting VDG outputs to RGB, you may be able to pull off the equivalent stunt 
and get a very sharp picture, for a deuce.
 
>   If I ever find a job my scan doubler for the tre is also going to 
>  support my deuce. The model deuce I have, a -3026, has ... terrible 
>  video noise. Anybody else with this model have the same problem? And it 
>  is not because of its age. It has always been bad.

Sometimes my older Cocos would feed a lot of RF interference down the outer 
coax of the RF cable that connected them to the TV antenna switchover box.  Put 
grainy noise in the picture.  Is that what you mean?

BTW, way back when I built a three-transistor circuit for my Coco One that 
combined the luminance and Phase A and B so as to produce distinct shades of 
gray from all 8 colors, for use on a mono monitor.  You could play Tandy's 
Backgammon and Chess carts, and tell the red and blue pieces apart.  Somewhere I 
have the diagram for that puppy, though I think I sold off my grand old graycase 
with its 64K and many extra rear connectors.  --Mike K.