[mythtv-users] What is your video ouput card for your tv ?

[Cory Papenfuss]

>>> Has anyone tried this adaptater ? http://www.sput.nl/hardware/tv-x.html
>>>
>>     I've made something similar for NTSC and the quality is great.
>
> Cory, it seems that the level of difficulty ro make something for NTSC
> would be harder than to make this for scart, right?  This would mainly
> be because vga is not compatible with NTSC signals in the same ways that
> vga and scart are?  I would be interested in building an interface like
> this myself, too.  Right now I have big underscan problems on my
> 9600pro, and if I can make something to connect to the vga port and
> allow myself to adjust modelines again, I would certainly try to do it.
> If you don't mind could you point me to some relevant sources?  I
> certainly won't bug you beyond asking if the information needed to do
> this is publicly available and could you point me to it.  Thanks a bundle.
> Raphael

 	Yes, you're correct.  VGA = RGBHV at lots of different H/V 
frequencies.  NTSC is only at *ONE* frequency (1/2 VGA 640x480), it is NOT 
RGB.  It is more or less component with only the Y at baseband.  The Pb 
and Pr are synchronously modulated on top of a 3.58MHz color subcarrier 
frequency.  It's quite complicated... that's why I cheated when I built 
mine.  I used an AD724 chip which does all of that for you with minimal 
circuit decorations to make it all go (a few resistors, a crystal, etc). 
Check the list archives for my previous posts.  Even after all of this, 
the modeline must set the frequencies right for NTSC.  The information is 
certainly available... the datasheet for the AD724 chip even has the 
schematic for a test circuit... more or less what I built.  Difficulties 
are that although it's not a very complicated circuit to build, it *IS* a 
circuit to build.  The "high" frequencies like 3.58MHz make construction 
quality more critical than building something like an LIRC tranceiver.  If 
you decide to build it and make a rats nest out of the thing, it'll likely 
look crappier than a good scanline converter / tvout.

 	SCART is a handy little connector that brings the RGB signals 
outside.  No modulation necessary... just get the frequencies (i.e. 
modeline) right.  It also happens to be in PAL-land, so PAL frequencies 
are appropriate when talking about interfacing to SCART.

-Cory

-- 

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* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
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