[mythtv-users] Hardware for Best TV-Out?

[Dan Lanciani]

Cory Papenfuss <papenfuss at juneau.me.vt.edu> wrote:

|> Keep in mind that a "real" (yet still not broadcast quality) RGB to NTSC
|> encoder is going to cost ~$500--and that is for an encoder *only* with
|> no rate conversion.  Not that I think a high quality encoder would really
|> help from what I can see of nVidia's output.  A transcoding TBC might help.
|> Unfortunately, mine has the component input option rather than RBG so I
|> can't try it. :(
|>
| 	It cost me about $10 in parts to build one.

I should have added "off the shelf" to the cost.

|No rate conversion, 
|just VGA->NTSC encoding (color subcarrier with UV modulation, etc).  Aside 
|from having to set the VGA card up for 480i timings, (read: no console, 
|only X), it works great.

How did you phase lock the color sub-carrier to the existing sync?

|The problem is that generating a reasonable quality NTSC signal is
|> not trivial (TV Typewriter Cookbook to the contrary notwithstanding :).  You
|> can't easily tack on cheap TV-Out functionality to a VGA card and get quality
|> results.
|
| 	Check out the AD724 chip.  A few passive components, one chip, and 
|a crystal is all you need.

I did look at that chip, but it wasn't clear that it solves the hard problem
of locking a free-running color sub-carrier to the sync in the incoming RGB
signal.  The documentation seems silent on the issue, but if you look at the
block diagram there is no obvious path from the sync inputs back into the PLL.
It will lock to an external carrier clock, of course, but if you have that then
you have already solved the problem. :)

				Dan Lanciani
				ddl at danlan.*com