[linux-dvb] Re: Help with J2 RGB

[Michal Dobrzynski <michal_dobrzynski@mac.com>]

In an email sent to me rather than the list you mentioned the 
following. I hope you don't mind me forwarding this part to the list as 
I wanted further opinions.

On 29/04/2004, at 10:19 PM, Emil Naepflein wrote:

> You have to terminate the RGBS lines with 75 Ohm to ground and don't
> connect anything to the regular outputs. I once experimented with RGB
> output with a RGB to S-video converter. This converter has switchable
> termination for each input signal. Without termination the picture was
> horrible as you have seen, with termination switched on the picture was
> fine, but not better than the picture on the direct S-Video output.
>
> In the meantime I dropped the RGB output all together because you 
> cannot
> expect much better quality without considerable effort to clean/filter
> the high-frequency RGB signal. The PC environment is just to noisy. I 
> am
> happy with the S-video signal into a Lumagen scaler which feeds an XGA
> DLP beamer with with an anamorphic ISCO lens with VGA. Depending on the
> quality of the transmission the image is breathtaking on a 243 cm wide
> 16:9 screen.
>
> Emil
So I'd just like to know whether I have indeed been chasing an 
impossible dream with the RGB output of J2. Is it true that in practice 
the RGB  will not give a visibly better picture than the S-Video? I 
certainly know that on my STB and DVD players the RGB gives a 
significantly better picture than S-Video. Is this impossible due to 
the noise in the PC?

If it is impossible then why have so many on the list claimed that this 
is the best way to go?

Furthermore is it significant that I am connecting the 75 Ohm resistors 
to the J2 ground at the SCART end? Should I be connecting to the SCART 
ground? Indeed is SCART from the TV delivering ground on pin 21? How 
about all the other ground signals on the SCART? Would it be better to 
connect the resistors to the SCART ground coming from the TV? Or would 
it be better to connect them to the J2 ground at the J2 end?

But wait, there more! What about shielding? How can I effectively 
shield the connectors at the SCART end? It's all essentially out in the 
open INSIDE the PC case. I could take photos to help explain what I 
mean.

I have secondary reason for wanting to use RGB though and that is so 
that I can use the pass through on my STB and DVD player to have 
everything going through one AV input and therefore one channel on the 
TV (for usability purposes associated with my parents). I have already 
tested that with good SCART cables there is no visible reduction in 
image quality. In order for this to work though all devices must be set 
to RGB output as the AV input on the TV is manually set to RGB and 
displays a black screen if the signal it gets is not RGB.

Regards,
Michal



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