[mythtv-users] Very poor picture quality from HD3000

[Brian Wood]

> ----- Original Message -----
> From: "Brian Wood" <beww at beww.org>

>> I know the signal strengths reported by some cards can be misleading, I've
>> heard some cards do not really implement that feature, and indicate the
>> same strength no matter what is fed to them. I'm pretty sure the HD-3000 is
>> one of those, though it may have been the early drivers and not the card
>> itself.

On Tuesday 22 September 2009 17:23:02 voidtrance at comcast.net wrote:

> The numbers are from the the little dialog that pops up in mythtv-setup
> during the channel scan. Both signal strength and S/N are in percent.
> It could be that the bar that represents S/N means db (so 13db, if that
> makes any sense - I am not a signals guy) but the character after the bar
> is '%'.
>

What does the picture look like? Are you getting blocking? Green blotches? 
What is making it "poor"? I understand it can sometimes be hard to describe.

In the analog world a 13db. video (not RF) S/N would be unwatchable, but with 
digital RF TV signals it might well produce a usable result. The thing about 
digital is it looks great right up to the point where it becomes total crap, 
a "cliff" threshold.

I think the cards that purport to tell you the S/N are actually using the BER 
(bit error rate) to approximate the S/N, which involves some assumptions, but 
is reasonable.

How is the audio? Can you even decode it?

I guess I can't ask you to get out your oscilloscope and tell me what the eye 
pattern looks like, but you should be able to get a usable picture from an 
HD-3000 if the signal looks OK directly into a TV set and you have >90% 
signal on the scan. I have got good pictures with approx. 55% on the scan.

I assume you're using the latest firmware for the card? I haven't kept up, so 
I don't know what's current.

I also assume you are using the correct frequency table for your source (cable 
or broadcast).

The damaged frames you are getting certainly look like a signal problem, are 
we talking OTA or cable here (ATSC or QAM)? I'm assuming you're in the USA by 
your email address.


-- 
Brian Wood
beww at beww.org