[mythtv-users] Analog tuner picture grainy
beww at beww.org
Tue Apr 14 12:37:26 UTC 2009
On Tuesday 14 April 2009 04:24:41 Steve V wrote:
> I think I have found the reason for my grainy picture. It seems to be some
> sort of interference in the current location of my backend computer. Moving
> everything to another location in the house improved things to almost DVD
> Now I just need to figure out what is causing the interference and I can
> put the backend back where it should be. I did think it was the PC itself
> but moving the PC cured the issue so I assume the problem is with the
If the new location has the machine plugged into a different AC outlet that
might be the difference. You might have dirty power, or some sort of common
mode interference, meaning the grounding might have problems at the original
Myth machines are prone to grounding problems due to the coax input cables
(CATV or antenna) having a different potential than the AC power ground (and
if you have externally-powered USB or F/W devices that's another ground
path). Audio cables can also cause problems, one reason to use optical
connections if you can. The cable from your machine to your monitor can also
cause trouble, especially if poorly shielded. The video cables with the
ferrite beads or blocks can help this situation.
Radio Shack sells ground-loop-busting analog audio cables, I've seen them
solve problems, but usually with audio hum.
WiFi and bluetooth devices, or any other RF, likes to get into things as well.
I have found consumer-grade AC power surge protectors to be generaly useless,
and sometimes actually cause problems themselves. Even the ones that work use
MOVs that are not self-healing, so once they take a shot they become
expensive standard power strips or worse.
(The self-healing units are slightly radioactive, so manufacturers don't want
to get into the restrictions involved, even though they are less
problematical than ionization type smoke detectors).
beww at beww.org
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