[mythtv-users] PVR-150 Tuner Quality Issues

Steven Adeff adeffs.mythtv at gmail.com
Mon Apr 17 13:16:38 UTC 2006


On 4/17/06, Brian Wood <beww at beww.org> wrote:
> On Apr 17, 2006, at 6:46 AM, Steven Adeff wrote:
> > On 4/16/06, Michael Horn <mjhorn at gmail.com> wrote:
> >>  Thanks everyone for the input so far. I've made some progress
> >> with the
> >> picture quality, through a combination of fine tuning the
> >> frequencies as
> >> well as adjusting some of the brightness,contrast etc settings on
> >> the card.
> >> Ive been adjusting the brightness and whatnot using ivtvctl -y
> >> brightness=xxx, but it seems that this is reset by mythtv each
> >> time the
> >> channel is changed. are there global or possibly per channel
> >> settings within
> >> myth I should be using instead?
> >
> >
> >
> > You can also buy a grounding block for your cable (few $$ at Radio
> > Shack or Home Depot). Or just buy a Home Theatre surge supressor that
> > has a cable/sat/ant passthrough which will ground and sometimes filter
> > for noise your cable/sat/antenna. If your using a UPS for your Myth
> > computer DON'T combine it with a surge supressor! But you can use one
> > for other equipment in your home theatre and run the cable/sat/ant
> > through it,
>
>
> I've found that the ground potential of your AC power wiring and that
> of your TV cable are almost never the same. In my case they are
> almost 2 volts different at my computer location, and this makes
> sense because both services are probably using different ground
> references, and the resistance of the grounding conductors will
> differ due to different distances, types of conductors etc.
>
> Add to this some devices that ground at multiple points, USB capture
> devices have "ground" at the RF connector shield, the USB connector
> and (possibly) the DC power supply, all of which are just about
> guaranteed to be different.
>
> The best bet is to tie all of these together at close to the computer
> as possible, but grounding can be a tricky thing, an sometimes
> lifting grounds from things and allowing them to float can actually
> improve things.
>
> In any case, if you play around with grounding, top priority should
> be given to the "safety" ground of the PC case (as opposed to the
> "neutral" of the AC power system, or the various signal grounds). You
> really do not want to wind up with a case that's "hot" with respect
> to earth ground, which could cause things like your family collecting
> on your insurance policy.

unless there's a short in your computer your case will never have
enough voltage to kill someone sitting on it, your powersupply would
shut off before that happened. As well, a single phase AC power system
does not have a neutral, just two prong power and a possible ground.
Your house ground should all be tied together before it reaches earth
ground, sometimes this isn't the case, but since your earth grounds
will be closely tied to earth and given the low amount of power
running through your home's ground the voltage on them should be
within millivolts of each other. That said, just make sure your
electrical equipment that requires a ground (ie has that 3rd prong) is
has a properly grounded wall socket and tie your cable line's ground
to it using a ground block or a Home Theatre surge suppressor. If your
equipment is not leaking voltage to ground (ie not broken) then all
the equipment will be referenced to the same ground and you won't see
a ground loop issue.

--
Steve


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