[mythtv-users] PVR-150 Tuner Quality Issues
beww at beww.org
Mon Apr 17 10:40:57 UTC 2006
On Apr 16, 2006, at 9:51 PM, Michael Horn 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
> Anyways, the picture is looking much better now, and the only
> remaining problem is of the interference the picture seems to be
> picking up on some channels. Wander, you suggested grounding my
> case, whats the best way to go about this to ensure its properly
> And what other sources of interference should I be on the lookout
> for/ what can I do to try and prevent them? I've tried to keep the
> unit as far from the rest of the electronics as possible, including
> speaker wiring and power cables. I have a dsl connection, so
> interference from cable internet isn't an issue tho it was a good
> Finally I believe the interference is restricted to just my myth
> box and not something picked up elsewhere in the cable line as the
> rest of the tvs in the house show no symptoms.
Wish I could see the interference, any chance of posting a link to a
screenshot ? A picture's worth 1K words. (are links OK on this list ??).
Ingress from the outside world can cause interference, usually worse
on some channels than others. That's why I wondered about a bad/loose
cable/connector. It can be hard to get connections sufficiently tight
on tuner cards, and you want to be careful to not over-tighten.
Normally this type of interference will be worse on channels used for
"off-airs" in your area, and on mid-band channels 14-22 (this can be
confused because your system might be "mapping" channels, so their
apparent number might not be the real allocation).
If your cable system is carrying FM signals an FM trap to block them
might help, they are around $3 at Radio Shack.
Interference can be caused by too much signal, much over +15dbmv can
cause beat products in the front-end of your tuner. While this is an
unlikely problem, given how signal-stingy cable operators are, you
might try inserting an attenuator in the line just to check.
The case grounding was a good suggestion, especially if you are
seeing 60/120 hz. hum (one or two horizontal bars floating slowly up
through the picture). What I did was get a "grounding block", which
is a female-female F-connector with an attachment point for a ground
wire, normally found outside the house, and connect it near the
computer with a #12AWG copper wire running from the block to the
computer case, it helped a lot for the AC-hum. UPS systems really
should have isolated grounds, but most consumer units do not.
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