[mythtvnz] Pixellation Every ~ 20 minutes

[Curtis Walker]

On 7 October 2012 15:43, Stephen Worthington <stephen_agent at jsw.gen.nz> wrote:
> On Sun, 7 Oct 2012 11:34:33 +1300, you wrote:
>
>>5. For some reason I can't check live signal strength using Alt+F7
>>which would help check if this is a signal/lock problem. I might just
>>swivel the aerial to Te Aroha instead of Hamilton Infill today, do a
>>retune and see if that helps. I used to use Te Aroha previously (well
>>before the current issues though).
>
> Going back to first principles here, just how sure are you of your
> signal levels?  The last time I had problems like yours, it turned out
> that our VHF antenna had come loose in the last gale and turned around
> until it was touching the UHF antenna.  That resulted in a loss of
> signal strength.  But I did not figure it out until I just happened to
> be looking at our roof one day and noticed the misaligned VHF antenna.
> All the signal strength and quality readings I was getting from my
> tuners said they were OK (or what I thought was OK).  But of course,
> each different tuner was reporting different numbers - only identical
> models will ever report the same.  What I actually had was marginal
> signal levels, and every so often the recording would have a bad
> patch, just like you are seeing.  The bad patches, like yours, did not
> seem to be occurring randomly - there seemed to be a pattern to when
> they happened, so I was looking for other problems initially.
>
> On fixing the VHF antenna, the reported signal levels only went up a
> little, but everything was working again.  So the levels before my
> problem must have been just on the good side, and during the problem,
> just on the bad side, of OK.  Since then, I have added another antenna
> amplifier as I have added another tuner to my mother's MythTV box, and
> that has boosted the levels way higher.  The VHF antenna has moved
> into contact again after more wind, but is not causing any problems so
> I am considering just leaving it like that.
>
> So, it might pay to check the antenna, the cables, splitters and
> amplifiers, just to make sure.  I have heard of problems caused by the
> dog or kids playing or vacuuming over the cables, and them coming just
> loose enough to cause problems.  And corrosion is an ever present
> danger, although where you are is not close to the sea salt that
> virtually guarantees a short life for any TV antenna.
>
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I can embarrassingly report that I *think* this is a signal problem.
Although the numbers look good, and the rest of the recordings are
glitch free, and it seemed to occur after a set period (indicating a
possible buffer or process problem).

Swinging the aerial to Te Aroha today, using the TV's in-built signal
meter and a compass to direct, I managed to increase baseline signal
strength to 80% and quality to 100%. The pixellation still occurred
during a recording in myth, but was a bit less - and when I watched
the actual TV (Panasonic VT20) during the mythTV live TV recording
pixellation, the signal quality was between 10 and 20%.

Interestingly, the TV itself had a worse picture than mythtv (so the
buffers are actually doing their best to maintain picture during
signal drop outs).

Seems like I'm back on the track to solving this despite some apparent
(to me at least) red herrings.