[mythtvnz] Pixellation Every ~ 20 minutes

[Paulgir]

On Mon, 08 Oct 2012 20:39:58 +1300, David Lowe <david at thistledown.co.nz>  
wrote:

>
>
> On Mon, Oct 8, 2012 at 8:40 AM, Paulgir <paulgir at gmail.com> wrote:
>> On Sun, 07 Oct 2012 18:01:44 +1300, Curtis Walker  
>> <sultanoswing at gmail.com> wrote:
>>
>>
>>>
>>> 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).
>>>
>
> For what it's worth (probably not much...) I have been watching this  
> thread closely for clues... last weekend >(the weekend some parts of the  
> country went solely digital) something happened to my reception. I'm  
> north of >Christchurch, reception a bit marginal at the best of times. I  
> notice that since that weekend, all channels are >reporting a weaker  
> signal; the Kordia multiplex being the worst and barely usable at 34%.  
> Others are OK at 45%.
> I figure all I can do is erect the new high gain antenna sitting in the  
> garage (along with the round tuit).
> But surely its no coincidence that the signal suddenly got weaker the  
> same weekend analogue started to get >turned off?
>
> - David

I have made some adjustments to my signal based on the suggestion that too  
much signal may be upsetting the tuners.

My pixellation problem closely follows Curtis Walker's description:

"On all TV recordings, after around 20 minutes, the picture starts  
becoming pixellated. Over the next 30 or so seconds it becomes more and  
more pixellated until it looks like an impressionist painting. The sound  
is generally OK, but does have the odd, brief "glitch" (a noise like a  
modem negotiating). After no more than a minute, the picture and sound  
suddenly return to normal."

I'm about 55km from the Waiatarua transmitter and can't drive the TV with  
an un-amplified signal so I have a mast-head amp which has adjustable gain  
and a 3 new 91 element antenna.I have had the gain set to 30+ dB.
The TV never showed pixellation when using the internal tuner.

The signal condition as displayed by the TV with the gain at 30+ dB is:

TV3   570 MHz   Quality  8  signal 9
TVNZ  538 MHz   Quality  10 signal 10
Prime 666 MHz   Quality  10 signal 10

The display goes to 10 ,so TVNZ and Prime are probably off the scale as  
far as signal is concerned.

On Friday I reduced the gain to around 20 dB the weather was fine with  
light winds:

TV3 570 MHz Quality 6 signal 6
TVNZ 538 MHz Quality 10 signal 10
Prime 666 MHz Quality 10 signal 9

I seem to be getting less pixellation events on TV3 although they may be  
longer in duration on TVNZ.

Yesterday the weather was crap; rain and wind was moving the trees and the  
antenna.

TV3 570 MHz Quality fluctuates from 2 to 10 ;signal 4 to 6
TVNZ 538 MHz Quality 10 signal 9 to 10
Prime 666 MHz Quality 9 to 10 signal 8

The TV's internal tuner was having trouble with TV3's signal - brief  
picture freezes and pixellation.

The MythTV reception,however, was better.TV3 was exhibiting,more  
frequent,brief,1 or 2 second duration pixellation, events that no longer  
showed a steady 1 minute long degradation to a full "impressionist  
painting" effect before correcting itself.TVNZ and Prime did not have  
these brief events but did have fewer (1 in an hour)of the longer  
pixellation events.

I think the next step for me will be to re-orient the antenna to see if I  
can balance the TV3 signal deficit against the Prime,TVNZ signal and then  
maybe find a more optimal gain setting that is good for all 3 signals.

Finally,can anyone tell me which signals ,in Auckland, originate from the  
Sky Tower and which from Waiatarua?

-Paul
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