[mythtvnz] Pixellation Every ~ 20 minutes

Sat Oct 13 22:39:33 BST 2012

On Sun, 14 Oct 2012 08:39:33 +1300, Nick Rout <nick.rout at gmail.com> wrote:

>
>
> On Oct 14, 2012 8:12 AM, "Paulgir" <paulgir at gmail.com> wrote:
>>
>> 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.
>>
>
> Why point your antenna in the wrong direction? Either it is pointing at  
> the transmitter or it isn't.
> Why not turn the amplifier back up so the TV works and then attenuate  
> the signal for myth's tuner?
>
>> Finally,can anyone tell me which signals ,in Auckland, originate from  
>> the Sky Tower and which from Waiatarua?
>
> I understand both transmitters transmit all 3 multiplexes. You need to  
> be pointing at one or the other.
>
>>
>> -Paul
>>
>>
> I'm not too concerned with the TV's internal tuner reception as I never  
> use it- all viewing is through Myth - >it was just an observation.
The signal can't be attenuated independently with the current set-up,I  
would need to get an inline attenuator which isn't a problem ,but I don't  
have one here at the moment.

My 35 years as a radio/electronics service technician tells me that in a  
hilly landscape, pointing directly at a UHF/VHF transmitter mast is not  
necessarily going to get you the best result.As I don't have expensive  
signal analysis equipment,I have to find the best orientation by trial and  
error.Moving a UHF antenna 100mm horizontally can make a huge difference  
in signal quality in some locations.

-Paul
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ourshack.com/pipermail/mythtvnz/attachments/20121014/1796e4ea/attachment.html>