How To Get Rid Of Pixelation

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theoldfarter

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#90282 19-Sep-2011 01:14

I live in Masterton & am 36 Kilometres from the Digital Terrestrial HD transmitter at Popoiti, which is a bit east of Greytown. I cannot see the transmitter.
Dedicated 16 metre run of new RG6, with F connectors crimped on by an antenna installer, into a MagicTV 3600 set-top box, into a 42 inch Plasma TV (no digital tuner).
I do not go through a wall plate, the RG6 comes into the lounge through a hole in the floor.

I have the antenna mounted on the roof, on a 2 metre pole which is secured by a roof mount, with 2 aluminium stays. It does not move around.
I have had an antenna installer up on my roof, aligning my single phased array antenna http://matchmaster.co.nz/uhf-tv-antennas/02mm-mdu18
& taking a signal strength reading. He got 60 decibels of signal. That must be when I am getting no drop-outs.

I have been getting occasional audio drop-outs for a while & some quite bad pixelation. I noticed the following, when I display my Magic TV set-top boxes RF Signal Monitor:

Ch 33 (TV3, Four ,C4) normally fluctuates between 79% - 80% Signal Strength & Signal Quality is 100%.

Ch 35 (TV1, TV2, U, TVNZ7) normally fluctuates between 76% - 78% Signal Strength & Signal Quality is 100%.

Ch 37 (Maori, Prime, Trackside) normally fluctuates between 75% - 78% Signal Strength& Signal Quality is 100%.

Over a ten minute period, the S/S will suddenly drop to low 50's. The S/Q will drop to 90%.
The signal & quality will come back up & drop again straight away to a different reading. My box samples once a second & those large variations take no more than a few seconds before all is normal again ... until the next time. I can have no pixelation for hours some days & other days, a fair bit.

I have tall thin Blue Gum trees 300 meters distance between my home & the transmitter.

With me getting the 75% to 80% S/S, I wonder why the signal fluctuates between those two values. I would have thought that the transmitter would put out constant power?
The antenna installer says that in his installing experience, the trees are far enough away to not cause a problem. If they were blocking/degrading the signal, I should be getting a much weaker signal, not the 60 decibels that I do.

I am going to replace my antenna with a twin phased array, this one http://matchmaster.co.nz/uhf-tv-antennas/phased-array/02mm-mdu36

If, after doing that, I still get the pixelation, what sort of masthead amplifier would I need to try?
It will only ever be used with the UHF antenna, no VHF or FM.
What brands/models are good & what to stay away from?

Hiamie

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#522832 19-Sep-2011 07:41

In my opinion, pixilation is usually a sign of poor signal, which in most cases is due to a weak signal. But not always, as interference, and intermodulation from to stronger a signal can also cause problems. I suggest you watch the UHF analogue signal on your TV for a while to ensure that the received signal remains strong and clear without any intermittent interference etc. If you do see problems with the analogue UHF signal, then you may be able to track the cause down, or optimise the antenna configuration to resolve it. A good analogue signal should yield a stable digital signal without pixilation - I hope!

MikeB4

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#522842 19-Sep-2011 08:12

Have you noticed it is worse in marginal weather conditions such as rain or wind? If you have trees between
your antenna and the transmiter line of sight this may well cause signal degredation exacerbated on windy days.

Given your locale Freeview'e satelite service may be better, it's not HD but you will get more stable reception.

Here is a crazy notion, lets give peace a chance.

B1GGLZ

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#522844 19-Sep-2011 08:13

Hiamie: In my opinion, pixilation is usually a sign of poor signal, which in most cases is due to a weak

+1
Have you access to another STB or Freeview TV for comparison? In my experience I have found that the tuners in STB's are usually far less sensitive than TVs and dedicated Freeview Recorders such as my Panasonic.
Sounds like you will need a masthead amp though. The Kingray from Jaycar is pretty good.

theoldfarter

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#523035 19-Sep-2011 14:18

Hiamie: In my opinion, pixilation is usually a sign of poor signal, which in most cases is due to a weak signal. But not always, as interference, and intermodulation from to stronger a signal can also cause problems. I suggest you watch the UHF analogue signal on your TV for a while to ensure that the received signal remains strong and clear without any intermittent interference etc. If you do see problems with the analogue UHF signal, then you may be able to track the cause down, or optimise the antenna configuration to resolve it. A good analogue signal should yield a stable digital signal without pixilation - I hope!

The Analogue signal has always been consistent in it's reception, which is excellent.
The Digital UHF HD transmitter is 90 degrees from where the Analogue signal is transmitted from.
There is no interferance from the Analogue.

Dedicated UHF HD antenna, not diplexed, run without breaks/joins to the MagicTV set-top box.

theoldfarter

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#523036 19-Sep-2011 14:23

KiwiNZ: Have you noticed it is worse in marginal weather conditions such as rain or wind? If you have trees between
your antenna and the transmiter line of sight this may well cause signal degredation exacerbated on windy days.

Given your locale Freeview'e satelite service may be better, it's not HD but you will get more stable reception.

That's what I am going to observe, when we get some bad weather next.

I have Freeview Satellite as well. I have a good home theatre set-up & enjoy the HD quality & 5.1 sound.
That is the main reason to try to get the reception better.

theoldfarter

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#523038 19-Sep-2011 14:30

B1GGLZ:
Hiamie: In my opinion, pixilation is usually a sign of poor signal, which in most cases is due to a weak

+1
Have you access to another STB or Freeview TV for comparison? In my experience I have found that the tuners in STB's are usually far less sensitive than TVs and dedicated Freeview Recorders such as my Panasonic.
Sounds like you will need a masthead amp though. The Kingray from Jaycar is pretty good.

Unfortunately, no access to either another set-top box or TV with built-in HD tuner.

The Magic TV set-top box is a dedicated Freeview recorder. http://www.magictv.co.nz/MTV3600TD-features.html

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theoldfarter

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#523042 19-Sep-2011 14:52

I have put up the twin phased array http://matchmaster.co.nz/uhf-tv-antennas/phased-array/02mm-mdu36

It has given me 3% more signal strength, according to the meter in the set-top box settings.
i.e. single phased 76%, twin phased 79%.

I will now observe for a week or so, as to what difference to the occasional pixelation it will make, if any.

Not to sure what a masthead amp would do with the signal that occasionally drops down to 50% for a second & then returns, with the corresponding drop in signal quality which results in audio drop-out & occasional pixelation. What do you think?

With a amp, will the signal that drops to 50%, not drop as far?
I know that the antenna will still receive a 50% signal but does not the amp boost that 50% and present a higher percentage to the box?

If so, what level of amplification would I need to get?

The Magic TV box is reported in these forums as not liking too strong a signal.
With that in mind, would I need to get a variable gain amp, if & when I get one?

Thanks for all your responses.

naggyman

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#523082 19-Sep-2011 15:42

In Masterton and get 90% signal strength. We have a reasonably high antenna. When the areal was directly connected to our TV we got 97% but now that it has been put into a spiltter it is between 87% and 90%. No pixelation or anything, sometimes get the audio dropouts.

Morgan French-Stagg

morgan.french.net.nz

Brunzy

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#523158 19-Sep-2011 18:00

Dont waste your money on an amp , and I was also going to suggest you did not need the other aerial.;-)
Were the signals you mentioned at the STBox , or at the Ae?
What you really want to know is what is the BER.
Is the issue on all muxes (Channels )
At 60 dbuv you should have no issues , an amp would only make things worse.
Do you have a cordless phone base unit nearby?
Is the RG6 going straight to the box , or do you have any moulded flyleads.
Possibly interference , but your installer would need a speccy that has a Merogram function , or maybe MER by carrier to prove, easier for you to try and eliminate other possibilities first

theoldfarter

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#524335 21-Sep-2011 23:08

Brunzy, the 3% increase was at the box, shown by it's RF Signal Monitor.

The pixelation appears to be on one mux only, Channel 33, 570 MHz, (TV3).

My cordless phone is approx 5 metres away, in another room.

RG6 goes from the antenna, down the side of the house, up through a hole I drilled in the floor and connects directly to the box. No other leads are used.

There was some stormy weather here a couple of days ago, constant downpour & high winds. I observed the trees, 300 metres distance between the transmitter & my antenna, sway all over the place & it made no difference to the Signal Strength or Signal Quality, shown by the boxes RF Signal Monitor. That monitor showed the same on a sunny day with absolutely no wind.

I believe you when you say a amp will do no good.

I had to Google what BER & "speccy that has a Merogram function , or maybe MER by carrier to prove" is.

I get the feeling that I could spend lots more money getting these things tested & still be no wiser as to what is causing the occasional pixelation.

I have the box on TV3 for the last 20 minutes & the SS is 79/80 & SQ 100. Go back to the picture there is no pixelation happening. I just watched NCIS that I recorded last night & it was fine.

I may have to just live with the occasional pixelation.