Deteriorating UHF reception

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Rikkitic

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Topic # 193594 16-Mar-2016 13:17

Although I live in a marginal area, my UHF reception has always been perfect thanks to a very high aerial on the roof. Now, just since the last couple of days, reception of TV3 and Four has suddenly deteriorated. I get a lot of pixellation and partial frames. My receiver does not have much in the way of diagnostic tools, but it does give a quality measurement and that bounces between +/- 40 and +/- 80. I have perfect reception on all other channels and the quality reading stays between 80 and 90 or so. It only drops below 80 on TV3 and Four. I assume this is just a signal strength indicator of some kind.

To help me diagnose this, I need to know if anything has changed at the other end. Does anyone know if anything is going on with the Mediaworks transmissions? Could this have anything to do with the arrival of Duke? I just rescanned all of my frequencies and I see no trace of Duke, but am not sure if I should. Any help on this would be much appreciated. I don't think anything has happened to my antenna, and it would be a real pain to fix if something has, so I'm hoping to find an explanation elsewhere.

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Reply # 1514430 16-Mar-2016 13:34

How old is your "very high aerial "? Any recent storm damage?

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ubergeeknz

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Reply # 1514434 16-Mar-2016 13:39

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I'd be having a look at your antenna first for any damage, just a quick visual inspection might reveal the problem

Rikkitic

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Reply # 1514618 16-Mar-2016 17:25

The aerial has only been up since 2011. I'm not aware of any damage though we have had some high winds recently. Usually I check it after a storm to see if it is still pointing in the right direction but I haven't looked recently as I have been immersed in another project. I will check it out.

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fe31nz

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Reply # 1514702 16-Mar-2016 20:20

Rikkitic:

To help me diagnose this, I need to know if anything has changed at the other end. Does anyone know if anything is going on with the Mediaworks transmissions? Could this have anything to do with the arrival of Duke? I just rescanned all of my frequencies and I see no trace of Duke, but am not sure if I should. Any help on this would be much appreciated. I don't think anything has happened to my antenna, and it would be a real pain to fix if something has, so I'm hoping to find an explanation elsewhere.

Duke is a TVNZ channel, so it is unlikely to be broadcast on a MediaWorks mux. Since TV3 and Four are affected, have you checked the other channels on the MediaWorks mux - usually TV3 PLUS1, Four PLUS1 and The Edge TV? If they are all affected, and not any channels from other muxes, then it is likely that the MediaWorks transmitter has gone to a lower power for some reason. It still could be your aerial setup though - when things go wrong, the lowest power mux is the one likely to see problems first, and also the highest frequency mux, if they are all the same power. Apart from the aerial, another common problem to check for is that the aerial connections inside the house are still fully plugged in. Vacuuming around the cables, or kids or pets playing can cause them to come loose unless they are all F-connectors.

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Reply # 1514739 16-Mar-2016 21:38

All good points. I got sidetracked by some other problems tonight but I will go through all this systematically tomorrow. I didn't check Edge but the plus ones are also stuffed so it is definitely the mux that is being affected. The frequencies of Mediaworks and TVNZ all seem close together, around 530 mhz or so, and I don't think that is likely to be a factor.

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raytaylor

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Reply # 1514775 16-Mar-2016 22:56

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Stuff to check:

Antenna

- Wind may turn it off the correct bearing
- Neighbours trees may have grown in the path
- New buildings affecting the fresnel zone
- Rust

Masthead amplifier (if you have one)
- Ingress water
- Transformer power supply died (sends power up the coax cable for the amplifier to work)

Internal amplifier or splitter (if you have one)
- Usually in the attic, behind a tv or homehub
- Power supplies can die

Coaxial Cable
- Needs to be UHF grade. VHF worked for me for a number of years until a tree grew in the path. The loss caused by the tree this summer and the existing loss on the VHF cable added up to drop the signal below the minimum required for the tv to decode the data and freezing started.

- Water can get into it and corrode

- Rats and mice like to chew on it in walls and attics

Decoder/Set top box / TV

- Heat over time can damage the radio chipset in the decoder and lower its sensitivity. Especially if a set top box is located in a closed cabinet.

Ray Taylor
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Rikkitic

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Reply # 1514904 17-Mar-2016 10:19

OK, problem solved. Thanks for the tips everyone. It turned out to be the antenna connection to the STB. Either the cable connector or the socket itself is iffy. I have never had trouble with it before and I don't remember touching it before the problem started, which is why I didn't think to look there in the first place. On reflection, I might have shifted some things around. The cats also like to sit there for the warmth.

It is not a complicated set-up. No amplifier, splitter, or anything like that. Just a straight RG6 cable run to the tri-boom high-gain antenna. Still no sign of Duke, though. Is it supposed to be transmitting on uhf now?

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Rangus

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Reply # 1516693 21-Mar-2016 07:42

You need to make sure the signal arriving at your Stb or at your tv has a quality of at least 90% and signal strength of around 30 to 40%. The signal strength overall on all freq should be around 55 to 60% dbuV over all freq on the terrestrial platform other wise if the signal is stronger than that you will get pixelation at different times .
If you running a yagi antenna and masthead amp maybe to strong. That's what I have found. I invested in a triple boon Matchmaster Dat75 UHF antenna it replace my yagi antenna and my amp where I live and made a big difference. At end of the day you need a terrestrial signal meter to read what you are receiving from you antenna. Hope that helps.

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Reply # 1516737 21-Mar-2016 10:13

I've just had a bout of pixellation on ch36 with other channels ok. The tv diagnostic showed all chans 75-85% strength, 3 at 100% quality and ch36 quality hopping up and down. Initially thought transmitter problem but reading this thread started checking cables. Found connector at tv had screen possibly touching centre. Now all chs 75-85% strength, 100% qual. Is that strength a really a potential problem?

Rikkitic

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Reply # 1516756 21-Mar-2016 11:09

Seems to be. That is what I experienced. Digital tends to be all or nothing. If you are right on the edge, but just over, you get perfect reception. If you are just under, it all falls to pieces. My connection problem was attenuating the signal, but it didn't bother the stronger channels, only Mediaview.

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Reply # 1516874 21-Mar-2016 13:01

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I had a similar issue with UHF signal to a Panasonic STB. Turned out that the HDMI connection was somehow affecting the UHF signal. I swapped the HDMI cable to a cheap one and the problem was fixed. I don't remember where I read it but seem to recall that HDMI interference with Panasonic STB's is fairly common.

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Reply # 1516931 21-Mar-2016 14:06

Given Duke has repurposed the TVNZ Pop Up channel, could it be that you have it already programmed in as something else, or it's identifying as the wrong channel when you scan for it?

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Rikkitic

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Reply # 1516932 21-Mar-2016 14:10

It definitely wasn't there when I looked for it. Pop-up channel was as usual. Maybe it is there now. I haven't checked again.

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littleheaven

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Reply # 1516953 21-Mar-2016 14:32

Rikkitic:

It definitely wasn't there when I looked for it. Pop-up channel was as usual. Maybe it is there now. I haven't checked again.

Have a look at the pop-up after 6pm and see what's showing - they're broadcasting Duke on it but I've seen reports it's still identifying itself as TVNZ pop-up.

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Reply # 1517046 21-Mar-2016 16:35

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kharris:

I had a similar issue with UHF signal to a Panasonic STB. Turned out that the HDMI connection was somehow affecting the UHF signal. I swapped the HDMI cable to a cheap one and the problem was fixed. I don't remember where I read it but seem to recall that HDMI interference with Panasonic STB's is fairly common.

The only way I can think of for an HDMI cable to affect RF reception is through ground problems, such as a ground loop introducing overwhelming 50 Hz hum. There should normally be no interaction between the two signals, but it is possible to design the circuit board in a product so badly that the grounding can become a problem. I do wish they had made HDMI an optical signal.

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