UHF reception issue

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Rikkitic

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#237929 25-Jun-2018 09:42

I live in an area surrounded by hills with marginal UHF reception. We have a DIY antenna installation on a high mast using a triplex like the one in this illustration. For several years this antenna has worked well. More recently we have started having reception issues, mainly with the TVNZ mux. The antenna is difficult to work on but we brought it down once, discovered some rust damage, cleaned and checked it, and put it back up. This did not improve our reception, however.

The TVNZ channels are significantly weaker than other muxes. Sometimes we get fairly bad pixelation on them, other times they are perfect, even for several days. I can find no pattern to the differences. They don't seem to be related to weather or wind conditions, or any other obvious variables. Sometimes it just works well, other times not. The only thing I have found that might be a factor is tropospheric ducting, but I have no idea if that is actually affecting this.

I don't know what the signal and quality indicators on our receiver actually measure, but on TV3 both are always steady on 100%. On TVNZ the signal is usually around 86% with the quality jumping between about 35% and 60%. As far as I can tell, these differences do not seem to affect our pixelation much. Sometimes we get a good picture for long periods, sometimes not, but in both cases signal and quality measures remain about the same.

I want to fix this issue if I can and I would like to know if anyone has any ideas or suggestions about this. Would another antenna or a masthead amplifier likely make a meaningful difference? I have a masthead amplifier and as an experiment I connected it at the receiver end of the cable. I did it this way because of the difficulty in accessing the antenna. It did improve the signal and quality measures, but it did not prevent the pixelation. I don't know how much difference it might make if correctly installed at the antenna end, but because of the difficulty of doing this, I am not keen unless I could be fairly sure it would really help.

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#2043445 25-Jun-2018 10:33

How old is the cabling? If antenna had rust, then cable and connectors could also be suspect?

Might be time for a brand new antenna plus re-cable by a professional installer? (At least that way you are covered by Warranty etc).

ObidiahSlope

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#2043471 25-Jun-2018 11:29

Do you have trees nearby which block the line of sight between the the antenna and the transmitter?

I know of someone whose DVB T reception works/doesn't work depending whether the deciduous trees blocking the line of sight have leaves on them.

If you are using braided coax as your feed investigate upgrading to RG6 coax.

Obsequious hypocrite

Rikkitic

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#2043473 25-Jun-2018 11:29

Installation is about 7 years old. Cabling is 25 meters of RG6. No obvious signs of deterioration when I checked it. Professional installation is not an option because of our location and mast height required. It would cost way more than it is worth to us. Either I fix this myself or learn to live with it.

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Wiggum

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#2043481 25-Jun-2018 11:56

Very difficult to provide recommendations without an idea of transmitter location, your address, environment etc. If it was working well before something has changed somewhere.

We have line of site to transmitter in Waikanae and have also sometimes suffered from same issues you are reporting. It got bad about a year ago, also with the TVNZ channels. What I did was just select the worse of the lot. Selected the Tivo signal quality option on the Tivo. Then got up on the roof and moved it around until we found the optimal signal. My wife stayed in the lounge and she just shouted out the window when the signal was the best. That sorted it out for us without the need to call in any professionals. Pointing directly to the transmitter for some reason is not always the best.

Rikkitic

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#2043485 25-Jun-2018 12:07

UHF signals do bounce and reflections sometimes provide better reception. As I recall (no longer certain) we originally pointed the antenna at the transmitter and left it at that since the reception was good. There are hills around us and we do not have direct line of sight. We are also officially outside the reception area because of the hills. Our location is Raukawa and the transmitter is Mt Erin. I am going to try repointing the antenna but it is not straightforward and requires some preparation.

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Brunzy

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#2043505 25-Jun-2018 12:50

It’s called a masthead for a reason ;-)
I’d be surprised if it didn’t help, remember you’ll have more signal (Approx 5dBuV) and less noise at the top of the mast.
Before you do I’d suggest if you can get someone to watch the signal and quality levels on the TV, try sliding the antenna up or down ( highest is no always best) within approximately 1 m whilst pointing in the same direction as now ,and see if you can get a better quality level.
If you do you can also try rotating it slightly left and right for maximum ,but please check the other in boxes to make sure none have deteriorated , you may have to make some sort of compromise to get them all within an acceptable range.

If you have obstructions in the way this can make a significant difference but if you are a long way from the Transmitter not as much

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Wiggum

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#2043511 25-Jun-2018 12:56

Rikkitic:

I don't know what the signal and quality indicators on our receiver actually measure, but on TV3 both are always steady on 100%. On TVNZ the signal is usually around 86% with the quality jumping between about 35% and 60%. As far as I can tell, these differences do not seem to affect our pixelation much. Sometimes we get a good picture for long periods, sometimes not, but in both cases signal and quality measures remain about the same.

This sounds really odd. 100% on certain channels, I don't think mine is even that high and we have LOS. If its really 100% on certain channels then I would guess that should rule out any antenna/cable issues. you may find that re-pointing that antenna slightly will increase signal quality on low signal quality channels, and lower signal quality on high signal quality channels. Its all about finding that sweet spot. I have found that anything near/below/or around 65% sometimes has pixelation.

Rikkitic:

Our location is Raukawa and the transmitter is Mt Erin. I am going to try repointing the antenna but it is not straightforward and requires some preparation.

Also check that the antenna cable is plugged directly into your TV. (No splitters or anything like that). This may help you problem solve the issues. I have also found that our Freeview TV for example is able to cope better with low signals than our Tivo box. So you may want to try plugging that antenna into something else to rule out any freeview hardware as your problem. have you Installed any new freeview hardware lately?

Rikkitic

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#2043540 25-Jun-2018 13:41

OK, since this is going somewhere here are some more details: At the moment we have three UHF receivers. One is an old Orton box I bought 7 years ago when we originally installed the UHF. Like most Chinese gear, it has some irritating quirks and inconsistencies so I don't use it anymore. For one thing, we turn off the power to most devices at the wall when we go to bed and the Orton has trouble remembering its settings. There are also some other things. But it does still work and is useful for comparisons.

Our Sony Bravia has its own DVB-T built-in but flexibility is limited and we don't like it. But it is also good for making comparisons.

The latest is a Mecool box I recently bought and have posted about elsewhere. This has satellite and UHF as well as Android for streaming. I had high hopes for this but have encountered some disappointments. But it is the one I am using at the moment, for both UHF and satellite.

The measurements cited above are from the Mecool. It always gives 100% for both readings on Mediaworks, and significantly less on TVNZ, which is also the only mux I have pixelation on. I don't know how the transmitters are set up but I have always assumed they were on the same mast. In any case, TVNZ used to work fine, now it doesn't. Maybe they have changed something.

The antenna is always plugged directly into the receiving device. There are no splitters or other things in the way. All three UHF receivers give similar results. Both the Bravia and the Orton display similar levels of pixelation. The Mecool seems to process this differently. Instead of displaying any pixelation, it freezes the image briefly then jumps ahead when the picture returns (sound usually continues normally). The periods of freezing seem to correspond closely to periods of pixelation.

We are a fair distance from the transmitter, maybe 20 kms or so. The hills obstructing our LOS are not immediately in front of us, so the signal still gets through. The nature of our home-made mast is such that it is very difficult to make any adjustments on it. Rotation is doable. Height adjustments are not. The mast would have to be brought down, a major undertaking, then put back up to test any changes. This takes a half day and is difficult on our steep, high roof. It is not something we like doing.

The most perplexing aspect of this is that sometimes we get perfect reception on all channels, including TVNZ, and this can continue for days. Then we go through a period where we get constant pixelation on the TVNZ mux. Then it improves again. I have no idea what can be causing this. It does not seem related to any obvious changes in weather or wind. I suppose with digital that if the TVNZ mux is right on the edge, it doesn't take much of a difference to go between perfect reception and crap reception. But I don't know what can be making that difference.

That is everything I can think of.

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Wiggum

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#2043547 25-Jun-2018 13:56

Rikkitic:

The nature of our home-made mast is such that it is very difficult to make any adjustments on it. Rotation is doable. Height adjustments are not. The mast would have to be brought down, a major undertaking, then put back up to test any changes. This takes a half day and is difficult on our steep, high roof. It is not something we like doing.

Sounds like you have a very complicated setup.

If you are going to be taking the antenna down, then why not put on one of those remote control antenna rotators? I had a friend that had one and it worked pretty well. That will save you time in the future if you ever need to adjust it again (And you will need to adjust it again). Also while up there, install the master head amplifier and be done with it.

Rikkitic

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#2043568 25-Jun-2018 14:30

When we originally did all this, we discovered that the antenna had to be pretty high off the roof to get an adequate signal. I think it had to be at least four or five meters. But the roof was steep and high on an old two-storey farmhouse and was made of tin. The only reasonable way to do the antenna was to put it on top of a long, steel mast made of pipes welded together, which were then strapped to the chimney (the only support point available). A proper tower would have been prohibitively expensive and maybe structurally impossible. We did the best we could with what we had. That is also how we will have to continue going forward. I'm just looking for ways (if there are any) to improve the existing set-up as much as possible. I will try rotating the antenna to slightly different positions, which is at least achievable.

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Brunzy

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#2043573 25-Jun-2018 14:37

Was the mast originally installed for an analogue transmission?

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Rikkitic

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#2043587 25-Jun-2018 15:09

No. I did use an analogue signal from Prime or Maori TV to locate the transmission site but the mast has always been only for DVB-T.

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Brunzy

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#2043610 25-Jun-2018 16:08

My reason for asking was if you’re not too close to the hills , then generally there will be somewhere on your roof at an easy working height, 1–2 m where there will be an acceptable signal.
The signal generally varies most in a perpendicular line to the transmitter but it’s not that easy without the proper equipment.
The Sony shows BER levels ,If your aerial is already 5 m up the pole then you have that amount of cable to wander around the roof and see if you can find a quality signal,
whilst someone checks the diagnostics below.

Rikkitic

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#2043656 25-Jun-2018 16:33

Good points. I no longer remember what we did initially but I'm pretty sure we would have checked different locations before going to the trouble of putting up the long mast. If and when we bring it down again, hopefully not until some time in the summer, we might check that. It would certainly be handier if the damned antenna did not have to be so high.

The hills are not that close, maybe a couple kms away. Perpendicular to the transmitter is mostly down the steep sides of the roof. On one side that might bring us into the trees (I would have to check), on the other side, below the roofline. One thing the high mast does is avoid that problem.

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B1GGLZ

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#2043658 25-Jun-2018 16:41

Can you post a photo of the mast and antenna?

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