TV aerial woes, kind of...

In article <118usjp$17ta8$ snipped-for-privacy@dont-email.me, John Rumm <see.my.signature@ nowhere.null> scribeth thus

How close to the TV and or aerial amp is this unit can you say?, as we have higher powered 5.8 G links up on our TV aerial with no adverse u issues it does seem rather odd I'd normally suspect that overloading the aerial amp and causing intermod ..

Mind you 35 miles away from that TX is likely to be a weak "ish" input signal, its not the most powerful one in the country!.

You sure you didn't mean Kilometres or by road?..

The amp is level with the top of the chimney - mounted on the mast near the lashing kits. So probably straight line distance from the WiFi aerials is say 6m. However that will be through at least 5 layers of foil lined plasterboard...

I did wonder that at the time when I realised what the cause was (the amp PSU and the splitter is probably only 1.5m from the wifi source).

However with hindsight I am somewhat sceptical. Partly because the aerial install is fairly well screened - all dual screen foiled coax, F connectors, metal clad splitter, and the internal construction of the PSU itself is impressive with the RF elements fully enclosed in a metal screening box. (although obs the aerial itself is not screened!)

However the more conclusive evidence is the fact that the TV in our bedroom was still working fine, as was my network connected TV tuner, and that is in the same comms cabinet as the router (although the wifi aerials are on mag bases on top of the cabinet). Both fed from outputs on the same splitter. I suspect it is a weakness in the LG tuner design. (the bedroom HiSense is only about 1.5m from the exterior wifi AP, and that still has 5GHz enabled at about 60% max power). Might be worth experimenting a bit since I can control the maximum wifi output power.

Yup 35 was an over estimate, I just measured it on google earth - it is just over 27 miles line of sight to Sudbury. When I installed the system I was balancing analogue and digital channels at the time, and not all the digital channels were being transmitted at full power, so used a decent quality 18 element Yagi and a variable gain amp so I could set a suitable level that would work for all.

Although I note that the local relay station (which only carried the public service muxes at the time I designed the system), now carries all six, and also operates as a SFN mirroring the Sudbury channels (29, 32,

So after all that, it was back to glitchy reception again today on all but the HD channels. The plot thickens... (still seeing 60+ dB on the text meter at the end of the co-ax going into the TV)

Another thing which I found by trial and error can affect Freeview reception is (some) LED lamps.

Our aerial is mounted above the eaves of a single-storey part of the house. Below the attic space is my study and next door to that is the lounge. The aerial cable runs through the loft space and down into the lounge. I hade a home-made PVR - a Raspberry Pi running TVHeadend with a USB Freeview adaptor connected to the aerial.

I noticed that recordings on BBC channels often had lots of glitches, but only later in the evening. It took me an embarrassingly long time to realise that late in the evening is when lights are turned on. Then I began turning off lights in turn to see if any of them cured the problem.

It turned out to be two LED GU10 lamps in a five-lamp fitting on the ceiling of my study, so directly under the TV aerial. I replaced those with lamps of another make, and all was fine. And the lamps which caused the interference were fine elsewhere in the house, further from the aerial.

What was weird was that it was a very precise frequency that was being interfered with. For my transmitter (Belmont) Mux PSB1 (for BBC channels) is on 482 MHz and the lamps were interfering with it. But other muxes on 490 MHz and 506 MHz were not affected at all: the signal strength and signal quality (SNR) readings were not affected, and I recorded an hour-long programme from all three muxes in turn and only BBC One (or any other channel in PSB1) was affected; channels on the other two had zero data errors, both with those lamps on and with them off.

The fact that both lamps of the same make did it looks like a design problem rather than a rogue component in one of them.

Unscreened wall plates?

Odd - I am close to Sudbury. Maybe 34 miles.

Ive got a log periodic in the roof feed a distribution amp. Mostly its flawless.

Trying to run off Sandy heath which is 35 miles away and the other side of hills, its very dubious, but the other side of those hills i'ts the preferred transmitter

Was it windy?

High signal level is no guarantee of quality if you are getting multiple

Oh there is somewhere a website that takes your postcode and analyses the terrain in between you and the nearest transmitter

QAM is pretty good at dealing with reflections off fixed items - its designed for that. I've generally found that aircraft, waving trees or long distance tropsheric skip is the major problems

I,e, there are Dutch transmitters directly 'behind' Sudbury from my location and in very cold weather I get breakup on Sudbury transmissions In the analogue days I could even see the pictures from these transmitters.

I have no trees in line of sight for at least 300 meters, but other people in this area who do have some issues. Even with good signal strength,

Very little air traffic beyond the odd warbird from Cambridge is ever over here, so again I don't have problems with that.

I dunno if your TV displays it, but there is often a 'signal quality' meter of some sort. Sometimes you can use that in conjunction with changing aerial position to optimise signal levels

I had to change aerials to one better suited to Sudbury digital. I've got a log periodic in the loft now that works very well.

Yup that is one weakness - some of the cable runs came with the house and are nothing special "low loss" coax into vanilla wall plates. The newer runs I have added are all in WF100 and modular screened wall plates. There are only two TVs in use at the mo, and one is on old coax. I could disconnect the unused ones...

Does beg the question though why the change in the last couple of weeks? It could be something outside of the house.

I might change the masthead amp - I have one on order that has 4G/5G filtering, and is also narrower band (only goes to chan 49).

Until recently, that was the case here...

Not really.

I could see some variation in signal level on Terry, but even at its lowest, still well above what I would have expected to be required.

(although worth noting when I was reading 60dB+ at the set back, while it was glitchy. Adding a 6dB inline attenuator was enough to get the TV to report "no signal")

It looks like it is a quality rather than quantity issue.

I expect there is static multipath since there is a relay about 2 miles away that runs SFN with Sudbury. Its ERP is only 4kW, and is 90 degrees off axis, but I would be surprised if some of that is not finding its way in. (I did not use that Tx originally because at the time it did not carry all the muxes)

Indeed it may well be.

Thats interesting. This you might see with a good speccy analyser!.

Shouldn't worry about that this problem isn't in the wall plates..

Indeed it is ..

Not surprising where you are Sir, and the bit of ground your on!..

Trees can be more bother than you would think ..

Many years ago we had to fix up a TV in a bit of a wooded country estate the aerial rigger had dome his bit TV delivered and no channels would work apart from a bit something waving around in the on screen noise.

In those days hand held level meters weren't yet invented, rigger was certain that the TV was dud. Telly went back to the workshop where it performed fine. So another TV was sent out and .. Exactly the same.

In the end 3 off 20 foot poles and joiners and stay wires were rigged and a stack of two Jaybeam 24 or maybe 48 element aerials and a very good masthead amp the best co-ax we had at the time was in use and we just about got a usable almost noise free picture!.

Can't say exactly were this was but the channel numbers and hence frequencies were at the top end of the band 5 and on windy nights the picture would come and go a bit I think in the end they used a satellite they could see the right bit of sky there, which was fortunate..

As long as the right sort of tiles aren't in use, all aerials ought to be outside IMHO..

That was in the end the only option for me when I was living at the bottom of a valley....

Well I didn't want to disturb the aesthetics, so under tiles it had to go. Under thatch covered with chicken wire did not seem optimal :-)

I can even get Tacolneston pointing right through a cable wall featuring metal mesh Though I haven't actually even rigged up an FM tuner now.

Most stations are on TV muxes or the Internet

Indeed, helped a mate sort his aerial. In theory, not a difficult location. Stuck a decent log periodic up near the apex of his gable wall. No need for any extra gain. However the signal was very variable until we also set about a row of trees on the path just outside his garden!

In my case I would not rule out trees, although it seems odd that it strikes at the time of year where they are losing leaves and general "lushness".

In the case of my local satellite signal they are acquiring increasing external wetness.

It's been a very dry summer. Perhaps the problem became evident once enough water could get up into those leaves.

Yup possible I suppose - the blighters do tend to grow when you aren't watching :-)

Sometimes, theres an airspaced co-ax cable that can fill up with water;!..

I once improved our TV reception enormously, by drilling a small hole in the co-ax at the lowest point of its run.