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All posts by Michael

Below are all of Michael's postings, with the most recent are at the bottom of the page.

Michael: Finally tried our digibox next door. Same result as at my father's house - reduced signal strength, steady 98% quality, fine picture.

So we have:
- digital TVs that work fine on our signal;
- a digibox and a HD recorder which do not work on our signal, producing a lot of pixellation and breakup, but the digibox does work next door and (in a dip) at my father's house. I haven't moved the HD recorder but I am assuming it would also work elsewhere;
- one older digital TV (not mentioned before) which is a bit iffy;
- results similar whichever TV points I use, and whatever configurations of equipment and cabling I use.
- it was worse in mornings and evenings, but more recently yhe problem seems to there all day.
- an aerial engineer confirmed some weeks a go that the signal as received at the TV point was OK, but (a) I'm not sure he looked at quality as wella s strength and (b) it was behaving when they called.

So it appears that the digibox, HD recorder and (to some extent) older digital TV cannot cope with the low (and highly variable) signal quality, but the newer digital TVs can.

There are four TV points in the house, fed from a rooftop aerial with a distribution amplifier/splitter in the loft. As far as I know there is no masthead amplifier (not sure how I can tell, though).

If I switch off the amplifier, the signal goes, as I would expect. So to test if it is the problem I would have to mess around up in the loft playing around with what I have found in the past to be rather awkward connections.

With this setup, is it possible that I could have too much signal strength, and that quality problems not apparent next door are being amplified into something which is upsetting half my equipment?

Is there anything else I can try?

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Michael: Ah yes. The main TV is an old analogue one so has to be fed via SCART from a box with a digital tuner.

The other TVs in the house are digital, an LG, a Mikomi (Argos own brand?) and a Samsung borrowed from my father. The Mikomi was a bit iffy on Ch 22/23/28 muxes at times but the others were working fine.

I said "were", you may have noticed. The LG got really bad on those muxes a couple of nights ago, and the digibox has also started playing up. The Mikomi also got much worse. No footie for me last night!

Then today I switched off the distribution amplifier in the loft, expecting this to lose nearly all the signal. But no, the HD recorder worked fine. So too the Samsung and the LG, though later that started to be really bad on the Ch 26 mux. The Mikomi in the kitchen seemed to lose signal altogether, but at the main TV point it worked better than usual. So, for the first time, I was onserving differences between different TV points in the house.

The signal strength shown on the kit that can show it was a lot lower. Quality seemed more settled (and sometimes consistently high) - except where a tuner was having problems. The digibox is better, but not by much.

This does seem to suggest that the problem for the HD recorder was too strong a signal. But reducing the overall signal by switching off the amp seems to cause other kit problems, at least in some locations. Trying to amplify it at some points and attenuate it in others would surely be a complex trial and error exercise.

Every time I write this stuff up, something else occurs which does not seem to fit the pattern. I'm starting to think that the distribution amp is malfunctioning, particularly as the problems were not there until a few weeks ago. Deterioration of internal cable, perhaps?

Outside foliage seems an unlikely culprit, as next door, with a similar aerial (and similar Freeview via a box) setup shows nice level quality. The main change in the immediate locality has actually been the removal of a large pine!

The whole think s starting to make my head hurt!

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Michael: Thanks, jb38. It was my experience with analogue which made me expect little or no picture, rather than a better picture, with the amp off, so what transpired was a major surprise to me.

I had wondered about putting an attenuator in line near the equipement but it would be guesswork as to how much I need.

Carrying TVs or other digital equipment up to the loft is liable to result in not having said digital equipment in working condition any more, which is one reason why I have not tried it yet. (Would a long cable down to floor level be expected to work? Think I've got some spare cable - without connectors - somewhere. I suppose that with a suitable connector - whatever it might be - I could connect each cable directly to the aerial as well.) The other is that the connections look awkward to me, and if there is a way of terminally messing up the cable, I will probably find it!

I think it is clear that the amp was amplifying the signal that the digibox and HD recorder were using, as the signal strength they show is markedly lower without and the signal has either been lost or is seriously degraded at other points. That's not the test you suggest, of course. I've been careful to say "amplifying the signal" rather than "working" because it might be doing so in a highly variable manner. If the PSU is giving a jerky supply, might that cause the behaviour I am observing? PSUs are usually presented as being specific to one device but I think I have a variable one knocking around somewhere, so it might be worth trying that (cue exploding amp in loft...).

Whatever is going on, it is something that has only been going on seriously for about eight weeks. As the aerial signal seems strong enough unamplified, and the kit I have tried elsewhere works fine, a malfuctioning amp does seem to be the fault that best fits the bill.

However, thinking about it, there have been some smaller, easily dismissed, deteriorations before this. In particular, I have a TV card in my computer connected to one point, and 9 times out of 10 I get a green mass of pixellation at the foot of the picture. Yet 1 time out of 10 it is fine! That's been the case since I got the computer a couple of years ago, but of course the cause could be completely, er, unconnected.

As it happens, I have even got the digibox working off the unamplified signal at the main point this morning. It does seem inconsistent, and I do worry that deterioration arising from the constant swapping around of cables might itself be an issue. I think I'll leave well alone for the weekend and see what happens.

Just for the record, there are four outputs from the amp, servicing five TV points. One of the cables must split out of sight; I think this is the one to the points which now seem dead, which makes sense as they would get the least signal at all.

Finally, thanks for all your help, and enjoy your holiday!

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Michael: Just an update. Tested the power supply and it gives a steady 5 volts DC, as it should do. Suggests to me that it has to be the amplifier/splitter itself.

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Michael: Sorted! Aerial technician replaced the splitter/amplifier with a straightforward splitter, and eveything works.

He said that the aerial was actually picking up too much signal. Also that when I unplugged the splitter/amp, the improved (but still variable) signal seen on the main TV was being picked up purely by the cable between the splitter and the aerial point, that cable being high quality and (if it matters) outside the house.

This begs a number of questions (though I am not too worried now everything is fine). If the aerial signal was too strong, how did it work before? My guess is that when it was working properly the amplification was less than the attenuation provided by splitting. At some stage it stopped splitting the signal properly, hence overload on some aerial points and poor or no signal on others. But what do I know?

Anyway, I have to eat humble pie about blaming it all on the Crystal Palace signal.

The other question, I suppose, is why the excessive signal was not diagnosed by the earlier technicians I had in. In their defence, things seemed to be working OK that morning, and the deterioration at other times was less than more recently; they only checked the output at one aerial point as well, rather than the input to the splitter.

So long and thanks for all the fish...

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