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All posts by Chris.SE

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


A bit late in the day for these comments, but for the record
@M J Levett-Scrivener
As Charles Stuart says you need to check your coax and TV connections and aerial connections. If there is any sign of corrosion, it's best replaced. You should have absolutely no problem with the signal strength even with your C/D aerial, but if you have to replace it do so with a group W.
@Melanie Axon
Very similar comment for you as well,you should have no problem with all multiplexes from Mendip.

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The current NOW TV box has BBC iPlayer, ITV Hub, All4 & Demand5 and a small selection of others from the ROKU store - not as many as a ROKU box but for ?15 it was a good investment. You can connect to your router by eethernet or wireless with this latest box which will also do 1080p if your set can do that.

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PSB3 down at my end 2000, no reports here yet - investigating.

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Well I also had low quality on the other muxes and bit errors. Whether it was total coincidence that when I went to "manipulate the coax" outside the signal varied (and disappeared) and then I was about to disconnect a connector inside to contemplate testing continuity to the aerial, the signal re-appeared and everything seemed to go back to normal. Checked the connection and all seems well now, so only time will tell if I get a re-occurence or a transmitter fault report eventually appears.

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C
Mendip (Somerset, England) Full Freeview transmitter
Tuesday 23 February 2016 3:14AM
Shepton Mallet

Joe:

Hi there, there've been no reported problems for the Mendip transmitter. My issue seems to have been a faulty connection!
If your aerials are horizontal and pointing NW then you are definitely using the Mendip Transmitter. There would be no reason to use a Relay Transmitter as you have an extremely clear line of sight to Mendip and should have a virtually perfect signal being only 7 1/2 km away.
If you are having problems with the communal aerial, I would report it to presumably your building custodian/landlord.

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Mendip (Somerset, England) Full Freeview transmitter
Thursday 19 May 2016 7:55AM
Salisbury

David: Have you noticed any degradation at all in the signal/quality for the main HD channels (BBC B mux) - BBC, ITV etc? This is on C58 from Mendip.
Sky News etc is on the Arq A (Com5) mux on C56. If you are also seeing some degradation of those HD channels, then I'd start suspecting some issues with damp/water in the aerial connections or the coax which will start affecting the higher frequency channels first.

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Stephen:
It sounds as though the effects of the 4G Phone masts haven't been explained in the best way. Any exceptionally strong signal in the same band as those you want to receive can have the effect of "desensitising" the receiver which makes it look as thought the desired signals are weaker.
As well as unwanted signals like the 4G phone ones, these exceptionally strong signals could also be the ones that you actually want to receive if you are close to a transmitter, or even if you have an aerial amplifier, you can overload the receiver if the signals were strong to start with.

MikeB has mentioned several things that can cause degradation of the signal. You say the aerial installation is more than 10 years old but that doesn't mean that it will have automatically have degraded if it was correctly installed and it was a reasonable quality aerial but Mike has made a number of suggestions of how to proceed with some basic checks, but frankly I wouldn't be paying 4 quid for a flylead just for some basic checks, you can pick them up much cheaper. If a cheap replacement reduces the signal then there's an excellent chance that there's nothing wrong with the original, but honestly I'd be surprised if you'll notice any significant difference.

Although COM7 is transmitted with a slightly lower power, there should not be significant difference in reception from Mendip at your location.
On the assumption that it is a single downlead from the aerial to just this TV set, I'd certainly check things out as Mike suggested.
You mentioned about a reduction in signal in heavy rain to 25% from 30% or so, I wouldn't be overly concerned about that if the rain is really heavy and the signal goes back up more or less immediately the rain clears - if it takes hours or even days then that suggests water getting into the aerial or cable somewhere, but what is of concern is that it is only in the 30% or so range to start with. You are high up in your location and in line-of-sight of at least 5 transmitters, but certainly should have no trouble receiving signals from Mendip (and you mentioned COM7 which is only transmitted from Mendip or Wenvoe of the 5), it would still be worth selecting your TV's Tuning menu just to be sure you are tuned to the Mendip COM7 mux on UHF Ch33.

As far as the 0% you experienced, I'm much further from Mendip than you are (and high up) and at the back end of last week I also noticed significant variation in signal strengths of some of the muxes but especially COM7 & 8 which dropped to the high 60's but is now back at the low 90's. I put this down to propagation effects and weather, as there's is definitely nothing wrong with my installation. Weather patterns have been considerably varied of late.

Even for a simple installation for Mendip, I'd still be surprised if you needed an attenuator, however if you have a more complex installation it would be best if you described it in more detail so that perhaps more detailed guidance can be given.
It's also worth just checking some basics such as the type of aerial installation and orientation. Is it pointing at Mendip - virtually due south of you (183?) and are the elements horizontal? Are the elements rods or X's? How many elements are there (if X's, count each X as one)? Roughly how long is the cable from the aerial to the set? Where is the 4G Filter located?

Does your TV Tuning menu show information like Bit Errors for each mux? If so, are there any? Or does it show "Quality" information as well as Strength?

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Stephen:
Hope you found the post useful.
Propagation effects can produce strange results on occasion and sometimes seem to defy logic as far as an explanation goes. My COM7 signal dropped by some 20+%, so in view of your "normal" strength it isn't too much of a surprise that yours could easily have gone to zero especially if an interfering signal from another transmitter appears. It doesn't happen too frequently that propagation changes very rapidly from one steadyish state to another but it does happen. Continuous fluctuation can be more common. However it's also worth considering the possibility of some sort of local interference. Did you have any other equipment (of any type) switched on at the time which isn't normally on. If it contains a switch-mode power supply that's not behaving itself, these can produce some very odd patterns of interference! I don't think it's too likely as such interference is usually at much lower frequencies, but nevertheless worth considering and easy to check by just switching suspect equipment on or off and checking the consequences.

As far as your aerial goes, have a look at it in daylight hours and count the elements and see what type they are. It's still possible that you might have too much signal, as Mike mentioned, if your aerial was a very high gain installed before switch-over when digital signals were much lower in strength - don't suppose you know what sort of strength your were getting back then, and if it were a different set it's sensitivity could well have been different so results may not be too meaningful.

On the other hand a 20m cable length is quite long and if it's a small lower gain aerial then this might account for the lower % strengths but I'm a bit dubious that this is the explanation for your location. Do you know what sort of signal your neighbours have been getting?

Regards, Chris.

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Stephen: I would say that the fact that you noticed this problem 2 "weekends" in a row is just coincidence. As I mentioned this is much more likely to be atmospheric conditions changing the propagation of UHF signals and distant signals from other transmitters on the same UHF channel starting to cause interference, which in simple terms can have the sort of effect we saw.
Remember that more than one of us happened to observe the issue, Scotty being the most recent, and no Transmitter engineering work was taking place - one of the first things I checked on the engineering pages - AND it would have been reported here on these pages as well, also if there had been a fault. See page 153 for the last reported issue on October 4th.

One thing I didn't mention (so as not to confuse people with less technical understanding of propagation effects) was that there was definitely a "lift" (as it can be called) on, when I was checking signals previously around that weekend as I was periodically picking up signals from another (distant) transmitter on other UHF channels which are not normally present. It was one of the ones I can regularly get when there is a "lift". There were similar conditions a couple of weeks earlier that I happened to spot (Tues.15th) when I was doing some re-tuning. In the days of analogue transmissions, people could notice such things more readily in the form of picture interference/patterning/foreign pictures - this sort of effect can be more common in the summer and some may recall mentions of "continental interference" at such times.

I mentioned "local" interference as it's always worth trying to check that there wasn't something else having an effect at the time to compound matters, but your fundamental problem Stephen is that your "normal" signal is low - in this 30% range, so any sort of "lift" or "interference" can knock out the signals more readily. Another reason I suggested checking what sort of signals your neighbours are getting is there may be very local conditions giving a "reduced" signal, examples of which can be tall buildings or other structures in or near the line of sight, tall trees etc.
As well as checking that you now don't have a fundamental problem with your aerial/cable installation causing a weaker signal (as previously mentioned by Mike and myself) you also need to check that you don't have too strong a signal as this can "desensitise" the receiver or, as you are already aware - a close phone mast having this effect. But remember all those sort of issues are likely to have an effect on reception of all your muxes rather than just one.

The situation with Scotty is slightly different in that he says he normally has 95% signal, but location - which way the aerial is pointing etc, and again the precise local conditions (buildings, trees etc) can have an influence on what is received.

Martin: The allocation of UHF channels for the various muxes at all transmitters is defined/stated in various OFCOM documentation.

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In recent times I have found that the ability to search the OFCOM website for useful information has markedly reduced. Maybe this is part of some government policy to limit the information that can be discovered by us mere plebs. Whilst I will admit my search efforts have not been totally exhaustive, on this occasion I have been unable to locate any current documents on the OFCOM site that refer to channel allocation!! Nor can I find anything on Arqiva's site.
Briantist: perhaps you'd be kind enough to clear this up for us, and if possible, links to any relevant documents.

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