All posts by Chris.SE
Below are all of Chris.SE's postings, with the most recent are at the bottom of the page.
Dylan:
There has been some Tropospheric Ducting around affecting different parts of the UK at different times throughout the last few days and this may have been the cause of your issues. On the other hand, the Black Hill transmitter was listed last week for Planned Engineering with "Possible service interruptions" that work might still be ongoing even though the transmitter isn't listed this week!
But furthermore, coverage from Black Hill is very patchy is significant parts of the KA6 area and we'd need a Full postcode to see what the Freeveiw Detailed Coverage checker was giving for predicted reception at your location. Other multiplexes may seem ok but COMs 7&8 might not be predicted to be good.
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j appleyard:
UHF channels used by Bilsdale are C27, C24, C21, C43, C46, C40, C55, C56 & C30 in the order PSBs1-3, COMs 4-8, and the Local mux.
Remembering the theoretical C+5 and C+9 rule, you've got a gaps there at C23, C32, C33, C48, C49, C52, C53, C54 but as interference could end up on an adjacent channel, personally I'd choose something well above C56, you've got the pick from say C60-C68.
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Bridgette Blaskett:
Hmm, you are not in a good spot there having very limited choice. Do you know which way your aerial is pointing and whether the rods are vertical or horizontal, there's a choice of which transmitters you MIGHT try and get, none with good reception!
To add to things, there has been recent Planned Engineering on some transmitters that you might possibly get but that is supposedly completed. However, to mess things up there has also been some Tropospheric Ducting recently (see https://www.bbc.co.uk/rec…iew) causing interference from other transmitters (UK or Europe).
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Bridgette Blaskett:
When I say which way your aerial is pointing, I mean rough compass bearing, not which transmitter, but if you know that, it could help.
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David Warner:
If you'd read my post here on the the 10 May 2020, 4:42 PM, (p12) you'd have noted that I stated about when such changes may/may not occur. In addition to that, PSBs 1&2 are very likely to be the last to be converted.
As regards you and your brother's reception, if you used the links I gave in reply to your other post which were highlighted by another poster here My Freeview box has no EPG, is blank on FIVE, ITV3, ITV4, ITV2+1, has no sound o | free and easy then you would have seen your brother's predicted reception which will be entirely dependent on his location and have no bearing on yours. I'll be making further comment over there after that post especially about your front end possibly being deafened (two of us now suggesting that possibility - "perfect" reception of the other multiplexes is no "guarantee" this isn't happening, nor to be fair that it is! - it's a possibility).
SFNs are NOT some sort of "short-term" experiment. Virtually all the transmitters in the National DAB networks are SFNs, and some Local muxes where there's more than one transmitter for the mux. Only Trial muxes and Local ones with one transmitter won't be an SFN.
COM8 was not using the full available bandwidth which enabled a FEC change on the 10th Feb. as I mentioned to you in reply to your other post BUT it is not currently transmitting with a 167kHz offset. IIRC it did at the time of the FEC change, but this no longer seems to be the case based on all available tech & reception data that I've seen. (Having said all that, I personally think that there may be a touch of SFN experimentation going on with COM8).
As regards the COMs 7&8 transmission powers at Crystal Palace, as I also mentioned, there's DUK/Freeview documentation that states they are 80+kW. However I also mentioned that there are many inconsistencies as even OFCOM documents have not been updated in some instances. Additionally there are many websites that are out of date and have incorrect information about COMs 7&8. Oh, btw, those replying to you here are professional engineers, there's no need to quote data from other websites which in this case is not 100% correct.
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David Warner:
Did you use the links provided then? I'm guessing not based on your further post on another page. Unfortunately this site has messed up the link to the Platform Management page (but you had the other option), you can get to it easily by scrolling to the bottom of the Freeview Home page and clicking the link under Corporate.
Just because you have "apparently perfect reception" of other multiplexes is NOT a compelling argument that you don't have overly high signal levels. How a set front end handles too much signal depends on it's front end design, some do it well with no obvious problems, some show immediate picture or sound breakup but quite often the sensitivity is reduced and so it can become "deaf" to weaker signals. And I already explained about the Transmission Mode for the Local multiplex which is why the coverage is "better" with lower power.
You said "this local low power multiplex comes in so strongly from Crystal Palace to Brixton that you don't need an aerial to receive it". You also said "The TV I use has a sort of signal strength indication - but this seems a bit unreliable." That's something else that can happen with too much signal, I did mention that a receiver "could falsely show less than 100% signal"
You have a 20 element yagi 3 miles from CP, that IS a compelling argument that you MIGHT have too much signal even when considering the railway viaduct.
But before I comment further on experimenting, we'll mention the trees. I'm going to quote part of an article written a few years ago by Bill Wright, a very experienced TV engineer, it was in analogue days, but the principles are EXACTLY the same for digital signals.
"The customer will say that he's enjoyed perfect receptionor what he regards as perfect receptionsince the days of John L. Baird.
Those trees have always been there and they've never affected reception before', he'll declare.
The dreaded credibility gap looms up in front of you! In reality the customer has probably always had rather unreliable reception, but it's never been quite this bad. Why does it happen? Why does one channel just disappear? The cause of the problem is multipath reception through the trees. The signal takes a number of different paths through the leaves and branches. In the simplest case, if signals following two such paths arrive at the aerial more or less in phase no great harm is done. But if they chance to arrive exactly out of phase and of equal strength the result is no signal. It's never quite as clear cut as this of course. The signal may take a multitude of paths, resulting in a complex and unpredictable pattern of standing waves, or peaks and nulls, at the receiving site. Because a relatively minor change in the tree structure can completely alter this pattern, reception can be acceptable for years until a null happens to occur precisely at the aerial location. Normal movement of the trees, even on fairly still days, is enough to cause great variations in received signal strength."
So, just to complicate matters further, the FEC change to COM8 will have had the effect of improving the signal in a lot of places, often seen an increase in signal strength (that could tip your front end just over the edge) BUT this isn't only seen just when using an omni-directional receiving aerial (that's really more applicable to DAB) as TV aerials have "side-lobes", "front-to-back ratios" aren't always the best, and another transmitter with an "Interfering signal" may well be within the beam-width of the receiving aerial. So in other words reception can become better or worse, it very much depends on location and those factors mentioned.
So what next. Well you MAY have a combination of multipath and too much signal.
Assuming the aerial is in exactly the same position as it was when you had good reception of COMs 7&8 then it seems to me that spending a fiver on a variable attenuator is a small price to pay for a bit of experimenting without which you have no clue as to what is going on.
This is where I would start. See what happens to your reception and set's signal strength for all multiplexes as you increase the attenuation. Assuming either that's not the problem or only part of it, then I'd try repositioning the aerial, not just tipping it or altering the bearing, move it several inches or even feet, taking care of where any metal objects, solar panels, roof flashing etc are, and trying to ensure they are not in close proximity or line of sight. Apart from this possibly changing the received strength, it'll probably have some effect on any multipath.
If you still haven't got a satisfactory result, try one of the other aerials. CLEARLY the Group A are NOT the ones to try. So you've mentioned the 10-element and also a Log-periodic, both will have different characteristics, so experiment. RF can be a bit of a black art, it's a case of suck it and see in this sort of situation.
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js:
Hi js. I did say "based on all available tech & reception data that I've seen", and I have to admit I didn't do an exhaustive check, so now apologies, and I misread my own data which was after I looked at DigitalBitRate for London COM8 http://www.digitalbitrate…g=en which is obviously erroneously quoting the frequency for C56 rather than measuring it. But what's worse is that the DUK/Freeview documentation is not showing C56- so consequently I was sloppy in checking other data. So apols as well to David Warner for that incorrect comment, not that it makes the slightest bit of difference to his reception problem, that issue is the same!
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Tony:
Talking Pictures LCN81 is on the ArqB multiplex (see Channel listings | Freeview ). This multiplex is broadcast from all main transmitters Welsh or English.
It's likely your Dad is getting his signal from Winter Hill whereas from what you are saying you are getting yours from Moel-y-Parc (but full postcodes would be needed to see what the Freeview Detailed Coverage Checker was predicting for those locations).
Both those transmitters are listed for Planned Engineering this week, Winter Hill with "Possible service interruptions" and Moel y Parc with "Possible weak signal".
If you retuned when there was no signal (off or very weak) it will clear correct tuning and you'll need to retune again when the signal is back to normal. You may have to try several times.
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Lisa:
It's simply down to the terrain - too many hills in the way. As StevensOnln1 has said you need to look at alternatives - primarily Freesat. Most modern TVs already have built-in satellite tuners, so all you need is the Dish and LNB, you get most of the same channels as the full gamut of Freeview, and a few others. None of the main transmitters Carmel, Preseli or BlaenPlwyf are ever going to reach your locale because of the terrain. It does also look as though you are just out of range of the Talley relay transmitter, but this only has the 3 PSB multiplexes in any case (for which channels on which Freeview multiplex see Channel listings | Freeview ).
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Monday 1 June 2020 2:13PM
Susan Hall:
Were the engineers that you had aerial installers or were they from at800 and ONLY checked interference?
Did they measure the signal strength at your aerial socket?
You mentioned a booster, does it have a variable gain control, there's the possibility you may have too much signal which overloads the receiver and can cause picture/sound breakup.
We can only advise on the options and possibilities with a full postcode to see what the Freeview Detailed Coverage Checker gives for your predicted reception at your location especially as you may have this choice between Caradon Hill and Huntshaw Cross.
(Note, there has been some Troposheric Ducting around the last few days in some parts of the UK which can affect reception by causing interference from different transmitters in the UK or Europe.)