All posts by Chris.SE
Below are all of Chris.SE's postings, with the most recent are at the bottom of the page.
Leitch:
The Craigkelly transmitter is on the North side of the Firth of Forth almost due North of Edinburgh and is a separate transmitter from the Black Hill transmitter which is about 2/3 of the way between Edinburgh and Glasgow.
UHF C29 at Craigkelly is the SDN multiplex. See Channel listings for Industry Professionals | Freeview for which channels are carried on which multiplex.
I can't find any current faults listed for Craigkelly by Freeview, and it's not listed for Planned Engineering this week, but it was last week. If you perhaps retuned when C29 was off-air, it may have cleared the correct tuning.
See in your TV's tuning section and try a Manual tune for UHF C29 which will hopefully restore your channels.
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Lewis:
I'm assuming that the terrain in your postcode isn't totally flat from the predicted reception figures I can see. As StevensOnln1 says UHF C55 is technically just above the range of a Group B antenna but SOME group B will still have sufficient gain and possibly better gain than a Group T/Wideband for C55 cf eg. C39, for example see ATV aerial gain tests : all the gain curves - A.T.V. Poles, Brackets, Clamps & Aerials and look at the curve for that Yagi 18B (this isn't especially any recommendation) it shows how variable different aerials can be.
I would avoid aerials such as these "tri-booms", the windage is high and many (or their chimney mountings) do not survive some of the storm winds we've had in recent years. Also avoid "bacofoil" aerials sold by many DIY outlets (easily damaged by pigeons!), go to a more specialist TV aerial shop or seller where you could be sure of getting a Group B (if that's what you decide) rather than a Wideband which many other outlets may only sell (and be careful looking at a certain very large online seller that has been in the news in the last day or two!).
I would check out the different brands of aerial being sold and it's gain curve if available (most respectable ones are). Avoid "5G" filtered if you want COM7 for the duration as they are specified only up to C48 and filtering isn't necessarily essential unless you have a mast close by.
All this is not helped by the fact that Wenvoe's tranmission power for the COMs is lower than that for the PSBs not that that always makes much difference. Also remember that COM7 is a temporary mux and will be closed in a years time according to the current licence.
This could very well be a case of experimentation if it's a job you are doing yourself. What sort of aerial have the neighbours got and which way do they point? Have you got an unobstructed view due S - no trees close by on the line of sight for example. Do remember to use decent quality double screened coax.
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Paul Redmond:
I doubt very much that the power has been dropped (unless there is some planned engineering going on, but that's a long time and that's a large area!). Weather conditions of late may not help, is this constant or variable?
BBC Radio 6 Music is on the BBC National mux, so you should have the same problem with all other main BBC stations.
If you find this is the case with other BBC stations and this persists, I'd try reporting it to BBC Engineering to see if they know anything or have any ideas.
Please keep us updated.
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Brian:
Rowridge hasn't been listed for Planned Engineering recently and I can't find any current faults listed (none of which doesn't mean there isn't any, as sometimes the lists aren't up-to-date but if there were any significant issues, I'm sure we'd see more people with problems.
What signal strength and quality do your normally get on COM6, and what is it on the other multiplexes?
There has been some sporadic Tropospheric Ducting around, see Effect of tropospheric ducting on Freeview | RTIS for a simplistic explanation. It's been very variable, and can come and go quite quickly, sometimes last longer.
Is your quality still 0%, this is usually an indicator of some interference, most likely due to these conditions?
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Brian:
Hmm. Well signal strength should be self explanatory, it's how strong you are getting the signal at the set after being attenuated in the coax and any splitters, connections etc. 70% should be fine for most sets, but as those channels have 100% quality, that's what counts. It's a measure of how much interference there is to the received signal. The lower the quality, the more difficult it is for the set to decode the signal and correct the errors. Eventually it can't, and you get pixelation and sound breakup.
The 50% signal on COM7 is also fine as should lower values be for most sets but, the weaker the signal being received, the more vulnerable it is to interference from any sources.
Those 70% and 50% figures suggest you could be some distance from the transmitter. A Full postcode would be helpful so we could look at the predicted reception, nevertheless you aren't doing too badly because to get COM7 your aerial would be horizontally polarised and COMs4-6 have lower transmission power than the PSBs and COM7 is a bit lower again.
You figures make me think that there could be some (very) local interference affecting C28 and C37.
Have you changed anything in your setup recently, moved any equipment about added anything, got something switched on that isn't normally, especially something with an analogue RF output - an old Skybox (or similar) or VCR? If the latter, change it's RF output channel to something above C60.
Have you got any new electrical equipment - of any type, including LED lamps or CFLs etc.?
Also make sure you don't have any HDMI leads close to (poorly screened) aerial and flyleads - especially those which aren't double screened coax. HDMI has been known to cause interference, though whether those channels are more vulnerable might depend on the particular equipment involved.
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Brian:
If the quality on a channel varies, then weather "effects" could be the most likely culprit. But there ought to be times when it is still 100% quality unless you are in a particularly bad location (you shouldn't be). If you aren't in the habit of checking such things on a routine basis, then it could be difficult to know whether things like Tropospheric Ducting is responsible or you have some other form of more stable interference that's been present for a while. Do check the HDMI lead situation and other equipment if you have any.
Also check that your aerial is intact (particularly when it comes to the reflector) and still pointing in the correct direction - bearing 223 degrees, virtually SW for your area.
One thing I've not mentioned to you is that Rowridge transmits both horizontal and vertical polarisation for the main 1-6 multiplexes, where as COM7 and the Local mux are horizontal only. The power for Vertical polarisation is also the same for the main muxes.
You are predicted to get "variable" reception for the COM muxes with horizontal polarisation, but good with vertical - you'd lose COM7 and the Local mux with vertical polarisation though. You might like to read a couple of our replies to viewer Stuart (from Bognor Regis) on p195, so the problem with reduced reliability for COMs4-6 could be interference from Crystal Palace, but it's slightly strange that you are only getting an issue on C28.
You are predicted to get good reception of the Local Mux though, and I'm struggling (off the top of my head) to think of which transmitter might be the source of your current issue, as most relay transmitters that might use C37 use vertical polarisation (and low power) - another reason to check your aerial is intact and pointing correctly.
Interference on specific channels could also come from a near neighbour. Might be worth asking what their reception is like for C28 & C37 if their aerial is horizontal. Interference from further afield such as faulty street lighting generally affects a broader range of frequencies, but Radio Frequency problems can sometimes be a bit of a black art!
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Bernard John:
What is obviously important with an aerial that old is its condition and that of the downlead and it's still pointing the correct way. You are so close to the transmitter - I guess you can see it! That said, before the 700MHz clearance programme Carmel was an aerial Group C/D and if that is what you have, it's performance at the lower channels now used by Carmel will not be as good. Although the PSB multiplexes are on lower UHF channels again they are also transmitted at higher power than the COM4-6 multiplexes. You might be able to see a Green plug in the end of the aerial if it's a Group C/D but not all manufacturers fitted correct coloured plugs and it might be black (possibly making you think it's wideband).
Unless you are certain the aerial is wideband I would assume the problem could be related to performance as well as possibly condition, weather can play havoc with connection boxes and cable insulation. Aerial misalignments, problematic connections, water ingress etc. can seem to affect reception of just AN individual or several multiplexes.
It should be pointing at bearing 28 degrees, fractionally E of NNE, but if you can see the mast, pointing it shouldn't be an issue.
Even so, you location is predicted to get variable/poor reception of the COM multiplexes (predictions are often based on external aerials at about 10m height).
See Channel listings for Industry Professionals | Freeview for which channels are on which multiplex.
I guess you may be on fairly high ground, so that interference from other transmitters using those channels (possibly Mendip) might be an issue in certain weather conditions. I do know that in such conditions, signals from Mendip can get to the Preseli's. Even though the aerial isn't pointing that way it will have what are called sidelobes, especially with smaller standard aerials which I assume this probably is being so close to Carmel, where it will be able to receive signals in those directions.
The trick to deal with this sort of interference problem (as that is quite likely) is to have the aerial positioned maybe not as high if there is a clear unobstructed view of Carmel, and somewhere which screens it (by eg. buildings) from the directions most likely to have the interfering sources. Also use an aerial likely to have better directivity and minimal sidelobes - a log-periodic could be the best option, if for some reason it's not the best, a Group K aerial will be better than wideband. Even consider loft mounting, but that can have issues with partition walls, water tanks, metal chimneys, lead flashing and so on requiring careful positioning.
Being on-site and maybe a little bit of experimenting to get the best arrangement and using an experienced (and recommended) aerial installer if it's not a job you are able to tackle yourself.
As for weather conditions, there has been quite a bit of "Tropospheric Ducting" around lately which has been quite variable. It can come and go in seconds or minutes or last for longer and doesn't always affect all multiplexes - it tends to be frequency dependent.
See Effect of tropospheric ducting on Freeview | Help receiving TV and radio for a simplistic explanation.
Some predictors are showing that there could be more over the next few days, but they aren't specific for the frequencies used by TV, and like weather forecasts they can change!
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Brian:
Just to add to the above, C37 interference might come from the Oxford transmitter which uses C37 for COM5. One coverage map suggest that some signals might get to some spots around the Petersfield area under normal conditions! Propagation can be quite frequency dependant in some circumstances.
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Kelvin Smith:
Does your set not have a manual tuning option? If so you can pick the individual channels it tunes to, and I would leave out C37 (unless you are keen to get the Wenvoe local multiplex as you can't get the Local one from Mendip on C30).
Thanks for the figures for the aerial direct to the TV, quite interesting. Not surprisingly you are getting more signal for the higher frequencies as most aerials have more gain at the high end.
This time there's no signal on C35. Considering the figures when the amp/splitter is connected, and comparing it to the other adjacent channels, I say it was likely interference due to Tropospheric ducting.
My guess for the most likely bet is Huntshaw Cross in North Devon it uses C32, C34, & C35 for its COM muxes.
So you might from time to time see issues with PSBs 1 & 2. Don't forget that propagation in such conditions can be very frequency dependant so it won't necessarily affect them all.
Well done for checking possible interference from other sources such as your router.
As for tuning, if you can't manual tune, pulling out the aerial plug at the appropriate time is an option some have used, but as you say it can be hit and miss. Tropo predictions suggest there could be more about in the next few days (even the BBC have a current warning).
Ridge Hill does have a better prediction for you but you'd lose BBC Points West, you can get ITV West on C29 as it has that as well as Midlands on C25.
When conditions are more settled you can see which HD mux, Mendip (C35) or Wenvoe (C47) gives the more stable reception. I doubt there's much more you could do, especially if you can't move the channel LCNs to where you'd want!
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Wednesday 23 June 2021 1:13PM
Morenna Beecham:
If you have a smart TV, then you can watch most of the main channels via the various "players" by streaming on-line if you have a broadband connection with sufficient speed and no data limits.
Otherwise there is Freesat, for which you will need a Dish and LNB.