All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Kevin Evans: Assuming you mean ITV1 +1, ITV skimped on equipment. They only had space for six variants on satellite, so only provided enough delay equipment and hired enough monitoring for those six variants.
The six:
London
Granada
Yorkshire West (Emley Moor)
Wales
Meridian South-East
Central West (Sutton Coldfield)
Wales, the West, and Westcountry regions all get ITV1 +1 Wales. Meridian and Anglia get Meridian South-East (Meridian is divided into South and South-East news regions). All of Central gets Central West (ITV1 Central is split West/East Midlands). I'm not sure which service Border gets. I believe Tyne Tees gets Yorkshire West - again, Yorkshire is normally split east/west.
Why these groupings? ITV sells advertising in macro-regions. There is a 'West' macro consisting of Wales, West and Westcountry, and a 'South East' macro consisting of Meridian and Anglia. There's also a 'North' macro but the Granada region is presumably too large or too important not to have a separate service.
Some of the satellite variants are encrypted, so the choice on Freesat is even more limited.
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Bernard Hunt: It really depends on how the receivers handle more than one version of the same channel. Some will indeed utterly ignore it and might not even allow it to be manually added. Others will put the first version found at 3 and the other up in the 800s (or the first space they find) - the Central version has the lower frequency. Still more will pick the best quality or strongest version - Central will be stronger at the moment as it's higher power, and it's probable that the lower frequency version will still have a higher received signal strength anyway.
If there's a clash of channels, the newest receivers should ask which region you want to store, although again some of them are then not storing the alternative at all, and some don't allow the alternative to be manually added after that. This is a problem when there are minor differences in the region name coming from one transmitter!
If you currently have the Central version at 3 (and 33) and your box doesn't have a way to change that, the easiest way is to delete them and manually tune C29.
I presume that the ITV1 +1 version on the Ridge Hill West mini-mux is Wales?
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Steve Craig: The switchover is being done on a geographical basis - there are dependencies which mean that some transmitters have to switch before others can. The easy bit was to do the area to the north and west of the Tees-Exe line, both because of the terrain (generally bigger hills and deeper valleys, meaning terrain blocks line-of-sight between transmitters) and because there is much less interference to and from overseas transmissions. South and east of this line, the country is much flatter and therefore a lot of low-power digital transmissions overlap with analogue transmissions at a relatively nearby transmitter. When the second transmitter goes high-power it breaks low-power digital at the first.
For example, two multiplexes at Waltham had to retune when The Wrekin switched over. The Wrekin is close to the Welsh border in Shropshire. Waltham-on-the-Wolds is east of Nottingham and Leicester, about half-way to Peterborough.
Sutton Coldfield and Emley Moor are switching together on one day - a 1,000 kW analogue transmitter and an 870 kW one - because they use the other's frequencies and are relatively close together.
However, I do feel that they could have gone more quickly than they have, by doing larger regions on one day, and perhaps doing it in one go rather than staggered over two weeks. I think they've been trying to reduce the number of calls that they receive on one day.
The aim is still to complete the switchover before the Olympics. The second half of the Meridian switchover is due to be announced next week, and I hope we'll see the Tyne Tees and Ulster details announced at the same time (though Ofcom is yet to even publish a frequency plan for these regions).
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David: The Guildford transmitter has been there since 1972 and Hannington's digital transmissions have always clashed with it (at least as far back as 2001, which is the furthest back that).
The broadcasters did increase the power over the years: Mux 2 started out at 5 kW, was increased to 10 kW in 2000 and then increased again to 20 kW in 2004.
The problem is that the transmissions are on the same frequency. The receiver sees the combined result of adding Hannington's digital to Guildford's analogue, which - from time to time, depending on what's being transmitted on both, and on weather conditions - causes too many errors for the box to be able to correct. Manual tuning will not help at all.
Of course, it's possible that some other issue has been slowly deteriorating and has now reached the point that Mux 2 has stopped working - but as I said, the prediction for that location is already non-existent so it's really hard to say whether you losing it is down to some changes in the interference level, or whether it's an equipment problem.
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Incidentally there *is* a frequency plan available through Digital UK at Postcode Checker - Trade View . It shows that the three PSB muxes rotate around (BBC A on C26, D3&4 on C29, BBC B/HD on C23) and ArqB will be on C40, not C50. This frees C50 for Pontop Pike which was to use C62, which will be released.
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Mark Peterson: Yes, this is expected. Hannington's current digital signals are restricted to the east - the aerial panels are mounted on the north-west corner of the mast and they point south, west and north. So while the maximum ERP of Freeview transmissions from Hannington is only 11 dB down on maximum analogue transmissions, that only applies in the served sector.
We don't know exactly what the limits are on Hannington's radiation pattern, but the levels you're getting do sound about right. A new aerial might give you the extra 10 dB of gain - it's always preferable to upgrade the aerial before adding amplification. Replacing the cables may also reduce the loss between the aerial and the TV, and reduce the amount of noise picked up.
They're right to warn about too much signal. It causes a problem called intermodulation, where the signal is distorted, causing frequency-shifted copies of the stronger signals to be created. The strongest 'intermodulation products' appear in adjacent channels. It's generally considered that keeping analogue signal levels below 80 dBuV is enough to prevent intermodulation. I believe the recommended digital limit of 65 dBuV is based on the average difference between analogue and digital levels.
At switchover, the digital services move to the unrestricted main antenna at the top of the mast, because they will no longer clash with Guildford primary services (as they take over Hannington's analogue frequencies).
The switchover dates are now final: 8 February and 22 February 2012. On the 8th, low-power Mux 1 and BBC Two analogue are switched off, and high-power BBC A launches from the main antenna. On the 22nd, all remaining analogue and low-power digital services are switched off and replaced by their high-power digital equivalents.
The commercial multiplexes will stay at 20 kW until Guildford switches over on the 4th and 18th of April. It's possible they won't move to the main antenna until these dates.
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I should add that Hannington digital is already very powerful - for the served sector - relative to the analogue signal levels, and to post-switchover power levels. The PSB muxes will only increase 4 dB and the COM muxes only 1 dB. The current low-power Mux C and D increase by 3 dB in June, from 10 kW to 20 kW, I believe to reduce problems when Sudbury switches over in July.
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Peter: The prediction for you is for very strong signals. If you have an amplifier or booster, try removing it. If that doesn't help, get an installer to come and check what's actually going on.
There is a limited amount of help we can provide remotely. It's really unfortunate that Freeview boxes don't have usable signal strength and quality meters that actually measure things in the units that the engineers use, which would tell us much more.
If the problem was restricted to ArqB I would suspect a damaged cable allowing in damp - cable damage usually causes more problems at higher frequencies than lower ones.
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Nick: You can find lists of free-to-air satellite services at Eurobird 1 & Astra 2A/2B/2D at 28.2°E - LyngSat and at Astra 2A / Astra 2B / Astra 2D / Eurobird 1 (28.2°E) - All transmissions - frequencies - KingOfSat .
As for why the box only retains the extra channels for a few days, no idea. Perhaps the box needs to remain powered?
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Thursday 5 May 2011 6:52PM
James Mooney: Does BBC Four work? Before switchover, Sky Sports channels are carried on Multiplex B.
If you're north of Birmingham, or your aerial points in the same direction as the Emley Moor transmitter, you could be getting interference from Emley Moor BBC Two (analogue) when the weather conditions are right or at night.