All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Tosh: The predictor is based on 10 dBd of aerial gain (middling - XB16E has 11-15 dBd) and 3 dB of loss in cables (high - WF100 is rated at 15-18.3 dB per 100m, which if linear would take about a 15-20m run to drop 3 dB). It's also based on a maximum of 16 dB of rejection of signal from behind and to the side, an acceptance angle of about 40° (20° either side of the middle), and 16 dB of cross-polar rejection - rejection from the other polarization, so - if using Sudbury - rejecting vertically-polarized signals from the relays. Again, real aerials will beat this, though the exact amount depends on the frequency and angle. Larger aerials will generally reject more unwanted signal and have a narrower acceptance angle.
Therefore, the predictions can be quite conservative. Still, a prediction of 'poor' or 'nothing' is likely to indicate a problem.
Masthead amplification might be useful if the issue is simply that the signal will be too weak, but it's more likely that the problem will be co-channel interference.
The Rouncefall mast will use the same channels as Sudbury for the PSB services, timed so that for most people, the signals will arrive within the 'guard interval'. This idea - called a Single Frequency Network - reinforces the signals, but only if the timing is right. If it isn't, it stops the receiver decoding it completely. This may be why, for CM9 4TT, Digital UK predict poor reception for the PSBs but good or variable for the COMs. Again, it will depend on exactly how your aerial behaves - in this case it's the polar response of the aerial (angle to transmitters) that is important.
For that postcode, the trade predictor reckons Rouncefall should start out good but deteriorate next year, presumably as Tyne Tees switches over or possibly continental transmitters, while it's expected to get more reliable results from Dover!
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David Reid, alan denholm: No problems are currently reported, click the 'BBC Reception test' links next to your messages and follow the wizard to report the problem.
Some viewers have found that they have too much signal after switchover. If you have a booster, try removing it, or try adding an attenuator instead.
Also check that the TV has tuned in the correct transmitter - David, you are also predicted to get good results from the Dunoon relay, and alan, you from the Rothesay Town relay, which Digital UK are showing that you're practically on top of.
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Graham Powell: To receive HD signals right now, you will need a Group K or wideband aerial. A newish Group B aerial - made in the last 15 years - should have some gain down at C34, but the results are likely to be poor. An older Group B aerial, not designed to receive Channel 5, probably won't pick up much down at C34.
The HD transmissions actually come from Lichfield, where Channel 5 analogue comes from. If Channel 5 analogue is poor, HD probably will be as well.
At switchover, all services move into Group B, so you should *not* need a new aerial. The HD multiplex moves to Sutton Coldfield, and takes over BBC Two's current analogue frequency.
All relays will carry the HD service. For reference, the broadcasters call this relay Kidderminster.
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Mark A., gareth: While only 81 of 1100 transmitters provide six multiplexes, those transmitters serve all but 8.5% of the population. The situation is worse in Wales, with 34% of the population not being served by any transmitter that provides the commercial multiplexes.
Channel 5 is carried on the PSB2/D3&4 multiplex and is available from all transmitters. There are a tiny number of new relays where some multiplexes don't start up until after the official switchover date, but these are generally ITV-only relays like Derby, where D3&4 *will* start on the official date.
Ofcom's current switchover timetable says that Tyne Tees and Ulster - the only remaining regions for which dates have not yet been published - must be completed by the end of 2012.
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Ian Hill: The card in the box contains the decryption keys necessary to decode encrypted subscription and free-to-view channels. If you take the card out you won't get the service you're paying for.
Assuming you're not just paying for the ability to receive the BBC, ITV, C4 and C5 channels via satellite, that is. You can do that for free. Compare freesat with Sky's free offer at Compare Freesat and Freesat-from-Sky TV | ukfree.tv - independent free digital TV advice .
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Gareth: When the broadcasters of the multiplexes for those channels decide that it's economic to do so. They were offered the opportunity to broadcast from more sites than they did before switchover, and they turned it down on cost grounds.
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Dale: Someone's made a mistake in programming the system, probably, because those are the dates for Oxford and its relays.
I suppose it's possible that if there was a problem with the programme feed to Sudbury, that it might be taking a feed from Oxford, or at least the multiplexer that feeds Oxford. Is it happening on all channels or just the BBC?
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Whoops, I forgot about the power boost that happened on Wednesday morning. (I'm in the area, but my aerial points to Crystal Palace, not Hannington.) Mux C and D were boosted to 20 kW. This is to offset the potential for interference from Sudbury BBC A and D3&4 when they go to high power on 6 and 20 July respectively.
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Mark A: "Transmitter Engineering" just reposts what the BBC put on their 'Solve your interference problems' troubleshooter, and what Digital UK post at
Digital UK - Planned Engineering Works . The BBC put "DSO Related" on their page if they were previously advised of the 'fault', that it would be due to planned engineering works for digital switchover.
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Wednesday 29 June 2011 5:42PM
Elizabeth Forsyth: Find out where the infra-red receiver for the TV is. There might be a little 'IR' symbol next to it, or it might be a visible glossy plastic window. Check that there's nothing blocking the path for infra-red light to pass between the remote and the TV's IR sensor. Also check that the IR sensor is clean, it's common to get fingerprints over them.
If none of this helps, you will need to get the TV serviced.