All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Nick Lloyd, Stuart: Fundamentally, you're out of coverage and as far as the broadcasters are concerned, always have been. You will be covered by the Margate relay after switchover.
The terrain blocks clear line-of-sight to the Dover transmitter and always has done - this is why the Margate transmitter exists at all. You're relying on fringe reception which is more likely to be affected by the ongoing switchover programme.
Until switchover, digital takes a major back seat to analogue performance. Some changes to interference levels were inevitable as the switchover programme proceeds, both here and abroad.
The broadcasters are only trying to match the predicted digital coverage to predicted analogue coverage. If the analogue coverage was below the threshold, they are not required to provide a digital service from that transmitter at that location. The commercial muxes are not even required to match that level of coverage.
Margate is fed off-air from Dover for analogue signals and cannot currently transmit digital services, because they just don't reach from Dover to Margate, at least not reliably enough to rebroadcast. Feeding relay transmitters from a leased digital communications line is much more expensive and only done where off-air relay is not possible. It's also very unlikely that there are any spare frequencies that could be used for any interim service.
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Daniel: These relay transmitters exist because there are areas that were not covered by the main transmitters, for analogue services.
At switchover, the relays will only transmit the three public service multiplexes: the services listed above.
If you're getting good quality analogue signals from one of the main transmitters now, you should get reliable digital signals after switchover. Virtually every transmitter in the country will be getting much stronger digital transmissions, at least equivalent coverage to analogue and sometimes more. (The only transmitters *not* getting much stronger digital are those where it was already practically equivalent.)
If you provide a full postcode we can work out which transmitter is most likely to provide the most reliable service.
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Simon E: Yes, too much signal is certainly a possibility. Overloading an amplifier or tuner with too much input causes distorted signals. It could be that there's too much signal going into the amplifier, or that the amplified signal is too big (after splitting) for the TVs.
Whether you can use a passive splitter depends on how much signal you get from the aerial alone.
I'd start by turning down the amplifier, if that's possible. If not, get a passive splitter, and if that breaks up too much, get a small adjustable one-channel amplifier to put in front of the splitter.
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Rudy Walker: the page really talks more about why it might be two frequencies that are a problem, and not really anything to fix it.
The mode used by Mux 2 and A before switchover requires higher signal-to-noise ratio than the other four multiplexes, which means that if your reception is deteriorating you would tend to lose these first. After switchover, all five SD multiplexes use the same mode.
The location you've provided is near NG17 8RH. That postcode appears to be problematic: Digital UK's predictor does not offer a six-multiplex prediction from any transmitter, at the moment. This might be a reduction of coverage due to interference from other transmitters having switched over, but it's more likely that you've never really been in reliable coverage and the current conditions mean it's not working right now.
You're between three main transmitters: Waltham, Sutton Coldfield and Emley Moor. Waltham provides the East Midlands service, but it's less powerful and there's a terrain problem which means the probability of finding reliable reception is lower than from the other two. There will also be a channel clash between the ArqB multiplex from Waltham and the D3&4 service from the Bolehill relay - both using C57 - which would likely mean you couldn't get reliable service on this multiplex.
You should get best results from Sutton Coldfield. Emley Moor is a slightly poorer alternative but there's not a lot in it.
The Nottingham transmitter has already switched over, but terrain blocks line-of-sight and the radiation pattern is concentrated to the east and south.
If the aerial currently points to Waltham, you would have needed to retune on 30 March and 13 April, as Mux 2 and A have changed frequencies for the last six months before switchover. Make sure you do a full device reset - some boxes will ignore a new location for channels that they already have stored. See how well it performs after switchover, and if it's not reliable enough, consider changing to one of the other transmitters.
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Mike Fisher: Sounds like you have a box which stores the version on the first frequency it finds, not the best version. The rating on Digital UK's postcode checker for Ridge Hill is higher, but that's if your aerial is pointing at the transmitter, not away from it!
You'll have to delete the channels and manually tune on C34, if you're certain that the aerial points to Bromsgrove.
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andy: Frequently people have overdone their efforts to receive the low-power digital signals before switchover, particularly where they were in the analogue coverage area but not in an area covered by the digital radiation pattern. After switchover, when transmissions move to the main antenna, they find that signals are too large.
If you have a booster or amplifier, you probably don't need it. Try removing it. If you don't have one or that doesn't help, you might need to add an attenuator if you're quite close to the transmitter.
I see you had a new aerial fitted in November - did you get a guarantee with it? Can you get the fitter back in to adjust the system?
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Ken mellers: Could be you're on Waltham and have a Group A aerial, although that would be really weird because Waltham is Group C/D for analogue. It could have happened if the aerial used to point to Belmont and was moved around to point to Waltham.
Waltham should produce better results than Belmont after switchover, but you should get a wideband aerial. At switchover, five of the digital multiplexes move into the old analogue group - only Mux A/SDN stays down in Group A.
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Ken mellers: It looks like signals are already going to be pretty strong, I would go with a small- or medium-sized log periodic such as AerialsAndTV.com's DM Log or Log 40. Online TV FM DAB Aerial sales not assume bigger is better - if you use too large an aerial you could have too much signal after (or even before) switchover. Larger aerials are pushed harder by the wind, and will move more, can bend masts or even damage the brick-work that the mast is bolted to.
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Sandy: Digital UK's Postcode Checker gives a 99% chance of getting reliable reception from Winter Hill.
Terrain does block line-of-sight, but it's less than 10 miles away from an extremely strong transmitter. I would recommend getting a professional installer to look at it - they should have the right equipment to figure out the right size aerial and calibrate it properly.
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Friday 6 May 2011 5:04PM
Ian Brown: Nottingham (Kimberley) was a relay of Waltham for analogue services. That is, it received the signal off-air from Waltham and rebroadcast it on different frequencies.
It wasn't possible to do this for digital as the signal from Waltham simply wouldn't reach that far (particularly as the power levels were originally half what they are now). Instead, Nottingham - serving a major town, significant for advertisers and to secure subscriptions for the original onDigital service - was fed independently by leased line, with satellite as a backup.
As it was fed independently, it was possible to switch Nottingham over before its former parent, or indeed any other transmitters in the region.
The fact that everything worked fine before switchover points to having too much signal. Amplifiers and tuners can only handle so much signal before distorting, and that distortion causes errors. The signal contains redundant information so that the box can correct many of those errors, but once the threshold amount of errors has been exceeded it can no longer correct them, and you get sound breaks and picture break-up.
Signal levels do vary naturally over time - this is nothing to do with the transmitter, all to do with signal propogation from the transmitter. This is why it can work sometimes, but not reliably.