All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Graeme White: Can you provide a full postcode please? That's the easiest way to see what the situation is.
If you get all the BBC channels and ITV1, C4, C5, ITV2, C4+1, More 4, E4 and ITV1+1, plus (if you have an HD box) BBC One HD, BBC HD, ITV1 HD and 4hd, that's everything transmitted by this transmitter. All other channels are only transmitted by major transmitters like Huntshaw Cross. It may be that you were previously using a main transmitter, but you may now be too far away from it. Coverage can change dramatically over very short distances - Digital UK actually recommend you provide a house number as well as a postcode, as it can affect which grid square you fall into. Grid squares are 100 metres by 100 metres.
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paul: The most likely transmitter shown for your location is the Wharfedale relay transmitter to your north-west. This only transmits the three PSB multiplexes. See Will there ever be more services on the Freeview Light transmitters? | ukfree.tv - independent free digital TV advice for more information on why.
Digital UK predict that, once it switches over, Bilsdale will also provide a three-multiplex service. However, the commercial multiplexes are expected to be too unreliable. It appears to be because the same frequencies are used at the Addingham relay transmitter, which is a bit further west of Wharfedale. They're also used at the Sheffield site.
Digital UK's predictions are based on an aerial model which performs worse, in terms of directional response and cross-polar rejection, than most real aerials, so it might be possible to receive from Bilsdale - but it would likely still be unreliable.
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andy: Freeview is *not* affected by this change. Programmes are sent to the transmitters by fibre-optic cable, with a satellite fallback from a completely different satellite cluster (a different part of the sky).
Cable head-ends might be fed by terrestrial or satellite signals, or directly by the broadcasters, I'm not sure which.
Conor: BBC One Nations variants in HD (i.e. Scotland, Wales, Northern Ireland) will be coming later this year, but no date is yet set.
NottsUK: That depends on whether it can actually be repurposed for anything else. The main problem is that 2D can *only* offer a spot beam footprint, it can't offer a Europe-wide service, while 1N has Europe-wide dishes as well as the spot beam. The most likely use would be feeds of some sort, or broadband - anything that can cope with a transponder failing at short notice!
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paul: Probably not. You could ask an installer to check after Bilsdale completes switchover on 26 September. You'd likely need an additional aerial, as Bilsdale carries BBC North East & Cumbria, and ITV1 Tyne Tees, not Yorkshire services.
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Be aware that HP and VP aerials from the same site may point in different directions. For example, you've done plots for both Hemdean HP and Hemdean VP, but you've used the VP radiation pattern for both. The page currently only shows my VP plot, the HP plot is at http://i1211.photobucket.….png .
Unfortunately I don't think we have plots for all HP/VP transmitters.
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Josh: The satellite is a relatively dumb relay device. It just transposes the signals sent up to it on a specific uplink frequency to a specific downlink frequency. Replacing one transponder with another is merely a case of sending a command to 2D to turn the old transponder off, and one to 1N to turn the new transponder on. Receiving equipment won't be able to tell the difference, because it's the same signal sent from the same uplink station.
Moving to 1N does *not* imply changing to DVB-S2. Channel 5 have been transmitting on 1N using DVB-S since before Christmas. You can generally expect SD channels to remain on DVB-S, for the widest possible compatibility, with HD channels generally moving to DVB-S2 transponders for the greater capacity. However, if a broadcaster doesn't have enough HD services to fill an -S2 transponder, they'll leave it DVB-S and fill it up with SD services.
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Christopher Coe: Dover transmits three of the multiplexes - 1, 2 and C - on two different frequencies. The second set, which aren't in the old aerial group, are often called 'Dover B' and are listed on this website at Freeview on Dover B TV transmitter | ukfree.tv - independent free digital TV advice (except, for some reason, Mux C on C39+ is missing). These two sets are transmitted from different sets of aerials pointing in different directions.
Many boxes just store the services in the order they were found, scanning from the lowest frequency to the highest. If you've just exchanged a grouped aerial for a wideband, but are out of the proper coverage area for 'Dover B', you may find that your box now tunes in 'Dover B' when it didn't before.
Check for another version of the channels in the 800s, or elsewhere in the channel list. If you want to move them to the proper positions, see Digital Region Overlap.
Digital UK's predictor does show a good chance of reliable results from Dover right now, on all except Mux A, but it doesn't differentiate between the two different frequencies available, it just shows the prediction for the best one, so I'm afraid I can't say which is best for you.
Unless you're splitting the signal to feed multiple TVs, you really shouldn't need a booster after switchover - indeed you shouldn't need one now. In fact a wideband aerial isn't necessary immediately after switchover either - all post-switchover services are in Group C/D. There are proposals on the drawing board to launch new services in a lower frequency range, which will require a wideband, but we're still waiting for information on whether Ofcom will dedicate this range to TV services, and on how they will be auctioning it.
If you still can't get it to tune in reliably, call the installer back.
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Alvin Pritchard: The only ways to fix the problem are to close some services, to allocate some additional frequencies, or to convert to a more efficient standard.
Despite the actually fairly low number of DAB receivers out there, the government have completely ruled out an upgrade to DAB+ until at least after switchover, possibly ever. This is, in my view, idiotic - voluntary takeup is stalling and will continue to stall with DAB as the deployed technology. Remember that DAB started up *before* digital terrestrial TV, it did so in an empty spectrum band, not one already congested with high-power analogue services, and it still hasn't achieved 50% of listening.
While you can do a piecemeal upgrade, as DAB+ is simply a different format of data carried on an underlying DAB data stream, you have to decide which service or services will no longer be receivable on DAB devices - unless you also have some more frequencies.
VHF Band III signals travel a long way and bend well over terrain - compared to UHF TV signals, but less far/bendy than FM (VHF Band II) or AM (Medium Wave, Long Wave) - so must be co-ordinated internationally and across the country. There are 24 frequencies that can be used (excluding those that overlap), but we only have rights to use some of them.
We have actually negotiated block 11A for the second national commercial ensemble. This was licenced to Channel 4 and partners as 4radio, but didn't launch. We could possibly launch national BBC DAB+ services on 11A, if there's some way to get DAB+ receivers to only tune in the DAB+ transmissions - and if someone else will pay for it, or the government will allow the licence fee to rise with inflation again, as the BBC are a bit strapped right now.
Or, of course, we could continue with DAB and fill National 2 with BBC and commercial services transferred from the other ensembles, allowing bitrates to improve for the other services.
Alternatively, we give up DAB completely as a bad loss - as DAB+ isn't significantly more efficient, it's actually less efficient in bits/Hertz - and encourage take-up of some other technology. The promising candidates are DRM+, which deploys in existing radio bands alongside existing transmissions, much as digital TV has, or DVB-T2 taking over DAB allocations. Yes, DVB-T2 was originally designed for TV but it's really just a way of transmitting an ensemble of data streams, and it's a lot more efficient than DAB or DAB+. If you're going to break everyone's receivers, you might as well do it properly!
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michael: The whole ensemble must be carried on all transmitters that carry it, because all transmitters using the same frequency must carry the exact same bits, very closely synchronized. Extending coverage to additional transmitters will probably require negotiation between the services carried on the ensemble and the multiplex operator, to distribute the costs accordingly. That is, if the existing frequency can continue to be used in the new location without either interfering too much with another user of the block, or too much self-interference.
DAB does allow for a service to be carried in different ensembles in different parts of the country, which I believe are linked (similar to RDS) allowing mobile receivers to retune automatically. For example (picking the top one from the list) Absolute Christian Rock transmits from numerous local ensembles, with different frequencies but always with service ID C7C9. However, because of the relative shortage of frequencies, it's unlikely that a very small service area would be created just to allow some services to opt out of an extension of the main coverage area.
In fact North Devon carries the same ensemble as Exeter & Torbay, only on block 10C rather than 11C. They have been licensed to the same operator. So radios will retune automatically on moving from south to north Devon and vice versa.
Ofcom's DAB coverage consultation is based entirely on equalling, as far as possible, both the BBC Local Radio and Independent Local Radio coverage areas. Ilfracombe is included as the second transmitter in the list, after Huntshaw Cross, although I have to admit I don't see where they get the population percentage increase from!
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Monday 20 February 2012 4:02PM
Lisa: BBC B on C30 will have a -167 kHz offset, as it neighbours the 'lower released spectrum' on C31-C38. If that is ultimately used for TV (still very much up in the air, Ofcom haven't designed the auction yet, but there wasn't much interest from phone or broadband companies) then the offset might be removed.