All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Steve P: It is only standard that BBC Two is the first channel switched off. This is because it has the lowest viewing figures of the four channels carried on every transmitter (or had when the plans were made, it has now passed Channel 4) and because it often had the best frequency allocation, as the first channel to start up on UHF, so high-power BBC A usually takes that over.
The move of a different analogue channel to BBC Two's old frequency will occur if the BBC A multiplex has been allocated the other channel's frequency. This might happen if BBC Two's frequency is one of those being released (31-38, 61-68, though sometimes 39 and 40 are freed and 61 and 62 retained temporarily). Or, if a relay has been allocated completely new channels. Sometimes, two of the four analogue frequencies are being released.
If an analogue swap occurs at DSO1 at a main transmitter, there may also be a channel swap at its relays, even if the clash with BBC A's frequency didn't occur, as then the relay equipment doesn't need to be retuned.
In the Sheffield/Chesterfield group next week, BBC A replaces BBC Two except at Hasland relay where it replaces BBC One, which replaces BBC Two for the switchover period.
For the Waltham group, in two weeks' time, BBC A replaces ITV1 at the main transmitter and all relays (except Derby, which doesn't transmit BBC Two at all).
At Emley Moor, on 7 September, ITV1 will move to BBC Two's frequency, as BBC A has been allocated ITV1's frequency.
At Belmont, Channel 4's frequency (C32) will be released, but BBC One, BBC Two and ITV1 frequencies are retained for the PSB services. It's not really clear why BBC A takes over BBC One's channel rather than BBC Two's, but that's what has been decided, so that leads to the situation here.
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KB Aerials Sheffield: Suggesting a multi-channel filter for a standard domestic installation is a little like using a sledgehammer to crack a nut! It'll do the job, but it's probably overkill and expensive.
It's worth noting that Emley Moor has never required a wideband aerial, it's always been Group B. Of course the grouping doesn't mean it picks up nothing at the lower channels, and often the polar response is more omnidirection out-of-group than within group.
In the centre of BD2, 24km from Emley Moor, I would think an attenuator will be *necessary* after switchover anyway (assuming 'high-gain' aerial and sat-grade cables in good condition). If that doesn't fix the overlap, using a diplexer as a filter should work to eliminate Group A frequencies. However, there is a possibility that the lower 'digital dividend' released area, C31-C38, will be used for future TV services - the diplexers I've seen have the split point at C36 or C38.
DUK's predictor reckons there's a good chance of getting Idle on C24/C21/C27/C42/C45/C39 - while this is on vertical polarization, it's not prepared to offer a prediction for Belmont, which David is already getting, and the cross-polarization rejection of the aerial is often similar to the front-back ratio. The predictor doesn't add off-beam rejection to cross-polar rejection, I assume you don't get any more rejection from being off-beam AND wrong polarization than from just one of those. If the box does pick Idle for the commercial muxes, even with a broadband filter, a narrow-band filter setup such as KB Aerials suggests is the only option.
It would be far cheaper to buy a new box that stores what it's told to, rather than mucking about with filtering, of course.
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Dave: You don't actually *need* a wideband for Sutton Coldfield, and with the imminent release of C61-C68 for 4G mobile phones, I would try to avoid fitting an aerial that covers that range. A grouped aerial is generally smaller for the same gain.
I would actually leave it until after switchover, you may find that your current aerial is sufficient, because the final digital power is so much stronger than current levels. If analogue pictures are clear or only slightly snowy, and if the Ceefax/Teletext test described at
Digital UK - The condition of your aerial is OK, you're likely to be fine.
If you only have an 'indoor' aerial at the moment, consider a 40-element Log-Periodic such as Online TV FM DAB Aerial sales . See Loft and indoor aerial installations for TV, FM and DAB and http://wrightsaerials.tv/….pdf for some thoughts about loft installs.
Roof installations usually produce better results as the aerial is further away from electrical cables and reflections in the loft. I would advise a slightly smaller aerial, such as a 25-element Log Periodic Online TV FM DAB Aerial sales . Do remember that bigger is NOT better - you can have too much signal, overloading the tuner and causing distortion, which the box then can't decode.
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joe: First, check that your box or TV can properly handle 8K mode. If it can't, it may have picked off-beam transmissions from Crystal Palace rather than the desired ones from Sandy Heath, when you retuned at switchover. The signals from Crystal Palace could still be strong enough to pick up, but a lot closer to the 'cliff edge', meaning they come and go. There is a list of some equipment known not to work at http://www.digitaluk.co.u…ment .
At present, Mux C at Sandy Heath is still using its pre-switchover 2K mode. Crystal Palace - which switches next April - is still broadcasting everything in 2K mode.
Some boxes will store the first channels they find when scanning, starting at C21 and working their way up, so it could still store Crystal Palace in preference to Sandy Heath. In this case, usually the other set(s) found is/are stored somewhere else in the programme guide - often at channel 800 and up.
Check the frequencies that the box shows for each channel group at the top of the page - this is often in the tuning menu or in System Status. If it says 25 for BBC One, 22 for ITV1, 28 for BBC Four/CBeebies then it's using Crystal Palace. You should do a full reset with the aerial unplugged, to clear all stored channels, then manually tune on C24 and C27 for BBC and ITV. If the box won't detect anything on those channels, try without the amplifier. If it still won't, it may not be able to handle 8K mode at all.
I would strongly recommend you don't try to change your roof-top aerial yourself. If you do require a high-gain aerial - and the prediction suggests that you won't, once all changes are finally complete (9 May next year, unfortunately) - a grouped aerial will be smaller for the same amount of gain. Those tri-booms are, frankly, overkill for most people.
If it's definitely tuning into Sandy Heath, the problem could easily be that water has got into the cables or outdoor connections - this affects the highest frequencies first and worst. ArqB is way up at C67 at present, and Mux A/SDN is shown as the lowest probability of reliable reception at your postcode, for now.
As you can see, it's not a simple answer, and professional assistance might get the problem sorted out sooner.
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Dumb Blonde: Looking at the manual for that TV, it doesn't list DVB-T2, the new system that the UK is using for Freeview HD broadcasts. The design may be slightly too old - the decision to use the new system was only taken in late 2007, the specification wasn't ready until mid-2008 and multiple prototype receivers were first shown in September 2009.
When buying new equipment, check for a 'Freeview HD' logo. This ensures that the TV, set-top box or recorder supports DVB-T2, the MPEG-4 AVC/H.264 compression scheme, and the encoded Service Information used by Freeview HD broadcasts.
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Richard Paskin: The Sagem PVR6240T is on Digital UK's list of equipment known to have trouble with the 'Split NIT' that the broadcasters started using in 2008. The Network Information Table carries information about all the multiplexes available from your transmitter, and that information no longer fits into one block - it is 'split' into multiple blocks. Receivers that expect it to be in one block will fail to store some channels when retuned, or store them in the wrong place.
There was supposed to be an over-the-air update available for this box, but if you missed it, try calling 0871 075 0710 for advice.
(Source: http://www.digitaluk.co.u…tnit ).
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Dean Morris: The Samsung SDT-7000 Plus dates from 2003/4, so could have trouble with 2K and 8K mode on different multiplexes, despite claiming to support both modes: although it doesn't appear on Digital UK's list of known bad equipment at http://www.digitaluk.co.u…ment , a Samsung box of a similar age does appear.
If it just doesn't like having a mix of modes, it should work properly after the second stage in two weeks (17 August), when all multiplexes from Belmont will use the 8K mode. If nothing works after that date, you'll probably have to replace the box. Don't forget to retune after 6 am on the 17th. Do ensure that you do a full retune/full reset/first-time installation, to clear out any previous channel information which might confuse the box.
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Richard Paskin: The source of that information was http://www.digitaluk.co.u…tnit . [This site treats any use of parentheses at the end of a comment as the poster's postcode.]
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Alan: If you'd bought it from a shop, I'd argue that a second failure indicates that it's not of satisfactory quality and they'd have to exchange it. The switchover help scheme is a bit of a grey area. Contact your local Citizens' Advice Bureau and see what they say.
I assume that you paid for satellite equipment to be installed, or was Freeview (through an aerial) not possible where you are?
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Saturday 6 August 2011 7:20PM
Alan: yes, the relays are another very good reason why ITV1 analogue would not be switched off early, or even BBC Two turned off. The relays, as the name indicates, receive the signal off-air from the main transmitter at Tacolneston and retransmit it on a different frequency. (Some may go via another relay.) It would definitely be unacceptable to leave some viewers completely without the channel.