All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.Nicks: As text services, Rabbit and Gay Rabbit take very little space. Certainly not enough space to provide even one TV channel - possibly not enough to even carry one radio station.
The ITV1 +1 and Channel 4+1 channels are the most wasteful on there, but the infrastructure for carrying regional content only exists on D3&4 - they would have trouble providing regional variations (minimal as they are: on C4 just the advertising is regional) on a commercial multiplex.
Legally, the ITV companies and C4 are required to carry the regional ITV service and Channel 4, Channel 5 and S4C in Wales. After that they are permitted to carry whatever *of their own services* they like on their half of the multiplex.
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Jo Drury: It comes down to money. The commercial multiplex operators didn't want to spend any more on transmitting from any additional sites. The regulator had been prepared to negotiate for 200 sites (currently, the commercial operators broadcast from 81 sites) in the international co-ordination meeting in Geneva in 2006, but the operators declined the option.
The Aldeburgh relay may not be your best option in this area, though as you say the coverage area is quite large. If you provide a full postcode we can check whether a six-multiplex service is available from another transmitter.
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michael: BBC Devon is required to be, and is already, carried on the Exeter and Torbay (East Devon) and Plymouth ensembles. Receivers can use channel information to roam between DAB ensembles in the same way they use RDS to roam between FM transmitters.
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Michael Lancaster: Permanent until switchover next April.
In fact the power level is not low. It's the same as the other multiplexes. However, because they use a different mode, they require effectively twice as much power as the other multiplexes to provide the same coverage. The reason for this is historical.
After switchover, all SD multiplexes will use the same mode. The HD mux uses a different mode entirely, which requires about the same power for the same coverage area, so all multiplexes will be equal from Crystal Palace as all have the same power level.
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David: This site's predictions are unreliable, because it doesn't have knowledge of all the transmitters' radiation patterns, and doesn't have detailed terrain information. Use Digital UK's postcode checker, which is based on the BBC's 50 years of knowledge of how UHF signals travel across terrain, and computes interference from every other transmitter in the country.
It looks like you have clear line of sight to both Sudbury and Aldeburgh, so I'm guessing that the poor projected result for Aldeburgh is either down to the radiation pattern, or due to interference from Crystal Palace, which uses the same frequencies. From November until April, Aldeburgh BBC A will clash with ITV1 from Crystal Palace, while the other two multiplexes clash with low-power multiplexes at CP (though 'low power' at CP means 20 kW). After CP's switchover in April, they will clash with two high-power multiplexes.
You should get a solid PSB service from Sudbury after switchover, but the three commercial multiplexes (A/SDN, C/ArqA, D/ArqB above) will stay on their current channels with little change in power until after Bluebell Hill switches over next June. The prediction, from 20 July, for SDN is variable while no prediction is offered for ArqA and ArqB. After the channel change on 27 June 2012, the prediction for SDN and ArqA is good, but ArqB remains variable. A reception change is shown in 2013 which will drop the COM muxes to variable - this may reflect switchovers on the continent, which I believe DUK always show in 2013, whenever they really happen.
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David Hutson: We can't really offer any detailed advice without a full postcode.
For best results from Rouncefall, you should use a Group B aerial oriented so that the rods run up-and-down rather than side-to-side. However, the transmitter also provides a fill-in function for Sudbury PSB multiplexes - Sudbury and Rouncefall form a 'Single Frequency Network', where the transmissions from both are timed carefully so that in the overlap area, the signals largely reinforce each other. If you're in this overlap area, you should probably aim your aerial at Sudbury as that transmitter provides a full service.
Rouncefall will not transmit the three commercial multiplexes, Mux A/SDN, C/ArqA and D/ArqB. You will need to use a main transmitter for those.
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Peter Stonebridge: There is no standard way to access digital text and not all channels carry it. For BBC channels, press the red button on the remote. For ITV1, C4 and C5, press TEXT.
Your TV may show some indication that text or interactive applications are available on the channel. My Humax box shows an 'MHEG' indicator.
Subtitles are always accessed using the dedicated subtitles button on the remote.
Poor signal quality could lead to the MHEG data for the text service not all being decodable, though I would expect you to get some picture and sound break-up as well. If quality is right at the top of the so-called 'cliff edge' you can get poor picture quality without actual break-up, and there might be problems with MHEG at this quality level as well, but it's a very narrow range at which this happens.
DUK predict that your reception of the BBC mux is currently variable. It should improve to 'good' next week.
Do be aware that it is possible to have too much signal as well as too little, and users of Sudbury will be particularly likely to end up having too much signal as the post-switchover digital power is only reduced slightly from analogue, while much larger than pre-switchover digital levels.
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Tony: Yes, the prediction at that location from Black Hill is currently shown as poor. It is expected to improve next year, possibly when the Tyne Tees region completes switchover.
Bridge of Allan only provides three multiplexes, but the probability of reliable reception is shown as good from all three.
You're likely to need a different aerial to use the relay. It transmits in Group A, which wideband aerials are relatively weak in, so a grouped aerial is advised. An existing Black Hill aerial would be Group B. The aerial would also need to point at the transmitter, and the aerial elements need to run up-and-down rather than side-to-side (vertical polarization rather than horizontal).
The predictor also shows that a reliable three-multiplex service should be available from the Craigkelly transmitter north of Edinburgh, though you'd get the Edinburgh STV news service rather than Glasgow. You need a wideband aerial for all six multiplexes, though the prediction for the commercial multiplexes is poor.
Aerials are designed to reject signals from the wrong group, from other directions, and from the other polarization, so it's likely that there is too little signal to just tune into one of the other transmitters.
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Jenny: Or indeed on the Belmont transmitter page - "Hull" is a radio transmitter only.
The predicted coverage is excellent, there are no reported issues at the transmitter, and no planned engineering work this week. Check that all cables are intact and connected properly, including the connection to the aerial. Do a visual check to ensure that the aerial is still intact and pointing in the right direction. It should be pointing roughly south-east for Belmont.
There is engineering work at the Bilsdale transmitter, for north Yorkshire/south Teesside, though it transmits the Tyne Tees service rather than Yorkshire, so you're not likely to be using it.
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Monday 27 June 2011 5:35PM
Northampton
Mr K P Brady: Does the problem happen on all channels, or only some? If all channels, it could be a case of impulse interference or electrical noise. Check whether the problem comes and goes as the central heating or hot water thermostat goes on and off, or a pump goes on and off. If so, get a heating engineer to replace the thermostat or the pump.
The aerial could be pointing at Dallington Park, less than a mile to the south-west, or
Sandy Heath itself, which is slightly south of east. If using Dallington Park, the aerial elements should run up-and-down rather than side-to-side, as they should for Sandy Heath.
If you're using Sandy Heath, and only some channels are affected, this could be expected at the moment. Channels carried on Multiplex A, C and D are currently showing no prediction for NN2 6BU, meaning they're not expected to be reliable, though your box may still be able to detect them well enough to store the location. We need a full postcode for a better prediction.
Dallington Park doesn't even carry these multiplexes, and there is no plan to ever carry them. Depending on the exact aerial and location, they still might come through strong enough from Sandy Heath to be detected - but not reliable - if the aerial does point to Dallington Park.
If using a shared aerial, contact the landlord or agent. See also PARAS - Professional Aerial Riggers Against The Sharks for other ideas of who to contact.
You can also replace the cables to reduce the pick-up of noise. If the TV connects to a wall aerial socket, you can replace just the 'fly lead' that does this last step. Try Online Satellite/TV/FM/DAB Cable, Leads and Connectors sales. . The wall socket might not be properly screened - this would be a job for the landlord if this is a communal system. Finally, it's recommended that if the cables are replaced, that 'satellite-grade' cables (with dense copper braid over copper foil screening) are used, to minimize noise pick-up.