All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
dean: Digital UK's trade predictor isn't giving any prediction for COM6/ArqB at the moment, and only 1% chance of reliable reception on COM5/ArqC. While the power on these two multiplexes has doubled, they have changed to a mode that needs slightly more than double the power for reliable reception.
A higher-gain aerial, or one with a tighter acceptance angle (these are often the same thing) might help, but you should know that there will be more channel changes and power increases over the next 10 months, which may bring these channels back anyway.
The predictor suggests that you might get Film 4 back from 16 November, if you retune, when ArqB moves from C54 to C63. The prediction only improves to 'variable' when the final retune happens on 27 June next year. There is a clash with the channels that Dover is currently using, which prevents the final channels and power levels from being used until then.
Your only alternative unfortunately is a Sky or Virgin Media subscription - these channels are not available free-to-air on satellite.
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victor michael minta: I assume you're using the Belmont transmitter - your aerial pointing north-east. So far, only the BBC channels have gone to high power - the other channels do so on the 17th. (Two multiplexes will remain on relatively low power until November.)
Digital UK's prediction is 99-100% across the board. This indicates high signal levels are expected. It's possible that you now have too much signal. If you have a booster or amplifier, try removing it or turning it down. If not, you could try adding an attenuator.
If your Freeview box is old - say before 2005 - it might not be compatible with the mode used after switchover. Check whether it's on the list at http://www.digitaluk.co.u…ment . There's another common fault of older equipment called 'Split NIT' - there is a list at http://www.digitaluk.co.u…tnit . These lists aren't complete, but if your box is on it, see the recommended actions there.
If you retuned very early on Wednesday morning, before 6am, they might not have finished making all the changes. In this case, if it was off-air at the time, your box may have tuned into fringe reception from another transmitter. Try doing another full reset.
Alternatively, if the aerial points south-west, you could be aiming at the Waltham transmitter. This does not start switchover until the 17th. If your box stores the first signal found, rather than the best quality, it may now be able to store Belmont BBC A when it couldn't before, but it's not strong enough to actually use. Check if you have another version of BBC One, Two etc in the programme guide at around 800. If that works, see Digital Region Overlap for some suggestions.
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Robert: Services can come and go with no changes at the transmitter. Signal propogation - how it travels through the atmosphere - differs with the make-up of the atmosphere, its temperature and pressure. That's just normal propogation. At night, you also get reflections and refractions off different temperature layers in the atmosphere - which can cause signals to travel further - and with the right conditions signals can bounce between layers in the atmosphere, making them travel much further. The increased interference can cause your reception to drop out.
The change in propogation - which RF engineers call 'fading' - isn't always the same on all channels at the same time.
All that said: Digital UK's trade predictor takes account of expected degrees of fading and unusual propogation, both in the wanted signal and in unwanted distant signals, in their prediction. It also includes allowances for urban scatter and from woodland. It still predicts that 97% of locations, in the National Grid square that the centre of your postcode is located in, should have less than 1% failures over time, on Mux 2. It's usually considered quite conservative, though it doesn't know about individual trees or large buildings close to your location, only grid squares that contain a large chunk of urban area or woodland.
As I previously said, I think your cables may be damaged from exposure to UV light, rubbing over brickwork or tiles, or junction boxes permitting water ingress. Water changes the properties of the dielectric in the cable, which increases the losses at all frequencies, but greater at higher frequencies than lower. That's made reception marginal and more susceptible to outright failure when there is a greater degree of fading. You need sufficient margin of signal level to cope, without exceeding the combined signal level that will overdrive any amplification - including the receiver's automatic gain control - and cause distortion.
Given your business, I would recommend that you replace your current multiple aerials with a well-designed Master Antenna TV system, with levels of each multiplex adjusted separately and unwanted signals filtered out. Look for installers offering MATV/SMATV systems. (SMATV = Satellite + Master Antenna). Any such system will need to be retuned at switchover stages (14 and 28 September) and at any future retunes.
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Linda: If you've just had a new aerial fitted, it's possible that you have too much gain. The Digital UK prediction is 100% across the board, which indicates very high signal levels. If you're using an amplifier or booster, try removing it. If that doesn't help, try adding an attenuator.
For suggestions on loft installs, see http://wrightsaerials.tv/….pdf and Loft and indoor aerial installations for TV, FM and DAB .
If it was fitted by a professional, I'd call him back to check the system.
The Pontop Pike transmitter uses Group C/D and always has done so, and will continue to do so after switchover, so unless there was a specific problem, there was really no need to change the aerial.
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andyboy: The change on 16 November, ArqB moving to C63 from C50, isn't expected to improve your reception of that multiplex.
Digital UK reckon that you will eventually get better results from Crystal Palace - London news - or Bluebell Hill - south-east news - once those transmitters switch over, if you have the appropriate aerial pointed in the appropriate direction.
Results from Sudbury are expected to remain variable even after the COM multiplexes go to their final channels and frequencies, on 27 June 2012. The problem might be adjacent-channel interference from Dover, so if your aerial is more directional than the model (it should be), you may be fine.
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Richard: Your aerial might be intended for Fenham, that is, it might be a Group A aerial and aimed at and oriented for Fenham. If so, you probably won't pick up enough of the signal from Pontop Pike even though the predicted coverage is actually better.
An aerial for Fenham would have the elements going up-and-down rather than side-to-side, and it will point west-south-west. For Pontop Pike the elements should go side-to-side and it should point south-west.
Checking the group is harder. The elements of a Group A aerial are larger, and spaced further apart, than a Group C/D or wideband. Often, a group A had a red plastic cap at one end, a group C/D would be green and a wideband black.
If you have a Group A aerial, you'd need a new aerial to use Pontop Pike, as it is designed *not* to pick up signals outside its group. It may be worth getting a wideband in case the broadcasters do win the auction for channels 31 to 38 and launch new services there. Given the prediction - 99-100% across the board - I'd go with a small-to-medium sized Log-Periodic aerial.
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P Howarth: Yes, the + indicates a positive offset of 167kHz. Your box should automatically detect this offset if you manually tune on C41. Likewise, the - indicates a negative offset of 167kHz.
These offsets are being applied to the channels bordering the regions being released, potentially for other services, to provide a small 'guard band', avoiding possible interference from those services. C41 may or may not actually get an offset, because C40 is now not being released. Sudbury, which also uses C41/C44/C47, is not using an offset on C41.
The channel numbers at Emley Moor between the 7th and 21st will be:
Analogue:
BBC One stays on C44
BBC Two shuts down
ITV1 moves to C51 replacing BBC Two
C4 stays on C41
Digital:
Mux 1 shuts down
BBC A starts up on C47 replacing ITV1
Mux A moves to C52 to release C43 for Sutton Coldfield, replacing Mux 1
Mux 2, B, C, D and low-power HD all stay on current channels (C40-, C46-, C50-, C49-, C39).
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David: Only if you don't want to record or time-shift. Recording/time-shifting costs £120 per year, and it's difficult to get Sky to sell you this minimum package, they'd far rather sell you a subscription at £234 per year.
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sam, Briantist: ...as long as you remember to record. Or pause when the programme starts, then fast-forward through the ads ;)
I find the +1 channels do serve a small purpose if you discover a programme is half-over on the main channel, or if you're already recording two other programmes. Still, it's usually repeated again at some other time during a week, or you should find it online if it's ITV1, ITV2, Channel 4 or E4. I prefer more content over +1 channels, I just would have preferred a different channel from UKTV's stable.
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Sunday 7 August 2011 8:18PM
lesley: When watching news on BBC One, do you get the East Midlands service, or the West Midlands service from Birmingham? If it's the latter, your aerial probably points south-west to Sutton Coldfield rather than south-east to Waltham or north-west to the Nottingham relay.
The Digital UK trade predictor reckons that you should get a better service from Waltham or Nottingham rather than Sutton Coldfield right now, and even after Waltham switches over (17/31 August) and Sutton Coldfield does (7/21 September).
Nottingham has already switched over - no analogue services - but the three commercial multiplexes are on low power. Retune on the 24th of August for ArqB, and the 27th of September for SDN and ArqA. If you can still receive analogue, you must be getting it from a different transmitter.
If you find you have a different news service on digital from that on analogue, your digital box may have tuned into a different transmitter from the one your aerial is pointing at. Check whether you have another version of the channels at number 800 or so, or anywhere else in the programme guide. If you do, see Digital Region Overlap for ideas of how to correct this.
Digital UK's prediction shows 100% across the board from Waltham, which indicates very strong signals. If you're sure you're using that transmitter, it's possible that you have too much signal. If you have a booster or amplifier, try removing it. If that doesn't help, try adding an attenuator. You should do a full retune each time you change something, so that the box doesn't keep incorrect information around.