All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.m Sim: Most likely, your aerial is pointing to the Oxford transmitter. There have been no planned engineering works. We can also see reported faults on the BBC channels, which shows a problem on BBC One analogue for half an hour on Friday night, but we don't have that information for ITV.
It's possible that if you have retuned in the last couple of months, that the fringe reception from Sandy Heath - which is on a lower frequency - is strong enough for your box to detect, and that it is a model that stores the first version found in the scan rather than the strongest/best quality signal.
If so, the solution is to delete the channels you're having a problem with, and do a manual tune on C68 for ITV1/C4/C5 etc, and C54 for CBeebies. See Digital Region Overlap for other ideas.
If that doesn't resolve the issue, it could be a cabling issue. The multiplex carrying ITV1 etc is right at the top of the frequency range, and there is more loss in cables at higher frequencies than lower ones. Particularly if it's wet, water can penetrate into junction boxes and into old, perished cables, which means they perform worse: again, higher frequencies are affected worse than lower ones. This is likely to be the problem if the analogue channels have become more snowy than before.
If this is the case, you probably need to have the cables replaced. At the very least, the seals on any junction boxes or outdoor amplifiers or splitters need to be checked or replaced to stop water getting in, but there's a good chance that the cable's dielectric - the plastic or foam material between the inner metal conductor and the outer metal screen - are saturated.
Do also check that the aerial is intact and still pointing in the right direction.
The power increases greatly at switchover, at the end of September. This might make things better for a while but a cable fault will typically get worse over time.
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Ian Young: All we can say is that the commercial multiplexes have no plans to extend services to any more transmitters. They were asked, in the planning stages, and they turned it down, saying it was too expensive.
Digital UK's trade predictor reckons that you could get a signal from Black Hill with the right aerial, but the reliability is expected to be poor. You might manage reliable service with a larger-than-usual aerial. However, the cost of installation might mean it's better to investigate satellite.
Dave is a subscription channel on satellite, so you'd have to pay Sky at least £19.50 per month. Virgin Media cable is not available in your area.
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KMJ,Derby: It appears that the Sudbury transmission on C49 was restricted to the west to protect Oxford C5, and that this may have been done by transmitting out-of-phase signals from the lower aerial panels on the west side of the 'digital' mast in addition to the main signals from the top of that mast.
There was no restriction on Mux A before switchover, so it's possible that the out-of-phase signals providing the restriction are no longer transmitted - if that's how it was done.
Information sources: Sudbury Transmitter (note MUX3 = Mux A in this table), U.K. Television Stations (UHF Digital System) for aerial heights which indicate that there was a contribution from both arrays for Mux 1 and B, and the pictures at mb21 - The Transmission Gallery .
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Mark: The three public-service multiplexes - which carry the BBC channels, the primary ITV and Channel 4 channels, Channel 5, and the HD channels - will broadcast at 100 kW from 14 August (BBC SD channels)/28 August (other channels).
The other three, commercial, multiplexes, will ultimately transmit at 50 kW. They are restricted to 12.5 kW until 18 April 2012. This is when the Crystal Palace transmitter group completes switchover. We haven't been given reasons for the power restrictions, but you can often figure it out by looking at the maps of other transmitters using the same frequencies. My guess is that this is to protect viewers of the High Wycombe transmitter, although this will continue to use these channels after switchover. Some of Hannington's north-western relays (Lambourn, Chisbury, Hemdean) also use these channels, and are moving to different channels at switchover. However, Hannington's switchover is in February.
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Ian: If you're north or north-west of the transmitter, or if your aerial points in that direction, you may be affected by occasional interference from ArqB from Winter Hill, which uses the same channel (C55). Winter Hill's power level on this multiplex is restricted to reduce the problems, but some people are still affected.
Try rescanning during the day, if you last rescanned at night, or vice versa. Signal propogation - how it travels - varies depending on weather conditions and on temperature layers in the atmosphere, so some variation is normal and to be expected.
The problem will go away at switchover, as Mux D/ArqB will be moving to a new frequency that will not clash with Winter Hill.
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james cobby: The centre frequency of C21 is 474 MHz, and each channel is 8 MHz apart. To convert a UHF channel number to a centre frequency:
f = 8 x (n - 21) + 474 MHz
where n is the channel.
Check your box's manual for where it displays the UHF channel for the service you're watching. It isn't necessarily in the tuning menu.
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Steve P: DVB-T is not designed for mobile reception. The receiver has to read the entire multiplex all the time, every bit transmitted, while for DAB (and DVB-H) it knows when the data for the station you're listening to will arrive, so it can power the receiver up just for the data it needs. The Doppler effect - frequencies shift if the receiver is moving - is also a problem, as inter-carrier interference occurs. This happens at speeds well below 60 mph for the mode of DVB-T used in the UK after switchover. The Doppler effect still affects DAB, but not as much, both because it transmits at lower frequencies and because it uses fewer carriers. It's the difference between being able to use it on a high-speed train (coverage permitting) and only at walking pace.
http://www.broadcastpaper….pdf
Only the BBC National Radio stations and a few commercial radio stations are broadcast on DVB-T. The commercial stations are carried on commercial multiplexes, which have significantly lower population coverage than the PSBs, due to not being carried on all transmitters, and also at lower power than the PSB muxes on many of the transmitters they are carried on. The commercial muxes are not regionalized, so you get 'national' variants of Capital FM and Heart rather than the local breakfast show.
DVB-T is not a replacement for radio broadcasting in whatever form.
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Souriau: We have absolutely no idea. Ofcom haven't published that information yet. The RTE multiplex is not yet licensed. The digital switchover plan does not show any frequencies allocated to this multiplex and that would be where we would expect to find the information.
It looks like it will be broadcast using DVB-T2 in 16QAM 1/2 mode, and therefore you will need a Freeview HD receiver, even if the stations transmit in SD to begin with. They will probably use MPEG-4 AVC/H.264 as that's what's used in the Republic.
The latest we have is at Digital Television - Technical guidance on the availability of TG4 in Northern Ireland after digital switchover .
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David Maxwell:
Tacolneston Transmitter group works on 13 and 14 July 2011
Engineering transmitter work will take place between 00:01hrs and 06:00hrs.
TV services that will be disrupted:
Analogue services - BBC1, BBC2 and ITV.
Digital services - Not affected.
from
Digital UK - Planned Engineering Works .
It's likely that they're performing high-power digital tests - BBC Two will be replaced by BBC B, ITV1 by D3&4, and BBC One by BBC A at switchover, while Channel 4's frequency will be released, so it doesn't need to be turned off for the test. The commercial multiplexes will get new frequencies, not replacing any existing services.
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Friday 8 July 2011 10:11PM
Keighley
Lorna Smith: Sometimes there could be a UHF channel clash between a main transmitter and a relay, or between two main transmitters, where there wasn't one before. The planners have tried to avoid it but sometimes it hasn't been possible to cram everything in, while releasing one-third of the available channels and minimizing the number of people who have to change their aerials to get the public-service channels.
People who are *only* covered by a relay transmitter that did not transmit Freeview before switchover will only get the three public-service multiplexes after switchover. I haven't seen the leaflets, so I'm not sure exactly what they say.
Looking at your previous posts, you gave the postcode BD20 8TT, which is expected to get very reliable reception. Indeed the prediction is so high that you may have too much signal after switchover. If you find that your reception is unreliable, remove any boosters or other amplifiers, and if that still doesn't fix it, add an attenuator to reduce the levels.