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
Netherton Braes (East Renfrewshire, Scotland) Freeview Light trThursday 17 March 2011 12:19PM
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Marcos Brooks: The transmitter at Netherton Braes does not currently transmit digital signals. If you have poor quality pictures on analogue, then you probably do need to have the aerial and/or cables replaced.
If you're picking up digital signals now, they're probably coming from the Black Hill transmitter. Check whether the aerial's rods are pointing side-to-side or up-and-down. If they're up-and-down the aerial is intended for use with Netherton Braes, and you're getting much less digital signal than you could be getting if you had the right aerial.
Netherton Braes will transmit only the public service multiplexes after switchover - it will be a 'Freeview Light' transmitter. For the full range of channels you would need to use Black Hill. This should be possible with a normal-sized aerial, and if you're only feeding one TV, without amplification.
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jo: If you have Freeview HD equipment, it should have asked you to select your region. Sometimes, the broadcasters add a character to the region description (usually a dot) to indicate that they've changed something. Some boxes don't handle this properly if they retune automatically, and only store the channels that still match the original region description.
You may be able to fix it if you do a full reset of the box, then select the region that has the most channels, if more than one is offered. You may lose the HD services, though. You might then be able to get them back by manually adding them.
If this does fix it, you should report the problem to the box's manufacturer.
Otherwise, I suggest entering your postcode under My Settings in the top-right corner, and leaving a message on the page for the suggested transmitter. It's probably Emley Moor, which was off-air from midnight to 6am yesterday.
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Andy: Weather conditions can cause transmissions to travel further than expected. The fact that a number of transmitters in the north and west of the country have already switched over means that there is now something to interfere with the transmissions, where there wasn't before. (Other digital transmissions on the same channel seem to cause more problems than analogue transmissions on the same channel.)
In addition, sites on the continent are now broadcasting digital only in the UHF band, where many analogue channels used to be broadcast at lower frequencies. It all adds up to a noisier environment than a few years ago.
On top of that, there may be periods where power has to be reduced slightly, if men are working on the mast, though this should only happen during daylight.
The 'analogue' aerial has pride of place at the top of the mast, has plenty of gain, and is able to handle plenty of power. The 'digital' transmission panels are bolted to the west side of the mast, and point due west, slightly west of north, and slightly west of south. To get the full coverage and power levels, digital signals move to the main aerial at switchover - this is why the transmitters are off-air for about six hours on the switchover days!
Just as your receiving aerial isn't really 'analogue' or 'digital', nor are the transmitting aerials. They're tuned to work best in one area of the UHF frequency band (for Hannington, between channel 35 and 68), but otherwise it just broadcasts whatever is fed to it.
The old 'analogue' aerial was erected in 1969 and had reached the end of its useful life at 41 years. Technology has moved on and the new designs can direct more power to ground level rather than up in the air. So a 'reserve' aerial was added in July 2010 to handle analogue transmissions temporarily, and the old main aerial replaced in October. However, I don't think there was time before the weather turned to get all the cables replaced and the new main aerial into service. That's what I think they've been doing over the last few weeks.
As for 'dropping dramatically' - digital requires a certain amount of signal quality to work, but above that level, you get no improvement. We call the amount of signal you have above this minimum level the 'headroom'. Deterioration in equipment and increases in noise reduce this 'headroom', but you won't notice a thing. Then it drops below the minimum required level, it starts to block and break up, and rapidly just goes to NO SIGNAL. Most digital boxes do not measure the headroom - their signal quality meters only report *uncorrectable* errors. This makes them completely useless.
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John8: you can see a more detailed picture of what's happening to which multiplex at Digital UK - Postcode checker problem is that around the 27th of September, another transmitter will start using C48 - I believe it's the Sandy Heath transmitter, where ArqB moves to C48 on 14 September. Since it is the same multiplex, if they co-ordinate it, it could reinforce the signal from Nottingham rather than interfering, but this has not been announced and the predictors treat it as interfering. Some time in 2012, the same problem will happen with the SDN and ArqA multiplexes when another transmitter switches over, or has a post-switchover event. Since the date isn't shown in any more detail, it's hard to say which this is and what the effect will be. Again, it could be Sandy Heath, and again it could be reinforcing as the same channels are used for the same multiplexes. (RG47SH)
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M
Crystal Palace (Greater London, England) Full Freeview transmitThursday 17 March 2011 2:10PM
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ian hayes: all aerials are HD compatible. The problem is that it is indoors. Indoor aerials are not very good, generally, and you lose a lot of signal because there isn't a clear line of sight to the transmitter, through both internal and external walls and neighbouring buildings.
Right now, the HD signals are broadcast at half the power of the other multiplexes - they need about the same power as multiplex 2 (e.g. ITV1) and A (e.g. ITV3) to work reliably.
You really need a roof aerial for reliable reception. If you did have one, you'd be expected to get reliable HD service now, and after switchover next year.
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Stuart O.: Sometimes the map doesn't show all the pins, particularly if you're using Internet Explorer, but in this case, I can only find one site that ever used C63 for Channel 4 - Glenridding in the Lake District. This switched over in July 2009 and no longer uses this frequency.
I searched the list at http://www.wolfbane.com/articles/uktv2.htm
The only things I can think of are that it's the RF output of a Sky or Freeview set-top box (yours or perhaps a neighbours, if you're sharing an aerial), or if you're using a communal system, a system where the channels are transposed to different frequencies. This is usually done if the signals from the transmitters are strong enough to be picked up directly by cables within the flat, which then arrive at different times from the signals received at the aerial, causing ghosting on analogue (and, likely, errors on digital).
If your TV, aerials or cables are very close to a neighbour's equipment, and that equipment isn't well shielded, it could be picking up a tuned version - but you'd expect it to change which channel is displayed when they choose a different channel! (RG47SH)
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Katie: I'm assuming you're using Freeview, digital TV through an aerial, rather than satellite.
The phone does use frequencies very close to the top end of the range used for TV. You can really only check that the cabling is in good condition, and possibly have it routed differently so the cable doesn't go past her room.
If there is a distribution amplifier, it might need better screening to prevent it picking up noise, or the power supply might be failing. If you're using wall-plate sockets, they might need to be replaced with screened ones if you haven't already done this.
Finally, older aerials were often not matched properly with the cable, because it didn't matter as much with analogue. You might need to replace the aerial with one of a similar size that has a 'balun', a device that matches the aerial properly to the cable.
If you haven't replaced the aerial or cables within about the last ten years, it may be time. Aerials and cables deteriorate with weather and sun exposure and this problem could just be a sign that they're no longer getting enough signal to where it's needed.
Has your region switched over to entirely digital yet? If not, it may be worth waiting until it does. For more specific advice, we'd need your postcode to see which transmitter you'd be using and how strong a signal you should expect.
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Simon Bramley: You can really only contact the channels that you want to watch and ask if they can get the commercial multiplex operators to serve your transmitter. The commercial multiplex operators are SDN Limited and Arqiva Services Limited. SDN is a subsidiary of ITV plc, and they don't have a website or other contact details that I can find. Arqiva Services is a subsidiary of Arqiva: their contact details are at 404 may be difficult to find free frequencies to broadcast from, as the plans were made on the basis that the commercial multiplexes would only broadcast from the 81 sites they did before switchover. When they were asked if they wanted to broadcast from any more sites, they said no. The channels will probably tell you to get Sky. Satellite transmission is much cheaper for them, and they can get some of the subscription revenue. Of the three multiplexes you do get, the BBC are only allowed to carry BBC channels on PSB1 (BBC A), and ITV and Channel 4 only allowed to transmit their own channels on theirs (PSB2/D3+4), plus they have to carry Channel 5's main channel. The HD multiplex is run by the BBC, but they're required to carry any HD channels that Ofcom specify. Currently it's ITV1 HD and 4hd as Channel 5 turned down the offer. (RG47SH)
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Mark Ward: There was engineering work at the Emley Moor transmitter from just after midnight until around 6am on Wednesday. This was announced on Digital UK's Planned Engineering Works page the day before.
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Thursday 17 March 2011 12:10PM
Reading
Ken Dalton: At a guess, you were using the Emley Moor transmitter, which was shut down for maintenance from around midnight to around 6am on Wednesday.