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Analogue and digital signal strength

The strength of an analogue signal is no guide to the strength of a digital signal

The strength of an analogue signal is no guide to the strength
published on UK Free TV

Many people ask why they can receive an OK analogue picture, but need to upgrade their aerial to get Freeview, or sometimes get perfect Freeview reception when the analogue picture is very poor.

The digital signals are currently broadcast at low power (this will change as switchover happens) to prevent interference with the existing analogue signals. Thankfully most Freeview boxes can work with these weak signals. The following list shows the strength of the digital signal compared to the analogue for the 80 Freeview transmitters.

Expr2 Aberdare: 15%
Angus: 2000%
Beacon Hill: 1%
Belmont: 1.43%
Bilsdale: 1.15%
Black Hill: 4%
Blaenplwyf: 1.66%
Bluebell Hill: 8.88%
Bressay: 10%
Brierley Hill: 1.22%
Bristol Kings Weston: 4.5%
Bromsgrove: 1550%
Brougher Mountain: 0.5%
Caldbeck: 0.82%
Caradon Hill: 0.76%
Carmel: 2%
Chatton: 4.16%
Chesterfield: 1.8%
Craigkelly: 2%
Crystal Palace: 2%
Darvel: 2%
Divis: 0.49%
Dover: 1%
Durris: 2%
Eitshal: 0.8%
Emley Moor: 0.93%
Fenham: 1%
Fenton: 0.5%
Guildford: 1%
Hannington: 4%
Hastings: 18.3%
Heathfield: 1.2%
Hemel Hempstead: 2%
Huntshaw Cross: 3.66%
Idle: 2%
Ilchester Crescent: 4%
Keelylang Hill: 1%
Keighley: 0.91%
Kilvey Hill: 3.83%
Knock More: 1%
Lancaster: 1.83%
Lark Stoke: 416.66%
Limavady: 0.8%
Llanddona: 1%
Malvern: 10%
Mendip: 1.83%
Midhurst: 1.25%
Moel-Y-Parc: 0.41%
Nottingham: 1.85%
Olivers Mount: 9.1%
Oxford: 1.6%
Pendle Forest: 18.2%
Plympton: 9.15%
Pontop Pike: 1.93%
Pontypool: 6%
Presely: 0.83%
Redruth: 1.85%
Reigate: 1500%
Ridge Hill: 2%
Rosemarkie: 10%
Rosneath: 2%
Rowridge: 4%
Rumster Forest: 1.33%
Saddleworth: 1.8%
Salisbury: 6.9%
Sandy Heath: 1.83%
Selkirk: 6%
Sheffield: 1%
Stockland Hill: 1%
Storeton: 2550%
Sudbury: 2.01%
Sutton Coldfield: 0.8%
Tacolneston: 2.66%
The Wrekin: 1%
Torosay: 0.62%
Tunbridge Wells: 1%
Waltham: 1.8%
Wenvoe: 1.16%
Whitehawk Hill: 3.67%
Winter Hill: 1.83%

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Saturday, 30 July 2011
Brian Parker
8:58 AM

i live near peterborough & we have had switch over but our tv keeps pixerlating iv'e got a digatal arial but sometimes we have no tv at all, can you help me please, thanks Brian

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Brian Parker's 1 post GB flag

11:30 AM

Brian Parker: Taking it that you are referring to Sandy (many Northern areas of Peterborough use Waltham) then it depends on what channels you are referring to, as remember you will only receive the main BBC and ITV stations at present as all others are still on low power, albeit that "some" can be picked up but in a very erratic fashion dependant on location.

Both main stations are quite powerful up in the Stamford area, and if its these main stations you are referring to then its liable to be caused by deficiencies with your aerial.

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jb38's 7,179 posts GB flag
Thursday, 4 August 2011
Alan Parker
11:32 AM

I have read recently that Digital TV signal strength broadcasting will not come onto full power until sometime in 2012. Is this correct and if so, what date?

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Alan Parker's 1 post GB flag
Mike Dimmick

2:54 PM

Alan Parker: It depends where you are.

Switchovers for the following regions aren't scheduled until 2012:

Meridian (excluding Oxford)
Tyne Tees (no dates announced)
Ulster (no dates announced)

Switchovers for some transmitters in these regions will require changes after the publicised 'switchover' dates, in 2012:

Anglia (Sandy Heath, Sudbury)
Border (Caldbeck)
Central (Oxford)
STV Central (Darvel)
West (Mendip)
West Country (Stockland Hill, Huntshaw Cross)

The interlocking nature of the frequencies used at sites around the country means that some changes have to be delayed so that as few people as possible lose any service they already had.

Where I say 'channel' below, I mean the radio frequency that the service or multiplex is transmitted on.

At almost all sites, the three public service multiplexes - carrying the BBC services, ITV1, ITV1+1, ITV2, Channel 4, C4+1, E4 (except Wales), More4, Channel 5, and the four HD services - start up on their final channel at switchover and at full power. This is because they are directly replacing the analogue channels, which don't clash with any pre-switchover services at other sites.

At some relays, the post-switchover channels are different from those used before switchover, and are not available until changes happen at other sites. Where this happens, a temporary channel is used, but at full power. In some cases, if a relay only transmitted two services - cases where the 'wrong' region was transmitted from the best main transmitter - the HD multiplex is postponed until later (e.g. Derby).

The three 'commercial' multiplexes, which carry the rest of the services, are harder. The analogue system was planned for four channels at each site, meaning at least two more frequencies have to be found for sites carrying the commercial multiplexes (only the 81 main sites that broadcast digital before switchover). Two chunks of space aren't available, either, with C31-C38 being released for some undefined future use and C61-C68 released for 4G mobiles, which often rules out at least one of the old analogue channels. They have to be co-ordinated with overseas broadcasters too. So there are often clashes between what has been allocated, and what is available at the time of switchover. Those clashes might be with a relay that will move to new channels at switchover, or with a low-power digital service elsewhere that is yet to switch.

Where this happens, the best option is usually to leave the low-power versions of the commercial multiplexes alone for the time being - on their original channels and original power levels - until the other site switches over and releases the required channel. Where possible, a (relatively) small increase in power is used, and/or a retune to use one of the frequencies used by a multiplex that has moved to its final location.

However, some services have started up in the BBC's spare capacity before switchover, and they must move to a different multiplex at switchover because this capacity is removed (for HD services). To do this requires the Mux C/ArqA and Mux D/ArqB multiplexes to change mode, and this mode needs more power. Many sites get a small power boost, but this may not be enough for all viewers to keep the services in the interim period before the final channels and/or power levels are available.

A few sites have to swap their interim channels for different temporary channels, before getting their final locations, to work around more than one clashing site.

If you provide a full postcode I can give an indication of when you will need to retune and whether any interim arrangements apply.

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Mike Dimmick's 2,486 posts GB flag
Wednesday, 10 August 2011
Jane Ashton
2:20 PM

Despite correct digital aerial viewing is now daily misery of pixelation, freezing, clicking sounds, sound loss and no reception.
This had been getting progressively worse. This is effecting neighbours also. Do we just have to wait it out until our switchover? Don't know when this will be.

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Jane Ashton's 1 post GB flag
Mike Dimmick

2:59 PM

Jane Ashton: You're most likely using the Rowridge transmitter on the Isle of Wight, which switches over next March.

Digital UK predicts a good chance of reliable reception now on Mux 1, 2, A and B, while C and D are expected to be variable. It's always more difficult on a long sea path, and you also have to contend with interference from northern France - I believe they are further along in their switchover than we are.

A new, taller mast has been built at Rowridge, to the west of the old mast, to improve coverage after DSO, but I'm not sure whether services use this mast yet.

It's still worth checking that your aerial is intact and pointing the right way, and the cables are in good condition. Cables should be well secured so they can't move about when the wind blows - if they have been able to move, they may have worn away the outer insulation against tiles or brickwork, or just pulled out of the connection. Also, the insulation does perish with exposure to UV light - as a rule of thumb, outdoor cables last about 10 years. Damaged insulation lets water in, which increases the amount of signal lost along the cable and can damage equipment if it manages to run all the way along the cable.

For other ideas, see 'Freeview reception has changed'.

The postcode predictor reckons that you'll get a very good chance of reliable reception from the PSB multiplexes after switchover, but the COM multiplexes may be variable. Once they reach their final channels on 18 April 2012, you will get better reception by rotating the aerial so the elements go up-and-down rather than side-to-side, as Rowridge will then transmit more power on vertical polarization than horizontal. Don't do it until then, as it doesn't use vertical polarization at all until switchover.

The change to VP is intended to combat interference from French stations.

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Mike Dimmick's 2,486 posts GB flag
3:41 PM

I live in Rhodes Greece
Get al l channels except 4and five but lose them at midday till 6pm anyone know why

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billy's 2 posts GR flag
Friday, 2 September 2011
8:03 PM

I have paid to have an aerial on the roof (stevenage) pointing to crystal palace. My freeview reception sometimes freezes momentarily and i sometimes get a black screen. I get a rubbish snowy picture on analogue.

Is the aerial aligned properly??

Thanks for your help.

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paul's 1 post GB flag
Saturday, 3 September 2011
Steve P

11:07 AM


Why do you not use Sandy Heath, which is far stronger?

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Steve P's 1,173 posts GB flag
2:08 PM

my duaghter has just moved into a flat in Edinburgh and cannot get a signal of any sort on her TV. Same problem with an indoor aerial and trying another TV.

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Sheena's 1 post GB flag
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