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Update on transmitter radiation patterns (BBC FOI request)

The BBC have responded to my request for an update to the sites that they have provided the "radiation patterns" for.

The BBC have responded to my request for an update to the sites
published on UK Free TV

I wrote to the BBC under the "Freedom of Information Act" in 2009 to ask them to disclose the radiation patterns used by the transmitters in the UK. This information shows the level of signal reduction from each transmitter in each direction, as the signals are not always broadcast at their full power (the "ERP") in all directions.

The response, which I posted here on 5th September 2009 can be see here: BBC Freedom Of Information - transmitter radiation patterns and these are now included in the transmitter pages on UK Free TV, as shown in this example:

Also provided was some information on the pre-switchover patterns for certain transmitters, see BBC FOI transmitter data - first draft from 12th September 2009.

I recently wrote again to the BBC asking them to disclose the information for the masts that were "redacted" (withheld) in the original request. These masts are listed at the foot of this article.

The response from the BBC today is shown below:

British Broadcasting Corporation Room 2252, White City, 201 Wood Lane, London W12 7TS Telephone 020 8008 2883 Fax 020 8008 2398 Email

Information Policy & Compliance

6 March 2012

Dear Brian,

Freedom of Information Act 2000 - RFI20120153

Thank you for your request under the Freedom of Information Act (the Act) of 9 February 2012, seeking the information which we had withheld from our earlier response to your previous request under the Act of 3 August 2009 (our reference RFI20091165).

In our reply to RFI20091165, we stated that we expected international negotiations regarding coordination of certain of the antenna patterns which you had requested to continue until the end of 2012. I am advised, however, that Ofcom has informed our spectrum planning team that these negotiations have not yet concluded and may in some cases still have some months to run.

Since we last wrote to you regarding this matter, it has also become clear that a further clearance of spectrum currently allocated to DTT is to be expected, for which international negotiations may start shortly. Therefore, I am afraid that it appears to us that negotiations surrounding these have not concluded.

For that reason, therefore, I regret that we must continue to withhold the data for these sites under the exemption in section 27(1) of the Act ("International Relations").

As set out in our response to RFI20091165, the exemption referred to above is a qualified exemption, which means that it must be tested against the public interest in favour of disclosure.

We note that for a number of transmitter sites (that is, all those marked as "Redacted" in the spreadsheet accompanying our last response to you), the exact radiation pattern that is to be employed is still subject to, or is likely to require, negotiations between HM Government (represented by Ofcom) and the equivalent administrations in these neighbouring countries.

The arguments in favour of disclosure are:

  • the antenna systems used for television transmission are, in part, funded by public money through the BBC's transmission contracts with Arqiva and the public has an interest in understanding what that money has been spent on; and
  • disclosure of the antenna radiation patterns would enable certain members of the public with specialist knowledge to gain a more accurate understanding of reception conditions in their area.

However, the arguments against disclosure of the characteristics of particular antenna systems are:

  • disclosure of the antenna radiation patterns into the public domain could lead to these being available to foreign administrations, which would substantially weaken HM Government's negotiating position with respect to international frequency clearance;
  • a weaker negotiating position for HM Government may lead to additional cost for the broadcasters (where antenna systems have to be re-built as a result of international coordination) and lower coverage for viewers (where antenna systems have to be restricted in order to protect foreign transmissions); and
  • the BBC is required to provide coverage of its services on digital terrestrial television to a certain proportion of the population by the completion of switchover and a failure or suboptimal result from international co-ordination may harm the BBC's ability to meet this obligation.

Therefore, I am satisfied that in all the circumstances of the case, the arguments against disclosure outweigh the public interest in disclosure for some of the antenna radiation patterns.

Appeal Rights

If you are not satisfied with this response you have the right to an internal review by a BBC senior manager or legal adviser. Please contact us at the address below, explaining what you would like us to review and including your reference number. If you are not satisfied with the internal review, you can appeal to the Information Commissioner. The contact details are: Information Commissioner's Office, Wycliffe House, Water Lane, Wilmslow, Cheshire, SK9 5AF, telephone 01625 545 700 or see

Yours sincerely,

Tom Everest
BBC Distribution

I am considering if making an appeal is the best course of action, or perhaps waiting until the end of 2012, when the mentioned negotiations may be complete.

Redacted masts

Aldeburgh Alderney Amlwch Angus Arfon Armagh Ballantrae Barrow Town Hall Barskeoch Hill Beacon Hill Beary Peark Beer Belcoo Belmont Benagh Berrynarbor Betws Y Coed Bevendean Bexhill Uhf Bilsdale Bincombe Hill Black Hill Black Mountain Blackwaterfoot Blaenplwyf Bluebell Hill Bowmore Hp Bowmore Vp Bow Street Brading Bridport Brighstone Brighton Central Brixham Broad Haven Brougher Mountain Budleigh Salterton Burnham Burnham On Crouch Bushmills Caernarfon Caldbeck Caldbeck Scotland Cambret Hill Camlough Campbeltown Caradon Hill Carmel Castlebay Castlederg Cemaes Cerne Abbas Chambercombe Charmouth Chartham Chatton Chideock Vp Clachan Clacton Claudy Clennon Valley Clettraval Coldean Combe Martin Conway Coombe Corfe Castle Countisbury Craigkelly Crystal Palace Dalton Darvel Darwen Dawlish Derrygonnelly Divis Dolybont Douglas Dover Dover Town Downderry Durris Eastbourne Eastbourne Old Town East Dean Ederny Eitshal Elham Emley Moor Exeter St Thomas Felixstowe Fenton Ffestiniog Findon Fishguard Folkestone Fremont Point Girvan Glenelly Valley Glengorm Glenmaye Gorey Gortnalee Gosforth Great Yarmouth Greenhill Guildford Gulval Hangleton Hannington Hartland Haslingden Hastings Hastings Old Town Haverfordwest Heathfield Hollington Park Horn Street Huntshaw Cross Hythe Ilfracombe Ipswich Stoke Isles Of Scilly Ivybridge Jurby Kendal Kilbride South Uist Kilkeel Killowen Mountain Kilmelford Kilvey Hill Kimmeragh Kingsbridge Kirkoswald Hp Kirkoswald Vp Lancaster Larne Laxey Leitrim Les Touillets Lethanhill Lewes Hp Lewes Vp Limavady Lisbellaw Llanddona Llandecwyn Llandrindod Wells Llandyfriog Llangranog Lochmaddy Hp Londonderry Long Mountain Looe Lowestoft Luccombe Lulworth Luscombe Valley Lydden Lyminge Margate Mendip Mevagissey Midhurst Millbrook Vp Moel Y Parc Morfa Nefyn Muldonagh Mynydd Pencarreg Newcastle Newhaven Newport Bay Newry North Newry South Newton Ferrers Occombe Valley Olivers Mount Overstrand Ovingdean Vp Oxford Patcham Penaligon Down Penmaen Rhos Penryn Perranporth Piddletrenthide Pinwherry Plumbridge Plympton Polperro Pontop Pike Poole Port Ellen Porthtowan Port Isaac Portnahaven Portpatrick Portslade Port St Mary Praa Sands Presely Preston Ramsgate Redruth Reigate Ridge Hill Ridge Hill West Roose Hp Rosemarkie Rosneath Vp Rostrevor Rothesay Rouncefall Rowridge Rowridge Vp Rumster Forest Rye Salcombe Salisbury Saltdean Sandy Heath Scoval Vp Sedlescombe Selkirk Sidmouth Skriaig Slapton South Knapdale St Austell St Brelades Bay St Davids St Dogmaels Steyning St Helier St Just Stockland Hill Stokeinteignhead Storeton Storeton Wales St Peter Port Strabane Stranraer Sudbury Sutton Coldfield Tacolneston Teignmouth The Wrekin Torosay Torquay Town Torteval Trefilan Trefin Trefor B Tunbridge Wells Ventnor Waltham Wells Next The Sea Wenvoe Westbourne West Kilbride West Kirby West Runton Westward Ho Weymouth Whitehaven Whitehawk Hill Winterborne Sticklan Winter Hill Woodbridge Woolacombe Woolwich Workington

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Wednesday, 7 March 2012
8:45 AM

Fantastic work on chasing the BBC on their radiation patterns.

I must say I do not understand the argument against release:
"...antenna radiation patterns into the public domain could lead to these being available to foreign administrations"
Since surely as part of the negotiations they must have informed counter parties of their coverage in order to agree the allocation? Are they suggesting that everyone sits around a table with no knowledge of how they will be affected and discuss frequency allocation on a best guess basis??

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Noel's 1 post GB flag
Mike Dimmick

11:18 AM

Noel: You can actually find the details of what we, and other nations, negotiated for in the ZIP file at . Warning: it's 280 MB, and contains the plans for all 121 European and African nations that participated.

At some point the ITU will notice that this should be behind their paywall.

There is one folder per country - our ITU region code is G. The rrc06_digital_plan_details.pdf file gives information about each DAB allocation (single-frequency network) and each TV transmitter above a certain power. Power is specified in dBW - divide by ten and then raise 10 to the resulting power (if using Windows Calculator there is a 10^x button) to get watts. The radiation patterns are given in section 23 and they are in effective height of the transmitting antenna in that direction. This is basically the height above the average height of surrounding terrain within a relatively short distance of the transmitter. Negotiations between countries are on the basis of these claims.

We've actually claimed far more than we're really using or going to use. As far as I can see, we've pretty much asked for omnidirectional patterns from all transmitters. You can compare using ITU's effective height calculator at Calculation of Effective antenna heights using the SRTM3 database which uses height data from NASA's Shuttle Radar Topography Missions - we probably used Ordnance Survey data which is more precise and more accurate.

Do be aware that the co-ordinates and heights given are referenced to the World Geodetic Survey 1984 (WGS 84) co-ordinates, not the UK's National Grid. The notion of mean sea level can be substantially different.

We've only negotiated a couple of hundred transmitters, from the set of over 1,100. The smaller relays are not expected to substantially affect international coverage. Their allocations are essentially extracted from the negotiated ones - and this is why, quite often, the relays of a main transmitter clash with the commercial multiplex allocations of it or another relay, and why the commercial muxes can't actually transmit from all the relays. For example, Aldeburgh (though not one of the top relays in terms of population coverage) was allocated 8 channels at 10 kW

Even if a transmitter site is listed, it may have adopted another channel from another site, if the net interference to other countries will be the same or less. For example, Sheffield was not allocated C39, but ArqB is using it there. That channel *was* assigned to Emley Moor, but it's not used at that site, and Sheffield's coverage area is effectively contained within the area we claimed for Emley Moor.

What the BBC are saying is that if they published the full details of the compromises of how the main sites are *really* running, rather than how we told the rest of the world that they *would* run, we'd have problems negotiating those allocations in future.

The plans can be updated by negotiating with expected interferers (part 28-2 - note Emley Moor is shown interfering with Ireland!) and ultimately notifying ITU-R, who will include the update in the next Radiocommunications Bureau International Frequency Information Circular. BR IFIC (Terrestrial) can be found at…g=en - look for GE06/nn updates. As far as I can see, though, we haven't sent through any updates for TV transmissions since the initial plan was finalized in 2006.

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Mike Dimmick's 2,486 posts GB flag
Mike Dimmick

11:50 AM

"the relays of a main transmitter clash with the commercial multiplex allocations of it or another relay" should read "of another main transmitter".

I didn't finish the comment about Aldeburgh. Aldeburgh got C21, C23, C25, C26, C28, C30, C32 and C33. We're clearing C31-C38 for new services (potentially) and therefore C32 and C33 can't be used, but that still leaves C21, C26 and C30 that it's not using. C26 and C30 were formerly analogue channels but C21 was a new allocation. However, as I said, the smaller relays had to be fit in somewhere. C21 was basically lost to Bramford. C26 is used at Ipswich Stoke, Linnet Valley and Thetford (Gorleston-on-Sea and West Runton were included in the ITU plan). I can't see clashes on C30, but without three spare channels they may not have bothered anyway.

Aldeburgh isn't a great example as it's only predicted to serve 9,500 homes. I have got a ranking spreadsheet of which relays serve the most households, extracted from http://consumers.ofcom.or….pdf . Top of the list is Rouncefall, which appears in the GE06 plan, and uses the same frequencies as its parent, Sudbury, anyway - it would add 51,000 households. The next two are Londonderry, 37,000 and Kidderminster, 33,000. I'm excluding Storeton (Wales), 41,000, as its purpose is to provide Welsh PSB services to people fully covered by Winter Hill, so most of them will already have commercial mux coverage from there. I haven't analysed the smaller relay clashes at Londonderry or Kidderminster.

If the commercial multiplex operators *had* indicated that they wanted to take up the additional 120 sites, or higher net coverage overall, the relay plans would have been fitted around that target. As it is, they haven't been, and now retrofitting the commercial muxes anywhere else is substantially more difficult. Bringing this back to the topic, that's one thing that we might have to negotiate with other countries.

The '600 MHz band', C31-C38, is also problematic because the actual frequency plan that's been worked out, using only three frequencies for each of layer 7 and 8 (9 is a Single Frequency Network on C36), doesn't match what we negotiated for those transmitter sites. Typically these were just conversions of the analogue frequencies previously used at those sites.

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Mike Dimmick's 2,486 posts GB flag
10:02 PM

What international borders are challenged by the Oxford TX? Maybe is to do with the channels in/near 800MHz? Or maybe the reason here is that the work is just not finished, so they don't know...!

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mst's 7 posts GB flag
Mike Dimmick

10:29 PM

mst: Section 28-2 of the Oxford pages indicates that the allocations were negotiated with France.

Transmissions can stretch a very long way, particularly in unusual weather conditions. We have to be sure that we're not interfering unduly even under those conditions.

The 800 MHz clearance does require another round of negotiation. That's why the relays have typically had the necessary retunes incorporated into the main switchover plan - since about mid-2011 - while the main transmitters will have to be retrofitted.

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Mike Dimmick's 2,486 posts GB flag
Wednesday, 2 May 2012
Justin Smith

4:41 PM

Are you saying the`ve released more transmitter patterns but not all of them ? Even if one accepts their arguments why they haven`t (and I don`t, I think it`s a very weak argument compared with freedom of information), I can`t see any reason at all why they can`t release all the relay patterns. After all we`re only talking about TXs up to 50/100W, and most of those on the coast aren`t aimed out to sea anyway. Then there`s any TXs in the north or west of the UK (esp Scotland), how can their transmissions affect any other country ?

On the subject of Oxford, that`s a C/D transmitter, C/D transmissions, being higher frequency, don`t travel as far as A group transmissions. I think any argument about possible co-channel issues should bear that in mind.

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Justin Smith's 41 posts GB flag
Friday, 18 May 2012

3:41 PM

Justin Smith: Just to clarify, the information in the original FOI request covers the relay transmitters, with a single exception.

You have to remember that it's not the "normal" conditions that have to be considered (as that's an easy computation) but the problems during "Inversion" where signals are carried much further than usual that have to form part of the process of allocation and co-ordination.

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Briantist's 38,907 posts GB flag
Monday, 21 May 2012
Mr P Watmough
5:50 PM

Why are some channels on waltham on low power very early in the morning ? Have you got co channel problems ?
Most noticed on Sky news, and about 0630 approx the signal strength sudendly doubles.
Checked at different locations with different aerial systems and different receivers. Explain and own up !

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Mr P Watmough's 6 posts GB flag
Tuesday, 22 May 2012
Mike Dimmick

3:44 PM

Mr P Watmough: They are not. Check that you are looking at signal *strength* and not signal *quality*. *Strength* should change gradually, it should only change sharply if an amplifier in the aerial system is switched on or off. If it really is, and you're using a communal aerial system, it's probably a fault in that.

Quality is a function of both the wanted signal strength and of the level of interference. The reported quality is usually some percentage of datablocks received without errors. The more interference, the more errors, but the error correction scheme automatically corrects as many as it can, up to the threshold of what's possible. Many boxes report only the rate of what couldn't be corrected. On these boxes, the aerial system should be set up so that the quality meter always reports 100%, even in the worst conditions.

Every frequency used for TV transmission in the UK is used at numerous different sites. They have been spaced far enough apart that they shouldn't interfere with each other, within the expected coverage area, for more than 1% of the time. However, for the COM muxes (SDN, ArqA and ArqB), there are usually more or closer interferers than for the PSBs (BBC A, D3&4, BBC B).

Changes in weather conditions cause changes in signal propogation. If signals usually change overnight, it can just be down to the regular daily warming or cooling of the atmosphere, which is termed 'tropospheric enhancement' as it enhances the signals from distant transmitters (i.e. interference).

If you really think you have discovered a fault, you should contact Sky or one of the other broadcasters on the affected multiplex. Arqiva do not take fault calls from the public, except for a small selected group of people who monitor their local transmitter. If the fault is occurring on one of the BBC multiplexes, you can report that through their engineering page at Radio & Television Investigation Service - Diagnostic form . Keep saying 'no' when it asks if this has answered your question, and eventually you'll get to a form that enables you to send an email.

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Mike Dimmick's 2,486 posts GB flag
Friday, 15 June 2012
Andy Ripley

7:06 PM

There's software out there that models propagation and gives a likely coverage, however they are not using a single omnidirection antenna, they are using array and they don't (as I have found) radiate evenly. It's this vital information that they hold back.
Yes it would be nice to have it, but it would show possibly a nice null on several of the muxes in my direction from Bilsdale. The signal strength is well down on several muxes even comparing them on the Spectrum Analyser connected to the antenna.

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Andy Ripley's 32 posts GB flag
Andy's: mapA's Freeview map terrainA's terrain plot wavesA's frequency data A's Freeview Detailed Coverage
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