All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
It's worth noting that a TLCS only allows broadcast on satellite and cable, it doesn't permit terrestrial transmission. For that, you need a Digital Television Programme Service licence. ITV plc don't yet have DTPS licences for those new services.
In the consultation for renewal of Mux C and D, Sky commented on this difference, and the fact that the multiplex licence requires Ofcom to review proposed changes in the channel line-up. Sky services are specifically mentioned in the Mux C licence and the Mux B, C and D licences specifically call out Sky and Sky-controlled companies (defined as a 'Relevant Person'), with no Sky services permitted on B or D and only three on C. Further, no more than 75% of C's capacity can be granted to Sky.
However, the review provision is actually just a literal copy of a section of the Broadcasting Act 1996. Likewise, the distinction between TLCS and DTPS is laid down in the same law. Ofcom cannot just decide not to enforce these conditions! (On the other hand, Ofcom failed to require a new technical plan adding more relay transmitters.)
I note the BBC are still yet to apply to renew the Mux B licence. Perhaps they're hoping that if it gets too close to expiry, government will step in and add it to the Royal Charter like Mux 1 (free) rather than pay to renew (£25k renewal fee, plus Administered Incentive Pricing from 2014).
Incidentally, have you seen that Ofcom are reportedly going to delay the 600 MHz auction: Ofcom postpones 600 MHz auction .
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Noel: You can actually find the details of what we, and other nations, negotiated for in the ZIP file at http://www.itu.int/ITU-R/terrestrial/broadcast/plans/ge06/dig_plan.zip . 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 http://www.itu.int/ITU-R/…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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"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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Tim h, Briantist: Usually the signal strength displayed is raw power, and isn't adjusted for the mode. Tim could have previously had significant interference on C34, but if it was sufficient to equal the expected new level from Rowridge I'd have expected no service possible!
Antennas do typically have substantially more gain at higher frequencies than lower ones, but again, 10 dB is a lot. C24 is too high for it to be Short Reflector Syndrome (a particular problem where the reflector elements are too short to be effective at C21-C22).
I do hope Arqiva haven't managed to cock up in the way they did at Hannington a few weeks ago!
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Graham: The Digital UK predictor does not show signal strengths. It shows the percentage of locations across the grid square that are expected to have sufficient signal strength, compared to interference from other transmitters, for 99% of the time, and for 50% of the time. The figures really show the relative difficulty of siting an aerial at your location.
In contrast, your box does not subtract the strength of the interference from the strength of the wanted signal and simply reports the total power received on the selected frequency. It is possible for equipment to reconstruct the desired signal internally, basically re-encoding after decoding, and subtract it from what was received, but this is typically only done by specialist measuring equipment. (Installers *should* use equipment that does this, in order to find the best location for the aerial).
If the 99%-time figure is over 70%, the square is considered 'covered', shown as 'good' (green) and the service will be protected against interference from any new services (e.g. 'white space' broadband, local TV services at another transmitter). If the 99%-time figure is below 70% but the 50%-time figure is above, it will be shown as 'variable' (orange). If both are below 70% but 50%-time is still over 50%, it will show as 'poor' (red). If below 50%, the square will be blank.
For you, your best bet is probably Midhurst, although it thinks your aerial is most likely pointing to Hannington. Commercial muxes from Crystal Palace will be poor after 18 April, despite the power increase, because they will use the same channels as the corresponding transmissions from Rowridge. Rowridge may be too weak to use, but it's certainly strong enough to cause you problems!
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Ron Lake: The IBA hasn't existed for 20 years. It was replaced in 1990 by the Independent Television Commission, itself replaced by the Office for Communications, Ofcom, in 2003.
Ofcom have the power to require a new Technical Plan from the multiplex operator when the licence is up for renewal, requiring additional coverage. They renewed Mux A (SDN) in 2010 and have just renewed Mux C and D (ArqA/B), to run from 2014, without making use of this power. Speculating, they may have decided that it's better to renew on current coverage levels rather than require more and risk the operator deciding not to renew. There's no guarantee that another operator would be prepared to take it on, either.
The licences run for 12 years. Outside the renewal period, Ofcom can only vary the licence with the agreement of the multiplex operator. Changing that would require a change in the law, so actually, your MP is probably the best bet.
This may also fall into 'be careful what you wish for'. Extending the commercial muxes from additional transmitters may mean that other relays have to be retuned, or put up with more interference, or shut down entirely.
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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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Lynda: the old location for BBC digital channels, on UHF channel C34, was closed down shortly after midnight. The new location, UHF C24, didn't start up until several hours later. Your recorder wouldn't notice the change until you retuned, or until it did its own automatic retune scan, but the service could still have been off-air at the scheduled recording time anyway.
You're lucky that your recorder apparently preserves its recording schedule across retunes! Most don't.
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Keith: The UK beam from Astra 1N is *intended* to only cover the British Isles with a small dish. You *may* be able to use it outside the British Isles with a larger dish, but you won't find any official information on how large that would be: the whole point is that channels are *not* supposed to be receivable outside the licenced area.
SatBeams - Satellite Coverage Maps - Sat Footprint Intelsat 10-02 (Intelsat 1002, Intelsat Alpha-2, Intelsat X-02, IS-1002) / Thor 5 (Thor 2R) / Thor 6 (IS-1W) indicates that it may be receivable with a 90cm dish.
This is not the permanent location for this satellite. It is only providing capacity temporarily while Astra 2E, 2F and 2G are built and launched - presumably the dish providing the UK spot beam on 1N is ultimately intended for some other purpose. The UK spot beam, on whichever satellite replaces 1N, may well be different again, and require a larger dish still. 2F is due to go up this autumn, so might go into service early next year.
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Tuesday 6 March 2012 4:01PM
Nicholas Wilmott: The commercial multiplex operators have decided to change to a less-robust, but higher-capacity, mode. They are rolling this out across the country over several months. So that fringe viewers don't lose services when they do change mode, where they had time to prepare it, they are broadcasting at less than the permitted levels. SDN seem to generally be using a 1.5 dB reduction, while Arqiva - at other transmitters - used a 3 dB reduction. At Mendip, ArqA and ArqB are still on low power to reduce interference at Salisbury, and not due to the mode change. ArqB had its mode change last year (8 November) and coverage may have reduced for some people.
If the transmitter started transmitting at final power levels before the mode change decision was made, then the power levels were not reduced.
Therefore, while SDN will increase power to 100 kW on 27 March (according to Digital UK's postcode checker - trade view, shown as 'COM mux FEC change'), this will not increase coverage due to the mode change; for some people the mode change may actually reduce coverage.
The ArqA and ArqB channel changes and power increases are still scheduled for 28 March. ArqA's mode change is expected to occur at the same time.
So far, SDN are only using the increased capacity in Wales, to carry CITV and The Zone. These previously weren't available in Wales, because E4 was carried instead, due to S4C bumping it from the D3&4 multiplex. New services on ArqA and ArqB are likely (in my view) to launch once London has switched over in April. ArqA will be in its final mode at all switched-over transmitters by 1 May, and SDN by 27 June: ArqB fully switched to the new mode on 23 November last year.