All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Mark Fletcher: Sorry, I managed to get Caradon Hill and Beacon Hill mixed up. Still, the reason for Stockland Hill's restriction is more to do with Crystal Palace low-power multiplexes than to do with Caradon Hill high-power.
Yes, there will be some interference between Stockland Hill commercial muxes and Caradon Hill PSBs. In general, though, the more rugged terrain means that there will be less of a clash than between Stockland Hill and Crystal Palace COMs.
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Chris Onion: The only real way to check is to see what UHF channel numbers are in use. I'm not sure, because BT's documentation is maddeningly thin, but these might be displayed in the 'DTT Signal Strength' screen. Try selecting this option when tuned to, in turn, BBC One, ITV1, ITV3, Pick TV and Yesterday and, if available, BBC One HD and see if a UHF channel is listed. Check whether the channel is the same when tuned to Yesterday and to Sky Sports 1.
The channel numbers should match those above for BBC A, D3&4, SDN, ArqA and ArqB respectively (plus BBC B for HD services). If the box has tuned to the Derby relay, you would see C48 for BBC A, C51 for D3&4 and C52 for BBC B (again, if you have HD).
That signal strength screen will also indicate if you have too little or too much signal. If it's showing 100% strength, it's probably too much. If you have a booster, you should remove it. If that doesn't reduce the displayed level or if you don't have one, try adding an attenuator.
If signals were too distorted, the box may have tuned to the Waltham signals instead. Boxes usually tune the strongest, the best quality, or just the first found, depending on the software in the box; however, for you, Sutton Coldfield should be both the strongest and, except for a few multiplexes before switchover and one now (SDN), the first found as well. If the box has tuned to Waltham, you will probably find the signal quality gets worse - do try a full retune following the instructions at How do I scan for Freeview channels? | Help | BT.com Help .
Before switchover, Sky Sports 1 and 2 were carried on the BBC's second multiplex, Mux B. This was on a lower frequency at Waltham than the equivalent service at Sutton Coldfield, so it could be that your box decided to tune that in rather than the SC service - explaining the loss of service when Waltham switched. However, I would expect that to have affected the whole of Mux B (BBC Four and CBeebies, BBC Parliament, BBC radio stations) and not just Sky Sports. Indeed I would also have expected it to affect Mux 2 and A which were also on lower frequencies than the Sutton Coldfield counterparts.
There's a thread on the DTT Signal Strength display at DTT Signal Strength - Technical Question - BTCare Community Forums .
Digital signal levels from Sutton Coldfield were relatively low compared to analogue, so the increase at switchover was very large. The new levels were designed to provide good coverage *without* changing the aerial. If the new, as you say, 'massive' aerial was selected and set up for the pre-DSO levels it could well have led to too much signal now.
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Mark A: Two EPG slots, so two charges. They are also listed separately in Annex 1 due to being audited separately by BARB.
The EPG slots cost £21,000 each; the Platform Contribution Charge is the large bit:
BBC Three: £871,045
BBC Four: £271,615
CBBC: £299,715
CBeebies: £776,750
Assuming that the aggregate viewing figures didn't drop for each segment of viewing, I would assume that the same total would be charged under your scenario as now.
Also, I don't think the BBC channels appear at the same EPG numbers in the Republic of Ireland EPG, so the charges in section B4 probably apply as well.
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Ian Grice: BY LAW Sky, and all other EPG providers, must put BBC One, BBC Two, ITV1, C4 and C5 at the top of their EPG. The idiots who drafted the law forgot to set down any rules about how much the EPG providers are allowed to charge for the privilege.
As previously stated, the majority of the charges are for 'platform contribution' (box subsidy), NOT for carriage in the EPG, although the complexities of different regionalization arrangements for different broadcasters means the number of sub-bouquets - and the charges for appearing in each one - has exploded.
Are YOU happy for your licence fee to subsidise new boxes for new Sky subscribers? I don't object to boxes being subsidised from the subscriber's own subscription fees - a hire-purchase model, like mobile phones - I DO object to the licence fee being hijacked for the purpose.
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I would expect that any frequency changes would be published in the ITU Radiocommunication Bureau's International Frequency Information Circular before Ofcom publish.
http://www.itu.int/ITU-R/…g=en
No indications of channel changes yet.
Where possible - where international clearance was already available for the new channel (due to it being a former analogue channel), or not required due to no interactions with other countries - the changes were implemented before DSO. Emley Moor is shown as having interactions with Ireland. Sutton Coldfield has no interactions listed so a swap of C49 to C39 could be made without affecting anyone else, even though we hadn't asked for it at Geneva 2006. Hannington BBC B could move from C51 to C39 because we had asked for C39, even though there was an interaction with France.
In the GE06 plan, we asked for channels 37, 39, 41, 44, 47, 48, 51 and 52 at Emley Moor, covering all previous analogue allocations, plus the new homes for ArqA and ArqB, all at 52.4 dBW = 173,780 W. C39 was presumably requested for the low-power HD service! It is now in use at Sheffield (the lower power there means it's still within Emley Moor's allocation, technically) in place of the original allocation of C49, to clear that for some other transmitter to use.
You can see that it's a complicated process with a bit of ebb and flow and negotiation required.
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Briantist: In the diagram at the top of the page, you did say Emley Moor 48 to 50 and 51 to 39. Obviously this didn't happen! As you say, it's not now likely to happen unless moving Emley Moor is a pre-requisite for accommodating Waltham or another transmitter using C61 or C62.
For Waltham we asked for 29, 35, 54, 56, 57, 58, 61 and 64, and no international interactions are shown - which does suggest that implementation there is delayed until something else, which does interact, can be moved out of the way.
The mix of what's in and what's not in the plan is odd. Nottingham is in, Stanton Moor isn't, but they have the same power level. It's not that all pre-DSO digital transmitters are in, Idle isn't.
All references are to the GE06 plan as it stood in August 2006, I haven't gone through all the updates to figure out the current state!
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mike Roberts: A number of propogation conditions can mean different frequencies travel more or less well. In general, the higher the frequency, the less it bends over terrain, so you would normally expect - from the wrong side of the Pennines - that the higher frequencies will be less strong than the lower ones. In addition, reflections - causing multiple paths from the transmitter to your aerial - interact differently with different wavelengths (the difference in path length is a different number of wavelengths at different frequencies) and therefore their effect on signal strength can cause changes through measurement.
The power levels as stated are envelope power limits, not absolute limits. In the worst case the different carriers making up the signal could all align the same way at one instant, or all different directions at another instant - the difference between these two conditions is potentially 76 dB! In practice the peak-to-mean ratio is clipped at 7-10 dB, but this is still enough for programme content to mean that different muxes with the same nominal maximum power output read at different levels (source: BBC RD - Publications - White Paper 156 DVB-T and Voltage Ratings of Transmission Equipment ).
Really, the box should measure the size of the pilot and TPS carriers, which do *not* change amplitude (though they do change phase), rather than the whole bandwidth, but that is the customary approach.
Finally, as Brian says, there may be differences in the radiation patterns. The radiation pattern of a full transmitting antenna is made up by combining many smaller elements. The UHF aerial for Emley Moor's second mast (this collapsed before the current tower was built) was eight tiers of 6 panels, each panel carrying 4 elements (8 *components* were fitted to each panel, but the active part was the vertical slot *between* the components, odd as that may sound). Again, the slots behave slightly differently at different frequencies - optimal resonance is achieved at 1/4 of the wavelength, so you can never tune the response of an aerial carrying more than one service perfectly for all of them. The overall radiation pattern is made up by the reinforcing and cancelling signals from each element on each panel.
That original antenna contained transformers to feed only 60% of the power into the two panels in each tier on the south-west face, compared to the other two faces. Pushing any more power into the Pennines was considered a waste. You can see the BBC's report on that antenna at BBC RD - Publications - R&D Report 1966-47 : UHF transmitting aerial for the Emley Moor Television Station , particularly how its radiation pattern differed at C44 (BBC One) and C51 (BBC Two).
Because the Emley Moor tower is now a listed building, the external appearance had to remain the same even while changing the antennas inside the fibreglass shrouds at the top of the mast. In turn, though, that meant that Arqiva didn't have to apply for planning permission to change the antennas as they had at most other sites. So we don't know anything about what the new aerial is like and what its radiation pattern might be.
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Andy: Yes, impulse interference can be a problem. It can be reduced by swapping the aerial for a new one which has a balun, a device that matches the properties of the aerial better to the properties of the cable. Older aerials tended not to have a balun or other matching device.
Aerials meeting CAI Standards 1-4 (which require a balun or otherwise matching to the cable) are usually marketed as 'digital' aerials, though there's nothing inherently digital about them. The testing to actually get the CAI Standard label is quite expensive, so many perfectly good aerials meet the standard but don't get the label. If another aerial in the same family has the label, it's likely this one matches up, the manufacturer just only did the testing for
Log-periodic aerials are inherently balanced and therefore don't need a balun.
You can also improve the screening of the cable - traditional so-called 'low loss' coax cable is now considered anything but. For best results, a dense copper braid screen over copper foil is recommended. This is normally marketed as 'satellite grade'.
You might also try moving your aerial around a little so it no longer points at the road. Aerials have a reasonably wide angle of acceptance before losing a significant amount of gain, so a few degrees to one side or the other may resolve the problem.
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Alan: Digital UK reckon the best transmitter for you, both now and after switchover, is Bilsdale West Moor. It's not that near Redcar; it's actually the other side of Middlesbrough.
Bilsdale transmits currently at 1.6 kW to 6 kW depending on the multiplex, compared to analogue at 500 kW. At switchover the digital signals will be 100 kW for PSB channels, 50 kW for COM channels. These levels are intended to give equivalent coverage compared to analogue for the COMs and slightly more for the PSBs.
The commercial multiplexes will be out of group after switchover, and you will need to change to a wideband or Group K aerial to get them. If you have *already* got a wideband, that might be the cause of some problems as they don't have a lot of gain at the lower frequencies currently used.
Results are currently expected to be variable on Mux 2 - carrying ITV1, ITV1 +1, ITV2, C4, C4+1, E4, More 4 and C5 - and Mux D, which carries Yesterday, ITV4, Film4 among others.
The Seaham transmitter will be 'Freeview Light', carrying only the public-service multiplexes: the BBC's channels, the ones I listed earlier for Mux 2, and the HD services BBC One HD, BBC HD, ITV1 HD and 4hd. By the time the Tyne Tees region has switched, BBC HD may have become BBC Two HD, and a fifth HD service may have joined the line-up.
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Wednesday 19 October 2011 4:17PM
Mark Fletcher: Caradon Hill doesn't use those frequencies, but Rowridge and Crystal Palace will do.