All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
chrism42: From Digital UK and Ofcom documents:
ArqB should already be on 170kW on C48. No further changes are shown for this multiplex.
ArqA goes to full power, 170kW, on C52 on 23 November.
SDN goes to full power, also 170kW, on C51 on 9 May 2012.
The restricted radiation pattern to the south - greater beam tilt, which means that the angle of greatest power is aimed closer to the transmitter than the final design - is removed on 27 June 2012. I believe this is more likely to be protecting Hastings low-power digital than Rowridge analogue, though it has an effect on both. The influence on Hastings means it has to wait until after Hastings DSO.
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Keith Seddon: It's necessary to make the box forget about the previous location of those channels. Many boxes don't have a 'delete' function and they won't store channels they think they already know about. A full retune is the easiest way to handle it.
The DVB specs have always allowed for the multiplexes to carry an additional Network Information Table with a flag saying 'next version', to warn equipment in advance of a retune. That table can tell the equipment where a multiplex is going to. I believe this was transmitted on all transmitters in the London region, because my Humax PVR-9200T told me about a retune on Wednesday morning (I use the Crystal Palace transmitter). The testing for the 'digital tick' logo hasn't always required that the box implements it.
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chrism42: Actually, looking at the map, I would think there is still some restriction on ArqB C48, as it appears to clash with the New Barnet and Chingford relays in north London. If PSB multiplex coverage has to be restricted to protect Rowridge and Hastings I'm sure those much closer relays need to be protected too!
Unfortunately we don't know what the restriction is.
Speculation: Hemel Hempstead was only allowed 400W on C48, the difference in distance to New Barnet should allow 126 kW before allowing for the fact that Sandy Heath uses horizontal polarization while Hemel Hempstead is vertical (the planners allow 16 dB, or 40x, for this difference). However, Hemel Hempstead had a fairly deep null at 120° (-18.5 dB), the direction of New Barnet; if Sandy Heath is omnidirectional that could have more of an effect. It looks like it is, the 'effective height' data submitted to the ITU planning conference in 2006 doesn't vary a lot and 170° to 180° is about middle of the range).
The note in the very latest 'Table of Digital Stations' simply says 'Until 27 June 2012, the transitional S1 antenna is used', which is the same as it says for the PSB multiplexes. Of course it may not *actually* be the same antenna, Sandy Heath was going to get one half for PSBs and one half for COMs.
http://licensing.ofcom.or….pdf
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Briantist: I was looking to see if there was a new version of Ofcom's Table of Digital Stations (Licensing section). I noticed the HTML page had been reorganized to put v4 into 'previous versions' but v5 hadn't appeared. However, with a bit of guessing of the URL, I found:
http://licensing.ofcom.or….pdf
The notes are now against the transmitter they refer to and are not truncated!
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Richard: The final switchover changes for Oxford will be 18 April 2012 because the channels selected for the COM multiplexes clash with the High Wycombe transmitter, a relay of Crystal Palace. There are other clashes e.g. Hemel Hempstead Mux 2, but High Wycombe clashes with all three.
At DSO 2 on 28 September, the COM multiplexes will move to their new channels and new modes, but will be on reduced power at 12.5 kW. That's greater than current levels but only one quarter of final levels.
Mux 2 will indeed move from C68 to C60 at DSO 2. To assess whether it will work reliably, try the Teletext test on ITV1 - go to Teletext page 284.
For a manual retune now, use C68. On the 28th, do a full reset of the box to ensure all old information is cleared out.
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Ross: For the two weeks between DSO 1 and DSO 2, Mux C moved from C48 to C51 (replacing Mux 1 which closed). This was to allow Sandy Heath ArqB to move to C48. In turn this is so Sandy Heath could release a channel that Sutton Coldfield needs next week.
This means you need to do a full retune, or delete the channels from Mux C and do a manual tune on C51. The box might still think it has BBC channels on C51 so might not store the new location, if you don't do a full reset.
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anthony:
1. They might not support 8K mode - check http://www.digitaluk.co.u…ment for a list of some known not to work
2. They might not support the larger NIT - check http://www.digitaluk.co.u…tnit
3. You could be suffering from Digital Region Overlap, where the box tunes into the first version it finds rather than the best quality. Strong signals will be found from Belmont first, then Sheffield, then Emley Moor. Check for other versions in the 800s - if they work better then do a manual retune.
4. You could have too much signal, making the Emley Moor signal too distorted to receive reliably. This would usually cause a box to choose one of the other transmitters instead, if strong enough to decode, but it might pick based on signal strength rather than quality.
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Briantist: Going back to the symbols used in the DUK documents - they use a hexagon for a 6-mux full-service transmitter and a triangle for a 3-mux Freeview Light transmitter.
The dotted lines are probably to do with Service Insertion Points, that Emley Moor and Sutton Coldfield are the SIPs for the West Yorkshire and West Midlands subregions respectively.
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Thursday 15 September 2011 11:44AM
Claire: Before Wednesday morning, Multiplex 1 was within the old analogue aerial group, Group B. It has moved up into Group C/D. You will need a wideband or Group E aerial to get it back, and you will need one for all services after switchover.
After switchover the PSB multiplexes will be in Group B, as will the SDN multiplex, but you won't get a full range of channels without a change of aerial.