All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Briantist: Sorry, just seen the spectrum analyzer photo that someone else posted, indicating actual low signal.
However, once the power does reach the full output, my point still stands: many people to the east of the transmitter may have had too large an aerial and/or amplification fitted to try to pick up the very, very weak signals that were all that were available. Too much signal on analogue manifests itself as noticeable, but not too annoying, patterning. A digital signal is wrecked.
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steve: ITV4 is carried on the ArqB multiplex, which transmits on UHF C55 from Winter Hill.
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Gh: You're in the 'Guilford Notch', an area where digital signals from Hannington were severely reduced to avoid affecting the analogue transmissions from Guildford, which use the same channels as Hannington's low-power signals.
For you, the difference between the old and new power levels is not 4 dB (2.5x). It's 26 dB (nearly 400x). Many boxes will be 'desensitised' if receiving a loud signal on one channel - it affects adjacent channels most, but nearby channels are also affected.
You will have to wait until 22 February to get ITV/C4/C5 and the other channels listed under Multiplex 2 back. The commercial channels will remain restricted until Guildford switches over: the ArqA multiplex will be derestricted on 4 April and finally SDN and ArqB on 18 April.
It's likely that you had a very big aerial and probably additional amplification to get digital from Hannington at all, before now. It's very likely that you will have too much signal after one of those dates - you will probably need to remove the amplification. Too much signal causes distortion, which causes a lot of errors, often too many to be corrected.
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Andy Fraser: "Transmitter Engineering" simply scrapes the BBC's Reception Problems wizard - click 'BBC Reception Test' next to your post. The BBC keep about a week's worth of data but show it as 'today', then 'yesterday', then as a date. "Transmitter Engineering" posts a new comment if the text changes, which means that it will post essentially the same information at least three times: on the date it occurred, the day after it occurred, and two days after.
I don't know if Briantist could clean it up so that "Transmitter Engineering" converted 'today' and 'yesterday' to dates, before comparing. It would be clearer if they were posted as dates. It would also be clearer if each item was on a separate line, rather than all being run together.
It also scrapes Digital UK's Planned Engineering Works page at
Digital UK - Planned Engineering Works .
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Alex: The HD channels are on lower power than the other multiplexes at present, and the multiplex also uses the same channel as one of the SD multiplexes from Reigate, at the moment.
This will change on 18 April: the HD services will move, taking over Channel 4 analogue's frequency, and be boosted to the same high power as the other multiplexes' new power levels - 20x the current power level.
Night-time does tend to cause interfering signals to travel further, something called 'tropospheric enhancement'.
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jay: Briantist's links are a bit out-of-date.
Basically, three of the four multiplexes that were changed to a more robust, but lower-capacity, mode in 2002, will return to a higher-capacity mode. Indeed two of them, along with one that didn't change in 2002, will now go to an even higher-capacity mode.
The pattern currently is:
Mux 1, B, C and D: 18 Mbit/s
Mux 2 and A: 24 Mbit/s
Total: 120 Mbit/s
After switchover:
BBC A (Mux 1) and D3&4 (Mux 2): 24 Mbit/s
BBC B (Mux B): DVB-T2, HD, 40 Mbit/s
SDN, ArqA and ArqB (A, C and D): DVB-T 27 Mbit/s
Total (SD): 129 Mbit/s
Total: 169 Mbit/s
The BBC have already cleared nearly everything off Mux B, by closing some services, compressing what was previously on Mux 1 slightly more heavily (though not as much as the other multiplexes), and moving some streams across. What now remains, of the BBC channels, will easily fit in the additional 6 Mbps of space on BBC A after the mode change. BBC Four and CBeebies time-share a slot, BBC Parliament uses a smaller slot (it runs at a lower resolution, if I recall), and each radio station uses about 256 kbps.
Clearing that space gave the BBC the opportunity to sublet some capacity, to allow services that would use the extra space on ArqA or ArqB after switchover to launch early. BT have leased some of the space to carry Sky Sports 1 and 2. These will move to ArqB at switchover.
Channel 5 and S4C have already made their moves from Mux A to Mux 2, that happened in September 2009. No BBC services will now be going to Mux 2.
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Stu Davies: It already is, and has been since November 2009 from the Winter Hill transmitter. You need a Freeview HD-branded TV, set-top box or PVR. Just 'HD Ready' is no good - see What does "Full HD Ready" actually mean? | ukfree.tv - independent free digital TV advice .
If you're looking at the manual, check that it lists DVB-T2 as well as DVB-T, if the Freeview HD logo doesn't appear.
Digital UK's postcode checker lists Moel-Y-Parc as the 'most likely' transmitter, from which the likelihood of HD reception is shown as variable, due to strong interference from Sutton Coldfield. To be honest I'd expect you to be using Winter Hill, with Storeton Wales supplying Welsh channels (including S4C Clirlun), if you want them. The Wrekin is also shown as a good option.
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Terry Bailey: First of all, check that your box or TV is not on either of these lists:
http://www.digitaluk.co.u…ment
http://www.digitaluk.co.u…tnit
These lists are not comprehensive, they list boxes known to have problems, but not necessarily every box that has problems.
If not, make sure you do a full retune from scratch - it might be called 'first time installation', 'default setting', 'factory reset', 'full retune', 'virgin mode'. If it prompts that it will delete all channels, say yes. Unfortunately a lot of boxes will not realise that the channels have moved to a new frequency and just won't store them, or if they do, will store them somewhere else in the channel list such as from 800 onwards.
There are even a few boxes that have separate memory for 2K-mode (used before DSO) and 8K-mode (used after) channels, and you have to be sure to clear both to get it to do the right thing.
If you're somewhere to the east of the transmitter, in the sector from north-east to south-east, you may find that the new level for the BBC channels is much higher than you had expected. This is because digital signals were previously (and, for the other channels, still are) heavily restricted to the east. You could have too much signal, if you have a large aerial and/or amplification. You might need to remove any amplifiers or boosters, or even add attenuation to bring levels down. This might mean that you lose the other channels while they're still on the restricted antenna.
The multiplex 2 channels (the group including ITV1, C4, C5 - see above for the full list) will be fully unrestricted on 22 February. You need to retune again on that date. The HD channels will launch on the same date, also unrestricted. The other channels will remain restricted until Crystal Palace switches over on 4 April (the Multiplex C group, including Pick TV and Dave) and 18 April (the remaining channels).
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tim w: The low-power digital channels had, and continue to have, a severe restriction in your direction (officially, you were actually not in the coverage area for digital). That means the power increase at switchover, as high-power services start, is not a measly 2.5x but up to nearly 400x. This may mean that you now have too much signal on the BBC multiplex.
If you have an amplifier or booster, try unplugging it or turning it down. You may find that the gain just from the aerial is too much - if so, you should try adding an attenuator.
High signals on one channel may desensitise the receiver, meaning it can no longer pick up the other very much quieter digital signals. The Multiplex 2 group should return after the second stage of switchover, on 22 February, along with the HD channels. The other channels will remain restricted until after Crystal Palace switches over - everything will be derestricted on 18 April (one group is expected to be derestricted on 4 April).
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Wednesday 8 February 2012 1:55PM
Briantist: That'll be too much signal caused by having too big an aerial. The Guildford Notch caused digital signals to the east to be cut by up to 22 dB. That means viewers due east have an effective 26 dB, near 400x, power increase between Mux 1 and BBC A.
Hannington's pre-switchover radiation pattern can be found on p8 of http://downloads.bbc.co.u….pdf (red line). The 'proposed' blue line was never implemented - I believe it reflects the old triangular cross-section antenna (when looking from on top). The new main antenna has a pentagonal cross-section, it has five faces, so will be somewhat different from that.