All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
I saw a comment from an Ofcom board member at a recent conference, but there's now information on Ofcom's website: the 600 MHz auction is being postponed, probably indefinitely, while Ofcom work out what to do about making mobile phone services co-primary between 700 and 800 MHz, as agreed at the World Radio Conference last month.
Ofcom | Update: Award of the 600 MHz Spectrum Band (550 to 606 MHz)
They have also decided that Programme Making & Special Events can continue to use this band until at least April 2013: Ofcom | PMSE Update - 16|03|12 .
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Pete, Sally: with reference to C33, Crystal Palace *will* still use it from 4 to 18 April. It will just be carrying ITV1 rather than BBC Two (because this channel will ultimately be released, BBC A takes over ITV1's frequency not BBC Two's, so ITV1 has to move out of the way). So you won't see any improvement until 18 April.
Crystal Palace *by itself* serves nearly 4.5 million households, and when you add all the relays it's at least 5 million. And yes, more of them are the ABC1s that the advertisers are particularly interested in. Unfortunately, Crystal Palace and Rowridge are both Group A transmitters, and there are only 10 frequencies remaining in this group after switchover (those above C30 are released). Two lots of six into 10 doesn't go, so some services had to use the same channels, unless Rowridge commercial multiplexes were put out of group. That would have required everyone to get a new aerial. However, the selected channels are *already* in use, for low-power digital multiplexes 1, 2 and B (BBC and main ITV/C4/C5 channels) at Crystal Palace, so they can't be used *yet*.
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Here's one for the confusion stakes: according to Digital UK's final Installer Newsletter, on 4 April, ITV1 will move to BBC Two's frequency, and BBC One will move to ITV1's.
This is because BBC A will use the channel below BBC One analogue, and therefore BBC One has to move out of the way. With ITV1 already being displaced at Crystal Palace (because BBC Two uses C33, being released), doing this double-bounce means that only the ITV1 transmitter's input needs retuning, rather than having to retune the ITV1 transmitter to C33 and the BBC Two transmitter to C26.
Having a digital channel one below an analogue one requires the analogue channel to be more tightly filtered, and presumably adapting the BBC One transmitter isn't worth doing for just two weeks!
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Dave Lindsay: While the designed channel range of group C/D aerials is C48 to C68, the frequency response of any Yagi aerial tends to be a sharp cut-off at the top end, but a gradual reduction in gain below the highest channels. Example: Gain (curves), Again .
Brian has chosen to represent this with a lighter shade of the group's colour, using frequency response curves from an Ofcom report to determine the colours. I'm not sure how successful this is, it probably isn't pale enough at C42.
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Ofcom have now published an Arqiva planning study considering how we can clear the 700 MHz band: http://stakeholders.ofcom….pdf . It doesn't completely rule out trying to implement additional layers, but since doing so would basically involve replanning all of Europe, I think we can assume that this has been kicked into the long grass.
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Matthew Hopkins, Dave Lindsay: Chances are this is to ensure that the suggested local TV service on C29 has a full 8 MHz. It will probably actually be C29-. The issue is caused by BBC B having a negative offset - which is to stay out of the way of whatever service ultimately ends up bordering at 550 MHz (i.e. the bottom of C31).
Nearly all receivers will automatically detect and apply the offset even if manually tuned. There are a number of receivers, based on Vestel's T810 chassis, that can't handle negative offsets in 8K mode, if they haven't had an update. See Unofficial Vestel PVR Information (UK) - T810 Freeview Recorder for a list of known models.
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Dave Bizzill: Digital UK reckon your best bet for reliable reception of the PSBs is the Luccombe relay, 1.3km to your south. This uses the same channels as Midhurst PSB1, COM5 and COM6, it's basically stomping all over the Midhurst signals. With COM6 still running on low power until after Heathfield switches over, and with the mode changes having increased the margin required, it's not surprising that it no longer works.
Rowridge COMs are on low power, and on their original channels, until Crystal Palace completes switchover. It may be beneficial to change the aerial to vertical polarization [VP], rather than horizontal polarization [HP], as Rowridge COMs will emit more power on VP than on HP after 18 April (they only transmit on HP at the moment). Just rotate it so that the elements run up-and-down rather than side-to-side. Also, you may benefit from using a Group A aerial rather than a wideband - widebands typically have best gain at the top end of the frequency range, actually the part that is no longer used for TV, and an aerial designed to just handle Rowridge frequencies will have more gain than the wideband at those much lower frequencies. *Maybe* you could use a Group K semi-wideband if you're concerned about picking up services that launch in the C31-C38 range in the future - this would have more gain at C21-C28 than the full wideband but less than Group A, for the same size aerial. See Gain (curves), Again and the Group K chart further down the page for a comparison. Your aerial is probably similar to the 'Triboom 46' (a Televes DAT45, I believe).
You will always get better results by putting the aerial outside. The loft has a large number of reflections, which can have the effect of changing polarizations, the roof tiles attenuate the signal somewhat, and the lower height means the aerial may have to see through more obstacles (though that's less of a problem for you as you say you're the highest point around).
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Peter: Going by the postcode you supplied back in September, Digital UK predict that you have a very good chance of a full service from Heathfield, after switchover. Right now digital is predicted to be unusable.
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M
Brighton (Central) (Brighton and Hove, England) Freeview Light Tuesday 3 April 2012 11:20AM
Brighton
Rob R: I plugged BN2 3BG into Digital UK's postcode checker. Brighton Central doesn't transmit the channels you mentioned, but you should be able to get a good service from Whitehawk Hill, which does. Alternatively there is a slightly lower, though still very good, chance of reliable reception from Rowridge, using its vertically-polarized transmissions, after 18 April (due to some restrictions, Rowridge is not yet broadcasting the COMs on VP and still on low power on horizontal polarization; the COMs will use more power on VP than on HP after the 18th).
You are likely to have to change your aerial to use Whitehawk Hill or Rowridge, as both use a different group of frequencies from those used by Brighton Central.
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Friday 23 March 2012 3:16PM
Kev: The 'Transmission Frequencies' section should really say 'Final Situation' - it doesn't take account of the short hangover period we're now in, where multiplexes A and C are yet to convert to their final mode, and A, C and ArqB are all running on pre-switchover channels.