<p dir="ltr">Alex - my thought entirely!</p>
<p dir="ltr">From <a href="http://james.cridland.net/blog/techcon-a-look-back/">http://james.cridland.net/blog/techcon-a-look-back/</a> - from 2011!! - "what would happen if two DAB frequencies were simply given to community radio services up and down the country, to run low-power DAB multiplexes themselves? What amazing additional choice we’d have then!"</p>
<br><div class="gmail_quote">On Sun, 8 Mar 2015 08:04 <a href="mailto:tlr@gairloch.co.uk">tlr@gairloch.co.uk</a> <<a href="mailto:tlr@gairloch.co.uk">tlr@gairloch.co.uk</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
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I simplistically presumed they settled on the 100W suggested limit on the basis that at the Band III frequencies of DAB it would give roughly the same coverage area (at 58dBuV/99%) as 25W on Band II (at 54dBuV/90%).
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NB the average
<strong>local</strong> DAB multiplex power is 1.3kW, not 2kW, but of course they tend to be from sites with much higher antennas than economically available to community stations, so the chances are the 100W represents an even tinier coverage area in comparison to current local multiplexes than might appear at first sight from a simple comparison of powers. But I can see it is much easier for Ofcom to control the allowed power than to get into arguments over exact percentages of area covered. Maybe 500W would have been more realistic if they wanted to take that simplistic approach, with a lower limit applied in the few cases where 500W coud cause difficulties.
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(I guess there is also the question that Ofcom is paying for the transmitters in the trial, and a band III amplifier running at , say, 250W is a lot more expensive than a 50W one, especially if one uses the technique of greatly underrunning a much higher power design to help achieve the necessary linearity.).
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Seems to me that block 5A, (currently unused, but allocated for local DAB) could be used as a UK-wide frequency block for terrain limited single station services up to 500W to deal with all the areas where there is a low density of local stations (ie only one within the interference range of a 500W TX) and it could be done tomorrow, without any fancy trials or risk of interference, clearing out one whole tier of demand without any fuss, leaving trials and more complicated sharing and co-channel planning issues to be threshed out over time in the other seven frequency blocks allocated to local ensembles in areas of more dense demand. It's also much lower in frequency than the other blocks, which reduces the demands on the low-cost software defined transmitter.
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Alex
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On 25 February 2015 at 13:04 Associated Broadcast Consultants <<a href="mailto:info@a-bc.co.uk" target="_blank">info@a-bc.co.uk</a>> wrote:
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We challenged the 100w limit in the consultation - suggesting that the "no greater than 40% of the local commercial Mux area" was an adequate limit. 100w is roughly 5% of the average existing DAB transmitter power, so presuming community stations don't deploy their DAB transmitters using tethered balloons or satellites etc they unlikely ever to get near 40% unless they deploy multiple numbers of transmitters (thus undermining the low-cost aim).
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The standard consultation deflection response was invoked (ie: address a different question) - stating that "it is not necessarily the case that allowing a higher power will in all cases reduce the number of transmitters needed". We never said it would in
<span style="text-decoration:underline">all</span> cases, but were suggesting that by removing the 100w cap you retain some flexibility when it
<em>would</em> make a difference in
<span style="text-decoration:underline">some</span> cases! Unfortunately though, consultations are single shot - no possibility to clarify the point or challenge the response.
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I think we can all imagine the real (unstated) reason why they are limiting it to 100 watts ;-)
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Don't get me wrong - 100w at 200MHz can still provide useful coverage if planned correctly (other DAB coverage planning services are available!), but in some cases more may be required. Otherwise we risk repeating the same problem that analogue CR has - the paltry standard 25w power is often inadequate and quite literally blasted off the dial by much stronger commercial and BBC signals. And this problem is even worse with DAB (for technical reasons that I will not go into here).
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Glyn
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Glyn Roylance - Principal Consultant
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<a href="http://www.a-bc.co.uk/" target="_blank">Associated Broadcast Consultants</a>
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