[cma-l] Ofcom announces trials to help small stations join digitalradio - 100w limit

[James Cridland]

Alex - my thought entirely!

>From http://james.cridland.net/blog/techcon-a-look-back/ - 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!"

On Sun, 8 Mar 2015 08:04 tlr at gairloch.co.uk <tlr at gairloch.co.uk> wrote:

>   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%).
>
>  NB the average *local* 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.
>
>  (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.).
>
>  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.
>
>  Alex
>
>
>
>
> On 25 February 2015 at 13:04 Associated Broadcast Consultants <
> info at a-bc.co.uk> wrote:
>
>  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).
>
>  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 all cases, but were suggesting that by
> removing the 100w cap you retain some flexibility when it *would* make a
> difference in some cases! Unfortunately though, consultations are single
> shot - no possibility to clarify the point or challenge the response.
>
>  I think we can all imagine the real (unstated) reason why they are
> limiting it to 100 watts ;-)
>
>  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).
>
>  Glyn
>  --
>  Glyn Roylance - Principal Consultant
> Associated Broadcast Consultants <http://www.a-bc.co.uk/>
>
>
>
>
>
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