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

Alan Coote alan.coote at 5digital.co.uk
Sun Mar 8 11:13:25 GMT 2015 

I can¹t help thinking that someone at Ofcom ran the simulations and came up
with 100W = 5km radius.

Therefore if small scale DAB became a reality it wouldn¹t annoy Radio Centre
too much (they¹d still complain as that¹s their mentality) and at worst
secondary legislation could make it happen.

Kind Regards
Alan


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From:  "tlr at gairloch.co.uk" <tlr at gairloch.co.uk>
Reply-To:  "tlr at gairloch.co.uk" <tlr at gairloch.co.uk>
Date:  Sunday, 8 March 2015 00:45
To:  "transplanfm at hotmail.com" <transplanfm at hotmail.com>, Associated
Consultants <info at a-bc.co.uk>
Cc:  "cma-l at mailman.commedia.org.uk" <cma-l at mailman.commedia.org.uk>
Subject:  Re: [cma-l] Ofcom announces trials to help small stations join
digitalradio - 100w limit

   
  
 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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