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

Sun Mar 8 15:25:14 GMT 2015

Hear hear. I've done a sample plot on 100W and I've managed to get three
times that distance in a fairly rural area. So it's certainly not a given.

Regards,
Cat Lake

*Social Technologist, Writer & Broadcaster*

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On 8 March 2015 at 14:01, Ian Hickling <transplanfm at hotmail.com> wrote:

> It seem there's a lot of second-guessing going on here from people who may
> know a lot about administration and encoding but possibly not so about the
> black magic that is RF propagation.
> There's no point in trying to relate 100W ERP to 5km for Band III DAB -
> just as it's equally irrelevant to relate 25W with FM to 5km - sorry.
> Topography, geology, refraction, refraction, foliation, antenna efficiency
> and launch conditions have far too large an influence.
> In terms of propagated signal transit, there's not a huge difference in
> practical terms between FM at say 100 MHz and DAB at 200 MHz when you take
> into account antenna size, efficiency, reflection and refraction.
> Because of the difference between demodulation formats, a  receiver can
> tolerate a much lower signal level on DAB than on FM to resolve an
> acceptable audio service.
> This was originally proposed at 20dB from the point of view of transmitted
> power but then revised to 10dB - meaning that a DAB transmitter in Band III
> would need one tenth of the ERP of an FM transmitter in Band II to achieve
> the same audience.
> Hence it is puzzling why Ofcom has set so high a required signal level for
> a DAB service area of the order of 72dBuV/m as opposed to 54 dBuV/m for FM.
> Beware - there is a distinct difference between a Power Decibel in
> transmission and a Voltage Decibel in reception!
>
> Let's not invoke DAB+ and DRM - Ofcom specifically rules them out in 2.30
> and 2.32
>
> Yes, Block 5A would be ideal as it's relatively clear, allocated and
> accessible to modern receivers - but Ofcom apparently doesn't accept that
> as it hasn't headed straight for it.
>
> As I've protested many times, there is technically nothing at all to
> prevent a standalone transmitter radiating a single programme stream to
> serve a discrete area either on DAB, DAB+ or DRM as far as I'm aware.  If
> I'm wrong I'd appreciate the exact reasons why.
>
> Looking at only the RF component in the transmission chain, several UK
> manufacturers could offer a 2U Band III 300W unit at around £2000 if the
> demand were high enough - no real cost differences from today's Band II
> units.
>
> Let's not get distracted - the encoding is software-defined - the actual
> RF transmitter is not!
>
> Ian
>
> ------------------------------
> Date: Sun, 8 Mar 2015 11:13:25 +0000
> Subject: Re: [cma-l] Ofcom announces trials to help small stations join
> digitalradio - 100w limit
> From: alan.coote at 5digital.co.uk
> To: tlr at gairloch.co.uk; transplanfm at hotmail.com; info at a-bc.co.uk
> CC: cma-l at mailman.commedia.org.uk
>
>
> I can’t 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 wouldn’t annoy Radio
> Centre too much (they’d still complain as that’s their mentality) and at
> worst secondary legislation could make it happen.
>
> Kind Regards
>
> Alan
>
>
> Hear Alan Every Week on Let’s Talk Business The UK’s Premier Radio
> Programme For Current and Future Entrepreneurs - Now Broadcast To Over 5
> Million People  <http://www.letstalkbusinessonline.com/>
>
>
> 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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