[cma-l] DAB trials
Cat Lake
connect at catlake.uk
Mon Mar 9 12:27:36 GMT 2015
We've seen them Phil. They do exist.
Regards,
Cat Lake
*Social Technologist, Writer & Broadcaster*
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On 9 March 2015 at 10:51, Fantasy Radio Office <office at fantasyradio.co.uk>
wrote:
> Thanks for your response Ian, but with respect, that's exactly what I
> said - Ofcom have 'sourced' suitable transmitters. Whether they've actually
> been built yet is of no consequence. I wouldn't expect there to be ten
> units sitting on a shelf just waiting to be delivered.
>
> I hope the trials prove to be of benefit to the industry.
>
> Phil Dawson
> FANTASY RADIO 97FM
> Devizes ,
> Wiltshire
>
> On 09/03/2015 09:27, Ian Hickling wrote:
>
> Not so I'm afraid Phil.
> The information that we have suggests that transmitters for the project
> will be produced specifically by a UK manufacturer already producing
> similar equipment for existing broadcasters.
> Ian
>
> ------------------------------------------------
>
> > Date: Sun, 8 Mar 2015 18:36:25 +0000
> > From: office at fantasyradio.co.uk
> > To: cma-l at mailman.commedia.org.uk
> > Subject: [cma-l] DAB trials
> >
> > Whilst we're delving deeply into the theory of RF propogation, I suggest
> > there could be another reason for Ofcom's suggesting 100 watts. Clearly,
> > to acheive 10km radius at 220MHz, you'll need more power than 5km at
> > 100MHz. So, perhaps Ofcom have 'sourced' a handful of 100 watt models,
> > which will be OK for this trial, which is all guesswork anyway.... It
> > has to be, as there are so many unknown quantities.
> >
> > Most importantly, whatever comes of this trial, it'll be an awful lot of
> > work for a handful of people. The most important consideration must be
> > 'how does this affect the listener?' and how will it benefit our
> > station? Probably the most overlooked questions in all of this debate.
> >
> >
> > Phil Dawson
> > FANTASY RADIO 97FM
> > Devizes ,
> > Wiltshire
> >
> >
> > On 08/03/2015 16:21, cma-l-request at mailman.commedia.org.uk wrote:
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> > > Today's Topics:
> > >
> > > 1. Re: Ofcom announces trials to help small stations join
> > > digitalradio - 100w limit (Tony Bailey)
> > >
> > >
> > > ----------------------------------------------------------------------
> > >
> > > Message: 1
> > > Date: Sun, 08 Mar 2015 15:58:21 +0000
> > > From: Tony Bailey <ravensound at pilgrimsound.co.uk>
> <ravensound at pilgrimsound.co.uk>
> > > To: cma-l at mailman.commedia.org.uk
> > > Subject: Re: [cma-l] Ofcom announces trials to help small stations
> > > join digitalradio - 100w limit
> > > Message-ID: <54FC719D.6080100 at pilgrimsound.co.uk>
> <54FC719D.6080100 at pilgrimsound.co.uk>
> > > Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
> > >
> > > Ofcom states that the coverage limit is set at 40% of the
> "corresponding
> > > local DAB multiplex area" and that a practical limit of 100 W ERP "may
> > > achieve a service area of approximately 10 km radius". A synchronised
> > > two tx (not repeater) system would be spaced at no more than 15 km
> > > apart. As pointed out below, this has to based on a practical antenna
> > > situation to have any relevance.
> > >
> > > Tony Bailey
> > >
> > > On 08/03/15 14:01, Ian Hickling 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/>
> <http://www.letstalkbusinessonline.com/>
> > >>
> > >>
> > >> From: "tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk>
> <tlr at gairloch.co.uk>"
> > >> <tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk> <tlr at gairloch.co.uk>>
> > >> Reply-To: "tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk>
> <tlr at gairloch.co.uk>"
> > >> <tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk> <tlr at gairloch.co.uk>>
> > >> Date: Sunday, 8 March 2015 00:45
> > >> To: "transplanfm at hotmail.com <mailto:transplanfm at hotmail.com>
> <transplanfm at hotmail.com>"
> > >> <transplanfm at hotmail.com <mailto:transplanfm at hotmail.com>
> <transplanfm at hotmail.com>>, Associated
> > >> Consultants <info at a-bc.co.uk <mailto:info at a-bc.co.uk>
> <info at a-bc.co.uk>>
> > >> Cc: "cma-l at mailman.commedia.org.uk
> > >> <mailto:cma-l at mailman.commedia.org.uk>
> <cma-l at mailman.commedia.org.uk>" <cma-l at mailman.commedia.org.uk
> > >> <mailto: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 <mailto:info at a-bc.co.uk> <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/>
> <http://www.a-bc.co.uk/>
> > >> _______________________________________________
> > >>
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