[cma-l] DAB trials
Ian Hickling
transplanfm at hotmail.com
Mon Mar 9 09:27:19 GMT 2015
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>
> > 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>
> > 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/>
> >>
> >>
> >> From: "tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk>"
> >> <tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk>>
> >> Reply-To: "tlr at gairloch.co.uk <mailto:tlr at gairloch.co.uk>"
> >> <tlr at gairloch.co.uk <mailto: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 <mailto:transplanfm at hotmail.com>>, Associated
> >> Consultants <info at a-bc.co.uk <mailto: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
> >> <mailto: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>> 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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