[cma-l] Community Radio on AM

[Associated Broadcast Consultants]

Absolutely right Alex - the frequency selective map would only be for
getting an "insight" or feel for the interference landscape - proper
computerised tools are needed to do it properly.

It's complex and scientific, but this post below gives a pictorial,
non-technical insight into the "Protection Ratios" that Ofcom use, and are
one of the reasons they often say there are no frequencies available:-

http://a-bc.co.uk/ofcom-fmvhf-protection-ratios-illustrated/


Glyn

-- 
Glyn Roylance - Principal Consultant
Associated Broadcast Consultants <http://www.a-bc.co.uk/>

On 24 September 2014 16:58, Two Lochs Radio <tlr at gairloch.co.uk> wrote:

>  Hi Glynn
>
> That's a nice map for browsing, but as far as mapping all transmitters to
> allow assessment of potential interference, it surely isn't the way to go.
> As you'll be well aware you need much more than a simple mapping of
> potential co-channels - you have to take into account image channels and
> the directional power templates of antennas at the very least, even before
> thinking about the intervening terrain.  You also have to take into account
> transmissions in neighbouring countries of course.
>
> I think all that can be done far more effectively in tabular form than on
> a map.
>
> Of course, the elephant in this particular room is not in any case what
> frequencies are or aren't occupied, but what parameters Ofcom applies in
> assessing their potential for mutual interference - eg should a 99%
> confidence level or a 90% confidence level be used, should second adjacent
> channel be regarded as safe or not? Those are what make all the difference
> to the assumed potential for interference between transmitters. Similarly,
> is potential interference acceptable for 0.1% or 1% of the time or
> location? All these parameters are really what set the technical bar as to
> whether or not there are channels available.  Then of course there are
> strategic and political issues, agrements for the BBC to have priority use
> of certain sub-bands etc.
>
> One thing that could be considered for releasing more community radio
> frequencies is for Ofcom to reuse channels more closely on the basis of a
> mutual agreement between stations that they will not complain about the
> remote possibility of mutual interference less than say 1% of the time in
> 10% of their fringe. We have transmitters on the same frequencies just a
> few miles apart, but terrain-limited with no significant mutual
> interference in locations of interest, because we were able to agree not to
> complain about our transmitters interfering with each other! A similar
> thing happens on 96.6 between Nevis Radio (Fort William) and MFR
> (Aviemore) in the Laggan area half way between them. I suspect many groups
> would be willing to accept a service that might be subject to a little
> marginal interference in some limited locations rather thna no licence at
> all.
>
> As for suggestions on the map, which is nonetheless nice to have, could I
> suggest you add in the Scottish not-for-profit stations that operate as
> non-profit community stations, but for historical reasons have commercial
> licences (Cuillin FM, Two Lochs Radio, Lochbroom FM, Argyll FM, Oban FM,
> Isles FM). That would give a more representative picture of community radio
> cover in the northwest of the UK, which otherwise looks a bit empty on the
> map! There are also community op-outs from MFR in the north-east.
>
> Also for adding the Northern Ireland stations there is a batch convertor
> for Irish grid references here
> http://www.osi.ie/calculators/batch.asp?alias=/services/gps-services/co-ordinate-converter
>
> Alex
>
>
> ----- Original Message -----
>
> *From:* Associated Broadcast Consultants <info at a-bc.co.uk>
> *To:* The Community Media Association Discussion List
> <cma-l at mailman.commedia.org.uk>
> *Sent:* Wednesday, September 24, 2014 2:54 PM
> *Subject:* Re: [cma-l] Community Radio on AM
>
> Further to Ian's update below - we recently mapped the Ofcom data for FM
> CR's onto an interactive Google Map that you can browse, zoom etc.  If you
> click on any site if gives the essential information.
>
> http://a-bc.co.uk/community-radio-station-map/
>
> If there is interest we might do a similar map for all UK transmitters
> (nearly 2000 of them) that you can filter by frequency - thus to get an
> insight into co-channel interference for any station/location/frequency you
> wish.  Or other variations if people have suggestions.
>
> Regards, Glyn
>
>



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