[cma-l] Community Radio on AM

[Two Lochs Radio]

I understand the 'complex scientific' side of it, but I still don't honestly see how the map helps give any insight other than in the crudest measure of overall density of stations. 

It shows the general density of stations and is a nice tool for browsing stations and frequencies, but it gives no visual representation whatever of frequencies or powers, so I don't honestly see how it gives even the vaguest insight into the interference landscape for a station.

It could maybe take useful steps in that direction with some development. For example if one could select a frequency or transmitter of interest and set a filter to show only stations of that frequency, or of that frequency plus adjacent and/or image channels it would start to give an idea of potential for interference. Combined with perhaps a crude free space range indication using semi-transparent overlays based on on powers and direction templayes it might beging to give a rough feel for the interference landscape for a given station. But as it stands I don't see how it does that in the slightest.

Not meaning to be picky, honest - I like it for what it is, and it does give a feel for the geographic distribution of CR stations, but it doesn't seem to me to offer any useful insight or even vague feel for the interference landscape.

Alex
  ----- Original Message ----- 
  From: Associated Broadcast Consultants 
  To: Two Lochs Radio 
  Cc: The Community Media Association Discussion List 
  Sent: Wednesday, September 24, 2014 5:37 PM
  Subject: Re: [cma-l] Community Radio on AM


  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


  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 
      To: The Community Media Association Discussion List 
      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









-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.commedia.org.uk/pipermail/cma-l/attachments/20140924/5c6ed476/attachment.html>