[cma-l] AMCR

Tue Sep 15 10:12:23 BST 2015

1 - Matching is relatively simple.2 - Power-handling capacity is not - an ATU must be capable of reliably dealing with 1kW in order to to give Ofcom's maximum permitted  EMRP of 70W.3 - Ensuring an efficient radiation pattern with a low-budget non-resonant length antenna is virtually impossible - it's a matter of an expensive and lengthy trial-and-error exercise.Conclusion?
Generation of AM MW is simple and relatively cheap.Getting it to the Customer is not - it's an entirely different ball game

Ian Hickling
Partner

Office: 01635 578435  (7am-11pm UK time)Carphone: 07530 980115 (only responds when driving)6 Horn Street, Compton, NEWBURY, RG20 6QS

Date: Tue, 15 Sep 2015 08:16:55 +0100
From: ravensound at pilgrimsound.co.uk
To: cma-l at mailman.commedia.org.uk
Subject: Re: [cma-l] AMCR

    Hello Marc et al,

      I mentioned DRM on AM because it would be easily implemented in a
      software box.  I think the Talk 107 test used two programme
      channels on one FM carrier.  In fact the main issue with medium
      wave is getting a stable earth system without ploughing a field! 
      Antennas can be short (most RSLs use them) but they aren't very
      efficient due to being very small impedance compared to the
      ground.  As has been pointed out this isn't a problem if you can
      site the antenna in (or on) water.  I wondered if given that SDR
      requires an rf box maybe a clever designer could come up with a
      low impedance amp that could include matching directly connected
      to the vertical antenna sitting on a ground plane.

      Regards,  Tony

      On 14/09/15 22:37, Marc Steele wrote:

      Hello,

        It's seems entirely feasible that you could build a basic
          AM transmitter with SDR technology. Even taking on DRM should
          be feasible.

        However, at the frequencies used, you still have the
          antenna problem (they need to be larger to match the longer
          wavelength) and tuning units to worry about. Well, that and
          all the other practical issues Ian mentioned earlier.

        Wasn't there some DRM experiments done a few years back on
          the old Talk 107 frequency in Edinburgh? IIRC, coverage was on
          a par with analogue FM but the quality wasn't great (it was a
          trade-off between the two).

        Regards,

        Marc.

        On 14 September 2015 at 19:53, Tony
          Bailey <ravensound at pilgrimsound.co.uk>
          wrote:

              Reading this thread may explain why none of the last
                London tranche AM licensees (new not existing) got on
                the air.  There are a number of LRSLs around the country
                on AM although of course they only have to radiate 1
                Watt.  Maybe it's a job for the SDR black box brigade to
                take on now that they've finished playing with DAB?  DRM
                anyone?

                Regards,  Tony Bailey

                On 14/09/15 15:11, Ian Hickling wrote:

                Hi Shankar
                  The point I am making is that in awarding an AM
                    Community Radio Licence, Ofcom should as a matter if
                    conscience and indeed good business practice make
                    sure that the Licensee is fully aware of the
                    additional costs and hazards over and above those
                    known and anticipated for the much simpler and
                    better-publicised FM platform.

                    These are, I suggest:

                      Few installation companies
                      Few experts with suitable knowledge and
                          experience
                      Poor listener acceptability
                      Poor licensing record - only 5 out of a
                          total of 274 UK awards
                      Low receiver availability
                      Lower audio quality
                      Subject to overseas interference outside
                          daylight hours
                      Unpredictable coverage
                      Very large and expensive antenna
                      Requirement for specific site size and
                          features
                      Low availability of UK-produced
                          transmitters
                      Low availability of suitable Aerial
                          Tuning Units.
                      Higher price for transmitters and
                          ancilliaries
                      Uncertainty as to CE-marking of imported
                          equipment

                    Do I need to go on?

                      Please - somebody correct me if you disagree?

                      Ian Hickling

                      Partner

                      Office: 01635 578435  (7am-11pm UK time)
                      Carphone: 07530 980115 (only responds when
                          driving)
                      6 Horn Street, Compton, NEWBURY, RG20 6QS

    -- 
Local Reports at http://www.ravensound.pilgrimsound.co.uk

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