[cma-l] AMCR

[Tony Bailey]

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 <mailto: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
>>
>>     <http://www.transplanuk.com/>
>>     /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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