[cma-l] AM community radio

[Associated Broadcast Consultants]

Just a thought possibly for a low cost antenna system...

When I was a student many moons ago in Manchester, Radio Rag used to
operate their AM transmitter from the student halls tower block I lived in.
  I don't know what you'd call it, but I guess it was an inverted monopole.
  100W transmitter up on the 12th floor feeding into a near vertical wire
radiator down to ground level.

Obviously if circularity in coverage is important that might be a problem
(but I don't recall the signal was that strongly impacted behind the
building).  But if your local council are obliging it might be a way to get
a reasonably efficient antenna quite cheaply.

Glyn

PS: Regarding the 3:1 argument I think the extra antenna efficiency/small
size may well be offset (possibly more than offset) by the propagation
advantage of the lower frequency.  Laser did not choose 558kHz by accident.



On 17 September 2015 at 18:44, Ian Hickling <transplanfm at hotmail.com> wrote:

> If only it were as simple as that!
> I must admit that I hadn't looked at it like that - 531 to 1,611 kHz
> gives a quarter wave range of of 141 metres to 46 metres - yes - three to
> one!
> But do you fancy buying/siting/building even a 46m guyed vertical radiator
> - 152 feet high?
> Apparently there are only 9 AM frequencies that Ofcom feels able to
> allocate to LP operation - I'll see if I can find out what they are.
>
> *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*
>
>
> ------------------------------
> Date: Wed, 16 Sep 2015 21:28:28 +0100
> From: tlr at gairloch.co.uk
> To: cma-l at mailman.commedia.org.uk
> Subject: Re: [cma-l] AM community radio
>
> Given that the MF AM band covers a 3:1 frequency range, is Ofcom at least
> able to allocate a frequency at the high end of the band, making any given
> given aerial design a third the size it would be at the LF end of the band?
> Just wonderin'!
>
>
>
> Alex
>
> On 16 September 2015 at 20:20 Ian Hickling <transplanfm at hotmail.com>
> wrote:
>
> All perfectly acceptable - but as an experienced  propagation engineer my
> concern is that any departure from a vertical end-corrected quarter wave
> radiator operating on a groundplane of at least .55 wavelength diameter,
> the  energy propagation pattern is uncertain and effectively impossible to
> either determine or plot.
> In order to take his order - and his money - I have to give the Client an
> assurance that he will be able to cover his audience effectively - and that
> simply isn't possible with a cut-down compensated radiator on a much
> smaller earth mat.
>
> *Ian Hickling*
> Partner
>
>
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-- 
Glyn Roylance - Principal Consultant
Associated Broadcast Consultants <http://www.a-bc.co.uk/>
<http://www.a-bc.co.uk/index.html>
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