[cma-l] Community Radio on AM

[Tony Bailey]

I've dusted off an old spreadsheet if anyone wants a copy.  It's based 
on the mf radio prop maths, don't ask me, I think it has some fiddle 
factors in it from memory.  The file was pre excel Supercalc etc., and 
as I now use Linux it's been re-saved as excel .xls from gnumeric.  You 
just change the power box value and reload it to get the field strength 
figures. I think it also produced graphs. The frequency is set at 1 meg, 
I have versions for the high end and low end but it's probably not that 
accurate.

I don't think this mail list accepts attachments so you'll have to email 
me direct.

Regards,  Tony Bailey

On 24/09/14 15:19, Alan Coote wrote:
>
> I'm going back a bit, but I recall Longley Rice only being useful for 
> VHF between 70Mhz - 250MHz. Either side, other models need to kick in. 
> I also remember there being a lot of fudge factors.
>
> Anything that is line of sight you could always use; Free Space Loss = 
> 20log(d km) +20log(f MHz) +32.4. Then subtract a bit for buildings and 
> trees, and a bit if the signal path is over water or damp ground, 
> subtract a bit more for cabling and connectors and then multiply by 
> the antenna gain... or just use software to do it for you!
>
> The above is useless for AM band propagation of course.
>
> Kind Regards
>
> Alan
>
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> cid:image001.gif at 01CE03CD.223AC920
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> The Media Production, Broadcasting and Training Company
>
> *From:*cma-l-bounces at mailman.commedia.org.uk 
> [mailto:cma-l-bounces at mailman.commedia.org.uk] *On Behalf Of *Two 
> Lochs Radio
> *Sent:* 24 September 2014 11:32
> *To:* The Community Media Association Discussion List; Martin Steers
> *Cc:* Ian Hickling
> *Subject:* Re: [cma-l] Community Radio on AM
>
> The only Ofcom community AM coverage plot I have happened to look at 
> in the past simply drew a nominal 5km radius circle - despite it being 
> over a hilly city with a river through it!
>
> The Canadian CRC's LRCOV online propagation calculator covers 20 MHz 
> to 40 GHz? using the standard Longley Rice propagation model, but as 
> you say analyzing the antenna propagation pattern is a prerequisite 
> for sensible results. The standard NEC tools will cover the AM 
> frequencies quite happily, but at such long wavelengths the effects of 
> ground proximity and nature and nearby metalwork/support guys make it 
> a fairly uncertain process unless you are dealing with high wires in 
> large open fields as used by the major broadcasters.
>
> Also AM propagation varies dramatically between day and night, though 
> this is generally of concern only to wide area broadcasters, not 
> community stations received from the surface wave unless they are 
> interfered with at night by a far distant sky wave.
>
>
> Alex
>
> (----- Original Message -----
>
>     *From:*Ian Hickling <mailto:transplanfm at hotmail.com>
>
>     *To:*Martin Steers <mailto:martin at martinsteers.co.uk> ; The
>     Community Media AssociationDiscussion List
>     <mailto:cma-l at mailman.commedia.org.uk>
>
>     *Sent:*Tuesday, September 23, 2014 4:02 PM
>
>     *Subject:*[cma-l] Community Radio on AM
>
>     I haven't done any real appraisals apart for the Farnborough
>     station which manages about a 2-mile radius in daytime hours which
>     is be barely adequate but does at least cover the core population.
>
>     I'm not aware of any computer coverage software that will cope
>     with MF - and of course there's the question of exactly the EMRP
>     value - and even more indeterminate - the antenna propagation pattern.
>     I'm sure other members will  have first-hand information.
>
>
>
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