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Re: [TowerTalk] 80M Delta Loop

To: w0mu@w0mu.com, towertalk@contesting.com
Subject: Re: [TowerTalk] 80M Delta Loop
From: "Jim Lux" <jim@luxfamily.com>
Date: Fri, 26 Jul 2024 17:49:59 -0400
List-post: <mailto:towertalk@contesting.com>
        


And, from an antenna pattern standpoint, the dielectric constant (which is 
highly moisture content dependent) is important.  I’d venture that changing 
epsilon from 4 to 16 has a much bigger effect than sigma from 1 to 5.
 You can probably work out a “lossy-ness” effect for near field too, that sort 
of combines skin depth, resistivity, and permittivity against frequency.


On Fri, 26 Jul 2024 09:14:58 -0600, Mike Fatchett W0MU <w0mu@w0mu.com> wrote:

That map is interesting.  Unless I read the map wrong the higher the
number the better?  I always thought our ground conductivity out here in
the plains of Colorado was poor.  At our house we have about 2ft of clay
and then sand.

W0MU

On 7/26/2024 8:42 AM, Brian Beezley wrote:
> There's a problem with using the FCC conductivity map to rank HF
> conductivities that I overlooked: skin depth is much smaller at HF.
> Soil with different conductivity may come into play at broadcast
> frequencies. This can invalidate a conductivity ranking applied to HF.
>
> The following table extrapolates 1 MHz permittivity and conductivity
> for ARRL average ground to HF using the Messier soil model.
> Conductivity is in mS/m and SD is skin depth in feet.
>
>  MHz  Perm Cond   SD
>  1.0  13.0  5.0  25.1
>  1.8   9.9  5.2  18.8
>  3.7   7.2  5.6  13.1
>  7.1   5.5  6.1   9.4
> 14.2   4.1  6.9   6.6
> 21.2   3.6  7.4   5.5
> 28.5   3.2  7.9   4.7
>
> For most bands there's quite an opportunity for soil variation to
> change HF conductivity by making deeper soil invisible to RF.
>
> I think it's best to ignore the FCC map for HF questions.
>
> Examples of ground constant variation with depth:
>
> http://ham-radio.com/k6sti/gcvar.htm
>
> Ground constant extrapolator:
>
> http://ham-radio.com/k6sti/extrap.zip
>
> Skin depth calculator:
>
> http://ham-radio.com/k6sti/sd.exe
>
> Brian
>
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