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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