[TowerTalk] 80M Delta Loop

[Mike Fatchett W0MU]

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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