[TowerTalk] was 80M Delta Loop - now Soil Conductivity

[kq2m at kq2m.com]

A huge issue with using a coarse tool like a Soil Conductivity map is 
that the worst and best terrain for Soil Conductivity are but a tiny % 
areawise and may not even be noticeable on a large scale map. And like 
with extremes in either direction, the likelihood of those conditions 
persisting over a large area at that same level is extremely small.

At my qth which is ledge and virtually no soil except for minimal dirt 
devoid of nutrients, you can go less than a mile away in almost any 
direction and you will see an absence of ledge and far darker, nutrient 
rich soil.  Travel another mile and you have farmland and loam and many 
small freshwater ponds and lakes.  20 miles SE of me you have Long 
Island Sound which is of course all salt water.

I have never attempted to measure soil conductivity at any of these 
locations but I would have to believe that it is far superior to what I 
have on my hilltop, at least in the near field.  And much of W1 is like 
this.

I leave the extremely varied conditions to those with the expertise to 
debate it.  :-)

73

Bob, KQ2M


On 2024-07-26 09:42, 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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