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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|