[TowerTalk] Vertical and radials

[Lux, Jim]

On 1/22/22 9:21 AM, Robert Harmon wrote:
> I love your perfect QTH description.   A hill of salt water, sloping gently in all directions.   hihihi
Calistoga has hot water under pressure, and I'll bet it's got plenty of 
dissolved minerals. So a big sprinkler fed from a hot spring at the top 
of your hill.
>
> I am having trouble finding ground conductivity fro my area in the north San Francisco Bay Area.  Napa county.
> Looks like my area shows a number 8.  Where is he chart to find out what this means in conductivity ?

millimhos per meter on the chart legend - that's milliSiemens/meter  in 
SI units.

Yes, that's not exactly averaged over large areas, it's more 
"interpolated from scattered measurements made in the 1930s and 1940s" 
for two purposes: LF and MF propagation estimates and powerline grounding.

https://www.fcc.gov/media/radio/m3-ground-conductivity-map has a 
slightly newer version, and also has some references to tabular data.



> Wish I could find a map that I could drill down closer to my QTH.  I know it is pretty good right now, we have had
> lots of rain the last few weeks.

There are some other datasets around, but they tend to be highly 
specific, because someone had a need to measure it.  And there's not 
many needs.  Munitions depots, electrical installations, etc. are most 
likely, along with some transmitter locations.  And there's no 
particular reason why those measurements would be collected into a nice 
database, or even publicly available.

You *might* be able to infer conductivity from a combination of geology 
and soil moisture.  Soil Moisture *is* something for which there are 
datasets from satellite measurements.  SMAP is a satellite specifically 
designed to do that measurement, and it's measuring in L band.