[TowerTalk] W7PUA Tiny Ground Probe

[Jim Brown]

On 3/4/2026 6:58 AM, RT Clay via TowerTalk wrote:
> Non-contact measurement of ground conductivity is a standard method in geophysics and archaeology.

As a young EE student, I worked for Carl Smith, who co-authored the FCC 
AM Technical Rules after WWII, in his practice designing antenna systems 
for new applications. In support of his own application for 10 kW 
daytime on 680 kHz in Charleston, WV, second adjacent channel to WLW 
about 200 miles away, he ran radials plotting field strength in that 
direction to prove non-interference. He eventually got the license.

I strongly suspect that method was used after WWII to construct the FCC 
maps that are still on the FCC website. To run a radial, field strength 
measurements were made with standard test equipment at many points at a 
single azimuth from a station operating on the frequency in question. 
Ground wave attenuation is strongly related to frequency, especially at 
LF, and multiple FCC curves for attenuation vs distance based on that 
data in the AM Rules are for small segments of the AM band, and the map 
generated using those curves.

I've downloaded the map (which is in pdf segments) to my website. 
http://k9yc.com/FCC-GroundMap.zip

73, Jim K9YC