Jim Brown wrote:
> I looked at the FCC map, and you're right, Bob, your soil
conductivity is poor.
That's a good use of the FCC map, Jim. I had completely written it off
for ham use once I discovered that it applies only to the AM broadcast
band. Values will be quite different at HF. But ranking 1 MHz ground
conductivity by location should yield the same HF ranking.
However, the map has a serious drawback: its resolution is so coarse
that only regional comparisons are valid. It's not possible to deduce
the ground conductivity at a particular QTH from the map values. For
example, N6LF in Oregon measures 1 MHz ground conductivity more than
four times as high as the FCC map indicates for his QTH.
The FCC maps were generated by measuring signal strength vs distance for
AM broadcast stations. At these frequencies ground permittivity plays
little part, but ground conductivity has a pronounced effect. This
article describes how the map was created:
https://www.dropbox.com/scl/fi/q96gzgvrpztuycqkkuuhw/FCC-Map-Article.pdf?rlkey=y1cao30j81kppq13yclvwweid&st=9vd6bx5y&dl=0
My latest on HF ground constants:
http://ham-radio.com/k6sti/hfgc.htm
Brian
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