[TowerTalk] 80M Delta Loop

[Brian Beezley]

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