You guys need to investigate a bobtail curtain.
I used one on 40 meters and it worked phenomenal in southwest Missouri.
An 80 meter one would work fine too.
73, Jim W7RY
On 7/25/2024 10:49 PM, Jim Brown wrote:
On 7/25/2024 5:01 PM, Brian Beezley wrote:
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.
I couldn't open the dropbox file -- it wanted me to sign in. But I do
have some background on this -- one of my summer jobs while in EE was
working for Pete Johnson in his consulting office using that map to
plot contours of patterns we'd computed for directional arrays he
designed. Those plots of curves of field strength vs distance on a
log-log scale are called a "nomograph," and my freshman EE curriculum
included a course in creating and using them.
This was in 1961-2. I strongly suspect that the map is at least a
decade older than that. And I do think I know how the data were
obtained -- by running radials (that is, measuring field strength
along a radial line extending from an AM broadcast transmitter at a
large number of points and matching graphs of attenuation vs. distance
for measured data to corresponding curves that are part of FCC AM
Technical Regs.
I mention Pete Johnson, because he and Carl Smith wrote those
technical regs after WWII. Carl was better known as the proprietor of
an electronics and radio technical school in Cleveland.
And yes, the data are quite coarse -- but I was able to say that
conductivity on low HF is poor in that area, because everything around
it is low. :)
73, Jim K9YC
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Thanks and 73, Jim W7RY
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