I have the Force 12 EF240X. This is the wire loaded elements that are about
45 ft long and a 24ft boom. I have tuned this antenna and have found the
resonance (not the 1:1 SWR) changes pretty significantly from 15 ft to 35 ft
to 80 ft. I don't have my original notes, but I recall seeing at least
100khz total shift. However, the 35 to 80 ft shift was maybe 20 - 25khz vs
the 15 to 35 ft shift being the rest. I always attributed it to the
additional ground coupling changing the net "loading" on the shortened
elements that got less impactful as it got higher.
I have not used the antenna in a couple of years. It was potent but the
construction weaknesses were an issue. Its on the "refurb" list but not a
priority.
Ed N1UR
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