Just for giggles and grins, today I ran a wire from the top of my
64-foot Trylon to ground level, and about 18 inches off the tower leg, put a
two-turn loop near the end of it (the wire) and connected it to the tower
ground system lead. No antennas or other wires on the tower except for the
lightning grounds buried 18 inches.
I placed my ac-powered dip meter's coil into the wire loop and measured
a slight dip at 6.9 MHz, and more pronounced dips at 14.05 MHz and the low
ends of 15 and 10 Meters. I had expected the tower to have a resonant
frequency near 7.0 (actually, I had expected a higher frequency as the tower
is not as slender as Rohn, and ought to measure electrically shorter).
1. Should I be concerned about this "natural resonance" of the tower on
20, 15 and 10?
2. If so, how can I detune the tower or otherwise end up NOT having a
Once the antennas have been installed (Skyhawk at 65 feet and D40
dipole at 78 feet), I'd like to construct an inverted-feed ground plane for
80M (coax center conductor to the radials,etc.) out of the tower and
possibly experiment with a sloper to NE (= Europe) for 160M (to temporarily
replace my inv L.) Will I be able to do this (theoretically) with the
resonances I found? I'm not expert at modeling yet, so I'm relying a great
deal on your opinions and experience.
Gene Smar AD3F
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