One more comment. Think of the detuning as the electrical equivalent
of a physically-long parallel L/C circuit.
If the structure above or below the point where you are detuning is
resonant or nearly resonant as a 1/2 wl or near any multiple of 1/2
wl, tuning for resonance in the decoupling section will make unwanted
radiation MAXIMUM and not minimum.
For example, if I were to detune a very tall tower that was nearly
resonant as a 1/2 wl, say a 200-foot tower with a yagi on top for 160
meters or a 100 foot tower with a yagi on top for 80 meters, detuning
would actually INCREASE unwanted tower current.
That's why you should always confirm what you are doing with a FS
meter, unless you know for sure the tower is not near 1/2 wl or a
multiple of 1/2 wl long electrically. For example, if I detuned my
318-foot tower with a system installed at 50 feet or so above ground,
resonance in the detuning system would result in MAXIMUM tower
current!
Exact or near-exact resonance only works when the tower would have
minimum current with the section you are tuning physically and
electrically removed from the tower.73, Tom W8JI
W8JI@contesting.com
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