Topband: Making my tower disappear - one more thing

[Tom Rauch]

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