Hi Rick, thanks.
Actually the problem I'm looking at is a bit more fundamental: at what
frequencies is a particular tower + antennas resonant at and how to do you
determine this accurately?
You would think the answer was very simple: hook a wire to the top and
measure the resonance with a dipper. Unfortunately when you actually try
this it doesn't work worth a damn, you can get very misleading reading and
there are very good reasons why it shouldn't work. But that is conventional
wisdom, at least in ham publications. Even if the conventional technique
works, do you really want to climb your 150' tower to do it. Wouldn't it be
much better if you could accurately do the measurements at ground level even
though the tower is firmly grounded.
There is a vast literature on tower detuning for AM but it turns out that
much of that really doesn't satisfy amateur needs where the resonances are
frequently 3/4 or even 5/4-wave. Also much of the literature tells you how
to fix the problem not how to make the initial determination.
I have a means for determining these resonances in grounded structures very
accurately but it requires a VNA which few hams will have. I was hoping to
dredge up some simpler means more practical for hams.
73, Rudy N6LF
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