... ok so that's just about the pitfalls of cutting formulas.
I think probably that you could scale up a wire model. A 5 inch
conductor is about 0.0015 wavelengths diameter at 3.5MHz. 0.0015 wl
at 440MHz is 1.01mm, not so far from 18AWG (1.024mm)
You could get your "k factor" there, I believe, or at least get close.
Maybe someone has trimmed their tower for resonance at whatever band
you want (you should mention it, the "formula" isn't based on the size
in inches, it's based on the size in wavelengths).
EZNEC or other modeling program will let you figure out the resonant
length you need without any real-world trimming.
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