I prefer the base insulator and series feed myself. Shunt feed or unipole
feed works great if the tower is close to a resonant length. It becomes
more difficult if the tower is much shorter than natural resonance.
Sometimes top loading will make shunt feeding easier, since it raises the
resonant frequency of a short tower. Series feed, if you can find an
insulator, gives you a lot more options in tuning up the tower.
Of course, if you are stuck with a typical ham radio style jury rig where
the bottom section was embedded several feet into the concrete base, you
have no choice. Unless the tower is short enough to stand without guys,
that is about the worst possible way to erect a tower. A tall guyed tower
is subject to much additional stress when the base is rigidly set in
concrete; it cannot sway or rotate in heavy winds, and that can cause
failure of the tower structure. If it is mounted with a base plate and pier
pin, or a ball-and-socket insulator as AM broadcast towers are constructed,
the base of the tower can follow the movements of the tower instead of
having the entire tower bend and twist under high winds.
Don k4kyv
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