The main problem in the half wave vertical, to achieve the theorical gain,
is in the peculiar distribution of the current return path that follows the
radiator's current distribution and therefore finds its maximum a quarter
wave away from the antenna base. Such fact leads to the requirement of a
much better and bigger ground plane (much more and longer radials) than it
is needed to maximize efficiency in the case of a quarter wave vertical.
In a few words, when the ground plane is less than optimum for an half wave
vertical, the losses may lead to a negative antenna gain.
Mostly, what amateurs consider an excellent ground plane is not enough for
an half wave vertical..
73,
Mauri I4JMY
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