spacing between
the reflector and driven element should be
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Gain vs Spacing
The gain of an an antenna with parasitic elements varies
with the spacing and tuning of the elements, and thus for any given spacing
there is a tuning condition that will give maximum gain this spacing. The
maximum front to back ratio seldom, if ever occurs at the same condition
that gives maximum forward gain. The impedance of the driven element also
varies with the tuning and spacing, and thus the antenna system must be
tuned to its final condition before the match between the coax and the
antenna can be completed. However, the tuning and matching may interlock
to some extent, and it is usually necessary to run through the adjustments
several times to insure that the best possible tunning has been obtained.
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