The post about adjusting the element length to eliminate the gamma capacitor
needs a little extra information added. I have recently been working with a
computer program in persuit of this very subject.
The capacitor apparently can be eliminated but the gamma rod must be
increased in diameter to equal or nearly equal the driven element diameter.
There is a minimum diameter that just barely will do the job but its length
is equal to the length of the element. In other words, an unequal diameter
folded dipole (or half folded dipole, actually)!
To have a more reasonable gamma length, say 60 inches on a 20 mtr yagi, the
gamma rod must be the same diameter as the element. As the rod is decreased
in diameter, the required length of the rod increases.
Another overlooked aspect of both gamma and tee matches is that the gamma/tee
rods hanging from the element makes it look like a big tapered element.
Remember what happens when you have big tapers in element diameters? Right,
you have to increase the length to compensate. I have built some 2m yagis
that needed driven elements longer than the reflector because of this
problem. Both the tee match and gamma match require that element impedances
to include capacitive reactance in order to transform and match
properly(shorter element length). No wonder these things are such a pain to
tune up with all these opposing forces at work!
Wonder what the effect of an element with a gamma match on one side making
that side electrically shorter than the other side without a gamma rod might
be? Probably some unbalance but who knows what that hurts?
Who said "I cut it off three times and it is still too short!"?
73 de Gerald, K5GW
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