Topband: gamma match question
Paul Kelley N1BUG
paul.kelley.n1bug at gmail.com
Sun Sep 24 10:03:32 EDT 2006
I have a question for the antenna gurus. This may be a stupid
question, but having searched the list archives and read every
reference I could get my hands on (and finding no answer) I've
decided to ask anyway.
I'm curious why all the shunt fed towers I've seen had the gamma
section running up only as far as the "tap" to the tower, never
extending above the tap point. Is there some reason to do it that
way, as opposed to making the gamma section longer than needed and
using a movable shorting strap to the tower somewhere along its
length? The latter would seem much easier to adjust, especially if
using a wire cage for the gamma section. When using a gamma match on
HF yagis the gamma arm typically extends beyond the tap point. I see
no reason why the implementation would be different when feeding a
tower, but wonder why I've never seen it done that way.
I've got nothing against experimenting, but with my tower project
way behind schedule I'm missing part of the season! Horrors! With
the tower not quite completed yet, my preliminary guess is that the
tap will need to be about half way up the tower. I'm thinking of
running the three-wire gamma cage say three quarters of the way up
the tower and then using a movable short, adjusting as necessary.
Any other time saving hints would be most welcome.
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