Topband: gamma match question

Paul Kelley N1BUG paul.kelley.n1bug at
Sun Sep 24 10:03:32 EDT 2006

Fellow topbanders,

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. 
Yes? No?

Any other time saving hints would be most welcome.

Paul N1BUG

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