Topband: gamma match question

Bill Tippett btippett at
Mon Sep 25 07:56:08 EDT 2006

 >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

         The latter works well.  If you have a MFJ-259B
or equivalent at the base, move the tap until R = 50 ohms,
note +jX ohms, and then calculate C needed to null it out.
My tap point was extremely close to the point indicated
by careful modeling, but I had a simple bare tower with
no other antennas on it.  Later when I added parasitic
elements, modeling again predicted the tap very accurately.

                                         73,  Bill  W4ZV

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