Simple, if you want to use only a capacitor in series to the line at the
base of the tower you need to find exatly the point on the tower to find the
50 ohm, while if you tap for example at the top of the tower, you need an
extra capacitor to ground, so became a gamma match...
When i have used this sistem on my 80 long tower, the point was about at 27
meters from the ground to have the 50 ohm, but this sistem with tall tower
is very narrow band, few Khz only, so if you need more bandwidht the better
is the gamma with remote control to set the capacitor.
Much better is a slooping dipole sistem, and much easy to realize...
Bye
Giulio
IK2DED
> 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.
>
> Thanks,
> Paul N1BUG
>
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