Topband: Update from AG6X shunt feed project

[Carl Braun]

All

I decided to take a chance at tapping the tower at 67' and apply some series capacitance to see how the structure would work there before tapping it at the 90' level.  Here is what I found:

The gamma arm spacing is at 33" and with 140pf in series I see 42+j0 ohms at the feedpoint.  Inside the shack at the end of the LMR 400 I see basically FLAT SWR from 1800 to 1850 and 1.5:1 at 1865...with the cap fixed at 140pf.

All of that with my skimpy (single 14AWG) gamma wire.

Tomorrow I plan on dropping the tower again to add the additional 2 or 3 wires to create the gamma wire cage.  My current PVC standoffs have been modified to accept three gamma wires spaced approx. 10" apart (though I'm only using one now as I said before). I'm assuming this MAY provide me with a couple more ohms getting me closer to the magical 50 but bandwidth is what I'm truly after.  If I still need a few more ohms I may extend the gamma and standoff arms out another 6" or so...which would be the MAX reach without installing new arm and standoffs.

So...with these low capacitance requirements (140pf now and possibly less with the multiple gamma wires) will I still need to scrounge my vacuum variable out of storage or will my 4500V Cardwell cap get the job done at 1500W?

Thanks to all who offered their advice and look for an update from me after the gamma cage is assembled and additional radials are installed

Carl AG6X