Topband: Shunt feeding the Skyneedle

[Tom W8JI]

Here's what changed though...when I had the gamma arm at 90' with the 14 
gauge gamma wire 24" away from the tower I was able to insert my Johnson 
60-160pf variable cap in series with the gamma wire to get approx 58-60 ohms 
at X=20.  The cap was 2/3 meshed at this point.  >>>

That's the right way. You have to cancel the reatcance of the drop arm to 
get a good reading. Maybe you need a larger capacitor to hit the bottom of 
the band? Resistance normally goes up in a case like yours as frequency is 
drecreased.

<<<NOW that I've lowered the gamma arm to the 67' level...I insert my 
variable cap and the antenna resonates at 1.970 MHz with R=36 ohms and X=0. 
For some odd reason the MFJ SWR reading shows 1.0:1 with this 36 ohm reading 
and, inside the shack, the Ft1000D shows 1.0:1 swr from 1.988 to 1.950 and a 
1.5:1 range of 2.007 to 1.930>>>

What does more capacitance do?

<<<<It now appears that the antenna is a bit short but why am I seeing these 
crazy high resistance readings with no variable cap in line?>>>

You should see them. The MFJ detector is a 50 ohm bridge. It will overflow 
and give all kinds of goofy readings when impedance is far away from 50 
ohms.

<<How can I lower the resonant freq without moving the gamma arm up? 
Increase the spacing of the gamma wire from the tower? Add more radials?>>>

I would have left it at the top and shorted the wire to the tower at 
different places until I found the sweet spot. But you have to dip the 
reactance out to really know what you have.

<<<
I was going to build a three conductor wire cage with the wires spaced 10" 
apart or so once I had an idea where the antenna resonates.  Would a fatter 
gamma trio drop the resonant freq or just change the capacitance value of 
the antenna?>>>

A fatter shunt wire will lower reactance and resistance. You will need more 
C, and the tuned resistance will be a bit lower.