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.
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