[TowerTalk] Shunt Feed

[Pete Smith]

My education has just been found wanting again.  I'm trying to set up a
shunt feed for my tower for 160m.  After tapping up the tower about 30
feet, I set up a test rig at the feedpoint to let me clip-lead in various
values of low-voltage ceramic caps in series with the shunt lead, to tune
out the presumed inductive reactance.  As I added capacitance to the series
cap in the shunt feed and measured the Z, I could see it come down as I
added more C -- in other words, it behaved as I expected.  I found that
with 440 pf in series, my Autek RF-1 says that minimum Z occurs at 47 ohms
at 1895 khz.  It is a relatively sharp minimum.  

Yet when I switch the meter to SWR, it says it is off-scale high.
Is this possible?  Doesn't minimum Z (R+j0)represent resonance?  And if
that minimum number is ~50 ohms, shouldn't the SWR be somewhere under 2:1.?
The meter reads all right on other antennas for other frequencies, and with
a 50-ohm resistor across the coax connector it reads close to 1:1 SWR at
1.8 MHz.

There must be something here I don't understand.  Any help gratefully
received.  

73, Pete N4ZR






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