Dave,
Thanks for undertaking all this work and publishing the results.
Since it does not appear to be due to coupling to the open
circuited elements, the remaining disparity between expected
element impedances and measured values still bothers me some.
One good outcome of your tests has been to show that the ground
screen is indeed functioning properly to isolate the antenna
system from excessive interaction with the underlying ground. I
would have been slightly uncomfortable with the small diameter
of the radial wires otherwise. Not for any theoretical reason but
because I have never actually used radial conductors that small.
I don't think the insulation on the radial wires is significant.
Do you mind answering a few more questions about the array?
1. What is the exact length, diameter, and mechanical
configuration of the elements?
2. Why are you operating them above resonance?
3. What are the details of the feedpoint? For example - is the
feedpoint exactly at the element / plane intersection or is
it higher up in the element? What is the physical length of
the conductive path from the feedpoint (measurement point)
to the ground plane?
4. How is the impedance bridge connected to the feedpoint?
Also, I'm not intimately familiar with this instrument. Is
the input balanced (ground isolated) or single ended? Is
there any shunting inductance across the input inside the
instrument?
5. What is the source of power for the bridge?
6. Does the bridge generate its own RF or is it dependent on an
external source of RF?
7. If the RF source is external, how does the RF get into the
bridge?
8. Can you describe the lead dress and connection points for the
phasing harness for the array? Is any of the array harness
left in place for the "removed elements" measurements?
Thanks again & 73, Eric N7CL
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