That might work if it were a dipole.
for a end fed wire?
The problem then is what represents the ground plane?
An Endfed half wave (or any random wire) is like any antenna
(dipoles for instance) dependent on height above ground and
the ground under it so a point measurement is exactly that.
Since a resonant half wave is also a high impedance typically
greater than 1800 ohms ( to as high as 6000 ohms) direct
attachment is likely not meaningful as the VNA is the counterpoise.
And maybe the hand holding it.
We are also talking about likely 7mhz range so less than an inch
is less significant.
This is where inference substitution is useful, build 1:49 transformer confirm
its behavior with resistors. Place that between the VNA and said wire and
measure impedance. No matter what the wire length will have to be adjusted
for resonance in the measured environment and like a jig in the form of some
many feet of COAX to simulate the antennas interaction with it.
Also how do you put the 67Ft wire that will be fed from only one end in series?
If you touch the far end at all you change the result. That said for a resistor or
cap any small part the techniques work well but a 67 foot in air is not a small
part.
I say this as I once watched an engineer try to measure a 6ft monopole for an
E-field antenna on a PNA indoors. He concluded it could not work despite
a working version outside the window. Much explanation later the light was
seen. Its how antennas behave not the instrument and measurement
technique. They must match to a practical level.
Both can be measured without a VNA using a signal generator, bridge,
RF voltmeter or receiver as null detector plus some sense of the antennas
environment so it will be realistic.
The upside is even if wrong the 2:1 circle is rather large for those trying to
measure a EFHW.
Allison
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