WB2UAQ,
Measuring antennas requires knowing what the ground is like.
as it does change the result as well as orientation and height above it.
I know the region and it does change depending on where you are
in that region.
Your trying to answer questions about EFHW antennas. Suggestion do
so at higher frequency like 20m or 10 M as scaling is handy and makes
getting numbers for .1 Lambda height (1meter at 10M) to say .5 lamda
(5M at 10M). Also for orientation and ability to replicate the identical
thing at multiple locations.
Hint it behave much like a dipole.
It as an antenna is the extreme case of an off center fed.
Things going on...
*The impedance of an antenna depends on orientation horizontal sees ground reflections
so there is a pronounced impedance change. (visible with dipoles.)
*Reflections from large bodies (for sloping or vertical) can be seen as modified
impedance as well depending if constructive or destructive.
*Vertical does not have the same interaction with the ground.
See above about large reflective surfaces.
*Also objects like a fence or trees will interact and load (interact with) the wire.
* Resonance effectively changes with height (follows reflected impedance).
* Interaction of the gear attached to the end of it. IF the gear has a cord and
cables it changes the dimension of the antenna as its part of the measurement
plane and the reflection (counterpoise) of it. A case of what you measure and
how can change the measurement.
* Measured impedance at resonance should be Rx, J0, as that changes the
results move around but if you adjust frequency you can see what R is at J0.
WHY? if above resonance it will be inductive or -Jx and below frequency it will
be +jx that colors the result.
This is why everyone has an opinion but authoritative answers are few.
The other part is pick any value and then draw the 1.5:1 or 2:1 circle and
see how much it can vary. For a 1:49 transformer that's about 1250ohms
or 3800 ohms for the 2:1 circle so small errors like accurate to two significant
digits is likely good enough and easily small enough as variation is height
or nearby objects will easily exceed that.
The side effect is someone will argue with you about it as they do not
understand measuring it. For that it must be repeatable and account
for the known variations.
Allison
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