"A load placed anywhere on the radiator other than the feedpoint is a
different story."
And base loaded vertical antennas don't have their loading coils at the
feedpoint ... the loading coil is ABOVE the feedpoint and definitely
affects the current profile.
What you are describing is simply a matching network at the antenna, and
of course that is no different than one at the rig if you ignore
feedline losses..
This has been a really dumb discussion.
Dave AB7E
On 7/4/2025 8:39 AM, Wes wrote:
Then the essence of this of this is what effect does a base loading
inductor have on the current profile on the radiator. My answer is none.
It's too bad we can't have attachments here so I'll try to describe it
with words. I "built" a model of a vertical in AutoEZ and used EZNEC
Pro/2+ V 7.0 running the NEC 5 engine to do the computations. I used
7.25 MHz with a height of 1/8 wavelength at that frequency (16.55
feet), diameter of 0.1 inch and 33 segments. I used perfect ground
and conductor loss of zero. The current source was 1.0A.
The feedpoint Z without any loading is 6.15 -j444.6 (SWR = 651). Using
the current plotting feature of AutoEZ, the current profile v. segment
is a nearly linear, negative slope line from (almost) 1.0A down to
(almost) zero. (Almost because current is reported along the length
of a segment, not at the ends) I used the snapshot feature to capture
this plot.
Next I added a series inductor at the feedpoint of 1.48 +j444.6
(Q=300). The calculated feedpoint Z=7.64 j0 (SWR = 6.55). The
current profile is nearly identical as before. The snapshot
completely overlays the newly calculated plot.
My conclusion: A non-radiating, high Q inductor at the feedpoint of an
electrically short monopole affects the feedpoint Z but has no effect
on the current distribution on the radiator, which is determined
entirely by its geometry. A load placed anywhere on the radiator
other than the feedpoint is a different story.
Wes N7WS
On 7/3/2025 4:19 PM, David Gilbert wrote:
The loss is the same (probably), but the current profile at the
antenna is different (definitely).
Dave AB7E
On 7/3/2025 4:10 PM, Wes wrote:
I'll confess some difficulty (probably my failing) in understanding
your point(s). To try and simplify the situation to something my
pea brain may understand, let's use a toroid at either location. Now
tell me what the difference is.
Wes N7WS
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