[TowerTalk] Good vacation antenna

[David Gilbert]

"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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