Recall that Kirchoff's Law was used by some antenna experts to challenge
W9UCW's result. In particular, the main concern was that placement of the RF
ammeters inside the coil ends perturbed the measurements -- except that when
the coil assembly was physically reversed (i.e., turned upside-down), the same
result was achieved on the ammeters.
The experts convinced ON4UN that current into the coil must be the same at the
output of the coil (otherwise Kirchoff is violated) and he subsequently revised
a section of his Low Band DXing book as such. A shame, as he should have kept
it as it was in prior editions. I believe by the 4th and 5th editions, the
pictorial diagram was removed that previously showed diminished RF current
across the center loading coil of a short vertical antenna.
Moral of a long story: Kirchoff's Laws don't apply to radiating coils.
Paul, W9AC
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Wes
Sent: Friday, July 4, 2025 3:37 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Good vacation antenna
I assume that you're referring to the Boothe article. I've only found part 1
of that, since ARRL in its infinite wisdom prevents download of the piece. But
he didn't need to measure this, it can be modeled; the EZNEC help file says:
"The currents at the ends of real loading coils are often substantially
different because of radiation and/or physical length. When this occurs, the
EZNEC load model, which has equal currents at the two terminals, does a poor
job of representing the coil, and considerable inaccuracy can result. Whenever
possible, a helix rather than a load should be used to model a loading coil."
I used a distributed coil model in a paper about short inductively loaded
antennas that I wrote 20 years ago and posted on the Rec.Radio.Amateur.Antenna
newsgroup.
Wes N7WS
On 7/4/2025 11:30 AM, Jim Brown wrote:
> On 7/4/2025 8:39 AM, Wes wrote:
>> 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.
>
> All good, but -- one of the things that long QEX piece showed is that
> EZNEC doesn't correctly model inductive loading! They did this by
> comparing the modeling result with measurements of built antennas.
>
> 73, Jim K9YC
>
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