[TowerTalk] Good vacation antenna

[Paul Christensen]

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 at contesting.com> On Behalf Of Wes
Sent: Friday, July 4, 2025 3:37 PM
To: towertalk at 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
>
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk