[TowerTalk] Choke on feed point of dipole

[Tom Hellem]

Hi Jim-
100 watts is going to be max.
But I am befuddled by the change in the resonant frequency when I added the
choke.
I repurposed an old 20 meter yagi D.E., and modeled it in Eznec using 14.1
mhz as
 the target freq. Upon testing, it resonated around 13 mhz and I had to cut
off 3 feet
to get it resonant at 14.1 mhz. Then, after I put the choke on, the Fr
dropped down
below 13 mhz, indicating I would need to cut off another 3 feet at least to
bring it back up to my 14.1 mhz target.

I am surprised that it ended up 3' too long initially. Usually a model has
gotten me to within a couple inches of the target freq.

Does the addition of a choke like this actually add to the length of the
antenna element?

73
Tom
K0SN


On Mon, Jan 12, 2026 at 3:20 PM Jim Brown <jim at audiosystemsgroup.com> wrote:

> On 1/12/2026 10:46 AM, Tom Hellem wrote:
> > Any ideas?
>
> This is a method I played with about ten years ago. It worked fine for
> 100W. I've never tried with with higher power. I expect that multiple
> chokes in series would be needed. That's easy to figure out -- the issue
> would be heating of the choke(s) -- transmit for a while, then go out
> and feel it. As long as you can leave fingers on the core, I wouldn't
> worry about it.
>
> http://k9yc.com/VerticalDipole.pdf
>
> 73, Jim K9YC
>
>
>
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