[TowerTalk] Choke on feed point of dipole

[David Gilbert]

I know what those are.  It's another design from N6BT, who I believe 
used to own Force 12.  As I said in a different post, he also came up 
with the VOR that coils the bottom half of a vertical dipole around the 
base.  He also made the antennas that had a short vertical section with 
spiral coiled elements on both ends of the vertical section (I don't 
remember what they were called). Essentially your H-shaped antenna with 
the horizontal sections wrapped in a coil.  They worked well also ... 
but none of those configurations are marketed anymore because there are 
simpler ways of achieving similar performance, even for portable 
operations.  A 17 foot extendable whip (you can buy cheap ones for as 
little as about $35 on eBay) with three or four radials can be set up in 
less than 10 minutes without any tree or other support and outperform 
almost any similar alternative.   Several folks have done YouTube videos 
on exactly that configuration, and I've made my own version ... which is 
how I know it can be set up in less than ten minutes.

And I still say that there is no practical advantage for trying to force 
a vertical antenna into being a dipole.  At least I can't find one that 
offsets the additional hassle of it.  If you think otherwise, I'd like 
to hear it.  Maybe the fact that the feedpoint impedance of a vertical 
dipole is higher than a quarter wave version with radials or some sort 
of counterpoise, but it's high enough (greater than 50 ohms) that you 
still need to match it.

Dave   AB7E


On 1/13/2026 12:34 PM, john at kk9a.com wrote:
> A vertical dipole can have shortened elements, making height less of an
> issue.  Force 12 used to make sideways H shaped verticals that were center
> fed.  I have used one on 40m and it was surprisingly good.  Here is a
> Force12 80m Sigma vertical:
> https://dxsupply.com/en/amateurradio/verticals-6-80-m/force12-80m/ 
>
> John KK9A
>
>
> David Gilbert ab7e wrote:
>
> "Assuming you have the height"
>
> That's the kicker, though, and it takes twice as much of it for
> relatively little additional performance.  I've modeled a 20m ground
> plane with four elevated radials and a 20m vertical dipole, both of them
> being 4 feet off the ground.  The elevation pattern is lower with the
> vertical dipole (17 degrees versus 23), but the maximum gain is almost
> identical.
>
> I agree that your suggestion (feedpoint at the bottom with a serious
> choke) is a practical way to make a vertical dipole, but you have to
> trim for tuning at the top whereas you can trim a ground plane at the
> radials near the ground.
>
> 73,
> Dave   AB7E
>
>