[TowerTalk] 1/4 wave vertical versus vertical dipole (was Choke on feed point of dipole)

[David Gilbert]

On top of that, based upon the modeling I've done over the years I've 
never found that a vertical dipole has any appreciable advantage over a 
1/4 wave ground plane.  Certainly not enough to justify the 
significantly greater hassle.

I also don't think that a "ground plane" necessarily needs a lot of real 
estate for the radials.  N6BT got great results just coiling up a single 
radial in a circle around the base of the vertical some distance off the 
ground (he called it a VOR), and when I modeled that approach it looked 
virtually the same as more elevated radials.

In fact, I've long thought that maybe we could just consider whatever is 
below the feedpoint of a quarter wave vertical to be a counterpoise and 
nothing more ... essentially just a place for balancing currents to have 
somewhere to go.  To that end, I recently modeled (using EZNEC Pro2+ v7 
and NEC5) a 160m Inverted-L with nothing but a 4 foot wire under the 
feedpoint connected to the center of a 6ft by 6ft ground screen 
positioned about a foot off the ground.  I put an inductive load in 
series with the 4 foot wire and adjusted it for resonance.  The net was 
about 18 ohms real with no reactance, and the pattern and gain was about 
what you'd expect from an Inverted-L.  It's not a radial system, it's a 
tuned counterpoise with a series inductance and a capacity hat.

It's a pretty twitchy setup, though, with the bandwidth being a bit 
narrow (if it was being fed by 18 ohm coax the 2:1 SWR bandwidth would 
be about 40 KHz) and resonance being quite dependent upon the actual 
distance above RF ground ... which is almost never where the surface of 
the earth is.  It certainly would need an L-Network to match the 
feedline.  But my point is that simply thinking in terms of a 
counterpoise might open up some opportunities for alternatives to a lot 
of wires.  It's not like we're going to change the far field vertical 
pattern no matter what we do at the base of the antenna.

In fact, I just checked Tom's website and his latest antenna, the 
Park-5, looks suspiciously like it uses a similar technique ... although 
I can't be certain of that.  It appears to have hairpin coils for 
matching against the three tripod legs that likely perform the same 
capacity hat function as the ground screen I modeled.  His manual even 
mentions that proximity effects can be significant.

73,
Dave   AB7E



On 1/12/2026 10:16 PM, Tom Hellem wrote:
> My hat is off to all of you fine gentlemen who contributed to this
> discussion.
> You have helped me see the light.
> I think the reasonable conclusion is that a center fed vertical dipole is
> a very difficult thing to make work, especially if the feedline cannot be
> brought away from the antenna horizontally for an appreciable distance.
> I’m going to try base feeding it with an LC network and see if I can get
> better results.
> Many thanks to everyone who provided input.
>
> Tom
> K0SN
>
> On Mon, Jan 12, 2026 at 6:57 PM Jim Brown <jim at audiosystemsgroup.com> wrote:
>
>> On 1/12/2026 5:23 PM, Jeff Blaine wrote:
>>> Tom, I'm emphasizing what Jim mentioned earlier.  If the antenna
>>> resonant point moved by adding the choke, then that means the feedline
>>> was participating to some extent as "part of the antenna."
>> Yes, but in Tom's configuration, even with the world's greatest choke,
>> the feedline can still be a parasitic element.
>>> My belief is that without a feedline choke, you simply cannot guarantee
>>> that the feedline will not participate.  So every antenna here (19 of
>>> them) has a feedline choke of some form.
>> Yes. And feedline chokes also reduce interstation interference, whether
>> SO2R or multi.
>>
>> 73, Jim K9YC
>>
>>
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