[TowerTalk] Choke on feed point of dipole

[Jeff Blaine]

I don't see the functional difference to have the feedline inside or 
out. Either way will work fine.  Having the coax inside is more "clean" 
for sure.  But  I had assumed the gentleman had an existing vertical 
dipole with the feedline running off to the side.  In that case, 
dropping that feedline so that it was lashed up to the element was a 
quick mechanical fix.  Adding the choke at the bottom of the element 
where the coax is essentially "terminates" that element.  Adjust the top 
most element tip for best SWR.

Of course antennas are a rabbit-hole topic that a guy can dig down as 
deep as he wants - and then some.  For me, I'm not in the blessed state 
of retired bliss so time is always a squeeze and getting something that 
works well and can be done without making it more complicated than it 
needed is part of the restrictions I have here.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 1/14/2026 6:35 PM, Jim Lux wrote:
> 	
>
>
>   
> Actually, what you do is run the feedline up through the bottom element (which is a tube). And then choke it at the bottom of that element.
> It makes what's also called a "sleeve dipole"
> And yes, the presence of the feedline near the end of the dipole does introduce potential issues
>
> Eh, what we need is coax with 31 mix in the jacket self choking feedline- I've actually looked into how one would make something like this for work - an antenna laying on the surface of the Moon for broadband usage without weird lobes)
>
>
> On Mon, 12 Jan 2026 22:16:34 -0700, Tom Hellem <tom.hellem at gmail.com> 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  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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