[TowerTalk] Choke on feed point of dipole

[David Gilbert]

"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


On 1/13/2026 11:35 AM, Jeff Blaine wrote:
> I would not hesitate to put up a vertical dipole.
>
> In fact my 30m beam is so directional I'm thinking of putting up one 
> here just to cut down on rotor wear & tear.  Assuming you have the 
> height, It's much simpler physically than doing a vertical as you 
> don't have the ground system to worry about.  And it gets the 
> important current maximum quite a way off the ground.
>
> The "easy" way to do this is to build the dipole as normal. **NO** 
> choke at the feepoint in this case.  The **GROUND** leg of the dipole 
> runs down to ground, next to the coax with the two secured together so 
> they are not blowing around separately.
>
> The important part is to put a serious coax choke at the end of the 
> dipole tip, on the ground side.  That means multiple turns through a 
> couple of type-31 ferrites.
>
> Antenna resonance is trimmed with the tip length at the top assuming 
> you have a pulley to pull it up.
>
> 73/jeff/ac0c
> alpha-charlie-zero-charlie
> www.ac0c.com
>
> On 1/13/2026 4:02 AM, Brian Beezley wrote:
>> Tom Hellem wrote:
>>
>> "I think the reasonable conclusion is that a center fed vertical 
>> dipole is a very difficult thing to make work..."
>>
>> Tom, at my last QTH I dropped a 40m dipole vertically from a tall 
>> eucalyptus. I fed it directly with RG-58 (no choke). The feedline ran 
>> roughly horizontal for tens of feet. (The tree was slightly down the 
>> slope of a hill from the shack.) SWR was fine. I remember generating 
>> pileups during Field Day as a 500 watt home station, but otherwise I 
>> was not that impressed with its performance.
>>
>> The gain and elevation pattern of a vertical antenna are quite 
>> sensitive to ground quality. Unless you have really good ground, a 
>> horizontal antenna may perform better, even at low angles, if you can 
>> put it at a decent height. "Decent" might not be that difficult at 14 
>> MHz and above, but it may be a problem below.
>>
>> When modeling a vertical antenna, these generic ground constants are 
>> much more appropriate than those your antenna analysis program offers:
>>
>> https://k6sti.neocities.org/hfgc
>>
>> Brian
>>
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