"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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