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Re: [Antennaware] Vertical Dipoles

To: <>, "David Gould" <>
Subject: Re: [Antennaware] Vertical Dipoles
From: "K9AY" <>
Date: Tue, 29 Dec 2009 14:00:25 -0600
List-post: <">>

One of my past projects was a no-radial multi-band vertical with a feed 
similar to what you propose. I found two alternatives for isolating the 
feedline. The first was a 1.77:1 transmission line transformer that improved 
the match and also served as a "current balun" or line isolator. The second 
method was simply buried coax with the shield grounded immediately below the 

I should note that the bottom of the tubing was not the high voltage 
point -- this was a "bent" vertical dipole with a portion of the bottom 
element extending horizontally at about 4 ft. height. The coax exited the 
tubing roughly 2/3 the distance from feedpoint to tip. With the latter of 
the two isolating methods noted above, the distance from ground to feedpoint 
was very close to 1/4-wavelength on 20M, providing some "natural" 
decoupling. (The design of the antenna was such that feedline isolation was 
of greatest importance on 20M.)

Hope this helps!

73 & HNY,
Gary, K9AY

> This may be slightly off-topic but hopefully not too much!!
> I would like to build a vertical dipole for 20m with the bottom about
> 1m off the ground, to compliment a beam, to give me a quick
> omni-directional alternative.
> What are the potential problems,  or issues to be aware of if I were
> to take the coax feedline down the centre of the tubing that makes
> the lower section of the dipole.  I have seen several alternatives
> where the coax is taken away from the centre of the dipole parallel
> to the ground, but I would prefer not to do this.
> Any thoughts gratefully received.  I guess a good feedline current
> choke might be a good idea at the base.
> Happy New Year to everyone and thanks for the various help over the years.
> 73,
> Dave, G3UEG

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