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[Towertalk] Helically wound vertical dipoles

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Subject: [Towertalk] Helically wound vertical dipoles
From: (Tom Rauch)
Date: Sat, 8 Jun 2002 06:50:16 -0400
> Has anyone had any experience (good, bad or ugly) with
> helically wound vertical dipoles? 
> characteristics or red flags that are peculiar to
> vertical dipoles?

Helically loaded antennas are generally equivalent to something 
slightly above base-loaded and worse than center loaded antennas in 
radiation characteristics and efficiency. Of course this can vary 
depending on the care and construction put into each, but in general 
a good center-loaded system will have better efficiency.

The main advantage of helical loading is the ease of antenna 
construction. You don't have figure out how to mount a loading coil, 
or wind a good HI-Q weatherproof coil.

The main difficulty with vertical "dipole" systems is keeping the 
feedline clear of common-mode currents, and keeping the antenna 
halves balanced. The big problem is getting the feedline past the 
lower antenna half without inducing excessive common-mode currents. 
It is a very difficult problem to handle.73, Tom W8JI 

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