The type of antenna you described is often referred to as a coaxial center fed
dipole. The problem you have to solve is removing the interaction of the coax
exiting the end of the array, RF decoupling the coax. This can be achieved by
sleeving the coax as it exits the tubing with Ferrite "beads" - I would
estimate about 10 to 12 would be adequate for 20m.
Regards,
Norm W4QN
________________________________
From: "antennaware-request@contesting.com" <antennaware-request@contesting.com>
----------------------------------------------------------------------
Message: 1
Date: Tue, 29 Dec 2009 17:38:38 +0000
From: David Gould <dave@g3ueg.co.uk>
Subject: [Antennaware] Vertical Dipoles
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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