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July 25th 03, 04:06 AM

(Mike) wrote in message . com...
Frank Jones (W6AJF) - Google is your friend

I was thinking about the coax collinear but I never could make them
work.
I did find a reference about the velocity factor if the center being
different from the sheild. This messed up the phase relationship.

It appear the original antenna this was copied from had the whole
antenna potted in wax to fix that. Maybe build one out of the air
dielectric coax I have in the garage?

The coaxial collinear works fine if done properly. You do NOT have to
put the thing in wax to make it work. I wrote a paper on how to do it
properly, but the key is to use sections 1/2 wave long taking into
account the VF of the line, so that the voltage across each gap
between adjacent sections is the same, and all in phase. The
feedpoint impedance will be somewhat reactive since the elements are
shorter than a half-wave, and the impedance will depend on the number
of sections (since they are all fed in parallel, and there's a mutual
impedance to consider), but you just provide the proper matching
network for that, and you provide proper decoupling from the feedline.
It's easy to put together an eznec or similar model to show that it
works fine in air, no wax needed. And it works in practice as well as
in theory.

The old ARRL writeup on the coax collinear was rather messed up, and
my lack of success building them a couple times led me to think it
through much more carefully and learn HOW to do it.

Cheers,
Tom