In article ,
Cecil Moore wrote:

By open stub, you mean there is no loop at the bottom of the "J"?

He means the bottom of the stub is the feedpoint, like this:

+------------------------------------------------------------
|
FP
|
+-----------------

And that looks like an unbalanced feedpoint so it should result
in common-mode currents, sorta like an off center-fed dipole.

If I recall correctly, Cebik has some discussion and modelling of such
open-sleeve J-pole designs in his "Tales and Technicals" section.
Start at http://www.cebik.com/vhf/jp1.html and go down about half-way.

The version of the "non-standard J-pole" which Cebik models is fed at
bottom center, in a dimensionally-symmetrical way. His current plot
seems to show equal currents at this feedpoint, and this would seem to
make the use of a choke or balun on the feedline somewhat less
significant than with a standard J-pole.

Cebik's model would need to be modified somewhat apply to the Arrow
open-sleeve J-pole, as the Arrow is fed at the very base of the one
element rather than halfway between the two.

Anybody care to model up the Arrow, with all three elements included,
with and without a separate wire representing the outside of the coax?

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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