On Aug 17, 4:58*am, Owen Duffy wrote:
I know that this is not consistent with the widely held view that a
common mode choke creates a demarcation point where common mode current
can flow on one side and not the other.

This is the pitch for the very popular Carolina Windom which advertisers
and promoters claim leverages the radiation from the vertical feedline
section on one side of the "isolator" but there is no undesirable common
mode current on the tx side of the "isolator".

Ideally, the high-impedance "isolator" causes a reflection of the
forward common-mode wave back toward the antenna. This ideally results
in a current node (minimum) at the "isolator" and ideally confines the
common-mode standing wave to the feedline between the "isolator" and
the antenna. That's the theory behind the Carolina Windom. How it
performs in reality is another question.

It should be easy to measure the common-mode current at a few points
between the isolator and the antenna and at a few points between the
isolator and the shack to determine just how effective the Carolina
Windom "isolator" really is. It should also be possible to model the
situation with EZNEC - no, not a perfect model, just close enough to
observe the effect of the "Isolator".

Does anyone know the choking impedance for the Carolina Windom
"isolator" over the spec'ed frequency range?
--
73, Cecil, w5dxp.com