On Sep 13, 2:07*pm, Owen Duffy wrote:
For these reasons, it is naive to think that a practical common mode
choke has such extremely high impedance that the common mode current
through the choke is zero, or even near to it.

Nobody said the Carolina Windom choke was that robust - just that it
is possible to design a choke with a high enough impedance to cause a
common-mode standing-wave node at the choke.

Even if it did drive
common mode current to zero or near zero at that point, that does not
mean there is no common mode standing wave, just that a node exists at
that point.

There is a common-mode standing wave on one side of the choke and not
on the other because the very high choking impedance reflects the
common-mode traveling wave on one side of the choke back toward the
source of the forward wave. I took a trapped dipole and dropped a wire
from one end to mininec ground. The standing-wave current is free to
flow through the choke and establish a standing-wave on the other side
- but it doesn't. Here is what a robust isolator is supposed to do to
the common-mode standing-wave current.

http://www.w5dxp.com/trapgnd.JPG

Again, I am not saying the Carolina Windom isolator is that good -
just demonstrating a principle that you seem to be missing above.
--
73, Cecil, w5dxp.com