You guys keep talking about coax-fed antennas. Yes, although it may be easy to
wind coax around a toroid and put it up at the antenna midpoint, that's not so
easy with open-wire line. This discussion was very coax-centric and I wanted to
open your minds that not everybody feeds their antenna with coax.
Balanced feedlines ("window line" or "open-wire" line) can have significant
common-mode current. They're not immune to the effect. (I know you know this;
I'm saying it for the benefit of all.) A device with high common-mode
impedance, located right at the output of the tuner, suppresses common-mode
current on a (balanced) feedline. That's it's purpose.
I'm in agreement with you about the 1/ cause of common-mode current and the 2/
cure for it. I'm simply saying that for convenience's sake, consider putting
the choke at the tuner output.
A choke with high Z to common-mode current, external to the tuner, in a
non-conductive box, with as short a connection to the tuner as possible, does
quite well at suppressing common-mode current. I'll be happy to share my
measurements with you.
There is no coax anywhere in my antenna system. So my solution was to put a
choke with high impedance to common-mode current right at the output of my
antenna tuner. I encourage users of open-wire line to do that.
Al W6LX
>>> In all cases of a radiator fed with coax,
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