I’ve measured common mode current when feeding a balanced line with a good DX
Engineering 1:1 balun and an unbalanced tuner, versus a real balanced
link-coupled tuner (Johnson Matchbox). To my surprise, the currents are closer
to equal with the unbalanced tuner and the balun! But the Matchbox seems
quieter.
More investigation needed...
Victor 4X6GP
> On 14 Jan 2019, at 2:44, Al Lorona <alor...@sbcglobal.net> wrote:
>
> 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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