Sorry, this is not what I measure with good equipment. The coaxial chokes
come out second on CMRR to the bifilar wound CMCs.
And to perfectly balance both sides of the wires (mine are 450-feet in a
doublet configuration), the surrounding soil to a reasonable depth must be
treated such that each side of the doublet or dipole present identical
dielectric constants and identical conductivity to each side. No ham does
that, not even Uncle Sugar in the vast majority of cases.
True, my CMRR measurements are made in a 50-ohm system. I would observe
EVERY antenna installation the amateur installs is different. There is no
single, one, CMC, current balun, or other balun functions that suit every
installation. Your data should show that. As a matter of fact, your data
is also taken in a 50 ohm system. True, this does not necessarily indicate
how the choke(s) will perform in practice.
HOWEVER, if one measures the complex impedance in which the choke is
embedded, then a good solid conclusion as to CMRR can be made based on the
50-ohm CMRR. At that point, it's just an application of Ohm's Law. I have
done so and know the complex impedance presented in the shack. The vast
majority of hams do not make this measurement. I have so I know what to
expect.
The bifilar wound CMCs perform better for my purposes. They provide a
high-Z against CM currents AND force balance in the two conductors at the
shack. In addition, I really don't care about added SWR losses with the
parallel conductor transmission line. Coax can not perform in my
application as such. Nor can coaxial current chokes (coax wound on a
toroid) force a balance. They function only as a current choke to currents
on the outside of the coaxial braid.
Every installation is unique. I have made the required measurements and
adjusted variables to best suit my and only my installation.
And, BTW, I'm well aware of the "third wire" or whatever it's termed in
professional circles.
Dave - WØLEV
On Mon, Aug 21, 2023 at 7:03 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 8/20/2023 4:27 PM, David Eckhardt wrote:
> > I do not use coax on the HF set of wires. I use parallel conductor
> > transmission line. No more than 8-feet of coax in my HF setup. So I
> > need to both reduce common mode currents and transition from CM to DM.
> > These CMCs accomplish both in my application.
>
> There's nothing magic about parallel wire line that provides balance. if
> It's what's at the termination that provides balance (or imbalance). And
> the common mode current is on both conductors, a value equal to the
> difference in the currents in the two conductors at each point. In other
> words, it's STILL part of the antenna, and chokes work exactly the same
> way, whether wound with coax or parallel wire line. My designs use both
> interchangeably, the practical differences being Zo in the range of 100
> ohms for the two-wire chokes.
>
> Yes, the chokes will work if well designed. But your CMMR measurements
> into 50 ohms tell us nothing about that. It's still the antenna model.
>
> 73, Jim K9YC
>
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--
*Dave - WØLEV*
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