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.
Dave - WØLEV
On Sun, Aug 20, 2023 at 9:17 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 8/20/2023 1:54 PM, David Eckhardt wrote:
> > I put this out earlier, but have made some changes and additions. Please
> > see the attment for measurements of CMRR (Common Mode Rdjection Ratio)
> made
> > in a 50-ohm system for each choke.
>
> The common mode circuit is an antenna, not a transmission line. If the
> line is coax, it's the outside of the shield. Common mode rejection
> depends entirely on the antenna into which it is inserted, and must be
> computed based on measurements of the choke, inserted as a load into a
> model of the antenna using NEC or other software. By the antenna, I mean
> the feedline with attachments on both ends, one to the antenna, the
> other at/near the shack. And like any antenna, voltage and current
> varies along it, depending on its geometry and terminations of each
> element.
>
> What we can measure in the lab is the common mode impedance of the
> choke. Before he died, G3TXQ published a piece with RSGB showing an
> excellent test jig. His measurements look very good to me, but his
> guidance for choke designs were faulty, because he failed to understand
> the significance of mfg tolerances on the chokes themselves, so I
> suspect that he measured only a few samples of the cores. This is
> something that engineers working in mfg learn -- the design has to work
> with every one of the parts from which it is built, including their
> individual mfg tolerances.
>
> 73, Jim K9YC
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--
*Dave - WØLEV*
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