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Mark pretty much covered why stacking cores of differing materials is a
really bad idea. I've never tried it from day one as I understand the
problems which Mark addressed. However, connecting CMC of differring
materials in series has can and is done in practice. Certainly I've found
over the last month of building and measuring CMCs for my applications that
the 31 material truly is better as an all-around core material for HF
applications. 42 material just does not have the ?r (or ?i) to properly
address 160-meters with few enough windings to address 75 through 10
meters.

Please note that I started (long ago) with RG-142 wound through large cores
of 43 material. RG-142 is the 'high power' coax made from Teflon and
silver coated conductive components and is generally light brown on the
outside. That approach is fine for coaxially fed antennas, but I use
parallel wire feeders for a multitude of reasons. I require a 'true' CMC
made of bifilar winding with no twists or core cross-overs on the toroids
to assure good choking impedance to CM currents AND assure proper
differential amplitudes and phases on the DM side of the choke. Therefore,
none of those I've previously put out on this group are of the coax
variety. All are bifilar windings on the cores as noted in the table. My
measured data (using the HP 8753C with associated s-parameter test set)
does NOT apply to chokes (current chokes) consisting of coax wound on the
cores.

I'll attach the latest 'Choke Table' as it stood last evening.

I just received my 4" OD 31 material cores from KF7P Metalworks in Utah.
More data coming........

Dave - W?LEV

On Fri, Jan 22, 2021 at 7:53 PM Max via groups.io <kg4pid=
[email protected]> wrote:

Could you increase the turns and re-measure? I'd like to see what happens
since I need a CMC choke for a milti band antenna.
These cores were stacked correct? I wonder about two in series, a 31 and a
43. Would there be a difference compared to stacking?
Max KG4PID
On Friday, January 22, 2021, 10:19:25 AM CST, Jeff Anderson <
jca1955@...> wrote:

On Thu, Jan 21, 2021 at 01:36 PM, Miro, N9LR wrote:

That would be asking for trouble, like having BJT (bipolar transistors)

in

parallel. On different frequencies, temperatures, flux one is destined

to take

more then the other, and that one heats even more and takes even more on
itself

I'm wondering if there is any empirical data or theoretical derivations
showing that paralleling ferrite cores of different materials is a bad idea.

From a heating perspective, it seems to me that if calculations show
either core, stand-alone, does not overheat in the spec'd application, then
there should not be a heating issue if the two cores are combined (unless
overall common-mode resistance *drops* below the common-mode resistance
presented by either core itself, but then what would be the point of
paralleling the two cores?)

From my own measurements, the common-mode resistance of paralleled 43 and
31 cores looks pretty good (see the attached chart). From this measured
data (taken on an HP 8753C) I don't see any reason why these two cores
should not be paralleled. If anyone has different data, I would very much
like to see it. After all, it's always possible my measurements are in
error, or that I'm looking at the issue incorrectly.

Thanks,

- Jeff, k6jca

--
*Dave - W?LEV*
*Just Let Darwin Work*