Yes, I've heard of the Snelling book as being a bible of sorts for this
sort of thing. I was really surprised to find just now that you can
download a copy (411 pages) from the internet archive here:
https://archive.org/download/SNELLING__SOFT-FERRITES__1969/SNELLING__SOFT-FERRITES__1969.pdf
73, Mike W4EF....................
On 12/8/2024 7:45 PM, Jim Brown wrote:
Both my AES Paper on ferrites and k9yc.com/RFI-Ham.pdf cite my primary
reference on dimensional resonance.
E. C. Snelling, Soft Ferrites, Properties and Applications, Chemical
Rubber Publishing, 1969 This, like all of Snelling’s books, is geared
toward non-suppression applications of ferrites. Lots of math and
physics. In 2005, when I was researching for the AES paper, KC9GLI,
then at U of Chicago, found a copy in the third sub-basement of the
engineering library, and loaned it to me.
At the time, Snelling was considered THE man by engineers at all the
ferrite mfrs.
73, Jim K9YC
On 12/8/2024 6:51 PM, Michael Tope wrote:
If you want to delve into the physical nature of the "dimensional
resonance" in ferrites, this PHD thesis by Glenn Skutt is probably
not a bad place to start. It's pretty dense with equations, but the
reference list is very extensive. Rudy Severns (aka N6LF) is
mentioned in the acknowledgement section and his name appears in
several of the references:
https://vtechworks.lib.vt.edu/items/ea42c327-ddc2-4ebd-94bb-1ed9eab600ac
It seems that the combination of high permeability and high
dielectric constant can make the wavelength in the material very
short. Thus, a core cross section of a few centimeters can be on the
order of a half- wavelength in the megahertz range. As a result of
this shortened wavelength there is an affect on the distribution of
magnetic flux in the ferrite cross-section that is analogous to the
distribution of current in a conductor (aka the skin effect). That is
about all I have been able to absorb.
73, Mike W4EF.................
On 12/6/2024 10:24 AM, Jim Brown wrote:
On 12/6/2024 9:52 AM, John Lyles wrote:
Powered Iron makes low loss toroids but are not useful as EMI
suppressors. The inductance and the net impedance is low also. As
we all know, ferrite works very well if you get the right mix.
Ferrites work for RFI suppression BECAUSE of their parallel self
resonance, and the chemistry of each mix determines both where that
resonance occurs and it's usefulness in suppression. NiZn
chemistries (for example, Fair-Rite #43, #52, #61) provide a single
resonance, usually fairly high-Q; MnZn chemistries (Fair-Rite #31,
#75, #77, #78) provide two, one based on windings, the second based
on cross- sectional area of the flux path. Fair-Rite's #31 is unique
-- it's dimensional resonance in convenient sizes lands in a sweet
spot for HF IF, and ONLY IF, turns are wound through it.
There's a lot more of what I've learned about this over 20 years of
study in k9yc.com/RFI-Ham.pdf and in the 2018 Choke Cookbook at
k9yc.com/publish.htm I began this study in 2004 to address RFI to
large sound systems and published it as an AES Paper in 2005. I
first published RFI-Ham.pdf, which addresses its applications to ham
radio, in 2007.
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