[Amps] Amps Digest, Vol 264, Issue 7

[Jim Brown]

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.