[Amps] Amps Digest, Vol 264, Issue 7

[Michael Tope]

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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