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.
73, Jim K9YC
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