I just studied both the pdf you referenced, then looked them up in the
Fair-Rite catalog. This is a MnZn ferrite material, and when used for
suppression, is using ONLY the dimensional resonance -- the clue is that
the resonant frequency does not move with more turns, but Z is
multiplied by the square of the turns.
Remember that for suppression, resistance is far superior to inductance,
because inductance can be cancelled by the capacitive reactance of a
cable that is shorter than a quarter wavelength. The curves show a
rather low Q (broad) dimensional resonance in the range of 2 MHz, with
enough resistance to be useful between about 700 kHz and 4 MHz for the
largest core -- 2675540002.
The good news is that you can increase the choking Z without changing
the resonant frequency, so it should be no trick to get 10K ohms at the
resonant peak with perhaps 8-11 turns, depending on the size of core used.
There's a conceptual discussion of all of this in k9yc.com/RFI-Ham.pdf
and in other materials on k9yc.com/publish.htm. The AES paper has a bit
more of the history and theoretical development, the RFI-Ham more
practical application, and has the benefit of my ongoing research after
the AES paper was published in 2005.
73, Jim K9YC
On 9/12/2013 8:40 PM, Michael Germino wrote:
Read about this a while back.
http://www.fair-rite.com/newfair/pdf/LowFreqSuppression.pdf
I have no experience with these and at the time, couldn't find where you could buy them.
Are there ferrites for RFI rejection in the 50 khz - 500 khz range? I've been
using material #31 and wonder if there is something more useful? If so, where
can I buy it?
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