[RFI] Ferrite Material

Dana Roode Dana Roode <K6NR@ARRL.net>
Mon, 03 Jan 2000 21:01:33 -0800

Hi all,

A few asked me about the choice of type -43 material in solving my
phone RFI.  -43 worked for me, but my main problem was at 28mhz.  I
think type 77(73) or -75(J) material might generally be a better
choice for HF.  I think this subject was recently discussed on the
list, so others can clarify.  The frequency graph in Amidon's "Ferrite
Cores for RFI Suppression" pamphlet indicate that -43 peaks in
impedance at about 200 mhz, getting significantly lower under 10 mhz. 
Type -73(77) peaks at 28 mhz, with significant impedance between 3 and
500 mhz or so.  Type -J looks good from under 1 mhz to 70mhz, with
peak impedance at 6 mhz.

Elsewhere in the same pamphlet, Amidon says:

"We recommend the #73 or #77 ferrite bead material for attenuation of
RFI resulting from transmissions in the amateur band.  The #43
material will provide best RFI attenuation from 30 to 400 mhz, and the
#64 material is most effective above 400mhz.  The #J material is
recommended for RFI from 0.5 to 10 Mhz, but it can also be quite
effective even below the AM broadcast band."

I'll have to double check with my neighbor to verify that I am not
getting into the telephone on 40, 80 or 160m.  I put 9 turns through
the -43 torroids, which is probably enough impedance even on the lower

I'm no expert on this and do not want to mislead anyone.  "Your
mileage may vary".


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