One small addition to Jim's observations.
Fair-Rite changed the chemistry of its Type 43 material a couple years
ago. The new Type 43 material has much better Q (lower loss) compared
with the old version, by a factor of more than 10:1 at some frequencies.
There was also a very small change in the quoted permeability at low
frequency, from 850 in the old to 800 in the new, if I recall correctly.
Z remains relatively unchanged from old to new, but the R+jX components
of Z are different, with more jX and less R at lower frequencies.
This chemistry change is important if (a) you have an old core in the
junkbox and (b) you are planning on using it in a tuned application or a
filter. Otherwise, no.
I'm working on an article for QEX on ferrite cored inductors and
transformers but it's still some distance from being ready for submission.
Jack K8ZOA
www.cliftonlaboratories.com
Jim Brown wrote:
On Fri, 12 Sep 2008 11:15:22 -0700, Dave G. wrote:
Can nyone provide me with the permeability number for the T37-2 and
the
FT37-43 cores???
I also suggest that you study the material on ferrites in
http://audiosystemsgroup.com/RFI-Ham.pdf
The discussion of ferrites in this tutorial is considerably more
advanced than what's on the Amidon site or in ARRL publications, and
should give you a much better understanding of ferrites, how they work,
and how to use them. Tne most important thing to understand is that
permeability of ferrites is not a single number -- it varies (a LOT)
with frequency. The commonly published number is the LOW FREQUENCY
permeability. The second most important thing to realize is that
ferrites are pure inductors ONLY at low frequencies. As frequency
increases, resistance and capacitance become increasingly important,
and at high frequencies R and C dominate (to the extent that there's no
L!). When we use ferrites to wind coils for transceivers, we mostly
care about L. When we use ferrites to suppress RFI, we only want R.
Most (all?) ferrite cores sold to hams by Amidon and others are
actually made by Fair-Rite, a very good US company based in NY State.
They publish an excellent catalog that includes extensive data on all
of their products.
http://www.fair-rite.com/newfair/index.htm
73,
Jim Brown K9YC
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