[Elecraft] HELP! Permeability of Ferrite Cores...

[Jack Smith]

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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