Post by Roy Lewallen
The 259B is, I maintain, a very good instrument for identifying core
materials and for use in the design of inductors, transformers, and
other magnetic components. I've used mine many times for the purpose
and gotten the results I expected. That was, I thought, the subject of
this thread, but it appears to have drifted elsewhere.
It has certainly drifted away from Australia, and towards the USA.
In the USA, it's a good bet that an unknown ferrite core will be made by
Fair-Rite, and probably one of the more common materials; or else it's
probably a dust-iron core from Micrometals. With help from the catalogs,
and a few known cores for reference, even quite limited test equipment
will have a good chance of identifying the specific product.
But that may not be true in the rest of the world. You may have a core
that is marketed in your home country but imported from another, but
having been manufactured in a third country using a process licensed
from... well, who knows any more? There are no world-standard sizes, and
no direct equivalents between magnetic materials from different
manufacturers. The best you can hope for is to identify the material as
being "somewhat like" a known Fair-Rite mix.
With such uncertainties about the material itself, you can afford far
fewer uncertainties about the measurement. If you don't have advanced
test equipment (or an advanced understanding of the limitations of
simpler equipment) then it may be better to forget about characterizing
the magnetic material. If you want to know if it will work in an HF
balun, it may be much easier to *make* a balun.
On the other hand, if you really want to chase down the problem of
identifying and characterizing unknown cores from anywhere around the
world, the following links may help.
No coincidence that this site is .au - they know about this problem in
There are very useful international cross-reference pages at:
Do remember that these are not exact equivalents, only the closest
available. Also note the huge gaps in the tables, where nothing even
Another very useful resource is DL5SWB's Mini Ring Core Calculator:
This software contains extensive libraries of cores from international
manufacturers, including dimensions and paint colours as well as
magnetic properties. If you know the identity of the core, it will
calculate the inductance from the number of turns. If you have an
unknown core, and can make some meaningful measurements, there are
separate functions to help identify it.
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)