In order to re-use/re-purpose salvaged ferrite bobbins/toroids/rods,
with unknown properties/permeability etc, I use this procedure.
Wind 100 turns of wire on the form and then measure the inductance,
using An LC meter. We will call this measurement L 100.
This then establishes a starting point, and the rest is just mathematical calculation.
The inductance value needed is called L req'd
which needs 'N' number of turns of wire.
Then use this formula:
The formula agrees with one found in the AMIDON literature.
They call the L 100 value AL
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Some estimation of an unknown ferrite can be gauged
by measurement of surface resistivity (using DMM):
low resistivity (low freq' application) Mn-Zn or
high resistivity (high freq' application) Ni-Zn ferrite.
FERRITES -- the 2 types explains.
� 3Q 2018