I had some of my ferrite cores mixed up in my junkbox. What I did is
thread them on to a
wire and mark them..so they wouldnt get mixed up again. I took some
known torroids and
did some inductance tests at various frequencies ..with 3 or 4 turns of
a 7 inch wire. I then
matched up the types that got mixed up. They were all ft37-43 and
similar sized other ones of different permeability.
Now with types that are surplus from unknown origin..you may be able to
match up inductance vs frequency graphs and match them up to known
types of similar/same size.
Ferrites are often used in broadband applications..ie 1.8 to 30
mhz..therefore you have to
select a number of frequencies for test measurements. I use the a
frequency in each amateur band.
See my web site:http://www.earlandrews.com for some more details. I use
an autek rf analyser for my inductance measurements. I may get around
to publishing more on this topic on my web pages this winter..stay
tuned. Also..another method is to measure the actual resistance of the
core with an ohmeter. I found this to be a very hit and miss and
rather difficult method. The inductance vs. Frequency method is
easier..but you need a test instrument ..and TIME!! 73 Earl VE3AB