Larry Benko wrote:

That is what I thought also Roy but the little L/C meter seems to work
pretty well with low Q inductors. It is not measuring impedance but
measuring a frequency of an inductor and known capacitor in an
oscillator. The Q does change the oscillating frequency but not that
much. As I said before it is super easy to tell the difference between
77/31/43/61 type ferrites. Of course the permeability difference
between those types is a factor of 2 or more so ultra accuracy is not
important. The original question was how to determine what type an
unknown core was and not what impedance it represented at a certain
frequency.

I just grabbed 3 FairRite 59XX003801 torroids (2.4" OD x 1.4" ID x .5")
in 3 materials and measured a single turn with the L/C meter.

Material 61 (u=125) calc. inductance = .173uH, measured = .177uH
Material 43 (u=800) calc. inductance = 1.07uH, measured = .930uH
Material 75 (u=5000) calc. inductance = 6.85uH, measured = 7.39uH

The calculated inductances came from the FairRite catalog. I would say
the "low Q" inductors measured pretty well and the materilas were very
easy to distinguish.

Yep, that's perfectly adequate to distinguish the types. You must have
made the measurements at a pretty low frequency. Type 75 has a Q of 1 at
about a MHz, and 43 at a few MHz, and they drop at higher frequencies.
Will the circuit oscillate with Q that low?

Roy Lewallen, W7EL

Roy Lewallen wrote:


Yep, that's perfectly adequate to distinguish the types. You must have
made the measurements at a pretty low frequency. Type 75 has a Q of 1 at
about a MHz, and 43 at a few MHz, and they drop at higher frequencies.
Will the circuit oscillate with Q that low?

Roy Lewallen, W7EL

Referring to http://www.aade.com/lcm2binst/HP.html the measurement freq.
was about 750KHz for the type 61 and 43 materials and about 70KHz for
the 75 material based on the inductances that were displayed.

73, Larry W0QE

Larry Benko wrote:
Roy Lewallen wrote:


Yep, that's perfectly adequate to distinguish the types. You must have
made the measurements at a pretty low frequency. Type 75 has a Q of 1
at about a MHz, and 43 at a few MHz, and they drop at higher
frequencies. Will the circuit oscillate with Q that low?

Roy Lewallen, W7EL


Referring to http://www.aade.com/lcm2binst/HP.html the measurement freq.
was about 750KHz for the type 61 and 43 materials and about 70KHz for
the 75 material based on the inductances that were displayed.

73, Larry W0QE

Darn typo. That should be 750KHz for the type 61 and 43 and 700KHz for
the type 75. Sorry.

73,Larry W0QE