Jim,
That is most interesting material, thank you! Will you all be including
a test fixture description as well? I am in the process of gathering
the materials to build a test fixture, and would like to see your designs...
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources
On 2/20/22 12:28, Jim Brown wrote:
On 2/20/2022 4:13 AM, Hare, Ed, W1RFI wrote:
The toroids are not marked, so it will not be certain what material
they are."
Thanks. For the next Handbook, I've given Ward details of a method to
identify a few MnZn ferrite materials with an ohmmeter. It was first
suggested by W1HIS, and I fleshed it out a bit further. It's pretty
simple. It worked with the three VOMs in my lab -- a Simpson 260, a
Fluke 8060A, and a nice little no-name digital VOM that I bought for
about $15 at a northwest Indiana hamfest at least 20 years ago.
With the meter on a high range scale, aggressively scratch the surface
of the ferrite with the probes so that they get through the coating, and
note the reading, if there is one. #31, #75, #77, and #78 are MnZn
mixes, and will show a reading in the range of 100K - 700K; #75, #77,
and #78 will be in the range of 1K - 10K. #43, #52, and #61 -- are NiZn
materials, which have MUCH higher bulk resistivities, and will show no
conductivity at all. These resistivity values, as well as initial
permeabilty (mu at low frequency) are tabulated in early pages of the
Fair-Rite catalog.
We're also including methods to zero in on the specific material
measuring inductance using traditional methods or studying the shape of
an impedance sweep with a well calibrated Vector Analyzer.
These methods, of course, depend on knowing AL or ui values for the
various materials. Fair-Rite's published data is FAR more extensive than
any other manufacturers; others publish little more than marketing or
limited applications data. For example, Laird (used to be Steward)
publishes ui values for only two of about eight materials.
73, Jim K9YC
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