That's a great idea, Rick -- if you have access to a test rig with
sufficiently low stray to get accurate data at that frequency and at
that impedance.
W1HIS came up with a simple method to identify a core material is #31 or
#43. Because the bulk resistivity is relatively low, you can measure
between two points on the core with a simple mechanical Ohmeter. The #31
material will show some conductivity, #43 and #61 will not. #77, #78,
and #73 have even lower bulk resistivity, so will show even more
deflection with an Ohmeter. W2DU used #73 for his string of beads common
mode chokes (the W2DU balun). His original designs used hundreds of them
to achieve a high choking Z, but those who sold them cheated, and used a
lot fewer beads, and those chokes could not handle power (because the
choking Z was not high enough).
The resistivity data is in a chart on pages 4 and 5 of the Fair-Rite
catalog (pdf page numbers 6 & 7). .The curves plotting u' and u'' are on
the following pages, one material per page.
73, Jim K9YC
73, On 4/12/2014 2:25 PM, Richard (Rick) Karlquist wrote:
If you just want to identify what type of ferrite you
have, the easiest thing to do is measure the frequency
at which the phase of the impedance is 45 degrees and
then compare this to the frequency where the
epsilon' and epsilon'' curves cross over.
Rick N6RK
On 4/10/2014 1:58 PM, Earl Morse wrote:
I confess, I am spoiled. I have access to a plethora of RF devices
such as network and impedance analyzers so I wouldn't have to make do
with making this measurement with a rigged up setup.
Earl
N8SS
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