It's good that you raised this, Jim. Fair-Rite is yet another example of
a great small business that was owned and run by engineers who happened
to be married. He was the Chem E, she was the EE. I met them in their
booth at an IEEE EMC engineering conference in Chicago in 2005. Not long
after that they sold the business and retired. That's probably when mfg
moved off shore. Several years ago, I heard from a local EE working mfg
that his company was having serious QC issues with their #61 cores of
the same sort you described.
My measurements of coax chokes were mostly done in 2007, the bifilar
chokes in 2009-10. Measurements that produced the families of data for
1-14 turns of the five different materials were done in a well known lab
in 2002-3 by my collaborator who has chosen to remain anonymous to avoid
"issues" at work.
I would NOT, however, solely blame QC for the problem with getting
consistent measurements on chokes, simply because the circuit Q of
practical chokes is quite low, typically around 0.5. Rather, I think
much of it is a measurement problem. It is VERY well known that
reflection-based impedance measurements have increasingly poor accuracy
for values of Z that vary by more than about 5:1 from the system
impedance of the measurement system (usually 50 ohms). This is because
the equation for Z involves the sum and difference of S11 and 1, so very
small errors in S11 result in large errors in Z.
This error is in addition to the stray C of the measurement fixture,
which can cause significant errors in the resonance of the choke. This
is significant with #31 and #43 chokes that are resonant above about 10
MHz, and huge errors in higher Q materials like #61. In both cases, the
actual resonance of the choke is higher than the measured value.
73, Jim K9YC
On Fri,7/8/2016 3:12 PM, Jim Thomson wrote:
Well you could work for Fair rite as a type 31 sales manager. Or better yet,
visit their new plant in China, where they make all these products, and figure
out
why they have such extremes and variations in their type 31 cores since the
chinese
plant opened. N3RR bought over 700 of em, 2.4 inch od cores, and found they
are all over the map, and even sent samples to Fair rite. Bill ended up
devising a
simple 1 turn test, then graded all 700 of em into various sub groups. No
wonder the
initial CMC results were not repeatable.
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