Several good points there, about the variability of ferrite cores.
Ferrites are, quite literally, "bakery products". Just like bread and
cakes, the properties of ferrites depend on the correct ingredients
measured out in precise quantities, on the precise manner in which those
ingredients are mixed, and also - most critically - on the
temperature/time profile of the baking and cooling.
Just like baking, the manufacture of ferrite materials is a complex
blend of science and know-how. Once a specific product has been
developed, consistency can only be achieved by repeating exactly the
same processes for every batch.
It is very easy to see how QC problems could appear from outsourcing
those critical processes to an offshore company that lacks the original
manufacturer's in-house know-how, with a language barrier that prevents
that information being accurately transferred.
73 from Ian GM3SEK
>-----Original Message-----
>From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
>Jim Brown
>Sent: 09 July 2016 00:23
>To: towertalk@contesting.com
>Subject: Re: [TowerTalk] AES SK
>
>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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