[TowerTalk] AES SK

Sat Jul 9 22:26:56 EDT 2016

More OT & re at least a related technology:  Long ago, I was involved 
with the DEC core memory design and core making.  Core making was an 
"interesting" operation since the only the "bakers" knew the magic for 
getting good cores.  Actually only about 30% of every batch was any 
good.  The good news was the bad cores got ball milled with the next 
batch of raw materials, then isostatically pressed, fired, ground up 
again, pressed again, fired, and finally ground into press-able powder, 
pressed in carbide dies, fired, and 100% tested.  We made billions all 
for DEC systems and were the last systems supplier to offer core memory, 
since real time systems customers loved never having to wait and wait 
for a reboot after a power failure.  The last generation cores were 
0.012" OUTside diameter and the all women core stringers in Taiwan put 
three wires through each of those tiny donuts.  And our core memory was 
cheaper to make than DRAMs until after the MOSTEK 64k chip hit its 
volume pricing valley.   Our ferrite "bakers" were really world class.  
DEC bought (cheap) the RCA core memory operation when RCA exited the 
computer business in 1971.

When one considers ferrite core memory technology it is a wonder it 
worked at all - half select noise, temperature sensitivity, aging, 
stress effects, magnetostriction, etc were large engineering and process 
control challenges.    At least cosmic rays didn't bother it and it 
didn't forget and it was the technology that made computers as we know 
them possible.

Grant KZ1W

On 7/9/2016 1:21 AM, Ian White wrote:
> 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 at contesting.com] On Behalf Of
>> Jim Brown
>> Sent: 09 July 2016 00:23
>> To:towertalk at 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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