[TowerTalk] Measuring Ferrite

[Jim Brown]

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
>>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>