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QSL via  

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eQSL

No Bureau cards, please!

They trashing my
incoming QSL!

   

1 turnDo a single loop through the core windows and measure the impedance with some sort of analyzer. Even an MFJ259B with a short connection to the jack will work well for this. If R=X someplace much higher, you can be sure it is a different mix. The Q=1 frequency, where R=X or where loss tangent crosses reactance, tells you the material better than anything else you can do.

If the resistance equals the reactance down somewhere around 2 MHz, it is 73 material.

(source W8JI)