On 2/20/2022 2:48 PM, Dave (NK7Z) wrote:
That is most interesting material, thank you! Will you all be including
a test fixture description as well?
Yes. One of several jigs I use is a BNC to Pomona male adapter with
alligator clips fitting over over the male pins. I use it at the end of
a suitable piece of RG400, and dangle it off the arm of a chair. For
calibration, I use a piece of #10 copper, folded over and covered with
solder as a short, a 1% large format 49.9 ohm chip resistor. To verify
calibration at high frequency, I use a similar chip resistor, 5K or more.
I don't trust this jig for precision much above 10-15 MHz, but it's
plenty good for this purpose.
I can get repeatable results measuring a single turn (one pass through
the core) for everything I've tested with the exception of #61, which
comes nowhere near data sheet values for ui for a half dozen cores I've
measured. This one must be identified by its extremely narrow resonance
at HF.
As of a few days ago, Ward had sent it to layout, along with printouts
of VNWA log impedance sweeps of the 12 and 16 turns through the six
mixes of Fair-Rite 2.4-in o.d. toroids in my stash -- #31, 43, 52, 61,
75, and 78.
73, Jim K9YC
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