If you're reading this, you have probably done exactly what I did the other week. You can see the scenario: I grabbed a bunch of Fair-Rite 240 size toroids, mix 43, 52, and 61, put them in a box (without writing on them) ready for me to build some test baluns. Doh!
So there I was with 6 toroids which kind of look similar, but I did not know what mix they are. Ok, I do know you can write easily with a sharpie on Mix 43; you can't with Mix 61, or sometimes you can with Mix 52. But I really needed to know what they were. What we would call a more scientific method to identify the mix type.
This is what I did. Firstly I was lucky to have all the jumbled up mixes also in boxes with labels on them. So I decided to do back to back comparisons of RF impeedance using my NanoVNA. This is how I did it.
Firstly (sorry, I should have taken the picture before I wrote on the core), I wound 9 turns of wire through each core and performed an S21 gain measurement using my NanoVNA to plot the return loss (RF impedance) of each core.
Then, looking at the plot and the mix characteristics of each mix as per Fair-Rite (see Fair-Rite), I could estimate which core is of which type. To put this simply, out of Mix 43, 52, and 61, I was expecting to see higher impedance on the lower bands for each core in order of the mix number. Or, higher impedance at the higher bands in order of the mix number.
These are the plots; look at the 160m, 20m, and 10m bands.
You can see from the plots I managed to get the mix right based on the plots. Each of the cores returned a plot as expected. The lower mix value has higher impedance on the lower bands and less impedance on the higher bands. As the mixes go up in number, the reverse is seen.
I did remember to write on the cores this time.
In my case, this worked because I knew what was in the jumbled box of toroids. If you have no idea what the toroids are, then that's another blog post.
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