Hello Kurt,
that is a wonderful description of what you three did a while go when measuring the performance of ferrite materials. Very cool stuff and because I'm just looking in exactly that topic I have a few questions questions to your fixture. I'm still on a "beginner level" using VNA for measuring ferrite impedances, so sorry for any stupid questiosn.
When you have inserted the ferrite bead and turning the adjustment knob it will contact the SMA F connector at some point. What type of SMA connector did you use? I would imagin that the inner conductor gets damaged pretty fast after using the fixture a few times? Or is that a "special" type of SMA with more robust inner-conductor design ?
Do you know if something similar is commercially available?
Secondly, I like to characterize the ferrits with DC-BIAS current from 0 up to 10 Amps.. That changes ferrite impedance and frequency, depending on saturation of the material.
See
For relatively large ferrite cores it might be easy just adding an additional wire through the inner dimeter, with a DC-current. That way the RF- and DC wires are separated.
But for smaller components like wound-beads (e.g. Fair-Rite 2961666671) I need to "inject" the DC current into the signal line of the VNA. Do you have any experience how to do that best? What kind of RF-filtering / DC-blocking needs to be build ? How is calibration performed then? The additional filtering will definitely change the overall S11 response, but I want to see only the ferrite effect on the Impedance and not any effect of that filter. The intended frequency range is up to 500 MHz for #61 material, but ideally for full span of nanovna up to 1 GHz.
