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Hi Ulrich
First of all I give you the link to another document not published but
in small "circles" and it will interest you I am sure
to the Test Chamber and Measurements
above 500MHz.pdf It might be entered in the browser directly as the io
groups messages does no like my notation ?
Regarding the adaptor, to which the male centerpin is engaging, is a
straight forward threaded SMA female female adaptor with a hex nut on
either side of the top plate, with a toothed washer on the top side.
For the male centerpin to find the female center bushing I just press
inserted a small 2mm long section of the Teflon part for a male SMA
adaptor. It has a hole of 1 mm and that is enough guidance for the
male pin to home in on the female bushing. I insert an image of both
sides, and in my case it was a bulkhead adaptor used but it does not matter what you use.
No wear to consider.
Just for the fun of it I show you my mico-chamber Regarding the DC
biasing I have no experience, but I do not see a big problem in that
either. The center pin resistance is very low so not much DC blocking
required to protect the VNWA TX out. The biggest problem is to know
the impedance of the RF isolation between the DC supply and the center
pin to be high enough. I imagine a SMA T adaptor and some sort of
resistive or inductive impedance to block the low impedance of the DC
supply. The impedance of the T adaptor seen from the RF isolation is
removed by the calibration on the output side of the T-adaptor
connected to the test chamber (with no DC current applied). So the
impedance for determining the inductance of the internal ground rod
without the toroid and with toroid is straight forward measurement as
such. How many Amps the SMA adaptors can carry is a matter for studying.
In my last mail I said some nonsense about the spreadsheet, which is
used for determining the rod impedance and that only. How to subtract
the inductance for the measurement with toroid is a matter of some
mathematics I think is covered by already available material else
revert to the matter Kind regards Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af
UlrichKraft
Sendt: 20. oktober 2019 15:25
Til: [email protected]
Emne: Re: [nanovna-users] Measuring ferrite beads #test-jig

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

cable-emi-suppression-cores/ 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.