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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

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.