I forgot to add that the NanoVNA measured Impedance (based on the S21 (or
S11) 2port series through):
[image: afbeelding.png]
matches quite nicely the theoretical simulation of a choke:
[image: afbeelding.png]
<the theoretical simulation got one parameter (stray capacitance of the
choke, not of the testing gear!) which was derived by matching the peak in
the simulation with the peak in the measured S21 curve>
I think I am more or less understanding what/how is measured with the
NanoVNA. Will try to make a web page out of that.
All the best,
Victor
Op za 11 jun. 2022 om 08:32 schreef Victor Reijs via groups.io
<pe1atn.victor.reijs@...>:
Hello Roger,
Using Series though, the NanoVNA measures both a S11 and S21 (for that
configuration, which I [of course] calibrated). The link I gave (
), calculates the Zdut using
these Sx1 from the 2port series through measurement. In the case of the
resistive DUTs the S11 measured with 2 port (red blue dotted) is almost
identical with the S11 measured with 1 port (orange dotted). The same I see
with the toroid DUT.
But I am not able to map the Zdut calculated with the S21 (green dashed;
measured in the series through 2 port).
So the Zdut (Zx) using with 2port series through and S11 based is different
from Zdut (Zx) using (the same) 2 port series through and S21 based. So all
stray capacitances, etc are the same (which I see part of the DUT).
All the best,
Victor
Op za 11 jun. 2022 om 07:26 schreef Roger Need via groups.io
<sailtamarack=
[email protected]>:
Victor,
I am not sure how you are measuring the DUT using S11 reflection and S21
series methods.
You have to measure them with the correct reference plane calibration and
this usually requires two different test jigs. What are you using for
S11
and S21 test jigs? Attached is one I use for S11 up to 30 MHz. I tack
solder the DUT as shown. My example uses an inductor but you can solder
the leads to your choke. The second one I built into a box and it works
well too. I posted my S21 series jig in the last topic
Roger
