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Victor, I notice that in these examples you are using the nanoVNA with the
saver software, connected to a computer via USB cable.

When I do a similar setup, I note that the USB cable to the computer can
significantly affect the measurement at HF frequencies. I found that I
had to use a high quality cable and put ferrite beads on it to decouple
that RF path. You may wish to experiment with that to see if it gives you
better stability in your results.

On Sat, Jun 11, 2022, 4:22 PM Victor Reijs <pe1atn.victor.reijs@...>
wrote:

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