I do this a little differently, for simplicity, as discussed in some of the
message threads (search for CMC, and you will find lots of methods/info
from discussions several months ago).
For insertion loss, with a coaxial coax choke like what you described, what
I care about is the loss through the center conductor when the shield is
working as a return path - so I just hook it directly to the coax port 0
and 1 connectors of the nano, and display the S21 loss curve in dB. A good
choke will have just a small insertion loss, typically less than .1 dB at
HF frequencies.
For common-mode rejection, what I care about is how much the shield
attenuates the signal - so I connect the shield only to the center
conductors of the port 0 and 1, and do another S21 loss curve. Then I see
20-40 dB of attenuation in a curve across 1-30MHz for my HF chokes. If I
want to see the impedance, I can also change the display to show R+jX and
get an estimate of the impedance, hoping for k's of ohms resistive and a
small reactive part. The measurement and values are not perfect, but is
easy to do. You can see a similar loss curve if you just hook the shield
across port 0, and display an S11 loss curve - but displaying the impedance
isn't correct in that setup, since it is the impedance of the reflection,
not of the choke.
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On Thu, Jul 7, 2022 at 2:25 PM WB2UAQ <pschuch@...> wrote:
As you said, short the input terminals and the output terminals and
measure S21 between the terminals with them floating. With the phase and
magnitude of S21 the common mode Z can be calculated. There are files in
this discussion group that do the calculation. Save the s2p data and
insert it into the spreadsheets.
For insertion loss measure S11 (return loss format) looking into the DUT
with the output terminals of the DUT shorted. Half the return loss is the
loss thru the DUT.
