Miro, the nanovna is designed to measure this way - think of the
calibration you do for a thru S21 measurement; it calibrates the error due
to the cable and ground paths.
For measuring the choke, there is no need to worry about this issue. Other
issues are present which have a much larger effect on the
resolution/accuracy of an S21 measurement - it is quite accurate for small
values of Z, but gets less and less accurate as Z exceeds several k-ohms.
But it is entirely sufficient to get a reasonable measure of the
effectiveness of the choke, especially for the values of insertion loss and
common-mode S21 attenuation.
On Thu, Jul 7, 2022 at 7:23 PM Miro, N9LR via groups.io <m_kisacanin=
[email protected]> wrote:
Some really good suggestions, but let me highlight "my problem" here :)
I'll only focus on measuring S21 in differential mode using 2 port setup!
On the port 0 I connect shield and center conductor (as with any coaxial
transmission line), on the other port I do the same. Simple connection,
nothing fancy. Shield to shield, hot to hot :)
Now I have internally bonded ground between shields at Port 0 and Port 1,
and i ALSO have shield of the coaxial cable connecting grounds of those two
ports!!! THAT DOES NOT SEEM RIGHT!
Chances are that DUT (the current balun in this case) will lessen the
impact of the internally bonded grounds by acting as the current balun, but
what if CMRR is small - parallel ground paths will add some measuring error!
I still need to take a look at the S11 concept suggested by WB2UAQ with
shorted output and 1 port measurement of S11, but that still does not give
me S21 in differential mode!
So, how will internal ground bonding affect 2 port setup for
measuring S21 in differential mode?
