Roger,
The renormalization is useful for measuring networks (like crystal or ceramic filters) which are designed for other impedance levels.
For example, it allows you to evaluate a 10.7MHz, 330ohm ceramic filter without needing to add matching networks.
I have used the feature to try different Z values to determine the design impedance of unknown filters.
I like the feature, but it may indeed be that few others will. It can be ignored if desired, but I would like it to be kept available.
--John Gord
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On Sat, Feb 8, 2025 at 10:42 AM, Roger Need wrote:
On Sat, Feb 8, 2025 at 09:15 AM, DiSlord wrote:
NanoVNA has a port renormalization function (called Port Z, see
DISPLAY->PORT
Z: 50) that allows you to see the measured S parameters at other port
impedances.
But since NanoVNA is only available for measuring S11 and S21 parameters,
the
following assumptions are made for renormalization: S22 = S11 and S12 = S21,
i.e. the DUT is symmetrical.
To simplify the calculations, a non-complex impedance value is used and the
new impedance of both ports is the same.
And now the question is to what extent it is necessary to make calculations
for different values ??of port impedance, because then the DUT is not
symmetrical?? and the assumption that the S22 = S11 and S12 = S21 are equal
is
not true.
Or this can be useful?
DiSlord,
I have tested your port renormalization function (called Port Z) for several
values of Z like 75 and 100 ohms. It calculated S11 and S21 correctly for
DUT's with the same input and output impedance. I personally don't see the
need to have different Z for the input and output of a DUT. I think it just
makes things more complicated and very, very few users would ever use this
feature.
Roger
