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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?

Since I use the nanoVNA only for amateur radio or tinySA related work, everything is nominally 50 Ohms. But for purely theoretical reasons I'm looking forward to any expansion on this subject you care to make. Always like learning more, even when it doesn't directly apply to what I do with these instruments. Thank you!

Why not just use a normalized Smith Chart? Ten the center resistance can
be anything you want.

Dave - W?LEV

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On Sat, Feb 8, 2025 at 5:15?PM DiSlord via groups.io <dislordlive=
[email protected]> 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?

--

*Dave - W?LEV*


--
Dave - W?LEV

Isn't that what the Z function does--allow normalisation of the chart to any resistance?

Yes, but I believe anyone (well........."maybe") can multiply any number by
unity: 1. Or maybe not???????

Even with a normalized chart center, the measurement system is still as
close to 50 ± j 0 as Eric can economically implement.

Dave - W?LEV

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Virus-free.www.avg.com
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<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Sat, Feb 8, 2025 at 5:33?PM Matthew Rapaport via groups.io <quineatal=
[email protected]> wrote:

Isn't that what the Z function does--allow normalisation of the chart to
any resistance?

--

*Dave - W?LEV*


--
Dave - W?LEV

VNA calibrated by 50Om - nominal port impedance
On measure S parameters possible calculate get Z parameters (by known Z0 = 50)

Next possible calculate from this Z new S` parameters but use Z` != 50 Om
This process named as renormalization and allow see now DUT work on other system impedances
This work on all S11 and S21 - so possible see how work filter on non 50 Om systems, or see SWR for 75Om and so on

Hi DiSlord and All

I already used the standard load= 50.83 Ohm ( DC measur by a good Multimeter's) instead of 50.00 Ohm for the Nano calibration, and a Z0= 78.9 Ohm to optimise my nominal 75 Ohm coax for the SWR and graphic smith and all seems working smoothly as it's expected for S11, measurements , but still no deep try's for S21 except Thru tests with my H4+1.2.40.
Very satisfayed right now with some precautions, very handy options and allow very accurates measurements. it's a great options , indeed an accurate professional 50 Ohm Load is expensive .
Thanks .
73's Nizar

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

Hi Roger

If the coding does not require a huge complication nor a large resources, it would be appreciated to have this option of the Z port2, it would also approach the enhanced response on H4 NanoVNA.

73's Nizar

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

But the measurement system - that of the NANOVNA - is always in a 50-ohm
system. To do it correctly, matching networks are required to match
anything other than 50-ohms.

Dave - W?LEV

On Sat, Feb 8, 2025 at 8:35?PM John Gord via groups.io <johngord=
[email protected]> wrote:

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


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

--

*Dave - W?LEV*


--
Dave - W?LEV

That isn't the point Dave... When converting back to real values, whether the center 1 represents 50 Ohms or something else makes a difference. Or have I got something wrong here?

Dave,
The measurement is indeed made in a 50-ohm system, but given a complete (S11, S21, S22, S12) set of S-parameters in a 50 ohm system, it is possible to calculate what the S-parameters would be in a different impedance system. (This works best for passives, less chance of strange non-linearities like oscillations with incorrect terminations.)
Since we only have S11 and S21, we assume that S12 = S21 (almost always true) and S22 = S11 (true enough for symmetrical devices like many filters).
If you have some ceramic filters give it a try. It is interesting to see the bumpy S21 response in the 50 ohm measurement turn into a much smoother S21 in the correct impedance framework.
--John Gord

On Sat, Feb 8, 2025 at 12:51 PM, W0LEV wrote:

But the measurement system - that of the NANOVNA - is always in a 50-ohm
system. To do it correctly, matching networks are required to match
anything other than 50-ohms.

Yes NanoVNA 50Om system, but possible use math to see how this DUT measured in different impedance system
For this S parameters converts to Z (DUT impedance constant and not depend from measured device) and after convert back to virtual Z` measured system impedance. This process named impedance renormalization.

As result measured DUT impedance not change, but S parameters transform

On Sat, Feb 8, 2025 at 10:55 AM, Team-SIM SIM-Mode wrote:

If the coding does not require a huge complication nor a large resources, it
would be appreciated to have this option of the Z port2, it would also
approach the enhanced response on H4 NanoVNA.

Nizar,

I am not sure what you are saying. The existing Port Z function allows one to calculate the S parameters for another system impedance like 75 ohms. For example if a filter had a designed input impedance of 75 ohms and an output impedance of 75 ohms you could set Port Z to 75 ohms and measure S11 and S21.

I think what DiSlord is proposing is that you could set two different impedances - one for input of the DUT (like 75 ohms) and one for the output (like 300 ohms) and they could be different. DiSlord is that what you are suggesting?

Roger

On Sat, Feb 8, 2025 at 09:26 AM, W0LEV wrote:

Why not just use a normalized Smith Chart? Ten the center resistance can
be anything you want.

Smith Chart is only for S11. The Port Z feature also works with S21.

Roger

On Sat, Feb 8, 2025 at 12:35 PM, John Gord wrote:

The renormalization is useful for measuring networks (like crystal or ceramic
filters) which are designed for other impedance levels.

Do you want different impedances on input and output? I believe that is what DiSlord is suggesting...

Roger

Roger,
I am happy with the in/out impedances being the same. I just didn't want the renormalization feature the disappear.
--John

Roger,

I believe DiSlord is indeed asking whether the ability to accurately
measure differing DUT input and output ports would be useful. It may not be
used often but there are definitely uses for testing baluns and other
asymmetrical two-port networks. I think “port renormalization” doesn’t
properly describe this type of measurement as opposed to 75/75 ohm
measurements. A different terminology would be better to describe 75/300
ohm measurements but I’m at a loss to come up with a description that makes
sense. Ideas wanted.

Tony AC9QY

On Sat, Feb 8, 2025 at 7:09?PM John Gord via groups.io <johngord=
[email protected]> wrote:

Roger,
I am happy with the in/out impedances being the same. I just didn't want
the renormalization feature the disappear.
--John

On Sat, Feb 8, 2025 at 03:24 PM, Roger Need wrote:

On Sat, Feb 8, 2025 at 12:35 PM, John Gord wrote:

The renormalization is useful for measuring networks (like crystal or

ceramic

filters) which are designed for other impedance levels.

Do you want different impedances on input and output? I believe that

is what

DiSlord is suggesting...

Roger

Here is renormalization in coppermountaintech
Analysis > Fixture Simulator > Port Z Conversion
(z)-c.html

Microwave circuit theories - need for complex impedance, for not complex Z` calculations more simple