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Jon, please wait for tomorrow as it's supper time here in N. Colorado.
I'll do another procedure using the Smith Chart and the VNA on measuring
the C and L.

Dave - W?LEV

On Wed, May 14, 2025 at 12:26?AM Jon via groups.io <vu2jo0=
[email protected]> wrote:

Dave,

I have been waiting for this post! Shall try out the first method as soon
as possible.

For the second and third methods, I have seen only potentiometers of 10K
and above here. Shall check again.

Can you kindly add a note on how to measure inductance and capacitance with
NanoVNA? Usually I measure that with my LCR meter. Never tried measuring
inductance and capacitance of the CMC which I homebrewed recently on an
FT240-43 toroid using RG316 ().

73
Jon, VU2JO

On Wed, May 14, 2025 at 5:01?AM W0LEV via groups.io <davearea51a=
[email protected]> wrote:

To start off, the common mode choke (CMC) I'm addressing is also referred
to as a transmission line transformer. Physically it consists of a

single

bifilar set of windings on an appropriate ferrite toroid. The windings
form a short (for HF) transmission line on the toroid core with unknown
impedance. Here are methods on measuring that impedance using a vector
Network Analyzer. The NanoVNAs work well for the purpose.

All the following are reflection measurements, so no need to complete the
through and isolation calibration options on the VNA. I'm assuming the

VNA

is properly calibrated over the required frequency range including any
fixtures or adaptors which might be used. It's best to attempt all of

the

following at a relatively low frequency unless you are specifically
interested in the higher frequencies. A wide sweep of frequencies is not
recommended. I usually use something around 2 to 3 MHz. This avoids the
effects of introducing unknown parasitics into the measurement.

All the following is without renormalizing which can introduce unknown
additional errors to the measurements.

From what I've read and utilized, the three methods are:

METHOD 1:

1) Connect one side of the CMC choke to the s11 port or source port.
2) With the "other" side of the CMC open terminated, measure and note

the

capacitance.
3) With the "other" side of the CMC short circuit terminated, measure

and

note the inductance.
4) Calculate the Zo using the following formula:

Zo = SQRT [L / C]

Be sure to use basic units, Farads and Henries.
1 pF = 1E-12 F 1 ?H = 1E-6 H


METHOD 2:

1) Connect one side of the CMC to the s11 port or source port.
2) Terminate the "other" port with a known (measured) potentiometer of
nominally 100 to 150-ohms over the frequency range of interest. Use
minimal leads from the pot. to the CMC.
3) While observing the Smith Chart on the VNA, adjust the potentiometer
such that both the capacitance (-j) and the inductance (+j) are
simultaneously minimized along the real, horizontal, axis on the Smith
Chart. The real axis is the only place on the Smith Chart that is purely
resistive.
4) Now remove the potentiometer and read its DC resistance on a DMM.

That

is Zo.

METHOD 3 (my favorite):

1) Connect one side of the CMC to the s11 port or source port.
2) Terminate the "other" port of the CMC with a known potentiometer
measured to be non-reactive over the frequency range of interest. A

value

of 100 to 150-ohms is useful since most of the CMC chokes have a Zo

between

70 to 125 ohms. Keep leads to an absolute minimum.
3) While observing the Smith Chart on the VNA, adjust the potentiometer
such that both the capacitance (-j) and the inductance (+j) are minimized
simultaneously along the central (real) axis of the Smith Chart.
4) Observe the numerals at the top of the VNA. You can read all the
"interesting" parameters of your CMC from that data, including the Zo of
the choke.

No calculations or renormalizing is required for this third and last
method, minimizing potential sources of error.

Dave - W?LEV


--
Dave - W?LEV

--

*Dave - W?LEV*


--
Dave - W?LEV

Dave,

I have been waiting for this post! Shall try out the first method as soon
as possible.

For the second and third methods, I have seen only potentiometers of 10K
and above here. Shall check again.

Can you kindly add a note on how to measure inductance and capacitance with
NanoVNA? Usually I measure that with my LCR meter. Never tried measuring
inductance and capacitance of the CMC which I homebrewed recently on an
FT240-43 toroid using RG316 ().

73
Jon, VU2JO

On Wed, May 14, 2025 at 5:01?AM W0LEV via groups.io <davearea51a=
[email protected]> wrote:

To start off, the common mode choke (CMC) I'm addressing is also referred
to as a transmission line transformer. Physically it consists of a single
bifilar set of windings on an appropriate ferrite toroid. The windings
form a short (for HF) transmission line on the toroid core with unknown
impedance. Here are methods on measuring that impedance using a vector
Network Analyzer. The NanoVNAs work well for the purpose.

All the following are reflection measurements, so no need to complete the
through and isolation calibration options on the VNA. I'm assuming the VNA
is properly calibrated over the required frequency range including any
fixtures or adaptors which might be used. It's best to attempt all of the
following at a relatively low frequency unless you are specifically
interested in the higher frequencies. A wide sweep of frequencies is not
recommended. I usually use something around 2 to 3 MHz. This avoids the
effects of introducing unknown parasitics into the measurement.

All the following is without renormalizing which can introduce unknown
additional errors to the measurements.

From what I've read and utilized, the three methods are:

METHOD 1:

1) Connect one side of the CMC choke to the s11 port or source port.
2) With the "other" side of the CMC open terminated, measure and note the
capacitance.
3) With the "other" side of the CMC short circuit terminated, measure and
note the inductance.
4) Calculate the Zo using the following formula:

Zo = SQRT [L / C]

Be sure to use basic units, Farads and Henries.
1 pF = 1E-12 F 1 ?H = 1E-6 H


METHOD 2:

1) Connect one side of the CMC to the s11 port or source port.
2) Terminate the "other" port with a known (measured) potentiometer of
nominally 100 to 150-ohms over the frequency range of interest. Use
minimal leads from the pot. to the CMC.
3) While observing the Smith Chart on the VNA, adjust the potentiometer
such that both the capacitance (-j) and the inductance (+j) are
simultaneously minimized along the real, horizontal, axis on the Smith
Chart. The real axis is the only place on the Smith Chart that is purely
resistive.
4) Now remove the potentiometer and read its DC resistance on a DMM. That
is Zo.

METHOD 3 (my favorite):

1) Connect one side of the CMC to the s11 port or source port.
2) Terminate the "other" port of the CMC with a known potentiometer
measured to be non-reactive over the frequency range of interest. A value
of 100 to 150-ohms is useful since most of the CMC chokes have a Zo between
70 to 125 ohms. Keep leads to an absolute minimum.
3) While observing the Smith Chart on the VNA, adjust the potentiometer
such that both the capacitance (-j) and the inductance (+j) are minimized
simultaneously along the central (real) axis of the Smith Chart.
4) Observe the numerals at the top of the VNA. You can read all the
"interesting" parameters of your CMC from that data, including the Zo of
the choke.

No calculations or renormalizing is required for this third and last
method, minimizing potential sources of error.

Dave - W?LEV


--
Dave - W?LEV

To start off, the common mode choke (CMC) I'm addressing is also referred
to as a transmission line transformer. Physically it consists of a single
bifilar set of windings on an appropriate ferrite toroid. The windings
form a short (for HF) transmission line on the toroid core with unknown
impedance. Here are methods on measuring that impedance using a vector
Network Analyzer. The NanoVNAs work well for the purpose.

All the following are reflection measurements, so no need to complete the
through and isolation calibration options on the VNA. I'm assuming the VNA
is properly calibrated over the required frequency range including any
fixtures or adaptors which might be used. It's best to attempt all of the
following at a relatively low frequency unless you are specifically
interested in the higher frequencies. A wide sweep of frequencies is not
recommended. I usually use something around 2 to 3 MHz. This avoids the
effects of introducing unknown parasitics into the measurement.

All the following is without renormalizing which can introduce unknown
additional errors to the measurements.

From what I've read and utilized, the three methods are:

METHOD 1:

1) Connect one side of the CMC choke to the s11 port or source port.
2) With the "other" side of the CMC open terminated, measure and note the
capacitance.
3) With the "other" side of the CMC short circuit terminated, measure and
note the inductance.
4) Calculate the Zo using the following formula:

Zo = SQRT [L / C]

Be sure to use basic units, Farads and Henries.
1 pF = 1E-12 F 1 ?H = 1E-6 H


METHOD 2:

1) Connect one side of the CMC to the s11 port or source port.
2) Terminate the "other" port with a known (measured) potentiometer of
nominally 100 to 150-ohms over the frequency range of interest. Use
minimal leads from the pot. to the CMC.
3) While observing the Smith Chart on the VNA, adjust the potentiometer
such that both the capacitance (-j) and the inductance (+j) are
simultaneously minimized along the real, horizontal, axis on the Smith
Chart. The real axis is the only place on the Smith Chart that is purely
resistive.
4) Now remove the potentiometer and read its DC resistance on a DMM. That
is Zo.

METHOD 3 (my favorite):

1) Connect one side of the CMC to the s11 port or source port.
2) Terminate the "other" port of the CMC with a known potentiometer
measured to be non-reactive over the frequency range of interest. A value
of 100 to 150-ohms is useful since most of the CMC chokes have a Zo between
70 to 125 ohms. Keep leads to an absolute minimum.
3) While observing the Smith Chart on the VNA, adjust the potentiometer
such that both the capacitance (-j) and the inductance (+j) are minimized
simultaneously along the central (real) axis of the Smith Chart.
4) Observe the numerals at the top of the VNA. You can read all the
"interesting" parameters of your CMC from that data, including the Zo of
the choke.

No calculations or renormalizing is required for this third and last
method, minimizing potential sources of error.

Dave - W?LEV


--
Dave - W?LEV

Please include Q=1 contour as it is ROYAL! That will allow resonator Q to be determined. As well, some other Q definitions.

How about a pipe? The sender doesn't even have to be aware of the pipe's
existence.

WIKIPEDIA - Named Pipe (Software)


73 de Andrew/N5ASE

On Tue, May 13, 2025 at 4:37?PM Team-SIM SIM-Mode via groups.io <sim31_team=
[email protected]> wrote:

Thanks Brian

Hope it will be a real time plotter one day soon , it's a dream.

73's Nizar

On Tue, May 13, 2025 at 12:24 PM, alan victor wrote:

Q of 1, 2, 3... These Q contours roughly align with SWR circles of 2.5:1, 4:1,
6:1

I plot SWR circles of 1.5, 2, and 3. Maybe I'll just plot Q contours aligned with those.

Thanks for the help, Alan.

Brian

On Tue, May 13, 2025 at 12:37 PM, Team-SIM SIM-Mode wrote:

Hope it will be a real time plotter one day soon

I'm not going to write another NanoVNA-Saver or NanoVNA-App. Someone can incorporate the features they like into those programs if they wish.

Brian

Thanks Brian

Hope it will be a real time plotter one day soon , it's a dream.

73's Nizar

Alan, if I were to display several Q contours simultaneously, what values would be most useful? This would require no user input.


Q of 1, 2, 3... These Q contours roughly align with SWR circles of 2.5:1, 4:1, 6:1

Larger values tend to be academic as they would most likely be classified as narrow band. Although that opinion is subjective. <:)

Thanks,

On Tue, May 13, 2025 at 11:25 AM, Team-SIM SIM-Mode wrote:

wondering if your software can download S11 and S12 data's on real time from
nanoVNA as Nano-App does ?

No. It runs from .s1p or .s2p files only. See splot.txt for details.

Brian

Hi Brian

Thank you , and great work , i am still not familiar to , it seems great and can be developped more , if any youtube video can help us step by step how to use it , it will be very helpfull . I need a real time plotting to adjust in real time the reisistor trimmer terminaison to focus the impedances on one graphical dot as small as possible on smith shart to measure characteristic impedances of coax's or baluns , wondering if your software can download S11 and S12 data's on real time from nanoVNA as Nano-App does ?

Congratulation for your good Work.
73's Nizar .

Alan, if I were to display several Q contours simultaneously, what values would be most useful? This would require no user input.

Brian

On Mon, May 12, 2025 at 12:38 PM, Brian Beezley wrote:

I'm trying to avoid keyboard input, such as specifying Q for one of these
curves

Routine I did inputs a single Q contour value. The Q=1 is a default value. No input required.
This value of unity at one time was used and provided with vna instruments as an overlay or etched into the screen.

On Tue, May 13, 2025 at 06:42 AM, Team-SIM SIM-Mode wrote:

it will be appreciated if we can renormalise also the port2 impedance independly of port1

Nizar, this program will do that:



Brian

Hi Jhon

A graphical X4 zoom option on the future firmware around the center of the Smith shart can help to show more easily the impedance focusing on the center plot of Smith diagram .

73's Nizar

Hi Jhon

In fact I redo the measurement of the characteristic impedance of the first balun with more care of bad contactes, i measure Zc=60 Ohm see screenshoot below , wich gives SWR = 1.2 with 50 Ohm coax and 1.3 with 78.5 Ohm Coax wich explaine the more losses with 78.5 Ohm renormalized coax , I think the renormalized impedance function on Dislord firmware + H4 is accuracy enought here to give a correct results , we assume here that coax has 78.5 Ohm and antenna has also 78.5 Ohm S11 = S21 , No problem right now about firmware modeling , butit will be appreciated if we can renormalise also the port2 impedance independly of port1 one on the future firmwares: it will be really wonderfull .

One important conclusion : if we want to fully optimize out ferrit balun we should measure it's characteristic impedance with a resistor trimmer terminaison and adjust it to much as near as possible the coax characteristic impedance to have less losses , NanoVNA H4 + DiSlord firmware should help a lot .

73's Nizar

Jim, I had the same thoughts myself, and earlier today I decided not to pursue graphical matching any further. My first impulse for a design problem of any complexity is to implement an optimizer. I do this all the time, even for rather straightforward problems. I have a standard local optimizer (Nelder-Mead) and a standard global optimizer (differential evolution). I've cycled through many possibilities for both over the years, mostly for antenna optimization, and I have settled on these two. They are fast, effective, and sure-footed. They are also blind. They find the best performance, according to your criteria of what's good, but they offer no insight on how they did it. The global optimizer can find a design in left field that you would never have thought to check. This is a virtue, but it can leave you wondering: how did it do that? I can now appreciate the attraction of graphical matching network design with a Smith chart since the process is so intuitive and suggestive. But I was reading a technical paper earlier today about constant-Q Smith matching where more sections bought you wider bandwidth and my first thought was: the choice of number of sections could be automatically optimized!

It has been a lot of fun learning about the Smith chart. All I ever really wanted to do was implement impedance renormalization, which just seems magical to me (intentionally misloading a circuit to allow measuring it without a matching network, but then unraveling the misloading later in analysis). The other thing I wanted to implement was the Y21 method, which magically suppresses stray shunt reactance when doing a series-through measurement. It's my idea of something for free. I've looked at a lot of commercial L and C .s2p files. The Y21 method exposes the labs with sloppy fixtures.

Now I've got to get back to coding. I've implemented circles with a precise pixel-by-pixel method instead of using the compiler circle function, which didn't produce high-quality output. Neither did my usual method of drawing line segments between points. How short a line segment is adequate? My homebrew circle generator produces noticeably cleaner constant-R Smith circles. Now I'm about to do it for the constant-X curves, which currently use line segments. I belatedly discovered today that those curves are really arcs of circles.

Brian

At some point, too, it's addressing a pretty niche need (essentially lumped component multisection filters). I would think that most people today designing a multi section filter use some sort of tool like ELSIE (for LCR, which is free) or one of the multitude of design tools like HFSS, ADS, QUCS, etc.. because they'll take into account things like component tolerances, standard values, loss in L and C, transformers. Not to mention things like coupled microstripline filters or cavities. Or, perhaps Scikit-RF - which doesn't do filter design, but sure is able to model quite complex circuits, and you could lash up an optimizer in Python around it.

Once you get beyond a certain complexity, using the computer design tools is probably a better way to go.

Perhaps as a way to gain insight, a Smith Chart design might be useful. But I think you're going to have a tough time doing something like trading off Butterworth vs Chebyshev vs Elliptical/Cauer on a Smith Chart (I think - never tried it - Done it on a pole zero, and on a Bode plot). Isn't the "have all the sections have similar Q" is really about getting passband ripple low and/or not having a really tight tolerance on some, and less on the others.

On Mon, May 12, 2025 at 11:31 AM, Donald S Brant Jr wrote:

The idea is to have each intermediate matching step wind up on/near the same Q
circle.

Don, this sound like high values for the constant-Q curves would be necessary. Is that right?

I'm trying to avoid keyboard input, such as specifying Q for one of these curves. So far the only keyboard entry needed is when renormalizing the reference impedance.

Brian

On Mon, May 12, 2025 at 01:47 PM, alan victor wrote:

The Q=2, 3, etc.... where the R,X ratio is 2,3, etc... and this facilitates
the constructs for matching over a desired band when a load model is imported
to the chart.

When making a graphical multi-section matching network solution, the constant-Q curves guide your component choices, to avoid unnecessarily constraining the bandwidth.
The idea is to have each intermediate matching step wind up on/near the same Q circle. Having any steps with higher Q than necessarily will constrict the bandwidth. Having steps of lower Q will necessitate more sections which will increase the loss. Or, if the bandwidth need is narrow you can use high-Q sections for some "free" bandpass filtering.
73, Don N2VGU