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@DiSlord
Is it possible to add a function for constant SWR-circles on the Smith-chart of NanoVNA, for example SWR 2 and SWR 3, perhaps in red color? Maybe also in the NanoVNA-App-D as I think it was possible in NanoVNA-Saver.
73/Torbj?rn/SM6AYM

Alan, currently I do not provide a way to display SWR circles and Q contours at the same time. Should I?

Brian

Hi Dave

This method of direct experimental measurement, without any computational artifice and without the risk of modeling errors or theoretical estimations, is simply my own used method, which I have already presented multiple times and illustrated in several recent topics in this IO group. Indeed, this experimental method is very elegant, accurate, and reliable, and involves no computational tricks.

I have specifically presented it as the method for measuring the characteristic impedance of coaxial or twin-lead lines, offering greater precision than other methods already shown in YouTube videos or even the classical recommended techniques that I have come across in this highly respectable IO group.

It has been suggested to me to use the recently introduced macro function by DiSlord called "Measure" + "Cable" in his latest firmware version 1.2.40. This function directly displays the cable’s characteristic impedance, its length, its attenuation in dB, and its specific attenuation in dB/100m. It's already a very good and reliable function, and above all, it's easy to use—there’s virtually nothing to do except connect the open-ended coax to port 1 for S11 measurements.

This function is indeed useful, but it provides a single Zc value valid across the entire frequency range. It is based on quasi-static C0 measurements, which are more relevant at relatively low frequencies, and it does not fully account for skin effect and other second-order behaviors that are difficult for a typical user—such as a radio amateur seeking ohm-level accuracy—to model precisely.

For example, I have already published the different characteristic impedance values of my RG213 cable depending on the frequency band, using the experimental method that involves centering the impedance circle at the center of the Smith chart with a fixed resistive load close to the nominal characteristic impedance of the coax, or by referring to the first-order value displayed by DiSlord’s macro function.

The method is simple, robust, and original because it is based on the very solid foundational concept of the characteristic impedance of an RF transmission line. This is, by definition, the impedance that produces a purely traveling wave and absorbs all the energy without any reflection—as if the line were infinitely long.

Therefore, in practice, we should observe a constant, purely real impedance across the entire measurement band as a first approximation (theoretically, a line’s characteristic impedance may not be purely real, but for low-loss lines it is often very close to real and commonly approximated by the well-known square root of L/C—this remains a very good first-order approximation).

Thus, for a ferrite balun, it is experimentally straightforward to connect an adjustable resistor in place of the antenna and connect the other side to port 1 for S11 measurements, in order to center the impedance plot across an entire frequency band on real axe dot.


This is entirely feasible for a small balun or a coiled coaxial cable whose second end is accessible in the shack, allowing the connection of an adjustable resistor (non-inductive, of course) in order to find the value that yields the smallest possible Smith chart impedance plot — ideally, a single point located on the real axis over the entire desired frequency band. This value can then be directly read using the NanoVNA cursor. It's one of the best methods to measure the characteristic impedance (Zc), while also enjoying the clear and safe visual illustration of its fundamental definition on a simple and tangible Smith chart using a compact NanoVNA.

So far, so good — but unfortunately, this method cannot always be applied so easily, especially when the cable is already deployed in space, fixed in place, and its far end is no longer accessible from the shack near the NanoVNA.

Fortunately, the new firmware by DiSlord (version 1.2.40) offers a solution by allowing the renormalization of the equivalent impedance for Smith chart display purposes. It’s important to understand that the actual impedances values remain exactly the same — only the graphical representation changes. So, there’s no risk of error introduced by the renormalization of Zc in S11 measurement mode.

The goal is no longer to focus the impedances on a single real point (since we can’t adjust accurately the resistor remotely — unless two people coordinate via phone), but rather to connect a fixed resistive load that is approximately correct, and then use the Zc renormalization feature of DiSlord to center the impedance circle on the middle of the Smith chart, indeed the impedances are no longer all reals but remain on a small cicle around the renormalized Zc end value.

The value of Zc that centers the impedance circle is the one to retain in the end. that why i appreciate a lot this renormalize graphical option offered By DiSlord firmware 1.2.40 and ask him many times if it"s possible to add a graphical X4 or X6 zoom option around Smith shart center , it will be very usefull , indeed here all is graphical with Smith Shart , zero external computing .

73's Nizar .

Excellent, Very nicely done.

By Royal command . . .

After much experimentation, I reverted to the standard grid with optional fill-in. I used the homebrew precision circle maker for the grids and SWR/Q curves.

Brian

Thanks a lot Dave, for the quick response. Here the sun is just rising up!
Shall look out for your post by evening (that will be 'tomorrow' for you!).

73
Jon, VU2JO

On Wed, May 14, 2025 at 6:04?AM W0LEV via groups.io <davearea51a=
[email protected]> wrote:

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

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