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Its a fact, that inductance value, vary according to frequency.
How does the nanovna measure ?
Does it use the saved selected frequency range inside the nano ?

The value of an inductor is a given and depends on several factors, but CERTAINLY NOT on the frequency

F8VOA , Marco

Op 18/07/2022 om 09:27 schreef Observer:

Its a fact, that inductance value, vary according to frequency.
How does the nanovna measure ?
Does it use the saved selected frequency range inside the nano ?

--

If You are not part of the solution , then You are the problem <<<

The NanoVNA will measure inductance over a frequency range, which you
configure in the sweep settings, just like with other measurements.

In theory, the inductance does not depend on the frequency, but the
inductive reactance does.
I'd like someone to correct me if I'm wrong, but from what I can see, VNAs
can't actually directly measure inductance (is there anything that can?),
and instead measures impedance, and then estimates inductance from
impedance. Since everything is an RLC circuit (in coils, don't forget the
resistance of the conductor, and the capacitance between the turns, which
affects the coil's self-resonant frequency), the estimate of the inductance
will change with frequency, sometimes drastically (again, keep the
self-resonant frequency in mind).

пон, 18. ?ул 2022. у 09:27 Observer <tvstreamdevice@...> ?е
написао/ла:

The term "inductance" has two meanings. It may mean the inductance exhibited by a coil or circuit at a frequency of interest. It also may mean the inductance at a low frequency where variation with frequency is negligible. The two values can differ due to coil self-resonance, change in effective coil diameter with frequency, change in dielectric permittivity or core permeability with frequency, or other factors. The first value usually is just called inductance. The second may be called true inductance, ideal inductance, or low-frequency inductance. The confusion comes when it too is called inductance.

When referring to inductance in public, you can avoid confusion by stating which meaning you're using.

Brian

Inductance may vary with frequency, e.g. when there is a ferrite core. The core material's properties are frequency dependent. Also, the effect of the interwinding capacitance increases with frequency and that will change the observed inductance.
Reinier

Inductance is independent of frequency. Inductance only depends on the materials used (this also means that the environment of the element is important). If you vary the frequency, the inductance NEVER changes.

Marco , F8VOA

Op 18/07/2022 om 14:18 schreef Reinier Gerritsen:

Inductance may vary with frequency, e.g. when there is a ferrite core. The core material's properties are frequency dependent. Also, the effect of the interwinding capacitance increases with frequency and that will change the observed inductance.
Reinier

On July 18, 2022 11:20 AM Marc et Nicole Feuggelen-Verbeck <f8voa54@...> wrote:

The value of an inductor is a given and depends on several factors, but
CERTAINLY NOT on the frequency

F8VOA , Marco

Op 18/07/2022 om 09:27 schreef Observer:

Its a fact, that inductance value, vary according to frequency.
How does the nanovna measure ?
Does it use the saved selected frequency range inside the nano ?

--

If You are not part of the solution , then You are the problem <<<

On 7/18/22 2:20 AM, Marc et Nicole Feuggelen-Verbeck wrote:

The value of an inductor is a given and depends on several factors, but CERTAINLY NOT on the frequency

An ideal inductor, perhaps, but any sort of practical real inductor with parasitic C between turns and the surroundings varies with frequency. The loss also changes with frequency due to skin depth changes (although that's a small effect).
There's also a small inductance change effect due to different distribution of current in windings due to skin effect.

Finally, if the inductor is on a core, pretty much every core material has frequency dependent properties.

What you say is correct but that is nitpicking : The value of an inductor does not change with increasing or decreasing frequency . 100?H now equals 100?H just as 100KOhm is equal to 100KOhm .

If not , the laws of physics must be rewritten . F=1/2(pi)(sqrt(LC))

An inductor is *a passive electronic component that stores energy in the form of a magnetic field*. In its simplest form, an inductor consists? of a wire loop or coil. The inductance is directly proportional to the number of turns in the coil , the used materials and the envirement but not the frequency.

End of story

Marco


Op 18/07/2022 om 15:42 schreef Jim Lux:

On 7/18/22 2:20 AM, Marc et Nicole Feuggelen-Verbeck wrote:

The value of an inductor is a given and depends on several factors, but CERTAINLY NOT on the frequency

An ideal inductor, perhaps, but any sort of practical real inductor with parasitic C between turns and the surroundings varies with frequency. The loss also changes with frequency due to skin depth changes (although that's a small effect).
There's also a small inductance change effect due to different distribution of current in windings due to skin effect.

Finally, if the inductor is on a core, pretty much every core material has frequency dependent properties.

--

If You are not part of the solution , then You are the problem <<<

Marco is correct. The inductance L does not change with frequency (except
for the small non-linear effects of the core materials).

HOWEVER, all real inductors also have parasitic capacitance and resistance,
which causes the Z (impedance, not inductance) to change with frequency.
And these effects are real, and can be quite large. So when the VNA
measures an inductor across a frequency range, you will see the impedance
(not inductance) change from something close to the pure 'L' inductance at
very low frequencies, to where the parasitic capacitance completely cancels
out that inductance at higher frequencies (at the LC resonant frequency)
and then the C becomes dominant at even higher frequencies. So it is often
useful to measure this impedance (or apparent inductance) at the frequency
the inductor will be used - where the modeling of its required valued was
done.

At DC and low frequencies, the Z of an inductor is dominated by its
inductance, and the Z and L are essentially the same. But at higher
frequencies the Z will be dramatically different, and depends highly on the
materials and construction techniques used in the inductor.

The nanovna and other vna's (and/or the software used to control them)
calculate the Z from the measured S11 or S21 parameters, often with a good
degree of accuracy. Then they calculate the L from the Z. There are more
limitations to the accuracy of this calculation.

A good LCR meter is likely a better tool to measure the 'L' of an inductor.

Stan

On Mon, Jul 18, 2022 at 10:11 AM Marc et Nicole Feuggelen-Verbeck <
f8voa54@...> wrote:

What you say is correct but that is nitpicking : The value of an
inductor does not change with increasing or decreasing frequency . 100?H
now equals 100?H just as 100KOhm is equal to 100KOhm .

If not , the laws of physics must be rewritten . F=1/2(pi)(sqrt(LC))

An inductor is *a passive electronic component that stores energy in the
form of a magnetic field*. In its simplest form, an inductor consists
of a wire loop or coil. The inductance is directly proportional to the
number of turns in the coil , the used materials and the envirement but
not the frequency.

End of story

Marco


Op 18/07/2022 om 15:42 schreef Jim Lux:

On 7/18/22 2:20 AM, Marc et Nicole Feuggelen-Verbeck wrote:

The value of an inductor is a given and depends on several factors,
but CERTAINLY NOT on the frequency

An ideal inductor, perhaps, but any sort of practical real inductor
with parasitic C between turns and the surroundings varies with
frequency. The loss also changes with frequency due to skin depth
changes (although that's a small effect).
There's also a small inductance change effect due to different
distribution of current in windings due to skin effect.

Finally, if the inductor is on a core, pretty much every core material
has frequency dependent properties.

--

If You are not part of the solution , then You are the problem <<<

On 7/18/22 10:10 AM, Marc et Nicole Feuggelen-Verbeck wrote:

What you say is correct but that is nitpicking : The value of an inductor does not change with increasing or decreasing frequency . 100?H now equals 100?H just as 100KOhm is equal to 100KOhm .
If not , the laws of physics must be rewritten . F=1/2(pi)(sqrt(LC))
An inductor is *a passive electronic component that stores energy in the form of a magnetic field*. In its simplest form, an inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns in the coil , the used materials and the envirement but not the frequency.

ideal inductors have zero diameter conductors with zero resistance, and the inductance is
proportional (approximately) to *square* of turns, (if all the turns are equally well magnetically coupled)


The *inductance* of a real inductor most certainly changes with frequency (as captured in standard works like those of Rosa and Grover)


for a variety of reasons - mostly that with finite sized conductors, the current is not distributed evenly, and that distribution depends on the frequency.

There is also an issue of "effective impedance" in that inductance can be partly cancelled by capacitance (in the worst case it completely cancels at self resonance).

End of story
Marco
Op 18/07/2022 om 15:42 schreef Jim Lux:

On 7/18/22 2:20 AM, Marc et Nicole Feuggelen-Verbeck wrote:

The value of an inductor is a given and depends on several factors, but CERTAINLY NOT on the frequency

An ideal inductor, perhaps, but any sort of practical real inductor with parasitic C between turns and the surroundings varies with frequency. The loss also changes with frequency due to skin depth changes (although that's a small effect).
There's also a small inductance change effect due to different distribution of current in windings due to skin effect.

Finally, if the inductor is on a core, pretty much every core material has frequency dependent properties.

I agree with Jim Lux. The inductance of an "ideal" inductor does not vary with frequency but any physical ("real world") inductor will have its inductance vary with frequency. In the case of an air coil the change will be small due to the skin effect and current distribution resulting from it but can still be measured as Jim pointed out in his reference.

In the case of an inductor made with some type of core material the change in inductance with frequency is much more noticeable especially with high permeability ferrite cores. With powdered iron or brass it will be much less than it is with a ferrite material. Attached are plots of 5 turns on a powdered iron toroid and 5 turns on a ferrite mix 43 toroid.

Roger

On Mon, Jul 18, 2022 at 03:27 AM, Observer wrote:

How does the nanovna measure ?

I believe it works like this:
It sends a pulse of RF at the Nano's 'start frequency' and analyzes the phase and amplitude of the return signal (like an echo?). Then it sends a pulse at the next frequency step, and so on for the number of steps programmed (usually 99, I think).
For each echo pulse, it calculates the L, C, etc. values from the phase difference between the transmitted pulse and the received pulse.
To see the data that actually results, look at the contents of an s1p or s2p file that the Nano can save (maybe only using the 'NanoVNA-Saver' program). (The -F nano can save s1p/s2p files to its own internal storage.)
--
Doug, K8RFT

On 7/19/22 5:54 AM, DougVL wrote:

On Mon, Jul 18, 2022 at 03:27 AM, Observer wrote:

How does the nanovna measure ?

I believe it works like this:
It sends a pulse of RF at the Nano's 'start frequency' and analyzes the phase and amplitude of the return signal (like an echo?). Then it sends a pulse at the next frequency step, and so on for the number of steps programmed (usually 99, I think).
For each echo pulse, it calculates the L, C, etc. values from the phase difference between the transmitted pulse and the received pulse.
To see the data that actually results, look at the contents of an s1p or s2p file that the Nano can save (maybe only using the 'NanoVNA-Saver' program). (The -F nano can save s1p/s2p files to its own internal storage.)

Not actually pulses, it's a CW measurement. It puts a CW signal out at a frequency, and uses a bridge to measure the impedance (or reflection coefficient) at that frequency by comparing the amplitude and phase of the signal from the oscillator vs whats at the device. Or, for a Through measurement comparing the signal going in the input and the signal coming out of the output.

The clever part is that one can measure some calibration standards (short, 50 ohm, open), and then the VNA can relate the measurements it makes to those you'd get with an ideal 50 ohm system, which is what it displays.

It takes a few milliseconds to do this, so it just steps through all 101 (or 201 or 401) frequencies in a couple seconds, and there's your data.

No Pulse, just analysis of peaks and nulls in the response.
i.e. 1/4 wave response and 1/2 wave response are opposite.

It puts a CW signal out at a frequency, and uses a bridge to measure the impedance (or reflection
coefficient) at that frequency by comparing the amplitude and phase of the signal from the oscillator vs whats at the device.

This part of the text (once translated into French) is not clear (understandable). Can you be more descriptive please.

I use the .Sp1 files to recalculate everything, which makes it possible to simulate from the frequency response of a real object (an antenna for example); for example to test an adapter, on paper (actually in Excel)

--
F1AMM Fran?ois

-----Message d'origine-----

De la part de Jim Lux
mardi 19 juillet 2022 15:00

On Mon, Jul 18, 2022 at 12:27 AM, Observer wrote:

Its a fact, that inductance value, vary according to frequency.

Yes that is true for real-world inductors that you test. Air coils have minimal variation but those with a core of powdered iron or ferrite material have more change with ferrite having the most. (see my posted graphs in another message.)

How does the nanovna measure ?

The NanoVNA has an internal bridge and the analog signals from the bridge are digitized by an A/D and then processed by the firmware. The first thing the firmware does is calculate what is known as the S11 parameter which is a complex (real and imaginary) number that is known as the "reflection coefficient". There are mathematical formulas that take the complex reflection coefficient and convert that to other useful parameters like VSWR, Return Loss and complex impedance (R+/-jX). Using the menu you can select which parameters you want the on-screen trace to display vs frequency.

The NanoVNA can display the reactance X vs frequency as a trace and can also output impedance (R+/- jX) as a marker on the Smith chart trace. The Smith chart trace chart is very useful and as you move the marker along with the rocker switch it can display various parameters for that frequency. You select which ones in the marker menu. It does have an option to automatically display inductance for +X measurements and capacitance for -X measurements. BUT users need to be aware that these calculations make a big assumption! The calculation from reactance to inductance/capacitance uses a simple formula that assumes the reactance measured is the result of only inductance OR capacitance and not a combination of the two. This means that for an inductor that you are testing the display inductance does not take into account any parasitic capacitance in the component.

If you use an external PC program like NanoVNA Saver or NanoVNA app you can plot inductance vs frequency for a component under test. But the calculation is still done using a basic conversion from reactance to inductance. A real world inductor is actually composed of resistance, inductance and capacitance. A simplified model of a typical inductor is attached. So the measurement made is not of the "actual inductance" L of the component but the "apparent inductance" that is calculated assuming all of the reactance X is due to inductance alone. Actual inductance and apparent inductance are very close for an inductor at low frequencies but as the frequency goes up the parasitic capacitance will have considerably more effect on the reactance X and the apparent inductance will increase rapidly until the self resonant frequency (SRF) of the component is reached. After this point the component will look like a capacitor.

Attached are some plots of a mult-ilayer inductor that has considerable self capacitance. The "apparent inductance" calculated by the program is not the actual L of the component. It is possible to calculate the actual L and inter-winding capacitance C using regression analysis or by attaching another small known capacitor across the inductor, calculating the new SRF and then doing some algebra on two equations with one unknown.

Does it use the saved selected frequency range inside the nano ?

It uses whatever ever stimulus frequency range you have selected.

Roger

On 7/19/22 11:44 AM, F1AMM wrote:

It puts a CW signal out at a frequency, and uses a bridge to measure the impedance (or reflection
coefficient) at that frequency by comparing the amplitude and phase of the signal from the oscillator vs whats at the device.

This part of the text (once translated into French) is not clear (understandable). Can you be more descriptive please.

There's no pulses - each measurement is made with a steady state signal.

For S11 measurements, it's like feeding a zero ohm output impedance signal generator through a 50 ohm resistor to the input of the unit under test. That forms a voltage divider.

You measure the signal generator output and the voltage (including phase) at the junction.

If the UUT is 50 ohms, then the voltage at the junction is exactly 1/2 and the phase is the same.


If the voltage isn't 1/2 or the phase difference isn't zero, then the UUT isn't 50 ohms, and you can calculate what it actually is.

That's sort of over simplified - there isn't such a thing as a perfect generator or a perfect 50 ohm resistor, and there's physical sizes involved, etc.

So what you do is measure 3 known impedances: 0, 50, and infinite.
From that you can calculate correction factors to turn raw measurements into calibrated numbers.

Furthermore, because the VNA comes from a world of microwaves, using directional couplers, the whole system is designed and the calibration algorithms are developed in terms of S parameters, which work better for those kinds of things. S parameters are defined in terms of incident and reflected waves, but that's just an alternate representation of the current and voltage at the various points.

If you were doing power engineering, you'd be working in Watts and Vars.
If you're doing low frequency systems people often work in Admittance and Impedance (e.g. Smith charts).

The S parameter heritage means that most of the papers and analytical tools is in terms of incident and reflected (a and b) waves, reflection coefficients, transmission coefficients, etc. So the calibration process tends to focus on developing ways to take your measurements of the standards and apply that mathematically to measurements of an unknown and produce calibrated S parameters, which is the de facto standard.


For instance, you'll see T parameters or ABCD chain matrices as alternate forms. I'm sure someone, somewhere, has developed calibration equations for those representations.

And there are other ways to do the measurement - A so-called 6 port analyzer requires only precise power measurements, with no phase measurement. That's handy when you need measurements for which mixers or phase detectors and such aren't available. (mm wave and terahertz, for instance)

I use the .Sp1 files to recalculate everything, which makes it possible to simulate from the frequency response of a real object (an antenna for example); for example to test an adapter, on paper (actually in Excel)

Yes, and if you want to fool with Python, scikit-rf has a whole set of tools to work with all the different representations, plot them, convert back and forth, and even do a variety of VNA calibrations.

Jim,

I am no RF expert but you really did a great job in your response. I seriously appreciated your thoughtful and informative response. I just joined this group and must admit I am very impressed with the shared and learned knowledge available. Having worked in electronics and design most of my life I learned many people guard knowledge like gold and share it even less. I just wanted to say thank you and thank those who freely and patiently share your experience and knowledge with others.

Darren

Yes, and if you want to fool with Python, scikit-rf has a whole set of tools to work with all
the different representations, plot them, convert back and forth, and even do a variety of
VNA calibrations.

Thanks for the explanation on the basic operation of the nanaoVNA bridge. It must not be easy to measure the phase!

Unfortunately, I don't know Python. I'm just getting by in C and C#.

For the conversion formulas, I struggled a bit but I restored them as well as the reciprocal formulas. This is how I realized that, concerning the Smith diagram, in fact, if an orthonormal reference mark is passed through the center of the abacus, it is in fact graduated in parameter S11. The real part is on the horizontal axis the imaginary part is on the vertical axis. I have never read that in the literature.

For amateurs put off, a priori, by the Smithn abacus, I would repeat to them that we no longer use this abacus to make graphic calculations. Moreover, these calculations were only made at a fixed frequency (a single frequency). Currently, as for the nanaoVNA and nanovna-saver, it is a means of presenting the parameters according to the frequency. The curve that we see on the Smith only exists because the frequency varies. Fortunately, there are markers to know to what frequency a point on the curve corresponds.

The .S1p files are ASCII files where each S11 parameter is saved, corresponding to each measurement, at a different frequency. Change the .S1p extension to .txt and notepad will easily open the file for you.
-----
# HZ S RI R 50
100000 -0.9837865399025408 0.1942964059291501
109812 -0.9820312153958951 0.21310478092053914
[...]
-----
If you display (chart) in Excel, you will find the curve that appears on the Smith diagram. It's actually very educational to understand the interest of the "Smith" representation.
--
F1AMM Fran?ois

On Tue, Jul 19, 2022 at 09:00 AM, Jim Lux wrote:

Not actually pulses, it's a CW measurement

Sorry, my mistake.
How long does the CW signal last, at 101 measurement points?
I thought that length would be called a pulse.
(In my Air Force AC&W radar technician days, a 6 millisecond transmission was called a pulse.)
--
Doug, K8RFT