On 20/07/2022 10:19, alex wrote: In my possible dumb imagination I would use a 10 or 20 dB attenuator to avoid mismatch on the NanoVNA side. Then measure the impedance. Then I would make an a-symmetrical attenuator from 50 to that first guess en measure again. This would only require some resistors. Or am I wrong?
73 Alex. PE1EVX I think that would make high/low measurements much less accurate! To the OP: As a suggestion, anything more than, say, 5 times from the nominal 50 ohms will be subject to increasing inaccuracy. Say 10 - 250 ohms you might be OK? Perhaps someone might like to confirm this? Perhaps better if you use a 4:1 transformer - the appropriate way round? 73, David GM8ARV -- SatSignal Software - Quality software for you Web: Email: david-taylor@... Twitter: @gm8arv
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In my possible dumb imagination I would use a 10 or 20 dB attenuator to avoid mismatch on the NanoVNA side. Then measure the impedance. Then I would make an a-symmetrical attenuator from 50 to that first guess en measure again. This would only require some resistors. Or am I wrong?
73 Alex. PE1EVX
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Is there a performance specification for the nanoVNA?
Particularly interested in V4.2 HW version as I have one
Kind regards
Ed G8FAX
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You won't need it. The nano measures it all.
What's your name?
Op 20-7-2022 om 10:34 schreef Observer:
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yep, I am experimenting with hf antennas, with unknown, or predicted high z or very low z
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yep, I am experimenting with hf antennas, with unknown, or predicted high z or very low z
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Are you going to use one?
Op 20-7-2022 om 06:00 schreef Observer:
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Anyone has used the nano with an antenna bridge ( or noise bridge ?) to measure antenna impedances other than 50 ohms, like 300 ohms and up ?
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Anyone has used the nano with an antenna bridge ( or noise bridge ?) to measure antenna impedances other than 50 ohms, like 300 ohms and up ?
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hate Youtube !
Often, they dont get to the point, waste time on bla bla, to incease the time
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Concerning your filter, note that:
nanoVNA makes its measurements with an internal 50 ? impedance generator. When you use this filter behind a PA, fortunately, its internal impedance is not 50 ?; otherwise the yield would be catastrophic. This difference greatly changes the transfer function of the filter.
On the other hand, when you measure the S11 at the input of the filter, the latter being charged at the output by 50 ?, the measurement is correct.
--
F1AMM Fran?ois
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-----Message d'origine----- De la part de Stan Gammons Envoy¨¦ : mercredi 20 juillet 2022 03:28
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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
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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
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On Jul 19, 2022, at 18:19, Jim Lux <jimlux@...> wrote:
?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.
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Hi All,
I have a 6 meter amp project I've been slowly working on. It's modifying
a Larcan lo-lo 1Kw amp used in a VHF channel 4 TV station to 6 meters.?
It's based on the work of K1WHS.
I got a low pass filter/dual directional detector from W6PQL and I have
the low pass filter finished.? I used my NanoVHA H4 to sweep the
filter.? Maybe I did it right.? Here's a screenshot from the sweep. Does
it look about right or in the ballpark?
73
Stan
KM4HQE
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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.
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Re: Correction of error introduce by a transmission line connect to the VNA port 1
On Mon, Jul 18, 2022 at 02:06 AM, Diane BONKOUNGOU wrote:
Hello Roger,
I have two coaxial cables that came with the NanoVNA. I cut one of them to
make the solder. I use the cable I didn't cut to do the calibration and
after connecting the one I cut, I correct the delay. That's why the delay
is so low. When I do the calibration directly at the input of the NanoVNA
and connect my SMA cable, the delay correction is difficult for me, the
phase(pink curve) is triangular like in the attached picture. When I made
the calibration at the cable I didn't cut and I connect the cable I have
cut the phase is just shifted I don't have triangular thing on the curve.
Best regards.
Diane, Unfortunately you are not using the edelay correctly. Once you have done your SOL directly at the NanoVNA connector you connect your test cable and do NOT attach the open end to anything. You then add edelay until the trace on the Smith chart rotates back towards the far right side on the horizontal axis of the Smith Chart ( the spot where you had a dot with no cable connected). Then you connect it to your device-under-test (DUT) and make your measurement. I suggest you first try attaching the end to some SMD resistors (50 ohm, 100 ohm and 25 ohm) to make sure you get are getting reasonable SWR, Return Loss and impedance numbers. The impedance numbers may not be what you expect because at the frequencies you are using even a slight extension to the DUT will result in a reflection coefficient phase shift. BTW - I am not a fan of using edelay to move the reference plane to the end of the cable. It works OK at HF frequencies because the cable attenuation is very low and a few cm of cable is only a tiny fraction of a wavelength. But at the frequencies you are using results may not be great. I suggest you do your calibration at the end of your test cable using SMD parts and get a better reference plane. Little pin jacks work well for me (photo attached). My last point is that the antenna you are using is an unbalanced antenna. One side is connected to the ground plane of the PCB board it will be used on. You have to do the tests just as it will be used in the final product. The PCB ground plane layout will have a big effect on the antenna characteristics because it forms part of the antenna. You also have to concerned that you don't affect the antenna when you attach your measurement cable. You need a way to prevent the outer surface of the test cable shield from becoming part of the antenna system. You will know this is happening if results change when you grab the cable with your hand. Roger
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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
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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
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No Pulse, just analysis of peaks and nulls in the response.
i.e. 1/4 wave response and 1/2 wave response are opposite.
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On Tuesday, July 19, 2022 at 07:54:25 AM CDT, DougVL <k8rftradio@...> 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.) -- Doug, K8RFT
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Re: Using VNA to test NFC tags
You know, I've had AN11276 for years but never looked at it because I don't design inlays. Thanks very much for bringing it into the conversation. Of course that's the right place to look for ideas.
If you are still curious, here is an old Type 2 NDEF spec, downloaded from NFC Forum legitimately in 2013 when the specs were still public.
Thanks for the help.
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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.
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David J Taylor
Arie Kleingeld PA3A
BHA_Darren
Roger Need
