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The complex impedance Z is given by Zo * (1+gamma) / (1-gamma)

Please can you explain me where is my mistake; I am like Saint Thomas.

Here is the digital test data (my antenna)
S11 = -0,310484238 +j 0,011489099
Zo = 50

With the formula
Z = Zo * (1+gamma) / (1-gamma)
it gives
Z = 95,02931686 + j 48,86414014

With my formula, it gives
Z = 26,3018063 +j 0,66894279
and this is what nanovna-saver displays

I must still have missed something :(

73
--
F1AMM Fran?ois

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

De la part de Jim Lux
dimanche 24 juillet 2022 00:58

On 7/23/22 8:41 AM, Ed G8FAX wrote:

The S1P files contains the real and imaginary parts of the reflection coefficient, Greek letter ‘gamma’.
The complex impedance Z is given by Zo * (1+gamma) / (1-gamma)

Excel has the capability of working and manipulating complex numbers, so the spreadsheet formulae can be simplified and use directly the values from the S1P file.

I believe complex number feature also exists in LibreOffice.
To obtain the impedance magnitude after this requires conversion to polar form.

ATAN2 is a useful function to use.

in Excel, IMARGUMENT returns the angle (in radians), IMABS is the magnitude

I can do the math.... I taught electronics including L - R- C circuits and conversions for 17 years. I was just looking for a quick way to find them on the Nano. And |Z| was my main interest.

Although I must say, the equations shown in the pdf look nothing like what I taught.... Mine was simply going back and forth between R +jX and Z Θ, normally using Pythagoras and trig functions.

I fired up a laptop with NanoVNA Saver and was able to get what I needed.

Thanks to all.

The S1P files contains the real and imaginary parts of the reflection coefficient, Greek letter ‘gamma’.

The complex impedance Z is given by Zo * (1+gamma) / (1-gamma)



Excel has the capability of working and manipulating complex numbers, so the spreadsheet formulae can be simplified and use directly the values from the S1P file.



I believe complex number feature also exists in LibreOffice.

To obtain the impedance magnitude after this requires conversion to polar form.



ATAN2 is a useful function to use.




Kind regards

Ed, G8FAX

On 7/22/22 10:50 PM, F1AMM wrote:

Admitting that it is of interest to examine the phase of the impedance, it is indeed necessary to start from the Touchstone S11 file (.s1p). It is an ASCII file where you find, on each line: the frequency, the real of the S11 then the imaginary of the S11. in the first line there is the standardization impedance (50 Ohms in general)
If you are interested, I have restored the "formulas" allowing you to recalculate the A+jB of the load from S11. It's not trivial even if it's quite simple if we start from the right bases. I do this in Excel.
I don't know how to pass this type of information on the forum.

You could just post a sample excel file.. (of maybe the first 10 lines of a S1P). That's what I've done.

Interesting discussion. I used to work for HP. Later sold Cascade probe stations. Calibration was always "difficult". Especially on wafer: how far do you overdrive (i.e. press the probe down), how many times has that standard been used, etc etc.

Seems to me we're expecting a bit too much from the nanovna. As someone already posted, its not a lab grade instrument. To me its a "how close am I" kind of tool. If I REALLY care I will use a better tool (I am fortunate enough to have an 8753).

Ron
N4XD

Hi Wayne,

Mark at QSL Communications sells several VNAs including the Hugen NanoVNA-H and the Deepelec NanoVNA-F (now DeepVNA-101).

This is the VNA page
Do your homework on overseas vendors.

Cheers...Bob VK2ZRE

I don't know how to pass this type of information on the forum.

Maybe it works with just the attached document.

The original document, more readable, is a .docx in French
--
Fran?ois

I've written a Windows utility that checks Touchstone files for |S11| > 1. It handles version
1.1 files, the kind NanoVNAs generate, as well as version 2.0. It lists maximum |S11| and the
number of frequencies where |S11| > 1. This utility may come in handy if you experience odd
problems processing NanoVNA data as I did.

Thanks a lot.

README.TXT is only for GND.EXE

Do you have help files for AVG.EXE and S11.EXE?
--
F1AMM Fran?ois

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

De la part de Brian Beezley
Envoyé : samedi 23 juillet 2022 02:12

Admitting that it is of interest to examine the phase of the impedance, it is indeed necessary to start from the Touchstone S11 file (.s1p). It is an ASCII file where you find, on each line: the frequency, the real of the S11 then the imaginary of the S11. in the first line there is the standardization impedance (50 Ohms in general)

If you are interested, I have restored the "formulas" allowing you to recalculate the A+jB of the load from S11. It's not trivial even if it's quite simple if we start from the right bases. I do this in Excel.

I don't know how to pass this type of information on the forum.
--
F1AMM Fran?ois

I've written a Windows utility that checks Touchstone files for |S11| > 1. It handles version 1.1 files, the kind NanoVNAs generate, as well as version 2.0. It lists maximum |S11| and the number of frequencies where |S11| > 1. This utility may come in handy if you experience odd problems processing NanoVNA data as I did.

Just download the ZIP, extract the files, ignore the ground probe stuff, put S11.EXE in a directory containing Touchstone files, and double-click on it.



Brian

Try to connect through any free VPN, pointing to Netherlands... They can!

On Fri, Jul 22, 2022 at 08:59 AM, Neil Preston W0NRP wrote:

I am trying to figure out if the Nano can display the lumped impedance and
phase angle numerically without having to calculate from r + jX. I expected
to read that from the POLAR menu, but some searching reveals that is just a
coefficient from -1 to +1.

???

I assume when you say "lumped impedance and phase angle" you mean display |Z| (sqrt of [r^2+X^2]) and impedance phase angle. The NanoVNA and the two popular PC programs (NanoVNA Saver and NanoVNA app) can calculate and display |Z| but do not have an impedance phase angle display capability. The "phase" option in the trace menu is the reflection coefficient phase angle which is not the same thing as impedance phase angle.

The polar display is for the reflection coefficient not impedance.

The easiest way to calculate the impedance phase angle is to import the Touchstone S11 file into a spreadsheet and do the calculation and plotting there.

Roger

On Fri, Jul 22, 2022 at 04:34 AM, Diane BONKOUNGOU wrote:

Hello,
Hi, I am a beginner in antenna design and tuning.
I want my antenna to have a resonant frequency of 2.45GHz for low-energy
Bluetooth communication.
And I want to know what to consider for the matching process.
I have made some measurements with Nanovna of my antenna. I have a resonance
frequency of 2.28GHz and at this frequency, I have an impedance of 47.8-7.06j.
Can I take the value of this impedance at this frequency for the matching
process or do I have to take the value of impedance at 2.45GHz?
Where to take the value of impedance for tuning?
Thanks.

You never posted in the other topic what you finally did to correctly measure the antenna with the NanoVNA. If you don't establish the "reference plane" rightat the antenna your impedance measurements will be way off and you won't be able to design a matching network. Even if you get a decent "reference plane" the antenna must be measured in circuit so that you have a the same ground plane as when the antenna will be used. Also the outer shield of your test cable may form part of the antenna and this will affect the measurements.

At these GHz frequencies you will have better results if you tune the antenna for resonance at the desired frequency instead of building a matching network. The reason I say this is that VSWR and Return Loss will only change slightly if your reference plane is not right on but the impedance will be off a fair amount. The reason is that the magnitude of the reflection coefficient stays the same and only the phase angle changes if the cable is slightly long or short. However the phase angle rotation results in a different impedance calculation. Even if you get a reasonable estimate of impedance you then have the issue of designing with components and PCB design at Bluetooth frequencies.

Roger

I am trying to figure out if the Nano can display the lumped impedance and phase angle numerically without having to calculate from r + jX. I expected to read that from the POLAR menu, but some searching reveals that is just a coefficient from -1 to +1.

???

On 7/22/22 8:36 AM, Zack Widup wrote:

You should measure the impedance at the frequency you plan on using. I have
found fairly large variations over a few MHz in this range before.
Zack W9SZ

Most simple antennas, near their design frequency, have an impedance curve that looks a lot like a RLC resonance. The real part changes fairly slowly, but the imaginary part changes quickly.


On the attached graph (impedance of a dipole), you can see that X changes from about -40 to +40 going from 90 to 100% of a half wavelength (resonance is at about 95% half wavelength), while R goes from 53 to 75 ohms over the same frequency range.

A 5% variation in frequency isn't huge (at 2.45 GHz, 5% is 120 MHz) - If you think of the antenna as a filter, it's not even down 3dB at 5%.

Zmag is the absolute value of the Z.

So if you put a L or C in to "cancel" the reactive part,

On Fri, Jul 22, 2022 at 06:14 AM, Miro, N9LR wrote:

I just ordered COILCRAFT TTWB-1-ALD on ebay (US seller), 20pcs for $25
including S&H (seller accepts "best offers"!)



0.3 - 190MHz @1dB, 0.08-450 @3dB, 6.5mmx6.5mm, SMD

Good, let us know how you get on with them, I'm sure there are others interested in using baluns with the nanoVNA.

Kind regards

Ed

You should measure the impedance at the frequency you plan on using. I have
found fairly large variations over a few MHz in this range before.

Zack W9SZ

On Fri, Jul 22, 2022 at 6:34 AM Diane BONKOUNGOU <dianebonk2@...>
wrote:

Hello,
Hi, I am a beginner in antenna design and tuning.
I want my antenna to have a resonant frequency of 2.45GHz for low-energy
Bluetooth communication.
And I want to know what to consider for the matching process.
I have made some measurements with Nanovna of my antenna. I have a
resonance frequency of 2.28GHz and at this frequency, I have an impedance
of 47.8-7.06j. Can I take the value of this impedance at this frequency
for the matching process or do I have to take the value of impedance at
2.45GHz?
Where to take the value of impedance for tuning?
Thanks.

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

Hello Douglas,
Thanks for your response.
Best regards

Le ven. 22 juil. 2022 à 12:55, Douglas Butler <sherpadoug@...> a
écrit :

I just ordered COILCRAFT TTWB-1-ALD on ebay (US seller), 20pcs for $25 including S&H (seller accepts "best offers"!)



0.3 - 190MHz @1dB, 0.08-450 @3dB, 6.5mmx6.5mm, SMD