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Folks,

I am interested in learning how much I can trust the results from my nanoVNA. I understand that a T-Check is a good approach to evaluate VNA performance. Here are the results of a brief investigation which I think turned out fairly well using my nanoVNA.

Here is the software used:
Firmware loaded from file NanoVNA-H__900_ch_20190924.dfu
Running nanoVNA-Saver version 0.1.0

Procedure:
I attached SMA to female BNC adapters to the SMA inputs of the nanoVNA. I performed open, short, load, through, and isolation calibration using a commercially available BNC 50-ohm load and short within the nanoVNA and saved the results in memory 0. I repeated this calibration using nanoVNA-Saver 0.1.0. The open was just the female BNC connector without any connection. The through was a 9-inch length of RG58C/U cable. No special termination conditions were used in the nanoVNASaver software.

I connected 50 ohms across a coaxial transmission line for the T-Check using a Tektronix "through" 50-ohm load typically used for a scope input termination. This device is intended for use up to about 3 GHz. A high quality ohmmeter showed the resistance of this termination to be 50.0 ohms at DC. Measuring S11 of this device with the nanoVNA device after calibration showed logmag of channel 0 <-50 dB below 300 MHz. Similar results were achieved with a miniVNA Tiny which I also use. I think it is a pretty good termination at these frequencies. I put the Tektronix 50-ohm load in the through connection mentioned above which I assumed satisfied the testing requirements for a T-Check. Comments on this approach are welcome.

Within nanoVNASaver I averaged 3 measurements and used 5 scans which produced 1010 samples across the bandwidth from 50 kHz to 300 MHz. I saved the resulting data in an S2P file from nanoVNASaver 0.1.0. I then copied S11 to S22 and S21 to S12. I understand that this is not completely valid because I did not reverse the test device and remeasure. I could reverse the connections and make another measurement but did not in order to save a little time. How bad is this? Is it worth the extra effort?

I then used the T-Check equation found on page 12 of the file "Reeve_S-ParamTestSet.pdf" found at



to compute the T-test result as a function of frequency which is plotted in the attached ".jpg" file.

My understanding from page 12 of the Reeve_S-Parameter TestSet file referenced here is that variations of less than +/- 10% are "Minor" and +/- 10% to +/-15% are in the "Acceptable" range.

Considering the attached plot, the results are +/- 2% up to 150 MHz. This seems excellent! Using the guidance mentioned, it appears that the errors in the nanoVNA are "Minor" below 200 MHz and "Acceptable" up to 300 MHz. The only range which exceeds the +/-10% criterion is from about 220 to 280 MHz with a worst-case deviation of < 13%.

How valid are my results given my procedure and equipment?

--
Bryan, WA5VAH

bryburns,

I think its always a good idea to keep in mind that the NanoVNA is a mass produced product intended for the hobbyist market. If your requirements need a certain level of confidence then your check seems good for that day, under those test conditions, and for your unit. I used a commercially made HP 50 ohm load as my standard until David Taylor pointed out that even though it was manufactured by HP its specs were lukewarm at best. My S11 measurements on known devices were slightly off, but that was because my NanoVNA OSL calibration was made with a load that was slightly off. Changing to a Mini-Circuits 50 ohm load solved the problem. To my point, what you observe may be confidence in repeatability and not in accuracy unless your calibration standard is well characterized. For my own measurement confidence, I keep several "gold" standards in my kit whose performance has been verified outside of the NanoVNA. I fortunate to have friends in my ham club who can check my "gold" standards on their calibrated workplace VNA's periodically.

Herb

Herb,

Thanks for your comments. You make good points to remember.

I am not presently in a position to have a "gold" standard available. That would be nice. And, I am not in need of absolute National Bureau of Standards calibration either. However, I am interested in knowing if the data is believable. Is the device doing better than generating random numbers. Well, I think the T-test I did suggests it is much better than that.

When I just look at the impedance of the T-Test circuit I used, the nanoVNA shows the impedance to be within an ohm of 25 ohms up to about 170 MHz. To me, this seems quite acceptable even though there may be a 4% error in the measurement. But, as you point out, that is referenced to the load I used to calibrate the VNA.

That load does show 50.0 ohms on a very good BK Precision ohmmeter at DC so there is hope it is pretty accurate, especially at low frequencies. I must say that this ohmmeter is the most precise device I own. I do have some 50-ohm loads that don't measure nearly as well at DC and show it in comparison to the one I use. For example - When I measure a load (two 10-dB pads hooked together) that is 54.3 ohms at DC and the VNA shows the parallel equivalent resistance to be between 54 and 54.5 ohms at all frequencies below 300 MHz, I assume that indicates the VNA is pretty good and my calibration load is pretty good over all of those frequencies. This seems to be better than about 0.6% accuracy to me. I would call this excellent for a hobbyist device. This seems to be a real indication of the accuracy of the measurements near 50 ohms?

I don't really need to know the impedance my amateur radio transmitter is working into to a better accuracy than 4%. In fact, I think that precision is far better than the SWR measurement in my amateur radio transceiver. I am sure you know the VSWR measurement is supposed to be 2.0 in this T-Check measurement. The worst VSWR measurement is above 1.94 at at or below 190 MHz and at or above 1.9 all the way to 300 MHz. So, this suggests fairly good accuracy for amateur purposes, especially for an inexpensive device like this.

I am also impressed that the measurements with the nanoVNA are fairly stable and repeatable. If, today, I check a calibration made yesterday against the same loads or cables used to generate the calibration, I get a very similar answer, often far less than a degree in phase variation and 0.1 dB in an amplitude for an open. Using the same through calibration I get very repeatable results for S21 amplitude and phase as well. I assume that this is mostly testing the VNA device and not the loads or the cable. I am sorry to report that is not true for other hobbyist VNA devices I have tried.

--
Bryan, WA5VAH

From: hwalker
[]
David Taylor pointed out that even though it was manufactured by HP its specs were lukewarm at best.
[]
Herb
==========================

Not me. Possibly Dr. Kirby.

Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

Thanks for the info on the T check.

On Sat, Oct 5, 2019 at 06:39 PM, <bryburns@...> wrote:

I then used the T-Check equation found on page 12 of the file
"Reeve_S-ParamTestSet.pdf" found at



to compute the T-test result as a function of frequency which is plotted in
the attached ".jpg" file.

Hello Bryan,
I am trying to calculate the T-Check value from the NanoVNA-Saver .S2P file with LibreOffice Calc,
but I did not got the T-Check formular adopted.

I then copied S11 to S22 and S21 to S12

This is already done in the attached file T-CheckR31.S2P
I attached also a screen shot from NanoVNA-Saver T-Ceck measurement.
The 49.85 Ohm resistor was soldered in a SMA Female-Female Adapter,
see attached photo T-Check_SMA-F-F_49.85Ohm_DSC08169.jpg

Could you please explain in detail how you applied the formular?

73, Rudi DL5FA

Attached spreadsheet contains the formula and you can paste your s2p file on the input tab

--
Erik, PD0EK

Hello Erik,
Thank you very much for your provided spread sheet.
At the moment I am still fighting with the decimal point/comma topic :-(
73, Rudi DL5FA

Hello Erik,
Now it works, see the attached diagram: NanoVNA_T-Check.png
Thanks again for the very good spreadsheet.
73, Rudi DL5FA

Hi Reuter
I had to modify your header to import the s2p file. There was a S too much
! ListType=Lin (This addition was probably not needed)
# HZ S RI R 50 (at the end of this line there was a S too much)
As you see your T-Check is peaking of 50% at 800MHz and should for an acceptable calibration be less than som 5%.
Reason is the your measurements is not error corrected and if you add two 10dB SMA inline attenuator on either side of you T adaptor then it might work
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 5. november 2019 18:10
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

On Sat, Oct 5, 2019 at 06:39 PM, <bryburns@...> wrote:

I then used the T-Check equation found on page 12 of the file
"Reeve_S-ParamTestSet.pdf" found at

.
pdf

to compute the T-test result as a function of frequency which is
plotted in the attached ".jpg" file.

Hello Bryan,
I am trying to calculate the T-Check value from the NanoVNA-Saver .S2P file with LibreOffice Calc, but I did not got the T-Check formular adopted.

I then copied S11 to S22 and S21 to S12

This is already done in the attached file T-CheckR31.S2P I attached also a screen shot from NanoVNA-Saver T-Ceck measurement.
The 49.85 Ohm resistor was soldered in a SMA Female-Female Adapter, see attached photo T-Check_SMA-F-F_49.85Ohm_DSC08169.jpg

Could you please explain in detail how you applied the formular?

73, Rudi DL5FA

Hi Erik
Thank you for the spreadsheet
I did mistakenly comment your T-Check to Reuters and did right away see the mistake
I imported your s2p file after modification of the header, as a surplus S at the end in the # HZ S RI R 50
Good question where is came from :::
As seen on the plot 50% at 800MHz and should be better tha 5% for an acceptable calibration. The reason is the missing error correction and by adding 10dB SMA inline attenuation on either side of the T-Check adaptor might improve as the Ch0 and Ch1 source/load impedances are not 50ohm
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af erik@...
Sendt: 5. november 2019 18:54
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

Attached spreadsheet contains the formula and you can paste your s2p file on the input tab

--
Erik, PD0EK

Hello Kurt,
Yes I know that the curve is not so very good.
But it was just a priciple test for the procedure chain:
NanoVNA-saver .S2P file save to a T-Check curve with minimal effort, with free tools.


The optimizing starts now :-)
73, Rudi DL5FA

p.s. the T-Check Software from R&S no longer works under Windows 10.

Hi Rudi
Understood, thank you.
UPS about the R&S TR-Check have you tried to run in W95 compatibility mode and as administrator ?
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 5. november 2019 22:38
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

Hello Kurt,
Yes I know that the curve is not so very good.
But it was just a priciple test for the procedure chain:
NanoVNA-saver .S2P file save to a T-Check curve with minimal effort, with free tools.


The optimizing starts now :-)
73, Rudi DL5FA

p.s. the T-Check Software from R&S no longer works under Windows 10.

On Tue, Nov 5, 2019 at 11:40 PM, Kurt Poulsen wrote:

UPS about the R&S TR-Check have you tried to run in W95 compatibility mode and
as administrator ?

Hello Kurt,

After reading T-Check.pdf from you from 2010-01-31,
I tried under Windows 10-64
The Installation files are from 1997.
When trying to start SETUP.EXE it was not possible.
Next I started the MS compatibility check, Windows 8 was recommended, and set.
That does not work too.
Next with administrator rights, no success.

Next try was to install under Windows 7-32. That works.
A test with the provided data file ZVR.S2P works.
But my from NanoVNA-Saver exported, extended S2P file was not accepted.
I could not figure out, what was wrong with the format.

Next I tried VNWA version 36.7.8.1 after reading your text from 2014-01:
How to perform a T-Check for a VNWA Calibration.pdf
A test with data file ZVR.S2P works.
But my from NanoVNA-Saver exported, extended S2P file was not accepted.
I could not figure out, what was wrong with the format.

Next I found the spreadsheet from Erik:
Thread: Trying to understand the T-Check outcome of the nanoVNA
/g/nanovna-users/message/3020
T-Check.xlsx (199 KB)
I could not make it to work with my data file.

Then I posted in /g/nanovna-users/message/6502,
asking for help.
Erik provided a new version of his spreadsheet T-Check.xlsx (220 KB)
/g/nanovna-users/message/6505

I imported my data file T-CheckR31.S2P and it worked, see
/g/nanovna-users/message/6517

I will optimise this spreadsheet to accept direct NanoVNA-Saver
exported S2P files, without modification.
I read, that in case of a symmetric T-Check hardware setup
you could copy to fill last 4 columns:
copy C2-S11Real to C8-S22Real
copy C3-S11Imag to C9-S22Imag
copy C4-S21Real to C6-S12Real
copy C5-S21Imag to C7-S12Imag

73, Rudi DK5FA

Hi Rudi
I did export a s2p file from latest version 1.5 of the NanoVNA-saver and it was imported right away in the VNWA
It is in the format RI meaning real Imaginary S parameter so why you have no success with the VNWA is a big question mark
I have made a note yesterday about a T-Check file with an extra S at the end of the # line but that is not the case here.
I have a comment about calibration when doing a T-Check.
When the two test cables are connected to the Ch0 and Ch1 it must be S11 reflection calibrate calibrated with the SMA male SOL standards connected to the female female adaptor so it constitutes a female calibration kit and in the NanoVNA-saver the female kit data entered. This way the reflection calibration plane is identical to the male SMA on the Ch0 test cable. In addition the delay of the female female adoptor must be entered in the nanoVNA-saver for thru calibration.
If this methos is not followed the exist serious phase errors between the reflection and transmission measurements and a T-Check will look crazy.
Did you follows those guide lines ??
I will do a test with the R&S T-Check software else as you have the VNWA it is much simpler. Import the S11 and S21 s2p file and copy S11 to S22 as well S21 to S12. The open a custom trace and in the Expression line and do a right click, then the T-Check formula is ready to be loaded and after pressing OK then set the trace to linear magnitude reference to 1 and reference position to 5 and the scale to e.g. 0.1/div which means one division equal to 10% and 0.01 equal to 1% / div
Give the custom trace a Caption name as T-CHK so the trace is name accordingly. You may save the Custum trace for later use
Kind regards
Kurt


-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 6. november 2019 07:08
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

On Tue, Nov 5, 2019 at 11:40 PM, Kurt Poulsen wrote:

UPS about the R&S TR-Check have you tried to run in W95 compatibility
mode and as administrator ?

Hello Kurt,

After reading T-Check.pdf from you from 2010-01-31, I tried under Windows 10-64 The Installation files are from 1997.
When trying to start SETUP.EXE it was not possible.
Next I started the MS compatibility check, Windows 8 was recommended, and set.
That does not work too.
Next with administrator rights, no success.

Next try was to install under Windows 7-32. That works.
A test with the provided data file ZVR.S2P works.
But my from NanoVNA-Saver exported, extended S2P file was not accepted.
I could not figure out, what was wrong with the format.

Next I tried VNWA version 36.7.8.1 after reading your text from 2014-01:
How to perform a T-Check for a VNWA Calibration.pdf A test with data file ZVR.S2P works.
But my from NanoVNA-Saver exported, extended S2P file was not accepted.
I could not figure out, what was wrong with the format.

Next I found the spreadsheet from Erik:
Thread: Trying to understand the T-Check outcome of the nanoVNA
/g/nanovna-users/message/3020
T-Check.xlsx (199 KB)
I could not make it to work with my data file.

Then I posted in /g/nanovna-users/message/6502,
asking for help.
Erik provided a new version of his spreadsheet T-Check.xlsx (220 KB)
/g/nanovna-users/message/6505

I imported my data file T-CheckR31.S2P and it worked, see
/g/nanovna-users/message/6517

I will optimise this spreadsheet to accept direct NanoVNA-Saver exported S2P files, without modification.
I read, that in case of a symmetric T-Check hardware setup you could copy to fill last 4 columns:
copy C2-S11Real to C8-S22Real
copy C3-S11Imag to C9-S22Imag
copy C4-S21Real to C6-S12Real
copy C5-S21Imag to C7-S12Imag

73, Rudi DK5FA

Hi Rudi
Correct about R&S T-Check, no way to get it to run on W10
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af Kurt Poulsen
Sendt: 6. november 2019 12:46
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

Hi Rudi
I did export a s2p file from latest version 1.5 of the NanoVNA-saver and it was imported right away in the VNWA It is in the format RI meaning real Imaginary S parameter so why you have no success with the VNWA is a big question mark I have made a note yesterday about a T-Check file with an extra S at the end of the # line but that is not the case here.
I have a comment about calibration when doing a T-Check.
When the two test cables are connected to the Ch0 and Ch1 it must be S11 reflection calibrate calibrated with the SMA male SOL standards connected to the female female adaptor so it constitutes a female calibration kit and in the NanoVNA-saver the female kit data entered. This way the reflection calibration plane is identical to the male SMA on the Ch0 test cable. In addition the delay of the female female adoptor must be entered in the nanoVNA-saver for thru calibration.
If this methos is not followed the exist serious phase errors between the reflection and transmission measurements and a T-Check will look crazy.
Did you follows those guide lines ??
I will do a test with the R&S T-Check software else as you have the VNWA it is much simpler. Import the S11 and S21 s2p file and copy S11 to S22 as well S21 to S12. The open a custom trace and in the Expression line and do a right click, then the T-Check formula is ready to be loaded and after pressing OK then set the trace to linear magnitude reference to 1 and reference position to 5 and the scale to e.g. 0.1/div which means one division equal to 10% and 0.01 equal to 1% / div
Give the custom trace a Caption name as T-CHK so the trace is name accordingly. You may save the Custum trace for later use Kind regards Kurt


-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 6. november 2019 07:08
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

On Tue, Nov 5, 2019 at 11:40 PM, Kurt Poulsen wrote:

UPS about the R&S TR-Check have you tried to run in W95 compatibility
mode and as administrator ?

Hello Kurt,

After reading T-Check.pdf from you from 2010-01-31, I tried under Windows 10-64 The Installation files are from 1997.
When trying to start SETUP.EXE it was not possible.
Next I started the MS compatibility check, Windows 8 was recommended, and set.
That does not work too.
Next with administrator rights, no success.

Next try was to install under Windows 7-32. That works.
A test with the provided data file ZVR.S2P works.
But my from NanoVNA-Saver exported, extended S2P file was not accepted.
I could not figure out, what was wrong with the format.

Next I tried VNWA version 36.7.8.1 after reading your text from 2014-01:
How to perform a T-Check for a VNWA Calibration.pdf A test with data file ZVR.S2P works.
But my from NanoVNA-Saver exported, extended S2P file was not accepted.
I could not figure out, what was wrong with the format.

Next I found the spreadsheet from Erik:
Thread: Trying to understand the T-Check outcome of the nanoVNA
/g/nanovna-users/message/3020
T-Check.xlsx (199 KB)
I could not make it to work with my data file.

Then I posted in /g/nanovna-users/message/6502,
asking for help.
Erik provided a new version of his spreadsheet T-Check.xlsx (220 KB)
/g/nanovna-users/message/6505

I imported my data file T-CheckR31.S2P and it worked, see
/g/nanovna-users/message/6517

I will optimise this spreadsheet to accept direct NanoVNA-Saver exported S2P files, without modification.
I read, that in case of a symmetric T-Check hardware setup you could copy to fill last 4 columns:
copy C2-S11Real to C8-S22Real
copy C3-S11Imag to C9-S22Imag
copy C4-S21Real to C6-S12Real
copy C5-S21Imag to C7-S12Imag

73, Rudi DK5FA

! ListType=Lin (This addition was probably not needed)

Hello Kurt,

This 'ListType=Lin' parameter was necessary :-)
Question: where did you found that parameter 'ListType=Lin'?
I looked in specification touchstone_ver2_0.pdf,
and in VNWA_HELP_36.7.8.pdf
and in How to perform a T-Check for a VNWA Calibration.pdf
and did not found it.

Now it works, see attached screen shot VNWA_nanoVNA-Saver_T-Check.png

Thank you very much for this hint and you help.

73, Rudi DL5FA

Hi Rudi
Super you are on the way now. I just did a T-Check for some N cal kit work presently working on and it was below 1 % all the way. That is the magic of 12 term error correction (actually 10 term as isolation not done)
Regarding the listType= lin I loaded into a text editor a s2p file I had saved long ago from the VNWA to study the header of the Touchstone file and there it was. It is just a comment line so why it had any impact I do not know
I checked the Touchstone specification version 1.1 and it is not part of the specification at all.
Kind regards
Kurt


-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 6. november 2019 16:34
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

! ListType=Lin (This addition was probably not needed)

Hello Kurt,

This 'ListType=Lin' parameter was necessary :-)
Question: where did you found that parameter 'ListType=Lin'?
I looked in specification touchstone_ver2_0.pdf, and in VNWA_HELP_36.7.8.pdf and in How to perform a T-Check for a VNWA Calibration.pdf and did not found it.

Now it works, see attached screen shot VNWA_nanoVNA-Saver_T-Check.png

Thank you very much for this hint and you help.

73, Rudi DL5FA

I need help from an expert.
My T-Check setup is now 2 x 50 cm RG402 coax cable and a SMA Tee with a 50 Ohm Load,
see picture NanoVNA_T-Check_SMA-Tee_RG402_DSC08175.jpg

The result, calculated with the spreadsheet from QRP is shown in
NanoVNA_T-CheckR-RG402.png

The S21 gain shows a big oscillation, see
NanoVNA_T-Check-T_RG402-50cm.png

If I remove the CH1 coax cable from the SMA Tee S11 looks like:
NanoVNA_50-Ohm-Load_RG402.png
So, I think the calibration was OK.

The attached file NanoVNA_T-Check-T_RG402.S2P can be
imported in VNWA, see VNWA_T-Check-T_RG402.png

How does that come?
What I am doing wrong?

73, Rudi DL5FA

Hi Rudy
Your problem is that you are not aware how a T-Check is processed. The oscillations you see is because your S11 calibration is done with the reference impedance 50ohm and when you the insert the T adaptor then you measure 25 ohm thru the test cable connected to Ch0 and that is causing impedance transformation. Besides that the output of the T- Adaptor connected to the Ch1 via the test cable is not 50ohm but the input impedance of Ch1 not 50 ohm and this input impedance is not transferred via the Ch1 test cable directly but also subject to impedance transformation thru the Ch1 test cable.
All in all a oscillation based on the sum of all these factors.
In a real VNA like the VNWA the T-Check measurement is done for a complete calibration of S11, S21, S12 and S22 via a test set and the build in 12/10 term error correction take place. The VNWA software does the figure out the output impedance og the TX port which can be monitored via a custom trace as SS and the input impedance of the RX Port seen via a custom trace called SL. The condition for a T-Check is simply the imperfections of the TX output and RX input is compensated as the were idealy 50 ohm.
There is a trick in the VNWA software the a full 12/10 term error correction can be performed by pressing the F2 key on the keyboard as then the t_Check adaptor is sweep in both forward and reverse direction and thus doing a full 12/10 term error correction. By a normal forward or reverse measurement only 6/5 term error correction applied. THE NanoVNA HAVE NO ERROR CORRECTION so you cannot do a T-Check the correct way
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 8. november 2019 16:28
Til: [email protected]
Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz

I need help from an expert.
My T-Check setup is now 2 x 50 cm RG402 coax cable and a SMA Tee with a 50 Ohm Load, see picture NanoVNA_T-Check_SMA-Tee_RG402_DSC08175.jpg

The result, calculated with the spreadsheet from QRP is shown in NanoVNA_T-CheckR-RG402.png

The S21 gain shows a big oscillation, see NanoVNA_T-Check-T_RG402-50cm.png

If I remove the CH1 coax cable from the SMA Tee S11 looks like:
NanoVNA_50-Ohm-Load_RG402.png
So, I think the calibration was OK.

The attached file NanoVNA_T-Check-T_RG402.S2P can be imported in VNWA, see VNWA_T-Check-T_RG402.png

How does that come?
What I am doing wrong?

73, Rudi DL5FA