Steps for TDR files

[Josi Grinboju]

Hi, I am trying to see TDR files and have 2 different files that one of them I can open it OK and the second one can't show me nothing on the TDR view

The difference I can see between them isrequency steps on each one.

The one that I can see OK has 10Mhz steps. The one that I can't see has 1.025 Mhz steps

Is there something I can modify on the settings to be able to see the file correctly?

[sma...@gmail.com]

Allow me to contribute to the community. First time I try.

For Time domain transform you have two mode:

- low-pass

- bandpass 

Low-pass mode is the one use for impedance profile often associated with TDR.

Low-pass mode made mandatory that the start frequency = step frequency up to stop frequency that will give an indication of the time domain resolution(shortcut it needs more explanation for that)

Since your files has 1.025MHz step if it does not start at 1.025MHz then you cannot use it directly in low-pass. You could however use it for bandpass time domain transform. But TDR in bandpass give another representation of the discontinuity.

I suggest that you plot your S2p or s4p file (magnitude and phase) and to an interpolation to be in the grid compatible for low-pass time domain transform. I m not aware there is a tool for that. Except maybe load the file in a VNA simulator, then change the frequency setting. I believe Keysight VNA simulator will allow you to do that, use the macro “Dummy DUT” and then adjust your frequency setting before saving the file again.

Xavier.

[Josi Grinboju]

I will try! Thanks for the input! I couldn't imagine that alone.

Cheers!

Josi

[Josi Grinboju]

I tried, but nothing is displayed. I guess we should change the settings on the VNA and measure again.

Thanks for answering.

[Michael Wollensack METAS]

You can open the console window of VNA Tools (Options / Sub Menu / Console). Then you will see a warning why VNA Tools is not able to convert your file to TDR.

[Josi Grinboju]

Hi Michael,

I can't find the Options menu you mentioned.

What version of the tool are you using?

Josi

[sma...@gmail.com]

Hi, 

If you can attached the file that give you problem and I will give a try.

On Monday, June 30, 2025 at 7:02:09 AM UTC+2 grin...@gmail.com wrote:

[Josi Grinboju]

here attached

[Michael Wollensack METAS]

Hi,

if I take a look at your file and try to convert it to to Time Domain, I get the following warning in the console window:

WARNING ComputeTimeScale:  Maximum frequency must be a multiple of the largest frequency step.

Your maximum frequency is 44000 MHz and your largest frequency step is 11.000250063 MHz.

If I divide those two numbers I get 3999.909 which is not an integer.

See appendix D Time Domain of the math reference of VNA Tools for additional information.

Workarounds:

At the moment you measured your data with N = 4000. I would remeasure that with N = 4400 then you have a df = 10.0 MHz. And 44000 MHz will be a multiple of 10.0 MHz.

or

Interpolate your existing measured data using a frequency list. Generate a text file with the extension *.fl. Each line is frequency point. It should contain the following content:

10e6

20e6

30e6

...

43980e6

43990e6

44000e6

So it should contain 4400 lines. Then you can selected this Freq List above the tree vies in the Data Explorer. If a frequency list is active, all selected files will be interpolated to those frequencies in the frequency list file.

Regards

Michael

[sma...@gmail.com]

Please try the modified s2p file

[Michael Wollensack METAS]

Your modified s2p file I can convert to time domain (band pass and low pass mode).

[Josi Grinboju]

it worked :) 

How do I modify the steps (without modify the meaning of the measurement) in order to open it on TDR?

[sma...@gmail.com]

I see you have the P9377 Streamline VNA from keysight.

open the the VNA FW without connecting to your HW, it will start it in VNA simulation. Go in Macro menu to search for the one named "Dummy DUT Tool", load your file. Your measured data become the simulated data on the display. change the frequency setting here I set the Start frequency 10MHz and step 10MHz, did not changed the stop frequency. then save the data as s2p. voila.

[Josi Grinboju]

Great!

Thank you very much for the lead! I will do!

Josi