Four ports measurements

[NicolasZ101]

Hi,
I'am trying 4 ports measurement (LibreVNA Version (64 bit): 1.6.0-b4a22176a - OS: Windows 10 Version 2009 - CPU Arch: x86_64).
Is it possible to automatically set the traces selection for export of 4 ports touchstone format to the right assignment? By default, everyone are at "none", and do it for the sixteen parameters each time we start the export menu is annoying.
Maybe to be sure to use the same reference frequency between LibreVNA, without an external clock, is it possible to "daisy chain" the ref freq of the first VNA (for instance carrying S11) out to In of the second VNA?

Thank you.
Nicolas.

[jankae]

Hi Nicolas, this annoyed me as well and I made some improvements to the Touchstone export a while ago. But they are not in the 1.6.0 version you are using. Please try updating to 1.6.4 (or even better: use the latest development version from here).

1.6.4 will preselect the most fitting traces when you export Touchstone files. The development version will also preselect the traces but if you then go and make changes to these selections, it will remember those changes when you open the export dialog again.

Maybe to be sure to use the same reference frequency between LibreVNA, without an external clock, is it possible to "daisy chain" the ref freq of the first VNA (for instance carrying S11) out to In of the second VNA?

Yes, you can connect the reference output of VNA 1 to the reference input of VNA 2. You then also need to set the reference out setting to 10 MHz and the reference in setting to auto. This will result in VNA 2 getting its clock from VNA 1. I recommend terminating the unused reference input on VNA 1, otherwise it might pick up noise and try to use that as a reference (because it will also be set for auto-detecting the reference input signal)

[NicolasZ101]

Hi Jankae,
thank you, I have update soft and firmware to 1.6.4 /only the vnafw file for the firmware/)
but for the frequency reference, there is something that does not work : look the "noisy" S33 or S44 (second VNA).
(same opposite problem VNA2-->VNA1, same problem with two GUI for each VNA )
It is attached a collection of device log and print-screen with and without 10MHz reference from the first VNA, even with the load in the unused ref input, I missed before. (Ext. reference led active on the second VNA).
Also it seems to depend on the power level... too high (ADC overload) or too low (LO unlocked).
I will try few weeks later with a few dBm 10MHz reference from another instrument feeding the two VNA in parallel.
Nicolas.

log1_with 10MHz from VNA1.txt
log2_with 10MHz from VNA1.txt
log3_with 10MHz from VNA1.txt
log_with internal reference.txt

[jankae]

there is something that does not work : look the "noisy" S33 or S44 (second VNA).

On my end it looks a bit better (not so much noise on S33/S44):

But I think you will be able to improve your results by using an external reference source for both of the LibreVNAs. When I designed the hardware, I did not have this use case in mind and the reference output of one LibreVNA is not the best signal to use as the reference input for the other.