Connecting to multiple PicoVNAs over SCPI

[IanButterworth]

Hi,
I'd like to connect 2 PicoVNAs to my local machine and individually control them over SCPI on localhost.

I assume this requires doing something like changing the port or limiting the IP address of one of them, but couldn't find guidance on doing that.

Many thanks,
Ian

[IanButterworth]

I have found that there is a menu in PicoVNA 5 where you can set the port that will be used on the next open. It's not mentioned in the manual, however.

This means it can work, but the procedure is a little awkward.

1. Turn both VNAs on
2. Open PicoVNA 5
3. Open settings in PicoVNA 5 > change SCPI port number (requires reopen, but leave window open)
4. Open another PicoVNA 5 process

Now both VNAs are online with different ports.

It would be nice if the port could be changed without restarting the software. Perhaps be a customizable option when selecting the unit in the startup window?

So it could be:
1. Turn both VNAs on
2. Open PicoVNA 5, select a VNA and leave default port
3. Open PicoVNA 5, select the other VNA and customize port

[M-Dawg]

Thank you for this very valuable feedback. It's good to know of your use case.

The reason that PicoVNA 5 needs to be restarted in order to change the SCPI port is: there may be multiple users connected to one VNA via SCPI. We judged that requiring an explicit reset (closing the software and restarting) is better than destroying the connections of potentially multiple remote users when hitting "Save" in the user preferences.

The workaround you've found is the one that we'd recommend in this instance.

In the next version of PicoVNA 5 (coming late April/early May 2024), we've made an improvement that may be of interest. It will be possible to start the software in "headless" mode from the command line (with no user interface). You can specify a VNA (serial number) to connect to and a SCPI port as command line arguments. This would mean you did not have a UI for one of the VNAs, but you could launch as many instances of the software in "headless" mode with different SCPI ports for each specified as command line arguments (perhaps using a shell script or batch file to automate the process).

[IanButterworth]

Thanks. The upcoming change sounds great.

I will say however that I've been seeing that when running two PicoVNA 106's concurrently just with the PicoVNA software and running them in continuous mode, one of them will crash.

The same happens when I leave them paused in the software and sequentially run & collect measurements on each via SCPI "INIT".

Is it known that this setup should work?

[IanButterworth]

Actually, we are able to replicate this failure with only a single device connected.

With a single PicoVNA5 window open and a single PicoVNA connected over USB, these are the SCPI commands we are using (in a pseudo code for loop)

Code: Select all

*IDN?
for i in 1:100
    INIT
    CALC:DATA S11,LOGMAG
    CALC:DATA S11,PHASE
    CALC:DATA S22,LOGMAG
    CALC:DATA S22,PHASE
end

It will work then at a random time the device will stop responding, and the PicoVNA window will say "device disconnected".

I note however that this appears to happen more frequently on our PicoVNA 106 sn. 083... vs. our newer sn. 11... unit. Both are tested with the same USB cable on the same PC USB port.