I didn't know about Touchstone, thank you for the hint about that file format!
At a brief search about Touchstone and by looking at the menu fields of the program seen in this video
https://youtu.be/ehmDhLn0Bm8, the file format seems easy to implement, and there are some Touchstone viewer programs already. Some viewers are free, and I bet some of them might be also FOSS. Will dig more about that later.
I never had a VNA, so I might be asking for weird things. What I have in mind is to use a dual channel DDS generator and a 4 channel digital oscilloscope to cobble up together a VNA, for hobby projects around the lab.
The generator has 2 independent channels that can be set to play identical signals, so one DDS output goes straight to one oscilloscope channel, as a phase reference. The other DDS output goes to the DUT. The remaining oscilloscope channels can be used to probe the DUT. (having in mind a 2 port DUT)
For example:
- one channel of the oscilloscope is sampling the generated signal (as a phase reference)
- the second channel is sampling the voltage at the input port of the DUT
- the third channel is sampling the voltage of the output port of the DUT
These 3 signals seem to me enough to calculate the instantaneous V and I at the input and output of the DUT, and from there to calculate the S parameters or to draw a Smith chart, assuming the input and output impedance seen by the DUT is 50 ohms.
Please let me know if I left out any measurement that can not be deduced from these 3 sampled waveforms: Vref, Vin and Vout.
After data acquisition, the ADC samples of Vref, Vin and Vout taken at each frequency needs to be converted into a datapoint to be displayed on the PC, with some nice formatted plots and sliders, and Smith charts, and engineering units on axis, and zoom, and click to show the values for a selected point on a plot, etc.
My hope was to find a free GUI for displaying and handling the plots, without having to program myself all the layout and the details for each chart and text box. Seems like that's exactly what a Touchstone Viewer software can do.
The data acquisition part had to be done anyway, and converting data to a Touchstone format seems easier than writing a custom GUI viewer. Either way, using an established intermediary file format can only be an advantage.