Hello, attempt at using with NanoVNA

[shabaz123]

Hi Scott,

This is great, thanks for sharing!

I gave it a shot, but wanted to run it by you, in case I’m doing something wrong. I’m not a calibration expert, so I apologize if I’m making basic mistakes here. On the other hand, if I can use it, then almost anyone probably can! : )

I have an OSL kit called SDR-Kits Female Calibration Kit of Rosenberger parts (PDF datasheet) and it comes with offset delay (or electrical length) values. Ordinarily, I would plug those values into the VNA, but I recently got a Nano-VNA (the H4 variant), and I’m completely new to these Nano instruments. I don’t think I can configure those values into the instrument.

The NanoVNA appears to be applying some default calibration, I left that calibration enabled (with hindsight I would have switched the default calibration off, I can do that if you think it’s needed). I left the NanoVNA at all the default settings for now, and it is set to a span of 50 kHz – 900 MHz.

Next, I connected a short length of cable (~ 90 mm) to the NanoVNA, and then attached the open/short/load, and obtained the .s1p files for the Open/Short/Load standards in that kit.
I named the files open_meas.s1p, short_meas.s1p and load_meas.s1p (attached in the zip file).

my_s1p_files.zip

Next, I ran the program cal_create.py, and it generated a file called 1x1.vnacal

cal_create.zip
my_vnacal_file.zip

Then, I attached a DIY 100-ohm load (two 200-ohm resistors in parallel across the back of a SMA female connector) and saved the measurement as dut_meas.s1p

I ran the program cal_apply.py, and it converted to a file called dut_meas_corrected.s1p

cal_apply.zip

I have placed the dut_meas and dut_meas_corrected .s1p files in the earlier my_s1p_files.zip file.

It certainly looks spot-on (Smith chart output below). Have I done it right? It feels odd not having typed the calibration standard offset delay (or electrical length) values anywhere, so I was wondering if I've done something wrong.

[scott-guthridge]

See the parallel discussion in EEVblog

[scott-guthridge]

Follow up: libvna version 0.1.4 adds delay parameters to the Solver.add_* methods and the Calibration.apply() method. These are one-way delays with positive values indicating that the device is farther away from the VNA than the reference plane. Note that for consistency with frequency given in Hz, the delays are given in seconds.