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I'm running into an issue trying to calibrate my NanoVNA H4 so that I can run S21 scans. I've done the calibration two ways: (1) using the NanoVNA-saver software and (2) using the on-screen menu on the VNA itself. The first method works fine but the second one does not. I don't know why there is this discrepancy.

Using the on-screen method, I run through the calibration menu procedure: open, short, load (50 ohms), isolation, and through (using a short SMA jumper cable between the CH0 and CH1 ports). I happen to be doing this over a frequency range of 100 kHz to 5 MHz. When I'm done I save the result and apply the calibration. Next I check the calibration by running an S21 scan, leaving the jumper cable in place between the CH0 and CH1 ports, If the calibration has been done correctly, I should see an S21 magnitude of 0 dB and S21 phase of 0 degrees across the frequency range. I do see 0 dB but the phase is wildly inaccurate, and varies between 177 degrees at 100 kHz to 141 degrees at 5 MHz.

When I do the same calibration using the NanoVNA-saver software and following the calibration steps in the software, I get the correct S21 results with the jumper cable connecting the CH0 and CH1 ports. It shows 0 dB and 0 degrees phase from 100 kHz to 5 MHz.

If I run an S21 scan of a two-port device like a filter, both the on-screen and NanoVNA-saver scans produce the same S21 magnitude but not phase. The phase that's displayed in the on-screen method varies all over the place and is clearly erroneous.

What am I doing wrong that I cannot get a correct calibration and S21 phase measurement with the on-screen method?

John W1FV

John,
Are you sure that your phase trace is looking at S21 phase and not S11 phase?
--John Gord

You nailed it. I was looking at S11 phase and not S21 phase. Thank you!

John W1FV