John,
Are you sure that your phase trace is looking at S21 phase and not S11 phase?
--John Gord
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On Thu, Jan 26, 2023 at 08:47 PM, John Kaufmann wrote:
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
