A tale of three VNAs

In researching the article Analysis of output matching of a certain 25W 144MHz PA  , I made measurements using a recently ‘upgraded’ nanoVNA-H v3.3 with oneofeleven firmware v1.1.206 nanoVNA-App.exe and default supplied firmware.

Some unexpected ‘bumps’ on the measured response of a short SC transmission line section were concerning, there was no apparent explanation.

The bump around 80MHz had no obvious explanation, and appeared to be an artifact of the measurement fixture, or the instrument. The s11 values from 70-150MHz are suspect.

The expected s11 response can be gleaned from a Simsmith simulation.

The line section was then measured using a VNWA3E calibrated with the same fixture.

Above, no sign of the bump, the response is quite as expected.

My baseline config of ttrftech firmware v0.8 and nanoVNA-mod client was calibrated with the same fixture and the same measurement made.

No sign of the bump there either. Of concern though is the low end results, |s11| should not be greater than 0dB.

So, same VNA, same fixture, same DUT and different results for the oneofeleven suite, not just different but an unexpected / unexplained bump.

I did create an issue on github re a bunch of other errors with computed ‘info’ values in the application, no response yet, but it is early days.

Some further testing on this issue is detailed at https://github.com/OneOfEleven/NanoVNA-H/issues/4 .

Update 15/03/2021: two issues listed at https://github.com/OneOfEleven/NanoVNA-H have quietly disappeared and new issues cannot be added, perhaps a sign that the software has gone unsupported.