Trace phase noise in NanoVNA

20.05.2021 10:10

A quick follow-up to my previous blog post where I was exploring the phase noise in my home-made vector network analyzer. One of the things I did last time was to estimate how much the final vector measurements are jumping around on the phase axis. For my system I got a result of approximately 1.4 degrees RMS at 1 GHz, which is quite bad. Commercial vector network analyzers have this trace phase noise error typically between 0.1 and 0.01 degrees RMS.

Since I had a Jupyter notebook with all the calculations already prepared I quickly ran a similar test on a NanoVNA-H for comparison. I disabled error network correction (i.e. no calibration, disabled CORRECTION in the CAL menu). I then took 200 measurements at 1 GHz with nothing connected to the CH0 connector. Here are the results in a polar plot with the calculated spread:

Trace phase noise for NanoVNA-H at 1 GHz.

I thought it would also be interesting to check how the phase noise varies with frequency:

Trace phase noise for NanoVNA-H versus frequency.

At the base frequency range up to 300 MHz, it seems NanoVNA-H is pretty much on par with professional instruments as far as this metric is concerned. At higher frequencies where it uses harmonic mode the trace phase noise gets worse, but it's still quite good. It stays below 0.15 degrees RMS up to 900 MHz and below 0.35 degrees RMS up to 1500 MHz.

Posted by Tomaž | Categories: Analog

Add a new comment

(No HTML tags allowed. Separate paragraphs with a blank line.)