nanovna-saver – a first look

The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.

I have long held the view that these things are most useful when accompanied by a capable PC client that performs flexible text book presentations of data.

Considering buying one, my first step was to perform a desk evaluation of a popular PC client, which seems to be nanovna-saver.

Before downloading it, I examined the first screenshot on the github page.

It gives evidence that the author does not follow industry standard convention for transmission line terms and theory.

In the results shown above (s11) impedance is 39.105+j39.292Ω and some transformations of that value.

Above is a cross check of key values.

The obvious and blinding error is that nanovna-saver reports the Return Loss as a negative value, the author does not subscribe to the industry standard meaning of Return Loss… very hammy. The value reported appears to be |s11| in dB.

Like most ham tools, they choose to talk in parallel R and X rather than admittance components (conductance and susceptance), but in fact the quantity labelled parallel X should be 1/B=1/-j0.01279=j78.19 which should be stated as X=78.19Ω. It does appear that the author has calculated the equivalent inductance, not the quantity stated to the left.

Above the plot title infers that S11 and Return Loss are synonymous.

They are not, ReturnLoss=-10*log(|s11|) dB (s11 is a complex quantity, it has magnitude and phase).

So, the graphics cannot be directly published (respectably) because of the hammy meaning attributed to Return Loss.

One might ask whether this lack of compliance with industry standard terms and the untidiness in labeling is more widespread, whether there is the rigorous attention to detail necessary in such software.

It has been my experience that authors of this type of stuff are resistant to correction. I will sit this one out for a while.