An online expert recently promoted this way of using a NanoVNA on 600Ω lines: Normalizing the NanoVNA for any characteristic impedance.
Essentially, he calls for SOL calibrating the VNA with the L or LOAD being a 600Ω resistor.
This does have the effect of ‘correcting’ all s11 measurements to be wrt Zref=600Ω, but most of the calculations of derived values like R, X, etc are wrong.
Above is an example where the NanoVNA-H4 was calibrated with LOAD=470Ω, and then that resistor measured. Note the |s11| is very small, it is correct. The Smith chart locus is a dot in the middle of the chart, it is correct… but the Smith chart marker legend shows Z=49.96-j0.0206Ω which is a gross error, it should be very close to 470Ω.
The instrument assumes that s11 measurements are wrt 50Ω, and this “trick” does not consistently transform the measurements to the desired reference impedance.
So, in summary, while this does centre the Smitch chart on the impedance used for the LOAD, and some other displayed data is correct, some displayed data is grossly wrong, and many available displays are grossly wrong.
There is a better way…
There are many variants of NanoVNA-H4 firmware, and each in many versions. Some may incorporate the “PORT-Z” transformation shown below, some may not.
Above is a NanoVNA-H4 using Dislord’s NanoVNA-D reporting v1.2.37. This version was downloaded as beta firmware and might not be generally available. Competetive variants might have the same feature.
The VNA was SOL calibrated with a LOAD=50Ω, and the PORT-Z set to 470 to change the reference Z for calculation of related displays.
Note the chart is centred on 470Ω (the DUT resistor), the marker legend shows 467-j5.057Ω.
So if you want to present the measurements wrt some impedance other than 50Ω, this is the better way to do it.
A similar feature exists in lots of one port antenna analysers, some allowing selection from a small set of alternative references.