Rather than the sensitivity of my hybrid to the impedances presented to its ports, it's the VNA's self reported port 2 input impedance of 53.5 ohms that's my concern. That's 7% from nominal. I would like the port 2 input impedance to be within a tenth or two of 50 ohms. People have also mentioned maybe the cables or even the thru are contributing to that, although I have yet to read about anybody claiming that the cables or thru that come with the nano VNA to be anything other than 50 Ohms.
I'm presently dealing with VHF centered around 146 MHz.
You have a standard you use for a load. Guessing a bit of an unknown. Then you have a port match which I am guessing is also a bit of an unknown. I say guessing as I assume if you had access to better equipment and standards, you would have already narrowed down the source of errors. Consider if they are each 5%, and both swing to the worse case your measurement is better than that.
Consider that the load is what you cal to. You are telling the VNA, that is 50 ohms at 146 MHz. Let's say that the part is really 25 ohms. The VNA will measure that as 50. And if your port is now 25, it will also display 50. Then there is the problem that you can't just measure the load with your DMM and expect to get anything meaningful.
All that said, I use a load that I had sorted from Mini-Circuits for my standard. I bought several of them and compared them with a set of metrology grade standards. I picked the best two, the second best being what I use with these low cost VNAs. I use the cheap supplied standards for the short and open. Next, I use the ideal model which assumes there are no parasitics and the standards are perfect. I know the VNA will require some warmup time but lets ignore that. Obviously, the errors are adding up already and I haven't even started.
Next, I calibrate the LiteVNA from 140-150MHz using the above standards. I did not torque anything. Looking at "Loads.jpg", I then measured the original supplied load (yellow), my home made load made up of 2X1206 resistors on FR4 (red), and finally reattached my Mini-Circuits load. It's off by ab out 0.6%.
Just as an FYI, I did measure the DCR of the Mini-Circuits at 50.042 ohms and supplied load at 51.029 ohms. I'm a bit surprised to see them read about 1 ohm difference at 145MHz.
Next, using the supplied cables, I measure port 2 "Port2.jpg". It measures roughly 51.5 ohms or about 2.6%. Now, think about it. Had I used the supplied load as my reference standard rather than the Mini-Circuits ANNE I sorted, the measurement would have been reported to be much tighter. You could fool yourself into thinking it was better but without knowing what these errors are, you are just guessing.
It's nothing that spending some cash couldn't solve. Or, if you have access to some better equipment and standards, you could start to sort things out.
This video had a lot of down votes, I am guessing from some very ignorant viewers. To me, it clearly demonstrates the direct effect of using a poor load for a standard.
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