Maybe I did not understand it correctly, but it appears to me that you
are using cables with open ends to connect to the transformers. If this
is the situation, how do you calibrate the nanoVNA?
I have made a set of cables using RG316 with SMA connectors at one end and short wires at the other. I also made a set of open, short, load and through connectors that the wires attach to so I can calibrate the VNA right to the end of the wires.
I know this is not going to work well at high frequencies but for around 10MHz it does seem to work and I have seen a few videos where others have done similar things which gave me the idea to try this.
I think this is similar to your suggested method except I have attached an extra bit of cable and am using my own SOLT connectors rather than the ones which come with the NanoVNA as I can calibrate right at the very ends of the wire.
In reply 11814 I can see the return loss on my cables is around -33dB when CH0 is connected to CH1 at 7MHz and using the supplied cables and through connector (reply 11835) it is around -43dB.
