Consider buying one of these
and use it between the nanoVNA and the ladder line (without your 1:1 balun). This will allow you to measure with best accuracy even if you have calibrated the nanoVNA with the standard calibration set.
Your 1:1 balun may not be optimal as the ladder line is 450 ohm and coax something like 50ohm (?)
To understand each impedance transformation connect the nanoVNA instead of the radio and switch to TDR mode.
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NanoVNA Wiki:
/g/nanovna-users/wiki/homeNanoVNA Files:
/g/nanovna-users/filesErik, PD0EK
