I can not find in Nanovna-saver port extension feature. If not exist, feature request it. Already calibrated reference plane easy sifted software to end cable/connector. Not a best precision method, but useful. Cable delay input parameter in picoseconds, more useful if selectable delay or/and delay computed from transmission line velocity factor with real cable length in millimeter. More useful, if not only cable delay used, coax cable loss used too. I see, nanovna support simple electrical lenght compensation. But useful if nanovna-saver support to with extended features.
