PDN means "power distribution networks", an odd term that had appeared for those low-Z nets of filtering MLCC caps in power rails, etc. ))
All this nets are characterized by very low Z at low frequency band starting from DC to a couple of MHz.
Regarding "original NanoVNA", I just have purchased one of the cheap clones from AliExpress, that are still available.
Then just flashed it with the recommended FW version from Joe's git repo.
--
Alex
