I have an early nanovna, I think - no shields and no silkscreen for Ch0. Trying to send back, as no S21 measurement, just noise. I tried updating firmware, using the STM app. When choosing dfu file, I immediately got message "incorrect file format", even before uploading to unit.. Should all dfu files be compatible with all nanovnas and the version of STM boot-loader that everyone seems to be using? Thank you.
