OK, Thx. Indeed I found out in the mean time that communication was OK as I tried to update the firmware and saw that the update program was communicating with the module OK
Thanks to the video mentioned in the TTN UNO topic I knew I had to be patient, but in the end the update succeeded after about 6 tries. Now looking at a shiny RN2483 1.0.0
@kersing Thx again