baseband is your radio. It will be flashed back with a ruu.
latest dev edition ruu: http://www.htc1guru.com/2014/03/android-dev-ruu/
latest GPE ruu: http://www.htc1guru.com/dld/ruu-zip-...58-1700-5-zip/
For the ruu.exe(DEV edition), just lauch the .exe file with phone in bootloader.
For the ruu.zip (GPE)
boot phone in bootloader
make sure the ruu.zip is in the same folder of adb and fastboot
fastboot oem writecid GOOGL001 fastboot reboot-bootloader fastboot oem rebootRUU fastboot flash zip name_of_file.zip ---> will fail first time and ask you to ''flush'' image again immediately fastboot flash zip name_of_file.zip so do the command twice. There's no progress bar, this can take up to 20 mins fastboot reboot
If you are going to use the GPE ruu, NEVER turn security back to S-ON and NEVER relock bootloader