How to Fix Samsung Galaxy Note 3 IMEI Null and Unknown Baseband problem

• first download odin
• second download modem file
• turn off your phone
• go  to download mode on your phone.(Press and hold Volume Down, Home and Power button)
• Connect your phone to your PC using USB cable
• After clicking the PDA button
  

• select modem file
• wait for a few seconds
• Odin  PASS.message and your phone will automatically reboot