I am trying to extend the range of my Phantom 3 Professional along the beach for a life saving drone.  I am trying to see if I could have a 2-3 mile range each direction from the homepoint with a call button / repeater stations posted along the beach in each direction.  Any suggestions or recomendations would be appreciated.  Thanks in advance.

Hi there, it is good for this job, and if the environment is good enough, FCC compliant can fly 3.1 mi (5 km) for the max transmission distance for Phantom 3 Pro (Unobstructed, free of interference). And the Phantom 3 series is the all in one drone, we don't recommend assemble the range extender. I suggest that you can refer to the tutorial and make sure that the antennas were pointed directly, make sure the firmware's consistency. Still, use a mobile device with a strong performance. Hope it helps.