Thanks for your help dz99.
But since the TX is going to be mounted on a blimp, its infeasible to have a YAGI antenna there, maybe an antenna that can transmit 360, and place a YAGI antenna on the receiver side.
Any suggestions for antennas on the TX side? I've searched online but could not find in the specs of the antenna "TX antenna gain", I assume I want the highest possible?
I don't know if any of the above made sense, I'm not RF expert as you can tell.
Thanks for your help