I am looking for applications on simple fuctions like thrusters on/off long range capabilities. Up to 5 miles total distance non line of sight. Anybody have any experience with HF or UHF controlled units?
In the FPV Tonka Summit thread over on rcgroups we use 430mhz EZ-UHF Tx/Rx units to control our ground vehicles. https://www.rcgroups.com/forums/showthread.php?1333642-FPV-Tonka-Summit
But microwave frequencies don't work well non-LOS. You'd need a tilt-up, crank-up antenna at your ground station to get the Tx antenna high enough for LOS. But for long-range control, UHF is definately the way to go. Unless you need an infinite number of axis, then you'd want 2.4Ghz, with the same mast setup, but perhaps a 2-watt WiFi booster on the Tx side, feeding a 7-turn helical antenna aimed right at the Rx antenna.
I assume this is for a surface vehicle, not an underwater one, right? As radio frequencies don't penetrate (fresh) water by more than 6 feet.