Takeaway:
Increase from 8600 ft stock to 15238 ft with the amps and antenna kit.
Details:
My takeoff point was from a hill about 400 feet above the surrounding land so I had good radio LOS. Prior distance was just over 8600 ft, where I got the first weak video warning, and turned back at that point. Interestingly, I got the same warning at about that point today, but kept going, and it went away, so I might not have reached the maximum on the earlier stock configuration flight. Also, I got other momentary weak video warnings that all went away after 1 or 2 seconds on this flight with the antenna and amp kit.
Eventually I got to 15238 feet, and got the same, but more frequent weak video warnings, along with the return to home battery warning, so I turned around. Periodically, I tried turning the antenna away from the A/C and saw no degradation of the signal at up to 45 degrees off angle.
I set my battery warnings to 10% and 15% so I expected I would get my first RTH battery warning at about 65%, but the warning came at 71%, so my understanding of the battery range warning aren't correct, so I chose not to push it. Also I was running out of unpopulated area.
Testing like this presents a problem because one can’t maintain a visual connection with the A/C at these distances. I bought the amp kit to increase my margins close in, not to run around the ragged edge. I wanted to try this once to roughly gauge what sort of increase I acquired. It looks like about a 77% increase in my environment. There was one set of high tension wires that I flew over about 1/3 of the way out, I estimate they are about 80 feet tall and I was probably about 300 feet above their tops. There were no transmission warnings when I was at my closest to them.
I think the kit provides a good value for the money and Tony was very helpful and provides super fast service. But this mod adds some additional complications: Another component to turn on and off, and charge, and since there are 2 amps and a battery, 3 additional potential failure points. It looks like I can also run it without the amps and just FPVLR's antenna. I will probably do that.