I have a P2 with Zen GoPro, 600 mw Immersion Tx. I have a nice wooded area behind my house I can fly over. Going south, I've ventured about a mile past a waste treatment plant. I get reasonably decent FPV video (5.8 Ghz) and no control problems (2.4 Ghz radio). I haven't ventured much beyond that, but only because I'm going slowly further and further out over relatively uninhabited area (lots of civilization on either side of the green zone). When I go north to the main road going into my neighborhood, I get about 900-950m out, and I trip a RTH and my phantom turns around and flys back. Its happened twice now. The only difference I can see is that about 3/4 of the way in the Northern direction are some power lines that cross through my neighborhood. I'm flying pretty high going north (200m, maybe a bit more) because of the tree line that obstructs my LOS. I can't really see the phantom, but the tree line is about 100m from where I set up on the ground, and the trees are a bit shy of 20m tall. So some basic math (I hope I remember trig) says as long as I'm over 200m at the high end, I still should be in good LOS. Going South (where I've been out to 1600m, I fly around 150m. The treelike is much further from my control point, so I shouldn't have to fly as high. So will transmission lines possibly be causing a problem? The transmission lines are 30m high at most, so at 200+m I'd think there would not be any interference.