I used to fly glider contests that were pretty close to large power lines. The launch was actually close to them, launching away from them. If you popped off and looped backwards, it was really close. Didn't like it, but didn't see anyone have problems radio wise. Did see one guy land on the wires, but that was entirely his own fault. he flew along them thinking he was beside them, and actaully landed on them. What a mess for him getting the power company to retrieve the plane.