According to the pilot, he initially overflew the field, and looked for power lines and transmission poles. He noticed one pole, but his attention was diverted, and didn't notice any other poles or power lines. The pilot made his approach, brought the helicopter into a hover, and hovered for about 1 minute. The pilot then looked for obstacles in his departure path, but didn't see any. He initiated the takeoff, and during the departure, the helicopter struck a power line. The pilot then performed an autorotation to the ground.