When you start the game you can head directly east from Sanctuary until you reach Skylanes Flight 1981. Here is a picture of its location,
http://vignette1.wikia.nocookie.net/fallout/images/9/91/FO4_... Once you reach this location, head North under the freeway watching your compass for an antenna. It should not be too terribly far. Once there, a raider will blow you away with a Fatman giving you this achievement. Here is a video demonstrating all of this. Good luck!