I was bored so I looked up train horns and this horn I came across on YouTube I have never really heard. It sounds like either a PRR GG1 Horn or it also sounds like horn that goes on an F3. You make the decision. http://www.youtube.com/watch?v=WtRXzET_vB4&feature=player_profilepage This is not my video.
That sure sounds just like the standard F unit horn.