if you are heading 300 degrees on the 120 radial all it is saying is that you are on the 120 radial flying towards the station (120+180=300) once you have passed over the station you will then be flying a hdg of 300 and will now be on the radial of 300 if you where flying a heading of 120 and on the 120 radial you would be flying away from the station (this is assuming no wind!!)