The German states were in such close proximity that radio and later television signals were basically impossible to block going from the West to the East. Eventually it got to the point during Erich Honecker's regime that they would broadcast segments on GDR programs instructing East Germans not to watch Western frequencies that carried propaganda and lies. Radio Free Europe was a big program coordinator that exploited this ideological weakness in the Iron Curtain. (McAdams, The GDR and Detente)

One of my old professors was a jock on RFE and told me stories about it back in the 1970s. Very cool stuff they used to do. On the fictitious side, the movie/play/whatever now Hedwig and the Angry Inch features this as a plot device. There are tons of literature out there on the history and goings-on of RFE if you're interested in reading about them. I don't personally know of any good ones, but many manuscripts about the GDR mention the radio intrusions as a major problem for the SED leadership.