That stands for Rundfunk im amerikanischen Sektor and means radio (or broadcasting) in the American Sector – of a place they used to call “West Berlin.”
Now Father Time has managed to take care of something that the East German jamming stations were never able to do back then in the good old bad old days: Shut this broadcasting tower down. With explosives, in this case.
Von Britz aus ging 1946 der Rundfunk im Amerikanischen Sektor (Rias) auf Sendung. Später entstand dort Europas damals leistungsstärkster Mittelwellensender, mit dem jahrelang auch die Störsender aus Ost-Berlin überwunden werden mussten. Heute gilt die Übertragung per Mittelwelle als veraltet.
Observing Hermann 
I don’t think this was the tower used by Armed Forces Radio Europe, which was popular with both Germans and American listeners. I think this tower was more to do with the old Radio Free Europe.
No, AFN was broadcast elsewhere – I believe directly from Saargemünder Str. across from Clay Headquarters here in Berlin. This was RIAS, in German.
Correctamundo. I think the TV transmitter was in Zehlendorf. The deal they made with the DDR was to keep it “low power”. Buildings at Andrews and Tempelhof could catch the signal with a beefy antenna that fed a “cable system”.
Not to confuse it with anything, this is also noteworthy: http://www.tudou.com/programs/view/3ZynKqxumBE
It’s the last English language broadcast of “Radio Berlin International” in 1990.