It's called the Armstrong Tower in New Jersey and it was built in 1938 by Edwin Armstrong, the acknowledged inventor of FM radio. If you like the stereo side of the dial, you have him to thank - although his life did not have a happy ending. 

According to the linked article, the tower was shut down in 1954, but it came back to life one more time after the terror attack in New York back on Sept. 11, 2001. 

"The Armstrong Tower powered up and broadcast in 2001 one following the 9/11 attack on NYC, which affected their abilities to broadcast in the city. The Armstrong Tower served the needs of the nation once again."

The Birthplace of FM Radio