stuckinthe80s

I know the Atari is in working order so that can be ruled out. I have a 55in Samsung LCD TV from 2013. I bought the RCA to Coaxial connector for the Atari. All I get on channel 3 of the 55in is a PBS network show. There is no change in the screen on the TV when I turn on the Atari. Any thoughts? Oh and I did a analog channel search. There is a game mode but it will not allow me to select that option in TV mode only in AV mode.