What is the business model of radio stations??

I mean like what do they do to make money?  We got stations up here that never run ads.  Never do news or weather, never even do a station break.  Never play new music.  They play a reasonable mix of older pop music, some of it a half century old. 
   How do they make enough money to pay the rent and the electric bill? 
   Could it be that Clearchannel bought them up and has plans for the future, but for right now they just keep them on the air to avoid loosing the license?