Have you ever taken a long trip and found an interesting program on the car radio but the signal constantly fades in and out and you become frustrated to the point where you are forced to search for another station....
This usually happens with an AM station but fortunately re-appears on the FM band. The process is called Simulcasting. It's like being in two different places at the same time and that's exactly what's happening.
The exact programing is being broadcasted on two different frequencies.