Damn Interesting Space Radio: More Static, Less Talk: "To demonstrate the degrading effect of distance on an everyday omnidirectional signal, one might imagine a spacecraft equipped with an Arecibo-style radio receiver directed towards the Earth. If this hypothetical spacecraft were to set out for the interstellar medium, its massive 305-meter wide dish would lose its tenuous grip on AM radio before reaching Mars. Somewhere en route to Jupiter, the UHF television receivers would spew nothing but static. Before passing Saturn, the last of the FM radio stations would fade away, leaving all of Earth's electromagnetic chatter behind well before leaving our own solar system. "
This is the whole propagation and inverse-square law thing. Once you start thinking about it unless someone is deliberately trying communicate with us it is terribly hard to find signals.
Just trying to do Ham radio stuff around our own planet is hard enough. Just trying to receive from Voyager at the edge of the solar system is challenging for scientists. Then don't forget all the radio noise all the suns in the region are spewing out.
This is a very hard problem.