For ship mounted sonar, the transducer received not only the required signal but also the ship noise. for distantsignal, the ship noise is a strong interference.
If they're right about what ET would do, so many people listening to so rich a region of the sky might even pick up the telltale signal of intelligent life on a distant world within a few years.
This paper discusses the key technologies for the design of signal collection circuit in distant electrocardiogram monitoring system, and presents an idiographic actualizing scheme.