Lots of discussion on that [1]. In general, the signal from our most powerful commercial radio transmitters will go below the background noise floor well befor

Lots of discussion on that [1]. In general, the signal from our most powerful commercial radio transmitters will go below the background noise floor well before 100 light years. However, a very low bandwidth pumped through something on the scale of the Arecibo dish at the transmitting end, and a helium-cooled receiver, could bridge many more light years. But then we're no longer talking about a sphere of a signal or even a big cone, but in astronomical terms an extremely tight-focused point-to-point laser that is more apt to just intersect cosmic dust and gases than an alien civilization. [1] https://www.quora.com/How-far-do-radio-signals-travel-into-space-before-they-degrade-to-a-degree-beyond-being-possible-to-be-detected https://www.quora.com/How-far-do-radio-signals-travel-into-s...