My thinking on this is that receiving a Extra Terrestrial signal is possible, but normal methods of signal processing make hearing these signals very hard. I think if the proper signal processing were used, these faint wisps of RF energy could be detected. The big problem here is distance, but another problem is that all those sources are antennas emitting these ET signals on another moving planet. Our planet is rotating on it's axis sweeping the receiving antennas here. It's also traveling around the Sun, and the Sun is going around the Galaxy. This is the movement of the Earth based detector. If there was a source on an exoplanet, that source would be rotating around that planets axis. And that planet would be going around it's star. And finally that star is moving in relation to our Sun. We can control the pointing of our radio telescopes very well, and we know very precisely the speed involved with everything involved with Earth, Sun, and our solar system, but that exoplanet is hard to pin down. That darn distance thing again. If there is any rotation of the exoplanet, it would mean that the signals coming from that planet will probably be very short blips as the signal sweeps past Earth, and we get a very brief 1us -100ms burst of signal. This makes the search much harder. If signal processing could be developed to better pick out a brief organized signal burst from an ocean of noise, then these kinds of signals might be able to be detected. It would have to be something different from the usual Fourier transforms processing that is done now. It would have to be fast, and spot quickly a short signal blip mixed with a ton of noise. This is a tall order.