Many years ago when we were graduate students, a radio engineer (now a professor at Georgia Tech) and I used to have long dinner time discussions about SETI. A point he made was the radio carrier frequency was the tip-off that a radio signal was artificial. The signal itself would be amplitude or frequency modulated and could be encrypted. He also mentioned the most likely signal to detect would come from a space tracking system like the now defunct Cobra Dane on Shemya island. The problem with detecting a radar signal is it sweeps the sky and almost never points at one location on the celestial sphere. All we would see is a sharp spike like a noise spike (SETI probably sees those all the time). Radio SETI is probably too hard based on current technology. I suspect a laser based SETI might actually make more sense if any(?) SETI makes sense (more band width). My concern here is that Nick Hoffman maybe correct about most "Earthlike" worlds being waterworlds. Technological civilizations maybe extremely rare in the galaxy, i.e. we're unique in the Milky Way.

Gary