Complex sentence: No signals attributable to extraterrestrial technology were found in that interval however to be detectable, however, such transmissions, if radiated isotropically, would need to be at least 10 times as strong as those from Arecibo Observatory.
Split into simpler sentences: No signals attributable to extraterrestrial technology were found in that interval. To be detectable, however, such transmissions, if radiated isotropically, would need to be at least 10 times as strong as those from Arecibo Observatory.