I enjoyed hearing about Peter's ideas about radar and passive radar. He mentioned people using the old AFSSS space fence that was turned off in Sept 2013. That was an excellent source for collecting data on orbiting objects, as it was a large transmitter of 800,000 watts that emitted a narrow beam of approx 8 degrees upward into space. It provided a fence type beam that would reflect the signal back toward Earth when an object passed though it. The beam covered almost the entiresouthern width section of the US. The beam reached way out there, much farther than advertised. When the moon passed over the beam area you could received the radar return from it too. Radio hobbyists used the space fence to track satellites, space debris, and other objects that went through the fence. Some say they got reflections from objects that must have been massive and slow moving, as returns from these showed patterns similar to the moon, but slower and bigger! Who knows what those were, but it sure is interesting.
Too bad they shut off that system.