An asteroid that's approximately 400-meters diameter--Asteroid 2005 YU55--will pass within 0.85 lunar distances from Earth on Nov. 8, 2011 and scientists will be bouncing signals off of it to obtain high resolution images as fine as two meters-per-pixel. With the right equipment, it should be possible to hear these echoes when the asteroid is in view.
The Southgate Amateur Radio Club Website has details on receiving opportunities. It says that because YU55 will be so close to Earth, the radar echoes should be detectable with antennas as small as one meter.
Two frequencies of the frequencies that will be used are 2380 MHz and 8560 MHz. The 2380 MHz signal will be a continuous wave transmitted from Arecibo Observatory (and set to precisely that frequency at the Green Bank Telescope operation) on Nov. 9, 2011 from 19:15-19:30 UTC. Due to Doppler shift, the received frequency will vary by as much as 2 kHz. The 8560 MHz signal will be transmitted from the Goldstone Deep Space Network facility between 01:30 and 02:00 UTC on Nov. 9, 2011. Observers may see that frequency shifted by as much as 6 kHz.
I wonder if YU55 will also reflect the signal from the Air Force Surveillance Radar. If so, echoes from it would be heard on www.spaceweatherradio.com.
Look for more details on this as the YU55 gets closer.
Radio World: Asteroid 'Fly-By' Will Produce Radio Echoes