NASA's experience with listening to radio signals from space may help U.S. law enforcement agencies perform electronic eavesdropping through building walls. A new through-the-wall audio surveillance system uses a powerful beam of very high frequency (VHF) radio waves instead of light. Using a horn antenna, a beam of microwave energy between 30 and 100 GHz is radiated through the wall. Although the radio reflection that passes back through the wall is extremely faint, the kind of electronic extraction and signal cleaning tricks used by NASA to decode signals in space can be used to extract speech. Click here to read the patent application.
