A method and apparatus determines the location of a signal transmitter located at an unknown location by using externally-induced intermodulation distortion emitted from the signal transmitter. A transmitter locator emits an interrogation signal having a frequency that is offset from the frequency...http://www.google.com/patents/US5706010?utm_source=gb-gplus-sharePatent US5706010 - Method and apparatus for determining location of an unknown signal transmitter 
