Test Results of the Joint FAA/DoD Investigation of GPS Interference

This paper describes the test results of the joint Federal Aviation Administration (FAA) and Department of Defense (DoD) effort to identify the source of interference to civil Global Positioning System (GPS) receivers, also known as the “wormhole,” observed in October 1994 just north of St. Louis, Missouri. The investigation focused on television transmissions as the possible cause of the interference. Flight tests were conducted in areas where theoretical analysis of TV transmissions indicated sufficient signal strength to affect GPS operation. These tests answered several technical questions regarding the potential for GPS interference and solved the “wormhole” mystery. This paper also describes the effects of electromagnetic polarization on GPS operations.