Multiple GPS RFI Sources in a Small California Harbor

James R. Clynch, Andrew A. Parker, Richard W. Adler, Wilbur R. Vincent, Paul McGill and George Badger

Abstract: After receiving multiple reports of GPS being jammed in and around the Moss Landing, CA harbor, an effort was mounted by the Naval Postgraduate School (NPS) and the Monterey Bay Aquarium Research Institute (MBARI) to locate the source. Jamming was reported both inside and outside the harbor. MBARI has a differential GPS station at their Moss Landing headquarters to support their research vessels docked there. Logging of the MBARI DGPS corrections established continuous jamming of their Trimble reference receiver. Many other receiver types were also jammed in the harbor. Three sources were eventually located. Spectra taken in the field as well as laboratory test results on the highest level source will be reported. The first, highest level, jamming was located and found to be a Radio Shack VHF/UHF marine TV antenna with a built in pre-amplifier. The unit was on a small fishing boat. It was purchased from the owner and extensively studied in a laboratory. It had a parasitic oscillation at the GPS frequency that was very sensitive to the presence of nearby metal objects, power-supply-voltage fluxations, electromagnetic fields from nearby building wiring, electromagnetic fields from VHF hand-held transceivers, and other things. The unit was forwarded to the FCC. Jamming of GPS still occurred in Moss Landing, but only at night. This was found to be correlated with external temperature. MBARI, NPS and the FCC searched for this unit. It was called Source-2. They quickly found a third RFI emitter that was a Shakespeare active VHF/UHF TV antenna. It appears the unit was manufactured at the same factory. This was called Source-3. The FCC got this source deactivated and continued searching for Source-2, eventually locating it. The levels at the MBARI site for the three sources were calculated. Source-1 (Radio Shack Antenna) had a level of -96 dBm. Source-2 varied in frequency and level. While on top of L1 it had a level of -106 dBm. Source-3 (Shakespeare Antenna) had a level at MBARI of -99 dBm. Source level cannot be computed because the signals suffered an unknown amount of attenuation going through a building and/or their location is unknown. The Source-1 to MBARI range was 325 m at an elevation angle of - 2.5 degrees.
Published in: Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002)
September 24 - 27, 2002
Oregon Convention Center
Portland, OR
Pages: 605 - 612
Cite this article: Clynch, James R., Parker, Andrew A., Adler, Richard W., Vincent, Wilbur R., McGill, Paul, Badger, George, "Multiple GPS RFI Sources in a Small California Harbor," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 605-612.
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