Jammers in the Commercial World of GPS

Blanc Wollschlager

Abstract:	The military world of electronic countermeasures is an environment where receivers are designed to perform in a high level of interference or jamming. The electronic battlefield is full of radio frequency interference, both intentional and unintentional, which disrupts communications, fools radar, overloads guidance systems ‘and in general causes havoc with sensitive electronic systems such as GPS receivers. The commercial radio world is aIso becoming more electronically h,az,ardous. Trying to listen to AM radio near a computer, having the garage door opener interfere with one’s TV or getting CB radio over :m intercom system are examples of our frequency spectrum getting filled with interfering signals which are “spilling over” into other frequency b‘ands. The FCC has adopted certain emission standards which attempt to control how much “noise” electronic devices give off, however these standards are much less stringent th:m their military counterparts. For GPS signals with typical power levels of - I25 dBm the interfering signals can pose a large in-band or near-band problem. Because the spread spectrum signal exists below thermal noise, any in-band noise also poses a large challenge to GPS reception. Harmonics from a cellular phone, a UHF radio, or a personal com- puter can cause a GPS receiver to be unable to navigate. Recognition of this problem is causing filter performance profiles such as ARINC 743A and others to become popular for GPS receiver interference rejection. In the future, simihu characterizations might well become an industry standard for ‘airborne commercial navigation, especially concerning inter compatibility of GPS and SATCOM. With the increasing use of SATCOM. which transmits from 1626.5 - 1660.5 MHz, GPS receivers not protected by filtration may suffer tracking failures when they ‘are in the proximity of a transceiver. Extensive testing of several commercially available active GPS ,antennas finds many of them woefully inadequate. Very low interference powers in the “near-b‘and” may cause their in-b,and gain to drop dramatically. This paper is borne out of Rockwell’s experience on Navstar GPS programs such as PLGR.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	933 - 937
Cite this article:	Wollschlager, Blanc, "Jammers in the Commercial World of GPS," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 933-937.
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