Illgen Simulation Technologies, Inc. Fact Sheet
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Date: December 1, 1998
Release: Immediately
Contact: Illgen Simulation Technologies, Inc, 805-692-2333 x 204; rlilley@illgen.com
Loran-C P-Static Eliminated Using Loop Antennas
Recent high-voltage tests by a team organized by Dr. Robert Lilley of Illgen Simulation Technologies show that Loran-C receivers equipped with loop antennas are essentially impervious to the in-flight electrical noise generated by aircraft during flight through precipitation. These high voltage tests were conducted to obtain data on loop antennas as part of a study sponsored by the FAA to evaluate Loran as an aid to WAAS/GPS using simulation and modeling techniques. 
Tests under extreme p-static conditions demonstrated that there was little degradation of loran reception or performance. Under such conditions, it is even possible to track most or all of the North American stations simultaneously using new Loran receiver technology. Under conditions where poor airplane bonding or static discharges caused by precipitation may interfere with loran reception, the new h-field antenna provides an elegant solution. 
The low profile loop antenna provides a convenient platform for a GPS antenna for combined GPS/Loran-C installations, although some may choose separate GPS and Loran antennas for true system redundancy.
In controlled tests with the aircraft generating precipitation static (principally corona discharge from trailing edges of the airframe) at levels known to be typical of severe in-flight conditions, receivers connected to aviation-quality "whip" or electric-field antennas suffered reductions in signal-to-noise (SNR) ratio of greater than 25 dB, causing a loss of navigational data. Simultaneously, identical receivers connected to "loop" or magnetic-field antennas were affected only slightly, with a SNR drop of no more than 2 dB, and with no observable effect on navigational accuracy. Both older-style hard-limited receivers and the newer linear-averaging receivers were used. Airframe p-static discharge currents ranged from zero to 400 microamps.
Current users of Loran-C in visual-flight rules (VFR) conditions do not need to retrofit or re-equip, as p-static does not occur in clear air. Users of IFR-approved Loran-C receivers with whip antennas can minimize the effects of p-static through careful airframe maintenance and by correct location and periodic checks and maintenance of discharger wicks. Any new Loran-C or combined GPS/Loran avionics could utilize loop antenna technology, easing or eliminating the p-static problem.
In previous and separate DARPA-supported studies, loop antennas have been used in tests of Loran-C plus GPS for use in urban canyons and other difficult locations, with excellent results. During the Illgen tests, a loop antenna maintained navigation fixes while inside a closed steel hangar, and with severe p-static discharge taking place on the aircraft. The combination may have promise in ground operations near airport buildings or other structures.
The tests were designed and coordinated by Dr. Robert Lilley, Illgen Simulation Technologies Vice President for Navigation and Communications. Receivers and antennas were provided and operated by LOCUS, Inc. technician Frank Richwalski and Megapulse, Inc. engineer Andrei Grebnev. Ohio University's Avionics Engineering Center provided the PA-32-301 aircraft and support facilities, arranged by Asst. Director Dr. David Diggle. P-static consultant and discharger manufacturer Robert Truax configured the high-voltage test environment. Truax performs electrostatic surveys and establishes static-wick discharger locations for the major airframe manufacturers.
Illgen Simulation Technologies is a Goleta/Santa Barbara, CA firm specializing in software development and test, navigation and communications. Madison, WI-based LOCUS produces Loran-C receivers presently in use for critical timing and monitoring applications. Megapulse is the Bedford, MA - based Loran-C transmitter manufacturer, with an interest also in receiver and antenna technology. Reports will be forthcoming from all three organizations, detailing the test configuration and the results.
"There is no longer the need to be concerned over Loran use under instrument weather conditions. Finally we have definitive proof that Loran really will 'be there,' just when you need it."