| An Evaluation of the Susceptibility of eLORAN to Intentional Interference
David J. Chadwick1 and Taehwan Kim2
1,2 The MITRE Corporation, 7515 Colshire Dr. McLean, VA 22102
Phone: 540-951-0529 Fax: 703-983-1364
US Citizens, Clearance Levels: Secret
chadwick@mitre.org , tkim@mitre.org
Applicable Topic: Homeland Security
ABSTRACT
This paper evaluates the susceptibility of enhanced Long Range Aid to Navigation (eLORAN) to intentional interference. The first part of this paper evaluates the effectiveness of eLORAN in a realistic intentional interference environment. The following postulated interference scenarios were analyzed:
A. An adversary taking over an AM broadcasting station and using its antenna tower to transmit signals at 100 kHz using a 5 kW transmitter.
B. Using a small General Aviation aircraft carrying a 500 W transmitter and a trailing-wire antenna.
C. Using a “suitcase-sized” 5 watt transmitter.
The primary factor limiting the effectiveness of these configurations to interfere with LORAN is antenna efficiency. For scenario A, the very low radiation resistance of an antenna that is designed to be operated between 540 kHz and 1705 kHz, when operated at 100 kHz, would require that a jammer be capable of an unfeasibly large output current, and be equipped with a large, complex matching network. The analysis shows that interference with LORAN receivers that are located more than 3.5 km from the antenna is almost impossible. Scenarios B and C produce harmful interference over much smaller areas.
The second part of this paper assesses a theoretical coverage reduction of eLORAN under a set of simplifying assumptions that includes the following:
(1) Jammer transmits the same power spectral density (PSD) signal as eLORAN.
(2) Jammer transmits at 100 W Effective Isotropic Radiated Power (EIRP).
(3) Homogeneous, smooth-earth propagation path over a variety of ground conditions, including seawater.
(4) A modernized eLORAN receiver is capable of tracking and decoding at -10 dB Signal-to-Noise (S/N) threshold, including a 12 dB non-linear receiver processing gain against atmospheric noise.
Under the worst conditions, it was found that a 100 W EIRP jammer will cause a 25 % to 35 % eLORAN coverage reduction, when operated near the limit of eLORAN coverage range.
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