Application of Phase Detection Frequency Domain Reflectometry for Locating Faults in an F-18 Flight Control Harness

The performance of a phase-detection frequency-domain reflectometer (PD-FDR) for locating open and short circuits (hard faults) in a Navy F-18 flight control harness has been tested, and the analytical expressions for accuracy verified. Nine different types of aircraft wires appear in this harness: twisted pair, shielded wires with 1-4 inner conductors, "filter wire," and bundles of individual wires. PD-FDRs in a variety of frequency ranges (12-25, 100-220, 150-300, and 180-400 MHz) are compared. Signal processing techniques are utilized to remove the reflections where the PD-FDR is connected to the wire harness, which is critical to obtaining accurate measurements, particularly for short lengths of wire. For this specific application, open and short circuits are located to within 2.5 cm (1 in) for PD-FDR200 and 11 cm (5.5 in) for PD-FDR25 for wires ranging from 9 cm to 9.15 m (6-360 in).