Electromagnetic Reverberation Characteristics of a Large Transport Aircraft

A demonstration test to investigate the reverberation characteristics of the avionics bay and cockpit of a typical commercial aircraft was conducted on a decommissioned Boeing 707-720B aircraft. The aircraft, located at the Aerospace Maintenance and Regeneration Center, Davis Monthan Air Force Base, Arizona, had a significant fraction of its electronics equipment remaining in the avionics bay and cockpit and the passenger compartment was essentially intact. A simulated avionics box was placed in an equipment rack and a trace on an internal circuit board was monitored. The simulated avionics box was also tested in the Naval Surface Warfare Center, Dahlgren Division (NSWCDD) mode stirred chamber (MSC). The avionics bay and cockpit were internally excited from 100 MHz to 18 GHz using a pair of horn and wire antennas placed in several locations. Aluminum foil tuners, each 2 x 2 ft, were located in the avionics bay and the cockpit. The internal electromagnetic environment was measured by a horn and a wire antenna placed successively in several locations in the avionics bay and cockpit. Limited measurements of the local ambient environment, both external to the aircraft and within the aircraft, were obtained for the FM band (88 to 108 MHz) and the VHF/UHF bands (100 MHz to 1 GHz). Cavity losses were characterized by comparing the received power to the input power. The cavity loss for the avionics bay was about 15 dB greater than the loss in the NSWCDD MSC. The loss for the cockpit was about 12 dB greater than the NSWCDD MSC. The observed stirring ratios (ratio of maximum received signal to minimum received signal at a particular frequency as the tuner rotates) were generally less than 10 dB up to about 800 MHz.