Effects of RF power deviations on BCAS link reliability

In the design of a Beacon Collision Avoidance Systems (BCAS) there is some freedom in the choice of specifications for BCAS transmitter power and receiver Minimum Triggering Level (MTL). Transmitter power should be high enough to provide adequate link reliability while being low enough to prevent interference problems. The question of providing adequate link reliability for the Discrete A Beacon System (DABS) mode of BCAS is addressed in this study. The study makes use of aircraft antenna gain data resulting from a model measurement program, and, is otherwise, analytical. It is concluded that appropriate nominal design values are transmitter power = 500 watts and receiver MTL = 77 dbm (referred to the BCAS unit). It is shown that these values provide sufficient power margin, at the air-to-air ranges appropriate for BCAS, so as to allow for adverse power deviations that might result from aircraft antenna gains, antenna cabling, and the expected transmitter and receiver deviations due to manufacturing nonuniformities and aging.