Signal Characteristics of a Very-High-Frequency Satellite-to-Aircraft Communications Link

The results of a series of very-high-frequency (VHF) aeronautical communications tests conducted with NASA Applications Technology satellites are summarized. The tests were undertaken to collect data which could be compared to the results obtained from a previously derived analytical model. Specifically, the objective of the program was the measurement of the received signal strength and fading characteristics, as received on board a typical commercial jet aircraft to determine the effectiveness of communication and to establish parameters which can be useful to the communication system designer. A discussion of the analytical model, including the antenna characteristics, is followed by a brief description of the test program. The results and conclusions included consideration of the signal amplitude behavior, signal-to-noise ratio, antenna pattern effects, multipath, and system gain and noise. Probability distributions of signal fading and examples of unusual signal reception are included. The probability distributions provide a guide to system designers in establishing communications reliability for specific systems. It was concluded from the tests that the received signal level exceeded the voice intelligibility threshold more than 98 percent of the time using the test system.