Results of an AM broadcast AVL experiment

A set of initial experiments has been performed in an industrial area comprised of one- and two-story metal and frame buildings to determine certain important charactersitics of an AM broadcast AVL concept. A triad of AM broadcast stations was phase-synchronized to create a hyperbolic grid over central Los Angeles. Three mobile phase tracking receivers were used to measure the average lane width, the LOP crossing angles, and the relative positioning error drms. Comparison of the theoretically derived plane earth lane widths and LOP crossing angles with the experimental results established that propagation anomalies exist which are able to produce noticeable lane distortion. The measured mean standard deviation of the relative positioning error, drms, obtained in the low-rise industrial test area for eight test positions was 5.9 m, corresponding to a 95 percentile value of 14.6 m. Following the conclusion of the low-rise industrial area tests, a series of measurements was conducted in the high-rise area of Los Angeles to determine potential system performance in a typical urban environment. Lack of receiver sensitivity and the inability of the tracking loop design to tolerate the negative modulation characteristics of the broadcast stations precluded the acquisition of sufficient quantitative data to make a performance acceptability determination. Nevertheless, the data from these tests were considered sufficient to warrant further development of the concept. Design of a new tracking receiver has been completed and concept testing will resume.