Spaced antenna diversity in temperate latitude meteor burst systems operating near 40 MHz: Variation of signal cross-correlation coefficient with time

The potential for meteor burst (MB) spaced antenna diversity is studied using cross-correlation techniques at a temperate latitude, using 37-MHz signals scattered over an 800-km path. Approximately 9 hours of data were analyzed from a 2-day period in February 1990, when the antenna separation was 10λ. The correlation variations with time of signals with durations ≥ 0.75 s, which were categorized as “underdense,” “overdense,” or “not known” (NK), were investigated. The cross-correlation coefficients of signals from underdense and overdense trails are high when correlated over their total signal envelopes, but this is not true when the signal envelope is segmented in time. NK signals are observed to be more uncorrelated than underdense or overdense signals and are, therefore, likely to be the most advantageous to a diversity system. Analysis of data from all three categories combined shows that 40% of signals with duration ≥ 0.75 s have correlation values of less than 0.6 after the first 0.25 s. The correlation-time dependency observed for NK and underdense signals is not identified for the overdense signal category. It is proposed that for underdense and NK signals the correlation-time dependency is due to the vector addition of other weak signal modes. These weak signal modes, however, have little effect on overdense signals which, typically, exhibit higher signal powers in the early stages of the signal envelope.