A software package for use in a ground receiving station detects a beacon-monitor tone transmitted by a spacecraft. To recapitulate from previous NASA Tech Briefs articles on beacon monitoring: An onboard computer processes data from onboard sensors to summarize the condition of the spacecraft in terms of one of four standard statuses, then a message is transmitted on a radio-frequency carrier as phase modulation at one of four subcarrier frequencies that correspond to the four statuses. The present software implements a weak-signal-detection algorithm. The received signal is heterodyned at nine frequencies and recorded into nine corresponding frequency bands. Nominally, there is a center carrier and four pairs of symmetrical status bands. After recording, each frequency band is subdivided into subbands with a fixed temporal duration. Within each frequency subband, there is a bank of time-sequenced subband processors. The optimal linear path in the corresponding time-frequency band space is obtained by maximizing the summed squared signal amplitudes. The maximum summed subband-processor output is selected and compared to a predetermined threshold to determine whether the corresponding status message should be deemed to have been transmitted. The frequency drift of the status tone signal must be small enough to allow the search algorithm to detect the signal over a time long enough to provide a low signal-detection threshold.

Contributors to the development of this software package were Sue Finley, Gabor Lanyi, Robert Sherwood, Miles K. Sue, John Szijjarto, and E. J. Wyatt of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Software category.

This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393-3425. Refer to NPO-21023.

NASA Tech Briefs Magazine

This article first appeared in the March, 2001 issue of NASA Tech Briefs Magazine.

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