Calibration and Evaluation of Blackbeard Time Tagging Capability

The Blackbeard instrument is a broadband radio receiver on the ALEXIS (Array of Low Energy X-ray Imaging Sensors) satellite. It detects and records transient VHF radio signals. During November and December of 1996, the Los Alamos Portable Pulser (LAPP) facility was used to transmit 31 broadband pulses to Blackbeard to evaluate the instrument's time tagging accuracy. LAPP firing times were used in conjunction with propagation delays to compute estimated times of arrival (ETOAs) for pulses reaching Blackbeard. ETOAs were compared to Blackbeard reported times of arrival (RTOAs), which were computed using information returned by Blackbeard and an algorithm presented in this paper. For the 31 pulser shots received by Blackbeard, the mean difference between ETOA and RTOA was 1.97 milliseconds, with RTOAs occurring later than ETOAs. The standard deviation of the difference was 0.43 milliseconds. As a result of the study, the algorithm used for accurate Blackbeard time tag studies has been modified to subtract 1.97 milliseconds from reported times of arrival. The 0.43 ms error standard deviation is now used to describe the uncertainty of Blackbeard time tags.