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5700 GPS Receiver User Guide 147
Event Marker Input and 1PPS Output 13
Reference
The pulse is approximately 8 µsec wide, with rise and fall times of
about 100 nsec. Resolution is approximately 40 nsec, but several
external factors limit accuracy to approximately ±1 µsec:
• Position errors, especially with user-entered reference. Each
meter of error can result in 3 nsec of error in the 1PPS pulse.
• Selective Availability (S/A). When in effect, S/A introduces
errors of up to 30 meters (100 nsec) in satellite signals, with
corresponding errors in the 1PPS pulse.
• Antenna cable length. Each meter of cable adds a delay of about
2 nsec to satellite signals, and a corresponding delay in the
1PPS pulse.
13.3.2 ASCII Time Tag Definition
Each time tag is output about 0.5 second before the corresponding
pulse, as shown in Figure 13.1. Time tags are in ASCII format on a
user-selected serial port. The format of a time tag is:
UTC yy.mm.dd hh:mm:ss ab
Where:
• UTC is fixed text.
• yy.mm.dd is the year, month, and date.
• hh:mm:ss is the hour (on a 24-hour clock), minute, and second.
ThetimeisinUTC,notGPStime.
• a is the position-fix type:
1 = 2D Position Fix for E,N only
2 = 3D Position Fix
3 = Single SV Clock-only fix
4 = Automatic Mode
5 = Reference Station Position
6 = Two-Dimensional with Fixed Clock
7 = Overdetermined solution for Clock-only