Lassen SQ, Reference Manual

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Lassen SQ GPS Receiver 6 3
Operation and Performance 4
4.9
GPS Timing
In many timing applications, such as time/frequency standards, site
synchronization systems and event measurement systems, GPS
receivers are used to discipline local oscillators.
The GPS constellation consists of 24 orbiting satellites. Each GPS
satellite contains a highly-stable atomic (Cesium) clock, which is
continuously monitored and corrected by the GPS control segment.
Consequently, the GPS constellation can be considered a set of 24
orbiting clocks with worldwide 24-hour coverage.
GPS receivers use the signals from these GPS “clocks” to correct its
internal clock, which is not as stable or accurate as the GPS atomic
clocks. GPS receivers like the Lassen SQ GPS receiver output a highly
accurate timing pulse (PPS) generated by its internal clock, which is
constantly corrected using the GPS clocks. This timing pulse is
synchronized to UTC within ±95 ns.
In addition to serving as a highly accurate stand-alone time source,
GPS receivers are used to synchronize distant clocks in
communication or data networks. This synchronization is possible
since all GPS satellite clocks are corrected to a common master clock.
Therefore, the relative clock error is the same, regardless of which
satellite or satellites are used. For timing applications requiring a
“common clock”, GPS is the ideal solution.
The position and time errors are related by the speed of light.
Therefore, a position error of 100 meters corresponds to a time error of
approximately 333 ns. The hardware and software implementation
affects the GPS receiver's PPS accuracy level. The receiver's clocking
rate determines the PPS steering resolution.
The Lassen SQ GPS receiver clocking rate is 3.126 MHz. This rate
corresponds to a steering resolution of ±160 ns.