GPS provides the timing reference for most precision time & frequency products.
The Global Positioning System (GPS) is a space-based, radio-navigation system that enables
extremely accurate positioning, navigation and timing (PNT). Originally designed as a 24-satellite
constellation, GPS is currently comprised of 31 satellites (July 2015). The system is based on a
ground, space, and control segment owned and operated by the U.S. Government as a national
resource. The U.S. Department of Defense (DoD) is the "steward" of GPS and responsible for
operating the system in accordance with the IS-GPS-200H system specification and, by U.S. law,
the Standard Positioning Service (SPS)
and Precise Positioning System (PPS) Performance Standards.
Although GPS is used primarily for navigation, the infrastructure is based on extremely accurate
atomic clocks. The atomic time standards in the monitoring and control stations, and satellites
form a composite clock (CC) that maintain the GPS system time referred to as GPS time. GPS time
is a monotonic time scale (i.e. not corrected by leap seconds) referenced to the US Naval
Observatory (USNO) Master Clock and steered to Coordinated Universal Time (UTC). The satellite
clocks are continuously monitored by Earth-based monitoring stations around the world and at
USNO. The control segment uploads the corrections to the satellites at least once per day. GPS
system time performance is critical as one nanosecond of clock error results in approximately one
foot of position error.
GPS provides the timing reference for the vast majority of precision time and frequency products
and applications today. Commercial GPS receiver modules used in timing applications, typically
optimized for navigation and low cost, provide a one pulse-per-second (1 PPS) UTC timing
reference. As this pulse is locked to the atomic-time-based GPS signals, it has very good long-term
stability but poor short term stability due to environmental, atmospheric, and other effects.
Therefore, this 1 PPS reference is not sufficient by itself for precision time and frequency applications.
EndRun uses a proprietary GPS receiver architecture, optimized for time and frequency
transfer. Sophisticated software algorithms perform integrity monitoring and frequency control
of a high-class quartz oscillator (TCXO or OCXO) or rubidium atomic oscillator. EndRun's advanced
timing and adaptive 3rd-order-frequency-control algorithms with Timing Receiver Autonomous
Integrity Monitoring (TRAIM) maximize the short and long term stability, accuracy and phase
noise of the GPS time and frequency standard's outputs.
This results in a best-in-industry time and frequency reference that can be used in a variety of
mission critical applications including communication systems, satellite earth stations,
government test ranges, high frequency trading, process automation, power system control,
television broadcast, and more.
Read about our GPS Time and Frequency Standards.