Symmetricom TimeSource 500, User Manual

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TimeSource 3500
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Description
097-72050-01 Issue 7: August 2003
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S S S S S S S S S S S S S S S S S S S S S S S S S S S S S
Global Positioning System
The United States Government developed the GPS navigation
system. It is a satellite-based, radio navigation aid designed to
provide global, all-weather, precise navigation and timing
capability to users 24 hours a day.
The satellites, circling the earth at approximately 12,550 statute
miles, are arranged in 6 orbits with 4 operational satellites in each
orbit. Each satellite has an orbital period of approximately
12 hours. This configuration assures that a minimum of
4 satellites, and as many as 12, are in view anywhere in the world
at all times.
The TimeSource 3500 tracks all satellites within its field of view.
The performance of each tracked satellite is observed and
compared to the others, and available for use in the timing
solution. A satellite with unacceptable performance data is
dropped from the timing solution.
GPS antennas must have line-of-sight access to the transmitting
satellites. Any structure that interferes with, or blocks, the view of
the satellites disrupts the reception of the signals, and can
adversely impact the timing performance of a receiver.
The TimeSource 3500 bridges frequent GPS outage periods with
BesTime algorithms, its ultra-stable Rubidium local oscillator and
advanced holdover technology. The technology anticipates the
outages and uses BesTime-generated predictor values to optimize
the performance of timing without direct satellite input.