CSI Wireless SBX-3, Reference Manual

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SBX-3 Reference Manual
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1. Introduction
The SBX-3 is a fully automatic, dual channel, 300 kHz, DGPS
radiobeacon receiver designed for integration into a wide array of
positioning products and applications.
This chapter provides a brief overview of GPS, differential GPS beacon
technology, and a description of the SBX-3 engine, Evaluation Module,
antenna options and accessories.
1.1 GPS
The United States Department of Defense (DoD) operates a reliable,
24 hour per day, all weather Global Positioning System (GPS). It
consists of a constellation of 24 satellites (plus active spares) orbiting
the Earth at an altitude of approximately 22,000 km, ground control
facilities, and end users of the system
1.1.1 How it Works
GPS satellites transmit coded information to users at UHF frequencies
(1.575 GHz) that allows user equipment to calculate a range to each
satellite. GPS is a timing system - ranges are calculated by timing how
long it takes for the GPS signal to reach the user’s GPS antenna. The
GPS receiver will calculate a range by multiplying the time of transit of
the signal by the speed of light.
To calculate a geographic position, the GPS receiver uses a complex
algorithm incorporating satellite coordinates and ranges to each
satellite. Reception of any four or more of these signals allows a GPS
receiver to compute 3D coordinates. Tracking of only three satellites
reduces the position fix to 2D coordinates (horizontal with fixed
vertical).