Hemisphere GPS MBX-4, Руководство пользователя

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1: Introduction
GPS
This chapter provides a brief overview of GPS, differential GPS beacon
technology, and a description of the MBX-4 receiver, antenna, and
mount.
The United States Department of Defense (DoD) operates a reliable, 24
hour a day, all weather Global Positioning System (GPS).
Navstar, the original name given to this geographic positioning and
navigation tool, includes a constellation of 24 satellites (plus active
spares) orbiting the Earth at an altitude of approximately 13,670 miles
(22,000 kilometers).
How it Works
These satellites transmit coded information to GPS users at UHF (1.575
GHz) frequencies that allows user equipment to calculate a range to
each satellite. GPS is essentially a timing system - ranges are calculated
by timing how long it takes for the GPS signal to reach the user’s GPS
antenna.
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).
The GPS receiver calculates its position with respect to the phase center
of the GPS antenna.