Garmin Personal Navigator GPS 100AVD Owner's Manual

Also see for Personal Navigator GPS 100AVD: Installation manual

Contents

Garmin Personal Navigator GPS 100AVD Owner's Manual Manual pdf 109 page image

APPENDIX AGPS — HOW DOES IT WORK?A.1 GPS OVERVIEWThe Global Positioning System (GPS) is a satellite based navigation systemthat provides precise position, velocity, and time information. This navigationsystem may be used in marine, aviation, and land vehicles, as well as byhunters, hikers, and military forces.The heart of the Global Positioning System, when complete, will consist of21 satellites and 3 spares. Circling the earth twice daily, these satellites willbe distributed among six orbits approximately 10,900 nautical miles abovethe earth. Each satellite continuously transmits precise timing waveformsand navigation messages including satellite status, orbital data, and clockcorrections.The satellite signal is modulated by two high-rate, bi-phase, shifted keycodes: a protected code (P-Code) and an unprotected code (C/A Code). TheP-code is reserved for military use, and the C/A Code is intended for publicaccess. This signal is extremely resistant to interference from weather,earth-based radio signals, and electronic equipment.Several ground stations are strategically located to monitor the satellites andaccumulate ranging information from the navigation signals. This informationis processed at the master control station for determination of orbital datawhich is then uploaded to the satellites.A typical GPS receiver consists of an antenna, signal processing electronics,and processor. The primary function of a receiver is to acquire signals,recover orbital data, make range and Doppler measurements, and processthis information in real-time to obtain the user position, velocity and time.A.2 COVERAGE AND ACCURACYAs with Loran-C, the actual accuracy of GPS depends in part on thegeometric relationship between the transmitters (i.e. the satellites) and theuser. Errors in range measurements may result in disproportionately largererrors in position depending on the geometry of the satellites being used fornavigation.A-1