Magellan MobileMapper Beacon User Manual - Page 30

• The low frequency has benefit in penetrating tree-cover, but it is also susceptible to man-made sources of noise from various electronics or electrically driven equipment. This susceptibility shows up in reduced SNR, which could lead to less reliable reception. • ·Local Area Service - beacon is a local area service where only one station is providing correction data to the user-base. This is a strength such that it provides good quality corrections when near the beacon site. Spatial Decorrelation does enter the picture as you operate away from the station. However, it's possible that Coast Guard beacon DGPS could handle large ionospheric disturbances better than WAAS/EGNOS, although a rare condition. Benefits of WAAS/EGNOS • High Frequency - WAAS / EGNOS transmit with a pseudo-GPS signal at L1 frequency. This signal will be available anywhere the GPS receiver's antenna can 'see' the satellite. This provides a very wide operating area, with the exception of behind certain large objects that can mask the signal. • Robust Reception - Being line of sight, and being transmitted on L1 frequency, the WAAS/EGNOS signal is typically easy to acquire. Interference with GPS is typically rare, which provides you with a robust service, when the satellite(s) can be viewed. • Wide Area Service - WAAS and EGNOS use a wide area format for their service. A network of reference stations compute corrections for the specific errors in the GPS service (ionosphere, satellite orbit, and clock corrections). It's possible that the reference stations in the network are not of sufficient density, and they cannot pick up subtle changes in the ionosphere. 26