Garmin GPSMAP 396 - Manual (Page 171)

GPSMAP 396 Owner’s Manual 63
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eArnIng About
gPs
Interface sub tab on the Main Menu but no DGPS device is
detected.
no Beacon Signal—DGPS receiver is attached, but not
transmitting RTCM data to GPS.
tuning Beacon—the receiver is tuning manually to a DGPS
frequency.
Using Differential—the unit is receiving DGPS corrections.
Scanning for Beacon—the DGPS receiver is scanning for an
available frequency.
What is WAAS/EGNOS?
The Wide Area Augmentation System (WAAS) is an FAA-funded
service to improve the overall integrity of the GPS signal and
increase position accuracy for users in North America. In Europe,
WAAS is referred to as EGNOS.
The system is made up of satellites and approximately 25 ground
reference stations positioned across the United States that monitor
GPS satellite data. Two master stations, located on either coast,
collect data from the reference stations and create a GPS data
correction message.
According to the FAA’s Web site, testing in September 2002, WAAS
confirmed an accuracy performance of 1–2 meters horizontal and
2–3 meters vertical throughout the majority of the continental
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United States and portions of Alaska.
WAAS is just one service provider that adheres to the Minimum
Operational Performance Standard (MOPS) for global Satellite
Based Augmentation Systems (SBAS). Eventually, there will
be several services of worldwide geostationary communication
satellites and ground reference stations.
All SBAS systems use the same receiver frequency; therefore any
operational SBAS system should be capable of providing your GPS
unit with increased accuracy at any location in the world.
Currently, enabling WAAS on your Garmin GPSMAP 396 in regions
that are not supported by ground stations may not improve accuracy,
even when receiving signals from an SBAS satellite. In fact, it can
degrade the accuracy to less than that provided by GPS satellites
alone. For this reason, when you enable WAAS on your Garmin
GPS receiver, the receiver automatically uses the method that
achieves the best accuracy. To enable WAAS, refer to page 6 .