Raven Phoenix 300 - Differential GPS (DGPS) Correction Sources

Manual No. 016-0171-548 Rev. C 3
Introduction
1
Sources of Error
Accuracy of a GPS receiver depends upon the ability of the receiver to correctly calculate the time signals from
each satellite take to reach the GPS antenna. There are several natural conditions which can introduce error
into this calculation and may cause problems when operating any GPS navigation system or receiver.
Four of the primary sources which can introduce errors are:
• Ionospheric and tropospheric delays on the radio signal
• Signal multi-path or reflection
• Receiver clock biases
• Orbital satellite (ephemeris) position errors
GPS is a line-of-sight system which means that a clear path must exist between the satellite and the GPS
antenna. Obstructions such as buildings, trees, parts of the vehicle like a fiberglass or metal roof, and human
bodies may interfere or completely block signals from the GPS receiver. Moreover, items such as electrical
motors, generators, alternators, strobe lights, radio transmitters, microwave dishes, radar, other active
antennas, etc., all generate electrical and magnetic fields which can interfere with GPS or L-Band signals.
Differential GPS (DGPS) Correction Sources
A correction signal or differential source from a known, stationary location on the surface of the earth may be
used to correct for the common sources of error and may also be capable of enhancing the accuracy and
precision of a GPS receiver. The following sections offer brief descriptions of the available differential
correction sources which may be used with the Phoenix 300 receiver.
SBAS (Satellite Based Augmentation System)
Regional SBAS corrections are differential services administrated by various private and government agencies
around the world. Many of these services are available without subscription or cost for agricultural use.
FIGURE 1. Regional SBAS Correction Sources
Note: Using SBAS corrections outside of the coverage areas indicated above can significantly degrade
the position solution provided by the Phoenix 300 receiver.
WAAS
EGNOS
SDCM
MSAS/QZSS
GAGAN