Ag Leader GPS 1500 Operators Manual - Manual (Page 4)

The receiver uses a complex algorithm incorporating satellite locations and ranges to each satellite to
calculate the geographic location. Reception of any four or more of these signals allows a GPS receiver
to compute three-dimensional coordinates.
D
IFFERENTIAL
O
PERATION
The Radio Technical Commission of Marine services (RTCM) has a differential service intended for
correction services. This includes the Space Based Augmentation Systems (SBAS), such as the Wide
Area Augmentation System (WAAS) and the European Geo-stationary Navigation Overlay System
(EGNOS). The GPS 1500 is compatible with each of these differential services.
SBAS
A SBAS-enabled reciever operates automatically anywhere within the coverage areas of the WAAS,
EGNOS or other SBAS programs.
WAAS and EGNOS explained
• WAAS is a free service of the Federal Aviation Administration (FAA) that allows regular GPS
positions to be improved to a DGPS level of accuracy. WAAS is available everywhere in the U.S.,
including Alaska, Hawaii and Puerto Rico. It can also be picked up in some of the border areas of
Mexico and Canada. There are no subscription charges incurred when using WAAS.
• EGNOS is a similar service that is available in Europe and western Russia.
Automatic SBAS tracking
The reciever will automatically scan and track satellite signals. This automatic tracking allows you to
focus on other aspects of differential operation without the need to tune the receiver. The GPS 1500
features two-channel SBAS tracking that provides an enhanced ability to maintain a lock on a SBAS
satellite when more than one satellite is in view. This redundant tracking approach results in more
consistent tracking of a SBAS signal when in an area where signal blockage of a satellite is possible.
e-Dif
A reciever that is equipped with e-Dif capabilities can operate anywhere in the world where normal GPS
signals can be viewed. e-Dif can be used anywhere on the globe where a GPS lock can be achieved.
e-Dif is for our customers who are not able to receive other types of differential signals due to location or
budget.
Once the reciever computes a differential correction, the user can operate for unlimited time and provide
good relative accuracy. Alternatively, the operator can regularly update e-Dif to maintain absolute
accuracy (typically less than 1 meter over 40 minutes).
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