ashtech DG16 Reference Manual page 24

of the last position fix. All measurements are referenced to the WGS-84 (World
Geodetic System-1984) ellipsoid model.
The DG16 features 14-channel/14-Satellite All-In-View operation; each of up to
14 visible satellites can be assigned to a discrete channel for continuous tracking.
Each satellite broadcasts almanac and ephemeris information every 30 seconds;
this information is recorded in DG16 memory automatically.
With the SBAS option installed, the DG16 can track up to two geostationary
satellites at a time and make available the SBAS ranging, ephemeris, and
differential correction data through the serial ports. The DG16 can process SBAS
corrections for differential positioning by converting the SBAS corrections to
RTCM SC-104 corrections. For more information on how to use SBAS in
differential operation, see Chapter 4, Differential Operation and "SBAS
Commands" on page 304.
SBAS supplements GPS with a ground reference network which provides a real-
time assessment of the system integrity. The stations use GPS data along with
differential corrections to improve accuracy by broadcasting through
geostationary satellites.
While satellite-based augmentation systems are developed to provide differential
corrections and integrity data for satellite-based aviation, their signals are
available free of charge to all other non-aviation satellite positioning users in the
respective coverage areas.
With the Beacon option [N] installed, the DG16 can receive differential corrections
from up to two different Beacon stations.For more information on how to use
Beacon in differential operation, see "Beacon Commands" on page 314. The
DG16 correction output is in RTCM-104 differential format. See "Beacon
Operation" on page 69 for additional information.
The DG16 is available as a board and as a sensor. From a functional point of
view, the DG16 receiver consists of two major sections: The radio frequency (RF)
section, and the digital section, where the signals from the GPS satellites are
converted to digital format and processed.
Both the board and sensor versions of the DG16 have two plus an optional third
RS-232 input/output (I/O) ports capable of two-way communication with external
equipment, and a coaxial RF port for the antenna.
The RF port can accept GPS and SBAS from the GPS antenna. A Beacon+GPS
antenna is used with the Beacon configured model. See "Antenna" on page 23
for more information on the antennae. The RF port also supplies power to the
antenna/LNA through the cable, eliminating the necessity of a separate power
4 DG14 and DG16 Board & Sensor Reference Manual