ashtech DG14, Reference Manual

Page: 85 / 390

Differential Operation 65
Differential Operation
the base station is unavailable. Enabled the auto differential mode with the
$PASHS,RTC,AUT,Y command. Table 4.4 describes how auto differential mode
affects position output at the rover receiver.
The DG16 can track two geostationary SBAS satellites at a time and make
ranging, ephemeris, and SBAS differential correction data messages
available through the serial ports. In addition, the DG16 can process SBAS
corrections for DGPS positioning and also provide the corrections for output
through the serial ports in RTCM SC-104 format.
The DG16 has several modes of SBAS operation:
• Automatic Mode—the receiver determines which SBAS satellite(s) to use
• Single Automatic Mode
• Dual Automatic Mode
• Manual Mode—you manually set which SBAS satellite(s) to use
• Single Manual Mode
• Dual Manual Mode
The default SBAS mode is Single.
Automatic Modes of Operation
In Automatic mode, the DG16 automatically searches for and tracks the
SBAS satellite listed in the available almanac. If no SBAS almanac is
available, the DG16 searches for and tracks the SBAS satellites in a
predefined re-programmable order: satellites 35, 33, 47, 51, 34, 36, 37, 38,
39, 40, 41, 42, 43, 44, 45, 46, 48, 49, 50. Use the
$PASHS,SBA,SSO
command to set a different search order.
Single Automatic Mode
In Single Automatic SBAS mode, the DG16 automatically detects all available
SBAS signals and selects the best ONE satellite, switching automatically as
Table 4.4. Auto Differential Modes and Position Output
Mode Position Output
Code Differential
Auto Differential Off
(Default code mode) Differential position output if the age of corrections is less than
maximum age (maximum age as defined in the rover by
$PASHS,RTC,MAX,xx). No position otherwise.
Code Differential
Auto Differential On Differential position is output if the age of corrections is less than
maximum age, otherwise an autonomous position is output.