NorthStar 2505 Installation Manual page 18

SECTION ONE Introducing the 2505
Page 8
Differential 3-D
The 2505 operates in differential 3-D mode when it receives
data from at least four satellites with adequate geometry and
differential corrections, from either WAAS satellites or
radiobeacons. This is the navigation mode with the highest
performance.
Differential 2-D
The 2505 operates in differential 2-D mode when it receives
data from only three satellites with adequate geometry and
differential corrections, from either WAAS satellites or
radiobeacons. This is the navigation mode with the highest
performance when differential 3-D mode can't be used.
3-D nav
The 2505 operates in 3-D nav mode when it receives data from
at least four satellites with adequate geometry, but no
differential corrections. This is the preferred navigation mode
when sufficient WAAS or radiobeacon corrections aren't
available.
WAAS/beacon differential mode
While beacon and GPS acquisition is occurring, the 2505's GPS
receiver is simultaneously searching for and acquiring the
WAAS differential signal from a geostationary satellite that
operates in the same frequency band as the GPS satellites. (To
avoid conflict, WAAS uses special PRN satellite identification
numbers.) Once the WAAS signal has been acquired and
settled, and provided that the GPS has entered navigation
mode, the 2505 can now enter WAAS or beacon differential
mode. WAAS and beacon modes are selected with a switch on
the connector panel. The switch functions are as follows:
• In the "WAAS/beacon" position, WAAS will be used, but
will revert to beacon if WAAS is lost or unavailable.
•
In the "WAAS only" position, only WAAS differential
corrections will be used, if they're available.
Dead-reckoning mode
The 2505 enters dead-reckoning mode when navigation mode
can't be maintained. The speed and direction are assumed
constant, based on the last known data, to allow the 2505 to
provide an estimated position.
2505 INSTALLATION MANUAL, Revision A