NorthStar Navigation GM1708 961XD - Manual (Page 40)

SECTION TWO - Installation
Page 30 961 INSTALLATION MANUAL Revision A
Once the unit is turned on and has acquired satellite data, you can check
the quality of the GPS signals being received by viewing the various satel-
lites’ SNR (Signal-to-Noise Ratio) readings.
GPS receiver status summary
To display information about the GPS satellites, press the STAR key to
display the SERVICE MENU screen, then press the GPS STATUS key. The
961 displays the GPS SATELLITE STATUS screen, showing the status of
the GPS receiver. This screen also displays the status of the DGPS
receiver, if installed (961XD).
Figure 22: GPS satellite status screen
The GPS SATELLITE STATUS screen shows the received Signal-to-Noise
Ratio (SNR) for each satellite (up to 12), and a map indicating where the
satellites are now located in the sky. Satellites are identified by their pseu-
dorandom number (PRN), a two-digit number assigned by the U.S. gov-
ernment. The center of the satellite map represents the center of the sky,
and the outer ring is the horizon. The view is looking down from above,
with East to your right and West to your left.
Also displayed on the screen is the following GPS data:
• ACCURACY
• HDOP (horizontal dilution of precision)
Accuracy is the estimated accuracy of the GPS system to be expected at
the current time. Your position readings should be more accurate than
this estimate 95 percent of the time.
HDOP is a technical measure of how good the satellite pattern is in the
sky for fix-taking purposes. HDOP depends on how many operational sat-
ellites are in view and where they’re currently located. HDOP is calcu-
lated from the satellites’ current positions, not on actual received signals,