Collecting Almanacs and Ephemerides
P/N 7010-0526
2-21
Collecting Almanacs and
Ephemerides
Each satellite broadcasts a navigation message that includes the
ephemeris parameters of the satellite, the almanac, and various other
information. The ephemeris parameters describe the orbital motion of
the satellite and are used to predict its location/trajectory. The
almanac gives the approximate orbit (course) for the transmitting
satellite and all other satellites in the same system only.
• GPS and GLONASS satellites broadcast ephemeris data
cyclically, with a period of 30 seconds.
• GPS satellites broadcast almanac data cyclically with a period of
12.5 minutes; GLONASS satellites broadcast almanac data
cyclically with a period of 2.5 minutes.
If the receiver has an almanac, you can considerably reduce the time
needed to search for and lock on to satellite signals.
The receiver regularly updates the almanac and ephemerides and
stores the most recent versions in its Non-Volatile Random Access
Memory (NVRAM).
1. Set up the receiver (connect the external antenna, if needed) in a
location with a clear view of the sky.
2. Turn on the receiver.
3. Wait for about 15 minutes while the receiver collects complete
almanac and ephemeris data from the satellites.
You will need to collect or update the almanac and ephemerides under
the following circumstances:
• If the receiver has been off for a long time.
• If the last known receiver position, stored in the NVRAM, is
different from the present position by several hundred kilometers.
NOTICE
If 15 minutes have passed and the receiver does not
lock on to satellites, clear the NVRAM. See
“Clearing the NVRAM” on page 5-9 for details.
To Next Page
Loading...
