Brandywine Portable Timing Unit, User Manual, Page: 21 / 31

MANUAL P/N 900000118 REV D
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5.4.2.1 GPS Modes
Mobile Mode : The unit will continuously update its recorded position in
accordance to the GPS constellation, the internal GPS receiver will not perform any
position averaging, and will continuously compute both position and time from all
satellites in view. This mode requires a minimum of five satellites to be visible at all
times.
This mode
MUST be used for portable applications.
Site Survey
: The GPS receiver is in the position fix mode while it averages a
specified number of sample positions. Once the averaged value is determined, the
receiver enters into position hold mode.
Only use this mode for FIXED antenna locations such as a rooftop antenna.
Position Hold:
In this mode, the PTU will begin to survey it’s location by collecting
and averaging the position that it computes from the GPS satellites. The averaged
position is then stored into the GPS receiver, and the receiver transitions to a timing
mode, where the averaged position is assumed correct, and time is only calculated
from all satellites in view. Erroneous satellite tracking data can be detected and
removed from the over-determined timing solution using the receiver’s built in
Receiver Autonomous Integrity Monitoring (RAIM) function. In locations where the
satellite visibility is poor, the PTU can operate with as few as 1 satellite visible in
this mode.
This mode gives the best results with a
FIXED antenna.
5.4.2.2 Cold Start GPS
Forcing a gold start on the GPS deletes all the current GPS almanac and real-time
clock data in the GPS receiver, and forces the GPS receiver to perform a sky-search
to acquire GPS satellite signals. Completion of a cold start can take up to 60 minutes.