User's Manual

Galaxy Tracking Systems, L.L.C. VTU User’s Guide
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8 VTU Operations
8.1 VTU Startup
The VTU initializes first time power is applied after installation. Most importantly, the
GPS receiver must find and track satellites, compute its position and synchronize to
GPS time. A clear view of the sky and the GPS satellite constellation is required to do
this. If the vehicle is parked in a garage or is shaded from the sky, it should be moved
to a location with an unobstructed view of the sky. The vehicle SHOULD REMAIN
STATIONARY until the GPS receiver has had time to initialize (30 minutes or less).
It is absolutely imperative that GPS initialize properly. All VTU and CBU
communications are synchronized to GPS time. An unsynchronized VTU may transmit
within some other VTU’s time slot (in which case both VTUs seem to disappear) or may
not transmit at all.
To verify that the VTU is ready for use, a series of commands are issued form the
command center. A number of ONE-SHOT commands are transmitted first. A ONE
SHOT requests a single response from the VTU no matter what its operating mode.
Any response from the VTU verifies the communication link and that VTU time keeping
via GPS has been established.
Next the VTU is commanded to IN SERVICE mode. Proper initialization of the VTU is
indicated when the correct time, GPS tracking status and position are returned to the
command center in the IN SERVICE response. If the status is not correct, additional
ONE-SHOT commands are transmitted to the VTU until the responses (IN SERVICE
messages) indicate that initialization is complete. At this point the VTU is ready for use.
Once the VTU has been initialized the first time, it will be able to reinitialize within a
minute unless it has been disconnected from vehicle battery power for a long period of
time (greater than a week).
8.2 VTU Operating Modes
The VTU operates in one of two modes, IN SERVICE or OUT OF SERVICE. In either
mode, the VTU receives commands over the UHF radio link from the command center.
The VTU confirms each command by responding with either an IN SERVICE or OUT
OF SERVICE message.
Commanded settings and status are maintained through power outages.
8.2.1 OUT OF SERVICE Operating Mode
The VTU is factory configured to begin life in the OUT OF SERVICE operating mode.
OUT OF SERVICE is a standby mode that is also used to verify unit communications.