GPS FUNDAMENTALS
There is a minimum of 24 operational GPS satellites at all times. The satellites, operated by the U.S. Air
Force, orbit the earth every 12 hours. Each GPS satellite transmits data that indicates its location and the
current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the
same instant. The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times
because some satellites are farther away than others. The distance to the GPS satellites can be determined
by determining the amount of time it takes for their signals to reach the receiver. When the receiver
determines the distance to at least four GPS satellites, it can by triangulation, calculate its position in three
dimensions.
To ensure the GPS unit receives enough satellite signals at acceptable signal strength, it must be mounted
so that it has a clear view of the sky. In hidden locations, such as under the dash, a clear view can be
challenging. In these locations, it is important to keep any metal interference as far as possible from the top
portion of the GPS unit so that the most accurate position can be calculated.
While GPS data collection has improved in ease and speed, some obstacles remain. Solid or dense objects
can block GPS signals. Wet trees with heavy branches and leaves can mask or attenuate GPS signals.
Mountains and buildings can block satellite transmission. Multipath signals can corrupt GPS data. Multipath
is a reflected signal from some nearby objects. The resulting propagation delay can affect measurement
accuracy. GPS electronics advancements have reduced the multipath threat but GPS field operators and
users should be aware of obvious multipath environments.
CHECKING THE CONTENTS OF THE BOX
The contents of the box containing the BT-1200 are shown below:
I
Model
Contents
BT-1200
1.BT-1200 Unit
2. 2 Mounting Screws
