4G PRIMARY
ALARM COMMUNICATOR
4
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 an 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.
(KEY FEATURES continued next page)
GPS VEHICLE
TRACKING SYSTEM
GPS VEHICLE
TRACKING SYSTEM
