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Congratulations!
You have purchased one of the finest 12-channel GPS receivers Low-
rance
®
has ever made. With its large LCD screen, easy to use menus,
and outstanding performance, we think you’ll be happy with your GlobalNav
310™ for many years.
GPS works from satellites that transmit information to the world at very
high frequencies. One disadvantage to this frequency is that it’s “line-of-
sight”. In other words, the signals don’t bounce around like your local
radio or television. If you don’t have a clear view of the sky, or if you’re
inside a metal boat dock or garage, the unit probably won’t be able to pick
up the signals from the satellites. This is common among all GPS receiv-
ers.
Like most GPS receivers, your GlobalNav 310 doesn’t have a compass
or any other navigation aid built into it. It relies solely on the signals from
the satellites to determine its position. Speed, direction of travel, and
distance are all calculated from position information. Therefore, in order
for it to determine the direction you’re travelling, you must be moving, and
the faster - the better. This is not to say the unit won’t work at walking
speeds - it will. But the faster you travel, the easier it is for the unit to
determine your direction.
Another factor that influences the GPS’ position and navigation capabili-
ties is called selective availability or S/A. This is small errors purposefully
injected into the transmitted signal from the satellites. The government
does this to degrade the system’s accuracy to civilian and foreign users.
Even with S/A, GPS is the most accurate navigation system ever invented
on such a large scale. The Government’s accuracy specification is 100
meters horizontally and 150 meters vertically 95% of the time. In other
words, the position shown on your GlobalNav 310 could be up to 100
meters in any direction from your actual position, and the altitude could
be plus or minus 150 meters from what’s shown on the screen, 95% of
the time.
There are two ways around the S/A problem. One is to have the govern-
ment simply turn it off. In fact, there is growing pressure on them to do
that, but it’s not likely to happen anytime soon. The other method is to
purchase a DGPS receiver and connect it to your GlobalNav 310. A DGPS
receiver (commonly called a beacon receiver), picks up correction sig-
nals broadcast from ground stations. The GlobalNav 310 takes these
corrections and applies them to the position and altitude screens, giving
you much better accuracy.