Garmin GPS Beginner's Manual - Buying.A.Gps.Receiver
GPS Beginner’s Guide
The signals are so accurate that time can be figured to much less than a millionth of a second, velocity can be figured to within a fraction of a
mile per hour, and location can be figured to within a few meters.
WAAS/EGNOS
The Wide Area Augmentation System (WAAS) is a system of satellites and ground stations that provides even better position accuracy than the
already highly accurate GPS. Europe’s version of this system is the European Geostationary Navigation Overlay Service (EGNOS).
The Federal Aviation Administration (FAA) developed the WAAS program. It makes more airspace usable to pilots, provides more direct en
route paths, and provides new precision approach services to runways, resulting in safety and capacity improvements in all weather conditions
at all locations throughout the U.S. National Airspace System (NAS).
Although it was designed for aviation users, WAAS supports a wide variety of other uses, for example, more precise marine navigation. To take
advantage of WAAS technology, you must have a WAAS-capable GPS receiver in an area where WAAS satellite coverage is available such as
North America. No additional equipment or fees are required to take advantage of WAAS.
Sources.of.Errors
Errors can affect the accuracy of the GPS signal. Take your GPS receiver to an area with a wide and unobstructed view of the sky to reduce the
possibility and impact of some errors. Here are some of the most common GPS errors.
Ionosphere and Troposphere Delays—the satellite signal slows down as it passes through the atmosphere. The system uses a built-in
model that calculates an average delay to partially correct this type of error.
Orbital Errors—this terminology refers to inaccuracies of the satellite’s reported location.
Receiver Clock Errors—the GPS receiver has a built-in clock that can have small timing errors.
Number of Satellites Visible—obstructions can block signal reception, causing position errors or no position reading. The more satellites
that your GPS receiver can view, the better the fix is.
Satellite Geometry/Shading—refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the
satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight
grouping.
Signal Multipath—the GPS signal bounces off of objects, such as tall buildings or large rock surfaces, before it reaches the GPS receiver.
This increases the travel time of the signal and, therefore, causes errors.
Buying.a.GPS.Receiver
Deciding which GPS receiver to buy can be overwhelming. Think about how you want to use the unit, for example, traveling or running. Keep
the following considerations in mind:
Product Level—do you want the basics, or do you want all of the bells and whistles? You can find a unit that fits your needs and budget.
Power Source—will you be using the unit away from an auxiliary power source? You might need to carry extra batteries. With some units,
you can use a vehicle adapter or AC power source.
Portability—do you have a preference between a portable or a built-in unit? Some units mount directly in the dashboard of your boat, car,
or aircraft.
Mapping Capability—do you want to know the general direction or street-level details of your chosen path? Map data can include streets,
restaurants, tourist attractions, marine data, topography, and so forth.
Mounts—a mount for your GPS can be useful to keep your hands free while navigating your bike, boat, car, or airplane. Many units come
with a mount, and several additional mounts are available.
Ease of Use—some receivers provide a tutorial or an easy-to-use touchscreen interface. Some even have turn-by-turn voice instructions as
you are navigating your route.
Antenna Configuration—where are you going to use the unit? With some units, you use only the built-in antenna. With other units, you can
attach an external antenna to give you better reception.
Price—which units fit your price range? An inexpensive entry-level unit can be a great way to enter the GPS world.
Software—whether you want to save your favorite locations or plan a trip, map software can help. You can use your PC or go directly to
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