Eagle Electronics 500C manual

The system requires signal reception from three satellites in order to determine a position. This is called a 2D fix. It takes four satellites to determine both position and elevation (your height above sea level — also called altitude). This is called a 3D fix.

Remember, the unit must have a clear view of the satellites in order to receive their signals. Unlike radio or television signals, GPS works at very high frequencies. These signals can be easily blocked by trees, buildings, an automobile roof, even your body.

Like most GPS receivers, this unit doesn’t have a compass or any other navigation aid built inside. It relies solely on the signals from the sat- ellites to calculate a position. Speed, direction of travel, and distance are all calculated from position information. Therefore, in order for unit to determine direction of travel, you must be moving and the faster, the better. This is not to say that it won’t work at walking or trolling speeds — it will. There will simply be more "wandering" of the data shown on the display.

GPS is plenty accurate for route navigation, but the U.S. Federal Avia- tion Administration has special needs for aircraft traffic control that go beyond basic GPS. The FAA has a plan under way to boost GPS per- formance even further with its Wide Area Augmentation System, or WAAS. This GPS add-on will include a time control element that will help airliners fly closer together while avoiding collisions. In addition to carefully spacing airplanes along travel corridors, WAAS will eventu- ally make instrument landings and takeoffs more accurate as it re- places existing aviation navigation systems.

Non-aviators can use WAAS signals to make their GPS navigation even more accurate. Your unit receives both GPS and WAAS signals. How- ever, WAAS has some limits you should know about.

First, the U.S. government has not completed construction of the WAAS system, so it is not yet fully operational. The ground stations are in place, but only a few of the needed WAAS satellites have been launched.

WAAS can boost the accuracy of land GPS navigation, but the system is designed for aircraft. The satellites are in a fixed orbit around the Equator, so they appear very low in the sky to someone on the ground in North America. Aircraft and vessels on open water can get consis- tently good WAAS reception, but terrain, foliage or even large man-made structures frequently block the WAAS signal from ground receivers.

You'll find that using your GPS receiver is both easy and amazingly accurate. It’s easily the most accurate method of electronic navigation

9