Lowrance electronic ifinder expedition c User Manual

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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 and even your body. 
Like most GPS receivers, the iFINDER doesn’t have a compass or any 

other navigation aid built inside. It relies solely on the signals from the 

satellites to calculate a position. Speed, direction of travel, and distance 

all are calculated from position information. Therefore, in order for the 

iFINDER 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 be more "wandering" of the data 

shown on the display. 
GPS alone is plenty accurate for route navigation, but the U.S. Federal 

Aviation Administration has special aircraft navigation needs that go 

beyond basic GPS. Consequently, the FAA has developed a program to 

boost GPS performance with its Wide Area Augmentation System 

(WAAS). The FAA commissioned the system on July 11, 2003. EGNOS 

(European Geostationary Navigation Overlay Service) is the European 

equivalent of WAAS. Like WAAS, it was created to make GPS position 

calculation more accurate.  
WAAS is designed to increase GPS accuracy to within 7.6 meters vertically 

and horizontally, but according to the FAA, it consistently comes within 1-2 

meters horizontal and 2-3 meters vertical. It does this by broadcasting cor-

rection signals on GPS frequencies. Your unit automatically receives 

both GPS and WAAS signals.