A. The U.S. and Canadian governments are setting up Differential GPS (DGPS) stations to transmit correction signals. They are usually broadcast on existing marine beacon frequencies around 300 kHz. They are operational in many coastal areas and on the river systems.

In addition to compensating for errors in the position, these correction signals also correct for deliberate degradation of the accuracy of GPS by the U.S. Department of Defense under their Selective Availability (SA) program. Please refer to the US Coast Guard's web site:

http://www.navcen.uscg.mil/

for locations and status of their differential stations.

The GARMIN GBR 21 is an optional receiver designed to receive the US Coast Guard's broadcast differential signals and supply these signals to your GARMIN GPS unit.

When connected to your GARMIN GPS, the GBR 21 will increase its accuracy to under 10 meters when within receiving range of Differential Beacon stations.