Garmin GA 38 GPS/GLONASS Antenna
Works with the GLONASS system as well as normal GPS, this external antenna is packaged in a low-profile waterproof housing and comes with 3 easy mounting solutions: pole, surface or under-deck (for the underside of fiberglass decks).
This antenna will give your chartplotter reception in metal boats when the internal GPS will not work
Use with: GPSMAP - 450,451,550,551,555,556,557,750,751,820,1020.
If you have a stand alone Garmin chartplotter / fishfinder combo GPSMAP 400, 500, 600, 800 or 1000 series, and are having trouble with satellite reception, this is the solution.
We only really notice problems when flush mounting units in aluminium hard top boats. Otherwise they normally get pretty good reception without the external antenna.