Garmin GSD 20 GPS receiver remote sonar sensor

The GSD 20 is a remote, black-box sounder that transmits 500 watts at 50/200kHz. It's designed to provide SONAR capabilities to the following units: GPSMAP 172, GPSMAP 172C, GPSMAP 182/182C, GPSMAP 192, GPSMAP 232, GPSMAP 276C, GPSMAP 296, GPSMAP 376C, GPSMAP 396, GPSMAP 2006/2006C, GPSMAP 2010/2010C, GPSMAP 3006C, and GPSMAP 3010C. The sounder module sends data serially in a Garmin proprietary format to up to two units on board. When viewed on Garmin chartplotters, you'll see full-featured sounder displays in either split- or full-screen presentations. Features include auto-ranging, 2X and 4X auto and manual zoom, optional fish symbols and See-Thru technology, which separates fish from thermoclines and structure.