Icom’s M510 with DSC has an internal GPS antenna so it's usually not necessary to connect it to an MFD via the NMEA 0183 wiring. Even if you need an external antenna, Icom’s external antenna is an easy to install accessory not only providing the information required to enable life saving DSC calling, but two other important features that add versatility to your VHF experience. First is Anchor Watch, an outstanding convenience and safety feature, rarely included on top brand VHF radios. It lets you set your anchor, then set a watch alert that will notify you if your vessel has slipped anchor and is drifting off the anchorage.