The CRG External Modem can be purchased separately from the CRG (Chameleon RTK Guidance).  It comes with a Microhard modem, antenna, and cabling to connect it externally to the CRG. It provides easy access to RTCM NTRIP correction services, which enables RTK level precision. It does require a data SIM card from a cell phone provider company in your area! (SIM card is NOT included) If you already have a CRG without an internal modem, and wish to have one installed, Agra-GPS offers a ship-back and retrofit service.  Please contact us for details.