Garmin 010-00423-02 GXM 30A XM Smart Antenna Delivers XM Satellite Radio, NavTraffic & Weather Services to Compatible Garmin Roughly 3-inches in Diameter USB Extension Cable Requires XM Satellite Subscription(s)** For Garmin GPS Models: GPSMAP: 376C, 378, 478 StreetPilot: 2730, 2820, 7200, 7500 Zumo: 550 **Traffic Services are Available Only in Select Cities Where XM NavTraffic Coverage Exists