GXM 30 XM smart antenna (includes flange mnt, USB ext. cable) delivers XM Satellite Radio, NavTraffic and Weather services to your compatible Garmin. Roughly 3 inches in diameter, the GXM 30 processes all XM information and sends the finished data to your unit for display. The GXM 30 requires a XM Satellite subscription(s). Traffic services are available only in select cities where XM Nav Traffic coverage exists.