The group's principal activity is to design and develop the xm radio system which was formed for the purpose of operating a digital audio radio service (dars). the group provides audio entertainment and information programming for reception by vehicle, home and portable radios through its high-power satellites rock and roll. these satellites offer 100 channels which cover music, news, talk, sports and children's programs with clear sound and coast-to-coast coverage. xm radios are available under the brand names sony, pioneer and alpine. the group also provides music formats and delivers a wide range of ethnic and informational programming. the group owns two fcc licenses to provide a satellite digital radio service in the united states. radio services are transmitted through the commercial satellites. advertising revenue accounted for 47% of 2001 revenues; Subscriber revenue, 46% and other revenue, 7%.