The military use GPS to track artillery shells, but the shell only has a transponder that receives the GPS signals and retransmits them on another frequency. Similar to using coax from a GPS antenna back to the receiver. The receiver reports where the antenna is located. They record tha data and post process, not reat time. Just a thought, Brooke Clarke, N6GCE -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads