APRS
(Automatic Position Report System) is a system developed by Bob Bruninga,
WB4APR, which uses amateur radio to transmit position reports,
weather
reports, and messages between users.
The investment can
be quite modest as in my case I have an old commercial GE Phoenix SX VHF
mobile ($30), a used KPC3 ($75) and a Magellan GPS receiver
($100-400). I recently upgraded to the Kenwood
TM-D700 radio that has full internal support for APRS.