Long-time packeteer Bob Bruninga, WB4APR, developed the Automatic Packet Reporting System (APRS), which allows packet radio to track real-time events. It deviates markedly from the usual message - and text-transfer activity. Instead, APRS concentrates on the graphic display of station and object locations and movements.

For example, if you know the latitude and longitude of your station you can add this information to the beacon transmissions sent by your packet TNC. Any monitoring station that's equipped with APRS software will translate the data and display your location on a computer-generated map.

Taking this idea a step further, if you own a portable Global Positioning System (GPS) receiver, you have precise position information at your fingertips. Connect the GPS receiver to your TNC and you can transmit your location information even as you're moving!

When any person in an APRS network determines where you're located, he can move his cursor and mark your position on his map screen. This action is then transmitted to all screens in the network, so everyone gains, at a glance, the combined knowledge of all network participants. In other words, everyone knows where you are. The map screen retains this information for future reference. This means that moving objects can be dead reckoned to their current locations with one keystroke--based on their previous positions.

With a small GPS receiver, a TNC and a hand-held transceiver stuffed in a cigar box, almost any object can be tracked by packet stations running APRS software. You can place these boxes on bicycles for a marathon event, and, of course, in automobiles. This system is an excellent tool for triangulating the location of a hidden transmitter or jammer.

• 2001: A Technological Odyssey 
  QST January 2001, p. 87
  Stan, WA1LOU gives us a "real fun" introduction to APRS
• Position Reporting with APRS
  QST June 1997, pp. 60-63
  An APRS primer
• Automatic Packet Reporting System
  Sidebar from QEX, February 1994
  APRS basics
  
• An Inexpensive KISS-Mode TNC
  QST November 2000, pp. 53-56
  This little four IC TNC isn't full-featured, but one designed to operate in KISS mode including TCP/IP and APRS.
• Build an APRS Encoder Tracker
  QST February 2002, pp. 28-32
  Track dozens of fixed or mobile items on a computer map with this affordable real-time project.
  
• An Inexpensive External GPS Antenna
  QST October 2002, pp. 36-39
  Save money, homebrew your own external GPS antenna from commonly available materials.
  

findU is a database archiving weather, position, telemetry, and message data.

Dire Wolf is a software "soundcard" AX.25 packet modem/TNC and APRS encoder/decoder