Automatic Packet Reporting System
Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet System (APRS-IS) and distributed globally for ubiquitous and immediate access. Along with messages, alerts, announcements, and bulletins, the most visible aspect of APRS is its map display. Anyone may place any object or information on his or her map, and it is distributed to all maps of all users in the local RF network or monitoring the area via the Internet. Any station, radio, or object that has an attached GPS is automatically tracked. Other prominent map features are weather stations, alerts and objects and other map-related amateur radio volunteer activities including Search and Rescue and signal direction finding.
APRS has been developed since the late 1980s by Bob Bruninga, callsign WB4APR, currently a senior research engineer at the United States Naval Academy. He still maintains the main APRS website. The acronym "APRS" was derived from his callsign.
In its most widely used form, APRS is transported over the AX.25 protocol using 1200 bit/s Bell 202 AFSK on frequencies located within the 2 meter amateur band.
Sample APRS VHF frequencies
- 144.390 MHz – Colombia, Chile, Indonesia, North America
- 144.575 MHz – New Zealand 
- 144.660 MHz – Japan
- 144.800 MHz – South Africa, Europe, Russia
- 144.930 MHz – Argentina, Uruguay
- 145.175 MHz – Australia
- 145.570 MHz – Brazil
- 145.525 MHz – Thailand
An extensive digital repeater, or "digipeater," network provides transport for APRS packets on these frequencies. Internet gateway stations (IGates) connect the on-air APRS network to the APRS Internet System (APRS-IS), which serves as a worldwide, high-bandwidth backbone for APRS data. Stations can tap into this stream directly, and a number of databases connected to the APRS-IS allow web-based access to the data as well as more advanced data-mining capabilities. A number of low-earth orbiting satellites, including the International Space Station, are capable of relaying APRS data.
While APRS is not a vehicle tracking system, I currently have that capability in one of my vehicles. But APRS is much more than that, it is a two-way tactical real-time digital communications system between all assets in a network sharing information about everything going on in the local area. On ham radio, this means if something is happening now, or there is information that could be valuable to you, then it should show up on your APRS radio in your mobile.
What's that number after the callsign??
That number is referred to as an SSID - Station Set Identifier. This allows someone to run multiple stations under their callsign. The generally accepted purpose of each number is below:
- -0 Your primary station; usually fixed and message capable
- -1 generic additional station, digi, mobile, wx, etc
- -2 generic additional station, digi, mobile, wx, etc
- -3 generic additional station, digi, mobile, wx, etc
- -4 generic additional station, digi, mobile, wx, etc
- -5 Other networks (Dstar, Iphones, Androids, Blackberry's etc)
- -6 Special activity, Satellite ops, camping or 6 meters, etc
- -7 walkie talkies, HT's or other human portable
- -8 Secondary Main Mobile or boats, sailboats, RV's
- -9 Primary Mobile (usually message capable)
- -10 internet (including smartphones), Igates, echolink, winlink, AVRS, APRN, etc
- -11 balloons, aircraft, spacecraft, etc
- -12 Alternate Mobile, APRStt, DTMF, RFID, devices, one-way trackers, etc
- -13 Weather stations
- -14 Truckers or generally full time drivers
- -15 generic additional station, digi, mobile, wx, etc