Part of our Getting On The Air: Modes, Operations, and Making Contacts guide.
APRS, the Automatic Packet Reporting System, is one of those things that a lot of hams have running without ever quite understanding how it works. It is the reason your handheld can show a map of nearby stations, the reason a rig at a POTA activation can beacon its location to the whole country, and the reason weather stations and repeater outages get reported automatically. Underneath, it is a surprisingly simple packet radio network built almost entirely by volunteers.
The basic idea
An APRS station transmits short digital packets, usually on 144.390 MHz in North America, containing information like GPS position, a short status message, or telemetry data. Those packets use AX.25 packet protocol at 1200 baud, encoded as audio tones that any FM radio can transmit and receive. A packet by itself only travels as far as line of sight allows, which is where digipeaters come in.
Digipeaters and the internet gateway
A digipeater listens for APRS packets and automatically retransmits them, extending their reach the same way a voice repeater extends a conversation. Most areas have wide area digipeaters mounted on hilltops or towers specifically for this purpose. From there, an even bigger extension happens through IGates, stations that listen for local APRS traffic and forward it onto the internet, where it lands on APRS.fi and similar tracking sites. That is how a hiker’s handheld beaconing from a mountain trail in one state can show up, in near real time, on a map viewed anywhere in the world.
What people actually use it for
- Tracking, both for personal use (letting family follow a road trip or a SOTA hike) and for organized events like marathons and bike races, where APRS trackers have become a standard tool for tracking participants and support vehicles.
- Short text messaging, station to station, which works even without cell coverage as long as you are in range of a digipeater or another APRS station.
- Weather stations. Many home weather stations report temperature, wind, and rainfall automatically over APRS, feeding into services that aggregate that data.
- Object and bulletin reporting, used by some EmComm and served agency operations to mark points of interest like shelters or repeater status on a shared map.
Getting on APRS yourself
Plenty of modern HTs and mobile radios have APRS built in, needing only a GPS source and the right frequency programmed in. If your radio does not, a small external TNC (terminal node controller) paired with almost any FM radio will do the same job. On the software side, a program like APRSdroid on a phone, or a dedicated tracker, gets you beaconing in minutes. It is one of the lowest effort ways to add real utility to a radio that might otherwise just sit on a repeater, and once you see your own call sign moving across a live map, it is hard not to get a little hooked.