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APRS (Automatic Packet Reporting System) is a real-time tactical communication system designed by Bob Bruninga (WB4APR, SK 2022). First developed in the late 1980s, APRS combines position reporting, two-way messaging, weather data, telemetry, and other information sharing into a single system that runs over amateur radio. If you have ever tracked a ham's position on a map in real time, you have seen APRS in action.
APRS is not just a position tracker — though that is its most visible feature. It was designed as a local tactical communication network where everyone in an area can see the same real-time picture of stations, objects, weather, and messages.
APRS uses AX.25 packet radio at 1,200 baud on a shared VHF frequency. In North America, the primary APRS frequency is 144.390 MHz; in Europe it is 144.800 MHz; other regions have their own coordinated frequencies. All stations transmit and receive on this single frequency using a random access protocol (stations transmit their beacons at intervals, with timing designed to minimise collisions).
Because APRS uses VHF, range is limited to roughly line-of-sight. To extend coverage, APRS uses digipeaters — stations (often on hilltops or tall structures) that receive APRS packets and retransmit them. A network of digipeaters provides coverage over a wide area. APRS uses a standardised path system to control how many times a packet is digipeated:
The recommended path for most stations is WIDE1-1,WIDE2-1, which provides good coverage without creating excessive traffic.
IGates (Internet Gateways) are stations that bridge between the RF APRS network and the APRS-IS (APRS Internet System). When an IGate hears an APRS packet on RF, it forwards it to the APRS-IS servers, making it visible worldwide on websites like aprs.fi. Some IGates also relay packets from the internet back to RF (bidirectional gating), enabling messages to reach stations that might not be in direct range.
The APRS Internet System (APRS-IS) is a worldwide network of servers that collects, distributes, and archives APRS data. Websites and applications connect to APRS-IS to display real-time APRS information on maps. The most popular web interface is aprs.fi, which shows station positions, tracks, weather data, and message status on a map.
Position reporting — The most common APRS use. Stations (fixed, mobile, or portable) transmit their GPS position at regular intervals. This creates a real-time map of amateur radio activity in an area.
Two-way messaging — APRS supports short text messages between stations, with delivery confirmation. Messages can be sent from radio to radio, radio to internet, or internet to radio (through bidirectional IGates).
Weather reporting — Weather stations connected to APRS transmit temperature, humidity, barometric pressure, wind speed and direction, rainfall, and other data. This information is fed into citizen weather networks and is used by the National Weather Service in the US.
Objects and items — Any APRS station can place "objects" on the map — markers representing events, hazards, net frequencies, or other points of interest. This is widely used in emergency communications to mark shelters, staging areas, and incidents.
Telemetry — APRS supports numeric telemetry channels for remote monitoring (battery voltage, temperature, signal levels, etc.).
Bulletins and announcements — Stations can transmit general messages visible to all APRS users in range.
Several radios have built-in APRS capability, with a TNC (Terminal Node Controller) and GPS receiver integrated:
With a dedicated APRS radio, you power it on, set the APRS frequency, enter your callsign and SSID, and it starts beaconing and receiving. Messaging is handled through the radio's interface.
You can add APRS to any VHF radio (including a basic FM handheld) by connecting a TNC or sound card interface and running APRS software on a computer:
Apps like APRSdroid (Android) and APRS.fi (iOS/Android) can connect to the APRS-IS network over the internet, allowing you to send position reports and messages without a radio. This is useful for monitoring but does not put a signal on the air (no RF component).
Some apps can also connect to a radio via a Bluetooth TNC (like Mobilinkd), providing a smartphone-based APRS station with RF capability.
APRS uses SSIDs (Secondary Station Identifiers) to distinguish between different stations operated by the same callsign. Your callsign is appended with a number: W1ABC-9 for a mobile station, W1ABC-7 for a handheld, W1ABC-1 for a digipeater, etc. Common SSIDs:
| SSID | Typical use |
|---|---|
| -0 | Fixed station or home station |
| -1 | Digipeater |
| -2 | Digipeater (secondary) |
| -5 | Smartphone (APRSdroid, etc.) |
| -7 | Handheld radio |
| -8 | Boat or marine mobile |
| -9 | Car or mobile station |
| -10 | Internet (IGate, etc.) |
| -15 | Weather station |
Set an appropriate beacon rate — Fixed stations should beacon every 30 minutes (they don't move, so frequent updates waste bandwidth). Mobile stations typically beacon every 1–2 minutes. Many APRS implementations support SmartBeaconing, which adjusts the beacon rate based on speed and direction changes.
Use a sensible path — For most situations, WIDE1-1,WIDE2-1 provides adequate coverage. Avoid long paths like WIDE2-2 or WIDE3-3 in areas with dense APRS activity, as they create excessive traffic.
Include useful information — Set a meaningful status text or comment. For a home station, include your location description. For a weather station, ensure your data is calibrated and accurate.
Don't rely on APRS for safety-critical communication — APRS uses a shared channel with no guaranteed delivery. Messages may be lost. For emergency communications, APRS is a valuable supplementary tool but should not be the sole communication method.
APRS is widely used in emergency communications and public service events. During emergencies, APRS provides:
ARES and RACES groups often train specifically on APRS deployment for served agency support.