APRS for Emergency Communications
The Automatic Packet Reporting System (APRS) is a digital communications protocol that broadcasts position, weather, and short message data over amateur radio. In emergency communications, APRS provides real-time situational awareness — showing the positions of deployed operators, tracking resource vehicles, monitoring weather stations, and passing short text messages — without requiring any internet infrastructure once the local network is established.
The APRS network
APRS operates on 144.390 MHz in North America. Stations transmit short data packets — position reports, weather data, messages, or status text — using 1200 baud AFSK audio via FM radio. Digipeaters relay packets across an area, extending the range of individual low-power stations. iGates receive packets and upload them to the APRS-IS internet network, feeding mapping sites like aprs.fi. In an EmComm scenario without internet access, digipeaters allow direct radio-to-radio APRS operation — deployed operators can see each other's positions on APRS-capable radios or laptops running Xastir or YAAC as long as they are within range of the local digipeater network.
APRS in EmComm operations
APRS provides specific capabilities that are valuable in emergency activations. Position tracking shows where deployed operators, EOCs, and resource vehicles are located — a significant advantage in large-scale events covering wide areas. Weather stations report current conditions from specific locations in real time. Short messaging allows operators to pass brief text messages without tying up voice frequencies. Object reporting allows command staff to mark key locations — fuel points, shelters, staging areas — on the shared APRS map. APRS is also used to track SKYWARN spotter positions during severe weather events.
| Setup Type | Hardware | Cost | Best For |
|---|---|---|---|
| Dedicated APRS radio | Kenwood TH-D74, TH-D75, Yaesu FT3DR | $350–500 | Mobile/portable — built-in GPS and TNC |
| Radio + hardware TNC | Any FM radio + Mobilinkd TNC3 | $50–150 for TNC | Flexible — use your existing radio |
| Software TNC (Direwolf) | Any radio with audio output + computer | Free software | Base station or laptop-based operation |
| Tracker only | Mobilinkd, Byonics TinyTrak | $50–150 | Vehicle tracking without display |
| Fill-in digipeater | Raspberry Pi + radio + Direwolf | $100–200 | Extending coverage in dead zones |
Do I need a GPS for APRS?
A GPS receiver is required for position reporting. Most dedicated APRS radios have GPS built in. For radios without built-in GPS, a Mobilinkd TNC3 includes GPS, or you can connect an external USB GPS to a laptop running Direwolf. Without GPS you can still manually enter your position as a fixed station, which is appropriate for a stationary EOC.
What is the difference between a digipeater and an iGate?
A digipeater receives APRS packets and retransmits them on the same frequency, extending range within the local radio network — no internet needed. An iGate receives packets and uploads them to the APRS-IS internet database, making them visible on aprs.fi. In a disaster with no internet, digipeaters keep local APRS functional for radio-to-radio tracking without iGates.
Can I monitor APRS without transmitting?
Yes — you can run Direwolf or connect an APRS-capable radio to a computer to receive and decode local traffic without transmitting. A receive-only iGate configuration is common for home stations that want to contribute to the network without being a full digipeater.
What software do I need for APRS on a laptop?
Direwolf is the most capable free software TNC for APRS, supporting both digipeating and iGate functions. For display and mapping, YAAC (Yet Another APRS Client) and Xastir are popular open-source options. All can receive APRS packets from a radio connected to your computer's sound card and display positions on a map.