What Is APRS? A Beginner-Friendly Introduction
Definition and Origin of APRS
APRS is an amateur radio-based system for real-time digital communications, and the data it carries can include GPS coordinates, weather station telemetry, text messages, announcements, queries, and other telemetry. APRS data can be displayed on a map, which can show stations, objects, tracks of moving objects, weather stations, search and rescue data, and direction finding data. Think of it as a live, community-powered data network built entirely on top of ham radio infrastructure.
Who Invented APRS and Its History in Amateur Radio
APRS was developed from the late 1980s forward by Bob Bruninga, call sign WB4APR, a senior research engineer at the United States Naval Academy. The initialism "APRS" was derived from his call sign. Bruninga implemented the earliest ancestor of APRS on an Apple II computer in 1982, and this early version was used to map high frequency Navy position reports.
The first significant use of APRS was in 1984, when Bruninga developed a more advanced version on a VIC-20 to report the position and status of horses in a 100-mile endurance run — this early version was known as the Connectionless Emergency Traffic System (CETS). During the early 1990s, CETS evolved into the Automatic Position Reporting System, and with the advent of GPS technology, the name was changed to the Automatic Packet Reporting System. Bruninga maintained the main APRS website until his death in 2022. In March 2022, the APRS Foundation was formed as a not-for-profit with the objective of preservation and advancement of the APRS digital communications protocol.
How APRS Differs from Traditional Packet Radio
As a multi-user data network, APRS is quite different from conventional packet radio. Rather than using connected data streams where stations connect to each other and packets are acknowledged and retransmitted if lost, APRS operates entirely in an unconnected broadcast fashion, using unnumbered AX.25 frames. APRS packets are transmitted for all other stations to hear and use, and packet repeaters called digipeaters form the backbone of the APRS system, using store-and-forward technology to retransmit packets.
Why Ham Radio Operators Use APRS Today
APRS provides situational awareness to all operators of everything that is going on in the local area, whether it be weather reporting, traveler info, direction finding, objects pointing to EchoLink and IRLP, or traffic reporting and emergency response. APRS is well-known technology among hams, with numerous applications in emergency communications, tracking, and weather reporting. Real-time data transmission is at the heart of APRS's appeal — in contrast to Winlink, which stores and forwards messages, APRS packets are instantly received, making it invaluable in emergency and public service settings.
How APRS Works: The Technical Foundation
Understanding the AX.25 Packet Protocol
APRS is transported over the AX.25 protocol using 1200 bit/s Bell 202 AFSK (Audio Frequency-Shift Keying) on frequencies located within the 2-meter amateur band. AX.25 is a data link layer protocol derived from the X.25 standard specifically adapted for amateur radio use. Every APRS packet begins with a source address (your callsign and SSID), destination address, and a payload containing position, message, or telemetry data. The 1200-baud rate keeps packets short and compatible with the narrowband FM radios that most operators already own.
Role of the TNC (Terminal Node Controller) in APRS
APRS exploits the ability of a TNC to transmit beacon packets that carry short strings of alphanumeric characters — a beacon is an unconnected packet. The TNC converts the digital data from your computer or GPS into audio tones that your FM radio can transmit, and it decodes incoming audio tones back into data. An APRS infrastructure comprises a variety of TNC equipment put in place by individual amateur radio operators, including sound cards interfacing a radio to a computer, simple TNCs, and "smart" TNCs.
How Position Beacons and Data Packets Are Transmitted
By taking data from a GPS receiver and incorporating it into beacon packets transmitted by a TNC, you can tell everyone on the network exactly where that GPS receiver is located. Any stations equipped with APRS software will display the position of the receiver on a computer-generated map. A beacon can be set to automatically transmit over the air at fixed intervals — typical intervals are every 5 or 10 minutes. By keeping the packets short and turning off transmitters between sends, many people can share the same frequency, and packets are often sent at slightly random times to avoid packet collisions.
APRS Digipeaters and How They Relay Packets
Digipeaters are essentially a simplex data repeater with an antenna at a high location — the digipeater hears your data on 144.390 MHz, reads the path information on the packets, and then retransmits the information again from a location with much higher altitude and clear of obstructions. All stations operate on the same radio channel, and packets move through the network from digipeater to digipeater, propagating outward from their point of origin. All stations within radio range of each digipeater receive the packet. Unlike most voice repeaters, a digipeater will transmit to and receive from another digipeater, so where a voice repeater gives you a single signal hop, a digipeater can get you two signal hops.
The APRS-IS (Internet Service) Network Explained
Internet gateways (I-Gates) link the radio network to the global APRS Internet System (APRS-IS), so people worldwide can access the information. GPS location data from your compatible radio or APRS device is sent out as a burst of data, with the hope that a nearby digipeater will collect it and forward it along to another repeater or an iGate — if bounced to another repeater, that repeater forwards it along, and eventually your data will be bounced to an iGate, which is a device that transfers your RF data to the Internet. APRS also supports global callsign-to-callsign messaging, bulletins, objects, email, and voice, because every local area is seen by the APRS-IS.
APRS Frequencies: What Channels to Use
North American APRS Frequency: 144.390 MHz
In North America, 144.39 MHz is dedicated throughout the continent. If you tune any 2-meter radio to this frequency you will, eventually, hear what sounds like an old dial-up modem — those are APRS packets. This single shared frequency is the key that makes the APRS network work: every digipeater, iGate, mobile tracker, and weather station in North America uses the same channel, ensuring maximum compatibility and network coverage without any coordination between individual operators.
International APRS Frequencies by Region
The system runs on one shared frequency in each region — 144.390 MHz in North America, 144.800 MHz in Europe, and 145.175 MHz in Australia. Keep in mind that if you are traveling outside of North America with an APRS-enabled device, you will need to change your frequency for that new region. New Zealand uses 144.575 MHz, while much of Southeast Asia, including Colombia, Chile, Indonesia, Malaysia, and Thailand, follows the North American standard of 144.390 MHz. Always check the regional APRS frequency before operating abroad.
HF APRS Frequencies and Use Cases
APRS is not limited to VHF. HF APRS is used by operators who need to share position or status data over much longer distances — particularly useful for maritime, expeditions, and areas with sparse VHF digipeater coverage. Common HF APRS frequencies include 10.151.5 MHz (LSB), 14.103 MHz (USB), and 30 meters at approximately 10.149 MHz. HF propagation conditions affect reliability significantly, so HF APRS is generally used as a backup rather than a primary system. The baud rate on HF is typically 300 baud to suit the narrower bandwidth constraints of HF amateur allocations.
ISS APRS Frequency
Set the frequency for packets to 144.390 MHz in North America for the terrestrial network; the ISS uses 145.825 MHz. This worldwide frequency is maintained by the ARISS program and allows ground stations on any continent to use the ISS as a relay digipeater during a pass overhead.
APRS Equipment: What You Need to Get Started
VHF/UHF Radios Compatible with APRS
A VHF or UHF transceiver is required to send and receive APRS packets — ensure it operates on the 2-meter band from 144–148 MHz for compatibility. Any FM transceiver capable of operating on 144.390 MHz can be used for APRS, from an inexpensive handheld to a high-power mobile rig. The Baofeng UV-5R is a popular option for budget-minded beginners, though its audio characteristics may require careful calibration.
Best TNC Options for APRS Operation
A TNC (Terminal Node Controller) encodes digital signals, and some transceivers have built-in TNCs while others need an external one — examples include the Kantronics KPC/KAM or Kenwood APRS transceivers. Hardware TNCs from manufacturers like Mobilinkd (the TNC3 and TNC4) offer Bluetooth connectivity to smartphones, making them extremely popular for portable and mobile use. The Mobilinkd units pair with any FM radio and connect to Android via APRSDroid or iOS via APRSdroid-compatible apps.
Smartphone and Software TNC Alternatives: Direwolf and APRSDroid
If your radio doesn't have APRS built in, you can connect it to a computer and generate APRS signals via special software — those signals get fed into your radio for transmission and reception of APRS data, which is called a soundcard interface. If you are using a Windows or Linux PC, including a Raspberry Pi, Dire Wolf is the recommended tool. Direwolf can be used as a standalone APRS tracker, digipeater, APRStt gateway, or Internet Gateway (iGate), and it replaces the need for specialized hardware TNCs by utilizing a computer's soundcard interface. Direwolf includes Forward Error Correction (FEC) through FX.25, compatible with existing systems, and can also act as a virtual TNC for applications like APRSIS32, UI-View32, Xastir, and more.
All-in-One APRS Radios: Kenwood, Yaesu, and More
For operators who want a plug-and-play APRS experience, dedicated APRS radios are the gold standard. The Kenwood TM-D710G and TH-D74A are legendary in the APRS community for their robust built-in TNCs, GPS receivers, and full two-way APRS messaging capability. The Kenwood D710 radio shows the station list, and the attached GPS with map display shows the location of other APRS stations. The Yaesu FTM-400XDR and FT3DR also support APRS natively with intuitive menu systems. These all-in-one solutions cost more upfront but offer excellent performance and require minimal configuration.
Budget-Friendly APRS Setup Options
You do not need to spend hundreds of dollars to get on APRS. A basic budget setup can consist of any 2-meter FM handheld radio paired with a Mobilinkd TNC3 (around $90) and the free APRSDroid app on an Android smartphone. Alternatively, a Baofeng UV-5R, a cheap USB sound card interface, and Direwolf running on a Raspberry Pi Zero W can form a complete iGate for under $40 in hardware. Technician-class license holders can participate fully, which makes it perfect for newcomers — you can start learning this digital ecosystem with simple equipment, just a basic handheld radio and a smartphone.
Setting Up Your APRS Station: Step-by-Step
Obtaining Your FCC Amateur Radio License for APRS Operation
All RF transmitting APRS stations require a valid FCC amateur radio license. Technician-class license holders can participate fully in
