APRS

APRS
Stands for	Automatic Packet Reporting System
Created by	Bob Bruninga, WB4APR
Mode type	Digital data, AX.25 packet
Data rate	1200 baud audio tones over FM (VHF)
Frequencies
North America	144.390 MHz
Europe	144.800 MHz
Space station	ISS digipeater: 145.825 or 437.825 MHz (437.825 MHz as of October 2026; check the ARISS status page)
Elsewhere	Varies; check the local band plan
Network
Relays	Digipeaters on the air; iGates to the internet
Popular map	aprs.fi

APRS, the Automatic Packet Reporting System, is a shared amateur data network for exchanging short, real-time information about what is happening nearby: where stations are, the local weather, the location of events and objects, and brief text messages. It was developed by Bob Bruninga, WB4APR, a senior research engineer at the United States Naval Academy, who began work on it in the 1980s and introduced it under the APRS name in the early 1990s. In North America it runs on a single frequency, 144.390 MHz on the 2-meter band, where every station can hear every other station in range, and through internet gateways its traffic appears on public maps such as aprs.fi.

Bruninga, who died in 2022, often pointed out that the "P" stands for packet, not position. Although APRS is best known for putting moving vehicles on a map, he intended it as a tactical tool for sharing any information of immediate local value.

History

APRS grew out of a map program Bruninga wrote in 1982 on an Apple II computer to plot the positions of US Navy ships. A few years later he adapted the idea for packet radio as the Connectionless Emergency Traffic System (CETS), which ran on Commodore VIC-20 and C64 computers and was used to support an endurance race. The software moved to the IBM PC in 1988 and took the name APRS in 1992.

Bruninga also founded the Appalachian Trail Golden Packet event, in which APRS stations are set up along the trail from Georgia to Maine each July, and he mentored Naval Academy midshipmen who built amateur satellites, starting with PCsat in 2001. PCsat was the first satellite to report its own GPS position directly to users. Dayton Hamvention gave him its Technical Excellence Award in 1998, and he died on February 7, 2022, at 73.

How it works

A mobile station's APRS position packet on 144.390 MHz is relayed on the same frequency by a digipeater on a high site and passed by an iGate to the APRS-IS servers, which feed public maps such as aprs.fi.

APRS stations send packets, short bursts of data in the AX.25 packet radio format, at 1200 baud over an ordinary FM radio. Unlike connected-mode packet radio, most APRS packets aren't sent to one particular station and acknowledged; they are broadcast for every station in range to decode and display, much as everyone on a voice net hears every check-in.

Two kinds of stations extend the network:

Digipeaters (digital repeaters) receive a packet and retransmit it on the same frequency, usually from a high site, so it reaches stations beyond line of sight. A setting in each packet called the path limits how many times it is relayed. For a mobile or portable station the usual recommended path is WIDE1-1,WIDE2-1, which allows up to two hops; longer paths flood the shared channel for everyone.
iGates (internet gateways) hear packets and pass them to the APRS Internet Service (APRS-IS), a network of servers that makes them visible worldwide. Some iGates also send messages from the internet back out on the air to the station they are addressed to.

Because everything shares one frequency, each station transmits only occasionally. Trackers in vehicles commonly use SmartBeaconing, which sends position reports more often at speed and when turning, and less often when parked.

What APRS carries

Position reports, from a GPS or a fixed location, with a symbol showing what the station is: a car, a house, a hiker, a boat or a balloon.
Weather. Home weather stations report temperature, wind, rain and pressure. Many also feed the Citizen Weather Observer Program, which passes the data to NOAA for use in forecasting.
Messages, short texts from one station to another that are acknowledged when received, plus bulletins and announcements addressed to everyone. Unlike email, APRS does not store a message for a station that is off the air.
Objects, such as a net control station, a shelter or a marathon aid station, placed on the map by one operator for all to see.
Telemetry and status text from balloons, satellites and remote sensors.

At public-service events and in emergency communications, APRS lets net control see where every vehicle is at a glance. The D-STAR digital voice system can carry GPS positions as well, and gateways pass them into the APRS network.

SSIDs

An APRS station is identified by its call sign plus an optional SSID (secondary station identifier), a number from 1 to 15 after a hyphen, so that one ham can run several stations at once. A widely followed convention uses the SSID to hint at the kind of station:

SSID	Usual meaning
None	Home station
-7	Handheld radio
-8	Boat or RV
-9	Mobile, usually a car
-10	Internet link or gateway
-11	Balloon or aircraft
-13	Weather station

The convention is only a guide. Map software uses the symbol in the packet, not the SSID, to choose the icon.

Getting on APRS

Some handhelds and mobiles from Kenwood and Yaesu have APRS built in, with a GPS receiver and a screen for messages.
Any FM radio can be used with a stand-alone tracker, a hardware TNC (terminal node controller), or a computer or phone running a software modem such as Dire Wolf. APRSdroid is a popular Android app.
To listen only, a software-defined radio tuned to 144.390 MHz with decoding software shows the local traffic.

After setting up a tracker, look up your call sign and SSID on aprs.fi. Its raw packet view shows which digipeaters and iGates heard you, which is the quickest way to find out whether your station is getting out.

External links

APRS, Bob Bruninga's APRS site, now kept for historical reference
aprs.fi, live APRS map
APRS: Putting ham radio on the map by G4ILO