APRS Web Tracker — Following Stations Live From Your Browser

An APRS web tracker is a webpage that follows a specific callsign — or a group of callsigns — in real time, drawing the station's current position on a map and updating it within seconds of each new beacon arriving from the worldwide APRS-IS network. Where a browser-based APRS map shows the whole network at once, a web tracker is the same toolkit narrowed down to one moving target: a friend driving across the country, a high-altitude balloon climbing toward the stratosphere, a sailboat crossing the Pacific, an EmComm volunteer on the way to a deployment.

This guide explains how live tracking from a browser actually works, what to expect in terms of update rate and accuracy, where the genuine limits sit, and how to use the APRS World station view to follow a callsign of your own.

The Core Idea

Every APRS station that beacons its position transmits a short packet containing — at minimum — its callsign, a latitude, a longitude, and a symbol code. That packet either makes it to an internet gateway (an iGate) directly or after one or two digipeater hops, and once on the gateway, it is uploaded into APRS-IS. From APRS-IS, any subscribed client can pick it up. A web tracker is just that — an APRS-IS client packaged as a webpage.

The flow looks like this:

1. The station's radio beacons on the local APRS frequency (commonly 144.800 MHz in IARU Region 1, 144.390 MHz in Region 2, varied in Region 3). See our frequency-by-country reference for the full table.
2. A nearby iGate hears the packet, decodes it, and uploads it to APRS-IS over TCP.
3. A backend service (in our case, the APRS World gateway at api.aprs.world) holds a persistent TCP connection to APRS-IS, parses every packet it sees, and writes the relevant fields to a database.
4. A browser connects to that backend over WebSocket or HTTPS, asks for the latest position of a specific callsign, and renders it on a MapLibre vector map.

End-to-end latency from PTT release to "marker moves on the map" is typically one to three seconds. Most of that is the time the radio spends keying up, the AX.25 frame on the air, and the iGate's debounce; the internet and the database hop together usually account for under 500 ms.

What a Web Tracker Shows You

A good APRS web tracker — including the APRS World station page — surfaces six categories of information per callsign:

• Current position. Latitude and longitude, with the canonical APRS symbol rendered at the right spot on the map. A blue dot for a boat, a red triangle for a balloon, a small car icon for a mobile rig, a house for a fixed station.
• Course and speed. Optional fields in the APRS spec. Mobile beacons usually include both — a heading in degrees and a speed in knots — which lets the tracker draw a directional arrow and project a likely next-position cone.
• Altitude. Optional too, but ubiquitous on balloon trackers. Combined with timestamp this produces a vertical-rate plot, which is the single most useful diagnostic for a balloon flight.
• Recent path. A sparse polyline of the last few hours of positions, so you can see where the station has been as well as where it is. Path density is a function of how often the station beacons (every two minutes for a typical mobile, every fifteen seconds for a balloon at apogee, every thirty minutes for a fixed weather station).
• Telemetry and weather. If the station beacons weather (temperature, humidity, wind, rain, pressure) or telemetry (up to five analog channels, eight binary), the tracker should show the latest values and a small chart of the recent series.
• Status, comment, and device. Free-form text the operator chose to embed, and the device firmware signature extracted from the path or a TOCALL — useful for spotting a Kenwood TH-D74 versus a LightAPRS-W versus a TinyTrak4.

A tracker that surfaces only the position and skips course/speed/altitude/telemetry is leaving most of the protocol's information on the floor.

Update Rate — What Is Realistic

A frequent expectation, especially from people coming to APRS from commercial GPS-tracker products, is that the map should "always be live, always now". APRS is genuinely fast, but it is not GPS-grade telemetry. A few things to set expectations:

• Mobile stations beacon every one to ten minutes, usually using a SmartBeaconing algorithm that increases beacon rate when speed or heading changes sharply. At a steady cruise on a highway, you should expect a position fix every two to five minutes.
• Fixed stations beacon every fifteen to thirty minutes. They do not move, so there is little point in transmitting more often.
• High-altitude balloons beacon every fifteen to sixty seconds during a flight and revert to slower intervals on the ground. Some carry a secondary tracker on a different frequency for redundancy.
• Weather stations beacon every five to ten minutes, often with a smaller and dedicated payload.

A web tracker that updates "live" can only update as fast as the underlying station beacons. If the marker has not moved in three minutes, in nearly every case the station has not transmitted a new packet — not that the tracker is broken.

Accuracy and the Long Tail of Edge Cases

Most APRS positions are accurate to within ten metres because they come from a GPS chip with a clear sky view. A non-trivial minority are not:

• Hand-typed home coordinates can be inaccurate by a few hundred metres if the operator rounded.
• Maidenhead grid square positions resolve to the centre of a 6-character grid (~5 km on a side) or a 4-character grid (~150 km on a side). Some clients still beacon grid squares.
• Compressed format truncation can lose a few metres of precision but is otherwise reliable.
• Stale packets in APRS-IS — a station that disconnected hours ago can have its last-known position re-emitted by a misconfigured iGate. Most modern viewers drop stations that have not been heard for several hours, which is why a callsign you tracked yesterday may not appear today.

Position accuracy is not a property of the tracker; it is a property of the source packet. A web tracker should display the timestamp prominently so you can judge whether the marker on the map represents the station "now" or "three hours ago".

History Depth

APRS-IS itself has no memory — it is a live mirror, not an archive. History depth depends entirely on the backend the web tracker is built on. For reference, the APRS World backend keeps:

• Raw packets for 24 hours (for replay and debugging).
• Position history for 30 days (per the database retention policy).
• Telemetry for 90 days.
• Messages indefinitely (subject to operator request to delete).

A station's page on aprs.world therefore shows you the last 30 days of where it went. Older history is gone — by design, because storing every position of every station forever is both a privacy concern and a database-cost problem.

Permalink and Embedding

A web tracker earns its keep when its URLs are stable. The aprs.world station page lives at https://aprs.world/station/<CALLSIGN> — copy it, paste it into a chat window, and the recipient lands on the same view without any redirect or session setup. You can bookmark it, share it on a forum, embed it in a club website, or wire it into a dashboard.

For builders, the same data is available under the public API at https://api.aprs.world. Hit GET /api/positions/<CALLSIGN> and you get the same JSON the webpage uses. There is no API key, no rate sign-up, no throttling beyond polite per-IP limits — it is the same backend the map uses, exposed straight.

Tracking Yourself

If you want to be the station on the other end — visible to anyone with a web tracker — the path is straightforward:

1. Get a valid amateur radio licence for your country.
2. Pick a radio path: an APRS-capable handheld (Yaesu FT3DR, Kenwood TH-D75), a phone-plus-radio combination running the APRS World mobile app, or a dedicated tracker like a LightAPRS or PicoAPRS.
3. Configure your callsign, an appropriate APRS symbol, and the country's APRS frequency.
4. Press beacon. Within a few seconds, your callsign should appear on aprs.world and any other APRS-IS-fed tracker.

You do not need an iGate, a passcode, or any internet account on your end. The volunteer iGate network handles the upload, and the APRS World backend handles the visualization.

Where to Go Next

• APRS Map in Your Browser — the broader pattern this guide is a slice of.
• APRS Alternatives — how aprs.world fits next to aprs.fi and other clients.
• APRS FAQ — quick answers to the most common questions.
• What is APRS? — the protocol background, if you have not read it yet.