APRS (Automatic Packet Reporting System) was developed in the 1980s by the American Bob Bruninga WB4APR and is now a registered trademark. It is an operating mode based on the Packet Radio Standard. The aim is digital two-way communication that makes short messages, object information, position data (GPS), weather data and much more available to a wide audience. APRS is therefore much more than just a way of tracking an object and that is why the letter P in APRS stands for “packet” and not, as is often mistakenly used, for “position”!
The APRS packets are transmitted in Europe on the frequency 144.800 MHz and can be received by other stations directly or via digipeater (Digi). It is also possible for the packets to reach the Internet via an I-Gate (Internet Gateway), where they can be viewed on a map, among other things. While a valid amateur radio license is required for HF transmissions from APRS, the data can be viewed on the Internet by anyone.
According to Bob WB4APR’s website, the APRS community has over 40,000 followers worldwide. When will you be one of them?
How does APRS work?
As already mentioned at the beginning, APRS is a further development of the packet radio protocol AX.25. However, the transmission of APRS packets does not require a connect as is usually the case with packet radio. The packets are transmitted directly on the 144.800 MHz frequency (Europe) via a 1200bps TNC in AFSK modulation mode. As no connect is required, there is no guarantee of reception.
The transmitted packets can be received directly by other stations. Two special types of APRS are transmissions via the ISS space station or operation via a shortwave station.
Digipeaters (or Digi for short) are used to increase the propagation radius. A digi receives the APRS packets and sends them out again (broadcasting). The special forms of digipeaters and the risk of overloading the APRS network will be discussed later.
In addition to HF broadcasting, APRS data can also be viewed on the Internet. The packets transmitted via HF reach the Internet via I-gates (Internet gateways). An I-gate is a digipeater that is connected to the Internet. This data can then be displayed on maps (e.g. on aprs.fi) or evaluated by computer programs such as “UI View”. It is also possible to track the path of a station (car, pedestrian, etc.). Weather data can also be evaluated and displayed graphically. It is also possible to send short messages or e-mails.
The other way round, Internet to HF, is also possible. In this case, however, only messages should be forwarded in order to avoid an unnecessary load on the channel.
Standard APRS frequencies in Europe
| Beschreibung | Frequenz | Bemerkung |
| Normale APRS Frequenz | 144.800 MHz | Voice Alert: 123,0 Hz CTCSS |
| ISS | 145.825 MHz | Up- und Downlink |
| 20m Kurzwelle | 14.103 MHz | 300 Baud / LSB |
| 40m Kurzwelle | 7.035 MHz | 300 Baud / LSB |
What you can do with APRS
Some of the possibilities of APRS have already been mentioned. But there are also many other ways to communicate via APRS and new ideas are constantly being added.
The following list shows the great variety:
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- Tracking the current weather situation thanks to the comparison of different weather stations
- Sending short messages “SMS” without a cell phone
- Finding a target by approaching an object (e.g. fieldday location)
- Marking of important locations such as hospitals, amateur radio stores, etc.
- Tracking e.g. of a vehicle on the Internet (wife can see how long it will be until the husband is home)
- Emergency call system with localization option (emergency beacon)
- Monitoring and evaluation of telemetry data
- Information from local repeaters and the direct QSY option (with suitable device)
- Find out more about a YL or an OM thanks to a direct query of the QRZ database
- Even non-radio amateurs can track APRS stations via websites such as aprs.fi
Operate APRS
How to operate APRS
There are many different ways to operate APRS. It very much depends on whether you only want to monitor other stations or whether you also want to actively transmit data yourself. Another decisive factor is how keen you are to experiment. In addition to commercially manufactured radios with integrated APRS functionality, there are numerous do-it-yourself projects. Interfaces between the radio, TNC and GPS also pose some challenges.
Experienced APRS users also have the option of operating a digipeater or an IGate.
The following is a non-exhaustive list of ways to become QRV in APRS:
- Website aprs.fi (view only, also for non-amateur radio operators)
- Computer with APRS software (e.g. UI-View), TNC and 2m radio
- Kenwood TM-D710 (mobile radio with APRS function), a GPS receiver is also required
- Yaesu FTM-400 (mobile radio with APRS function) GPS is already integrated
- Kenwood TH-D72 (handheld radio with APRS function) GPS is already integrated
- Yaesu VX-8GE (handheld radio with APRS function) GPS is already integrated
- Tracker (e.g. TinyTrack from Byonics or Opentracker) with 2m radio and GPS receiver
- IPhone with APRS app (e.g. iBCNU), a valid amateur radio call sign is required for full functionality
- Special tracker for weather station (e.g. AnyFrog or WX3in1) with 2m radio and weather station
- Advanced users can extend the APRS network with a digipeater (repeater for APRS data) or an IGate (interface to the Internet).
Digipeater
In APRS, a basic distinction is made between two types of digipeater (digi). These are so-called WIDE digis and fill-in digis.
There is also a third type, the IGate. In the broadest sense, an IGate can also be regarded as a Digi, as it forwards the packets to the Internet.
The different types of digi are briefly described below.
WIDE digi
The WIDE digi is the classic type of digipeater. It forwards all packets with WIDE1-1 to WIDE7-7. As path settings with more than 3 hops (WIDE3-3) do not correspond to current practice, there are more and more digipeaters that shorten the path to 3 hops. A WIDE digi is usually in an exposed location so that it has the largest possible catchment area.
Fill-in digi
The fill-in digi serves as a feeder. It is set up at locations where no WIDE Digi can be reached directly. Its function is to send the received parcels to the WIDE Digi.
A Fill-in Digi can only be addressed with the path setting WIDE1-1. Other path settings are ignored.
IGate
The IGate is required to connect APRS to the Internet. Packets received via HF are forwarded to the Internet, where they can be viewed on special websites.
However, modern IGates can also be routed from the Internet to HF. This route is mainly used to send messages.
IGates are often combined with a digipeater.
Path settings
So that the transmitted APRS beacons can not only be distributed locally, there are so-called digipeaters (Digi). These digis forward the received packets so that they can be received by other stations or other digis. If such forwarding were to take place indefinitely, the 144.800 MHz frequency would be more than overloaded within a very short time.
To prevent this from happening, there are so-called path settings. These path settings restrict the forwarding of a packet via digipeater. This is also referred to as hops.
The packets should be distributed within a useful radius of approx. 50 km via HF. They should also reach the Internet via an IGate (HF – Internet interface) so that anyone can see the beacon on aprs.fi, for example.
These path settings are also referred to as the New n-N paradigm. Bob Bruninga WB4APR has created this paradigm to counteract the many packet collisions on the APRS frequency.
Essentially, it is about the following points:
- Abandon the outdated path rules RELAY, WIDE, TRACE
- Consistent use of WIDEn-N
- Normally an N of maximum 2 is sufficient, in regions with few digis an N of 3 can also be used
- Fixed stations address their next Digi directly
Basic settings:
| Station | WIDE-Digi erreichbar | Nur Fill-in-Digi erreichbar | Intervall |
| fest | Digicall ist bekannt:regulär: Digicall,WIDE2-1 maximal: Digicall, WIDE3-2 |
Digicall ist bekannt: |
30 min. |
| fest |
falls Digicall unbekannt: |
falls Digicall unbekannt: |
30 min. |
| beweglich |
regulär: WIDE1-1,WIDE2-2 |
regulär: WIDE1-1,WIDE2-2 |
1 min. |
| Objekt | WIDE2-1 oder kein Hop | WIDE1-1 oder kein Hop | 10 min. |
| Wetter | WIDE2-2 | WIDE1-1,WIDE2-1 | 15 min. |
| Digipeater | WIDE3-3 / proportionale Pfade | 30 min. |
Quelle: www.aprs-dl.de
These path settings are a recommendation which is also supported by the European APRS community.
Modern digipeaters are now able to shorten the number of hops so that the APRS frequency remains “clean”.
Further information / links
| Link | Beschreibung |
| www.aprs.org | Website of Bob Bruninga WB4APR |
| www.aprs-dl.de | German website with extensive information on APRS |
| www.swiss-artg.ch | A recommendation of the SWISS-ARTG APRS working group regarding APRS APRS settings |
| aprs.fi | Display of APRS data on the Internet |
| www.ui-view.org | APRS software for Windows |
| www.yaesu.com | Manufacturers of APRS-compatible radios (e.g. VX8, FTM-350 etc.) |
| www.kenwood.de | Manufacturer of APRS-compatible radios (e.g. TH-D72, TM-D710 etc.) |
| www.byonics.com | US manufacturer of trackers, etc. |
| www.hinztec.de | Manufacturer of trackers for weather stations (anyfrog), etc. |
| www.avmap.it | Manufacturer of APRS-compatible navigation devices (e.g. for Kenwood TM-D710) |