APRS

The APRS system has been around for many decades and was one of the central applications of the packet radio network that existed at the time (1980s, 1990s). The network has largely disappeared, but APRS continues to enjoy great popularity.

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  1. PICOAPRSLITE APRS TRx without enclosure, for balloons
    PICOAPRSLITE APRS TRx without enclosure, for balloons

    Extremely small and lightweight APRS tracker, temperature and air pressure sensor, transmit power 0.5 - 1 W

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    €139.00
    incl. VAT, plus shipping €116.81
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    SKU PICOAPRSLITE
  2. PicoAPRS V3 Holder for cars
    PicoAPRS V3 Holder for cars

    Vehicle mount for PicoAPRS V3 with Velcro strap. Plastic, black

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    €15.80
    incl. VAT, plus shipping €13.28
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    SKU PICO-CLIP_V3

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FAQ

Can I use APRS with any radio?
Yes, as long as the modulation signal is easily accessible for transmission and reception. This works best if the radio has a "Data" socket.
What equipment do I need to use APRS?
A radio, a TNC capable of packet radio and software. Alternatively, you can use the radios from Kenwood: TH-D72, TH-D74, TH-D75, TM-D700, TM-D710 and the AT-D878UV from Anytone. An APRS tracker can also be used to transmit instead of a TNC.
Where can I see the position of an APRS subscriber?
This is very easy to do on the websites https://aprs.fi and https://aprs.to, for example.
How does the data from an APRS transmitter get to the Internet, e.g. to the aprs.to website?
This is done via so-called APRS gateways. Many radio amateurs operate a pure receive gateway. Other stations operate as digipeaters (relay stations) and transmit the data to an APRS-IS server at the same time.
Where can I find out more details about APRS?
The best place is the website of the inventor, Bob Bruninga (WB4APR sk), aprs.org. Here you can find the protocol specification and all other information.

The origins and versatility of APRS: Positioning, data transmission and tactical situational awareness before the digital age

The original idea of APRS is to transmit one's own position and other brief information by radio and to pass it on to other participants either directly or via a suitable infrastructure. Packet radio technology, the radio-based network technology, is used for this purpose. The packet radio method is also referred to as AX.25, based on the "X.25" model. X.25 is the ITU designation for a whole family of data transmission protocols for wide area networks. The "A" in "AX.25" indicates that these procedures were adapted to amateur radio.

The basic idea was initially to determine one's own position via GPS and send it out by radio. At the same time as Packet Radio (1980s), the US GPS satellite system became available to civilian users at a reasonable price.

One of the main drivers of the APRS system was Bob Bruninga, WB4APR (sk), who, together with the Tucson Amateur Packet Radio Group (TAPR), created the standards that allow the APRS network to function to this day. APRS is a registered trademark of Bob Bruninga, WB4APR.

In addition to the own position, other ideas were quickly added, namely to transmit further location-related data and thus generate a tactical situation picture on a map. These are mobile stations, but also fixed objects such as a field day site, an antenna site, a café, a petrol station, etc. Weather data was also added, which is displayed on the map for the location of the weather station. Remember - this was all long before the internet and useful things like Google Maps or Open Street Map!

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Evolution of packet radio technology: from FM devices and modems to innovative trackers and networked digipeaters

To operate packet radio, you need an FM device and a modem (aka TNC, Terminal Node Controller). And, of course, a PC that controls the TNC via a serial interface. This is too much effort in the vehicle. This is why simple systems, so-called trackers, were quickly developed that analyse the data signal from the GPS antenna and convert it into a packet radio modulation together with the callsign and the current status. This audio signal is then sent to the transmitter. A receiver was initially not used.

At that time, the packet radio network consisted of so-called digipeaters, which, like FM relays, were operated at high-altitude locations. In contrast to FM relays, these digipeaters were also networked with each other, ideally via amateur radio on higher bands (23 cm, 13 cm), but also via the first data connections in the telephone network. As mentioned above, this was long before the Internet was easily accessible to the public.

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APRS data worldwide at a glance: The emergence of the APRS Internet Service (APRS-IS) system and its importance for global observation

But who could display and analyse the APRS data? Initially, it was only fixed stations with PCs that could receive the region's signals. Suitable software displayed the received information on a map. But very quickly the need arose to distribute the APRS data over greater distances, ideally nationwide. This became possible with the advent of inexpensive Internet connections, and the APRS-IS (APRS Internet Service) system was created. One of the best-known addresses for this system is https://aprs.fi, a website that records all data from the APRS network and displays it on a map in a web browser. This makes it easy to monitor all moving and fixed APRS stations. And since amateur radio is basically an "open" system, i.e. it works without encryption, this data can be viewed by anyone in the world.

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Efficient collision avoidance in packet radio: ALOHA cycles and the development of tracker-capable systems for improved transmission security

An important technical aspect of packet radio is collision avoidance. In other words, the attempt to avoid the simultaneous transmission of two or more uncoordinated stations. There are various approaches to this in commercial network technology. The so-called ALOHA cycle, also known as CSMA/CA, has become established. In simplified terms, it works like this: First listen to see if the channel is free. If yes - transmit. If not, wait a short random time and then try again. This works quite well as long as the number of participants in a region remains manageable and everyone adheres to certain rules. Other, fairer and safer procedures were too time-consuming and not easy to realise with amateur resources.

However, the above-mentioned trackers have a problem - they do not have a receiver with which they can check the channel for activity. This is why these devices were quickly replaced by improved systems that could also listen. And the equipment manufacturers also jumped on the APRS bandwagon. The Kenwood TM-D700 was one of the first mobile devices that, together with an optional GPS antenna, represented a complete APRS radio system. Other manufacturers followed suit, and today Yaesu, Alinco, Anytone and Kenwood, among others, offer mobile and handheld radios that provide APRS directly. The handheld radios usually have a GPS/GNSS antenna built in.

The evolution of packet radio: Gateways as modern intermediaries for APRS data in the global network

Now that the packet radio network has long passed its peak in the 1990s and has largely disappeared, the digipeaters that transmitted the APRS data received have also disappeared. Today, this task is performed by so-called gateways. These are receivers or transmitting amateur radio stations that listen on a fixed frequency and transmit the received APRS data to the Internet. The APRS-IS system also continues to exist and ensures the worldwide transmission of the corresponding data. If you are interested, you can find all the important information on https://www.aprs-is.net/. However, you only need this background knowledge if you are a software developer, not as the operator of a gateway or an APRS station.

There are also gateways that receive information from the APRS-IS server and send it out on the radio side in order to transmit the position data of other stations. Simple procedures ensure that only regionally relevant data is transmitted. This also reduces the amount of data, as the APRS-IS system ultimately collates the data from all participants worldwide. You don't want to forward them all unfiltered via a gateway...

The transmitted data has changed little since its introduction. As the length of the APRS data packet is limited, a lot of work is done with compression and fixed coding of individual bits. In addition to the callsigns and the position, simple, predefined status messages are transmitted. In APRS jargon, these are called "MIC-E" statuses. However, free texts are also possible, although these are quite short (approx. 100 characters). Participants usually use this option to transmit their first name or similar information. Specialised systems can also record measurement data and transmit it via APRS. For example, the operating status of an amateur radio relay can be transmitted by radio.

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Callsigns and identification in APRS: The importance of SSIDs and symbols for a versatile map display

The callsign is of course particularly important in APRS data. After all, we radio amateurs have to label our transmissions with our own callsign. The packet radio system allows several devices to participate in the network at the same time. For this purpose, the so-called "Secondary Station Identifier" (SSID) is appended to the callsign; the permissible value range is from 0 to 15. This procedure with the SSIDs is also used with APRS, and here the SSIDs have gained an additional meaning. They identify the type of station, i.e. whether it is a vehicle, a pedestrian or another system. At the same time, the data packet encodes the symbol with which the station is to be displayed on a map. A very versatile system has been established here that leaves nothing to be desired.

New ways in data distribution: The "New-N Paradigm" in APRS and its role in effective range control

This procedure became necessary in order to limit the range of the data. The popularity of APRS and the density of stations in different regions meant that some gateways were completely overloaded with data traffic, with some of the data coming from distant regions and being irrelevant to the local situation. The 'New-N Paradigm' tells a gateway or digipeater whether the data packet should still be forwarded or not. Only information such as "WIDE1-1" or "WIDE2-2" is given as the digipeater path. Each digipeater counts down the number at the end of the path specification; if zero is reached, the packet is no longer forwarded and is therefore discarded. This is the only way to ensure that all participants can transmit their data even in densely populated regions. We radio amateurs are already very familiar with this mutual consideration from other operating modes.

The timeless fascination of APRS: the durability and appeal of a seemingly outdated but proven radio transmission system

APRS may seem a little outdated. However, its popularity shows that there is a great deal of interest in continuing to use such older methods. The reason for this is the simplicity of the system, the availability of easy-to-use devices and also the sophistication of the APRS protocol. APRS will continue to inspire us radio amateurs for a long time to come.