Amateur Position Reporting System

(APRS)


What is APRS?

An Automatic Packet/Position Reporting System (APRS) using maps and other data displays transforms ordinary packet radiointo a real-time communications and display system.

It makes possible, for example, the tracking of mobile communications systems e.g. motor vehicles, boats, aircraft, communications satellites etc. - it is a global network.

How Does it Work?

A radio beacon is transmitted at regular intervals, usually on 144.800MHz. The beacon consists of a data string containing:

The originating stations callsign, positional information (longitude/latitude - usually derived from a gps) and some additional data, such as a symbol to identify the station type eg fixed, mobile or weather etc.

In the case of a weather station, positional data will be transmitted as well as weather data, such as wind speed/direction, temperature, barometric pressure and rainfall etc.

In the case of mobile stations the longitude/latitude may be derived from an onboard Global Positioning System (GPS), linked to the radio, and may provide the vehicles speed, direction and altitude.

As a general rule, fixed stations beacon every 30 minutes and mobiles every 3 minutes.

The transmitted beacons are then re-transmitted by all the stations in range of the originating station. There is a limit to the number of hops each beacon can make, but over flat terrain a radius of 100 miles is easily achievable with 3 or 4 hops from the originating station.

If there is a  fixed station within the coverage area of a mobile station  which is connected to the internet and offering a 'gateway' service, then beacons can be transmitted world-wide.

My APRS station MB7UEK, an internet gateway,has now been permanently closed down.

Receiving stations running appropriate software, such as UI-View,can display the symbols on a map, and can watch the progress of mobiles a they move along their route. The software will also provide details such as their speed and direction.

I used to travel regularly for a time from Herne Bay to Aylesham via Brenley Corner and the A2 and was called on the radio by a local amateur who had been watching my progress - he asked if I knew how fast I was going!

Mobile Operation


My last reported mobile position


The symbol chart to the left of the map shows only one of the 2 symbol tables. Full details of the APRS Symbol Set (Rev H) are available online from wa8lmf.net/aprs/APRS_symbols.htm There are also useful notes which explain the format of a standard APRS position report on his site. Just follow this link.

Full APRS Specification in .pdf format