Mac's web site
APRS is an abbreviation for Automatic Packet Reporting System, and it is a graphical method of broadcasting positioning information in "real time" from packet radio-equipped stations. It was originally designed by Bob Bruninga WB4APR in the early 90's, but it has seen explosive growth in the last few years due to excellent software such as UI-View and Kenwood's APRS enabled rigs.
People often ask why get involved with using APRS, which I find rather bemusing. I often wonder why we are also not asking each other to justify why we rag-chew while mobile or play with getting signals around the world. At least with APRS you can see other people exist, when calling frequencies are often silent all evening. Whether you get hooked or not will be for your own reasons, all I ask is that you give it a try for a few days and see for yourself. It does not even need to cost anything, presuming that you already have a receiver or transceiver on 2m and a PC.
A screen grab from my home station
When APRS equipped stations send latitude and longitude information, their locations are instantly shown on a map on your PC screen. As well as the actual location, the course, speed and altitude of the station can also be included.
Even the US Space Shuttle has used APRS, with stations down here on the ground literally "watching" it, or at least its position, on their PC screen as it goes overhead. Many stations have also used the digipeater on board PCSAT, a purpose built satellite, to relay their APRS positions over a wide area. PCSAT was developed by students from the US Naval Academy and it was built entirely from standard amateur equipment for a total cost of $30,000 including the launch.
PCSAT and the "team"
UK emergency groups such as Raynet are a "natural" for APRS and it has been used extensively in Berkshire for support of the user services, such as St. John Ambulance.
I find that APRS provides an excellent indication of changes in radio propagation on VHF and over time you can build up a accurate picture of coverage from your home station.
What do I need?
There's software readily available for DOS, Windows, Apple and Palm PDAs. Take a look at www.tapr.org/ if you'd like to download the latest versions of APRS and try them out. All the software I've detailed is either shareware, freeware, or public domain, so you can try it out without first putting your hand in your pocket. I would strongly recommend UI-View written by Roger Barker G4IDE. A link to a mirror of Roger's original site is on my LINKS page. Sadly Roger died of cancer on the 8 September 2004, but I am sure that such an advanced and user friendly software application will continue to be the best in the world for many years to come. Add-on utilities continue to be written and enhanced, plus the "family of UI-View users" is continuing to support it via the Yahoo eGroup.
To take a look at what's on the air right now, point your browser at www.apritch.myby.co.uk/netaprsuk.htm (Use page up or down to zoom and alt-click to centre the map)
Running the software (See my other APRS page for how to set up
Do I need a GPS receiver?
APRS while you are on the move
The TNC (or TinyTrak) then periodically automatically beacons APRS position reports, at intervals you've set in your TNC, from the virtually continuous NMEA data stream sent by the GPS to the TNC. Such stations are called 'trackers' and many stations around the world have also added such a system to their car. You could of course add one to yours, your partner could then see where your are at any time and get your meal ready when you arrive home from work! One station in the USA even watched his stolen car being driven across town on his APRS map. The police couldn't believe it when he told them his car was still on the move and that he was tracking it! I watched my car being "test driven" by a garage mechanic at 80 mph in a 30 mph limit, past a school. I complained when I collected the car at the end of the day and hence saved the £20 charge for the test.
Any GPS receiver capable of outputting its data in standard NMEA-0183 format can be connected, and the position information sent by the GPS to the computer will automatically place you on the map.
Messaging, position intervals and digipeating
Each new message line is transmitted immediately, then a few seconds later. After every transmission, the period is increased, until an ACKnowledgement message is received.
To get your APRS packets that bit further, many stations have set up specific digipeaters covering given areas. Individual stations can of course also be used as digipeaters and
in the United Kingdom they would set their software 'Alias' to
Wide-area digipeaters are normally set to digipeat stations that have "WIDEn-N" as their UNPROTO path (where n and N are a number between 1 and a maximum of 7 e.g. WIDE3-3). In the UK many stations in the past used and alternative to WIDEn-N, called TRACEn-N e.g. TRACE3-3. TRACEn-N was used so that receiving stations can see which digipeaters the beacon has travelled via. However many digipeater owners have now modified their software so that WIDEn-N also traceable. Each digipeater will add its own callsign and decrement the number by one e.g.
12:59:05T G4IQI>APU25J,WIDE3-3,RFONLY <UI C Len=60>:
This tells me that my home station transmitted a beacon at 12:59 and 5 seconds, it was retransmitted by my local wide area digi MB7UJ, then G1GQJ heard MB7UJ's retransmission.
PLEASE NOTE THAT WIDE4-4 UP TO WIDE7-7 IS COMMONLY USED IN THE UK, HOWEVER IN MORE DENSELY USED AREAS WIDE2-2, OR WIDE3-3 SHOULD BE USED.
It is possible to use WIDEn-N to allow your beacon to go via up to 7 digipeaters. Some digipeaters will not add its callsign to the path. The following example shows a mobile station using an UNPROTO of WIDE1-1,WIDE3-3. It was first digipeated by MB7UJ. However it is not possible to identify all the three WIDE digipeaters.
13:01:01R G3XYZ-9>UP4RVR,MB7UJ*,WIDE3-3 <UI R Len=15>:
If you compare the example above, you will also notice that the second line is also very different. The beacon from my home location shows the latitude and longitude in an uncompressed format that can be easily read. The beacon from G4XYZ's vehicle is in a compressed format known as MIC-E. With MIC-E transmissions the latitude, longitude, speed direction etc. are contained in both the second line and in UP4RVR (this is called the destination address field). UI-View can also compress its beacons as can be seen in the following examples from my home station. It is worth turning on Compressed beacon as it reduces the amount of data and therefore increases the capacity of the network. It should be noted that this is not the same as MIC-E compression:
Compressed beacon by UI-View:
The destination address field in the above two example beacons is used to identify the software type and version e.g. APU25J is for 32 bit UI-View version 1.99. It is also possible to use another encoding format which uses raw GPS information.
Raw GPS beacon:
Within the current UK licence it is permitted for any station to port beacons from radio onto the internet servers, however to transmit information from the internet onto radio requires a Notice of Variation (NoV). It is very easy to overload the radio frequency with the vast amount of beacons on the internet, so this should not even be considered without a lot of experience of local conditions and without the agreement from other local stations. The distance that these internet ported transmissions should always be very limited and not normally sent via the digipeaters.
The best Windows APRS software in the world - UI-View
UI-View screenshot. Click on the image to see it at higher resolution (96kb).
The program can be used with virtually any type of packet hardware, or with AGWPE. This means you can use packet modems, or your sound card running AGWPE software. UI-View's name is derived from the fact that it does everything via UI (Unnumbered Information) frames, e.g. beacons.
What's the difference between UI-View and APRS?
With that, have fun, and enjoy getting going with APRS
This information was partially based on an article written by G4HCL with additional sections and updates by G4IQI.