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Amateur Posistion Reporting System (APRS)

What is APRS?

  • APRS is a protocol.
  • The APRS protocol allows the sharing of data pertinent to an area of interest.

These areas of interest can be as small as a building to the size of a continent. Information shared can include anything from a position to weather data, to dynamic boundaries, to email, to telemetry, to custom data types and more. You can even play chess by APRS. There are so many things that can be done with APRS, it's rather difficult to describe. A generalized description often used is similar to:

A tactical, real time situation awareness system.

For more information and detail on the many aspects of APRS, visit any of the many available web sites for some ideas. A few of the more popular sites include:

Using google search and a little effort, you'll find many viewpoints, opinions, tools and ideas. Much more than I can cover here!

Even if you were to read every APRS site on the Internet, you'd likely not have a full perspective of all the way that it can or is being used for. By design, APRS is intended to meet YOUR needs.

The closest we have to an Official APRS "Bible" would be the APRS Spec v 1.0.1 (Aug 31, 2000) hosted at TAPR. "The Spec", created by the APRS Working Group, was an attempt to define the on the air protocols.

The spec was valid at the time of publication. At that time it was THE definitive guide of how to 'do' APRS on the air. As an active and dynamic technology, APRS changes and develops with time. You can find clues to these changes on Bob's web site - but it may take a bit of digging. Sadly, the spec itself has not been kept up to date with current practices - but as as core guide, remains very useful.

Using APRS in Wyoming

On the air

The national APRS frequency of 144.390 (FM AFSK) is used throughout Wyoming. If you've a TNC or can connect the audio output of your radio to your PC's sound card - you're ready to get involved. Even if you don't have a radio - just a PC and an internet connection, you can join in.

Suggested paths (RF only)

Fixed Stations

Nothing longer than WIDE2-2 (2 hops) is suggested for anywhere in WY. What I-gates we have are relatively close (network wise) to the higher level digipeaters.

Mobile Stations

Nothing longer than WIDE3-3 (3 hops) is suggested for anywhere in WY. In many places, 2 hops will suffice.

If you can't get to an I-gate - usually - in 2 hops, you're not likely to get to one. Of course, this is a generalization and a suggested start point. If you *know* you need a longer path to reach a desired station, by all means use it! But, if you habitually use excessive paths - causing congestion on the RF network - don't be surprised to find your access has been limited by the digi operators. Nothing personal - but we do have to protect the system. The capacity of the RF network is limited.

If you have questions about using a good path, please - do ask!


A digipeater is a "Digital Repeater", using a 'store and forward' scheme, they repeat what they've heard, extending the effective range of participating stations. Each time a packet, a position report, is digipeated, it's called a 'hop'. It's tempting to use the maximum number of hops to get your packets out there! Don't do this. It creates RF network congestion and is considered bad form. To limit hops, a pathing scheme has been developed.

New Digipeaters

Generally, new digis are always welcome! Please do be aware of your surroundings - if you already have good coverage, adding a new digi doesn't really help anyone and, in fact, may only contribute to RF congestion. But you know your area - be smart and considerate. You're providing a service to your fellow hams. Plan accordingly. If you've any doubts - ask!

Digi Setup

It is recommended that all digipeaters in Wyoming support the new, WIDEn-n path scheme. If you're not familiar with this 'new' scheme - please, ask.


Most WIDEn-n compliant digipeaters often have the option to include their own call in the 'has been digipeated' via section of the TO: frame. The so called "WIDE ID" config. This was originally done as a duplication prevention scheme. However, newer digipeaters have the ability to calculate hash values for the contents of their packets and use these for duplication prevention. As each didipeater configured with "WIDE ID" adds it's call sign to the TO: frame (ie "v WIDE2-2" becomes "v W7VNJ*,WIDE2-1"), growing the packet size at each hop, it takes more and more time to transmit the frame. Fortunately, the current load on the RF network in WY isn't so heavy that this behavior can't be tolerated. But, we are approaching a 'break over' point in growth where needlessly increasing packet sizes will be a very real detriment to all users.

It is suggested to configure all new digipeaters to use "WIDE NOID". This config will simply decrement the 'digipeated' count and retransmit. WIDE2-2 becomes WIDE2-1, etc. And not result in ever increasing packets sizes.

For diagnostic purposes, digipeaters can be configured to use the aliases of TRACE and TRACEn-n. This allows the sender of each packet to force the digipeater to add it's callsign to the TO: frame - in the same manner as "WIDE ID" does - but selectviely - allowing one to see exactly how and where their packet traversed the RF network.

TRACE paths should not be sent out, normally. But configuring your digipeater to support 'TRACE' allows folks to study and troubleshoot the RF network as needed.

Internet Gateways (I-gates)

These are radio/PC combinations that allow packets to flow into the APRS-IS. As well as feed select traffic from the APRS-IS to the RF network. There are several around the state. A few, are setup as 'listen only'.

The Casper I-gate at KA7O-15 feeds local RF traffic to the CSPR-WY.ka7o.net APRS server. This server provides the worldwide APRS Internet System (APRS-IS) feed to the I-gate. Of course, only locally pertinent traffic is gated back to RF. To be gated from APRS-IS to RF, the receiving station must have been heard on RF by the I-gate within the past 30 minutes. A few, select messages are always gated to RF as appropriate. These would include generic destinations, such as WY or SCOUTS and warning notices from the National Weather Service office in Riverton (RIW).

APRS IS Servers

Running an APRS server is an advanced task. You will require a fast, reliable internet connection and server grade hosts. The security and reliability concerns alone all but demand the use of a *nix type server. Intentionally opening your LAN to 'wild' internet connections is risky. APRS-IS servers can be run on Windows systems, but it's not recommended.

For nearly 20 years now, KA7O has run an APRS server for the Rocky Mnt region. You can view the server status at the CSPR-WY server's status page. This server is available and open to all licensed hams in the Rocky Mnt area using the standard APRS-IS ports. You area also welcome to use the 'round robin' server pool at rotate.aprs.net.

Web Client

Web clients are the easiest way for someone to 'dip their toe' into the APRS pond or just take a quick look at what's going on. If you know the callsign of a station, you can see their current position on either of two web sites. The first is Map.Findu.com<callsign-ssid> . For example, to see my -6 station, visit http://map.findu.com/ka7o-6.

The second site, aprs.fi is more general in that it can show all the traffic for an area.

Both use Google maps and the usual map controls work well.


If you've any questions - feel free to ask on the discussion board, at a CARC meeting or on the RM-APRS email reflector hosted at Yahoogroups.com.

APRS Clients

The staggering array of software and devices is simply a testament to the ingenuity of the Amateur Community. Simply keeping up with new projects, updates and new ideas is almost a full time job. Thankfully, the APRS community keeps a good list of what's available.


X Amateur Station Tracking and Information Reporting
This is my personal client of choice. I use this at work, on the road and in the shack. Here's a "step by step" how to that'll guide you in getting Xastir up and running on a Fedora system. Just follow along and enjoy!

The following image is a 'snapshot' showing a few weather stations, my motorcycle, a 'sailboat' and some of the trails recorded during that day.

APRS Activity, Casper 18May 2006


APRS is a registered trademark of APRS Software and Bob Bruninga, WB4APR.