Most amateur radio operators probably think of tracking an object on a map when they hear the term APRS but it’s a whole lot more than that. APRS is the Automated Packet Reporting System and it is a powerful tool for situational awareness, emergency communications, and seamless global messaging. I’ve seen firsthand how APRS can keep stations connected across long distances, using a combination of RF and internet, ensuring critical data gets where it needs to go.
I am hooked on this powerful form of packet radio and I can’t recommend it enough. Given what I know now, I would be hesitant to buy a radio that does not have APRS capability.
In this series, I will attempt to bring the many layers of this very robust system into focus, starting with the foundational elements. First we need to understand it’s capabilities and how folks are already using APRS. For this exercise, I urge all licensed hams to sign up for an account on aprs.fi. This gives you access to detailed information about your own tracks and allows you to legally inject messages into the APRS network that could get transmitted via RF from one or more stations around the world.
After you’ve done that, check out my article on Using PinPoint APRS with APRS-IS to learn how can utilize this powerful pair of tools to explore the rich landscape of APRS messages, location beacons, weather updates, and more. You can do this all without a radio. Just be a licensed ham with some time on your hands and a desire to have fun learning this amazing aspect of 2-meter packet radio.
The more I use APRS, the more amazed I become with how immensely useful it is. I think a lot of people dismiss it or never give it a second thought because they don’t understand its power, utility, versatility, and resiliency. Sending a text message from an HT or mobile rig to another radio where the message is then passed to the internet and eventually makes its way to a gateway system that then processes and delivers it to a cell phone user as a standard SMS message is pretty darn cool. This capability alone should interest a lot of folks. Any licensed ham who lives, works, or plays in a remote area where cell phones don’t work reliably should consider becoming very familiar with APRS.
As you can tell, I’m pretty energized and intrigued by this beastly service. Since the primary APRS frequency is in the two-meter band, it is fully available to all license holders regardless of your license class.
What Is APRS?
Developed by Bob Bruninga, WB4APR (SK), APRS was originally conceived as a way to allow amateur radio operators to share positional information and other data using the AX.25 packet radio protocol over common VHF/UHF frequencies. It’s like having a digital heartbeat for the hobby, where stations broadcast their location, status, and various bits of data automatically or on demand. Whether you’re tracking your mobile station on a road trip or monitoring weather conditions across the county, APRS can do it.
One of the things that makes using APRS so exciting is its wild versatility. Beyond just transmitting location data, APRS can also be used for sending text messages, alerts, bulletins, and even telemetry from remote sensors. This rich blend of features turns APRS into a vital tool—not only in everyday amateur radio operations but also in emergency communications and public service events where real-time situational awareness can be a lifesaver.
How Does APRS Work?
Let’s peel back the layers of APRS and first look at how it functions in the field. At its core, APRS is all about digital data packets that are sent over radio frequencies. When you activate your APRS station, it periodically sends out a data packet containing a host of information. Typically, this includes your current GPS coordinates, altitude, speed (if you’re mobile), and any additional status information you’ve configured—like weather sensor data or custom messages.
One of the most exciting aspects of APRS is that it operates in near real-time. You can track a friend’s vehicle during an event or keep an eye on weather conditions in remote areas where no other connectivity exists—all with APRS. The speed and reliability of APRS make it a unique tool for both everyday operations and emergency communications.
On a slightly more technical level, the card below explain how a packet is assembled and prepared for transmission over packet radio.
Assembling and Transmitting an APRS Packet
- Data Capture: Your APRS-equipped radio or Packet TNC (Terminal Node Controller) collects data from your keyboard and GPS or other sensors using a serial interface or directly via features built in to the rig.
- Packet Formatting: This data is formatted into a standardized APRS packet. The packet format adheres to specific rules defined by the protocol specification so that receiving stations know how to interpret it. This includes your callsign, a destination, path options, message payload, and more.
- Transmission: The fully assembled AX.25 packet is then sent to an encoder and converted to an AFSK 1200 baud audio stream that can be piped to your the transmitter. Your radio keys up and sends the encoded audio form of the packet for reception by nearby stations and APRS infrastructure. In North America, 144.390MHz has been set aside for this purpose.
- Reception and Re-Transmission: Nearby APRS stations and packet repeaters known as “digipeaters” pick up the transmission and re-transmit them over the same frequency.
- Processing: Some digipeaters are directly connected to the internet so that when they receive an RF transmission, in addition to repeating or “digipeating” a packet, those packets are also handed off to internet-connected servers known as the APRS-IS or “APRS Internet System” where they are stored away along with other packets arriving from around the world.
- Monitoring: Position reports and messages sent over APRS that are captured by an igate or internet-connected digipeater can viewed on the https://aprs.fi/ website. Data from around the world comes together in this amazing live mesh of information. What’s more exciting is that all licensed hams can sign up for an account there and do even more, like sending data to the APRS network from desktop and mobile applications and services.
The Role of Digipeaters in APRS
Now, let’s peel back another layer and talk about perhaps the most vital link in the APRS world: The lofty digipeater, these are often high-level, high-power machines on mountain ridges, high-rise buildings, and on tower structures. The term “digipeater” is short for “digital repeater,” and as the name implies, these devices are the workhorses that help APRS signals travel further than they otherwise would. Unlike a duplex repeater used for voice communications, the digipeater does not simultaneously transmit while receiving a packet.
How Do Digipeaters Work?
When your APRS station sends out a data packet, it is typically received by another APRS receiver within a limited range. However, if you’re in an area where stations are spread out, or if you’re transmitting from a low-power mobile setup, your signal might not reach every corner of the region. This is where digipeaters come into play.
A digipeater listens for APRS packets on a specific frequency and a number of different paths. When it detects a matching packet that hasn’t been repeated yet, it “digipeats” that packet. This very effectively extends the range of your transmission, allowing stations that were out of direct range to still receive your data.
One major distinction between a digipeater and a typical phone/voice repeater is that there is no duplex/offset configuration to complicate things. All operations take place on one frequency. The short and bursty nature of APRS makes it practical to receive and transmit on one frequency.
Why Are Digipeaters Important to APRS?
The importance of digipeaters can’t be overstated. Without them, the APRS network would be severely limited by the natural constraints of radio propagation. Digipeaters create a dynamic, self-healing mesh network that fills in the gaps and ensures that data flows smoothly, even in challenging conditions. This is especially critical during emergencies when rapid and widespread communication is essential.
Digipeaters have turned what would have been a spotty, localized signal into a robust, wide-area network of reliable data and communication. Whether you’re using APRS for routine operations or emergency communications, digipeaters help ensure your message is heard far and wide.
From my location in San Jose, I can reach the WR6ABD digipeater on Loma Prieta summit in the Santa Cruz Mountains. With its 3,700′ (1,100m) elevation and clear line of sight, this digipeater has a range of over 150 miles (240km). I frequently see APRS location beacons from vehicles driving in the Sierra Nevada Mountains, several hours’ drive away from my location, thanks to this high-level digipeater.
What are APRS Path Settings?
If you’ve ever tinkered with APRS settings, one of the first mysterious things you likely encountered was the “path settings” option. This can seem a bit confusing at first, but once you understand the concept, you’ll appreciate just how crucial these paths are in managing how your APRS packets traverse the network. You can put a comma-separated list of digipeater callsigns in the path field and your packet will get relayed along that path toward its destination. Pretty cool, huh?
The path setting is used primarily for two very important tactical callsigns: WIDE1-1 and WIDE2-1. Nearly every digipeater or igate on the planet will listen for one or both of these callsigns and act accordingly. Some digipeaters listen only for WIDE1-1, others only respond only to WIDE2-1, and some will respond to a packet addressed to either path.
What does WIDE1-1 Mean?
When you place one of the special WIDEn-N tactical callsigns in your path, you are selecting which type and how many digipeaters you would like to have respond to your packet transmission. When you see a path entry like WIDE1-1, the WIDE1 portion is a tactical callsign and the -1 is an SSID that is used in this case to specify how many hops a packet should travel before “expiring”. So, together, WIDE1-1 is a tactical callsign with an SSID. It really is that simple.
Digipeaters often listen to a number of different paths and handle traffic differently based on which path a packet was heard on. WIDE1-1 and WIDE2-1 are not the only tactical callsigns used with APRS.
There are special paths as well. For example, some regional or special use paths trigger digipeaters to log packets to the internet but not digipeat them over RF. Paths like this are particularly useful in times of disaster when digipeater traffic could be very high yet lower priority telemetry and automated position reports still need to be reported from remote locations to the internet. It’s this “log it and move on” path that reduces RF clutter in the immediate area while still providing outside observers with the information they need to manage an emergency situation, track first responders and evacuation routes, or manage civic events. Remember: APRS is primarily a tool for situation awareness.
WIDEn-N and Direct Paths using APRS
- WIDE1-1: This path is specifically designed for mobile stations and low-power transmitters that need assistance reaching the larger APRS network. It acts as a request for fill-in digipeaters—typically home stations or small, localized digis—to re-transmit the packet once, giving it a better chance of being picked up by a full-service digipeater or an i-gate.
These fill-in digipeaters only respond to WIDE1-1 and do not process higher order WIDEn-N paths, helping reduce unnecessary network congestion while still supporting weaker stations. In areas of moderate APRS traffic and good digipeater coverage, WIDE1-1 is usually adequate for all fixed stations, unless you need additional range and WIDE1-1 is not getting you there. - WIDE2-1: This APRS path is a request for a single hop from a high-level, full-service digipeater, typically a high-elevation, backbone, or regional digipeater with wide area coverage and good line-of-sight to other high-level digipeaters.
Unlike WIDE1-1, which relies on low-level fill-in digipeaters, WIDE2-1 packets are ignored by the fill-in digis and only get relayed by digipeaters listening for packets on the WIDE2-1 path. This makes WIDE2-1 useful for stations that are already within range of a high-level digipeater and only need one hop to ensure their packet is heard by an i-gate or other infrastructure further into the network.
Because it limits the number of retransmissions, WIDE2-1 helps reduce unnecessary network congestion, making it a more efficient path choice for fixed stations or mobile operators in well-covered areas. However, a packet sent using only WIDE2-1 may not be heard or digipeated. For this reason WIDE2-1 is often paired with WIDE1-1 in a comma separated list so the local fill-in digis can pick it up and improve your changes of being heard by the high-level or possibly more distant WIDE2 digipeater. - WIDE2-2: This path requests two hops from full-service digipeaters, providing even greater coverage across a broader region. When a packet is sent with WIDE2-2, the first digipeater to receive it will rewrite the path, changing WIDE2-2 to WIDE2-1, before sending the packet on its way. The next digipeater processes the packet labeled as WIDE2-1 and forwards it one final time before the path is fully consumed.
This allows stations in more rural or remote areas to reach IGates or be heard over a wider area, but it also increases network load. While WIDE2-2 is commonly used by fixed stations or mobiles in less dense APRS regions, it should be avoided in high-traffic areas, as excessive use can lead to network congestion and packet collisions.
Many digipeaters are configured to ignore longer paths like WIDE2-3 or higher, making WIDE2-2 the practical limit for most APRS networks. Some digipeaters are programmed to ignore packets if the SSID has a higher value than the tactical call, example WIDE2-3 would be ignored because the value in the SSID (3) is higher than the value applied to the tactical call (2). - Direct Paths: In some scenarios, especially when communicating with a known station or a specific group, you may want to use a direct path setting to bypass the broader network, eliminate digipeaters, and reduce delays. Using direct paths will be covered in my next post.
How Do Path Settings Affect Your Packet’s Journey?
The path setting you choose has a direct impact on how far your APRS packet will travel. If you set the path too aggressively (e.g., allowing too many digipeater hops), you risk clogging the network with redundant traffic. On the flip side, a path that’s too restrictive might not allow your packet to reach its intended audience.
For example, when I first started with APRS, I was tempted to use the “WIDE” settings liberally, assuming that more hops would automatically mean better coverage. However, I quickly learned that optimal settings require a balance—ensuring that my packets travel far enough to be useful without overwhelming the network.
Choosing a path is a bit like adjusting the power on your radio: Too little and you’re not heard; too much and you could create problems somewhere. Remember FCC Part 97.313(a) – Transmitter Power Standards: “An amateur station must use the minimum transmitter power necessary to carry out the desired communications.”
This rule applies equally to use of digipeaters and WIDEn-N path options. Turn down the power if you don’t need it. And in the case of digipeaters, narrow your path, especially if you’re in a congested area with lots of digipeaters, lots of users, and good coverage.
Practical Tips for Managing APRS Path Settings
- Start with the Defaults: If you’re new to APRS, stick with the default path settings recommended by your software radio’s default settings. These defaults are designed to work well in a variety of conditions should work to get you going.
- Experiment Cautiously: Once you’re comfortable, try tweaking the path settings in controlled scenarios. See how your changes affect the range and reliability of your packets. This experimentation is a great learning experience and can help you tailor your APRS setup to your specific environment.
- Stay Informed: APRS isn’t static—community standards and network configurations evolve over time. Keep an eye on forums, local ham groups, and APRS community updates to ensure you’re using the best settings for current conditions.
- Coordinate with Neighbors: If you’re operating in an area with several active APRS stations, a little coordination goes a long way. Sharing your experiences and settings can help everyone optimize their operations and reduce network congestion. It’s been a lot of fun learning the APRS traffic patterns of the area and even sending messages back and forth with a few local hams.
Bringing It All Together
So far, we’ve covered the basics of what APRS is, how it works, and the pivotal roles played by digipeaters and path settings. APRS is more than just a digital mode; it’s a vibrant, evolving system that brings together the best of amateur radio’s analog and digital worlds. Whether you’re tracking your own position, sending out critical weather updates, or just enjoying a “short message” QSO with a friend, APRS offers a lot of possibilities for experimentation and connectivity.
APRS has completely captivated me for several weeks now. It is pretty cool knowing that my station’s data can hop from one digipeater to another, and eventually appear on a global map for anyone to see.
My Personal Experience Using APRS
The first time I saw realtime data popping up on aprs.fi and moving around the map, I was totally hooked. It was thrilling to see this vast amount of public data updating before my eyes. I had to figure this out! What I’m sharing here is the stuff I’ve learned over a few weeks pouring through numerous documents on the subject, many of them woefully outdated.
Using APRS: Part Two Coming Soon!
As we look forward to the next part of this series, I’m excited to dive deeper into the more advanced features of APRS. In part two, we’ll uncover how to send messages to the public telephone network, explore how using APRS can integrate with other communication systems like Winlink, and even look at some real-world applications that prove APRS is more than just an interesting fascination—it’s a vital tool in our modern world of ham radio communications and should be part of everyone’s toolkit.
Until then, keep your radios tuned, your software updated, and your curiosity stoked. Using APRS is a fun way to expand your ham radio experience into the digital world. It’s also a great opportunity to learn something new and connect with a worldwide community of APRS operators.