APRS: The OG IoT

As a computer scientist, I was required to take a networking fundamentals course. This course showed us how the modern day internet works and how each OSI layer interacts with one another. We sniffed network packets and learned how to wire ethernet cables. This semester, I'm taking an Internet of Things (IoT) course, which definitely goes hand-in-hand with my networking class.

Of course, my amateur radio adventures had to include some form of computer science/networking crossover. And that is where the topic of APRS comes in.

What is APRS?

Automatic Packet Reporting System (APRS) is a networking system specifically designed for amateur radio use. It utilizes the Bell 202 1200 baud system from 1976, which was modulated via AFSK. The mastermind behind the development of APRS was Bob Bruninga, WB4APR (SK). Originally it was coded and conceptualized on an Apple II computer! Today, APRS is used on the HF (10 and 14 MHz) and 2m bands exclusively for the movement and throughput of information such as GPS location/tracking, weather reports, and even messaging! Besides Winlink, this is where the Internet of Things and ham radio cross over.

Our modern-day Internet infrastructure has allowed us hams to post our whereabouts via the APRS-IS system. Just like normal VHF/UHF communications, APRS ranges can be extended using digipeaters or transmitted to online graphic map overlays such as aprs.fi via iGate, or internet gateway, systems. In fact, it's not hard to make your own iGate or digipeater using components like a Raspberry Pi Zero or an actual desktop environment. Thanks to software programs like Direwolf, Xastir, PinPoint APRS, APRSDroid, and more, we now have APRS support for almost every OS platform imaginable.

A lot of people complain that APRS is the most useless mode. They argue that it requires the internet for it to function properly, and if the internet went down, so did the APRS network. This couldn't be further from the truth! While it is true that the internet is required to track operators who send out GPS coordinates, this isn't the only use for APRS. APRS can be used for things like weather observations (check out the CWOP - Civilian Weather Observation Program, for example), packet messaging, and so much more! Nothing in ham radio, with the exception of things like AllStar, requires or necessarily needs an internet connection. In fact, APRS is, in essence, an internet in itself.

How does APRS work?

APRS packets are a modified version of the X.25 packet protocol, AX.25. APRS is a store-and-forward system, meaning that received packets are forwarded just like IP packets. Instead of a wired network, APRS relies on RF infrastructure to pass along information. On the HF bands using an SSB transceiver, a maximum baud rate of 300 baud is allowed to keep bandwidth low and to comply with FCC standards. However, on VHF FM, 1200 baud is the agreed-upon standard, since FM takes up more bandwidth. It is more common to see APRS traffic on 2 meters, though HF operations certainly take place.

Positional APRS utilizes GPS technology from satellites constantly orbiting the globe. GPS receivers connected to APRS systems collect latitude and longitude data, which is encoded via a physical TNC or a virtual TNC like Direwolf. Email, like GPS position, can be sent over the airwaves as well. It is similar to Winlink. Weather reports are also available to hams thanks to systems like WXBOT or WXYO.

Where can I find activity?

In the United States and the vast majority of North America, 144.390 MHz is the center of APRS activity. Around my QTH, APRS activity is occasional but not rare. I can get stations as far away as southern Iowa and southeastern Nebraska. These stations are generally digipeaters though or higher-powered stations up to 50 watts, I suppose. If you plan on traveling, tune your 2 meter radio to the APRS frequency when you're on the highway - you'll be surprised to find a fair amount of activity from different operators and forwarded packets!

To track an APRS station, you can visit aprs.fi. This website posts live data of received positions from iGates around the globe. 

Come to think of it, I might want to build my own iGate or digipeater, and I plan on it in the near future. If you are ever in the Maryville, MO area, tune to 144.390 - I'm sure you'll get through to it. I plan on making it quite simple: a Raspberry Pi Zero running Direwolf that is configured to digipeat across (hopefully!) a good portion of NW Missouri and iGate to the APRS-IS network. I have yet to figure out what radio I'll use since a 5W Baofeng won't get very far unless it's on a hilltop. Perhaps an old VHF mobile is in the cards for me, and boy I have plenty of those!