Hello! W3RAZ again here on Gear Diary, for some more amateur radio goodness. Today I am writing about APRS. APRS? What’s that? We’ll it’s in many ways the precursor to Google Latitude and all of these apps on phones that have you checking into places, but it was invented 20 years ago by WB4APR, Bob Bruninga. It uses one of the most commonly used digital modes in Amateur Radio, Packet.
APRS or Automatic Position Reporting System is a system for using a GPS, where a Terminal Node Controller (similar to a modem) and a radio are used to report your stations position as you are driving around in your car, on a bike, in a bus or on foot. In the very beginning, you had to set almost everything up on your own, and the program you used ran on DOS. Since then, there have been ports of APRS made to Windows, Mac, , Android, and , and there have been many other innovations that really make this a fun tool to have in your ham radio bag.
APRS Starts with Packet Radio
APRS uses a digital mode that is very common on the VHF and UHF bands, Packet Radio. Packet is similar to the old modems we use to use to connect to the internet and Bulletin Board Systems in the 90′s except that there is no dialing. You just tune your radio to the frequency and if you listen to it with a regular radio, you will hear tones that sound a lot like the old modem tones. With a Terminal Node Controller, a radio, your computer and a terminal emulation program you can log in to Packet BBS systems that are similar to the BBS systems of the 90′s and send e-mail and even download files over ham radio at the slow 1200 or 9600 baud speeds. They use a protocol that is specific to ham radio called AX.25. Packet is limited to 9600 Baud at the fastest rate but this is more than fast enough to transmit position data which is what APRS does.
More than Just Position Data
APRS is more than just position data. You can also connect a weather station and send weather data, like the amount of rainfall, the current wind speed and direction and more on the APRS map. Other stations can see this and then use it for monitoring severe weather conditions.
You can also send non station APRS objects or icons. One example could be the current position of Hurricane Isaac. If a station on the APRS network gets a position update from the weather service, they can update the position on the APRS map and emergency workers can monitor the position of the storm in relation to the location of the emergency workers. This isn’t commonly seen in my area, but I have seen examples of APRS being used in this manner. Above is the latest APRS.fi map, which shows the position of Isaac as well as several Weather stations in the keys which show on the map as a blue circle with a white WX in the circle. Clicking on the circle reveals the current wind speed, direction, temperature and rain fall.
APRS has the ability to send messages to stations you see on the map. Even some of the APRS radios that are on the market now can do this in a similar manner to a text message on a cell phone.
Advances Since the 90s
Now that we’re a couple of decades away from the beginnings of APRS, there are many more convenient ways to use APRS, and some don’t even use a radio.
APRS is now on the internet with sites like APRS IS and APRS.fi. APRS IS and APRS.fi both use the same APRS data. Since all positions are repeated by digipeaters on the APRS network, and some of these relay the information to the internet, you have a complete view of the area with all of the recent station reports on a map and its on the web and viewable by anyone even without an Amateur License. The only real difference between the two sites is APRS.fi uses Google Maps as its map source plus APRS.fi looks nicer as well. APRS IS is a java applet and I have had some issues getting it to work so I prefer APRS.fi.
The Android and iOS ports of APRS uses the phones 3G or 4G connection to report your position to APRS IS and then it reaches the packet network. These apps should only be used if you have a call sign so you need to have a license to use these apps. The reason is your call and position packet will eventually be digipeated via radio so radio connected stations can see you so you will have to have privileges on the bands used by APRS. These programs also both ask for your call as soon as you start them the first time and will not work without this. There are APRS viewers that non hams can use on these platforms as well.
Finally there are a selection of handheld radios and mobile radios that make it easy to report your position on the APRS network. These usually have integrated TNC’s, GPS systems and some firmware that makes it easy to use the second transceiver on most of these radios to transmit your position data while letting you use the other transceiver for voice conversations. The top two handhelds that have this functionality are Kenwood’s TH-72A and Yaesu’s VX-8GR. Kenwood also has a mobile rig for setting this up as well. The Kenwood TM-D710A plus an AvMap G6 GPS will give you a really nice APRS setup in your mobile with nearby stations automatically showing up on your AvMap’s display. Also, if you have a D-star(more on this later) Rig with a GPS like the new Icom ID-31A, your position data will be sent every time you key up and then sent to APRS IS via the internet gateway installed on most D-star repeaters.
Why is APRS Useful?
The weather data can be used by your localnet to report rain fail amounts and max wind speeds back to the national weather service. The Amateur Radio Emergency Service commonly will use APRS when working public service at events like The Race for the Cure and other races. They have a base station setup to view the APRS network and they place an APRS capable station behind the last runner. This way the net control station or the guy in charge of the communications for the race can easily see where the last runner is and then they can radio the communicators at the water stations when they can shut the water station down.
In every day use, your family can use this to keep track of where you are. All they have to do is look on APRS IS or APRS.fi and see when you are headed home. Of course you COULD use Google Latitude to do this, but this is a much more fun way to do the same thing. The packet network and the internet connections to APRS are also much more reliable than 3G and 4G networks mostly because the VHF and UHF radios used are much higher power and have a better range than 3G/4G radio towers. There are also fewer people using the local APRS packet network than using cellular data networks so it’s much easier to get your position data to the internet … if you have a license!
APRS is a technology that when it was first invented by WB4APR, was looking for a use. I remember when the first APRS stations were setup in my area. We didn’t really know what to do with it at the time, but we played around with it, made improvements over time, and now the uses are almost infinite. This happens quite frequently in Amateur Radio, and it’s one of the many reasons I still love playing with my radios.