Our pool of popular guest writers in expanding! KD0WBK (Bob) volunteered to write about a project he has been working on that's interesting and covers a topic many new hams may be unfamiliar with. That's right up this blog's alley.
First, let me introduce myself. My name is Bob McNamara, KD0WBK. I live in south Minneapolis and am a commercial photographer (www.bobmcnamara.com) by trade. One of my hobbies is overland travel, traveling off road long distances in out-of-the-way places, mainly the desert southwest. In my travels I have been out of cell phone range for days at a time and always wished I had some way to communicate in an emergency. This brought me to Ham radio. I recently upgraded my license to General and am looking forward to QRP (low power) operating in the HF bands on my trips.
As I learned more and more about Ham radio I kept coming across the APRS system and really thought this could be a fun area to explore.
So just what is APRS? Well first, before we start down this path, a disclaimer; I am not an expert in APRS (or anything, really). I only know what I have learned and it is just the tip of the APRS iceberg I am sure some of what I will share here is just plain wrong. I hope others with more knowledge will chime in with corrections and better advice. OK, let's go!
APRS: Automatic Packet Reporting System. APRS is a fairly mature digital communications system. It has been around for over 20 years and uses a single frequency (144.39) on the VHF 2 meter band throughout North America. So what can you do with it? Lots of stuff. Position reporting, weather reports, email, texting, and much more. I am going to only discuss position reporting in this post. If some of you are interested, I'd be glad to cover other areas in the future.
How would you like to have your friends and family be able to track your location while you drive around? (Ok, I am well aware that there are times that you and I do NOT want to be found, but stick with me here). How about having the ability to track and see on a map other hams in your area and be able to send them text messages? Or, maybe you are traveling with a group of vehicles and it would be fun to see where they are at all times. You can do this with APRS.
So how does all this work? Its pretty simple: a GPS receiver gets your position from the GPS satellite system and sends it over a cable to a computer that processes the information and sends it, at a predetermined interval, over another cable to a TNC (terminal node connector) that converts the digital signal to analog and sends it, over yet another cable, on to your radio that transmits it to a digipeater (digital repeater) that bounces around to other digipeaters until it gets to an IGATE which is an internet gateway and off it goes into the interwebs.
Whew. That was complicated! And it used to be. Until recently, you needed a GPS receiver, a laptop, a TNC and a radio all connected with a whole bunch of cables in your car. Not anymore!
I'll take a quick breather here to acknowledge the manufacturers that have developed radios with built in GPS and TNCs to simplify APRS. These are great rigs, but they are also expensive, and with that high cost you get tiny little screens that are not able (except at additional high cost and more cables) to show maps.
Here's the quick, simple and relatively inexpensive solution I use:
#1: Cheap Chinese HT (must work on 2 meters FM)
#2: Android Tablet or Phone* (no data connection or cell service needed)
#3: Mobilinkd TNC and cable
#4: APRSdroid app
* Yep, you NEED to have an Android phone or tablet. No need for a data connection of any kind, so if you have an old Android phone laying around that's not active on the cellular networks, that's fine. New 7 inch generic tablets are available for less than $70 now and they work great. Please, no Apple fanboy flames. Apple does not support the KISS Bluetooth protocol that is needed here.
Let's say you're lucky and have an old Android phone laying in the kitchen drawer next to that $35 HT you got on Amazon -- you're half way there! Simply buy the Mobilinkd TNC with cable that matches your HT ($69), and the APRSdroid App ($4.95) from the Google Play store, and you're set (all links are below).
There is some simple setup for the TNC and app which is well documented on their websites, so I won't go over that. Just know that this is REALLY simple to setup and get working. The Mobilinkd TNC has a rechargeable battery that is good for 48 hours of use. I simply plug it into my HT, hold it to the HT with a rubber band, plug in a mag mount antenna and toss it in my glove box.
The Android device must be able to see some sky to get a good GPS fix. The Mobilinkd TNC will pair with the Android device over Bluetooth, eliminating the messy cables. Once you start the APRSdroid app, it will connect to the TNC and start to send out data packets of your location. The radio also receives data packets from other users and the local digipeaters.
There are three main screens in the app that you will use; Hub, Log and Map. The Hub screen shows all the nearby users, starting with you (green background) and then the rest sorted by their distance from you. Each entry has the user call-sign, their distance, and direction from you, and any comment they want to show. Usually hams will comment out the frequency they are monitoring so you can give them a call.
If you tap one of the entries, you can see all the raw data from that station, as well as map them to the Map screen. Once you map them, the app will follow them on the map. You can also map yourself and follow your own progress. Keep in mind the map is only charting the data that is being sent at intervals, so the motion on the map is not as smooth as a continuous GPS signal would be. In the setup directions on the APRSdroid site there are instructions on how to download a great vector based map of the USA to use. By using the downloaded map, you do not need to have a data connection as you travel, and its free!
The Log screen shows all raw data that is sent and received. Your out-going data is highlighted in green.
So now you are sending and receiving data with your set up, how can you share your location with friends? That's the easy part! Have your friend go to www.APRS.FI. Here you will see a Google map with menu choices on the right side. You can type in the call-sign of the person you want to see, as well as the historical time period you want. This will show your current (or last known) position as well as a trail indicating your past locations over the period of time requested. Click around on the mapped data points to see elevation, speed, direction, etc. You can also choose to see all the stations in the area.
Here's a map of the Twin Cities showing 24 hours of APRS traffic. Each station is shown with a different color trail:
So just how well does it work? Like all things radio, it depends. The GPS signals are pretty good and very reliable, so it comes down to the availability of digipeaters in your area. I just took a trip to Santa Fe, New Mexico and had good coverage for most of the trip. There were a few holes in coverage in western Oklahoma and central Nebraska. Had I been using a higher power rig instead of the HT, I might have been able to hit some of the more distant digipeaters. Coverage along major highways and in cities is really good.
Here's a map showing digipeater coverage from 2010:
That's the basics of APRS position reporting. There is much, much more that APRS can do. I really like the ability to send texts to other users anywhere and even send email to ANY email address when out of cell coverage (but still in digipeater range). Check out the websites below for more info and comment below if you have questions, corrections or whatever.
73s.
Bob KD?WBK
www.APRS.org Main source for all things APRS
www.APRS.FI One of many web sites to track positioning
www.AprsMail.org Position tracking and send/receive email
www.Mobilinkd.com Place to get your Bluetooth TNC
www.APRSdroid.org Place to get setup info on the app and maps
Note: To those of you that have cellular connected Android phones, yes you can just use the APRSdroid app to send your position information directly to the web over your data connection. But come on now... REAL HAMS USE RF! ; )
The Android device must be able to see some sky to get a good GPS fix. The Mobilinkd TNC will pair with the Android device over Bluetooth, eliminating the messy cables. Once you start the APRSdroid app, it will connect to the TNC and start to send out data packets of your location. The radio also receives data packets from other users and the local digipeaters.
There are three main screens in the app that you will use; Hub, Log and Map. The Hub screen shows all the nearby users, starting with you (green background) and then the rest sorted by their distance from you. Each entry has the user call-sign, their distance, and direction from you, and any comment they want to show. Usually hams will comment out the frequency they are monitoring so you can give them a call.
If you tap one of the entries, you can see all the raw data from that station, as well as map them to the Map screen. Once you map them, the app will follow them on the map. You can also map yourself and follow your own progress. Keep in mind the map is only charting the data that is being sent at intervals, so the motion on the map is not as smooth as a continuous GPS signal would be. In the setup directions on the APRSdroid site there are instructions on how to download a great vector based map of the USA to use. By using the downloaded map, you do not need to have a data connection as you travel, and its free!
The Log screen shows all raw data that is sent and received. Your out-going data is highlighted in green.
So now you are sending and receiving data with your set up, how can you share your location with friends? That's the easy part! Have your friend go to www.APRS.FI. Here you will see a Google map with menu choices on the right side. You can type in the call-sign of the person you want to see, as well as the historical time period you want. This will show your current (or last known) position as well as a trail indicating your past locations over the period of time requested. Click around on the mapped data points to see elevation, speed, direction, etc. You can also choose to see all the stations in the area.
Here's a map of the Twin Cities showing 24 hours of APRS traffic. Each station is shown with a different color trail: 
So just how well does it work? Like all things radio, it depends. The GPS signals are pretty good and very reliable, so it comes down to the availability of digipeaters in your area. I just took a trip to Santa Fe, New Mexico and had good coverage for most of the trip. There were a few holes in coverage in western Oklahoma and central Nebraska. Had I been using a higher power rig instead of the HT, I might have been able to hit some of the more distant digipeaters. Coverage along major highways and in cities is really good.
Here's a map showing digipeater coverage from 2010: 
That's the basics of APRS position reporting. There is much, much more that APRS can do. I really like the ability to send texts to other users anywhere and even send email to ANY email address when out of cell coverage (but still in digipeater range). Check out the websites below for more info and comment below if you have questions, corrections or whatever.
73s.
Bob KD?WBK
www.APRS.org Main source for all things APRS
www.APRS.FI One of many web sites to track positioning
www.AprsMail.org Position tracking and send/receive email
www.Mobilinkd.com Place to get your Bluetooth TNC
www.APRSdroid.org Place to get setup info on the app and maps
Note: To those of you that have cellular connected Android phones, yes you can just use the APRSdroid app to send your position information directly to the web over your data connection. But come on now... REAL HAMS USE RF! ; )
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