GPS Tracker for APRS - Summer 2001

The GPS Tracker I made works very well and was so easy to build. The only problem I had was that I could never find any GOOD web pages about GPS Trackers. So I decided to do my best to make my own and explain everything about building and operating one.

Task 1:

The first thing you need to decide before you build a GPS Tracker is whether or not you want to use APRS with your tracker. I'd recommend that you do use APRS with yours. It's the only way to actually see where you and other stations are.

Task 2:

The second task to do is decide on the hardware you will be using. You will need a total of 3 main things to compose your tracker, 1. Radio, 2. TNC, 3. GPS. The picture below is of the inside of my GPS Tracker.

The radio you choose is your choice. Handhelds and mobiles are both fine for trackers. The main idea of a tracker is to have a gps, tnc, and radio all in one small box so you may want to go with a handheld. Any handheld will work as long as it has external microphone and speaker jacks. You also want to be able to power your radio with 12V DC so it might be wise to choose a radio that can operate on 12V DC. (I've seen some that are 7.5V DC)

The next thing you need is a TNC. The only TNC I'd recommend is the Kantronics KPC-3+. The only reason this is the only one I recommend is because it's the only one I've used. From my experience it is very easy to use and configure. It is also small in size.

The last thing you will need is a GPS. As you probably know there are many GPS's to choose from. It took me about a week to look through them all and decide which one I wanted. I finally chose the Garmin GPS-35. I chose this one for 2 reasons. One, I don't have a high budget and two, I only need the GPS for a tracker. The GPS-35 look like a GPS antenna. It has the GPS built in. That eliminates the need for an antenna . Also, some people use there GPS for other things such as hiking. This GPS DOES NOT have a screen on it. It inputs everything right into the computer. So I saved a lot of money buying a GPS that did not have a screen and was built into and antenna. I believe retail price for the GPD-35 is about $150. The picture below is the GPS-35.

Here's what I used:

TNC: Kantronics KPC-3+

RADIO: Icom T2H Sport

GPS: Garmin GPS-35

Task 3:

Now that you have your radio, tnc, and GPS, we can get to the fun stuff assuming that you've tested the radio, tnc, and GPS to make sure they work. (Go to the bottom of this page to get a GPS program that will SHOW you that it works.)

The next thing to do is find a box to put it all in. Some people use ammo boxes, battery boxes, waterproof boat boxes, and I used a small cheap tool box. You want to make sure that everything will fit and that's including cables, voltage regulators, and a lead acid battery (if you want one).

Now you need to get the all the connectors and cables to make everything work together. Look at the picture below to see what I have on the top of my tracker. There are 2 DB-9 connectors for the GPS, and computer, and a BNC connector for the antenna. I just drilled and used a file to shape the holes for the DB-9's to fit into. The good thing was that the box is hard plastic so it is relatively easy to file and drill into.

As you will see in the picture below, the connectors on the top of the tool box are just extensions to the connectors inside. For example, the DB-9 on the right just extends the connector on the back of the TNC so the computer cable can just plug into the top of the box rather than inside of it. It is the same for the GPS. The DB-9 has only 4 wires; 2 go to the TNC, 2 go the terminal strip for power. So the connectors also just make everything neater. The whole idea of having a track like this is so all you have to do is plug in your computer, power, and GPS into the top of the tracker.

Assuming you have all of your connectors mounted on your box.

The next thing to do is attach all of your wires. This is kind of hard to explain but very easy to do. Below is a wiring diagram of the wiring between the DB-25 computer port on the Kantronics KPC-3+ and the DB-9 on top of the tool box. The reason there is a DB-9 is because all new computers use DB-9 connectors rather than the old DB-25. I bought a DB-9 extension cable from Radio Shack that has a DB-9 female on one end (to computer) and a DB-9 male (to DB-9 on top of box).

Next is to wire the radio port of the TNC and the GPS port on top of the box.

To wire the DB-9 radio port to the radio look at the wiring diagram below.

So now you should have your TNC wired to the the DB-9 computer port on top of the box and to the radio speaker and microphone plugs. Next we are going to wire up the GPS.

Im going to show you what I did for the wiring. I think it is the easiest way to wire a GPS to the TNC. *NOTE: The fallowing diagram and paragraph are only for the KPC-3+. They will NOT work with the KPC-3.

The other DB-9 on the top of the box is the GPS connector. On the end of the cable going to the GPS I added a female DB-9 connector. Below is a diagram of the wiring for the GPS port on the box. Note the text on the left of the diagram. It says where the wires from the GPS connect to the KPC-3+. They connect to the DB-9 RADIO port of the KPC-3+.

Task 4:

All that is left is to power everything. As you can see in the picture below I power everything via the terminal strip mounted on the left side of my tracker box. I have wires from the radio, tnc, and DB-9 GPS port connecting to the terminal strip. I also have about 6 inches of wire running from the terminal strip to outside of the box for the main power input. If you look at the specs of the TNC, GPS, and radio you will notice that they don't pull anymore than about 5 or 6 amps total. Most cigarette lighters in cars can handle from 15 to 20 amps. So I just added a cigarette lighter plug on the end of my wires going into the GPS Tracker.

THAT'S IT!!! You've finished building it. Easy wasn't it? Now is the easy part. Configuring it all to work together.

Task 5:
Configuring

The first thing to do is make the TNC recognize that there is a GPS connected to it. So first you need to power up everything and make sure the GPS in a location where the satellites can see it (on a window seal). Next open a Packet terminal program such as WinPack and type the fallowing commands when you're in command mode. Do not type the parentheses, they are just to show that, that is a command to type.

<GPSPORT 4800 NORMAL CHECKSUM>

<GPSHEAD 1 $GPRMC>

<GPSHEAD 2 $GPGGA>

<GPSTIME VALID RMC>

<CD SOFTWARE>

<CONMODE Converse>

<LTP 1 GPSLJ V RELAY,WIDE2-2>

<LTP 2 GPSLJ V RELAY,WIDE2-2>

<BLT 1 EVERY 00:03:00 >

<BLT 2 EVERY 00:03:05>

Those are all of the commands NEEDED to get the GPS and TNC to talk to recognize each other.

So now what you have done is told your TNC to transmit the $GPRMC string every 3 minutes and the $GPGGA string every 3 minutes and 5 seconds. The GPS puts out many different NMEA strings and loads them into the TNC buffers. The TNC transmits the strings according to the BLT command.

Task 6:

The final step to making your tracker is using it with WinAPRS. The only APRS program that I have used is WinAPRS. There really isn't much to it though. First power everything up and give the GPS a few minutes to aquire the satellites. Now you need to turn your radio to the national APRS frequency of 144.39. Next open up WinAPRS and put in you callsign and other necessary data. Then you need to select the baud rate of the TNC in the SERIAL PORT window of WinAPRS. Now just select the map of your area and click OPEN VHF TNC under the CONFIGURATION menu of WinAPRS. You should start seeing other station popping up on the map including you.

Thats it!! Your finished. I hope you like your new GPS Tracker as much as I do.