APRS Tracker

APRS Tracker

This week, my brother is relocating from the San Francico Bay Area to Texarkana, Texas.  I’m helping him move, so for the next two weeks we’ll be on a road trip through California, Arizona, New Mexico, Texas, and maybe a little bit of Oklahoma.  We’re planning to see the Very Large Array, visit Truth or Consequences, and check out The Black Hole in Los Alamos.  That is, if the trailer stays connected and we don’t break down too many times on the way.

I though this would be a good opportunity to dust off my APRS tracker so friends and family can watch our progress.

What is APRS?

APRS, short for Automatic Packet Reporting System, is a radio network that uses amateur radio frequencies to relay short messages.  Think of it as a precursor to twitter, developed 20+ years ago by Bob Bruinga, WB4APR.  The messages usually contain GPS coordinates, and they are relayed via radio to internet connected stations that send the data to the APRS-IS network.  Database servers, such as findU, cache the packets so that client software can access them without needing a radio or realtime access to the network.

The coolest client I have seen so far is aprs.fi, a clever mashup of APRS and Google Maps:

APRS map of San Francisco
APRS map of San Francisco

The hardware:

I made this APRS tracking box a couple years ago, so I’m a little fuzzy on the construction details, but it consists of the following parts:

  • A Trimble ACE III GPS module, originally used in a police car, $5 on eBay.
  • An external mag-mount powered antenna for the GPS that I found at HSC, also $5.
  • A Tinytrak3+ microcontroller-based APRS encoder and modem, $30
  • My old Kenwood TH-79A handheld 2 meter/144-148 MHz ham radio
  • A mag mount whip antenna for the HT, found at the electronics flea market.
  • An aluminum box, probably the most expensive part.
  • Some cables to glue all the pieces together, mostly salvaged from my junk box.

The APRS tracker acquires a GPS fix and the current GPS time.  Every so often (fully configurable), it transmits my position over the radio, where it is received by other APRS relay stations in the area.  Speed, direction, and altitude are also included with the position packet.  I connected a piezo buzzer to the TX signal so I hear a beep when the position is transmitted.  Within a few minutes, a point corresponding to the position shows up on the map at aprs.fi or in the findu database.

It’s really neat to play with, especially on long trips.  On a trip to Moab two years ago, my position was received by the APRS network even in areas with no cell coverage, which included most of Utah!

Note that to use the APRS system, you need to have an amateur radio license.  If you’ve ever been interested in amateur radio, this is a really good reason to get your license and start experimenting!

11 thoughts on “APRS Tracker”

  1. I wish satellite APRS would switch to using the 900mhz & 1,200mhz ham bands. This would allow us hams to utilize considerably smaller and more portable directional patch antennas with our handheld radios.

    Considering the SPOT GPS Tracker reliably operates on 1,600mhz and only 0.4 watts of RF output power I think we could accomplish even better results with a 5 watt APRS handheld on 900mhz or 1,200mhz with a pocket sized directional antenna.

    1. I agree, 900MHz and 1.2GHz seem like perfect bands for a new APRS network. I think the challenge is that the existing infrastructure is limited to 144Mhz – a lot of the equipment is very old and couldn’t easily be converted to one of the higher bands. That means that a new network will have poor coverage unless you can somehow provide an incentive for existing repeater operators to upgrade.

      1. I think the most effective use of APRS on the 23cm & 33cm bands would be to have a geosynchronous APRS satellite with an uplink frequency on 23cm & 33cm then a downlink frequency on the standard 2m 145.825mhz frequency. That way the pre-existing land based Internet Gate receivers could still be utilized. Then we could all eventually be carrying around pocket sized APRS ham radios capable of transmitting to a satellite without the current need of cumbersome antennas for 2 meters.

  2. Lots of great comments here, let me respond to a few:

    Sean: GPS coverage problems and outages are a pain, most noticeable is when I am driving on the lower deck of the Bay Bridge – zero signal for several miles! Someone could make the ultimate APRS rig by combining a modern GPS receiver with something like the Sparkfun IMU. Chris Anderson posted a blurb about an open source Kallman filter for it here: http://diydrones.ning.com/profiles/blogs/705844:BlogPost:14328

    A good GPS plus the IMU and Kallman filter could allow the system to flywheel through the GPS outages and still report a reasonably accurate position (limited by the accuracy and drift of the IMU).

    Robert / jrocky – The D7A would be cool but part of the reason I put this project together was that I already had the TH-79A. For years it was mostly just sitting on a shelf collecting dust, so I was happy to find a use for it.

    neko68k – Thanks for the offer, we ended up making a quick stop in Albuquerque to see the Balloon Museum. Traffic kept us from being able to see much else (we had a huge moving truck, so getting around in traffic was a real problem). My brother and I spent 2 days in Santa Fe, though, and made a side trip to Los Alamos, which was really cool! I really enjoyed seeing New Mexico for the first time (and the food was fantastic, too!)

    N0QBH – I have long been interested in making an AVR-based packet modem. I’ll check our your project – thanks for the link!

  3. Yeah, I used the ‘D7A for my motorcycle ham rig. The pictures are of my first real embedded project, using an AVR Butterfly board to display and change the frequency.

  4. Kind of OT. If you’re going to travel through Albuquerque, I recommend a ride up the Trammway. Longest free span in the world. The view from the top is great and you get a discount on the ticket to ride if you eat at the restaurant at the top or the bottom(dont eat at the top). Also if you need a hotel to stay at in Albuquerque I can shamelessly plug the one I work at 😀 Catch me in email and I might be able to swing you a fair rate.

  5. With the Kenwood TH-D7A/[G] and a GPS device that supports NMEA/NMEA96 connected is all you will need. The TH-D7A[G] has a built in packet modem that supports APRS.

  6. Cool thing, APRS! We used it to track the follow-up boat on a boat race. It was really neat watching the progress on a laptop computer many miles from the activity. Good antennas are a must, a centrally located Digipeater on a high location and good strong GPS receivers. Our major problem was when it hit the canyon and the older GPS we were receiving got kind of wonky as its view of the sky narrowed.

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