Long-distance High Frequency APRS Tracking Using The FreeTrak63


If you dabble in the ham radio hobby we’re sure you’ve heard of GPS position monitoring or tracking using APRS packet data commonly transmitting over the VHF ham band and FM modulated. One of the issues you’ll face using this common method is range limitations of VHF. [Mike Berg] a.k.a [N0QBH ] tipped us off to his latest project to greatly increase the range of a standalone APRS system utilizing the HF bands on single-sideband (SSB).

There are some unique challenges transmitting packet data using SSB over HF bands.  High Frequency APRS has been around for decades utilizing FSK AX.25 packet transmissions at 300 baud, but it was quite susceptible to noise and propagation aberrations. More recently PSK-31 at the slower 31 baud speed helped alleviate many of these issues. [Mike] utilized the somewhat updated APRS with PSK-63 and the “APRS Messenger” program to overcome these challenges. [Mike’s] hardware solution consists of a PIC 16F690 micro which is coded to receive data from a GPS receiver, convert it into PSK-63 and then transmit on 30 meters over an attached HF radio. A second receiving station or stations at great distances can pick up and decode the transmission using the “APRS Messenger” program connected to the receiving radio over the computer’s soundcard. The program can then forward the tracking information, if good, to tracking websites like FindU.com and APRS.FI.

You can build your own FreeTrak63 by downloading [Mike’s] parts list, assembly code, HEX file, manual and schematic. The PCB is available on OSH Park if you don’t want to make your own or wire point-to-point. Let’s not forget to mention how hackable this hardware is, being really just an eight bit DAC, micro, serial in and radio out. One could reprogram this hardware to do other modulation schemes like AX.25 packet or MFSK16, the sky’s the limit. If short-distance on VHF with existing Internet linked receiver networks using an Arduino compatible platform is more to your taste, then checkout the Trackuino open source APRS Tracker.

20 thoughts on “Long-distance High Frequency APRS Tracking Using The FreeTrak63

    1. I think we either differ in definition of “vehicle” or “portable”. The only annoying part for HF portability is the antenna, and that… well, that’s been hacked over and over again for many years.

      For myself, I have hiking staffs that happen to to be resonant at about forty meters (and have a secondary use as inductors for … um…. “localized EMP”, with minor arcing that looks pretty). And I still think the bow and radio wire-over-the-tree method deserves points for style, even though it is admittedly better for the non-tracking applications of GPRS (like answering “how fast is that front moving towards us?”) than the tracking ones.

      1. For a quarter-wave dipole at 40m, wouldn’t you be looking at a 10m staff? And how much power do you need? I haven’t seen portable (meaning handheld) radios capable of more than 5W, no idea if that’s enough.

        1. (also a reply to Kumo) Pretty simple design, it’s a coiled dipole on two pieces bamboo of reasonable diameter (around 4 cm) and around 150cm long. They separate while walking. The cap hats turn out to be a bit of a pain, but hey! 40 meters that can be walked with!

          vpoko: Electrical lengths can vary considerably from physical, and the speed-of-light calculation is, conveniently, a maximum length. So I started with a half wavelength of speaker wire, and trimmed until it worked ok-ish, then adjusted the capacitance capping until it worked well enough with my radio. And I don’t need much power, but that’s because the design was for playing with a rock mite while climbing mountains – qrp to start with and then dozens of advantages being up high and far away from crowded places. Still works OK with an old receiver at home that I play around with sometimes, and just want a “Hey Rocky, watch this!” antenna to plug in.

          All in all it’s a hack job at it, but it works for me.

  1. Cool idea! My only beef is that the DAC is not buffered in his schematic. Most audio inputs are relatively high impedance, but taking shortcuts like that can sometimes lead to serious problems. But if it works, I guess its not that big of a deal.

    Also, you can get portables with more than 5W output, but they usually require an external power source. Yaesu makes one, the FT-857 (incidentally, the one shown featured with the project), which is capable of 100W. It is a seriously nice piece of kit, and will probably be my next radio purchase…

    Also, I am excited to see more Amateur Radio hacks here on Hackaday! A lot of people don’t realize how much home-brew and ‘making’ or ‘hacking’ is part of the Amateur radio community!

  2. I like seeing these ham radio articles on HAD. There’s still some proverbial meat left on the old Ham radio bone for modern hackers. The simplest example that comes to mind is the higher power transmitters that are legally available to ham radio operators for the transmission of telemetry or remote control. Or perhaps the higher power allowances for hams in the 2.4 GHz band.

  3. Congrats, for the idea of building a standalone HF APRS tracker.

    My only objection, is the choice of a R-2R resistor ladder, instead of a PWM DAC. The software would use less resources and you wouldn’t have to solder all these resistors on the board.

    1. The firmware is written in assembly and open sourced to encourage experimentation.
      I’m hoping some entrepreneur type hams build and sell this device so non builders can get involved. At this time, I’m involved with electronic assembly for a living and have no desire to do it as a hobby :)
      73 Mike N0QBH

  4. Please we are looking for ssb single side band radio transmitter position tracker. The tracker either GPRS or the like should be ablev to tracker the position of a high frequency transmitter position when the the frequency of a transmitter is keyed in to it.and display it on a map thanks engr patric

    1. i dont see why a simple PIC could not decode gps data from a cheap module and waggle a i/o line up and down with enough force to produce an aprs or psk signal directly that with a buffer transistor and good (read: tuned, not huge) could be capable of global reporting. i often work across the atlantic on 1 watt of power, so with the right highpass filter to match the band used (and that can be chosen by the PIC) a little board running on a lithium battery should do just fine.

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