If you are a bussy person and would like the finished project, I can provide the labor for $100 + shipping and your parts. You can contact me by Email

How does the basic APRS network work?

This project was inspired by Bill Theeringer post on Yahoo canard newsgroup: about his GPS pocket tracker. I wanted to have a real time tracking device for my flights. But most commercial units are expensive, require monthly subscription and work on the cellphone networks the operation of which is typically nonworking and illegal at altitudes. APRS (Automatic Position Reporting System) works with a small transmitter sending periodic position reports from an onboard GPS receiver. The signal is received by voluntary ham digi-peater or IGate stations and it is eventually sent to internet sites that can display the position of the tracking device.

The photo on left shows the project as of 2006/03/22. When the project is ready you may be able to track my aircraft position on internet

The original PocketTracker that Bill used is no longer available.

I got a separate TNC (Terminal Node Controller - or "modem"), the OpenTracker, from Argent Data and the tiny Deluo gps unit from same website. I found a cheap (made in China) Walkie Talkie that can transmitt the APRS frequency (144.39 MHZ) on eBay Its probably not much good for general ham use but sufficient for this one APRS frequency - its 2.5W Tx power should be better than the pocket tracker 0.25W. Warning - it takes two weeks to ship from Hong Kong - after payment.

You can see all the parts fitted into a Radio Shack 6x4x2" box - with the tiny Deluo GPS sticking up on top - click on image for larger view. So far I have spent about $200 for various parts. There are some alternatives.

1) The TinyTracker TNC (almost identical to OpenTracker) from Byonics

1b) TigerTrak TM-1 from tigertronics

2) The 5W MFJ-8621X2 from MFJ Enterprises, about $150, is specifically made for APRS. But after waiting 1 month on back order I gave up on them.

3) The Kenwood TH-D7A handheld (about $350) has built-in APRS, just add GPS input (about $75 for a Deluo). I might have gone for that one if I knew what I know - I spent about $200 for my parts - plus all the work.

4) Bill also said that older 2M handheld ham radios can be found on eBay for cheap.

04/02/2006 update: Passed my amateur tech test on Mar 28. But after testing my kit there is a problem between the OpenTracker TNC and the Jingtong radio I purchased. The TNC output signal is too low to drive the radio audio input. So instead of spending tons of time modifying the circuit I plunged and ordered the Kenwood TH-D7A - $319 from Austin Amateur Radio I will still use the Deluo gps unit for it and maybe can re-sell the Jingtong radio.

Finally here is my GPStracker that works using the Kenwood TH-D7A and re-using the Deluo gps unit. It is in a similar box, the main circuit needed was a 7805 5V voltage regulator to run the Deluo GPS. The main problem now is that there are no ham APRS receiving stations in my SD vicinity. You can see more construction details here

09/27/07 Update: I got a MicroTrak 300 (MT300) kit from Byonics and put it together on left as shown. It is a TNC and low power (300MW) transmitter all in one. I managed to put it all in a very compact RadioShack 5 x 2 1/2 x 1 1/2 project box, including the battery. It can be switched between the internal battery or external 12V source.. The white plug (made from epoxy with filler) connects the Deluo GPS to both the internal serial and 5V power source. Unplugging the GPS allows connection to a PC for programming the MicroTrak 300. The whole thing weighs 8 ounces. During tests, the MT300 didn't do too badly at altitude - reaching about 30 miles directly to my iGate with a rubber ducky - but had more gaps in transmission compared to my Kenwood TH-D7A. A standard quarter wave ground plane antenna would have been better. But I don't have room inside my aircraft for that neither want to go to the bother mounting one outside. Where it did not perform as well was in ground vehicles with a simple magmount 1/4 wave roof antenna. Obviously more power or a better antenna makes a difference.

05/07/06: I have become ambitious and constructed an APRS Internet Gateway (IGATE) receiving station. There are no "Digipeaters" or IGATEs in my central SD vicinity to transmit tracker signals to internet APRS servers. My IGATE system components are: 1. a roof antenna 2. a 144.39 MHZ receiving radio (iCom V8) 3. a "receiving" TNC (TNC-X kit) ) 4. a computer (a used $250, 700 MHZ IBM notebook from eBay) connected to live internet (my DSL connection) 5. Some sort of APRS/IGATE software (I am using UI-View32, and you can see the essential setup for IGATE here. Other setup data is as it comes with software.) The APRS IGATE setup shown on the left is now working receiving GPStracker signals and sending APRS position reports to internet APRS servers. The system will serve other APRS trackers in the local area as well as myself. Aircraft reception range should be very good. For some $500 bucks you can setup an IGATE station too and help aviation. There is a lack of IGATEs in rural Montana, central Iowa, parts of Nebraska and western states. (Note: Some IGates stations can have multiple functions - weather station and/or APRS server and/or digi and IGate. So it is actually better than it appears. You can verify that by chasing "nearby" APRS traffic at findu.com in different directions and checking which IGate sent it to internet - the call sign after "qAO," in the raw code.)