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APRS

In a nutshell, Automatic Position Reporting System (or APRS) determines its position via GPS, then sends its position via radio to a remote receiving station. This receiving station is then able to track the movement of the APRS equipped vehicle. APRS has been around in the amateur radio community for over 10 years but today there are quite a few commercial systems using the APRS concept including Lo-Jack and OnStar.

The components required for APRS are fairly simple and one can equip their car, boat, horse, etc with APRS for under a couple hundred dollars. As shown in the photo, a GPS receiver determines its position based on differences in timing signals from several of the satellites in the GPS constellation. This data is fed into a tiny computer (TinyTracker3 in the photo) that processes this data into the format required by the APRS network. It then periodically generates an audio signal (radio modem tones) and passes it to the VHF radio attached. Once its on the air, another station recieves the signal and passes it into the global APRS network.

Once the data is in the APRS network database, various Web-based utilities can be used to display the location of the APRS node, and the path its been on over an arbitrary timeframe. The following 2 links show where my system is, where I've been, and how fast I'm driving. Scary huh? I think its only a matter of time before insurance companies are going to require a technology like this in order to qualify for reasonable rates.

Dude, where's my car?

• http://www.findu.com/cgi-bin/find.cgi?call=kc5cqm-9
• http://db.aprsworld.net/datamart/switch.php?call=kc5cqm-9&maps=yes

Dude, where's my bicycle?

• http://www.findu.com/cgi-bin/find.cgi?call=kc5cqm-4
• http://db.aprsworld.net/datamart/switch.php?call=kc5cqm-4&maps=yes

Update: I've been able to run the APRS system off a 5-watt solar panel and a 7.2 amp/hr gel cell battery. The GPS and APRS tracker draw about 80mw during operation, and I get about 6 hrs of good sunlight a day. So far the gel cell has been reading about 12.9 volts in the evenings, and dropping down to about 12.3 by morning. After a couple days of cloudy days the voltage dipped to around 12.0v, but it came right back up after a day of solid sunshine. This has proven sustainable.