For a little more information on the build process for this tracker, see its post on the old 4hv.org forum.
After evaluating a variety of tracking methods based on fm transmitters with high gain antennas running at various frequencies, and even a RDF system based on detecting the phase between 2 antennas (the idea being that if the antennas are pointing strait toward the transmitter the phase would be the same, but perpendicular to the transmitter they would be out of phase by an amount that could be calculated by the distance between the antennas and the speed of light), I ultimately decided that I didn't like any of them and wanted to switch to a system that would tell me exactly where the rocket is. The only practical way of doing this was to use a GPS receiver paired with a wireless modem that would transmit coordinates back to a base station, which could be entered into a handheld gps unit and the rocket could be found quite easily. After some research I managed to find a GPS module and RF modem that would fit in my 38mm diameter airframe, and was reasonably priced (about $75 each for the modems and $60 for the GPS).
The GPS module I decided on was a lassen IQ GPS, paired with an small patch antenna. The wireless modem I used was an xe900s-500.
After getting all of the parts in (that was an awesome christmas morning!) I made up a quick prototype and did a little testing, and after sorting out a few bugs in the xecom modules (they must have been a very early revision, one of them had the status LEDs installed backwards, one did not auto detect the parity while the other did, little things...) I managed to get a proof of concept working:
Unfortunately, the range for this tracker was useless. I couldn't get a connection for more than a few hundred feet, and I was lucky to be able to talk to the rocket while it was on the bad not to mention in the air. In retrospect it was probably due to not mounting the antennas on a proper ground plane, and that it could probably have been salvaged with slightly better RF design. But regardless, the protoboard construction didn't hold up to the rigors of rocket born flight, so a better design was needed. Thus was born GPS Tracker Rev 2.
questions? comments? Want to help? email me firstname.lastname@example.org