The Satpack is an ATmega328 controlled satellite tracker with doppler tuning. To calculate the position of the satellite, they use qrpTracker, which is an Arduino friendly program based on James Miller’s Pan-13. Next, the Arduino tunes the radio to listen to the transmitted Morse code. Amazing! It’s open source, so check out the link for a lot more information on building your own Satpack.
Here’s a video of the Satpack code tracking a few satellites. Note that the tone of the cubesat drifts a bit. The keps were a bit old, but in a addition, I just got a letter from James Miller, the author of Plan 13 who recommends some constants that are more in keeping with the earth model used in today’s GPS engines.