GPS receivers may be available for well under $100 these days, but what’s the fun in buying one when you can build it yourself? According to [Andrew], the creator of this device, he was inspired by Matjaž Vidmar who developed a GPS receiver from scratch over 20 years ago. His article can be found here and includes some nicely hand-drawn diagrams as well as a lot of theory.
However, [Andrew's] article is a bit more up-to-date and features plenty of theory itself. He explains how he built his four-channel GPS receiver, able to track four satellites at the same time. This is the minimum number of satellites needed to track your position using such a device.
GPS technology is quite incredible, and the amount of soldering as well as the understanding of the theory behind it required to build such a device is astonishing. Interestingly (sadly?), it seems we are beyond the time of LORAN hacks, but if you have an old one to share, be sure to send it in! For something a bit easier, maybe one could try making a GPS “cateye” to track what your pet does all day!