GPS receiver

Contact Garmin, in Olathe, KS

...Jim Thompson

Any other sources?

GPS World and GPS New Product Digest are two of the leading trade journals.

You could use GNURadio and a USRP to do this (although the near-baseband IF might end up in slightly odd locations based on which transverter you use, although hopefully this won't matter to you). Most GPS receivers today use a highly integrated IC where you don't have any access to various intermediate RF signals.

Since GPS signals are below the noise level of a typical (couple dBi) antenna, just synchronizing to the chipping code involves a fair amount of effort if you've never done this sort of thing before. I've seen people "cheat" in the past (especially for university research projects where the research doesn't involve anything having to do with those low signal levels) by aiming a high gain dish up at a particular satellite such that their SNR is positive prior to the process gain provided by despreading. You're be in hog heaven if your university happens to have a radio telescope lying around!

You may want to re-post your question to a newsgroup such as sci.geo.sattellite-nav or alt.sattellite.gps if they're available to you... some of the folks who hang out there would know off the top of their heads what kind of radios let you access various internal signals that could be of value to your research.

---Joel Kolstad

Analysing the baseband is quite simple, for the C/A signal, you just need a 1.5m (or so) dish. For the military signal, a 34m dish should be OK.

There are a handful of exceptions to that rule, though, and I recently stumbled across these open-source GPS receiver projects:

The chip maker's reference design is close enough to some commercial receivers' designs that replacement firmware can be written, for educational purposes or (presumably) for specialized tasks that don't have a large enough market to support a commercial offering.

The two links up there are related, but the cwkelley site has some links to other projects along the same lines.