This guy's site (without a reasonable index page :/, use Google for it) has all kinds of interesting timing reference stuff.
True, I really should make an index page. I mostly throw stuff up and send links to the people I want to see it.
Cheap nav-type gps'es aren't really good timing wise - but then again, one person's 'awful' may be another person's 'awesome'. We all start somewhere. I did PPS measurements on two common receivers, the garmin GPS-18x, and the S1513R which is a Skytraq Venus 6 series.
http://n1.taur.dk/gps18x/http://n1.taur.dk/s1513r/Together with a cheap OCXO, you get, from a 'normal' user's perspective, a rather awesome _traceable_ reference.
My advice: If building a GPSDO has your interest, build one, quick. Then, if you are dissatisfied with it, build another. Don't plan endlessly for a better one you never get around to building.
This one I never got around to finish:
http://n1.taur.dk/gpsdo2a.pdfIt is basically 'lab notes' on a GPSDO, the most interesting part being the super-cheap interpolator to get nanosecond resolution from a 10MHz clock. Some of the PICs have a roughly-a-nanosecond interpolator on-chip, but I didn't have one of those.
/Kasper Pedersen