> With the wrong date and time, the GPS should not find almanac data, so will > not lock.
I don't think that's the right way of describing the problem. The satellites broadcast on a known frequency, but that gets shifted all over the place by Doppler. ("All over" means a big shift relative to the bandwidth of the signal.) If you have a recent almanac and you know the date/time and location, then you can compute the Doppler and look in the right frequency and find the satellites quickly. In this context, "find" means hearing a signal at an expected frequency. If you don't hear anything where you expect it, then you get to check nearby frequencies. If you don't find anything nearby, you get to give up and start searching the whole Doppler range. It's the difference between warm start and cold start. Once you do find several satellites, you can figure out the date/time and location and after a while get a new almanac. Assume you have done all that. You still don't really know the date. It's like looking at a clock on the wall. It tells you the time but not the date. (Or looking at a digital display that tells you the month and day but not the year.) The GPS signal tells you the date within a 1024 week epoch, but it doesn't tell you which epoch you are in. Telling it the date has the side effect of telling it the epoch. Real early GPS gear punted this problem. There is no way to tell them the epoch. I don't remember any details, but there have been various discussions about gear that is now useless. (With some simple post processing, you could fix that. That's assuming you have a serial interface rather than a 7-segment display.) -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.