> I am curious if the first local oscillator on a GPS receiver must actually > be locked or coherent to the reference oscillator in the GPS receiver > typically running at some 10 MHz approximately. Or as long as the first LO > is quite stable it doesn't matter because the receiver can track the code. >
It doesn't matter, so long as the first LO is in the ballpark so that the Doppler search is not needlessly large. I'm not so familiar with the early receivers, but I imagine a single reference oscillator serves for everything---there would seem to be no reason to have more than one unless the antenna/downconverter were physically separate from the rest of the receiver. If an older receiver used a physical source at 10.23 MHz, it would still need to be offset slightly for each satellite because of "code doppler", but this choice of frequency might slightly simplify the circuitry. Current receivers would use any convenient physical rate, then synthesize the code rates. Cheers, Peter _______________________________________________ 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.
