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Dumb question: I use GPS to know where I am and where I am going when traveling. What do you use it for at a fixed location where you already know where you are? Tracking continental drift, or what?
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a GPS receiver provides a once per second "tick", referred to as 1PPS (one pulse per second).
this 1PPS signal is the result of the atomic clock ensemble aboard each GPS satellite.
due to the satellites relative motion, and a bit of atmospheric hocus-pocus (technical term), there is a bit of jitter (time variation) from one pulse to the next.
but, if you average thousands of these pulses (i.e., over thousands of seconds), you end up up with an astonishingly accurate 1PPS metronome.
this metronome can be used to steer a traditional crystal oscillator into perfect timekeeping, and thus provide a near-atomic reference 10MHz signal.
this process is called "disciplining", where an accurate reference signal is used to constantly correct a less inherently accurate slave signal.
and, hence, the GPSDO -- GPS disciplined oscillator.
a GPSDO marries the excellent phase noise (short term) characteristics of an oven stablized AT cut quartz crystal with the unerring (long term) stability of the atomic clocks orbiting in the GPS satellite constellation. low noise, and no drift -- that's the way i like my reference frequency sources!
ar-jedi