jim...@earthlink.net said: >> Well, at JPL we regularly lock two crystal oscillators together that are >> over a billion km apart with added Allan deviation of less than 1E-15 at >> 1000 seconds with a radio link at 7.15 GHz. It's how we measure the >> distance and velocity to spacecraft (a few cm in range and mm/s in >> velocity) and from that figure out the gravitational fields (among other >> things)
> It's just how we do radio science/ranging - you transmit a spectrally pure > signal from earth (typically oscillator locked to a maser), at the > spacecraft you have a very narrow band PLL (traditionally a VCXO) that > locks to the received signal, and you generate the downlink signal from > that same oscillator, transmit it back to earth, and compare. A "spectrally pure signal" gets you a frequency offset for velocity, but it doesn't get any timing info. How do you get range? -- 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.
