One option not yet considered is to use a portable clock (or clocks) transported regularly (every 20 minutes?) between stations for frequency comparisons. It may be feasible to use a set of rubidium clocks (for the station clocks and the portable clocks) in this manner at least for short baselines.
Bruce On Thursday, May 05, 2016 11:14:37 AM Bruce Griffiths wrote: > In the same vein if it takes 1000 seconds to measure the relative phase of a > pair of clocks to within 500ps then the relative ADEV of the clock pair at > 1000 sec needs to be somewhat less than 5E-13. > For 100 s averaging the relative ADEV of a clock pair needs to be better > than 5E-12 @ 100sec. > For 10s averaging the relative ADEV of the clock pair needs to be better > than 5E-11 @ 10s. > Thus if the measurement takes too long the cost of the local clocks becomes > unaffordable. > Comparison techniques that don't require more than 10-100 sec of averaging > are preferable to keep the cost of the local clocks sufficiently low. > > Bruce > > On Wednesday, May 04, 2016 03:03:59 PM Tom Van Baak wrote: > > Hal, > > > > > How close could you get if you brought two of them together, compared > > > phase, drove them to the site for a nights work, drove them back to the > > > same location and compared the phase again. > > > > That's essentially asking what the ADEV (or, TDEV) is for tau 1 day. Rb > > isn't near good enough. Neither is Cs, for that matter. > > > > See www.leapsecond.com/tmp/5071a-12-run8-5d-10d.gif for a plot of a bunch > > of 5071A Cs clocks. They are compared together for 5 days to determine > > their relative phase and frequency offsets and then go on a 5-day trip. > > You can see how the phase drifts as random walk does its thing. It's way > > more than 500 ps per day. > > > > That's why the OP cannot use free-running clocks. He needs some method to > > actively keep them in tight phase lock or passively compare them to within > > 500 ps in order to adjust the timestamps in post-facto. > > > > /tvb > > > > ----- Original Message ----- > > From: "Hal Murray" <[email protected]> > > To: "Tom Van Baak" <[email protected]>; "Discussion of precise time and > > frequency measurement" <[email protected]> Cc: <[email protected]> > > Sent: Wednesday, May 04, 2016 10:30 AM > > Subject: Re: [time-nuts] Fw: Optical transfer of time and frequency > > > > > [email protected] said: > > >> Any of these methods is going to be a challenge, given their 500 ps > > >> requirement and their $2k budget. > > > > > > How stable are surplus rubidium oscillators? > > > > > > How close could you get if you brought two of them together, compared > > > phase, drove them to the site for a nights work, drove them back to the > > > same location and compared the phase again. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the > > instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the > instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
