[time-nuts] Fw: Optical transfer of time and frequency

[Bruce Griffiths]

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" <hmurray at megapathdsl.net>
> > To: "Tom Van Baak" <tvb at leapsecond.com>; "Discussion of precise time and
> > frequency measurement" <time-nuts at febo.com> Cc: <hmurray at megapathdsl.net>
> > Sent: Wednesday, May 04, 2016 10:30 AM
> > Subject: Re: [time-nuts] Fw: Optical transfer of time and frequency
> > 
> > > tvb at LeapSecond.com 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.
> > 
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