[time-nuts] Timing Distribution in Mountainous Terrain
jimlux at earthlink.net
Fri Sep 10 13:53:48 UTC 2010
David C. Partridge wrote:
> Jim is it possible you just gave a workable solution: Equip each site with a small radio telescope and watch pulsars.
> Aren't pulsars a reliable accurate time source or do they not provide the 30nS over ten days accuracy?
Pulsars *are* pretty stable.. the problem is whether propagation is
stable enough. Maybe with a flywheel..
GIMF (pulsar time stability) and it turns up a paper by Petit on DTIC
(the research was done in 1995 at BIPM in France)
Covers performance and all the perturbations (gravitation effects from
stars alongside the propagation path, propagation through atmosphere, etc.)
take home value: for tau of few years, ADEV of few parts in 1E15.
OTOH this paper also says the measurement uncertainty is 1 microsecond..
Also, one might look at:
Relativity and Timing in X-ray Pulsar Navigation
This paper is about XNAV (think GPS in deep space, using X-ray pulsars
as the S/Vs)... it seems to show that ModifiedADEV is 1E-13 (an order of
magnitude worse than "atomic clock"; presumbably Cs) at tau of 0.1 year.
ANother chart shows the relative performance of a whole raft of clocks
(and you can see why everyone is excited about JPLs Hg-ion clock...) In
any event PSR 1937+21 is about 1E-12 at tau of 500,000 seconds..
probably not good enough for the OP's need. (PSR 1937+21 has a period of
about 1.5 msec, by the way.. if pulsars are really a spinning star,
that's mighty impressive)
describes work on another millisecond pulsar.. the abstract says 100ns
uncertainties, and long term (3yr) residuals of 500 ns.
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