[time-nuts] Timing Distribution in Mountainous Terrain

David C. Partridge david.partridge at perdrix.co.uk
Fri Sep 10 08:27:11 UTC 2010


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? 

Regards,
David Partridge


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of jimlux
Sent: 10 September 2010 06:14
To: richard at karlquist.com; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain

Rick Karlquist wrote:
>
> I would like to point out that the environmental sensitivities of the 
> 5071A are unmeasureable, and the measurement threshold is far below 
> 5.8E-14.  I would estimate that the 5071A (and ONLY the 5071A among 
> commercial clocks) could get the job done provided that you could 
> compare its frequency to GPS to the stated accuracy.  This would be 
> using the 5071 as a secondary standard.  You still need to deal with 
> the short term stability of the 5071A, depending on your system needs.  
> JPL uses H masers as flywheels.


We also use the maser as a very low phase noise signal in the 10-1000 second tau range..
We multiply it up and send the (very clean) signal out to the spacecraft, it gets tracked by a loop with a few Hz BW, then sent back to earth where it's compared to the maser again to measure Doppler.

Basically we measure doppler and doppler rate over a few minutes, assuming that the transmitted signal is constant during that time (which the maser is, for all practical purposes).  Over a longer time span (e.g. the time between transmit and receive, which could be many hours, implying that we are transmitting from one station and receiving from
another) I assume we use atomic standards and/or astronomical sources (pulsars).

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