[time-nuts] Timing Distribution in Mountainous Terrain

[jimlux]

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).