On 09/10/2010 07:17 AM, jimlux wrote:
Ralph Smith wrote:
On Sep 9, 2010, at 8:01 PM, 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.
I would imagine the cost of a 5071A per radio station would make the
check writers swallow hard, and adding an H Maser into the mix would
really get their attention. Especially if you need redundancy.
there's also the possibility mentioned earlier of using a lower quality
standard at each station and flying (driving) a higher quality clock
(5071) around often enough to keep them trued up.
If it's far enough in the future.. Hg ion traps have a lot of
potential.. smaller, lower power, etc. than Cs
Commercial availability is somewhat limited. A problem with Hg ion traps
would be ROHS, unless they can be exempted or assumed to be within the
telco exempt, which would be a legal twist on the commercialisation aspect.
Another aspect I have been wondering about is the trap hold-length, I
think I recall that there was some issues relating to that...
I think, though, that some sort of self calibrating array using the
target of interest is a better scheme.. multiple receivers at each site
separated by some distance. Getting milliradian angular resolution is a
piece of cake.
That moves the expense, and I don't think the available receivers have
that option. They intend the spatial separation to be in kms and not m.
Cheers,
Magnus
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