[ntp:questions] National time standard differences

John Ackermann N8UR jra at febo.com
Fri Feb 12 13:22:50 UTC 2010


David J Taylor wrote:
>> The flying clock tests were closed loop (I think there's a more 
>> accurate term for the process) where the clock, including both its 
>> initial time error and its frequency offset (rate difference from USNO 
>> or NIST), was well characterized via radio and against a set of 
>> similar clocks prior to take-off.  At the end of the trip, the clock 
>> was measured again.  The time difference between departure and arrival 
>> was proportionally applied to the measurements taken along the way.  
>> e.g., if the clock was known to be 10ns/day fast during the trip, you 
>> adjust a measurement made on the 3rd day by 30ns.  There were lots of 
>> additional statistics applied to improve the measurement results.
>>
>> John
> 
> Thanks, John.  Was the measurement down to the nanosecond level?
> 
> Cheers,
> David

Hi David --

I haven't had a chance to review the article about the 1964 trip, so 
don't recall all the details, but I know that the HP advertisement about 
the experiment had a tag line that after seventeen days or whatever, 
"somewhere along the way we lost a microsecond."  So they clearly were 
measuring at sub-microsecond levels.

That first experiment was done with HP 5060A cesium standards and there 
have been several generations since; the HP 5071A that's been available 
since the early 90's is perhaps three orders of magnitude better than 
the 5060A.

BTW -- someone cited a paper showing relativistic effects of a 
round-the-world flying clock trip in both directions.  That, I believe, 
was done with the 5071A.  Another great experiment -- done by an amateur 
time-nut, Tom Van Baak -- took three 5071As on a camping trip up a 
mountain in Washington state and verified Einstein's prediction of a 
change in clock rate with elevation.  Take a look at 
http://www.leapsecond.com/great2005/index.htm and be amazed.

John




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