[ntp:questions] National time standard differences

John Ackermann N8UR jra at febo.com
Thu Feb 11 20:30:29 UTC 2010


Richard B. Gilbert wrote:

>> But if they are comparing time standards, it does not matter where the
>> clocks were manufactured, but where they are synchronized with the time
>> standard, and that is surely in Washington, not Palo Alto. You do not 
>> try to synchronize a clock in Washington via phone lines or
>> microwave links with Palo Alto surely.
> 
> ISTR that NIST has facilities in both Colorado and Hawaii.  The 
> Washington DC area has the U.S. Naval Observatory.

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




More information about the questions mailing list