[time-nuts] 1 pps Sync'ing

Attila Kinali attila at kinali.ch
Mon Jun 25 16:37:20 UTC 2018


On Mon, 25 Jun 2018 10:46:54 -0400
Bob kb8tq <kb8tq at n1k.org> wrote:

> Does UTC exist ( real time ) at the 1 ns level? 

Currently, it does not. The clock comparison uncertainties are
still in the order of 1-3ns for short distances (several 100km)
and grow quite a bit once you go over something like 2000-3000km.
Unless you are using a dedicated fiber. But very few labs can
afford to have a fiber connecting them to another lab.

Also consider that, even within a lab, doing sub-ns accurate
time comparisons is challenging. All delays and their drifts
need to be precisely measured, characterized and factored in. 
There is a reason why the SR-620 is still the main workhorse
in metrology labs, even though we have equipment available
that beats the SR-620 in terms of resolution and stability.
It's just not necessary to go below 20ps as the other factors
cannot be eliminated with that high precision/accuracy anyways.

If only precision time comparison is required, IIRC the current
limit is around 50-100fs. And even that requires a lot of work
and characterization.

			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson



More information about the Time-nuts_lists.febo.com mailing list