[time-nuts] synchronizing a large number of weakly coupled oscillators

Magnus Danielson magnus at rubidium.dyndns.org
Thu May 13 10:13:22 UTC 2010


On 05/12/2010 08:47 AM, Eugen Leitl wrote:
>
> Has anyone utilized a network of locally, weakly coupled
> oscillator synchronization (a la http://www.projectcomputing.com/resources/sync/index.html )
> for precise timekeeping purposes?
>

You have to realize that if you have N clocks interlocked, then their 
common frequency will tend to the average or weigthed average (if 
coupling is not the same). A single clocks deviation will not have full 
effect. It will help to solve phase noise if you monitor the full 
ensamble of clocks, but this effect is best at short-term stability.

It will not solve any form of common environmental effects such as 
temperature shifts. Mother earth turns, if faces the sun or the dark 
space. AC equipment may first-degree correct for it, but their cycling 
will replace it. The environmental effects would dominate iin the 
time-spans we would be interested in.

So in the end, many oscillators isn't as powerful as it may sound at 
first. For a network, the solution is to let some nodes have 
considerable better oscillators and steer the clock selection 
accordingly. This is what is done in SDH networks. See for instance 
ITU-T G.781. There is a tutorial from ETSI which designation just 
slipped my mind.

The use of mutually synchronised oscillators was investigated in the 
telecom world. I don't recall that anything useful came out of that, but 
searching for "mutual synchronisation" should get you some hits. I could 
dig up a few articles if you care to read about it. I consider it a dead 
end for the above reasons.

Cheers,
Magnus



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