[time-nuts] synchronizing a large number of weakly coupled oscillators
lists at rtty.us
Thu May 13 11:22:51 UTC 2010
.... and allow for meshes in your synchronization to combat path issues.
On May 13, 2010, at 6:13 AM, Magnus Danielson wrote:
> 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.
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