[time-nuts] ensemble oscillators for better stability

Tom Van Baak tvb at LeapSecond.com
Sat Dec 29 17:11:58 UTC 2012

> Hi,
> I've been playing around with 2 HP 5065A standards to see if averaging
> them will give better stability.


So that's an interesting experiment. I think the key is keeping them in tight phase so that what you gain in combined performance is still better than what you lose with the additional mixing electronics.

A couple of comments that come to mind.

1) This was a topic some years back -- for internal use, hp tightly combined multiple 10811 oscillators so that the net phase noise or short-term performance was significantly better than any one of the constituent oscillators.

2) It would be nice to be able to extend this to more than 2 oscillators, in such a way that you gain by sqrt(N) without corresponding losses due to increased noise.

3) You already realize that being able to keep coherence between the standards as long as possible is highly desirable.

4) Consider that none of the UTC(k) timing labs use your technique. The reason is that it's far easier to compare N frequency standards in near-realtime (like every second or every 100 s, etc.) combining the measurement *numbers* than it is to combine the actual *electrons* coming out of the frequency standards in realtime.

So this is one reason why I keep encouraging those of you building amateur, inexpensive, high-resolution, multi-port phase comparators.

If you had a couple of these comparators you'd simultaneously measure each of your 5065A and perhaps several other standards all using a common reference. It wouldn't really matter which standard was the reference, since the data is all pair-wise relative.

It's trivial to create an ensemble in software, based on multiple phase measurements that arrive by spi or gpib or rs232. With that calculated mean phase you can then ex post facto apply a correction to each of the oscillators in the ensemble. It's like sawtooth correction; you take the pulse as you see it, but you apply a freshly calculated correction factor.


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