[time-nuts] Divide by five ->Ensemble

Chris Albertson albertson.chris at gmail.com
Sun Nov 9 16:54:06 EST 2014

On Sun, Nov 9, 2014 at 12:45 PM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
> The main point is that NTP picks *one* source from among it’s batch of
> inputs and uses that. The ADEV of the output can be no better than the ADEV
> of the output.

The statement above is not correct.  NTP does not select just one clock.
The statement below is correct and is  what NTP actually does.   If you
look at the output from "ntpstat" you might think NTP selects one clock but
internally it's not going that.  The display is misleading.

In the case of an ensemble of clocks combined with a better approach the
> ADEV of the output can be better than the ADEV of the best clock in the
> group.

It's best to read this http://www.eecis.udel.edu/~mills/ntp/html/warp.html

In simple terms it searches for consensus range of time where all the error
bars of the various clock overlap and then eliminate clocks who d't agree
with the consensus.  Of those still "in" it figures out and kind of
weighted average.

I think you could do the same thing.  First find the set of 10MHz
oscillators who are in phase with each other to within some statistical
limit and then you compute the weighted average phase

Maybe start with "Clock Select Algorithm".

Chris Albertson
Redondo Beach, California

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