[time-nuts] Good references on holdover?

[Tim Shoppa]

The state of the art 20 years ago is described here:
http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf

They understood their OCXO very very well. And you can find EFC trends on
the web for hundreds of different Z3801A's (and similar) if you want to see
how the EFC trends (and occasionally jumps). It is very intuitive to watch
the smoothed EFC graphs build over time.

They were specifically meeting a telco spec for 24 hour holdover. Your 3
second requirement is, um, a bit different! I have no idea what your local
clock is, or what you are locking to, if 3 seconds is a long time.

Tim N3QE

On Fri, Feb 6, 2015 at 4:21 AM, Javier Serrano <
javier.serrano.pareja at gmail.com> wrote:

> Dear all,
>
> We would like to start working on holdover performance for White
> Rabbit [1]. This is a new domain for us. Our main use case is a WR
> switch losing its reference because someone disconnects a fiber. We
> can have redundancy, but it will take some time for a switch to change
> over to another reference. During this time, the oscillator in that
> switch will be free-running. We want to minimize the phase drift
> during that interval, which we think should be a couple of seconds
> maximum. We have never worked on holdover, and I am wondering if we
> can do something smarter than the obvious feeding of some constant
> voltage to the VCXO, based on averaging during the locked state. Does
> anybody know of any good references on holdover?
>
> Thanks!
>
> Javier
>
> [1] http://www.ohwr.org/projects/white-rabbit/wiki
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