On 2/6/15 1:21 AM, Javier Serrano 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?
The only thing that might be better is if you have a control loop that
forms a model and generates corrections based on that, so that while you
holdover, it's not just a constant tuning voltage, but perhaps a slow ramp.
For instance, if your control loop has estimated the aging rate (and you
have an oscillator that ages really, really fast), you could do that.
or if your control loop ingests the temperature and has calculated the
temperature/frequency transfer function.
But it seems that you have a fairly short holdover time requirement
(seconds, maybe a few minutes?) I'm not sure the environment changes all
that much in that time span. A simple "hold the control voltage" might
be as good as it gets.
I've looked into more complex schemes for situations where you are
tracking out something that changes fairly rapidly (Doppler shift for an
orbiter) and in a way that isn't a nice linear slope (which could be
done nicely by a PID kind of loop).
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
