[ntp:questions] failing-over flaky upstream servers

Paul paul-ntp-questions at lookmumnohands.net
Thu Mar 12 18:12:58 UTC 2015

> >   3. PPS signal derived from GPS.  Excellent accuracy, but only
> >      available say 90% of the day due to satellite visibility.
> You should get a better (timing) receiver.  I have an 18x-LVC in the
> "window" of my interior office in a rehab'ed machine room (they did
> cut out some exterior windows) and I get a "valid" signal 97% of the
> time.  Admittedly it's probably all multipath but it manages
> sub-millisecond offsets from more reliable clocks.

Yes, I probably should  :-)

This; too; is a Garmin GPS18-LVC.  As for my bold claims of 90%
availability... turns out I was rather overstating it.  78% is more
like it.  It's sitting next to an external window.  As you'd well
know, the PPS signal stops when the unit is tracking less than three
satellites.  At least the NMEA sentences keep coming.

> > If I recall correctly, in order for PPS to function it needs a
> > "prefer" peer, and I am unsure what the best selection is.
> Versions  prior to 4.2.8 allowed you to use PPS + LOCAL.

Now that sounds quite sensible.  I'm using a custom compiled 4.2.6
here at the moment, so looks like I'm in luck.  (The whole "prior to
4.2.8" thing is a bit of a worry.  On the face of it, it sounds like a
regression, though no doubt there was a good reason for the change.
Trouble is I'll now need to remember never to upgrade /for that
particular reason/.)

> A new GPSDO can be had for much less than a Cesium (Cs) or Rubidium
> (Rb) standard if you do want to go that way.

Well, yes.  Maybe next time around!

> In each case you probably want to use orphan mode.

Was not aware of that.  I will need to do some reading.


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