[time-nuts] Lucent KS-24361/Z3812A GPSDO initial setup

Bob Camp kb8tq at n1k.org
Sat Oct 25 14:22:40 EDT 2014


Remember - these gizmos are designed as a CDMA base station reference, not as a Time Nut frequency (or time) standard. They (likely) had a +/- 100 ns spec on the gizmo for static time error when locked to GPS. The little trained squirrel inside makes an executive decision to move the PPS when it gets to close to that (or some other) limit. 

The filter algorithm in these adapts to the rate of change of the OCXO. On a unit that has been on the shelf since 2000 or 2001, it probably will take a while for the OCXO to settle down and hit a low aging rate. Until it does, the filter will not “stretch out” to it’s longest tau / lowest bandwidth. You can watch the thing switch, it’s pretty obvious on a phase plot when it does. The switch points are where the back and forth phase change slows way down compared to what it was doing. 

> On Oct 25, 2014, at 12:05 PM, Bob Stewart <bob at evoria.net> wrote:
> Regarding my comment earlier that my GPSDO and this Z3812A don't agree on phase.  I see just now a fairly quick phase movement of the phase between the two, and I see that there is a line on the Satstat program that may explain this:  1PPS TI +50.0 ns relative to GPS.  Just a few minutes ago, it said -90.0 ns.  Watching a bit more closely, the phase difference seems to track this figure +/- the phase error on my unit.
> Can anyone shed any light on this?

Bottom line: Hook it up on an independent power supply. Give it it’s own antenna. Put it in a corner away from drafts and crazy temperature changes. Just forget about it. Let it run forever and ever. It will (eventually) settle down and do a pretty good job. How far it settles depends on a lot of things, including just how good the particular OCXO you have is. 


> Bob - AE6RV
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