Hi The gotcha may be that they only slip time under unusual conditions. Warmup / settling in could be one such condition. It may take some detailed looking to spot it.
Bob > On Oct 25, 2014, at 3:45 PM, Bob Stewart <[email protected]> wrote: > > Hi Bob, > > The antenna is actually outside. It's mounted to the eave just below the > roof line. It seems to be a better antenna than the one in the attic. It's > the best I can do at the moment. > > I'll have to do a comparison of the PPS from this and the PPS from my LEA-6T. > I think they're reporting the phase offset of the 10MHz to the PPS, but as > you say, I haven't measured it yet. > > Bob > > From: Bob Camp <[email protected]> > To: Bob Stewart <[email protected]> > Cc: Time Nuts <[email protected]> > Sent: Saturday, October 25, 2014 2:01 PM > Subject: Re: [time-nuts] Lucent KS-24361/Z3812A GPSDO initial setup > > Hi > > Spend the effort, get an antenna outside the house. Beg / borrow / steal a > UPS. Even a brand new one is less than you paid for the 3812. > > The PPS output on these is not typically designed as a “smoothed’ time > reference. The HP / Symmetricom design philosophy seems to have been that > dropping or adding time was an ok thing to do. Your 90 ns to 50 ns change is > a prefect example of this in action. > > One simple experiment: Set up a divider on the 10 or 15 MHz output. A dead > bug mounted PIC will do, there are many other alternatives. Compare that PPS > to the PPS out of the device. If your divider works properly, it should give > you a quick way to see if they are slipping the PPS relative to the OCXO. > > Bob > > > > > > > On Oct 25, 2014, at 2:44 PM, Bob Stewart <[email protected]> wrote: > > > > Hi Bob, > > > > The thing is: I don't really need a frequency standard other than as a > > reference for my GPSDO project. I'll have to look into pulling out that > > message every second to see if the correction makes it a suitable phase > > reference. No, the nanosecond level probably isn't suitable for your > > needs, but I think it fits mine. My target audience remains the hobbyist, > > not the professional. > > > > It will be interesting, as it ages in, to see how it likes the antenna at > > the south window that it's sharing with my project. If I don't see any > > glitches, it may be time to pull the wire through the attic, rather than > > through the window. I guess I could also get some good information running > > it with the antenna in the attic for awhile. But you do make a good point > > about power supplies. Santa may bring a small UPS for Christmas to power > > this, my project, and the splitter. > > > > At the very least, this gives me a lot of information about GPSDOs that I > > didn't have in the past. And there's that EFC pin-out back near the OCXO > > that I could watch with my 3456A, to see what the dynamics are on a "real" > > GPSDO, once it ages in. > > > > Bob > > > > From: Bob Camp <[email protected]> > > To: Bob Stewart <[email protected]>; Discussion of precise time and frequency > > measurement <[email protected]> > > Sent: Saturday, October 25, 2014 1:22 PM > > Subject: Re: [time-nuts] Lucent KS-24361/Z3812A GPSDO initial setup > > > > Hi > > > > 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 <[email protected]> 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 > > > > > > > > Bob - AE6RV > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] > > > To unsubscribe, go to > > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
