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
> > _______________________________________________
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>
>
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