[time-nuts] Setting up PRS10 with M12+T GPS

[bg at lysator.liu.se]

Jerry, Magnus,

> Considering the M12+T PPS noise, you won't need anything stellar. A
> PICTIC II will do just fine... or if you trust the PRS-10 readings, run
> from that.
>
> What would make this better would to use a sawtooth-correction to PPS
> delay setup, as the PRS-10 measurement resolution will be about on par
> with that. Would lower the effects of hanging-bridges, even if one
> suffers less when dealing with a rubidium.
>
> Adjust the PRS-10 PLL bandwidth/time-constant, the default value is most
> probably not optimum, you can go further up in time. Do check the manual.

But do not have a large PLL time-constant, while you are checking basic
functionality. Time-constants are shown in a table on page 35 in the
manual.
With default (PT=8) settings it will take hours for the pll to get close
in. Any tinkering with moving the pulse (PP) or delay calibration (TO)
will take forever to show if you got the sign right or hade the right
offset size... ;-(

Calibrate the Time offset (TO) according to the example on page 32 in the
manual, by looping the 1pps_out to 1pps_in on the PRS10, keep in mind that
you should use the cable, buffers, etc that later will take your GPS 1PPS
to the 1PPS_in on the PRS, so that you really take care of all delay from
the GPS 1pps to the PRS10, including internal PRS10 delays, that might
have changed from previous calibration.

Also have in mind that the 1pps disciplining wants 256 good measurements
in a row just to start closing the PLL.

Take the time constant down to 0, and make yourself confident that all
offset calibrations are right and that you are tracking the right edge of
the GPS 1PPS etc. After all tinkering to get the basics right then
increase the time-constant to filter out 1PPS noise and outliers.

To check performance later, you could check that the PRS10 timetag (TT)
stays very low, by polling each second and logg these values.

I am not at all an expert on PRS10. Have spent the weekend trying to get
two units to sync to each other. I would like to have a simple (quick
feedback) way of making sure that most time bias'es are removed. A
free-running Tbolt for example gives a low noise 1PPS, and quickly
tracking that, would make bias elimination much less time consuming.

Anyone having an efficiant scheme for setting up a PRS10?

--

    Björn
>
>> On Wed, May 2, 2012 at 9:46 PM, Jerry Mulchin<jmulchin at cox.net>  wrote:
>>
>>> I need some guidance from the collective.
>>>
>>> I just finished rebuilding my PRS10 lab standard and it is now using a
>>> M12+T GPS module.
>>> I have completed my site survey and it is now in "hold position mode",
>>> TRAIM is enabled
>>> with 500ns alarm setting and the 1PPS is enabled during non-TRAIM alarm
>>> conditions.
>>>
>>> The PRS10 is set for default 1PPS steering, but all of the other
>>> parameters are just as
>>> I received the unit 5 years ago.
>>>
>>> My questions are these;
>>>
>>> 1.) Should I reset the PRS10 to its Default settings or just adjust
>>> selected parameters to
>>> align the unit for proper operation with the M12+T unit? And if that is
>>> the case, what parameters
>>> need adjusting?
>>>
>>> 2.) Are there any special settings, other than what WinOncore sets,
>>> that I
>>> should make to the
>>> M12+T unit?
>>>
>>> 3.) After all this is completed, how do I know that the PRS10 is
>>> properly
>>> tracking GPS and
>>> maintaining frequency accurately? I don't have a Cesium reference, but
>>> I
>>> do have an un-disiplined
>>> LPRO-101, but I don't think that really helps me determine frequency
>>> accuracy.
>>>
>>> I will be adding the sawtooth correction eventually to the M12+T 1PPS
>>> output, but observed
>>> negative sawtooth with WinOncore shows +/- 14ns changes with some
>>> bridging
>>> occasionally.
>>>
>>> While I don't ever want to claim NIST traceability, I would like to be
>>> a
>>> close as possible, and I
>>> guess that is the bottom line need here. So what else do I need to do
>>> to
>>> get as close as possible?
>>>
>>> Thanks for any help.
>>>
>>>
>>>
>>>
>>> Jerry Mulchin
>>>
>>>
>>>
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