[time-nuts] PPS sync

Chris Albertson albertson.chris at gmail.com
Mon Jun 5 01:06:14 EDT 2017

One of the GPS units is likely sending a saw-tooth message out the serial
line that exactly describes the 0 to 100ns drift.   This is why they call
it "saw tooth" the function ramps up slowly then falls to zero.  A device
like a GPSDO that uses the PPS would need access to the serial data to read
the sawtooth correction,

On Sun, Jun 4, 2017 at 9:36 PM, Jerry Hancock <jerry at hanler.com> wrote:

> 1) I have my TAPR M12 Kit working now next to my lucent RFTG-U REF0/1
> pair.  I was comparing the PPS outputs triggering on the Lucent as channel
> 1 and the M12 as channel 2.  I can’t tell which is moving around but the
> symptoms are that at T0 (not the top of the minute or hour) they are in
> sync within a nanosecond.  From T1 to T20 they move progressively out of
> sync until hitting around 100ns and then snapping back to being in sync. I
> would think that if both were moving that it wouldn’t be that consistent,
> no?
> Since I can’t tell which is moving, most likely both,  I plan to take the
> disciplined 10Mhz out of the Lucent and divide it down with my TAPR TADD-2
> to 1PPS.  I would think that would be more stable on a PPS by PPS basis and
> compare again.
> Any other ideas?
> 2)  When I first fired up the M12 and let it do a survey, it was off for
> some reason by 7KM.  I then set the M12 reference location to the Lucent
> location as I know it to be correct.  I was thinking though, would the PPS
> phase comparison in 1, above, be impacted by the reference locations being
> off?  Both GPS cables are the same length.  The only thing I don’t know is
> the internal processing delay of the units.  The SynTac software allows you
> to take this into consideration for PPS timing when using the M12.
> Interesting unit by the way.  Lots of configuration options exposed with
> the Syntac software.  Not that I would replace Lady Heather or anything,
> I’m just using it while I get some of these issues figured out.
> Jerry
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.


Chris Albertson
Redondo Beach, California

More information about the time-nuts mailing list