[time-nuts] Ublox 6T receiver, noisy PPS.

Dan Kemppainen dan at irtelemetrics.com
Mon Jan 19 12:27:15 EST 2015

Hi All,

I'll respond to all here, since I'm a little slow at times...

John, This unit has been up and running for at least a month. I've 
restarted the GPSDO a few times, but the GPS has remained on. So, if 
your unit is up for extended periods of time and you see something 
similar, please report back.

Azelio, That spec is much worse than what I've been seeing. Not having a 
CS and other equipment it's hard to know exactly how good/bad the GPS 
really is. However the TIC in the GPSDO reporting short term (<500s) 
differences against the OCXO on the order of +/-3nS Peak (6nS 
Peak-Peak). Long term (24 hours) there are furnace/HVAC swings that 
appear to push that up to +/- 7nS or 8nS (14 to 16nS Peak-Peak).
About a week ago, those short term levels jumped to +/-25nS Peak (50nS 
Peak-Peak). I let it run, over several days saw no improvement. After 
the 48hour survey, it dropped back to the 'normal' levels instantly.

Bob, This unit is using sawtooth correction. The saw tooth correction is 
on the order of +/-10.3 nS max. It absolutely improves the measurement! 
It appears in the log file that the PPS was still getting  corrected. My 
feeling is it's doubtful the OXCO was doing it, as the survey in changed 
the results.

Do you have a feel for what a 1.8m/6ft error in antenna coordinates 
would do PPS results?

Any other insights you might have would be appreciated.



> Hello Dan,
> I have a LEA-6T running; have a nice external antenna, etc - it's been
> running for several days - I will check the 1PPS and report if I find
> anything like what you've discussed.
> Regards,
> John

> I have noticed the sudden improvement of the PPS wander after the
> survey on a LEA-5T but the RMS wander is 30ns (see the timing appnote
> GPS.G6-X-11007 from uBlox) uncorrected and 15ns if sawtooth corrected.
> Your 3ns is strange, not the 30ns.

> Hi
> It sounds like you are not doing sawtooth correction. If that is correct, then you may have been watching hanging bridges.
> Bob

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