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

Azelio Boriani azelio.boriani at gmail.com
Tue Jan 20 02:44:49 EST 2015


So, your PPS wander is measured by the GPSDO internal TIC and the
result is sawtooth corrected and usually gives 6ns, suddenly it went
to 25ns. Well, the first move, IMO, is to connect an external TIC and
track the GPS PPS against the GPSDO PPS and see whether, when you have
the jump, it is recorded only by the internal TIC or not. You have a
log file: what's in it? You said that the PPS was still getting
corrections but what about the uncorrected PPS wander? Was it still
the same after the jump? Can you share your log file with the data
before and after the jump? I'm assuming the log file has the raw PPS
measurements and the applied corrections listed every second.

On Mon, Jan 19, 2015 at 6:27 PM, Dan Kemppainen <dan at irtelemetrics.com> wrote:
> 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.
>
>
> Thanks!
>
> Dan
>
>
>
>
>
>
>>
>> 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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