[time-nuts] Trimble Resolution SMT GG weirdness

[Azelio Boriani]

Yes, the sawtooth correction is limited to tens of ns and is rapid: 10 to
30 seconds usually, the wander is larger and very slow.
If you want to build a simple GPSDO with a PPS output and disciplined by
the GPS PPS, take a look at my design:
http://www.c-c-i.com/exchange/
file: PiAutoTIC1.zip


On Tue, Apr 23, 2013 at 12:39 PM, Daniel Ginsburg <dginsburg at gmail.com>wrote:

>
> On 23.04.2013, at 12:50, Azelio Boriani wrote:
>
> > Daniel,
> > a timing GPS receiver is not a GPSDO so its PPS is wandering about the
> > nominal position. Using a digital oscilloscope, I can see how much the
> > total wander is by activating the infinte persistence mode of the
> display.
> > After 10 minutes, 1 hour, 1 day or whatever you have an idea of the total
> > "coverage" of the wander. The trigger comes from a Z3815A reference. To
> see
> > the "dance" of the PPS coming from a GPS receiver, a simple crystal
> > oscillator as a reference is enough: use your microprocessor to generate
> a
> > PPS from its clock and visually compare this generated PPS with the GPS
> PPS
> > by a 'scope.
> >
>
> Ah, I see now. Preoccupied with issue at hand I wasn't attentive enough
> and I somehow thought that you were talking about 112ns wide sawtooth,
> while in fact you were talking about wander in sense of ... well ...
> wander. Sorry for the confusion.
>
> >
> > On Tue, Apr 23, 2013 at 7:49 AM, Daniel Ginsburg <dginsburg at gmail.com
> >wrote:
> >
> >>
> >> On 23.04.2013, at 6:15, Hal Murray wrote:
> >>
> >>>
> >>>> I wonder, what kind of timing GPS gives 112ns wander?
> >>>
> >>> How good is your antenna?  112 ns is roughly 112 feet.  That's not at
> all
> >>> surprising if your antenna is inside or under trees.
> >>>
> >>
> >>
> >> Not perfect, but should be reasonably good. It's an external magnetic
> >> antenna on my windowsill.
> >> Anyway, +-400ns I'm seeing translates to +-120m in position. My surveyed
> >> location is better than this.
> >>
> >>> You might watch the number of satellites and/or watch the position
> while
> >> it
> >>> does a survey.
> >>>
> >>
> >> 6-10 SVs, with PDOP in range 1.6 - 3.9 (about 2.0 most of the time).
> >>
> >>>
> >>> --
> >>> These are my opinions.  I hate spam.
> >>>
> >>>
> >>>
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