[time-nuts] Correcting jitter on the 1 PPS signal from a GPSreceiver.

Tim Shoppa tshoppa at gmail.com
Sat Sep 13 20:39:12 EDT 2014


"Within 15 ns to GPS or UTC (1 Sigma)" means that the 1 sigma spread is
30ns.

You have two units and assuming completely uncorrelated errors that would
mean expected 1 sigma spread between them, of 42ns.

Seeing frequent cases of 80ns delta when the 1 sigma spread is 42ns, should
not be surprising.

Tim N3QE

On Sat, Sep 13, 2014 at 6:41 PM, Peter Reilley <peter at reilley.com> wrote:

> I see in the Trimble Resolution T data sheet that they
> say that the PPS signal is "within 15 nS to GPS or UTC (1 Sigma)
> when using an over determined solution in stationary mode.".
> I take this to mean that the PPS signal should be within 15 nS
> and that comparing 2 units that there should be no more than
> 30 nS between the two edges.   This is comparing the rising edges.
>
>
> Pete.
>
>
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
> Sent: Saturday, September 13, 2014 6:26 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from a
> GPSreceiver.
>
> Hi
>
> Where are you getting the "15 ns accuracy" number from? When I look at the
> Trimble spec's they have a number of errors described (like sawtooth) that
> are larger than 15 ns.
>
> Bob
>
> On Sep 13, 2014, at 10:41 AM, Peter Reilley <peter at reilley.com> wrote:
>
> > I have 2 Trimble Resolution T receivers and I have compared the 1 PPS
> signal
> > between the 2 units.   They are spec'ed at 15 nS accuracy.    I am seeing
> > about
> > 80 nS of jitter between the two.   This is with about 6 satellites in
> view.
> >
> > I was thinking about ways to improve this.   Since this is a stationary
> > installation,
> > can you use the jitter in the reported location (latitude and
> > longitude) to correct for the 1 PPS jitter?
> >
> > The location data is derived using the internal GPS disciplined
> > oscillator so both
> > pieces of information should show the same jitter error.   If you compare
> > the reported
> > location with the known fixed location you should be able to use that
> > error to correct for the 1 PPS error.
> >
> > Does this make sense or am I missing something?
> >
> > Pete.
> >
> >
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