[time-nuts] Trimble Resolution SMT GG weirdness

Daniel Ginsburg dginsburg at gmail.com
Tue Apr 23 10:39:14 UTC 2013


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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