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

[Bob Camp]

Hi

If you add the +/- 20 ns of sawtooth on top of that you can quickly get some pretty big numbers.

Bob

On Sep 13, 2014, at 8:39 PM, Tim Shoppa <tshoppa at gmail.com> wrote:

> "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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