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

Bob Camp kb8tq at n1k.org
Sun Sep 14 09:10:59 EDT 2014


Hi

If it’s the same Res-T that I’ve seen the data sheet on, yes it does have sawtooth correction data coming out of it. You do have to take out the sawtooth to get it to run as well as it can.

Bob

On Sep 13, 2014, at 8:52 PM, Peter Reilley <peter at reilley.com> wrote:

> I don't see any mention of sawtooth correction in their documentation.
> I take that to imply that sawtooth correction is not necessary to get 
> the 15 nS that is spec'ed?
> 
> Does the 15 nS imply that the internal clock is 33 MHz?   That is: +-15 nS
> is 30 nS which is 33 MHz.   Is that correct?  Or do they need a higher
> internal
> clock so that all errors sum to less than 15 nS? 
> 
> Pete.
> 
> 
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
> Sent: Saturday, September 13, 2014 8:03 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from
> aGPSreceiver.
> 
> Hi
> 
> I'm sure they expect you to take out the sawtooth error before you do the
> comparison. Are you doing that?
> 
> Bob
> 
> On 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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