[time-nuts] GPSDO vs Rb standard

[Bob Camp]

Hi

The purpose here is to estimate the stability of a GPSDO. For that, you don't need "perfect". You simply need to get the Rb close enough that it's error is manageable.

Bob

On Sep 18, 2013, at 8:18 PM, Azelio Boriani <azelio.boriani at screen.it> wrote:

> The GPS's PPS wanders but it can be used to have an idea whether your
> Rb is fast or slow. How much the wander will be, depends on the type
> of GPS receiver, the antenna position and the survey, the GPS clock
> granularity (the sawtooth). Given a suitable amount of time (5
> minutes, for example) you can see if the Rb PPS is fast or slow. I
> have measured up to 200nS of PPS peak-to-peak wander using a Z3815A as
> a reference.
> 
> On Thu, Sep 19, 2013 at 1:37 AM, Bob Stewart <bob at evoria.net> wrote:
>> Hi John and Azelio,
>> 
>> The problem with the GPS 1PPS is the +/- 52ns sawtooth.  Without some magic hardware, you're left with using a stable 1PPS and then calibrating that to the correct frequency.  If my software does what my math says it does, then my OCXO is very close to correct.  Testing is time consuming to say the least.
>> 
>> Bob
>> 
>> 
>> 
>> 
>> 
>>> ________________________________
>>> From: "John C. Westmoreland, P.E." <john at westmorelandengineering.com>
>>> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>>> Sent: Wednesday, September 18, 2013 6:13 PM
>>> Subject: Re: [time-nuts] GPSDO vs Rb standard
>>> 
>>> 
>>> Azelio and Fellow Time Nuts,
>>> 
>>> Isn't the GPS 1PPS signal supposed to be 'precise' to within what error?  I
>>> imagine this is in the specs of the specific receiver -
>>> but I was wondering if some of you have actually measured what that is -
>>> and could report the numbers that you have found.
>>> 
>>> Thanks!
>>> John Westmoreland
>>> 
>>> 
>>> 
>>> On Wed, Sep 18, 2013 at 3:07 PM, Azelio Boriani <azelio.boriani at screen.it>wrote:
>>> 
>>>> Instead of using the Rb's PPS, use the GPS receiver's PPS. Maybe you
>>>> will find out that the Rb is slow... you can also check the Rb's PPS
>>>> against the GPS's PPS.
>>>> 
>>>> On Wed, Sep 18, 2013 at 11:47 PM, Bob Stewart <bob at evoria.net> wrote:
>>>>> I hooked the Rb's 1PPS to the trigger input on my old Tek 455, 10MHz
>>>>> GPSDO to Channel A, .05us trace, and turned the lights out so I could
>>>>> see it.  The 10MHz is marching right to left about 1 cycle every 20
>>>>> seconds.  So, can I say that the Rb considers my GPSDO to be too fast by
>>>> about 5ppb?
>>>>> 
>>>>> 
>>>>> Bob
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