[time-nuts] Home made GPS disciplined atomic clock

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Jan 25 14:23:17 EST 2009


Esa Heikkinen wrote:
>> Do not forget the Trimble was never intended to be a frequency standard.
>>     
>
> Ok, then it might be a better idea to use only it's 1 PPS output to 
> count the frequency of the some other oscillator and build own steering 
> electronics for that. Infact my original plan was to do right that.
>
> If the count/steering period is set long enough there should be any 
> problem caused the satellite hopping or such things anymore. Let's say 
> that if I make 24 hours running average for 10 MHz using Trimble's 1 PPS 
> as a reference to determine the oscillator control then I would get the 
> better results, right?
>
> But if LPRO is useless, which oscillator should I seek for main output? 
> With low short therm drift and good phase noise characteristics etc?
>
> Also the goal is to build the reference with surplus (etc) parts as a 
> hobby project, no interest to invest thousands for that.
>
>   
Esa

Given the large PPS output jitter wrt to the OCXO output frequency, this
is probably a bad idea.

There's nothing wrong with the idea of using a rubidium standard, you
just need to cleanup its output first by phase locking a low noise OCXO
with a suitable loop time constant to the rubidium output first. Use the
cleaned up output as the 10MHz  signal for the Thunderbolt and lock the
rubidium standard to GPS using the thunderbolt with a suitably long loop
time constant.

This should result in low phase noise and drift during holdover.

Bruce




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