[time-nuts] GPS noise reduction

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Apr 6 00:24:35 EDT 2008

Richard H McCorkle wrote:
> Bruce,
> The 100M OCXO is undisciplined so your first case should
> be satisfied.
> Thanks,
> Richard

To achieve proper averaging of the TIC measurements the location of the 
TIC oscillator output zero crossing has to slowly wander with respect to 
the OCXO zero crossings so that the averaged TIC measurements are made 
over a wide range of relative phases (ideally over a range of 1 TIC 
oscillator period or more). For short averaging times the TIC OCXO may 
be too stable.
You will need to measure the relative drift/wander between the TIC 
oscillator and the OCXO zero crossings over the averaging period to 
ensure that there is sufficient variation.

Either a time interval counter like a 5370 could be used for this.
Failing this an analog phase comparator can be used (first divide the 
TIC oscillator down to the same nominal frequency as that of the OCXO).

You also need to characterise/measure the sawtooth corrected PPS jitter.


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