[time-nuts] 1PPS for the beginner

Mike Cook michael.cook at sfr.fr
Tue Aug 14 02:55:19 EDT 2018


> Le 14 août 2018 à 04:29, Chris Caudle <chris at chriscaudle.org> a écrit :
> 
> On Mon, August 13, 2018 9:16 pm, Chris Burford wrote:
>> I have a (generic?) GPSDO which contains an Oscilloquartz STAR 4+ OCXO
>> that I am using to steer a PRS10 RFS. I'm a little confused on where the
>> 1PPS is coming from with respect to the GPSDO.
> 
> A GPS disciplined oscillator contains a GPS receiver which outputs 1PPS
> based on receiving the GPS signals and calculating the position  + time
> equation. That PPS signal is noisy in time, it jitters around relative to
> the ideal 1 second period.  The GPSDO implements a long time constant PLL
> to synchronize the output of the OCXO to the long term average frequency
> and phase of the GPS PPS, so what you see externally is 10MHz directly
> from the OCXO, 1 Hz (PPS) which is divided down from the 10MHz OCXO, and
> those are controlled by a PLL so that long term the phase of the PPS
> divided down from the OCXO follows the PPS calculated by the GPS receiver,
> but with lower jitter.
> 
> -- 
> Chris Caudle
> 
> 
> 
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