[time-nuts] Software Sawtooth correction prerequisites?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat May 12 07:30:36 EDT 2007

Tom Clark, K3IO wrote:
> If you have a 10 MHz oscillator, simply feed it into the "D"
> input into a latch clocked by the de-sawtoothed GPS 1PPS. The output of
> the latch is a 0 or 1 depending on the precise phase of the oscillator.
> You want this latched 0/1 measurement to average to ½ over a long term
> (seconds). As the statistics deviate from a 50/50 split, you tweak the
> oscillator. The ~1 nsec of residual noise from the sawtooth corrected
> GPS rcvr acts a natural dither. No counters, no ramps, no big A/D
> converter -- it couldn't be simpler! And if the 10MHz (=> 100 nsec phase
> ambiguity) is too fine for your oscillator, then divide it to 5 MHz
> (=>200 nsec) or 1 MHz (=> 1µsec). This should be good enough to pull in
> a xtal that is off by 1:10e6.

How does one do robust statistical filtering of outliers when one uses 
this technique??

> I hope these comments helped a bit -- 73, Tom

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