[time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit

[Dr Bruce Griffiths]

Hal Murray wrote:
>> Noise like the oncore sawtooth isn't always a bad thing.
>>     
>
> I was going to comment on that area...  Thanks for the reminder.
>
> The problem is that the sawtooth isn't noise in the normal Gaussian sense.  
> If you happen to hit a long/wide hanging bridge, the resulting offset may get 
> past your PLL filter.
>
> It might be possible to avoid hanging bridges by dithering the sawtooth.  I'm 
> thinking of something like a heater under the xtal for the GPS unit that gets 
> driven by a medium frequency - slow relative to the normal sawtooth but fast 
> relative to the PLL time constant.  This somehow feels not-good, but I can't 
> see the obvious screwup.
>
>   
Hal

Avoidance of hanging bridges requires that the GPS receiver oscillator 
frequency not be a Hamonic of 1Hz at any time.
Using a heater as you suggest will not solve this problem.
Ideally it would be best if it were not a rational multiple of 1Hz either.
Its generally simpler and easier to use the PPS sawtooth correction, if 
available.
Resultant residual jitter is closer to Gaussian.

Bruce