[time-nuts] GPS: ADEV or MDEV?

[Dr Bruce Griffiths]

Hal Murray wrote:
> [context is avoiding hanging bridges]
>
>   
>> Ovenize it to control the sawtooth frequency?
>> Temperature controlled oscillator! :-)
>> Should be fairly simple to acheive, really just a FLL.
>>     
>
> I was wondering about that a while ago.  Is the basic idea feasible?
>
> Assume you had a good crystal with an A/D driving a voltage control input and 
> wired that up to your GPS unit.  You would need to lock that crystal to the 
> PPS output from the GPS, but you don't want an exact lock, you want to be off 
> by a fraction of a HZ, say 1/10th or 1/20th.
>
> One problem is that as soon as you lock it up, the normal results are no 
> longer random.  You could easily get locked on so that your 10 or 20 samples 
> per sawtooth are biased by up to 1/N of the sawtooth.  As long as N is big 
> enough that's probably OK.
>
> It might be better to lock on the the steep edge of the sawtooth, getting 
> samples from just before and just after the big step.
>
>
>   
Hal

Surely it would be much simpler (in principle at least) to just to add 
sufficient Gaussian phase noise to the GPS receiver clock so that 
potential coherence problems are virtually eliminated.

Bruce