[time-nuts] GPS: ADEV or MDEV?

Hal Murray hmurray at megapathdsl.net
Tue Apr 10 14:38:34 EDT 2007


[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.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.






More information about the time-nuts mailing list