[time-nuts] DPLL for 10MHz

Attila Kinali attila at kinali.ch
Mon May 7 16:54:23 UTC 2012


On Mon, 7 May 2012 10:30:56 -0500
Bill Dailey <docdailey at gmail.com> wrote:

> Does anyone have any knowledge of a simple (just soldering a
> few connections and maybe programming a hz/volt rate) PCB for
> synchronizing a precision OCXO to a GPSDO?  I am trying to improve
> short term stability with a high stability OCXO and dont want to
> "cut into" my fury and replace the OCXO.  I cando it manually but
> this seems like it would be nice and desirable for many yet I can't
> find anything.  I presume it would have to be digital because of the
> long time constant.

What speaks against a simple design as used in the GPSDO by James Miller[1]?
Or if you want a better PLL than just an XOR gate, use a 74x4046.
They are still available in DIL, so building a complete PLL is possible
on a veroboard. This should be enough if you want to improve the short
term stability below 0.1s, where the fury rises above it's long term humb.

If you want to flatten down the humb the fury has (the one between a tau
of 1s and x*1000s), then you need a very stable OXCO to begin with.
Also, then i think the best approach would be to scale down both
signals to 1kHz and use a PICTIC II to measure the phase difference
between them. Then you can implement the control loop in the PIC of
the PICTIC II and drive an _external_ DAC with it.

			Attila Kinali


[1] http://www.jrmiller.demon.co.uk/projects/ministd/manual.pdf
-- 
Why does it take years to find the answers to
the questions one should have asked long ago?




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