[time-nuts] I've designed a GPSDO, but how "good" is it?

Attila Kinali attila at kinali.ch
Sun Aug 16 20:45:08 EDT 2015

On Sun, 16 Aug 2015 23:27:43 +0200
Attila Kinali <attila at kinali.ch> wrote:

> > I've been saying out loud that the oscillator is ±1 ppb from GPS over the
> > 1000 second window. I know of Allan variance, but I don't have anything else
> > handy I can use for comparison. I also can't really afford to send one off
> > for testing to a proper lab. 
> With not having any other reference, you can use the EFC voltage
> and its relation to frequency as a guestimator for the ADEV. But
> be aware that the EFC is not 100% linear and the instability of your
> voltage reference etc pp affects this value as well. There was some
> discussion about this technique a couple of years ago (IIRC 2008)
> on this mailinglist. But i cannot find at the moment... it had some
> weird name too... Maybe someone with a better long term memory can
> chip in on that.

Found it. It is called "tight pll" or "tpll", you can find a summary here:

				Attila Kinali

I must not become metastable. 
Metastability is the mind-killer.
Metastability is the little-death that brings total obliteration.
I will face my metastability. 
I will permit it to pass over me and through me. 
And when it has gone past I will turn the inner eye to see its path. 
Where the metastability has gone there will be nothing. Only I will remain.

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