[time-nuts] DIY GPS-DO

[Azelio Boriani]

Ah, yes, now I see: you suggest to keep track of the FOM and DOP from
message #21 and move the oscillator to minimize them. Interesting and
doable.

Interesting, as usual, the references by Attila: I'm searching for the book
by Roland E. Best.

On Sat, Mar 10, 2012 at 3:59 PM, Attila Kinali <attila at kinali.ch> wrote:

> On Sat, 10 Mar 2012 14:07:33 +0100
> Filip Ozimek <me_super at o2.pl> wrote:
>
> > could you recommend me a good project of GPS-DO? I've got a GPS module
> > with 1PPS output and a 20 MHz VCXO.
> > As I understand to do a phaselock to 1 PPS signal one must build some
> > kind of digital PLL. But I'm not sure
> > how to calculate a correction signal to the VCXO and how to test such
> > a disciplined oscillator.
>
> Start with reading the following documents:
>
> [1]:
> James Miller's GPSDO based on a 10kHz output of an Jupiter GPS unit.
> It is by far the most simple system i've seen sofar. It's mostly analog
> (beside the dividers) and uses a XOR based PLL for the FEC generation.
>
> [2]:
> A GPSDO around a PIC16C73 from Brooks Shera. It is basically what you
> want to do.
>
> [3]:
> A GPSDO that is based on an FLL (frequency locked loop) by Betrand Zauhar.
> Similar to the one above, but because it's using an FLL instead of an
> PLL it has a slight frequency offset (instead of a slight phase offset)
>
> You also want to read:
> "Phase-Locked Loops" by Best.
> The best book on PLL's i've found. Explains everything you need to know.
>
> [4]:
> The PICTIC as an example how to build a time interval counter that is
> good to <1ns (see [5] for information on PICTIC performance).
>
> Depending on the stability and accuracy you want to accheive, it might
> also be possible to use one of the modern uCs that run with >100MHz
> clocks and use its internal timer as TIC. It will give you an measuremnt
> accuracy better than 10ns, which is in the range of the width of a good
> timing GPS receiver (see [6]), this would simplify your circuitry
> quite considerably.
>
> Over the past years, there have been numerous discussions on GPSDOs
> on this mailing list. I suggest you walk trough the archives and
> read some of them.
>
>
> HTH
>
>                                Attila Kinali
>
> [1] http://www.jrmiller.demon.co.uk/projects/ministd/manual.pdf
> [2] http://www.rt66.com/~shera/QST_GPS.pdf
> [3]
> http://ve2zaz.net/GPS_Std/Downloads/VE2ZAZ_GPS_Derived_Std_QEX_09_10_2006.pdf
> [4] http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic
> [5] http://www.ke5fx.com/pictic.htm
> [6]
> http://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_(GPS.G6-X-11007).pdf
>
>
> --
> Why does it take years to find the answers to
> the questions one should have asked long ago?
>
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