[time-nuts] DIY GPS-DO
ernieperes at aol.com
Sun Mar 11 07:56:16 UTC 2012
have a look at trhis side...
From: Magnus Danielson <magnus at rubidium.dyndns.org>
To: time-nuts <time-nuts at febo.com>
Sent: Sat, Mar 10, 2012 5:19 pm
Subject: Re: [time-nuts] DIY GPS-DO
On 03/10/2012 04:11 PM, Azelio Boriani wrote:
> 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
The oscillator time and frequency bias is already being supplied, so no
need for a PICTIC to measure. Just read the message coming down the
serial line and use that for steering.
> Interesting, as usual, the references by Attila: I'm searching for the book
> by Roland E. Best.
It's a fairly good startingpoint, but I also find Garners PLL book a
dense and highly readable book.
> 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:
>> 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.
>> A GPSDO around a PIC16C73 from Brooks Shera. It is basically what you
>> want to do.
>> 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.
>> The PICTIC as an example how to build a time interval counter that is
>> good to<1ns (see  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 ), 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.
>> Attila Kinali
>>  http://www.jrmiller.demon.co.uk/projects/ministd/manual.pdf
>>  http://www.rt66.com/~shera/QST_GPS.pdf
>>  http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic
>>  http://www.ke5fx.com/pictic.htm
>> Why does it take years to find the answers to
>> the questions one should have asked long ago?
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