[time-nuts] GPS W/10KHz
EWKehren at aol.com
EWKehren at aol.com
Sat Feb 8 22:50:15 UTC 2014
The problem with the PLL analog version is the same as with any digital
GPSDO. The saw tooth is present at 10 KHz just like 1 Hz. To the best of my
knowledge there is no GPS receivers out there for less than $ 1000 with out
saw tooth. Timing receivers output the correction value and you can either
with software or a variable delay do correction.
I encourage you to pursue your idea since for more than ten years I had the
privilege to communicate with some of the sharpest minds on that subject
and obviously the missed something.
That also applies for the three of us that have been working intensely on
developing and testing the next generation of GPSDO's that we hope to
introduce to time nuts soon.
In the meantime with the ever increasing price of Tbolts, Shera is worth
a second look. When we worked on the last code release of Shrea using a
Morion we got consistently better than 1 E-11. Yes some of the IC's are hard to
find and that is why I used more readily available parts and did a new
board layout.
Also did one using a $ 1.20 Altera gate array.
Bert Kehren
In a message dated 2/8/2014 12:33:48 P.M. Eastern Standard Time,
albertson.chris at gmail.com writes:
On Sat, Feb 8, 2014 at 3:44 AM, Volker Esper <ailer2 at t-online.de> wrote:
>
> you don't need 10kHz to build a GPS disciplined oscillator. GPSDOs are
> build with control loop response times in the range of some hours, so
> the loop will be absolutely happy with a 1PPS input.
>
Of course you are correct. Most GPSDOs are driven with a 1Hz pulse. But I
think maybe the OP is not building just any GPSDO but maybe he is looking
to repair a specific GPSDO that is designed to use the old (and now rare)
Rockwell GPS. If that is the case he needs the old Rockwell or needs
to redesign his system.
If you are starting from scratch to build a new GPSDO it's easier now. All
you need is some kind of a phase detector (74HC4046 ?) and a small uP that
has a good built-in DAC. The uP checks the phase once per second and
adjusts it'sDAC accordingly.
--
Chris Albertson
Redondo Beach, California
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