It's a design decision. Most GPSDO sold are made by companies
that buy an OEM GPS timing receiver and then create a GPSDO
with the usual assortment of OCXO, TIC, computer and DAC.

The exception would be if you are a GPS company and can
integrate the components, as Trimble did with the Thunderbolt.

But most companies selling GPSDO, and all amateurs building
homebrew GPSDO, have to use the separate component method.

Note the really high-end GPS timing receivers use an external
reference clock and don't even bother to lock it. The advantage
with this is 1) you don't need the DAC (which just adds noise),
2) you can use good clocks like cesium or masers which don't
have EFC, and 3) you collect the phase error information for
post-processing -- which is much more accurate than trying to
steer an oscillator in real time. And also, 4) you can run multiple
receivers off the same clock if necessary.

We're waiting for some brave soul to implement an SDR-based
GPS timing receiver; we can all then experiment with the TBolt
model instead of the TIC/DAC model of GPSDO.

/tvb

There are several projects that do this.

There is one written using GNU Radio.  I forget the details but I saw
it years ago.

http://www.kamieniecki.com/krys/gps
proof of concept only, not finished

http://gps.psas.pdx.edu/
Not really SDR but
... firmware that is meant to run on the receiver board itself, giving
you direct access to the GPS chipset.

Chris Albertson
Redondo Beach, California

On 31/01/12 20:43, Attila Kinali wrote:

Yes. If you look up old papers, they already did this with Oncores,
Cesium clocks and synthesis.

If you've done it right, it lowers the receivers noise. The position
becomes less shaken by the jerk effect of the oscillator noise, while
frequency and drift also affects the solution to some degree. This
side-effect is covered in literature if you look for it.

Produceable.

No pain, no gain?

Cheers,
Magnus

On 31/01/12 22:14, Rob Kimberley wrote:

I'll have it.

The russian version is here:
http://morion.com.ru/uploaded/FE-5680_manual_rus.pdf

Browing through it, it becomes obvious that this describes the new
5680As that we got, with 60 MHz clock and all.

Steering resolution is also as Javierr reversed out.

Cheers,
Magnus

On Tue, 31 Jan 2012 21:19:50 +0000 (UTC)
cfo xnews2@luna.kyed.com wrote:

Thanks! The links worked... Dunno why using the webpage does not...
Maybe some strange interferance with my firefox version and their
javascript stuff...

The STM32F4 looks quite good. Two 32bit timers with multiple channels
(although the documentation does quite a job to hide that fact). Only
downside is that the pins for the 32bit timers are shared with the
ethernet interface, which makes most of them unusable. But i'll have
to have a better look, maybe RMII can free up enough pins for it to
work w/o an FPGA.

Thanks again!

		Attila Kinali

--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

On Tue, 31 Jan 2012 15:27:45 -0800
Chris Albertson albertson.chris@gmail.com wrote:

No, the system doesn't have to be small, but i'd like to have ultimate
control over every part of it. Which is kind of hard if you are running
an PC with some OS on it. Yes, i could programm the PC using the same
tools as i use for a uC, but then i'd simply waste a lot of time doing
work that others have done already... not to mention a lot of computing
power.

Beside... a uC system is easier to tinker with than a PC :)
And my main goal is to have a system to experiment with.
That requirement will probably make it more expensive than a Atom Mainboard,
but it will be much more fun and a lot more to learn :)

		Attila Kinali

--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

On Wed, 01 Feb 2012 01:52:16 +0100
Magnus Danielson magnus@rubidium.dyndns.org wrote:

I have not seen any such papers yet. Do you have any pointers or hints
what to search for?

		Attila Kinali

--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

On Tue, 31 Jan 2012 16:21:40 -0800
"Tom Van Baak" tvb@LeapSecond.com wrote:

I'm planning that... I don't think it's too difficult to do, given
all the information (papers and books) that are available on how
to build GPS receivers. But it will be a damn lot of work.
So don't hold your breath. It will probably take a couple of years
until i even get around to design a board for it, not to mention to
write all the code.

		Attila Kinali

--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

I have opened the FTS125: the fixed OCXO 20MHz is fed using the EXT_CLK pin
7 on the CW25. Maybe it is possible to drive a CW12 with an external high
quality 20MHz but maybe a suitable firmware is then needed.

On Wed, Feb 1, 2012 at 10:28 AM, Attila Kinali attila@kinali.ch wrote:

Attila,

I don't have a link either. I would look at the usual T&F web sources:
PTTI, NIST, FCS, EFTF, ION-GPS, IEEE.

If you can't locate it let me know and I'll ask around to see who might
have done the experiments.

/tvb