[time-nuts] Re: PRS-10 sawtooth correction with microcontroller

[Bob Camp]

Hi

If you buy the right option, you get a FS740 with a Rb. Since the hardware in the box
also works fine with an OCXO, it is unlikely that they do anything odd with the Rb other
than simply tune it. 

Bob

> On Dec 25, 2022, at 9:28 AM, Greg Maxwell via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Has anyone tried talking to SRS?  If TO doesn't do the right thing
> already then it should only require a modest bit of firmware to do so,
> and then a $1 microcontroller and gps unit (perhaps a nice new dual
> frequency one) would turn the FS725 into a great GPSDO.
> 
> Anyone know if the FS740 rubidium version contains a PRS10? I would
> assume-- might be interesting to spy on its serial communication.
> 
> On Sun, Dec 25, 2022 at 1:16 PM Matthias Welwarsky via time-nuts
> <time-nuts at lists.febo.com> wrote:
>> 
>> On Donnerstag, 22. Dezember 2022 00:22:37 CET James Wilson via time-nuts
>> wrote:
>>> After running in many of the familiar problems of connecting a GPS timing
>>> module 1PPS signal to a PRS-10, I want try building a software sawtooth
>>> correction board. I’ve seen previous discussion of some of the commands to
>>> use for adjusting the PLL and PPS control on the PRS-10 and getting the
>>> sawtooth error from ublox GNSS modules, but not a start-to-finish
>>> description of how to put everything together.
>> 
>>> My idea to use a microcontroller with multiple UART ports; one connected to
>>> the ublox module and the other connected to the PRS-10, with level shifters
>>> as needed. The microcontroller sits between the two devices, and gets the
>>> PPS sawtooth correction info from the ublox (specifically via the
>>> UBX-TIM-TP message and its qErr field), and then adjusts the PRS-10’s PPS
>>> time offset by this value to null out the sawtooth for the next pulse.
>> 
>> I suggest you try correcting the 1PPS pulse of the timing module itself, using
>> a variable delay line. I don't have a particular part in mind, Maxim might
>> have something.
>> 
>> There was a very elaborate GPSDO project discussed last year on this list that
>> used this technique.
>> 
>> BR,
>> Matthias
>> 
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