[time-nuts] Re: General query about disciplining circuitry

[AC0XU (Jim)]

1W is the notional power budget for the discipliner.

I am interested in optimizing designs for precision time, precision frequency, and precision time and frequency (three cases). I am o.k. with the idea of  not adjusting the oscillator phase to perfectly match GNSS but to instead record and track the offset without actually tweaking the oscillator for time/phase. That might be the best, and maybe that approach reduces the distinction between precision time and precision frequency.

The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I am interested in doing as well as the oscillator will support. In a future design I will be using an oscillator with 1e-12 adev @ 1 sec, but the current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform is moving, and no radio mfr publishes performance specs for this case.

Thank you for reminding me about the sawtooth. I will need to study the sawtooth behavior of the radio. One I am looking at now is the OEM7 series.

Again, given that there are many possible approaches to precision phase measurement, and being pretty sure that I want to do more than implement a frequency counter, I am looking for advice. 

Thanks!





At 09:31 AM 2/3/2023, Bob  Camp wrote:
>Hi
>
>I would back up a bit first Â
.
>What sort of oscillator is being disciplined? If the 1W is the total power budget, that rules out
>most OCXO’s. Why ask? The stability of the oscillator does get into this pretty quickly. 
>
>What is the end goal? Are you after precision time or precision frequency? While they are
>connected, the approach to optimize one is not quite the same at the approach for the other.
>
>What are the stability goals either for time or frequency? 
>
>Is this a mobile / portable application? If so that also impacts a lot of this and gets into a whole
>other set of questions. 
>
>To at least partly answer the question you asked:
>
>The PPS comes out of the GPS at the same time as the sawtooth correction information. In
>most cases, you want to marry those two up immediately. That way the correction does apply
>to the data you took. Does this matter in your case? Thus the long list of questions above. 
>
>Bpb
>
>> On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts <time-nuts at lists.febo.com> wrote:
>> 
>> I can image all sorts of disciplining circuits for controlling a digitally-controlled oscillator against GPS. Presumably, I will measure oscillator phase at the 1 PPS times and run those values into a Kalman Filter. I think my question is about how best to measure the oscillator phase, given the constraint of low electrical power (<1W). There are zillions of commercial devices that do this but the mfrs generally do not advertize the details. I plan to use either an MCU or an FPGA, depending on which is more advantageous.
>> 
>> I looked at
>> <https://hackaday.io/project/6872-gps-disciplined-xcxo/details>https://hackaday.io/project/6872-gps-disciplined-xcxo/details 
>> and that seems interesting. I don't have to worry about VCO control because my oscillator has a digital control.
>> 
>> What about measuring the phase of a large divider PLL locked to the reference? With I-Q outputs the phase can be measured with a very slow ADC applied to a sample-and-hold triggered by the 1 PPS.
>> 
>> Thanks!
>> Jim
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe send an email to time-nuts-leave at lists.febo.com