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

[Bob Camp]

Hi

I would back up a bit first ….

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