[time-nuts] GPSDO Alternatives

Bob Camp lists at rtty.us
Thu Dec 6 12:08:23 UTC 2012


Simple answer - no, not in a precision part. They are neither high enough resolution or deterministic enough to give you very high resolution. 

More complex answer - you can do just about anything if you are willing to limit the best possible outcome. With the normal integration times you probably will be in the 1x10^-9 to 1x10^-10 noise (ADEV) range.

You would do better with an input capture port. They would be more deterministic, but they still have limited resolution. If they are driven by a clock multiplier, they likely will have a jitter component on their clock. Since low jitter is not a money spec in these low end parts, there can be some issues there. 

There are many cheap / simple ways to to the counter. Five dollars will easily solve the problem with change left over to pay for breakfast coffee.

Next up on the expanded list is a way to align the pps signals. If you tune your OCXO by 0.1 ppm to align them, it will take you 100 days to get to the first stage of lock. If you use a CPLD to do that part, you can toss much of the counter in with it. You still have change from your five dollars. 


On Dec 6, 2012, at 4:59 AM, Don Latham <djl at montana.com> wrote:

> Chris:
>> The question I have again is about a simple phase detector.
> I did ask if the arduino interrupt ports could be used as a phase
> detector; one on the GPS and one on the OXCO. Too much jitter? If the 12
> MHz clock is too slow, would an 80 MHz clock ARM arduino style processor
> work? I'm simply too new at this to decide.
> Don
> -- 
> "Neither the voice of authority nor the weight of reason and argument
> are as significant as experiment, for thence comes quiet to the mind."
> De Erroribus Medicorum, R. Bacon, 13th century.
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> Ghost in the Shell
> Dr. Don Latham AJ7LL
> Six Mile Systems LLP
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