[time-nuts] Best Rubidium Frequency Standard
KA2WEU at aol.com
KA2WEU at aol.com
Sun Mar 13 14:22:25 UTC 2016
Good morning ,
what is wrong with the Standford Research Rubidium standard with a 1
sec sync pulls form a GPS satellite ?"
Ulrich
In a message dated 3/13/2016 10:16:11 A.M. Eastern Daylight Time,
kb8tq at n1k.org writes:
Hi
With “real” (who knows how real) Rb based GPSDO’s selling below $250, it’
s not clear that running an Rb in a lash up that makes it look like a
TBolt is a worthwhile exercise. Unless you can get the time constants out into
the “several days” range, a manual adjust is a much better way to go.
Since we are talking about a “I just want to plug it all in” sort of approach
here, anything more than “set and forget” appears to be out of the
question.
Bob
> On Mar 12, 2016, at 10:48 PM, Charles Steinmetz <csteinmetz at yandex.com>
wrote:
>
> I wrote:
>
>> With the right settings, a PRS10 *does* work extremely well with the
PPS input from a GPS. They do generally take several days or more to lock,
because of the long time constants involved.
>
> Bob replied:
>
>> I would call having to wait a few days for it to lock a bit of a
disadvantage. Even more so for those with an antenna challenged environment that
gives them dropouts every few hours.
>
> Well, one is certainly free to use shorter time constants to achieve
lock faster. The very long TCs simply allow one to exploit the exemplary
stability of the PRS10 for performance much better than what an OCXO-based
GPSDO can deliver. If you are content with the stability of, say, a TBolt, you
can replicate that performance by adjusting the PRS10 loop to match TBolt
dynamics -- in which case it will lock in a comparable time.
>
> WRT holdover, the long TC and the inherent stability of the PRS10 mean
that it will stay very close to the GPS PPS even over long holdover periods,
so re-acquiring lock does not take nearly as long as acquiring it
initially. For the same reason, a PRS10 set up for maximum stability can acquire
lock even if there are holdover periods during the acquisition process (in
both cases, assuming that the GPS does not output "bad" PPS pulses when it
is not locked to GPS).
>
> In principle, one might be able to begin the process by setting the
PRS10 loop "tighter," then changing the loop constants in one or more steps
after it achieves initial lock. I have not tried this, and do not know if
changing the loop programming on the fly upsets the PRS10 phase. If not, it
should work (and one could even program a BBB, 'uino, or other small
processor to do it automatically).
>
> Best regards,
>
> Charles
>
>
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