[time-nuts] Best Rubidium Frequency Standard

KA2WEU at aol.com KA2WEU at aol.com
Sun Mar 13 10:22:25 EDT 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
> 
> 
>  _______________________________________________
> time-nuts mailing list  -- time-nuts at febo.com
> To unsubscribe, go to  
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the  instructions  there.

_______________________________________________
time-nuts  mailing list -- time-nuts at febo.com
To unsubscribe, go to  
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the  instructions there.


More information about the time-nuts mailing list