Hi It is not what is done in the Efratom Rb’s. Their pps input is set up to get things on frequency / on time quickly. The assumption is that you plug it into a pps to get it “right” and then take off on your mission. That takes them into the short (for a Rb) time constant region.
Bob On Aug 24, 2014, at 5:56 PM, Brooke Clarke <[email protected]> wrote: > Hi Bob: > > I think that's what's done in the SRS PRS10 > http://www.prc68.com/I/PRS10.shtml > > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > http://www.prc68.com/I/DietNutrition.html > > Bob Camp wrote: >> Hi >> >> If you lock an Rb to GPS, you need / want / should do it with a *very* long >> time constant. Numbers in the one day to several days range are commonly >> seen. If you lock it up with a tighter (shorter time constant) loop, it will >> just wander around as it follows the GPS input. That’s what would happen if >> you hook your Rb to your Trimble and turn on the disciplining on the Rb. It >> will significantly degrade the stability of the Rb. >> >> If you have a temperature stable environment (or create one) you can get >> some very good results with an (good) Rb locked to a (good) GPS via a proper >> long time constant setup. It’s not easy, but it can be done. >> >> Bob >> >> >> On Aug 23, 2014, at 6:31 PM, Ed Palmer <[email protected]> wrote: >> >>> Hi Dave, >>> >>> On 8/23/2014 3:51 PM, Dave M wrote: >>>> Thanks for that suggestion, Ed. After a bit of reading in the X72 >>>> Reference Guide, it appears that the X72 does have a 1PPS input. That >>>> would be considerably easier than trying to interface the Rb into the >>>> GPSDO. Still trying to understand what the manual is telling me. Next >>>> thing is to determine if my unit has that option enabled (firmware >>>> option). That will be a chore for after the holiday... really busy next >>>> week. >>>> >>>> What would that (1PPS disciplining) do for me... in terms of maintaining >>>> the Rb frequency accurately set? Would it be as accurate as having the Rb >>>> disciplined via the EFC input? >>> It's kind of overkill, but by connecting the 1 PPS from the NTBW50AA to the >>> X72, the X72 will be disciplined to the 1 PPS so the frequency will be >>> accurate. The question is how well will it be disciplined, i.e. what will >>> the Allen Deviation graph look like. I have a few X72 and SA-22c (X72's >>> cousin), but none of them have that option. I don't know of any published >>> data on it. Maybe you can tell us how well it performs. >>> >>> In general, I just don't see the point of disciplining a Rb standard to >>> GPS. I don't understand what will be gained by doing it. I have a Z3801A >>> and a Tbolt plus a free-running FRK as a house standard. I occasionally >>> compare the FRK to the Z3801A but the drift is so low (~1e-12 per month >>> over 9 months) that I see no reason to link them. >>> >>> One exception that I recently discussed on another forum was a guy who >>> lives in a ground floor, north-facing condo. He might need to have a >>> disciplined Rb standard due to poor GPS visibility. >>> >>> Ed >>> >>>> Thanks, >>>> Dave M >>>> >>>> >>>>> Message: 5 >>>>> Date: Fri, 22 Aug 2014 16:19:45 -0600 >>>>> From: Ed Palmer <[email protected]> >>>>> To: Discussion of precise time and frequency measurement >>>>> <[email protected]> >>>>> Subject: Re: [time-nuts] EFC info on Trimble 34310-T OXCO >>>>> Message-ID: <[email protected]> >>>>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed >>>>> >>>>> Have you checked your X72 to see if it has the 1 PPS discipline >>>>> option? >>>>> That would be a lot easier (and probably better) than your proposed >>>>> transplant. >>>>> >>>>> Ed >>>>> >>>>> On 8/22/2014 12:39 PM, Dave M wrote: >>>>>> Does anyone have any info on the OXCO in the Nortel/Trimble >>>>>> NTBW50AA-17 GPSTM receiver? The OXCO is labeled as Trimble 34310-T. >>>>>> I see some Trimble 34310-T oscillators on Ebay with pinouts labeled, >>>>>> but no other info. >>>>>> >>>>>> Specifically, I'd like to know the EFC characteristics for it. I'm >>>>>> thinking of the possibility of pulling the OXCO out of the GPSTM and >>>>>> subbing in a 10 MHz Rubidium, and using the GPSTM to discipline the >>>>>> Rubidium. My Rubidium is a Symmetricom X72, recently purchased. It >>>>>> seems to be working well. >>>>>> Does anyone know the differences between the three OXCOs used in the >>>>>> GPSTM receivers ("T", "T2" and "Oak")? >>>>>> >>>>>> Thanks for some insight, >>>>>> Dave M >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
