Alan G3NYK----- Original Message ----- From: "Volker Esper" <ail...@t-online.de> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Sent: Saturday, December 22, 2012 8:44 PM Subject: Re: [time-nuts] time-nuts Digest, Vol 101, Issue 152
Plot 1: MDEV of the time interval reported by GPSDO Yes, Said, that are important issues.By the way: I'm now writing in two threads, I don't know, why the original thread ("Z3805A cooling requirements?") was splitted... Can we please move to the original thread?I am sure, that the noise of the GPSDO PPS-TI data is much to high to recognize the effects. I'm going to make a new setup, where I'll compare the GPSDO PPS with an external oscilator, e.g. an HP 10544 or the "high stability reference" within my SMX signal generator.Volker Am 22.12.2012 05:07, schrieb Said Jackson:Hi Volker,What is being plotted here? Efc? Time interval as reported by the GPSDO? External counter versus a stable reference?It looks like the resolution is approaching 10ns/s (1E-08 at 1s), and that the short term effects may be hidden in this noise?The effects are clearly visible in your first GPSCon plot, not sure if we can see the short term noise in these plots..The 10811 I had tested went from ~3E-012 at 100s to ~2E-011 when the fan was on, I think both values are quite a bit below the noise floor of your plot so probably hard to measure.Bye, Said Sent from my iPad On Dec 21, 2012, at 6:47 PM, Volker Esper<ail...@t-online.de> wrote:Said,Unfortunately I don't have the equipment to measure the phase noise of an HP 10811 (yet).But I did some work on evaluating the results of my fan experiment. Within this posting you'll find two diagrams. The first (named "1_DF9PL...") shows five MDEV curves (Modified Allan Deviation), each of them measured at different times. Total time span is 30.5 hours.At small tau values (up to 1000 s) only a slight increase of sigma over time can be noticed. However, at a tau of 5000 s or greater you can watch sigma making a big bump. Ok, that's what we expected before.In diagram no. 1 it's somewhat fussy to recognize the change of a particular sigma(tau). Now, that we've got curious, we want to see, how the sigma(tau) changes over time. So I've been providing a second diagram ("2_..."), where sigma(tau) is a function of the time.You can see, for example, the curve of tau=20480s developing a big hump, and falling back to a proper value after about 1800 minutes. All curves at a tau greater or equal 2560 do so.At smaller values the curves are esentially less affected, but - they are not back at their starting value after 1800 minutes (30 hours)! You could guess, that the hump moves up to longer times with increasing sigma - but it doesn't. There is something significantly different below tau=2560s.1 hour ago, I switched off the fan and laid back the aluminium cover. We wait and see.And now, dear time nuts, it's time to go to bed. Volker Am 21.12.2012 18:53, schrieb Said Jackson:Mark,Your plot still shows excursions of +/-1E-010, about 100x higher base noise than the Z3801A/Z3805A are capable of achieving. Wonder where that noise is coming from? This noise is probably much higher than the thermal effects.The original post was the question "does my Z380xA have reduced stability if I add a fan" or similar, I think the answer is shown to be "yes".Volker, I wonder if you also see fan-induced spurs in the phase noise from 1Hz to 100Hz. I would not be surprised if the fan vibration adds significant spurs to the 10811A crystal.Bye, Said Sent from my iPadOn Dec 21, 2012, at 9:42 AM, Mark Spencer<mspencer12...@yahoo.ca> wrote:This plot should show the frequency change more clearly. (Same data just presented differently.)It seems to me that the noise goes may be going down a bit for a minute or so just after the fan is turned on but I don't believe these plots provide conclusive evidence of this.Regards Mark SpencerMessage: 7 Date: Fri, 21 Dec 2012 09:27:29 -0800 From: Said Jackson<saidj...@aol.com> To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Cc: Discussion of precise time and frequency measurement <time-nuts@febo.com> Subject: Re: [time-nuts] Z3805A cooling requirements? Message-ID:<83ce0384-2996-4155-b51b-9d79910b2...@aol.com> Content-Type: text/plain; charset=us-ascii Great plots guys! Looking at these results I think my original claim still holds: ADEV goes up when a fan is involved versus no fan, even on a double oven 10811.. Clearly visible on the 10811, maybe not so much on the MV89 but that unit seems to have frequency moves into the xE-010 region on Marks plot so maybe the effect is just a bit hidden? Bye, Said Sent from my iPad On Dec 21, 2012, at 5:44 AM, Volker Esper<ail...@t-online.de> wrote:...and the picture of the experiment...The picture enclosed can give you a firstimpression. What we see isthe difference time between the GPS signal and theOCXO (blue)("PPS-TI"), which is an HP 10811. In red we can seethe EFC. The totalspan is 24 h. Before I applied the fan, the noise was at amaximum of about +/- 20 ns.Some hours after starting the fan the noise is muchgreater. That shouldhave a significant impact on the ADEV. I don't put the ADEV curves here, I make up for itwhen the EFCcompensation is completely out of the scope, thatwill be in about 12hours. I don't have the ADEV at 1 s, but the ADEVat 10 s has beenalmost constant. The ADEV at about 1000 s has anasty bump now.IMHO that fits to the physical facts: the airflowwill surely not affectthe 10 s ADEV since the OCXO tries its best toisolate the oscillatorfrom short time temperature influences. However,the turbulent air flowthat I applied will influence the longer timeADEV.Have a nice solstice Volker Am 21.12.2012 12:44, schrieb Volker Esper:Yes, I made such a setup, it's now running 22hours. I'll post theresults in two hours or so (if nothing evilhappens to the earth,meanwhile). Volker Am 21.12.2012 03:35, schrieb saidj...@aol.com:Wish I had more time to play with thissetup.How about fellow time nuts spend some timeand present similar testdata on their OCXO's to compare? I was interested in the 1s to 100s ADEV,and my runs were from 8minutes to 20 minutes, certainly enough time tocapture data for 1s to 100s ADEVmeasurements.. bye, Said In a message dated 12/20/2012 14:17:59Pacific Standard Time,mag...@rubidium.dyndns.orgwrites:On 12/20/2012 01:34 PM, Bob Camp wrote:Hi Temperature transients are not a goodthing for an OCXO. If youdeliberately use the fan to create atransient, then yes the OCXO willnot be happy. The question it - what happens afterthe transient has settledout? The plot you have still looks a lot like a stepfunction.I agree. Temperature steps stresses theOCXO oven loop and easilycreates a gradient over the crystal. As theoven loop tracks in, thefrequency returns to around normal. Thetrouble with forced air over acrystal is that the metal shield couplesvery well and acts like a heatsink. A think plastic cover over it andforced convection doesn't havethe same effect. There is even being usedby at least one vendor. Worksvery well for the extra cents ofmanufacturing cost.The HP10811 is recommended to be put in aairflow-quiet corner of theworld. Look at it's mounting in theHP5370A/B for instance.Cheers, Magnus_______________________________________________time-nuts mailing list -- time-nuts@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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.<DSCF1758_bb.jpg> _______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there.------------------------------ _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts End of time-nuts Digest, Vol 101, Issue 152 *******************************************<MV89A Fan turned on at 460 seconds v2.png> _______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there._______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there.<1_DF9PL_GPSDO_1_sigma(tau)_alle_MDEV_b.jpg> <2_DF9PL_GPSDO_1_sigma(tau)(t)_alle_MDEV_b.jpg> _______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there._______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there._______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
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