Hi
> On Jan 12, 2017, at 4:06 PM, Bob Stewart <b...@evoria.net> wrote: > > Hi Bob, > OK, like Bugs Bunny, I'll venture out on the limb, cut the limb, and see > whether I fall or the tree falls: > Wouldn't it take 1801 samples to get 18 seconds at 100S tau? Maybe I didn't > state that properly, but I think you get my meaning. Also, I've never > actually taken the time to look at the formula or the code to see how the > ADEV is calculated. But doesn't it use a sliding boxcar type of calculation? > Nope, the proper approach for ADEV is to decimate the sample set. Bob > Or is that some other *DEV? My point is that for 1801 seconds, aren't there > a lot more than 18 samples put in the 100S bin? And I've probably stated > that incorrectly, too. > > Bob > > > From: Bob Camp <kb...@n1k.org> > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency > measurement <time-nuts@febo.com> > Sent: Thursday, January 12, 2017 2:38 PM > Subject: Re: [time-nuts] General questions about making measurements with > time interval counter. > > Hi > > Keep in mind that when you do 1800 samples at 1 second, that data will only > meet the > 100 sample requirement out to tau = 18 seconds. Past that you are in the > “under 100 samples > region”. > > Bob > >> On Jan 12, 2017, at 2:32 PM, Bob Stewart <b...@evoria.net> wrote: >> >> Hi Bob, >> OK, thanks for explaining. When you and others use highly technical terms >> like "small number of samples" it's not always clear to me what you mean. >> =) Ten samples? That's not enough for anything. Normally I run at least >> 1800 samples; at least if I plan to share them with someone. >> >> Bob ----------------------------------------------------------------- >> AE6RV.com >> >> GFS GPSDO list: >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >> >> From: Bob Camp <kb...@n1k.org> >> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >> measurement <time-nuts@febo.com> >> Sent: Thursday, January 12, 2017 1:03 PM >> Subject: Re: [time-nuts] General questions about making measurements with >> time interval counter. >> >> Hi >> >> It varies from 5370 to 5370. You see a lot of plots that run out to 10 >> samples or less. Anything below 100 samples >> is risky in some senses. >> >> Bob >> >>> On Jan 12, 2017, at 12:25 PM, Bob Stewart <b...@evoria.net> wrote: >>> >>> Hi Bob, >>> OK, what's a small number of data points? Attached is a screencap of >>> captures for 25, 50, 75, 100, and 150 seconds. Yeah, at 25 seconds, the 1S >>> tau is up at 4.56E-11, but it falls pretty quickly. I will mention that >>> this particular 5370 is much better than my other one. So, maybe this one >>> is an exceptional example? >>> >>> Just for grins, I also included a screencap of the phase points. >>> >>> Bob ----------------------------------------------------------------- >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >>> >>> From: Bob Camp <kb...@n1k.org> >>> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >>> measurement <time-nuts@febo.com> >>> Sent: Thursday, January 12, 2017 11:04 AM >>> Subject: Re: [time-nuts] General questions about making measurements with >>> time interval counter. >>> >>> Hi >>> >>> There is a big difference between RMS and single shot. Single shot, the >>> 5370 is a very different beast. >>> That’s not a big deal when you have a few thousand readings and it all >>> averages down. Unfortunately >>> we all love to do runs with a very small number of points and then draw >>> conclusions from them. As the >>> sample size goes down, you no longer have a 2 to 4 x 10^-11 beast, it’s >>> more like 5X that. >>> >>> Bob >>> >>> >>>> On Jan 12, 2017, at 11:31 AM, Bob Stewart <b...@evoria.net> wrote: >>>> >>>> Hi Bob, >>>> Normally I see somewhere between 2E-11 and 4E-11 at 1S tau on my 5370A, as >>>> in the blue trace on the attached plot. Am I misunderstanding your >>>> meaning? Granted, I am clocking the 5370A with a GPSDO, but I believe I >>>> see about the same thing with the HP10811. This test was 1PPS vs 1PPS on >>>> two different units. >>>> The plot also has a test run by Tom, in orange, using his H Maser and a >>>> Timepod to show how poor the 5370 is compared to the Timepod below about >>>> 60S tau. These are essentially apples vs apples tests. >>>> >>>> Bob >>>> >>>> >>>> >>>> >>>> From: Bob Camp <kb...@n1k.org> >>>> To: Discussion of precise time and frequency measurement >>>> <time-nuts@febo.com> >>>> Sent: Thursday, January 12, 2017 8:27 AM >>>> Subject: Re: [time-nuts] General questions about making measurements with >>>> time interval counter. >>>> >>>> Hi >>>> >>>> There are a number of ways to improve the resolution (and accuracy) of >>>> your data without spending >>>> big piles of cash. They have been discussed here on the list many times >>>> over the last few years. >>>> What I’m suggesting is that you dig into that ahead of taking data. You >>>> will dive into it eventually as you >>>> look more and more at devices that are locked to some sort of stable >>>> reference internally. >>>> >>>> Ideally you would like a device with a floor 5X to 10X better than what >>>> you are measuring. For ADEV style >>>> data, the 5370 is a 1x10^-10 sort of device single shot (so 1x10^-9 is the >>>> limit at 10:1). With a lot of averaging >>>> (which is not something you do with ADEV) you can get about 5X better than >>>> that as a floor. In either case, it is getting in the way of any >>>> readings that are much below 1x10^-9 at one second. A low cost XO can hit >>>> that level of performance. >>>> >>>> Bob >>>> >>>> >>>> <ADEV.png>_______________________________________________ >>>> 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. >>> >>> >>> <ADEVs.png><Phase.png>_______________________________________________ >>> 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. > > > > _______________________________________________ > 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.
