[time-nuts] Best counter setting for ADEV?

Azelio Boriani azelio.boriani at screen.it
Fri Oct 5 09:25:25 UTC 2012


OK, now I understand: you are not interested in anything less than 100K
seconds with your 1nS counter. Taking samples every 100K seconds from very
stable sources with a 1nS counter hides the entire step between (for
example) a 1E-14 and 2E-14. You can't see 1.1E-14, 1.2E-14, 1.3E-14 but,
yes, you have a 1E-14 resolution at 100K seconds.

On Fri, Oct 5, 2012 at 1:19 AM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> Doing the repetition may give you a more fine grained idea of what the
> clocks are doing. It does not impact the resolution of the single
> measurement.
>
> A single ns in 100,000 seconds is indeed 1.0x10^-14…
>
> Bob
>
> On Oct 4, 2012, at 6:11 PM, Azelio Boriani <azelio.boriani at screen.it>
> wrote:
>
> > OK, because you think: (Y-X)/100K is the drift of the two clocks for each
> > second over 100K seconds and for each second I have a 1nS/100K
> resolution.
> > Now think about this: repeat the measure over and over and after each
> 100K
> > seconds you have your table. This table (your counter is 1nS) can have
> > figures like, say, 52nS, 53nS, 58nS, that is with a 1nS step. Your drift
> > maybe not exactly 52: it maybe 52.1 52.3 52.4 but you only see 52. So you
> > are loosing an entire nS between 52nS and 53nS. If you have a 100pS
> counter
> > you can see 52.0, 52.1 and so on.
> >
> > On Thu, Oct 4, 2012 at 10:13 PM, Bob Camp <lists at rtty.us> wrote:
> >
> >> Hi
> >>
> >> If I have two clocks:
> >>
> >> 1) I know they are X ns apart at time = 0
> >> 2) I know they are Y ns apart at time = 100,000 seconds
> >> 3) The resolution of the X and Y measurements is 1 ns
> >>
> >> I know the relative time between the two clocks to a lot better than
> >> 5.0x10^10...
> >>
> >> Bob
> >>
> >> -----Original Message-----
> >> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> >> Behalf Of Azelio Boriani
> >> Sent: Thursday, October 04, 2012 3:43 PM
> >> To: Discussion of precise time and frequency measurement
> >> Subject: Re: [time-nuts] Best counter setting for ADEV?
> >>
> >> If you take 2 samples out of a 1nS counter than you can estimate your
> >> measure with a 500pS resolution (5E-10) with an uncertainty (noise) of
> >> 7E-10.
> >>
> >> On Thu, Oct 4, 2012 at 8:58 PM, Bob Camp <lists at rtty.us> wrote:
> >>
> >>> Hi
> >>>
> >>> What if I only take two single measurements:
> >>>
> >>> One at time = 0, the other at time = 100,000 seconds.
> >>>
> >>> No averaging, no signal processing just two measurements. I look at the
> >>> time
> >>> difference  between the two signals at time = 0, and then again a bit
> >> more
> >>> than a day later.
> >>>
> >>> Bob
> >>>
> >>> -----Original Message-----
> >>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
> On
> >>> Behalf Of Azelio Boriani
> >>> Sent: Thursday, October 04, 2012 2:48 PM
> >>> To: Discussion of precise time and frequency measurement
> >>> Subject: Re: [time-nuts] Best counter setting for ADEV?
> >>>
> >>> You're right: it is better to put it down correctly:
> >>> for a theoretical resolution of 10E-14 at 100K seconds, start with a 1nS
> >>> counter that takes 1 second samples for 100K seconds and average those
> >> 100K
> >>> samples. You have your resolution and a noise (an error bar) of 3E-12.
> If
> >>> you use a 100pS counter and do the same run, you will end up with a
> >> 10E-15
> >>> reolution and 3E-13 noise, and so on. It turns out that to have a real
> >>> 10E-14 measure (@100K seconds), not blurred with noise, you must start
> >> with
> >>> a 10pS counter.
> >>>
> >>> On Thu, Oct 4, 2012 at 6:41 PM, Bob Camp <lists at rtty.us> wrote:
> >>>
> >>>> Hi
> >>>>
> >>>> Maybe we're talking about two different things here.
> >>>>
> >>>> Simplistically, resolution is simply what the counter puts out as a
> >>> usable
> >>>> LSB. There are a lot of examples out there that will do a one
> >> nanosecond
> >>>> single shot measurement. That measurement includes the normal trigger
> >>> noise
> >>>> and "stuff" in the counter. There are a few assumptions about slew
> rate
> >>> of
> >>>> the input.
> >>>>
> >>>> If I take two one shot measurements spaced 100,000 seconds apart, my
> >>>> resolution over that period is 1.0x10^-14. The measurement is
> >>>> representative
> >>>> of what the sources have done to that level. Weather the sources are
> >>> stable
> >>>> to that level is independent of the resolution of the measurement.
> >>>>
> >>>> Bob
> >>>>
> >>>> -----Original Message-----
> >>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
> >> On
> >>>> Behalf Of Azelio Boriani
> >>>> Sent: Thursday, October 04, 2012 12:27 PM
> >>>> To: Discussion of precise time and frequency measurement
> >>>> Subject: Re: [time-nuts] Best counter setting for ADEV?
> >>>>
> >>>> Yes, for a theoretical resolution of 10E-14 at 100K sec start with a 1nS
> >>> and
> >>>> average for 100K seconds but ending up with a noise (an error bar) of
> >>>> 3E-12.
> >>>>
> >>>> On Thu, Oct 4, 2012 at 4:25 PM, Bob Camp <lists at rtty.us> wrote:
> >>>>
> >>>>> Hi
> >>>>>
> >>>>> For a *resolution* of 1.0 x 10^-14 at 1.0 x 10^5 seconds I only need
> >> a
> >>>> 1.0
> >>>>> x
> >>>>> 10^-9 second reading out of the counter. Indeed, 5 or 10X more than
> >>> that
> >>>>> would be better if I was after a 1 x 10^-14 accuracy.
> >>>>>
> >>>>> Bob
> >>>>>
> >>>>> -----Original Message-----
> >>>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]
> >>> On
> >>>>> Behalf Of Azelio Boriani
> >>>>> Sent: Thursday, October 04, 2012 7:58 AM
> >>>>> To: Discussion of precise time and frequency measurement
> >>>>> Subject: Re: [time-nuts] Best counter setting for ADEV?
> >>>>>
> >>>>> Taking 10 samples from a 1nS counter leads you to a 100pS resolution
> >>> but
> >>>>> the noise at best (if it is really random) is reduced by SQRT(10).
> >> So,
> >>> as
> >>>>> already pointed out here, there is no real substitute for lower
> >> noise,
> >>>>> higher resolution measurements.
> >>>>>
> >>>>> On Thu, Oct 4, 2012 at 3:01 AM, Bob Camp <lists at rtty.us> wrote:
> >>>>>
> >>>>>> Hi
> >>>>>>
> >>>>>> A 1 ns resolution TI counter will do the measuring part just fine.
> >>>>> Hitting
> >>>>>> the number, is where it gets a bit crazy. A *good* GPSDO might get
> >>> near
> >>>>>> that.
> >>>>>>
> >>>>>> Bob
> >>>>>>
> >>>>>> On Oct 3, 2012, at 8:56 PM, Kevin Rosenberg <kevin at rosenberg.net>
> >>>> wrote:
> >>>>>>
> >>>>>>> On Oct 3, 2012, at 6:52 PM, Kevin Rosenberg <kevin at rosenberg.net
> >>>
> >>>>> wrote:
> >>>>>>>> Nice plot! Yes, I'd have trouble measuring 10E-14 at 10E5
> >> seconds.
> >>>>>>>
> >>>>>>> Sorry, 1E-14 at 1E5.
> >>>>>>>
> >>>>>>>
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