[time-nuts] Best counter setting for ADEV?

Thu Oct 4 22:11:57 UTC 2012

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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