[time-nuts] Best counter setting for ADEV?

Bob Camp lists at rtty.us
Thu Oct 4 20:13:26 UTC 2012


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.
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > time-nuts mailing list -- time-nuts at 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 at 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 at 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 at 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 at 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 at 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 at 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 at 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 at febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.





More information about the time-nuts mailing list