[time-nuts] Best counter setting for ADEV?

Bob Camp lists at rtty.us
Thu Oct 4 12:41:46 EDT 2012


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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