[time-nuts] Best counter setting for ADEV?

Bob Camp lists at rtty.us
Tue Oct 2 16:33:02 UTC 2012


Hi

So to do things the "same way", start your time measurement at something
less than 1 ms and do the math to get to 1 second and beyond. One advantage
over the frequency reading would be that you will know what math has been
done. The math *does* very much matter....

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Tuesday, October 02, 2012 9:39 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Best counter setting for ADEV?

Azelio,

In frequency average mode the 53132A makes something like 200,000
measurements per second, according to the manual. This is why the instrument
does so well as a smoothed frequency counter. The resolution "gain" is some
fraction of sqrt(200000), subject to the normal caveats like the need for
independent samples. That's why these counters have reduced resolution when
the input frequency is too close a multiple/fraction of the timebase.

Details on this technique (used also in the Pendulum CNT-9x counters):

"New frequency counting principle improves resolution"
http://tycho.usno.navy.mil/ptti/ptti2005/paper67.pdf

See also this fine presentation by Staffan Johansson:
http://www.npl.co.uk/upload/pdf/20060209_t-f_johansson_1.pdf

Or, google for: continuous time-stamping frequency counter

/tvb

----- Original Message ----- 
From: "Azelio Boriani" <azelio.boriani at screen.it>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Tuesday, October 02, 2012 5:30 AM
Subject: Re: [time-nuts] Best counter setting for ADEV?


> Hmm, the frequency mode sigma is the same as the TI mode sigma for
200*tau.
> That is if I take the sigma at 200*tau from the TI mode I have the same
> figure of the frequency mode. Maybe the frequency mode 2 seconds sample
> time uses 100 averages per second.



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