[time-nuts] Data Collection for Allan Deviation

Bob Stewart bob at evoria.net
Sat Aug 1 17:49:41 EDT 2015

Hi Poul,
Here's an example of what I'm talking about.  See description and notes.  The blue trace is the one using the clock in the 5370A.  The other tests match pretty closely down to around 60s or so.


      From: Poul-Henning Kamp <phk at phk.freebsd.dk>
 To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
 Sent: Saturday, August 1, 2015 4:10 PM
 Subject: Re: [time-nuts] Data Collection for Allan Deviation
In message <1925117252.232793.1438455428192.JavaMail.yahoo at mail.yahoo.com>, Bob Stewart writes:
>Hi Poul,

>"0)  Make sure that the counter does not get its reference frequency
>    from any of the input signals."
>Does your rule 0 hold if one of the input signals is a Cs standard? 
>I believe I've posted in the past that the ADEV from 1 tau to 100
>tau is a bit noisy if I use the internal 10811 to clock the 5370A. 
>I noticed the same on my 5335A.

For me it is a rule of principle:  If the HP5370 is clocked from the
same source I'm measuring, I can have no expectation of a well
behaved noise from the triggers.

The "noise" you saw is probably exactly that:  Overly optimistic
results if you clock the counter from one of the DUTs

Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG        | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.


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