[time-nuts] Allan Deviation recipe?

[Gary E. Miller]

Yo Hal!

On Tue, 19 Jul 2016 14:28:32 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:

> [You sent that to 3 lists that I'm on.  I'll reply here.

Yeah, but time-nuts is the one list that knows more about this than
I do.  So good choice.

> I think your X axis is off.  Your left edge is 1 second and you don't
> have data for that.  peerstats is every 64 seconds. (unless you
> mucked with maxpoll)  I'm guessing the software you used is assuming
> they are every second.  There may be a command line parameter.

I'm taking the time and offset from the /var/log/ntpstats/peerstats
file.  So the data is collected every minpoll (16 seconds), timestamped
in seconds with millisecond precision.  The offsets are also in seconds.

Should I set the left edge to 16 seconds?

> The normal ADEV is V shaped.  The left slope is noise in the
> readings.  The right slope is drift in the clock.  That assumes you
> have a good reference clock, where good means much better than the
> DUT.

Well, the data is the data.  I used Tom Van Baak's adev5 program
to do the calculations.  Given that the system is GPS stabilized
on PPS I can't see why the accuracy should not get better over long
durations.

> In this case, there is no long term drift since ntpd is tracking
> GPS.  You will probably get a traditional V if you disable ntpd.

Well, I'm trying to measure ntpd, so chicken and egg here.

> There is a slight step in the NMEA data at 1000 seconds and maybe a
> similar step in the PPS data at the right edge of the graph.  I don't
> know what that means.

At Tom's suggestion, I upped the sampling from Octaves to 50/decade.
I also added TDEV.  Now there is some structure in there.

https://rellim.com/graphs/adev.png

Some weird things in there...

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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