[time-nuts] NTP, PPS and < 10 us offsets

Chris Albertson albertson.chris at gmail.com
Wed May 15 13:33:00 EDT 2013

i've seen that myself, NTP's compensation can almost be used as a way to
measure room temperature.   You can see the AC cycles.   For this reason I
keep the NTP server in a walk in closet that lacks heating duct.  The room
temp cycles slowly.

I've also read but can't remember where about a project to replace the TTL
can oscillator in a PC with a better quality one driven from a OCXO.  That
is a lot of work for small gain.

One thing about that study.  I notice the author had t remove the PPS
reference clock.   It looks like he was unabe to get the graph to move at
all with PPS attached.   I'd like to see the same study done with a good
PPS reference clock let connected.  Likely the results would be
uninteresting, just a flat graph.

On Wed, May 15, 2013 at 12:51 AM, Hal Murray <hmurray at megapathdsl.net>wrote:

> albertson.chris at gmail.com said:
> > Maybe not you, but I think some people think "Oh my, NTP is not checking
> the
> > time very often.  It must not be accurate."   That is thinking backwards,
> > you need the long poll interval to see small errors in rate.   But this
> > assumes a stable local clock.  NTP balances this.
> That "balance" is assuming a classic ADEV type V curve.  That assumption
> works better in old non-green systems that burned lots of power in an idle
> loop when they didn't have any work to do.  With modern systems, it's easy
> to
> change the temperature significantly by starting/finishing a big chunk of
> work.
> External temperature changes can also be important.  Every now and then, I
> like to repost this link.  This seems like a good opportunity.
>   NTP temperature compensation
>   http://www.ijs.si/time/temp-compensation/
> --
> These are my opinions.  I hate spam.
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Chris Albertson
Redondo Beach, California

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