[ntp:questions] Re: Question on loopstats and PPS

David L. Mills mills at udel.edu
Fri Dec 16 01:07:24 UTC 2005


Mauro,

Stick a disable ntp in the configuration file so the clock oscillator 
wioll flywheel. Hook up your GPS receiver with PPS or add a nearby 
primary server known for outstanding performance. Set the minpoll and 
maxpoll to 4 and leave the machine running for a week or more. Capture 
the time offsets and calculate the Allan deviation yourself. Be careful 
to avoid things like daily room temperature variations, etc. You are 
looking for really tiny needles in the haystack.

Dave

Mauro Fiacco wrote:
> Pedro,
> 
> I know that the 6th field is the Allan deviation... However, it was
> calculated only for 64seconds interval (time constant of 6). 
> 
> I am interested in the curve at much higher update intervals.
> 
> Any idea?
> 
> Regards,
> 
> Mauro
> 
> On Wed, Dec 14, 2005 at 02:58:14PM -0200, Pedro Torres wrote:
> 
>>Date: Wed, 14 Dec 2005 14:58:14 -0200
>>From: Pedro Torres <torres at pop-pr.rnp.br>
>>To: questions at lists.ntp.isc.org
>>Subject: Re: [ntp:questions] Question on loopstats and PPS
> 
> 
> 
>>Hi Mauro,
> 
> 
>>Em Qua 14 Dez 2005 12:27, Mauro Fiacco escreveu:
>>
>>>Hi to All,
> 
> 
>>>I am tryng to evaluate how good is my NTP server. It runs freeBSD and
>>>uses a rubidium PPS signal to discipline the frequency (no time
>>>correction).
> 
> 
>>>The following loopstats is typical:
> 
> 
>>>53667 64119.201 0.000000000 32.241623 0.000000954 0.003332 6
>>>53667 64184.203 0.000000000 32.233749 0.000000954 0.004881 6
>>>53667 64248.196 0.000000000 32.233749 0.000000954 0.004227 6
>>>53667 64311.199 0.000000000 32.233749 0.000000954 0.003661 6
>>>53667 64377.202 0.000000000 32.233749 0.000000954 0.003170 6
>>>53667 64443.205 0.000000000 32.223343 0.000000954 0.005883 6
> 
> 
>>>The Time offset is 0, as it does not know any better; the stability is
>>>reasonable... But why the frequency offset (4th field) is so high?
> 
> 
>>>The status reported by ntptime, shows that the FLL and PPSSIGNAL are
>>>active.
> 
> 
>>>Shouldn't the frequency be corrected within the capability of the PPS
>>>signal?
> 
> 
>>>I understand that this value may be the frequency offset measured by
>>>PPS.
> 
> 
>>>In this case my question is: how can I calculate the Allan deviation of
>>>my server without knowing the actual frequency offset?
> 
> 
>>I think 6th field is Allan deviation.
> 
> 
>>Pedro
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> 
> 
> 




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