[time-nuts] wander and jitter measurements

[Magnus Danielson]

Hi,

If you have a 1PPS the nominal rate is exactly 1 Hz. If your PRS-10 runs at +750 ns on every pulse then it has a frequency offset of 750E-9=7.5E-7 from the nominal frequency. You can expect jitter and wander on the PPS, as deviations from the frequency it has.

Cheers, 
Magnus

<div>-------- Originalmeddelande --------</div><div>Från: mike cook <michael.cook at sfr.fr> </div><div>Datum:29-06-2014  09:58  (GMT+01:00) </div><div>Till: Discussion of precise time and frequency measurement <time-nuts at febo.com> </div><div>Rubrik: Re: [time-nuts] wander and jitter measurements </div><div>
</div>Thanks for your responses and the links.

My DQ3, Can I deduce offset from jitter comes from the following and while Bill's response was a succinct NO, I am still wondering.

Maybe it's my interpretation of "nominal" and "ideal". Here is scenario :

I have a 1PPS which is offset from a reference (PRS10 in this instance) by +750ns . If I take the wander about the "ideal" as per G.810 , it is systematically +ve by that figure, + or - some ps , so the offset is shown in these figures. However, if I take the DUT's signal as being "nominal" as per Magnus's statement, ie using the DUT's signal as reference, then of course I cannot see the offset.   

Mike


Le 29 juin 2014 à 02:02, Magnus Danielson a écrit :

> Mike,
> 
> A frequency offset is just a long term shift from nominal rate.
> 
> Wander is "slow" variations and jitter is "fast" variations of phase.
> The separation between "slow" and "fast" is a bit arbitrary, but the 10 Hz division-line is handy as it describes different sources, where wander is the in-bandwidth noise accumulation where as jitter is usually damped pretty well by being outside of the jitter bandwidth.
> 
> See ITU-T G.810, G.813, G.823-825.
> 
> Cheers,
> Magnus
> 
> On 06/27/2014 07:37 PM, bill wrote:
>> On 6/26/2014 2:39 AM, mike cook wrote:
>>> A few dumb questions:
>>> 
>>> But first a quote from the ITU ( doc G.180 )
>>> 
>>> ""4.1.12 (timing) jitter: The short-term variations of the significant
>>> instants of a timing signal from
>>> their ideal positions in time (where short-term implies that these
>>> variations are of frequency greater
>>> than or equal to 10 Hz).
>>> 
>> DQ1 yes
>> 
>> DQ2 Frequency offset would come into the Wander category except it
>> defined differently.
>> 
>> DQ3 No
>> 
>> 
>> That gives my take on your q questions. Its been 23 years since I had
>> think about jitter and wander as chairman of T1X1.3 committee
>> 
>> Bill
>> K7NOM
>>> 4.1.15 wander: The long-term variations of the significant instants of
>>> a digital signal from their
>>> ideal position in time (where long-term implies that these variations
>>> are of frequency less than
>>> 10 Hz).
>>> NOTE – For the purposes of this Recommendation and related
>>> Recommendations, this definition does
>>> not include wander caused by frequency offsets and drifts.""
>>> 
>>> DQ1. These both refer to phase variations, so with the exception of
>>> the frequency range specified, are they mathematically equivalent?
>>> 
>>> DQ2.  The note on wander excludes frequency offsets, but that is not
>>> specified for jitter, so do I have to include a frequency offset in
>>> jitter measurements? It seems to me that it make no sense to do so.
>>> 
>>> DQ3.  Can I deduce an underlying frequency offset from jitter (wander)
>>> by  taking an RMS value over some window of values?
>>> 
>>> 
>>> regards,
>>> Mike
>>> 
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>> 
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