[time-nuts] wander and jitter measurements

Magnus Danielson magnus at rubidium.dyndns.org
Sun Jun 29 00:02:15 UTC 2014


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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