[time-nuts] Hadamard variance

Steve Rooke sar10538 at gmail.com
Fri Apr 10 11:45:10 UTC 2009


Bruce,

2009/4/10 Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
> Just dont get too carried away.
> Remember that the Hadamard deviation is only insensitive to linear
> frequency drift.
> If the drift is quadratic for example then it will affect the Hadamard
> deviation.

Point well taken. In that case we need a new deviation measurement
with 4 elements then :-)

73,
Steve

> Bruce
>
> Steve Rooke wrote:
>> Hi Tom,
>>
>> 2009/4/9 Tom Van Baak <tvb at leapsecond.com>:
>>
>>> I use it sometimes when I need to. But note that in most cases
>>> you do NOT want to ignore drift. If you measure an OCXO for
>>> the purpose of using it in a clock or appliance or radio or test
>>> equipment you really do want to know if it has drift or not. ADEV
>>> will show this, while HDEV will not. So you have to be careful
>>> about using statistics that deliberately and quietly ignore effects
>>> that may be important to your application.
>>>
>>
>> Indeed, I was thinking that HDEV would be a good tool to characterise
>> free running OCXOs with it's insensitivity to drift but, of course, I
>> would use ADEV to measure the performance of a GPS locked system or
>> one running in holdover mode.
>>
>>
>>> But before you run off and use HDEV for everything note that
>>> the other practice that is far more common -- simply remove
>>> frequency drift from the raw data before computing an ADEV
>>> on the residuals. If you look at plots in professional journals you
>>> will often find comments to the effect that phase, frequency, or
>>> drift offsets have been added or removed prior to making said
>>> phase, frequency, or stability plots.
>>>
>>
>> I had no intent to use HDEV exclusively, it seems like a useful tool
>> to analyse free-running oscillators to measure the affects of noise
>> while screening out drift (which we have some means of handling in
>> holdover circuits). As a selection tool it seemed quite useful and I
>> was asking if others felt the same way.
>>
>> Agreed, it is possible to factor out drift by pre-processing the data
>> and then using just ADEV to compare all aspects of any open or closed
>> system.
>>
>>
>>> Here, to see the difference that HDEV makes (or not) see:
>>> http://www.leapsecond.com/pages/hdev
>>>
>>
>> It seems to have an effect removing some of what must be drift with
>> the OCXO plot but adds nothing to the PPS one. Do I take it that the
>> OCXO was free-running and the PPS was locked to GPS, as this would
>> account for the differences?
>>
>>
>>> The command line program that I use (ADEV3) these days:
>>> Tool for ADEV, MDEV, HDEV:
>>> http://www.leapsecond.com/tools/adev3.exe
>>>
>>> Source code (compiles in windows, bsd, or linux)
>>> http://www.leapsecond.com/tools/adev3.c
>>>
>>
>> Thanks for the pointers, I'll have a look at this instead.
>>
>> 73,
>> Steve
>>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet



More information about the time-nuts mailing list