[time-nuts] Frequency standards for different tau in Allen Dev measurement

[Magnus Danielson]

Hi,

For white phase modulation noise and flicker phase modulation noise,
ADEV depends on filter bandwidth, but not for the others, according to
theory. This is naturally an approximation, but it works out like that
pretty much in real life too, so it works as an approximation... until
you try to do the math yourself and find out where it does not fit
together properly. Oh well, that is for nuts like me to care about and
you others do not need to bother.

Turns out the approximation of filter is "interesting". A lot of madness
lies there as one tries to do correct analysis, and it all turns out to
be more or less esoteric.

Cheers,
Magnus

On 2020-02-21 22:27, Bob kb8tq via time-nuts wrote:
> Hi
>
> With phase data on ADEV, you are pretty much always *under-sampling* the data.
> As you go to longer tau’s you do not do any bandwidth fiddling. The sample rate
> drops and drops, but the bandwidth stays the same. 
>
> Bob
>
>> On Feb 21, 2020, at 4:04 PM, Chris Caudle via time-nuts <time-nuts at lists.febo.com> wrote:
>>
>> On Fri, February 21, 2020 2:27 pm, Bob kb8tq via time-nuts wrote:
>>> Which is why downsample is probably a better term since it does not
>>> involve fiddling bandwidth.
>> I would expect that you would still have to meet Shannon-Nyquist criteria
>> and low-pass filter before reducing the sampling rate.
>> I don't have a firm grasp on the mathematics of how this translates into
>> the final ADEV values, but I can't imagine that aliases are going to
>> improve the quality of the data.
>>
>> -- 
>> Chris Caudle
>>
>>
>>
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