[time-nuts] Method for comparing oscillators

[Steve Rooke]

2009/8/7 Magnus Danielson <magnus at rubidium.dyndns.org>:
> Steve Rooke wrote:
>>
>> 2009/8/6 Magnus Danielson <magnus at rubidium.dyndns.org>:
>>>
>>> Ulrich Bangert wrote:
>>
>> ...
>>>>
>>>> Well, stability over time is what exacly is displayed in a
>>>> tau-sigma-diagram
>>>> of an oscillator. Since only a few words before he is saying that he is
>>>> NOT
>>>> intersted into Allan Deviation plots, then he is perhaps interested into
>>>> something else?
>>>
>>> Yes. Sigma-Tau plots of the Allan Deviation fame (with friends) addresses
>>> the instability of the noise part of things. For crystal oscillators and
>>> other non-atomic oscillators "linear" factors in frequency drift is not
>>> best
>>> specified, described or measured using that method, which was invented
>>> purely to be able to handle the phase noise side of things, not the slow
>>> frequency drift.
>>
>> For these sorts of measurements on drifting oscillators would it not
>> be prudent to use the Hadamard Deviation?
>
> Hadamard Deviation does not fully cancel the non-stable drift.

>From the flow of the discussion I gathered, perhaps incorrectly, that
we were talking about the fairly linear drift in crystal oscillators
for which HD handles. If there is a non-stable drift, it's going to be
an interesting exercise to be able to process that out of the data
easily. Agreed if the drift can be characterized to fit some form
function but I would call that a stable drift anyway. I also had the
impression, and please correct me if I'm wrong, that the use of the
additional adjacent data point in HD calculations resolved the issues
with drift at any point in the data stream.

Cheers,
Steve

-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.