[time-nuts] ADEV from phase or frequency measurement
azelio.boriani at screen.it
Sat Mar 1 07:57:46 EST 2014
This is because usually a counter that has the time interval feature
behaves better in time interval mode. As already pointed out here, use
always the time interval mode to take samples for the Allan deviation.
In frequency mode the counter uses average or various tricks to smooth
readings, so better to switch to time interval mode in order to take
clean samples for the post processing.
On Sat, Mar 1, 2014 at 1:25 PM, Volker Esper <ailer2 at t-online.de> wrote:
> Thank you, Tom, so far. Yes, I know that I have to use different
> formulas, but - of course - I didn't calculate the ADEV curves myself, I
> let some software do the job, namely Ulrich's Plotter and TimeLab as
> well. Plotter has a menu item, where you have to check if you deal with
> phase or frequency data, so I assumed the software would do right.
> I am confused. The ADEVs of the phase data are about 10 times better and
> have a different shape...
> Am 01.03.2014 12:37, schrieb Tom Van Baak:
>> Hi Volker,
>> Either phase or frequency raw data can be used to generate an ADEV plot, but you have to use different methods depending on the data type.
>> See the two formulas for Allan Variance in: http://www.wriley.com/paper2ht.htm
>> Usually we use the "x" form of the formula, where x is an array of phase samples. But if you have frequency samples then use the "y" form instead, where y is an array of frequency samples.
>> Note you can also convert phase data to frequency data (by differentiating) and use the "y" form. Or convert frequency data to phase data (by integrating) and use the "x" form.
>> ----- Original Message -----
>> From: "Volker Esper" <ailer2 at t-online.de>
>> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
>> Sent: Saturday, March 01, 2014 3:15 AM
>> Subject: [time-nuts] ADEV from phase or frequency measurement
>>> Hello dear fellow time-nuts,
>>> I stumbled over a question that may sound stupid to you:
>>> Is the usual ADEV plot the result of a phase or a frequency measurement?
>>> I get totally different results when comparing a phase and a frequency
>>> measurement of the same source. Or am I doing something totally wrong?
>>> Thanks a lot
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