[time-nuts] Best counter setting for ADEV?

Adrian rfnuts at arcor.de
Thu Oct 4 08:34:55 EDT 2012


Azelio,

as an example, with a 53131A you have an output 'granularity' of +/- 500 
ps.
No matter how much averaging happens inside the counter, if the least 
significant digit is 500 ps, then the (ADEV) measurement limit is always 
5E-10 at 1 sec as I posted in the initial post to this thread. This is 
not the accuracy of the counter, it's simply the available display and 
output string resolution.
At 10 sec., the ADEV limit of the same counter is 5E-11 etc. etc. 
finally getting limited by the reference source and other effects.
If the DUT's ADEV is in the 1E-13's, any measurement values below 1000 
sec. are void and represent just the measurement limit of the +/- 500ps 
counter.

Now I'm waiting to receive 'glasses' for my 53131A that are in transit :)

Adrian


Azelio Boriani schrieb:
> Taking 10 samples from a 1nS counter leads you to a 100pS resolution but
> the noise at best (if it is really random) is reduced by SQRT(10). So, as
> already pointed out here, there is no real substitute for lower noise,
> higher resolution measurements.
>
> On Thu, Oct 4, 2012 at 3:01 AM, Bob Camp <lists at rtty.us> wrote:
>
>> Hi
>>
>> A 1 ns resolution TI counter will do the measuring part just fine. Hitting
>> the number, is where it gets a bit crazy. A *good* GPSDO might get near
>> that.
>>
>> Bob
>>
>> On Oct 3, 2012, at 8:56 PM, Kevin Rosenberg <kevin at rosenberg.net> wrote:
>>
>>> On Oct 3, 2012, at 6:52 PM, Kevin Rosenberg <kevin at rosenberg.net> wrote:
>>>> Nice plot! Yes, I'd have trouble measuring 10E-14 at 10E5 seconds.
>>> Sorry, 1E-14 at 1E5.
>>>
>>>
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