[time-nuts] Best counter setting for ADEV?

Bob Camp lists at rtty.us
Thu Oct 4 10:22:29 EDT 2012


Hi

But I don't *have* to take data only at one second points for a one second
ADEV. I can take data faster and then process it. That's what the counter
does in frequency mode. I can do the same thing with time readings.

The big advantage there is that with higher speed time readings, I can
control how the math works and *hopefully* get a valid ADEV out the other
side. With the counter doing it's magic math in the frequency mode, you are
entirely at the mercy of an unknown HP coder who might or might have been
thinking ADEV when he wrote the code.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Adrian
Sent: Thursday, October 04, 2012 8:35 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Best counter setting for ADEV?

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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