[time-nuts] question Alan deviation measured with Timelab and counters

[Bob Camp]

Hi

Ok, I didn’t think I’d seen the plots before. 

I agree that the plots look like “counter limited” data. That’s a fine explanation at the shorter Tau’s. I also agree that some sort of periodic “stuff” is getting into one of the signals and creating the ripple. What I’m wondering about (and what makes me question the setup) is the fact that the data is still “counter limited” at the mid to low parts in 10^-13 level at just a bit over 100 seconds. A telecom  Rb is doing pretty well to be at 1x10^-12 at 100 seconds. Most GPSDO’s are doing well to be mid parts in 10^-12 at that tau. Simply put, the data continues to be counter limited to a pretty low point. 

Bob

> On Jan 18, 2015, at 7:13 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> Hi Bob,
> 
> On 01/18/2015 04:25 AM, Bob Camp wrote:
>> Hi
>> 
>> I’m a little concerned about the measurement setup here. Based on the quoted text, there have been a few messages in the thread that have not showed up here.
> 
> The messages got accidentally posted in the wrong thread.
> 
>> =========
>> 
>> The “start” input on the counter is defined below. The “stop” input is not defined. Is the counter running in time interval mode or in frequency mode?
>> 
>> IF it’s in time mode - what is the stop hooked to?
>> 
>> IF it’s in frequent mode - what is the gate time set to ?
>> 
>> Is the “standard input” the missing front panel input or is it the external reference input on the back panel?
> 
> I was also considering the setup strange in this regard. Common switched in?
> 
>> =========
>> 
>> I’m looking at the data on the link:
>> 
>> http://www.ptp-images.com/affiche-directement-l-image-kccsz71c9a.html
>> 
>> In both cases the slope is roughly 1/tau. Both plots end up in the 3 to 4 x 10^-13  range at 100 to 300 seconds. That’s suspiciously good performance for a rubidium or a GPSDO. Which is what makes me wonder about the setup.
>> 
>> The Blue plot (1 pps?) ran for 18 minutes and has 1,114 points in it. The Pink plot ran for about 9 minutes and has a bit over 500 points in it. Both seem reasonable for a 1 pps to 10 MHz sort of setup. That may explain part of my confusion above.
>> 
>> Again - I apologize if this all got explained in a post that went missing here.
> 
> Not really. The plots looks to me like measurement setup baseline plots, with some sine noise in them.
> 
> Cheers,
> Magnus
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