[time-nuts] Low-Cost Rubidium Performance

John Ackermann N8UR jra at febo.com
Thu Feb 9 15:43:08 UTC 2012

On 2/9/2012 7:51 AM, WarrenS wrote:
> Indeed,
> ADEV is for random freq variation not easily measured by other means.
> Temperature fluctuations do not cause random freq changes and the
> temperature's effect should be removed if one wants accurate long term
> ADEV numbers.
> Even daily diurnal cycles due to temperature can have major negative
> effect on ADEV numbers as low as 2000 to 3000 seconds,
> and if there is an Heater or AC cycling, then any ADEV numbers about a
> few hundred seconds can be due to TempCoeff, which should not be
> measured with ADEV or included in ADEV plots.
> This is much the same as a single outlier data point that can screw up
> the whole ADEV plot and make it pretty much meaningless and unrepeatable.
> Ditto for linear ageing, Should be remove first if one wants true ADEV
> plots.

Hi Warren --

JimL responded before I did, making pretty much the same point -- I 
think ADEV is a tool to measure performance in the environment that you 
want.  If you want to measure the best-possible performance of a device, 
you want to control for all external factors.  But if you want to see 
the real-world performance, you want to measure in the real-world 

FWIW, these tests were done in my basement lab.  I don't have my 
temperature monitoring stuff set up yet so don't have data, but the 
furnace isn't cycling too frequently, and there is relatively little air 
flow from the registers into the area (the thermostat is upstairs and we 
just bleed a little air into the basement).  We don't do a huge amount 
of day/night setback at this time of year, so I suspect that the 
temperature is remaining stable within 2 or 3 degrees C.  I suspect the 
seasonal variation is greater than the short term.  But on the project 
list is getting several temperature sensors installed to feed a data 

On the very long term project list, I'd like to climate control my clock 
room to maintain better than 1 degree C, but that one is down the road.


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