[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:
> 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
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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