[time-nuts] Changing ADEV, (was Phase, One edge or two?)

Bob Camp kb8tq at n1k.org
Sat Oct 25 16:16:01 EDT 2014


Hi


> On Oct 25, 2014, at 3:34 PM, Tom Van Baak <tvb at LeapSecond.com> wrote:
> 
>> How many hours / days/ months / years had the OCXO been off power before the run was started?
>> 
>> How soon after turn on did you start taking data?
> 
> Hi Bob,
> 
> On the ocxo.dat data set, the frequency drift rate was down to just 5e-11 a day so it's likely the OCXO had been powered for many days, even weeks. I don't know for sure w/o finding an old log book. The web page says the data came from "run3004/log50187.txt", which is was a free-running TBolt in November 2008 measured with a TSC 5120 against a locked HP 58503B. I can re-run the measurement if you wish.
> 
> Why do you ask?

I ask because the most common place I see ADEV changing over time without systematic issues is when they have been off power for a long time. If you warm them up and run them for a while, the ADEV tends to become much more predictable. 

Bob


> I have many data sets here, both with lower drift (e.g., rubidium or masers), or higher drift, or a variety of phase measurement instruments. Lots of samples is usually better than few samples, but it doesn't take a lot to pin the stability of an oscillator down to a couple of dB.
> 
> In some cases, computed ADEV is not a number that gets more precise or more accurate the more data you collect. You can hit a floor and it starts to diverge if you collect for too many weeks or months. This is expected. HDEV would be better.
> 
> An analogy: no one is interested in the mean of 1,000,000 days of earth temperature data. Yes, it will be a "very precise" number, if you apply the mindless sqrt(N) rule-of-thumb. But once you get enough data, looking at periodicity, jumps, outliers, and trends over time is usually far more important than blindly calculating a simple mean or standard deviation from an entire data set.
> 
> You can argue all day if the ADEV(tau 1000s) should be 3.7e-12 or 3.75e-12 or 4e-12. Regardless, it's clearly about halfway between 1e-12 and 1e-11. Below 1 dB, the rest is what day it is, what hour you started the run, how long you collected data, or how your lab feels that day. Here's an example of ADEV(tau 1000) from adev6:
> 
> C:\Tmp>adev6 /a < ocxo.dat 1000
>    1000       0/400000  a 3.706451e-012 398000
> 
> C:\Tmp>adev6 /a < ocxo.dat 1000 40000
>    1000       0/400000  a 4.100519e-012 38000
>    1000   40000/400000  a 3.912714e-012 38000
>    1000   80000/400000  a 3.736134e-012 38000
>    1000  120000/400000  a 4.413685e-012 38000
>    1000  160000/400000  a 3.050424e-012 38000
>    1000  200000/400000  a 3.692079e-012 38000
>    1000  240000/400000  a 3.367214e-012 38000
>    1000  280000/400000  a 3.223972e-012 38000
>    1000  320000/400000  a 3.742055e-012 38000
>    1000  360000/400000  a 3.897041e-012 38000
> 
> C:\Tmp>adev6 /a < ocxo.dat 1000 4000
>    1000       0/400000  a 7.804138e-012 2000
>    1000    4000/400000  a 4.085721e-012 2000
>    1000    8000/400000  a 3.368610e-012 2000
>    1000   12000/400000  a 2.890283e-012 2000
>    1000   16000/400000  a 2.408464e-012 2000
>    1000   20000/400000  a 5.823737e-012 2000
>    1000   24000/400000  a 4.127749e-012 2000
>    1000   28000/400000  a 4.310555e-012 2000
>    1000   32000/400000  a 3.375545e-012 2000
>    1000   36000/400000  a 4.166632e-012 2000
>    1000   40000/400000  a 3.052641e-012 2000
>    1000   44000/400000  a 4.718652e-012 2000
>    1000   48000/400000  a 4.238576e-012 2000
>    1000   52000/400000  a 5.275587e-012 2000
>    1000   56000/400000  a 5.695453e-012 2000
>    1000   60000/400000  a 3.669497e-012 2000
>    1000   64000/400000  a 3.107038e-012 2000
>    1000   68000/400000  a 4.863025e-012 2000
>    1000   72000/400000  a 1.882393e-012 2000
>    1000   76000/400000  a 2.395768e-012 2000
>    1000   80000/400000  a 1.606562e-012 2000
>    1000   84000/400000  a 6.180515e-012 2000
>    1000   88000/400000  a 3.201972e-012 2000
>    1000   92000/400000  a 2.023414e-012 2000
>    1000   96000/400000  a 1.515005e-012 2000
>    1000  100000/400000  a 2.343072e-012 2000
>    1000  104000/400000  a 4.249873e-012 2000
>    1000  108000/400000  a 2.676816e-012 2000
>    1000  112000/400000  a 1.656133e-012 2000
>    1000  116000/400000  a 2.411179e-012 2000
>    1000  120000/400000  a 4.081474e-012 2000
>    1000  124000/400000  a 2.997803e-012 2000
>    1000  128000/400000  a 2.095393e-012 2000
>    1000  132000/400000  a 5.760947e-012 2000
>    1000  136000/400000  a 7.075811e-012 2000
>    1000  140000/400000  a 1.769521e-012 2000
>    1000  144000/400000  a 3.358276e-012 2000
>    1000  148000/400000  a 4.893182e-012 2000
>    1000  152000/400000  a 1.936321e-012 2000
>    1000  156000/400000  a 1.578596e-012 2000
>    1000  160000/400000  a 3.601683e-012 2000
>    1000  164000/400000  a 2.287769e-012 2000
>    1000  168000/400000  a 3.073412e-012 2000
>    1000  172000/400000  a 2.291148e-012 2000
>    1000  176000/400000  a 5.813071e-012 2000
>    1000  180000/400000  a 3.669111e-012 2000
>    1000  184000/400000  a 1.766833e-012 2000
>    1000  188000/400000  a 2.527836e-012 2000
>    1000  192000/400000  a 1.982012e-012 2000
>    1000  196000/400000  a 2.387086e-012 2000
>    1000  200000/400000  a 4.483388e-012 2000
>    1000  204000/400000  a 1.825970e-012 2000
>    1000  208000/400000  a 1.405565e-012 2000
>    1000  212000/400000  a 5.431766e-012 2000
>    1000  216000/400000  a 1.325479e-012 2000
>    1000  220000/400000  a 1.874571e-012 2000
>    1000  224000/400000  a 8.372485e-012 2000
>    1000  228000/400000  a 4.277784e-012 2000
>    1000  232000/400000  a 2.616340e-012 2000
>    1000  236000/400000  a 3.765100e-012 2000
>    1000  240000/400000  a 1.840977e-012 2000
>    1000  244000/400000  a 2.921888e-012 2000
>    1000  248000/400000  a 1.532576e-012 2000
>    1000  252000/400000  a 2.774957e-012 2000
>    1000  256000/400000  a 5.713711e-012 2000
>    1000  260000/400000  a 4.725035e-012 2000
>    1000  264000/400000  a 3.428511e-012 2000
>    1000  268000/400000  a 2.549448e-012 2000
>    1000  272000/400000  a 8.913688e-013 2000
>    1000  276000/400000  a 4.408449e-012 2000
>    1000  280000/400000  a 2.503479e-012 2000
>    1000  284000/400000  a 1.883790e-012 2000
>    1000  288000/400000  a 3.782682e-012 2000
>    1000  292000/400000  a 3.132628e-012 2000
>    1000  296000/400000  a 2.913452e-012 2000
>    1000  300000/400000  a 2.021695e-012 2000
>    1000  304000/400000  a 3.370930e-012 2000
>    1000  308000/400000  a 2.043129e-012 2000
>    1000  312000/400000  a 5.285278e-012 2000
>    1000  316000/400000  a 3.020556e-012 2000
>    1000  320000/400000  a 3.454389e-012 2000
>    1000  324000/400000  a 5.324399e-012 2000
>    1000  328000/400000  a 4.481485e-012 2000
>    1000  332000/400000  a 1.773463e-012 2000
>    1000  336000/400000  a 4.372101e-012 2000
>    1000  340000/400000  a 5.504813e-012 2000
>    1000  344000/400000  a 3.117502e-012 2000
>    1000  348000/400000  a 5.678955e-012 2000
>    1000  352000/400000  a 2.934761e-012 2000
>    1000  356000/400000  a 3.119271e-012 2000
>    1000  360000/400000  a 2.867365e-012 2000
>    1000  364000/400000  a 5.534214e-012 2000
>    1000  368000/400000  a 1.696574e-012 2000
>    1000  372000/400000  a 1.954016e-012 2000
>    1000  376000/400000  a 3.051420e-012 2000
>    1000  380000/400000  a 5.290654e-012 2000
>    1000  384000/400000  a 3.908393e-012 2000
>    1000  388000/400000  a 2.984008e-012 2000
>    1000  392000/400000  a 2.348755e-012 2000
>    1000  396000/400000  a 4.209189e-012 2000
> 
> /tvb
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