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Power accuracy questions

Question asked by rf_engineer_5 on May 2, 2014
Latest reply on Oct 8, 2014 by FrancisSmall
If you look at the E4419B's power meter data sheet there is a declared absolute accuracy of +/-0.02dB.  The spec also states that you need to add in the linearity deviation if you exceed a certain power level to the sensor.   Based on many readings I have done, it seems that if you stay below that power level then you can assume that sensor linearity deviation is fairly negligible.  Perhaps this is a wrong conclusion.  When I use Agilent's uncertainty calculator I am somewhat confused in how to interpret the results.  After I factor in the sensor choice, and provided I stay within the best linearity range, I end up seeing uncertainty levels as follows:

ULU: +0.075dB
LLU: -0.076dB

It seems that one would never be able to hit the +/-0.02dB spec if the uncertainty is so much greater.  What am I missing here?