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DATE
DOCUMENT NAME
DOCUMENT #
PAGE
April 8, 2008
Harman Multimedia - JBL Radial Micro - EMC Test Report
2006 100765 EMC Rev.1
67 of 74
3. Practical Explanation of the Meaning of Radiated Emissions Measurement Uncertainties
In general, a “Statement of Measurement Uncertainty” means that with a certain (specified) confidence
level, the “true” value of a measurand will be between a (stated) upper bound and a (stated) lower bound.
In the specific case of EMC Measurements in this test report, the measurement uncertainties of the
conducted emissions measurements and the radiated emissions measurements have been calculated in
accordance with the method detailed in the following documents:
In general, a “Statement of Measurement Uncertainty” means that with a certain (specified) confidence
level, the “true” value of a measurand will be between a (stated) upper bound and a (stated) lower bound.
In the specific case of EMC Measurements in this test report, the measurement uncertainties of the
conducted emissions measurements and the radiated emissions measurements have been calculated in
accordance with the method detailed in the following documents:
o ANSI Z540.2 (2002) Guide to the Expression of Uncertainty in Measurement
o NIS 81:1994, The Treatment of Uncertainty in EMC Measurements (NAMAS, 1994)
o NIST Technical Note 1297(1994), Guidelines for Evaluating and Expressing the Uncertainty of
o NIS 81:1994, The Treatment of Uncertainty in EMC Measurements (NAMAS, 1994)
o NIST Technical Note 1297(1994), Guidelines for Evaluating and Expressing the Uncertainty of
NIST Measurement Results (NIST, 1994)
The calculation method used in these documents requires that the stated uncertainty of
the measurements be expressed as an “expanded uncertainty”, U, with a k=2 coverage
factor. The practical interpretation of this method of expressing measurement
uncertainty is shown in the following example:
the measurements be expressed as an “expanded uncertainty”, U, with a k=2 coverage
factor. The practical interpretation of this method of expressing measurement
uncertainty is shown in the following example:
EXAMPLE: Assume that at 39.51 MHz, the (measured) radiated emissions level was equal to +26.5
dBuV/m, and that the +/- 2 standard deviations (i.e. 95% confidence level) measurement uncertainty
was +/- 3.4 dB.
dBuV/m, and that the +/- 2 standard deviations (i.e. 95% confidence level) measurement uncertainty
was +/- 3.4 dB.
In the example above, the phrase “k = 2 Coverage Factor” simply means that the
measurement uncertainty is stated to cover +/-2 standard deviations (i.e. a 95%
confidence interval) about the measurand. The measurand is the radiated emissions
measurement of +26.9 dBuV/m at 39.51 MHz, and the 95% bounds for the uncertainty
are –3.4 dB to + 3.4 dB. One can thus be 95% confident that the “true” value of the
radiated emissions measurement is between +23.1 dBuV/m and +29.9 dBuV/m. In effect,
this means that in the above example there is only a 2.5% chance that the “true”
radiated emissions value exceeds +29.5 dBuV/m.
measurement uncertainty is stated to cover +/-2 standard deviations (i.e. a 95%
confidence interval) about the measurand. The measurand is the radiated emissions
measurement of +26.9 dBuV/m at 39.51 MHz, and the 95% bounds for the uncertainty
are –3.4 dB to + 3.4 dB. One can thus be 95% confident that the “true” value of the
radiated emissions measurement is between +23.1 dBuV/m and +29.9 dBuV/m. In effect,
this means that in the above example there is only a 2.5% chance that the “true”
radiated emissions value exceeds +29.5 dBuV/m.
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