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Nemko USA, Inc. 

 
 

 

 

 

Nemko USA, Inc. 

 

 
1.   Introduction 
 
ISO/IEC 17025:1999 and ANSI/NCSL Z540-1-1994 require that all measurements contained in a test 
report be “traceable”.  “Traceability” is defined in the International Vocabulary of Basic and General 
Terms in Metrology (ISO: 1993) as:  “the property of the result of a measurement... whereby it can be 
related to stated references, usually national or international standards, through an unbroken chain of 
comparisons, all having stated uncertainties”.    
 
The purposes of this Appendix are to “state the Measurement Uncertainties” of the conducted emissions 
and radiated emissions measurements contained in Section 5 of this Test Report, and to provide a practical 
explanation of the meaning of these measurement uncertainties. 
 
2.  Statement of the Worst-Case Measurement Uncertainties for the Conducted and Radiated 

 

Spectrum Analyzer with QPA & Preamplifier 

30 MHz - 200 MHz 

+3.9 dB, -4.0 dB 

Spectrum Analyzer with QPA & Preamplifier 

200 MHz-1000 MHz 

+/- 3.5 dB 

Spectrum Analyzer with Preamplifier 

1 GHz - 18 GHz 

+2.5 dB, -2.6 dB 

Spectrum Analyzer with Preamplifier 

18 GHz - 40 GHz 

+/- 3.4 dB 

NOTES: 
1. Applies to 3 and 10 meter measurement distances 
2. Applies to all valid combinations of Transducers (i.e. LISNs, Line Voltage Probes, and Antennas, as appropriate) 
3. Excludes the Repeatability of the EUT 

Nemko USA, Inc. 

 

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: 
 

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 

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: 
 

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. 
 

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. 

 
 
 

Nemko USA, Inc. 

 

 

 
Nemko USA, Inc. operates a comprehensive Periodic Calibration Program in order to ensure the validity of 
all test data.  Nemko USA’s Periodic Calibration Program is fully compliant to the requirements of 
NVLAP Policy Guide PG-1-1988, ANSI/NCSL Z540-1 (1994), ISO 10012-1 (1993-05-01), ISO Standard 
17025, ISO-9000 and EN 45001.  Nemko USA, Inc.’s calibrations program therefore meets or exceed the 
US national commercial and military requirements [N.B. ANSI/NCSL Z540-1 (1994) replaces MIL-STD-
45662A]. 
 
Specifically, all of Nemko USA’s primary reference standard devices (e.g. vector voltmeters, multimeters, 
attenuators and terminations, RF power meters and their detector heads, oscilloscope mainframes and plug-
ins, spectrum analyzers, RF preselectors, quasi-peak adapters, interference analyzers, impulse generators, 
signal generators and pulse/function generators, field-strength meters and their detector heads, etc.) and 
certain secondary standard devices (e.g. RF Preamplifiers used in CISPR 11/22 and FCC Part 15/18 tests) 
are periodically recalibrated by: 
 

o  A Nemko USA-approved  independent (third party) metrology laboratory that uses NIST-

traceable standards and that is ISO Guide 25-accredited as a calibration laboratories by 
NIST; or, 

o  A Nemko USA-approved  independent (third party) metrology laboratory that uses NIST-

traceable standards and that is ISO Guide 25-accredited as a calibration laboratory by 
another accreditation body (such as A2LA) that is mutually recognized by NIST; or, 

o  A manufacturer of Measurement and Test Equipment (M&TE), if the manufacturer uses 

NIST-traceable standards and is ISO Guide 25-accredited as calibration laboratory either by 
NIST or by another accreditation body (such as A2LA) that is mutually recognized by NIST; 
or 

o  A manufacturer of M&TE (or by a Nemko USA-approved independent third party metrology 

laboratory) that is not ISO Guide 25-accredited.  (In these cases, Nemko USA conducts an 
annual audit of the manufacturer or metrology laboratory for the purposes of proving 
traceabilty to NIST, ensuring that adequate and repeatable calibration procedures are being 
applied, and verifying conformity with the other requirements of ISO Guide 25).