DOWNLOAD Harman Kardon GO AND PLAY (serv.man3) Service Manual ↓ Size: 3.09 MB | Pages: 80 in PDF or view online for FREE

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 +26.5 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 +29.5 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). 

 
In all cases, the entity performing the Calibration is required to furnish Nemko USA with a calibration test 
report and/or certificate of calibration, and a “calibration sticker” on each item of M&TE that is 
successfully calibrated. 
 
Calibration intervals are normally one year, except when the manufacture advises a shorter interval or if 
US Government directives or client requirements demand a shorter interval.  Items of 
instrumentation/related equipment which fail during routine use, or which suffer visible mechanical 
damage (during use or while in transit), are sidelined pending repair and recalibration.  (Repairs are carried 
out either in-house [if minor] or by a Nemko USA-approved independent [third party] metrology 
laboratory, or by the manufacturer of the item of M&TE). 
 
Each antenna used for CISPR 11 and CISPR 22 and FCC Part 15 and Part 18 radiated emissions testing 
(and for testing to the equivalent European Norms) is calibrated annually by either a NIST (or NVLAP) 
ISO Standard 17025-Accredited third-party Antenna Calibration Laboratory or by the antenna’s OEM if 
the OEM is NIST or NVLAP ISO Standard 17025-accredited as an antenna calibration laboratory.  The 
antenna calibrations are performed using the methods specified in Annex G.5 of CISPR 16: 2003 or ANSI 
C63.4: 2003, including the “Three-Antenna Method”.  Certain other kinds of antennas (e.g. magnetic-
shielded loop antennas) are calibrated annually by either a NIST (or NVLAP) ISO Standard 17025-

Nemko USA, Inc. 

 

accredited third-party antenna calibration laboratory, or by the antenna’s OEM if the OEM is NIST or 
NVLAP ISO Standard 17025-accredited as an antenna calibration laboratory using the procedures 
specified in the latest version of SAE ARP-958. 
 
In accordance with FCC and other regulations, Nemko USA recalibrates its suite of antennas used for 
radiated emissions tests on an annual basis.  These calibrations are performed as a precursor to the FCC-
required annual revalidation of the Normalized Site Attenuation properties of Nemko USA’s Open Area 
Test Site.  Nemko USA, Inc. uses the procedures given in both Subclause 16.6 and Annex G.2 of CISPR 
16: 2003, and ANSI C63.4: 2003 when performing the normalized site attenuation measurements. 
 
 

Nemko USA, Inc.