CISPR TR 16-4-1:2003/AMD2:2007

TECHNICAL CISPR
REPORT 16-4-1
AMENDMENT 2
2007-04
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE
Amendment 2
Specification for radio disturbance and immunity
measuring apparatus and methods –
Part 4-1:
Uncertainties, statistics and limit modelling –
Uncertainties in standardized EMC tests

Reference number
CISPR 16-4-1 Amend. 2:2007(E)
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TECHNICAL CISPR
REPORT 16-4-1
AMENDMENT 2
2007-04
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE
Amendment 2
Specification for radio disturbance and immunity
measuring apparatus and methods –
Part 4-1:
Uncertainties, statistics and limit modelling –
Uncertainties in standardized EMC tests

PRICE CODE
Commission Electrotechnique Internationale V
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

– 2 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

FOREWORD
This amendment has been prepared by CISPR subcommittee A: Radio-interference

measurements and statistical methods.

The text of this amendment is based on the following documents:

DTR Report on voting
CISPR/A/713/DTR CISPR/A/729/RVC

Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
_____________
Page 10
2 Normative references
Add the following new references:
CISPR 16-1-4:2007, Specification for radio disturbance and immunity measuring apparatus

and methods - Part 1-4: Radio disturbance and immunity measuring apparatus - Ancillary
equipment - Radiated disturbances
CISPR 16-2-3:2006, Specification for radio disturbance and immunity measuring apparatus
and methods - Part 2-3: Methods of measurement of disturbances and immunity - Radiated
disturbance measurements
Page 11
3 Terms and definitions
Replace the existing heading of Clause 3 by the following:

TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 3 –

3 Terms, definitions, and acronyms

Add new subclause 3.1 as follows, and renumber terms 3.1 to 3.20 as 3.1.1 to 3.1.20:

3.1 Terms and definitions
Add, on page 14, the following new subclause:

3.2 Acronyms
AF antenna factor
EUT equipment under test
GUM ISO/IEC Guide to the expression of uncertainty in measurement
ILC interlaboratory comparison
LPDA log-periodic dipole array
MIU measurement instrumentation uncertainty
OATS open-area test site
RRT round-robin test
SAC semi-anechoic chamber
SCU standards compliance uncertainty

Page 57
8 Radiated emission measurements
Replace the existing title and text of Clause 8 by the following:
8 Radiated emission measurements using a SAC or an OATS in the frequency
range of 30 MHz to 1 000 MHz
8.1 General
8.1.1 Objective
This clause provides information and guidance for the determination of uncertainties
associated with measurement equipment and the measurement method used for radiated

emission measurements in the frequency range of 30 MHz to 1 000 MHz in a SAC or on an
OATS. Furthermore, a rationale is provided for the various uncertainty aspects described in
several parts of CISPR 16 that are related to the radiated emission measurement method (see
Clause 7 of CISPR 16-2-3).
In CISPR 16-4-2, the uncertainty considerations for SAC/OATS-based radiated emission
measurements are limited to measurement instrumentation uncertainties (MIU). This part
addresses all uncertainties that are relevant for compliance testing, i.e. the standards
compliance uncertainty (SCU), which also includes the MIU.
The rationale for the methods of uncertainty estimation provided in this Clause 8 is intended
to serve as background information for the parts of CISPR 16 that are related to the
SAC/OATS-based emission measurement method. This background information may be used
by the CISPR subcommittees to improve the existing standards as far as uncertainties are
concerned. In addition, this clause provides information for those who apply the radiated
emission measurement method and who have to establish their own uncertainty estimates.

– 4 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

8.1.2 Introduction
Clause 8 provides information on the uncertainties associated with the SAC/OATS-based

radiated emission measurement method as described in CISPR 16-2-3. The uncertainty

estimates for the SAC/OATS radiated emission measurement method described in

CISPR 16-4-2, or for example in LAB 34 [11], address only some of the uncertainty
components present in actual compliance tests performed in accordance with CISPR 16-2-3.

Uncertainty estimates in the aforementioned documents account only for the measurement

instrumentation uncertainties (MIUs), whereas uncertainties due to the set-up of the EUT

including its cables, and due to the measurement procedure itself, are not taken into account.

In this clause, all uncertainty sources that are relevant for the measurement uncertainty of the

compliance test, termed as the standards compliance uncertainty (SCU), are considered. One

basic assumption for these SCU estimations is that the EUT does not change. In other words,
the uncertainty of the SAC/OATS radiated emission measurement method is considered
based on using the same EUT as measured by different test laboratories. The laboratories will
use different measurement instrumentation, a different test site, different measurement
procedures, and different operators. Often the laboratories may also apply different
measurement set-ups or different EUT operating modes. The latter EUT-related sources of
uncertainty may become significant, and can contribute to poor reproducibility.
The uncertainty estimation described in this clause is done in accordance with the basic
considerations on uncertainties in emission measurements given in Clause 4.
8.2 Uncertainties related to the SAC/OATS radiated emission measurement method
This subclause describes the preparation of the uncertainty estimates for the SAC/OATS-
based radiated emission measurement method described in Clause 7 of CISPR 16-2-3. For
reference, a schematic overview of the radiated emission measurement method is given in
Figure 8-1. This figure shows an EUT set up on a positioning table in a SAC. The receive
antenna measures the sum of the direct and reflected emission from the EUT.

Receive antenna
mast
SAC
Receive antenna
Direct
Table top
ray
EUT
EUT
cable
Reflected
ray
Receive antenna
cable
EUT
table
Ground plane
Receiver
IEC  506/07
Figure 8-1 – Schematic of a radiated emission measurement set-up in a SAC

TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 5 –

8.2.1 The measurand
Previously, the measurand for the SAC/OATS-based radiated emission measurement method

in CISPR 16-2-3 was only incompletely defined. In Clause 4 of CISPR 16-1-4, which covers

the frequency range 9 kHz to 18 GHz, a reference antenna (balanced dipole) was specified in

the range 30 MHz to 300 MHz. For convenience, this measurand was called the reference
electric field strength (E-field), i.e. the E-field measured by the CISPR reference antenna. In

the frequency range 300 MHz to 1 000 MHz, a reference antenna was not defined, and the

measurand is the electric field strength.

Recently work was begun in CISPR/A to implement E-field as the quantity to be measured

over the frequency range of 30 MHz to 1 000 MHz, with an amendment under development at

the time of writing.
In this subclause it is assumed that the quantity to be measured is the E-field. However, this
is not a complete description of the measurand, because as described in the ISO GUM the
measurand definition also requires statements about the influence quantities.
From a metrological viewpoint, a more appropriate description of the measurand associated
with the SAC/OATS-based radiated emission measurement, is as follows:
The quantity to be measured is the maximum field strength emitted by the EUT as a function
of horizontal and vertical polarisation and at heights between 1 m and 4 m, and at a horizontal
distance of 10 m from the EUT, over all angles in the azimuth plane. This quantity shall be
determined with the following provisions:
a) the frequency range of interest is 30 MHz to 1 000 MHz;
b) the quantity shall be expressed in terms of field strength units that correspond with the
units used to express the limit levels for this quantity;
c) a SAC/OATS measurement site and positioning table shall be used that complies with
the applicable CISPR validation requirements;
d) a CISPR-compliant EMI receiver shall be used;
e) the application of alternative measurement distances, such as 3 m or 30 m rather than
the nominal distance of 10 m (see 8.2.3.3a), is considered to be an alternative
measurement method; correlation factors shall be used to translate results obtained at
these measurement distances to 10 m results (see 8.2.3.3a for the consequences in
terms of uncertainties);
f) the measurement distance is the horizontal projection onto the ground plane of the
distance between the boundary of the EUT and the antenna reference point;
g) the EUT is configured and operated in accordance with the CISPR specifications;

h) free-space-antenna factors shall be used.
The measurand E is derived from the maximum voltage reading V by using the free-space
r
antenna factor AF:
IQ
E =V + L + F + C (8-1)
r c A
∑ i
i
where
E
is the field strength in dB(μV/m) as described in the measurand description;
V
is the maximum voltage reading in dB(μV) using the procedure as described
r
in the measurand description;
L is the loss in dB of the measuring cable between antenna and receiver;
c
– 6 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

-1
)
F
A is the free-space antenna factor of the receive antenna in dB(m );

IQ IQ
C is the sum of the correction factors C that may be applicable for the
∑ i i
i
various influence quantities as described in 8.2.3.

8.2.2 Uncertainty sources
This subclause summarises the sources of uncertainty associated with the SAC/OATS-based

measurement method. From Equation (8-1) it can be seen that the uncertainty is determined

by the uncertainty of the measured voltage, the uncertainty of the cable loss, and the

uncertainty of the antenna factor.

The uncertainty of the measured voltage is determined by the uncertainties induced by the
EUT, the set-up, the measurement procedure, the measurement instrumentation and the
environment. Figure 8-2 gives a schematic overview of all the relevant uncertainty sources.
This fish-bone diagram indicates the categories of uncertainty sources that contribute to the
overall uncertainty of the measurand. An important set-up uncertainty source is the
reproducibility of the set-up of the EUT.

MEASUREMENT
PROCEDURE
Nominal measurement -
SET-UP
distance
EUT Receiver settings -
EUT cables -
Height scanning
influence type -
receive antenna-
of EUT
Azimuth
EUT units -
Reproducibility -
scanning EUT -
Receiver performance -
OVERALL
Climatic -
UNCERTAINTY
ambient
Test site performance -
Electromagnetic -
Receive
ambient
antenna performance -
Receive antenna cable -
Mains
connection -
Repeatability -
MEASUREMENT
INSTRUMENTATION ENVIRONMENT
IEC  507/07
Figure 8-2 – Uncertainty sources associated with the SAC/OATS radiated emission
measurement method
—————————
1)
Free-space antenna factors are used as a figure of merit for the antenna. It should be noted the field strength is
not measured in a free-space environment but over a ground plane. See 8.2.3.5 h) for further information.

TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 7 –

8.2.3 Influence quantities
For most of the qualitative uncertainty sources given in Figure 8-2, one or more influence

quantities can be used to “translate” the uncertainty source in question. Table 8-1 shows the

relationship between the uncertainty sources and the influence quantities. If an influence

quantity cannot be identified, the original uncertainty source will be used in the uncertainty
estimate. For each of the uncertainty sources and influence quantities, details are provided

below.
NOTE The uncertainty sources and influence quantities terms used in this subclause and in the remainder of

Clause 8 may deviate from similar terms used in CISPR 16-4-2. This is justified for the following reasons: a) Some
of the influence quantities are specifically applicable for SCU, and are not applicable for the MIU-only estimates of

CISPR 16-4-2; b) Some of the influence-quantity terms used in CISPR 16-4-2 are not quantified or are not clearly

identified. For instance the term “site imperfection” is a qualitative term used in CISPR 16-4-2. The term “NSA
deviation” used in Table 8-1 is more appropriate because it reflects a specific and well-known quantity.
Furthermore, the term ”noise floor proximity” is not clearly defined, while the term “signal-to-noise ratio” is a well-
known and quantifiable term.
Therefore it is intended to harmonise with the terms used in this document in future maintenance of CISPR 16-4-2.

– 8 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

Table 8-1 – Influence quantities for the SAC/OATS radiated emission measurement
method associated with the uncertainty sources of Figure 8-2

Subclause
Uncertainty source Influence quantity
no.
8.2.3.1 EUT-RELATED
a) Size of EUT
Influence of type EUT on other uncertainty
sources
b) Type of disturbance
c) Product sampling
Reproducibility of EUT
d) Modes of operation
8.2.3.2 SET-UP-RELATED
a) Layout of EUT unit(s) and cable(s)
b) Termination of cable(s)
EUT set-up
c) Measurement distance tolerance
d) EUT height above ground plane tolerance
8.2.3.3 MEASUREMENT-PROCEDURE-RELATED
a) Nominal measurement distance Nominal measurement distance
b) Receiver settings Receiver settings
c) Height-scanning step size
Height-scanning of receive antenna
d) Start and stop position tolerance
e) Azimuth-scanning of EUT Azimuth step size
8.2.3.4 ENVIRONMENT-RELATED
a) Climatic, ambient Temperature and humidity tolerances
b) Electromagnetic ambient signals Signal-to-ambient-signal ratio
c) Mains voltage variation
Mains connection
d) Application of mains coupling devices
8.2.3.5 MEASUREMENT-INSTRUMENTATION-

RELATED
a) Receiver accuracy
b) Mismatch at the receiver input
Receiver performance
c) Measuring system reading
d) Signal–to-noise ratio
e) NSA deviation
f) Test-site performance EUT positioning table
g) Influence receive-antenna mast
h) Free-space antenna factor uncertainty
i) Type of receive antenna (directivity)

j) Antenna-factor height dependence
k) Receive-antenna performance Antenna-factor frequency interpolation
l) Antenna phase-centre variation
m) Antenna unbalance
n) Cross-polarisation performance
o) Cable loss uncertainty
Receive antenna cable
a
p)
Mismatch
q) Measurement system repeatability Measurement system repeatability
a
When a single cable is used, there are two sources of mismatch between the antenna and the
receiver:
a) between the antenna and the cable;
b) between the cable and the receiver (=mismatch at receiver input).
If a test lab uses several cables to interconnect the antenna and the receiver, additional mismatches
may be present. In the estimation of MIU, typically only a single mismatch influence quantity is
included.
TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 9 –

8.2.3.1 EUT-related influence quantities

a) Size of EUT
Various influence quantities depend on the type of the EUT, i.e. large EUTs, small EUTs,

EUTs with single or multiple attached cables. The electromagnetic behaviour of these

different EUT types may cause different contributions to uncertainty. Influence quantities

that are affected by the size of the EUT are included as part of the EUT set-up-related

influence quantities in 8.2.3.2. For the EUT-related uncertainty source, no specific

uncertainty value will be assigned to the size of the EUT, to avoid double counting of

uncertainties. Instead, the size of the EUT shall be considered as an influence quantity for
the uncertainties of the set-up-related uncertainty sources discussed in 8.2.3.2.

b) Type of disturbance
The type of the disturbance (broadband, narrowband or intermittent) radiated by the EUT
may affect the magnitudes of the uncertainties induced by the receiver and by the
measurement method applied (e.g. probability of intercept of broadband signals).
c) Product sampling (if applicable)
This influence quantity is especially important if the measurement is repeated by the
manufacturer for quality assurance reasons, or if the 80 %/80 % rule is to be applied. If
the manufacturer performs a type test, the manufacturer may repeat the measurement
using different samples of the same type of EUT. In case of market surveillance that
involves measurements on different samples by another test laboratory, the 80 %/80 %
rule may also be applied.
d) Modes of operation of the EUT
During the measurement, meaningful modes of operation shall be selected such that
representative and worst case radiated emissions are obtained. In cases that the modes of
operation are not specified, different operators and/or test laboratories could select
different modes in conjunction with different receiver settings and scan speeds, which may
induce significant reproducibility uncertainties, and therefore affecting SCU.
8.2.3.2 Set-up-related influence quantities
a) Layout of EUT unit(s) and cable(s)
Despite the specification of the EUT set-up in product standards, this influence quantity
may cause significant uncertainties when different operators and different test laboratories
configure a given EUT. Especially for an EUT that consists of several enclosures and
interconnecting cables, the uncertainty due to the many degrees of freedom allowed for
setting up the EUT may be significant. This influence quantity contributes to the SCU.
Results of the CISPR/A RRT in the frequency range 30 MHz to 300 MHz [f3] revealed that
the uncertainty induced by the set-up for the specific EUT was approximately 7 dB. The
uncertainty associated with the set-up of an EUT depends largely on the type of the EUT.
Table 8-2 provides qualitative guidance for the set-up uncertainty as a function of EUT

type. Above 200 MHz, the effect of different cable layouts is reduced.
Table 8-2 – Relation between and type of EUT and set–up-related uncertainties
Type of EUT Set-up uncertainty
Table-top battery fed Very low
Table-top: single unit, single cable to mains Low
Table-top: multiple units, multiple cables to mains and auxiliary equipment High
Floor-standing equipment, single cable to mains Low
Floor standing equipment, multiple cables to mains and auxiliary equipment High

– 10 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

b) Termination of cable(s)
Different test laboratories may use different cable decoupling devices, such as CDNs,

decoupling transformers, absorbing clamps, LISNs, or some combination thereof, or none.

These different decoupling devices affect the common-mode impedance, as seen from the

EUT, and may produce different disturbance levels. Disturbance levels also depend on the

category of the EUT (mains connection with or without protective earth) and on the type

(dimension) of EUT (see references [f4], [f2] for further details). A summary of the

expanded uncertainty results for the EUTs of [f2] is given in Figure F.1 of Annex F.

Between 30 MHz and 200 MHz, application of different termination devices, such as

common-mode absorbing device (CMADs), CDNs or LISNs, may cause a significant

variation of results, i.e. 10 dB to 20 dB expanded uncertainty below 100 MHz. This
influence quantity may be significant when estimating the SCU, especially below 200 MHz.
c) Measurement distance tolerance
The uncertainty in measurement distance arises from uncertainties due to determination of
the perimeter of the EUT, distance measurement, and antenna mast rigidity. No correction
is made for errors in the measurement distance between the perimeter of the EUT and the
reference point of the receive antenna. Typically a measurement distance tolerance of
± 10 cm can be expected, the effect of which is largest at small measurement distances.
The maximum uncertainty varies as a function of nominal measurement distance and as a
function of EUT height [27]. For table-top EUTs at 3 m measurement distance, the
resulting uncertainty is approximately ± 0,4 dB (rectangular distribution). In practice, this
maximum uncertainty is often estimated from the field variation of a source in free space
at a certain nominal distance. It should be noted that oftentimes for larger measurement
distances, the free-space estimate does not provide a conservative value [27]. See Table
E.3 and Table E.4 in Annex E for uncertainty values as a function of measurement
distance.
d) EUT height above ground plane tolerance
The uncertainty of the standard EUT height above the ground plane, i.e. 0,8 m for table-
top EUTs, is typically ± 1 cm. The resulting effect is a change in the interference
(radiation) pattern at the measurement location. Depending on the step size of the height
scanning of the receive antenna, this influence will induce an uncertainty of the measured
maximum electric field strength, the effect of which is largest at small measurement
distances. This uncertainty has an effect mostly at frequencies where the maximum field
strength is measured at either the lower or upper limits of the antenna scan height
(typically at the lower limit, near 1 m), provided that the height-scan step size is
sufficiently small. The uncertainty varies as a function of measurement distance,
polarisation, and frequency range, and as a function of nominal height of the EUT [27]. It
is shown in [27] that the effect of a 1 cm height tolerance is quite significant (± 0,5 dB) for
a nominal EUT-height of 0,4 m. For a table-top EUT (nominal EUT-height of 0,8 m) and
3 m measurement distance, the height uncertainty of ± 1 cm causes an uncertainty of
approximately ± 0,3 dB (rectangular distribution). See Table E.3 and Table E.4 in Annex E
for uncertainty values as a function of measurement distance.
8.2.3.3 Measurement procedure-related influence quantities
a) Nominal measurement distance
For SAC/OATS-based radiated emission measurements, the nominal measurement
distance is 10 m (see definition of measurand in 8.2.1). If an alternative measurement
distance is applied, for example 3 m, then a conversion of the 3 m results into emission
results expected at the nominal measurement distance of 10 m shall be applied.
NOTE 1 The application of an alternative measurement distance, such as 3 m or 30 m rather than 10 m, is
considered to comprise an alternative measurement method. Conditions for the use of alternative
measurement methods, including uncertainty considerations, are described in CISPR 16-4-5/TR:2005.
In practice, such conversions are often done assuming that the emission from an EUT at a
certain measurement distance may be converted to another distance by applying the free-
space field-strength attenuation formula, i.e. 20 dB/decade or 1/r behaviour.
NOTE 2 In Ed. 5.2 of CISPR 22 the NOTE in 10.3.1 states that an inverse proportionality factor of 20 dB per
decade shall be used to normalize the measured data to the specified distance, for conformity assessment.

TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 11 –

However, the exact conversion very much depends on the type of EUT, the actual

measurement distances involved, and frequency. Different RRT results (see 8.2.6) confirm

that the correlations for a specific EUT do not follow the simplified free-space conversion

rule of 20 dB/decade. As an example, Figure F.5 of Annex F shows the actual and free-

space converted results from 3 m to 10 m distances for a small table-top EUT, based on

results from an RRT [f7], [f8].

The correlation of results obtained from a SAC/OATS 3 m measurement distance to a

10 m measurement distance is done by subtracting 10,5 dB from the results at each

frequency. For the example of Figure F.5, the actual correlation factor varies with

frequency between 5 dB and 9 dB, and the average correlation factor is 7,6 dB. This

correlation factor shall be used as a correction of the results [Equation (8-1)]. Generic
correlation factors applicable to any EUT are generally not available. Use of a single
correction factor value for the entire frequency range causes an uncertainty that becomes
relevant when 3 m and 10 m emission measurement results for the same EUT are
compared. Such a comparison can occur in market surveillance situations, for example.
Consequently the resulting uncertainty contributes to the SCU. Note also that this
influence quantity does not contribute to the MIU, because uncertainty contribution is
present even if measurement instrumentation and site effect uncertainties are negligible.
The results of Figure F.5 show that use of a correlation factor of 10,5 dB yields overly-
compensated results at 10 m. From a compliance determination point of view it may be
more appropriate to apply a smaller correlation factor. The selection of the correlation
factor determines the resulting uncertainty, as far as the difference in results obtained at
different measurement distances is concerned. From the aspect of market surveillance,
the difference in results may have less of an impact because it is more important that the
measurement data is below the applicable limit in both cases. In this case it might be
prudent to apply a conservative correlation factor, e.g. 5 dB.
b) Receiver settings
Some flexibility is provided in the measurement method standards for receiver settings, as
performed either manually or under software control. This may lead to uncertainties that
are dependent on the type of disturbance (broadband/narrowband or intermittent) emitted
by the EUT (see CISPR 16-2-3). Some examples are the sweep time setting, setting of
input attenuation, and reference level setting.
c) Height-scanning step size
The height of the receive antenna is varied between 1 m and 4 m. The operator or the
measurement automation software establishes the step size for the height variation. The
height step size influences the probability of missing the maximum electric field strength at
the measurement position. The associated uncertainty also depends on the type of EUT
(height above ground plane, polarisation of the disturbance) and on the measurement
distance and frequency. The lobe height of the interference pattern is smallest for table-
top EUTs at the highest frequency and at the shortest measurement distance of 3 m.
Under these conditions, the step-size induced uncertainty will become highest. Below
200 MHz, the associated uncertainty is negligible provided that the step size is less than

25 cm. At higher frequencies (> 200 MHz) the uncertainty may be significant [27]. For
example, at a 3 m measurement distance and for a step size of 25 cm, the measured field
may be 1 dB lower than the value measured using a near-continuous scan (height step
size of 0,01 m). A reduced step size of 10 cm will reduce this deviation to 0,2 dB. The
latter figure is what is included in the example uncertainty estimates listed in Annex E
(0 dB to -0,2 dB, rectangular distribution, and a correction factor of +0,1 dB). At 10 m and
30 m measurement distances, the step size may be reduced considerably to maintain the
same step-size induced uncertainty of +0 dB to -0,2 dB. For EUT heights of 0,4 m above
the ground plane, the step-size induced uncertainty is negligible. In general, a continuous
height scan minimizes this error contribution. However, with smaller height step sizes,
measurement time may increase drastically, because sufficient dwell time at each
incremental height is used to accommodate EUT operations.
d) Start and stop position tolerance (height scan)
The uncertainty in height of the start and stop position is typically a few centimetres.
Depending on the receive antenna height step size, measurement distance and frequency,
this will affect the probability of measuring the maximum electric field strength. This
uncertainty is related and similar in nature to the uncertainty-related to EUT height

– 12 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

tolerance. This uncertainty is significant at those frequencies where the maximum field

strength is measured at either the lowest or the highest positions of the antenna height

scan (generally at the lower limit near 1 m). There is an additional uncertainty if the

height-scan step size is too large. The uncertainty is largest at the measurement distance

of 3 m and in the case of predominantly vertical polarisation of the disturbance source

[27]. For a table-top EUT at 3 m measurement distance, and with a receive antenna start-

position tolerance of ± 3 cm, the resulting uncertainty is ± 0,6 dB (rectangular distribution).

For EUTs at a height of 0,4 m, the resulting uncertainty is ± 0,2 dB. See Table E.3 and
Table E.4 in Annex E for uncertainty values as a function of measurement distance.

e) Azimuth step size
The azimuth radiation pattern of an EUT radiating in free space becomes more directive at

higher frequencies. However, the ground reflection tends to make the overall azimuth
pattern omni-directional again, whereas grating lobes appear in the elevation pattern. The
EUT must be rotated in azimuth in order to capture the maximum emission, and thus the
azimuth step size and the azimuth start position determine the probability of intercept of
the maximum electric field strength within a certain tolerance. The associated uncertainty
does not depend on measurement distance. A continuous rotation will minimize this effect.
8.2.3.4 Environment-related influence quantities
a) Temperature and humidity tolerances
These environmental influence quantities are considered to have a negligible impact on
the result of the measurement for measurements done in a SAC. If an OATS is used, then
depending on the dimensions and shape of the conducting ground plane, the influence of
water on the ground plane, the ground properties beyond the ground plane, and wet or dry
nearby vegetation may have an impact on site performance. So this influence quantity
should be taken into account in the test site performance [see 8.2.3.5 0]. In addition,
sensitivity of the measuring equipment (antenna, receiver) to environmental parameters is
generally negligible.
The insertion loss of the cable between antenna and receiver varies with temperature.
This may cause repeatability problems for OATS measurements. The cable loss should be
measured at a temperature close to the temperature at which the emission measurements
will be made. The use of white-sheathed cable can reduce short-term variations caused by
intervals of direct sunlight and cloud cover.
Similarly, for measurements done at an OATS, direct exposure to sunlight may cause
temperature variations within the EUT and consequently variation of the level of radiated
emission. This influence quantity will contribute to the SCU. The use of an
electromagnetically-transparent shelter (radome) may reduce the impact on the EUT from
sunlight irradiation and humidity.
b) Signal-to-ambient-signal ratio
When using an OATS, the ambient levels of radiated emissions from radio transmitters
may negatively impact the measurement of radiated emissions at specific frequencies, or

even render emissions measurements impossible. The associated uncertainty of the
measured disturbances that coincide with the ambient radio frequencies may therefore be
significant. In general these ambient signals are not coherent with the measured
disturbance, and therefore can be treated as a noise signal. The resulting errors depend
on the ratio of the disturbance signal and the ambient signal, and the level of the internal
receiver noise [23], [24]. For measurements done in a SAC, the uncertainty due the
ambient radiated signals is negligible.
c) Mains voltage variations
The EUT shall be operated using a supply that has the rated voltage of the EUT (see 6.3.4
of CISPR 16-2-3). If the level of disturbance varies considerably with the supply voltage,
the measurements shall be repeated for supply voltages over the range of 0,9 to 1,1 times
the rated voltage. EUTs with more than one rated voltage shall be tested at the rated
voltage that causes the maximum disturbance. Deviations of the mains voltage deviations
from the nominal may introduce uncertainties if the level of disturbance power depends on
the mains voltage level. The magnitude of this variation will be highly dependent on the
type of EUT, and therefore should be evaluated for each EUT. Consequently, this

TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 13 –

influence quantity will contribute to SCU. However, no specific uncertainty figure can be

estimated for this influence quantity.

d) Application of mains decoupling devices

The different mains filters and mains decoupling devices, such as CDNs, decoupling

transformers, variacs, LISNs or combinations thereof, used in various laboratories may
give rise to different disturbance levels, also depending on the category of EUTs (mains

connection with or without protective earth). See also 8.2.3.2 b) about mains connections.

8.2.3.5 Measurement instrumentation-related influence quantities

a) Receiver accuracy
The accuracy can be obtained from the specifications sheet or the calibration certificate of
the receiver. If calibration data is not available, or if only verification was performed, i.e.
verification that the parameters are within specifications, then the specification values
should be used and treated as rectangular-distributed values to calculate the uncertainty.
If calibration data is available (i.e. a specific value for each parameter and an associated
uncertainty, probability distribution, and confidence level), then this information can be
used to calculate the uncertainty contribution. If necessary, the uncertainty for different
types of signals/responses may be considered, i.e. CW accuracy, pulse-amplitude
response accuracy, and pulse-repetition response accuracy. See also Annex A of
CISPR 16-4-2 for detailed considerations about the accuracy of the receiver.
b) Mismatch at the receiver input
Mismatch uncertainties will occur due to the mismatch of the measuring cable connected
to the receiver. This mismatch uncertainty depends on the receiver input impedance, the
input attenuation setting of the receiver, the antenna impedance, and the impedance and
attenuation properties of the measuring cable, which are functions of frequency. See also
Annex A of CISPR 16-4-2 and [f4]. The return loss of biconical and hybrid antennas
generally gets worse at low frequencies, such that an attenuator typically is used between
the antenna and the cable to reduce VSWR to less than 2,0 to 1 [CISPR 16-1-4, 4.5.2 c)].
The VSWR of the receiver input has a maximum value of 2,0 to 1 (for zero dB input
attenuation – which should be avoided, however), and VSWR of biconical and log-periodic
dipole array (LPDA) antennas are 4,6 to 1 (maximum 10 to 1 or more) and 2,0 to 1,
respectively. The mismatch uncertainty has a U-shaped distribution [25]. Typical values
for mismatch uncertainties are +0,9/-1,0 dB below 200 MHz, and ± 0,3 dB between
200 MHz and 1 000 MHz (data taken from [f4], [22]).
c) Measuring system reading
Receiver reading uncertainties depend on receiver noise, display fidelity, and meter scale
interpolation errors. The latter should be a relatively insignificant contribution to the
uncertainty for measuring systems with electronic displays (least-significant digit
fluctuation). However, for analogue meter displays, this latter uncertainty contribution shall
be considered.
d) Signal-to-noise ratio
For radiated emission measurements, the receiver noise floor will influence measurement
results, especially at the larger measurement distances of 10 m and 30 m. In general, the
impact of the noise also depends on the type of noise. Boltzmann (random) noise has far
less effect on a signal than does a coherent noise signal. The internal receiver noise is
random noise, and the resulting error when measuring a disturbance will depend on the
disturbance-to-noise-level ratio [23], [24]. For example, a random noise level of 10 dB
below a CW signal causes an error of +0,7 dB on the CW signal, but an unwanted random
noise level of 3 dB down causes an error of +1,4 dB. In general, a larger measurement
distance will reduce the disturbance-level-to-internal-noise ratio [23]. Also, the use of pre-
amplifiers near the antenna will influence the noise floor level. Therefore, it is difficult to
give uncertainty estimates as a function of measurement distance due to the internal noise
floor level of the receiver. Table E.3 and Table E.4 in Annex E give some typical
uncertainty estimates as a function of measurement distance. The proximity of the actual
internal noise floor to the applicable emission limit can be used to estimate the resulting
error.
– 14 – TR CISPR 16-4-1 Amend. 2 © IEC:2007(E)

e) NSA deviation
The imperfections of a SAC or OATS test site, for example caused by non-ideal absorbing

walls or a finite and irregular ground plane, directly affect the result of a radiated emission

measurement. The test site imperfections depend on the type of EUT (large, small) and on

frequency. The test site performance is quantified by the normalized site attenuation

(NSA), wherein the EUT is represented by a transmit antenna of similar type as the

receive antenna, and the NSA is evaluated for several positions of the transmit antenna in

the test volume. The test site pass/fail criterion for the NSA-deviation is ± 4,0 dB. Note

that an NSA measurement includes uncertainty components such as linearity of the

receiver, stability of the generator, and uncertainties of the two antenna factors. See also

5.6.3 and Annex F of CISPR 16-1-4. For purposes of this subclause, the intrinsic NSA

performance should be used, i.e. the uncertainty of the NSA measurement is subtracted
from the NSA results. An example of the uncertainty estimate associated with the NSA-
measurement method, including uncertainty contributions from instrumentation, is given in
Table 8-3. The resulting expanded uncertainty is ± 2,0 dB. Table 8-4 shows how this
uncertainty affects a NSA measurement of a site with an intrinsic (actual) site deviation
performance of ± 3,0 dB (rectangular distribution).

Table 8-3 – Example of uncertainty estimate associated with the NSA measurement
method, 30 MHz to 1 000 MHz
UNCERTAINTY SOURCES Uncertainty
Probability Standard
Divisor
distribution uncertainty
Influence quantities value (+/-dB)
ANTENNA-RELATED
Transmit antenna factor uncertainty 1,0 Rectangular 1,73 0,58
Receive antenna factor uncertainty 1,0 Rectangular 1,73 0,58
SETUP-RELATED
Tolerance measurement distance 0,1 Rectangular 1,73 0,06
Tolerance transmit antenna height 0,1 Rectangular 1,73 0,06
Tolerance start & stop position
receive antenna
0,1 rectangular 1,73 0,06
TEST PROCEDURE-RELATED
Repeatability 0,5 Rectangular 1,73 0,29
MEASUREMENT
INSTRUMENTATION-RELATED
Stability generator 0,1 Normal 2,00 0,05
Linearity receiver/analyser 0,5 Rectangular 1,73 0,29

Mismatch at the input 0,4 U-shaped 1,41 0,28
Mismatch at the output 0,4 U-shaped 1,41 0,28
Measuring system reading 0,1 Rectangular 1,73 0,06
Signal to noise ratio 0,1 Rectangular 1,73 0,06
Combined standard uncertainty   1,01
Expanded uncertainty Normal 2,00 2,01

TR CISPR 16-4-1 Amend. 2 © IEC:2007(E) – 15 –

Table 8-4 – Relationship between intrinsic and apparent NSA

Standard
Value Probability
Divisor
(+/-dB) distribution
uncertainty
Uncertainty NSA measurement 2,0 Normal 2,00 1,00

Test site deviation (=intrinsic NSA spec) 3,0 Rectangular 1,73 1,73

Combined standard uncertainty    2,00

Expanded uncertainty (= apparent NSA
spec)  Normal 2,00 4,00
The calculation of the overall or apparent NSA (NSA including measurement uncertainty)
obeys the rules of the uncertainty calculations, because the NSA is also a statistical
quantity that varies independently from the NSA uncertainty. In conclusion, a site that
complies with the NSA specification ± 4,0 dB has an intrinsic test site deviation of ± 3,0 dB
(rectangular distribution). See also 8.2.3.4a) for the impact of weather on OATS
performance. If the measured NSA is less than the ± 4dB specification level, then the
actual measured (intrinsic) values can be used in the uncertainty estimates thereby to
reduce the overall MIU.
f) EUT positioning table
Support tables for EUTs are constructed of wood or other types of non-conducting
materials. The dielectric properties of these materials or absorbed moisture may affect the
emission results, especially above 200 MHz (see 5.9 of CISPR 16-1-4) for table-top
equipment. An estimate of the deviation can be obtained using the meas
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