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Making Conducted and Radiated
Emissions Measurements
Application Note
Table of Contents
1.0 Introduction to Radiated and Conducted Emissions Measurements ........... 3
1.1 Precompliance versus full compliance EMI measurements ...............................4
1.2 Systems for performing precompliance measurements ......................................4
2.0 Precompliance Measurements Process........................................................... 5
2.1 European norms descriptions ...................................................................................6
2.1.1 EN55011 (CISPR 11) ISM ..................................................................................6
2.1.2 EN55014 (CISPR 14)...........................................................................................6
2.1.3 EN55022 (CISPR 22)...........................................................................................6
2.2 Federal Communications Commission ....................................................................6
2.2.1 FCC requirements summary .............................................................................6
3.0 Emissions Testing ................................................................................................ 7
3.1 Introduction ..................................................................................................................7
3.2 Conducted emissions testing....................................................................................7
3.3 Radiated emissions measurements preparation ................................................ 10
3.4 Setting up the equipment for radiated emissions measurements ................. 10
3.5 Performing radiated emissions measurements .................................................. 11
4.0 Problem Solving and Troubleshooting ............................................................ 13
4.1 Diagnostics testing setup ....................................................................................... 13
4.2 Problem isolation ..................................................................................................... 14
Appendix: A Line Impedance Stabilization Networks (LISN)................................15
A1.0 Purpose of a LISN ................................................................................................. 15
A1.1 LISN operation ................................................................................................ 15
A1.2 Types of LISNs .................................................................................................. 16
A2.0 Transient limiter operation................................................................................... 16
Appendix B: Antenna Factors ................................................................................ 17
B1.0 Field strength units ............................................................................................... 17
B1.1 Antenna factors .............................................................................................. 17
B1.2 Types of antennas used for commercial radiated measurements ........ 17
Appendix C: Basic Electrical Relationships ......................................................... 18
Appendix D: Detectors Used in EMI Measurements .......................................... 18
D1.0 Peak detector ......................................................................................................... 18
D1.1 Peak detector operation ................................................................................. 18
D2.0 Quasi-peak detector .............................................................................................. 19
D2.1 Quasi-peak detector operation ...................................................................... 19
D3.0 Average detector ................................................................................................... 19
D3.1 Average detector operation ........................................................................... 19
Appendix E: EMC Regulatory Agencies ................................................................ 20
Glossary of Acronyms and Definitions ................................................................. 22
2
1.0 Introduction to Radiated and Conducted Emissions Measurements
The concept of getting a product to The frequency range for these com- experience an electromagnetic com-
market on time and within budget is mercial measurements is from 9 kHz patibility problem, such as when an
nothing new. Recently, companies to 30 MHz, depending on the regula- electric drill interferes with TV recep-
have realized that electromagnetic tion. Radiated emissions testing looks tion, there must be a source or gen-
interference (EMI) compliance testing for signals broadcast for the EUT erator, coupling path and receptor. An
can be a bottleneck in the product through space. The frequency range EMC problem can be eliminated by
development process. To ensure suc- for these measurements is between removing one of these components.
cessful EMI compliance testing, pre- 30 MHz and 1 GHz, and based on the
compliance testing has been added regulation, can go up to 6 GHz and With the advent of the European
to the development cycle. In precom- higher. These higher test frequencies requirements, there is an additional
pliance testing, the electromagnetic are based on the highest internal focus on product immunity. The level
compatibility EMC performance is clock frequency of the EUT. This of electric field that a receptor can
evaluated from design through pro- preliminary testing is called precompli- withstand before failure is known as
duction units. Figure 1 illustrates a ance testing. product immunity. The terms immu-
typical product development cycle. nity and susceptibility are used inter-
Figure 2 illustrates the relationship changeably. This document will not
Many manufacturers use (EMI) between radiated emissions, radi- cover immunity testing.
measurement systems to perform ated immunity, conducted emissions
conducted and radiated EMI emis- and conducted immunity. Radiated
sions evaluation prior to sending their immunity is the ability of a device or
product to a test facility for full com- product to withstand radiated electro-
pliance testing. Conducted emissions magnetic fields. Conducted immunity
testing focuses on unwanted signals is the ability of a device or product
that are on the AC mains generated to withstand electrical disturbances
by the equipment under test (EUT). on AC mains or data lines. In order to
Product development cycle
Initial Design Lab Production Production
investigation breadboard prototype prototype unit
Yes Yes
viable pass pass pass pass
No No No No No
R E D E S I G N Production
Figure 1. A typical product development cycle
Emission Immunity = Susceptibility
Conducted
Radiated
Figure 2. Electromagnetic compatibility between products
3
1.1 Precompliance versus full Precompliance measurements are 1.2 Systems for performing
compliance EMI measurements intended to give an approximation precompliance measurements
Full compliance measurements of the EMI performance of the EUT. The components used in systems for
require the use of a receiver that The cost of performing precompli- precompliance measurements are as
meets the requirements set forth ance tests is a fraction of the cost follows: signal analyzer with N6141A
in CISPR16-1-1, a qualified open of full compliance testing using an EMI measurement application, line
area test site or semi anechoic expensive facility. impedance stabilization network
chamber and an antenna tower and (LISN), transient limiter and anten-
turntable to maximize EUT signals. The more attention to detail in the nas. To isolate problems after they
Great effort is taken to get the best measurement area, such as good have been identified, the close field
accuracy and repeatability. These ground plane and a minimal number probes (11945A) are used.
facilities can be quite expensive. In reflective objects, the better the
some specific cases, the full com- accuracy of the measurement. The environment for precompliance
pliance receiver can be replaced by testing is usually less controlled
a signal analyzer with the correct than full compliance testing
bandwidths and detectors as long environments. See Figure 3 for the
as the signal analyzer has the sen- components used for precompli-
sitivity required. ance testing.
EMI precompliance measurement system
Log periodic
antenna
X-Series analyzer with N6141A
EMC measurement application
HP 11940A
Biconical
HP 11941A
antenna
MONITOR
Close-field probe set
POWER OUTPUT
CAUTION
HIGH VOLTAGE
GND
Diagnostics
LISN Agile
nt 11
947A
Transient Tripod
limiter
Figure 3. Components of a preproduction evaluation system
4
2.0 Precompliance Measurements Process
The precompliance measurement With the answers to these questions,
process is fairly straightforward. you can determine which standard
However, before making measure- your product must be tested against.
ments on your product, some prelim- For example, if you determined that
inary questions must be answered. your product is an information tech-
nology equipment (ITE) device, and
1. Where will the product be sold
you are going to sell it in the U.S.,
(for example, Europe, United
then you need to test your product to
States, Japan)?
the FCC 15 standard. Table 1 below
2. What is the classification of the prod- will help you choose the requirement
uct? for your product.
a. Information technology
equipment (ITE)
b. Industrial, scientific or
medical equipment (ISM)
c. Automotive or communication
d. Generic (equipment not found
in other standards)
3. Where will the product be used
(for example home, commercial,
light industry or heavy industry)?
Emissions regulations (summary)
FCC CISPR EN's Description
18 11 EN 55011 Industrial, scientific and medical equipment