Making Conducted and Radiated Emissions Measurements

Making Conducted and Radiated Emissions Measurements
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 frequency range for these commercial measurements is from 9 kHz
to 30 MHz, depending on the regulation. Radiated emissions testing looks
for signals broadcast for the EUT
through space. The frequency range
for these measurements is between
30 MHz and 1 GHz, and based on the
regulation, can go up to 6 GHz and
higher. These higher test frequencies
are based on the highest internal
clock frequency of the EUT. This
preliminary testing is called precompliance testing.
The concept of getting a product to
market on time and within budget is
nothing new. Recently, companies
have realized that electromagnetic
interference (EMI) compliance testing
can be a bottleneck in the product
development process. To ensure successful EMI compliance testing, precompliance testing has been added
to the development cycle. In precompliance testing, the electromagnetic
compatibility EMC performance is
evaluated from design through production units. Figure 1 illustrates a
typical product development cycle.
Figure 2 illustrates the relationship
between radiated emissions, radiated immunity, conducted emissions
and conducted immunity. Radiated
immunity is the ability of a device or
product to withstand radiated electromagnetic fields. Conducted immunity
is the ability of a device or product
to withstand electrical disturbances
on AC mains or data lines. In order to
Many manufacturers use (EMI)
measurement systems to perform
conducted and radiated EMI emissions evaluation prior to sending their
product to a test facility for full compliance testing. Conducted emissions
testing focuses on unwanted signals
that are on the AC mains generated
by the equipment under test (EUT).
Product development cycle
Initial
investigation
viable
Yes
Design
breadboard
Lab
prototype
pass
pass
No
No
R
E
Production
prototype
E
pass
pass
No
No
D
Production
unit
S
I
G
Yes
No
Production
N
Figure 1. A typical product development cycle
Emission
Immunity = Susceptibility
Conducted
Radiated
Figure 2. Electromagnetic compatibility between products
3
experience an electromagnetic compatibility problem, such as when an
electric drill interferes with TV reception, there must be a source or generator, coupling path and receptor. An
EMC problem can be eliminated by
removing one of these components.
With the advent of the European
requirements, there is an additional
focus on product immunity. The level
of electric field that a receptor can
withstand before failure is known as
product immunity. The terms immunity and susceptibility are used interchangeably. This document will not
cover immunity testing.
1.1 Precompliance versus full
compliance EMI measurements
Full compliance measurements
require the use of a receiver that
meets the requirements set forth
in CISPR16-1-1, a qualified open
area test site or semi anechoic
chamber and an antenna tower and
turntable to maximize EUT signals.
Great effort is taken to get the best
accuracy and repeatability. These
facilities can be quite expensive. In
some specific cases, the full compliance receiver can be replaced by
a signal analyzer with the correct
bandwidths and detectors as long
as the signal analyzer has the sensitivity required.
Precompliance measurements are
intended to give an approximation
of the EMI performance of the EUT.
The cost of performing precompliance tests is a fraction of the cost
of full compliance testing using an
expensive facility.
The more attention to detail in the
measurement area, such as good
ground plane and a minimal number
reflective objects, the better the
accuracy of the measurement.
EMI precompliance measurement system
Log periodic
antenna
X-Series analyzer with N6141A
EMC measurement application
HP 11940A
Biconical
antenna
HP 11941A
MONITOR
Close-field probe set
Diagnostics
POWER OUTPUT
CAUTION
HIGH VOLTAGE
GND
LISN
Agile
nt 11
947A
Tripod
Transient
limiter
Figure 3. Components of a preproduction evaluation system
4
1.2 Systems for performing
precompliance measurements
The components used in systems for
precompliance measurements are as
follows: signal analyzer with N6141A
EMI measurement application, line
impedance stabilization network
(LISN), transient limiter and antennas. To isolate problems after they
have been identified, the close field
probes (11945A) are used.
The environment for precompliance
testing is usually less controlled
than full compliance testing
environments. See Figure 3 for the
components used for precompliance testing.
2.0 Precompliance Measurements Process
The precompliance measurement
process is fairly straightforward.
However, before making measurements on your product, some preliminary questions must be answered.
1. Where will the product be sold
(for example, Europe, United
States, Japan)?
2. What is the classification of the 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)
With the answers to these questions,
you can determine which standard
your product must be tested against.
For example, if you determined that
your product is an information technology equipment (ITE) device, and
you are going to sell it in the U.S.,
then you need to test your product to
the FCC 15 standard. Table 1 below
will help you choose the requirement
for your product.
3. Where will the product be used
(for example home, commercial,
light industry or heavy industry)?
Emissions regulations (summary)
EN's
FCC
CISPR
18
11
EN 55011
––
12
––
15
13
EN 55013
15
Description
Industrial, scientific and medical equipment
Automotive
Broadcast receivers
14
EN 55014
Household appliances/tools
15
EN 55015
Fluorescent lights/luminaries
22
EN 55022
Information technology equipment
––
EN61000-6-3,4
Generic emissions standards
16
––
16
EN 55025
Measurement apparatus/methods
Automotive component test
Table 1. Comparison of regulatory agency requirements
5
2.1 European norms
descriptions
2.1.1 EN55011 (CISPR 11) ISM
Class A: Products used in establishments other than domestic areas.
Class B: Products suitable for use in
domestic establishments.
Group 1: Laboratory, medical and
scientific equipment. (For example:
signal generators, measuring
receivers, frequency counters,
spectrum analyzers, switching mode
power supplies, weighing machines
and electron microscopes.)
2.1.3 EN55022 (CISPR 22)
Equipment with the primary function
of data entry, storage, displaying,
retrieval, transmission, processing,
switching or controlling is considered
ITE. For example, data processing
equipment, office machines, electronic equipment, business equipment
or telecommunications equipment
would be considered ITE.
There are two classes of ITE, Class
A which is not intended for domestic
use and Class B which is intended for
domestic use.
Group 2: Industrial induction heating
equipment, dielectric heating equipment, industrial microwave heating
equipment, domestic microwave
ovens, medical apparatus, spark erosion equipment and spot welders. (For
example: metal melting, billet heating,
component heating, soldering and
brazing, wood gluing, plastic welding,
food processing, food thawing, paper
drying and microwave therapy equipment.)
2.1.2 EN55014 (CISPR 14)
This standard applies to electric
motor-operated and thermal appliances for household and similar
purposes, electric tools and electric
apparatus. Limit line use depends
upon the power rating of the item.
EN55014 distinguishes between
household appliances, motors less
than 700W, less than 1000W and
greater than 1000W. Limits for
conducted emissions are 150 kHz to
30 MHz, and limits for radiated emissions are 30 MHz to 300 MHz.
2.2 Federal Communications
Commission
The FCC has divided products to be
tested in two parts, Part 15 and Part
18. Part 15 is further divided into
intentional radiators and unintentional
radiators.
Unintentional radiators include TV
broadcast receivers, FM receivers,
cable system terminal devices, personal computers and peripherals and
external switching power supplies.
Unintentional radiators are then again
divided into Class A devices that are
used in industrial, commercial or
business environments and Class B
devices that are marketed for use in a
residential environment.
Part 18 devices are ISM.
2.2.1 FCC requirements summary
The frequency range of conducted
emissions measurements is 450 kHz
to 30 MHz and the frequency range
of radiated emissions measurements
is 30 MHz to 1 GHz and up to 40 GHz,
based on the device clock frequency.
FCC requirements (summary)
Equipment type
Broadcast receivers
Household appliances
Fluorescent lights/luminaries
Information technology equipment
Equipment classification
Class A Industrial
Class B Residential
Industrial, scientific and medical equipment
Table 2. FCC requirements summary
6
FCC part
Part 15
Part 15
Part 15
Part 15
Part 15
Part 15
Part 18
3.0 Emissions Testing
3.1 Introduction
After the appropriate regulations
have been identified, the next step
is to set up the test equipment and
perform radiated and conducted
emissions tests. The first group of
tests is conducted emissions. The
typical process is to interconnect the
appropriate equipment, load the limit
line or lines, add the correction factors for the LISN and transient limit.
Conducted emissions measurements
are easier than ever!
X-Series analyzer with N6141A
EMC measurement application
Agilent 11967D LISN
3.2 Conducted emissions testing
1. Interconnect the signal analyzer
to the limiter, LISN and EUT as
shown in Figure 4. Operation of
the LISN and limiter is covered
in Appendix A. Ensure that the
power cord between the device
under test (DUT) and the LISN is
as short as possible. The power
cord can become an antenna
if allowed to be longer than
necessary. Measure the signals on
the power line with the DUT off.
If you see the signal approaching
the established limit lines, then
some additional shielding may be
required. Do not use ferrites on
the power cord because common
mode signals from the DUT may be
suppressed causing a lower value
measurement.
2. Next, be sure you are measuring
within the appropriate frequency
range for conducted emissions
measurements, 150 kHz to 30 MHz.
Agilent’s EMI measurement
application uses a scan table
to make it easy to select the
appropriate frequency range as
shown in Figure 5. Deselect any
other ranges that are selected.
11947A
Limiter
Figure 4. Conducted measurements interconnection
Figure 5. Scan table
7
Device
under test
3. Load limit lines and correction
factors. In this case, the two
limit lines used for conducted
emissions are EN55022 Class A
quasi-peak and EN55022 Class A
EMI average. To compensate for
measurement errors, add a margin
to both limit lines.
4. Correct for the LISN and the
transient limiter which is used to
protect the input mixer. The correction factors for the LISN and
transient limiter are usually stored
in the signal analyzer and they can
be easily recalled. View the ambient emissions (with the DUT off).
If emissions above the limit are
noted, the power cord between
the LISN and the DUT may be
acting as an antenna. Shorten
the power cord to reduce the
response to ambient signals. See
Figure 7.
5. Switch on the DUT to find signals above the limit lines. This
is a good time to check to make
sure that the input of the signal
analyzer is not overloaded. To do
this, step the input attenuator up
in value, if the display levels do
not change, then there is no overload condition. If the display does
change, then additional attenuation
is required. The margin is also
set so signals above the margin
will also be listed. To identify the
signals above the margin of either
limit line, select scan and search
to get the peak amplitude and
frequency. The amplitude and frequency of the signals is displayed.
In this case, 14 signals were captured.
Figure 6. Conducted emissions display with limit lines and margin
Figure 7. Conducted ambient emissions
8
6. Finally, the Quasi-peak and average of the signals need to be
measured and compared to their
respective limits. There are three
detectors: Detector 1 will be set
to peak, Detector 2 to Quasi-peak
and Detector 3 to EMI average.
7. Review the measurement results.
The QPD delta to Limit Line 1 and
EAVE delta to Limit Line 2 should
all have negative values. If some
of the measurements are positive,
then there is a problem with conducted emissions from the DUT.
Check to be sure there is proper
grounding if there are conducted
emissions problems. Long ground
leads can look inductive at higher
conducted frequencies generated
by switcher power supplies. If
power line filtering is used, make
sure that it is well grounded.
Figure 8. Scan and search for signals above the limit
Here are some additional hints when
making conducted measurements. If
the signals you are looking at are in
the lower frequency range of the conducted band (2 MHz or lower), you
can reduce the stop frequency to get
a closer look. You may also note that
there are fewer data points to view.
You can add more data points by
changing the scan table. The default
in the scan table is two data points
per BW or 4.5 kHz per point. To get
more data points, change the points
per bandwidth to 2.25 or 1.125 to give
four or eight points per BW.
Figure 9. Quasi-peak and average delta to limit
9
3.3 Radiated emissions
measurements preparation
Performing radiated emissions measurements is not as straightforward
as performing conducted emissions
measurements. There is the added
complexity of the ambient environment which could interfere with
measuring the emissions from a DUT.
There are some methods that can be
used to discriminate between ambient environment and signals from the
DUT. In more populated metropolitan
areas, ambient environments could
be extremely dense, overpowering
emissions from a DUT. Testing in a
semi-anechoic chamber can simplify and accelerate measurements
because the ambient signals are no
longer present. Chambers are an
expensive alternative to open area
testing. Following are some methods
for determining if a signal is ambient:
1. The simplest method is to turn
off the DUT to see if the signal
remains. However, some DUTs are
not easily powered down and up.
2. Use the tune and listen feature of
the signal analyzer to determine if
the signal is a local radio station.
This method is useful for AM, FM
or phase modulated signals.
3. If your device is placed on a
turntable, rotate the device while
observing a signal in question. If
the signal amplitude remains constant during device rotation, then
the signal is more likely to be an
ambient signal. Signals from a DUT
usually vary in amplitude based on
its position.
4. A more sophisticated method of
ambient discrimination is the two
antenna method. Place one antenna at the prescribed distance as
called out by the regulatory body,
and a second antenna at twice
the distance of the first antenna.
Connect the two antennas to a
switch, which is then connected to
the signal analyzer. If the signal is
the same amplitude at both antennas, then the signal is likely to be
an ambient signal. If the signal at
the second antenna is 6 dB lower,
then the signal originates from the
DUT.
Precompliance Radiated Measurements
X-Series analyzer with N6141A
EMC measurement application
Biconical
Antenna
Tripod
Figure 10. Radiated emissions test setup
10
Device
under test
3.4 Setting up the equipment
for radiated emissions
measurements
1. Arrange the antenna, DUT and
signal analyzer as shown in Figure
10. Separate the antenna and the
EUT as specified by the regulator
agency requirements. If space is
limited, then the antenna can be
moved closer to the DUT and you
can edit the limits to reflect the
new position. For example, if the
antenna is moved from 10 meters
to 3 meters, then the amplitude
must be adjusted by 10.45 dB. It
is important that the antenna is
not placed in the near field of the
radiating device which is λ/2π or
15.9 MHz for 3 meters. Most commercial radiated emissions start at
30 MHz.
2. Set up the signal analyzer for the
correct span, bandwidths and limit
lines with margin included. After
the signal analyzer has been powered up and completed its calibration, use the scan table to select
Range 3, and deselect all others.
This gives a frequency range of
30 MHz to 300 MHz, bandwidth
of 120 kHz and two data points
per bandwidth. Load limit lines for
EN55022 Class A. To get the best
sensitivity, switch on the signal
analyzer’s preamplifier and set the
attenuator to 0 dB.
3.5 Performing radiated
emissions measurements
The goal of radiated emissions testing is to identify and measure signals
emitting from the DUT. If the signals
measured using the correct detector are below the margin set at the
beginning of the measurement, then
the DUT passes. These measurements must be repeated for each face
of the DUT. The orientation change
of the DUT is achieved using a turntable. The test sequence follows:
1. With the DUT off, perform a scan
and search of the signals over the
band of interest, and store the list
of frequency amplitude pairs to a
file you may want to mark ambient.
2. With the DUT on and oriented at
the 0 degree position, perform a
scan and search.
Figure 11. Ambient radiated emissions signals
3. A second group of signals will be
added to the existing ambient signals in the list.
4. Search for duplicates using the
“mark all duplicates.”
5. Delete the marked signal, which
now leaves only the DUT signals
(and those that were not present
during the ambient scan).
Figure 12. Duplicate ambient signals marked
11
6. Perform measurements using the
QP detector and compare to delta
limit.
7. If the signals are below the limit,
then the DUT passes. If not, then
some work needs to be done to
improve emissions.
Store the signals shown in Figure 14
for future reference when troubleshooting problems.
Repeat the process, Step 1-7, for
another position of the turntable,
such as 90 degrees. If you have
stored the ambient signal in the previous measurement, then you recall the
list and process with Step 2, which is
where the DUT is switched on.
After you have observed the DUT on
all four sides you will have a list of
signals for each side. If you note a
signal that is the same amplitude for
all four sides of the DUT, it could be
an ambient signal that was missed
during the ambient scan.
Figure 13. Duplicate signals deleted
Figure 14. DUT signals with quasi-peak measurement compared to limit
12
4.0 Problem Solving and Troubleshooting
After the product is tested and the
results are recorded and saved, your
product is either ready for full compliance testing and production, or it
must go back to the bench for further
diagnosis and repair.
If your product needs further redesign, the following process is recommended:
1. Connect the diagnostics tools as
shown in Figure 15.
2. From your previous radiated tests,
identify the problem frequencies.
3. Use the probe to locate the source
or sources of the problem signals.
4. With the probe placed to give the
maximum signal on the analyzer,
save the trace to internal memory.
4.1 Diagnostics testing setup
It is recommended that the spectrum
analyzer mode be used for diagnosis.
Correction factors for the probe
should be loaded from the internal
memory. The Agilent 11945A probe
kit contains two probes, one for 9 kHz
to 30 MHz and another for 30 MHz
to 1 GHz frequency range. Place the
signal analyzer into the spectrum
analyzer mode. Connect the probe
for the appropriate frequency range
and recall the correction factors from
internal memory.
Diagnostic measurement set-up: emissions
X-Series analyzer with N6141A
EMC measurement application
5. Make circuit changes as necessary to reduce the emissions.
6. Measure the circuit again using
the same setting as before, and
save the results in another trace.
7. Recall the previously saved trace
and compare the results to the
current measurement.
Device under test
HP 11940A
Close-field probe
Circuit under test
Figure 15. Diagnostics setup interconnection
13
4.2 Problem isolation
Using information stored earlier from
the conducted and radiated tests,
tune the signal analyzer to one of the
problem frequencies with a narrow
enough span to give adequate differentiation between signals. Move
the close field probe slowly over the
DUT. Observe the display for maximum emissions as you isolate the
source of the emissions. After you
have isolated the source of the emissions, record the location and store
the display to an internal register.
See Figure 16.
The next step is to make design
changes to reduce emissions. This
can be accomplished by adding
or changing circuit components,
redesigning the problem circuit or
adding shielding. After the redesign,
compare the results again to the
previously recorded trace.
Figure 16. Preliminary diagnostics trace
With your probe on the trouble spot,
compare the emissions before and
after repairing the problem. As you
can see from the difference between
the two traces in Figure 17, there has
been about a 10 dB improvement in
the emissions. There is a one-to-one
correlation between changes in
close field probe measurements and
changes in far field measurements.
For example, if you note a 10 dB
change in measurements made by a
close field probe, you will also note a
10 dB change when you perform a far
field measurement using an antenna
and a signal analyzer.
Figure 17. Diagnostics traces before and after redesign
14
Appendix A: Line Impedance Stabilization Networks (LISN)
A1.0 Purpose of a LISN
A line impedance stabilization network serves three purposes:
1. The LISN isolates the power
mains from the equipment under
test. The power supplied to the
EUT must be as clean as possible. Any noise on the line will
be coupled to the X-Series signal
analyzer and interpreted as noise
generated by the EUT.
2. The LISN isolates any noise
generated by the EUT from being
coupled to the power mains.
Excess noise on the power mains
can cause interference with the
proper operation of other devices
on the line.
A1.1 LISN operation
The diagram in Figure A-1 below
shows the circuit for one side of the
line relative to earth ground.
Line Impedance Stabilization Network (LISN)
50 μH
From power source
1 μF
To Receiver or EMC analyzer (50 Ω)
Impedance (ohms) 60
50
40
30
20
10
.01
.1
1
Figure A-1. Typical LISN circuit diagram
3. The signals generated by the
EUT are coupled to the X-Series
analyzer using a high-pass filter, which is part of the LISN.
Signals that are in the pass band
of the high-pass filter see a 50-Ω
load, which is the input to the
X-Series signal analyzer.
To EUT
0.1 μF
1000 Ω
The 1 µF in combination with the 50
µH inductor is the filter that isolates
the mains from the EUT. The 50 µH
inductor isolates the noise generated
by the EUT from the mains. The
0.1 µF couples the noise generated
by the EUT to the X-Series signal
analyzer or receiver. At frequencies
above 150 kHz, the EUT signals are
presented with a 50-Ω impedance.
The chart in Figure A-1 represents
the impedance of the EUT port versus frequency.
15
10
100 Frequency (MHz)
A1.2 Types of LISNs
The most common type of LISN is
the V-LISN. It measures the unsymmetric voltage between line and
ground. This is done for both the hot
and the neutral lines or for a threephase circuit in a “Y” configuration,
between each line and ground. There
are other specialized types of LISNs.
A delta LISN measures the line-toline or symmetric emissions voltage.
The T-LISN, sometimes used for telecommunications equipment, measures the asymmetric voltage, which
is the potential difference between
the midpoint potential between two
lines and ground.
A2.0 Transient limiter operation
The purpose of the limiter is to protect the input of the EMC analyzer
from large transients when connected to a LISN. Switching EUT power
on or off can cause large spikes
generated in the LISN.
The Agilent 11947A transient limiter
incorporates a limiter, high-pass
filter, and an attenuator. It can withstand 10 kW for 10 µsec and has
a frequency range of 9 kHz to 200
MHz. The high-pass filter reduces
the line frequencies coupled to the
EMC analyzer.
Types of LISNs
H
N
V symmetric
V
1
et
ric
un
V1
sy
ric
et
2
m
ric
un
m
V
mm
et
sy
m
Ground
V sy
m
m
sy
m
1/2
un
V asymmetric
V-LISN
etric
1/2
V sy
mm
etric
V2 unsymmetric
Vector Diagram
V-LISN: Unsymmetric emissions (line-to-ground)
-LISN: Symmetric emissions (line-to-line)
T-LISN: Asymmetric emissions (mid point line-to-line)
Figure A-2. Three different types of LISNs
16
Appendix B: Antenna Factors
B1.0 Field strength units
Radiated EMI emissions measurements measure the electric field.
The field strength is calibrated in
dBµV/m. Field strength in dBµV/m
is derived from the following:
Pt =
total power radiated from an
isotropic
radiator
PD =
PD =
B1.1 Antenna factors
The definition of antenna factors
is the ratio of the electric field in
volts per meter present at the plane
of the antenna versus the voltage
out of the antenna connector. Note:
Antenna factors are not the same as
antenna gain.
B1.2 Types of antennas used for
commercial radiated measurements
There are three types of antennas
used for commercial radiated emissions measurements.
Biconical antenna: 30 MHz to
300 MHz
Log periodic antenna: 200 MHz to
1 GHz (the biconical and log periodic
overlap frequency)
the power density at a distance r from the isotropic
radiator (far field)
Pt /4πr2
Broadband antenna: 30 MHz to
1 GHz (larger format than the biconical or log periodic antennas)
R = 120πΩ
PD = E2/R
E2/R = Pt /4πr 2
E=
Biconical Antenna
(30 - 300 MHz)
(Pt x 30) 1/2 /r (V/m)
Far field1 is considered to be >λ/2π
Broadband Antenna
(30 - 1000 MHz)
Antenna factors
Biconical
@ 10m
dB/m
30
Log Periodic
@ 1m
Log Periodic Antenna
(200 - 1000 MHz)
25
20
15
10
5
Figure B-2. Antennas used in EMI emissions measurements
0
200
600
400
Frequency, MHz
800
1000
Linear units: AF = Antenna factor (1/m)
AF = Ein
E = Electric field strength (V/m)
V out
V = Voltage output from antenna (V)
Log units: AF(dB/m) = E(dBµV/m) - V(dBµV)
E(dBµV/m) = V(dBµV) + AF(dB/m)
Figure B-1. Typical antenna factor shapes
1. Far field is the minimum distance from a radiator where the field
becomes a planar wave.
17
Appendix C:
Basic Electrical
Relationships
Appendix D:
Detectors Used in EMI Measurements
The decibel is used extensively in
electromagnetic measurements. It
is the log of the ratio of two amplitudes. The amplitudes are in power,
voltage, amps, electric field units
and magnetic field units.
D1.0 Peak detector
decibel = dB = 10 log (P2/P1)
Data is sometimes expressed in
volts or field strength units. In this
case, replace P with V2/R.
If the impedances are equal, the
equation becomes:
dB = 20 log (V2/V1)
A unit of measure used in EMI measurements is dBµV or dBµA. The
relationship of dBµV and dBm is as
follows:
Initial EMI measurements are made
using the peak detector. This mode
is much faster than quasi-peak, or
average modes of detection. Signals
are normally displayed on spectrum
analyzers or EMC analyzers in peak
mode. Since signals measured in
peak detection mode always have
amplitude values equal to or higher
than quasi-peak or average detection modes, it is a very easy process
to take a sweep and compare the
results to a limit line. If all signals
fall below the limit, then the product passes and no further testing is
needed.
D1.1 Peak detector operation
The EMC analyzer has an envelope
or peak detector in the IF chain that
has a time constant, such that the
voltage at the detector output follows the peak value of the IF signal
at all times. In other words, the
detector can follow the fastest possible changes in the envelope of the
IF signal, but not the instantaneous
value of the IF sine wave.
(See Figure D-1.)
dBµV = 107 + PdBm
This is true for an impedance of 50
Ω.
Output of the envelope detector follows
the peaks of the IF signal
Wave length (l) is determined using
the following relationship:
λ = 3x108/f (Hz) or λ =
300/f (MHz)
Figure D-1. Peak detector diagram
18
D2.0 Quasi-peak detector
Most radiated and conducted limits
are based on quasi-peak detection
mode. Quasi-peak detectors weigh
signals according to their repetition
rate, which is a way of measuring their
annoyance factor. As the repetition
rate increases, the quasi-peak detector does not have time to discharge
as much, resulting in a higher voltage
output. (See Figure D-2.) For continuous wave (CW) signals, the peak and
the quasi-peak are the same.
Since the quasi-peak detector always
gives a reading less than or equal to
peak detection, why not use quasipeak detection all the time? Won’t
that make it easier to pass EMI tests?
It’s true that you can pass the tests
more easily; however, quasi-peak measurements are much slower by two or
three orders of magnitude compared
to using the peak detector.
D2.1 Quasi-peak detector operation
The quasi-peak detector has a charge
rate much faster than the discharge
rate; therefore, the higher the repetition rate of the signal, the higher the
output of the quasi-peak detector.
The quasi-peak detector also responds
to different amplitude signals in a
linear fashion. High-amplitude, lowrepetition-rate signals could produce
the same output as low-amplitude,
high-repetition-rate signals.
D3.0 Average detector
The average detector is required for
some conducted emissions tests in
conjunction with using the quasi-peak
detector. Also, radiated emissions
measurements above 1 GHz are performed using average detection. The
average detector output is always less
than or equal to peak detection.
Quasi-peak detector output varies
with impulse rate
Peak response
Quasi-peak
detector reading
D3.1 Average detector operation
Average detection is similar in many
respects to peak detection. Figure D-3
shows a signal that has just passed
through the IF and is about to be
detected. The output of the envelope
detector is the modulation envelope.
Peak detection occurs when the post
detection bandwidth is wider than
the resolution bandwidth. For average detection to take place, the peak
detected signal must pass through a
filter whose bandwidth is much less
than the resolution bandwidth. The
filter averages the higher frequency
components, such as noise at the output of the envelope detector.
Average detection
A
Quasi-peak
detector response
t
Test limit
t
Envelope detector
Filters
Test limit
Average detector
t
Figure D-2. Quasi-peak detector response diagram
Figure D-3. Average detection response diagram
19
Appendix E
EMC regulatory agencies
The following is a list of address and
phone numbers for obtaining EMC
regulation information.
IEC
CISPR
Sales Department of the Central
Office of the IEC
PO Box 131
3, Rue de Verembe
1121 Geneva 20, Switzerland
IEC www.iec.ch
CISPR (http://www.iec.ch/zone/
emc/emc_cis.htm#guide)
ITU-R (CCIR)
ITU, General Secretariat, Sales Service
Place de Nation
1211 Geneva, Switzerland
Telephone: +41 22 730 5111
(ITU Switchboard)
Fax:
+41 22 733 7256
http://www.itu.int/ITU-R
Australia
Australia Electromechanical
Committee Standards Association
of Australia
PO Box 458
North Sydney N.S.W. 2060
Telephone: +61 2 963 41 11
Fax:
+61 2 963 3896
AustraliaElecto-technical Committee
(http://www.ihs.com.au/standards/iec/)
Belgium
Comite Electrotechnique Belge
Boulevard A. Reyerslaan, 80
B-1030 BRUSSELS
Telephone: Int +32 2 706 85 70
Fax:
Int +32 2 706 85 80
http://www.bec-ceb.be
Canadians Standards Association
(CSA)
5060 Spectrum Way
Mississauga, Ontario
L4W 5N6
CANADA
Telephone: 416 747 4000
800 463 6727
Fax:
416 747 2473
http://www.csa.ca
Denmark
Dansk Elektroteknisk Komite
Strandgade 36 st
DK-1401 Kobenhavn K
Telephone: +45 72 24 59 00
Fax:
+45 72 24 59 02
http://www.en.ds.dk
France
Comite Electrotechnique Francais
UTE CEdex 64
F-92052 Paris la Defense
Telephone: +33 1 49 07 62 00
Fax:
+33 1 47 78 71 98
http://www.ute-fr.com/FR
Germany
VDE VERLAG GmbH
Bismarckstr. 33
10625 Berlin
Telephone: + 49 30 34 80 01 - 0
(switchboard)
Fax:
+ 49 30 341 70 93
email: [email protected]
India
Bureau of Indian Standards, Sales
Department
Manak Bhavan
9 Bahadur Shah Zafar Marg.
New Delhi 110002
Telephone: + 91 11 331 01 31
Fax:
+ 91 11 331 40 62
http://www.bis.org.in
Canada
Standards Council of Canada
Standards Sales Division
270 Albert Street, Suite 200
Ottawa, Ontario K1P 6N7
Telephone: 613 238 3222
Fax:
613 569 7808
http://www.scc.ca
20
Italy
CEI-Comitato Elettrotecnico Italiano
Sede di Milano
Via Saccardo, 9
20134 Milano
Telephone: 02 21006.226
Fax:
02 21006.222
http://www.ceiweb.it
Japan
Japanese Standards Association
1-24 Akasaka 4
Minato-Ku
Tokyo 107
Telephone: + 81 3 583 8001
Fax:
+ 81 3 580 14 18
(http://www.jsa.or.jp/default_english.asp)
Netherlands
Nederlands Normalisatie-Instituut
Afd. Verdoop en Informatie
Kalfjeslaan 2, PO Box 5059
2600 GB Delft
NL
Telephone: (015) 2 690 390
Fax:
(015) 2 690 190
www.nni.nl
Norway
Norsk Elektroteknisk Komite
Harbizalleen 2A
Postboks 280 Skoyen
N-0212 Oslo 2
Telephone: 67 83 87 00
Fax:
67 83 87 01
(http://www.standard.no/imaker.
exe?id=4170)
South Africa
South African Bureau of Standards
Electronic Engineering Department
Private Bag X191
Pretoria
0001 Republic of South Africa
(https://www.sabs.co.za/Sectors/
Electrotechnical/index.aspx)
Spain
Comite Nacional Espanol de la CEI
Francisco Gervas 3
E-28020 Madrid
Telephone: + 34 91 432 60 00
Fax:
+ 34 91 310 45 96
http://www.aenor.es
Sweden
Svenska Elektriska Kommissionen
PO Box 1284
S-164 28 Kista-Stockholm
Telephone: 08 444 14 00
Fax:
08 444 14 30
(http://www.elstandard.se/standarder/emc_standarder.asp)
Switzerland
Swiss Electrotechnical Committee
Swiss Electromechanical Association
Luppmenstrasse 1
CH-8320 Fehraltorf
Telephone: + 41 44 956 11 11
Fax:
+ 41 44 956 11 22
http://www.electrosuisse.ch/
United Kingdom
BSI Standards
389 Chiswick High Road
London
W4 4AL
United Kingdom
Telephone: +44 (0)20 8996 9001
Fax:
+44 (0)20 8996 7001
www.bsi-global.com
British Defence Standards
DStan Helpdesk
UKDefence Standardization
Room 1138
Kentigern House
65 Brown Street
Glasgow
G2 8EX
Telephone: +44 (0) 141 224 2531
Fax:
+44 (0) 141 224 2503
http://www.dstan.mod.uk
United States of America
America National Standards Institute
Inc.
Sales Dept.
1430 Broadway
New York, NY 10018
Telephone: 212 642 4900
Fax:
212 302 1286
(http://webstore.ansi.org/ansidocstore/default.asp)
FCC Rules and Regulations
Technical Standards Branch
2025 M Street N.W.
MS 1300 B4
Washington DC 20554
Telephone: 202 653 6288
http://www.fcc.gov
FCC Equipment Authorization Branch
7435 Oakland Mills Road
MS 1300-B2
Columbia, MD 21046
Telephone: 301 725 1585
http://www.fcc.gov
21
Glossary of Acronyms and Definitions
Ambient level
1. The values of radiated and
conducted signal and noise
existing at a specified test
location and time when the
test sample is not activated.
2. Those levels of radiated and
conducted signal and noise
existing at a specified test
location and time when the
test sample is inoperative.
Atmospherics, interference
from other sources, and circuit
noise, or other interference
generated within the measuring
set compose the ambient level.
Amplitude modulation
1. In a signal transmission system,
the process, or the result of the
process, where the amplitude of
one electrical quantity is varied in
accordance with some selected
characteristic of a second
quantity, which need not be
electrical in nature.
2. The process by which the
amplitude of a carrier wave is
varied following a specified law.
Anechoic chamber
1. A shielded room which is lined
with radio absorbing material to
reduce reflections from all internal
surfaces. Fully lined anechoic
chambers have such material on
all internal surfaces, wall, ceiling
and floor. Its also called a “fully
anechoic chamber.” A semianechoic chamber is a shielded
room which has absorbing
material on all surfaces except
the floor.
Antenna (aerial)
1. A means for radiated or receiving
radio waves.
2. A transducer which either emits
radio frequency power into space
from a signal source or intercepts an
arriving electromagnetic field,
converting it into an electrical signal.
Antenna factor
The factor which, when properly
applied to the voltage at the input
terminals of the measuring instrument, yields the electric field
strength in volts per meter and a
magnetic field strength in amperes
per meter.
Antenna induced voltage
The voltage which is measured or
calculated to exist across the open
circuited antenna terminals.
Antenna terminal conducted interference
Any undesired voltage or current
generated within a receiver, transmitter, or their associated equipment
appearing at the antenna terminals.
Auxiliary equipment
Equipment not under test that is
nevertheless indispensable for setting
up all the functions and assessing
the correct performance of the EUT
during its exposure to the
disturbance.
Balun
A balun is an antenna balancing
device, which facilitates use of coaxial feeds with symmetrical antennae
such as a dipole.
Broadband emission
Broadband is the definition for an
interference amplitude when several
spectral lines are within the RFI
receivers specified bandwidth.
Broadband interference
(measurements)
A disturbance that has a spectral
energy distribution sufficiently broad,
so that the response of the measuring
receiver in use does not vary significantly when tuned over a specified
number of receiver bandwidths.
22
Conducted interference
Interference resulting from conducted
radio noise or unwanted signals
entering a transducer (receiver) by
direct coupling.
Cross coupling
The coupling of a signal from one
channel, circuit, or conductor to
another, where it becomes an
undesired signal.
Decoupling network
A decoupling network is an electrical circuit for preventing test signals
which are applied to the EUT from
affecting other devices, equipment,
or systems that are not under test.
IEC 801-6 states that the coupling
and decoupling network systems
can be integrated in one box or they
can be in separate networks.
Dipole
1. An antenna consisting of a straight
conductor usually not more than a
half-wavelength long, divided at
its electrical center for connection
to a transmission line.
2. Any one of a class of antennas
producing a radiation pattern
approximating that of an
elementary electric dipole.
Electromagnetic compatibility
(EMC)
1. The capability of electronic
equipment of systems to be
operated within defined margins
of safety in the intended
operating environment at
designed levels of efficiency
without degradation due to
interference.
2. EMC is the ability of equipment
to function satisfactorily in
its electromagnetic environment
without introducing intolerable
disturbances into that
environment or into other
equipment.
Electromagnetic interference
Electromagnetic interference is the
impairment of a wanted electromagnetic signal by an electromagnetic
disturbance.
Electromagnetic wave
The radiant energy produced by the
oscillation of an electric charge characterized by oscillation of the electric
and magnetic fields.
Emission
Electromagnetic energy propagated
from a source by radiation or conduction.
Far field
The region where the power flux
density from an antenna approximately obeys an inverse squares law
of the distance. For a dipole this corresponds to distances greater than
l/2 where l is the wave length of the
radiation.
Ground plane
1. A conducting surface or plate
used as a common reference
point for circuit returns and
electric or signal potentials.
2. A metal sheet or plate used as
a common reference point for
circuit returns and electrical or
signal potentials.
Isotropic
Isotropic means having properties of
equal values in all directions.
Monopole
An antenna consisting of a straight
conductor, usually not more than
one-quarter wave length long, mounted immediately above, and normal
to, a ground plane. It is connected to
a transmission line at its base and
behaves, with its image, like a dipole.
Narrowband emission
That which has its principal spectral
energy lying within the bandpass of
the measuring receiver in use.
Open area
A site for radiated electromagnetic
interference measurements which
is open flat terrain at a distance
far enough away from buildings, electric lines, fences, trees, underground
cables, and pipe lines so that effects
due to such are negligible. This site
should have a
sufficiently low level of ambient
interference to permit testing to the
required limits.
Polarization
A term used to describe the orientation of the field vector of a radiated
field.
Immunity
1. The property of a receiver or any
other equipment or system
enabling it to reject a radio
disturbance.
2. The ability of electronic
equipment to withstand radiated
electromagnetic fields without
producing undesirable responses.
Radiated interference
Radio interference resulting from
radiated noise of unwanted signals.
Compare radio frequency interference below.
Intermodulation
Mixing of two or more signals in a
nonlinear element, producing signals
at frequencies equal to the sums and
differences of integral multiples of
the original signals.
Radio frequency interference
RFI is the high frequency interference
with radio reception. This occurs
when undesired electromagnetic
oscillations find entrance to the
high frequency input of a receiver
or antenna system.
Radiation
The emission of energy in the form of
electromagnetic waves.
23
RFI sources
Sources are equipment and systems
as well as their components which
can cause RFI.
Shielded enclosure
A screened or solid metal housing
designed expressly for the purpose of
isolating the internal from the external electromagnetic environment.
The purpose is to prevent outside
ambient electromagnetic fields from
causing performance degradation and
to prevent emissions from causing
interference to outside activities.
Stripline
Parallel plate transmission line to generate an electromagnetic field for testing purposes.
Susceptibility
Susceptibility is the characteristic
of electronic equipment that permits
undesirable responses when subjected to electromagnetic energy.
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Printed in USA, July 12, 2010
5990-6152EN
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