Making Conducted and Radiated Emissions Measurements

Making Conducted and Radiated Emissions Measurements
Keysight Technologies
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................11
3.5 Performing radiated emissions measurements...............................................12
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............................................................................................. 20
D3.1 Average detector operation.................................................................... 20
Appendix E: EMC Regulatory Agencies.............................................................21
Glossary of Acronyms and Definitions..............................................................23
03 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
1.0 Introduction to Radiated and Conducted Emissions
Measurements
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.
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). 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.
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 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.
Product development cycle
Initial
investigation
viable
Yes
Design
breadboard
Lab
prototype
pass
pass
No
No
R
Production
prototype
D
E
pass
pass
No
No
E
Production
unit
S
I
G
Yes
No
N
Production
Figure 1. A typical product development cycle
Emission
Immunity = Susceptibility
Conducted
Radiated
Figure 2. Electromagnetic compatibility between products
04 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
1.2 Systems for performing precompliance measurements
The components used in systems for precompliance measurements are as follows:
signal analyzer with N6141C EMI measurement application, line impedance stabilization
network (LISN), transient limiter and antennas. To isolate problems after they have been
identified, the close field probes N9311X-100 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.
3.5 Performing radiated emissions measurements
EMI precompliance measurement system
Log periodic
antenna
X-Series analyzer with N6141C
EMC measurement application
Biconical
antenna
MONITOR
POWER OUTPUT
CAUTION
HIGH VOLTAGE
GND
LISN
Agile
nt 11
947A
Transient
limiter
Close-field probe set
Diagnostics
Figure 3. Components of a preproduction evaluation system
Tripod
05 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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)
3. Where will the product be used (for example home, commercial, light industry or heavy industry)?
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.
Emissions regulations (summary)
EN's
FCC
CISPR
18
11
––
12
––
15
13
EN 55013
15
EN 55011
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. Comparision of regulatory agency requirements
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.)
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.)
06 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
2.1.3 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.
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
FCC part
Broadcast receivers
Part 15
Household appliances
Part 15
Fluorescent lights/luminaries
Part 15
Information technology equipment
Part 15
Equipment classification
Class A Industrial
Part 15
Class B Residential
Part 15
Industrial, scientific and medical equipment
Table 2. FCC requirements summary
Part 18
07 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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. Keysight’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.
Conducted emissions measurements
are easier than ever!
X-Series analyzer with N6141C
EMC measurement application
LISN
Device
under test
Limiter
Figure 4. Conducted measurements interconnection
Figure 5. Scan table
08 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
Figure 6. Conducted emissions display with limit lines and margin
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).
Figure 7. Conducted ambient emissions
09 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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 (See Figure 8).
Figure 8. Scan and search for signals above the limit
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.
10 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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 (See Figure 9).
Figure 9. Quasi-peak and average delta to 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.
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 semianechoic 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.
11 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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.
Precompliance Radiated Measurements
Biconical
Antenna
X-Series analyzer with N6141C
EMC measurement application
Tripod
Device
under test
Figure 10. Radiated emissions test setup
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.
12 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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).
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.
Figure 11. Mark ambient noise and delete it
Figure 12. Duplicate ambient signals marked
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. DUT signals with quasi-peak measurement compared to limit
13 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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.
Diagnostic measurement set-up: emissions
X-Series analyzer with N6141C
EMC measurement application
Device under test
HP 11940A
Close-field probe
Circuit under test
Figure 14. Diagnostics setup interconnection
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 Keysight N9311X-100
probe kit contains four H-field probes, covering 30 MHz - 3 GHz frequency range, with
different sensitivity and resolution. 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.
14 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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 15).
Figure 15. Preliminary diagnostics trace
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.
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 16. Diagnostics traces before and after redesign
15 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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.
A1.1 LISN operation
The diagram in Figure A-1 below shows the circuit for one side of the line relative to earth
ground.
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.
Line Impedance Stabilization Network (LISN)
50 μH
From power source
To EUT
0.1 μF
1000 Ω
1 μF
To Receiver or EMC analyzer (50 Ω)
Impedance (ohms) 60
50
40
30
20
10
.01
Figure A-1. Typical LISN circuit diagram
.1
1
10
100 Frequency (MHz)
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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
three-phase circuit in a “Y” configuration, between each line and ground. There are
other specialized types of LISNs. A delta LISN measures the line-to-line 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.
17 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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 = the power density at a distance r from the isotropic radiator (far field)
PD = P t /4πr 2
R=
120πΩ
PD = E2 /R
E2 /R
= P t /4πr 2
E=
(P t x 30)1/2 /r (V/m)
Far field1 is considered to be >λ/2π
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)
Broadband antenna: 30 MHz to 1 GHz (larger format than the biconical or log periodic
antennas)
Antenna factors
Biconical
@ 10m
dB/m
30
Biconical Antenna
(30 - 300 MHz)
Log Periodic
@ 1m
25
20
15
10
5
0
200
600
400
Frequency, MHz
800
1000
Broadband Antenna
(30 - 1000 MHz)
Log Periodic Antenna
(200 - 1000 MHz)
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
1Far
field is the minimum distance from a radiator where the field becomes a planar wave.
Figure B-2. Antennas used in EMI emissions measurements
18 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
Appendix C:
Basic Electrical Relationships
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.
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:
dBμV = 107 + PdBm
This is true for an impedance of 50 Ω.
Wave length (l) is determined using the following relationship:
λ = 3x10 8/f (Hz) or λ = 300/f (MHz)
Appendix D:
Detectors Used in EMI Measurements
D1.0 Peak detector
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).
Output of the envelope detector follows
the peaks of the IF signal
Figure D-1. Peak detector diagram
19 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
Quasi-peak detector output varies
with impulse rate
Peak response
Quasi-peak
detector reading
Quasi-peak
detector response
Test limit
t
Test limit
t
Figure D-2. Quasi-peak detector response diagram
Since the quasi-peak detector always gives a reading less than or equal to peak
detection, why not use quasi-peak 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 quasipeak detector. The quasi-peak detector also responds to different amplitude signals in
a linear fashion. High-amplitude, low-repetition-rate signals could produce the same
output as low-amplitude, high-repetition-rate signals.
20 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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
t
Envelope detector
Filters
Average detector
Figure D-3. Average detection response diagram
21 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
Appendix E
EMC regulatory agencies
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/emc/iec_emc/iec_emc_players_cispr.htm)
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/
(CSA)
Canadians Standards Association
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.ds.dk/en
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.cenelec.eu/
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.ceb-bec.be
Germany
VDE VERLAG GmbH
Bismarckstr. 33
10625 Berlin
Telephone: + 49 30 34 80 01 - 0 (switchboard)
Fax: + 49 30 341 70 93
http://vde-verlag.de/english.html
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
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
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
22 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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
http://www.nen.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/toppvalg/nek/
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-and-Services/Sectors/
Electronics/index.asp
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
http://www.bsiglobal.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.gov.uk/uk-defence-standardization
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/
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
23 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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 semi-anechoic 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.
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.
24 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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.
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.
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.
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.
Radiated interference
Radio interference resulting from radiated noise of unwanted
signals. Compare radio frequency= interference below.
Radiation
The emission of energy in the form of electromagnetic waves.
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.
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.
25 | Keysight | Making Conducted and Radiated Emissions Measurements – Application Note
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Published in USA, April 10, 2017
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