ELECTROMAGNETIC COMPATIBILITY (EMC) ISSUES IN TELECOMMUNICATIONS, DATA AND COMPUTER
COMMUNICATION NETWORKS
by
Dominic B. O. Konditi
Multimedia University of Kenya.
NAIROBI. Kenya.
At The EACO 2014 Assemblies Conference
Arusha, Tanzania.
18th – 21th June, 2014
Abstract: The increase in the number of transmissions systems, band congestion and the broadening of the use of the
electromagnetic spectrum due to digital migration and the associated equipment being more sensitive due to miniaturization of the
solid state devices, electromagnetic interference becomes a serious threat to the communications systems normal operation in terms of
their availability and reliability. Moreover, as communications speeds increase, noise and its potentially disruptive effects also increase
and can render the wireless communication links vulnerable and ineffective. Thus, with the widespread distribution of information
technology equipment in today’s society, higher reliability is required for transmission systems. As a result, service interruption involving
even temporary voltage spikes is of critical importance. Keeping this in mind, this paper, discusses the cause, effect and solution of
electromagnetic interference on telecommunication, data and computer communication by incorporating EMI control measures at various
levels of equipment manifestations. Finally, Standards are cited to assist in good practice to mitigate electromagnetic interference within
networks.
Key words: Electromagnetic Interference (EMI), Electromagnetic Compatibility (EMC), Telecommunication
networks, Broadcasting networks, Health Networks, Electromagnetic Environment, Electromagnetic
Spectrum (EMS), Standards.
1.0 INTRODUCTION
Firstly, we need to understand what electromagnetic fields are before we discuss electromagnetic
interferences.
-
Electromagnetic fields have frequencies which range between 100 kHz and 300 GHz as
illustrated below.
-
Electric and magnetic fields are all around us – for example, natural electric fields in
thunderstorms cause lightning to leap across the sky, and man-made electric fields are found in
the fluorescent lamps that light up our streets.
-
Magnetic fields are also well known to us; the Earth’s magnetic field causes a compass needle
to point North and helps many birds and fish to navigate.
1
1.1 SOURCES OF ELECTROMAGNETIC FIELDS
 The electromagnetic environment consists of natural radiation and man-made electromagnetic
fields that are produced either intentionally or as by-products of the use of electrical devices
and systems.
 The natural electromagnetic environment originates from terrestrial and extraterrestrial
sources such as electrical discharges in the earth’s atmosphere and radiation from the sun and
space.
 Characteristic of natural fields is a very broad band spectrum where random high peak
transients or bursts arise over the noise-like continuum background such as electro-static
discharges (ESD) and elecro-dynamic discharges (EDD) from natural and artificial sources.
Fig. 1 Electromagnetic Spectrum
2
Fig.2 Showing Trees and Buildings Do Not Block Magnetic Fields.
2.0
DISCUSSIONS
Before embarking on the discussion of electromagnetic interferences and their sources, it is in order to define
the terms that are relevant to the discussion: A telecommunications network is a collection of terminal
nodes, links and any intermediate nodes which are connected so as to enable telecommunication between the
terminals. The transmission links connect the nodes together. A broadcasting network is a collection of radio
or TV stations that air programming from the same centralized source. In telecommunication, the term
electromagnetic environment (EME) has the following meanings: For a telecommunications
system is the spatial distribution of electromagnetic fields surrounding a given site. The
electromagnetic environment may be expressed in terms of the spatial and temporal distribution of
electric field strength (volts per metre), irradiance (watts per square metre), or energy density (joules
per cubic metre) (Source: Wikipedia).
Proceeding with our discussion, Electromagnetic Compatibility (EMC) is the ability of a system
or device to function satisfactorily in its electromagnetic environment without introducing
intolerable electromagnetic disturbance to anything in that environment. Electromagnetic
Immunity is the ability of a system or device to perform without degradation in the presence of
an electromagnetic disturbance. Electromagnetic Interference (EMI) is any electromagnetic disturbance
that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics and
electrical equipment. It can be induced intentionally, as in some forms of electronic warfare, or
unintentionally, as a result of spurious emissions and responses, intermodulation products. Any EMI
situation requires not only an emission source but also a receptor. Electromagnetic Interference (EMI),
Electromagnetic Compatibility (EMC) and Environmental Effects (EE) are important considerations in any
electronics product development and critical for systems integration.
Legally, products must comply with international EMC standards which have been developed to
control conducted and radiated emissions from electrical and electronics systems.
3
Products must not be susceptible, or in other words, must be immune, to electromagnetic interference
such as Electrical Fast Transients (EFT) and Electrostatic Discharge (ESD). Furthermore, systems
may be required to operate in severe electromagnetic environments such as during lightning strikes,
and withstand threats such as electromagnetic pulses (EMP).
Trade-offs between EMC and competing design requirements present major challenges to engineers
[1].
2.1 ELECTROMAGNETIC INTERFERENCE SOURCES
An EMI source can be any device that transmits, distributes, processes, or utilizes any form of
electrical energy where some aspects of its operation generates conducted or radiated signals that can
cause equipment performance degradation. Any EMI situation requires not only an emission source
but also a receptor. A receptor is also called a "victim" source because it consists of any device,
when exposed to conducted or radiated electromagnetic energy from emitting sources, will degrade
or malfunction in performance. Many devices can be emission sources and receptors simultaneously.
For example, most communication electronic systems can be emission and receptor sources
simultaneously because they contain transmitters and receivers. Figure 2 shows a taxonomy of
different receptors that are susceptible to EMI. The emission source taxonomy, receptors can be
divided into natural and man-made receptors. Similarly, we can give the taxonomy of the different
sources of EMI.
Figure 3 shows a taxonomy of different receptors that are susceptible to EMI.
-
Inadvertent jamming is a form of electromagnetic interference which manifests itself as signal
interference. It may arise from electromagnetic compatibility issues, where legitimate electrical or electronic
equipment causes excessive electromagnetic interference. Within some jurisdiction, in e.g., the European
Union the Electromagnetic Compatibility (EMC) Directive [EC89/336 as amended] requires manufacturers and
importers to satisfy specific requirements to ensure that equipment supplied does not cause excessive
interference. Inadvertent jamming may also occur where a radio signal transmitted by one user disrupts the
use of the radio spectrum by another user.
- Cable wiring and harnessing can be a significant EMI concern. Cables are required to distribute electrical
power and transmit electrical signals for the operation of various systems. Since cables are usually routed to
accommodate its function, it is often difficult to quantify its environment and it usually varies over both
frequency and electric and magnetic field amplitudes. Cables can be EMI radiating sources if they act as
radiating antennas, or be susceptible to EMI if they are receiving antennas. Cables can also be coupling
paths. In addition, cables are sometimes harnessed together, so interference can also be between two
cables that are close in proximity. Therefore, their performance is very difficult to predict. Many
specifications classify wiring or cable types into four to six categories but these classifications are generally
4
qualitative in nature. More quantitative classifications should look at levels of power transmitted, or
susceptibility of termination.
- Connectors are contacts that either link or separate two cables or other equipments. There may be
anywhere from several to hundreds of individual wire-pins or coaxial sheaths making simultaneous
contact via a connector. EMI problems from connectors are usually related to poor contact which
may result in arcing, or overheating that leads to arcing. Poor contact connections can also result in
driven-circuit voltage variations from the contact impedance modulation of the driving-circuit
source. Impedance coupling from outside sources can happen in connector grounding paths.
Improperly shielded connectors or poor cable-connector-equipment- enclosure contact can cause
radiated emission penetration or leaking through apertures.
- Grounding is one of the least understood EMC subjects, despite the fact that it seems
straightforward. Improper grounding is the source of many EMI problems. Grounding is necessary to
prevent shock hazard, which occurs when a wiring or component insulation in an equipement frame
or housing breaks down. Grounding also protects against lightning damage. Grounding is also
necessary to reduce EMI due to electric field flux coupling, magnetic field flux coupling, and
common impedance coupling. There are two reasons why grounding is not understood well. One
reason is that shock and safety control requirements existed before the electronics and high
frequency area, so traditional grounding techniques were developed to satisfy those requirements. A
second reason is that sometimes a conflict occurs between requirements for safety grounds and EMI
control. [Violette87]
Different considerations must be taken into account with shielding. Shielding is the use of
conductive materials to reduce radiated EMI reflection or absorption. Usually, the theoretical
attenuation offered by materials to electric, magnetic, and electromagnetic waves does not match that
achieved in practice. This is because a shielded enclosure or housing is not completely sealed. Any
shielding application has some kind of penetrations and apertures like meter windows, cover plates
and access cover members, and push buttons. These apertures cause leakage and therefore
compromises the integrity of the shielding material. Shielding integrity can be restored through the
use of EMC gaskets, EMC sealants, and conductive grease. Gaskets provide either temporary or
semi-permanent sealing applications between joints and structures. Sealants include conductive
epoxies which are used to join, bond, and seal two or more metallic surfaces, and conductive
caulking which is used to shield and seal two or more metallic mating members held together by
other mechanical means. Conductive grease provides a low-resistivity contact path between mating
members. [Violette87]
-
Fig.4 Depicting the EMC Paradigm.
5
 Power supplies (switching), power rails, motors, relays:
When an electrical circuit is energized or de-energized, it will emit a small amount of RF energy
that will be of very short duration. If you have radios on top of a building that have hundreds of
circuits that are turning on and off all of the time — such as air handlers, air conditioner
compressors and elevator motors — the sum of these very short random pulses will become a
constant roar to the radio systems on the building and the radio receiver noise floor will be
high. Besides the transient pulses described above, electrical motors put out RFI when the
brushes on the armature are worn. New brushes and cleaning the inside of the motors usually
fix these problems.
o Multimedia (MM) products are classified as unintentional radiators, i.e. products which do not
contain an antenna to intentionally transmit RF power can and do cause interference with each other.
The types of interference usually fall within one of nine RFI classifications: Intermodulation,
Spurious emission, Spurious response, Co-channel interference,
interference, Transmitter noise, Harmonics and Image frequency.
Adjacent
channel
2.1.1 EMI and Air Transportation
The use of some electronic/digital and electrical equipment has been prohibited in aircraft, particularly
during take-offs and landings. Radio transmitters such as cellular phones and remote-controlled toys, are
known to induce transient currents in electric wires (or cables) that can be amplified in the unshielded
aluminum frame of an aircraft [4, 5]. The aluminum frame acts as a phased array antenna or a resonant
cavity, thus compounding the effect of both internal and external EMI. This may result in change in the logic
level of the bit stream, leading to rejection by error-correcting routines and eventual interruptions.
High Intensity Radiated Emissions (HIRE) from radar, microwave relay stations, radio/TV transmitters and
high power AM/FM radio broadcast systems can lead to disruptions in airplane navigation and
communication systems and to possible loss of aircraft and human life. The electromagnetic pulse (EMP) is
designed to permanently disable electronic devices within the reception area of the emitted signal which can
originate from a nuclear or non-nuclear source. EMP is a directed energy source that can induce electric and
magnetic fields in the electronic systems to produce damaging current and voltage surges, and can produce
catastrophic results with the power delivery systems, transportation systems (navigation and air traffic
control), emergency services, and financial and banking services [6].
2.1.3 EMI and Medical Devices
There have been reported cases of adverse effects of EMI on medical devices such as implanted cardiac
devices (e.g. pacemakers and defibrillators), apnea monitors, powered wheel-chairs, blood pumps, hearing
aids and electronic imaging devices [8, 9, 10]. Operation of these devices have been affected by EMI sources,
particularly cellular phones.
GSM phones that operate on (digital) TDMA can produce loud tones in some hearing aids up to 30 metres
away and can reach 130 dB which is equivalent to the sound of an airplane at take-off [4]. The pocket and
attached types of hearing aids are the most susceptible to EMI, though the easiest to control by shielding.
Device manufacturers are also required to pay attention to shielding at the initial design stage, and work in
consultation with the designers and manufacturers of EMI emitting devices. Restrictive use of wireless
devices in hospitals and clinics could also be recommended, though difficult to enforce since both wireless
communication devices and medical equipment must co-exist. Nonetheless, good consumer education on
EMI and its effects should be provided, for example, through equipment’s operating/instruction manuals.
Implanted cardiac devices such as pacemakers and implantable cardioverter-defibrillators have become
victims of EMI which can produce ventricular standstill in the medical devices. [8, 9]. Digital cellular phones
6
may, for example, interact with pacemaker function by inhibiting the pacing out system, particularly when
the antenna is located near the pacemaker’s pulse operator header. Patients with pacemakers need to be
regularly and carefully evaluated for any source(s) of EMI and other environmental factors that may
interfere with their operation.
Other major sources of EMI include fluorescent tubes, motors (or motorized equipment) and microwave
ovens. The low frequency sources (fluorescent tubes, transformers, TVs and motors) work on electricity
utility grid and are known to chronically stress the pineal gland which controls all the hormonal balances in a
human body [10]. When the pineal gland is stressed, melatonin levels go down and sleeping problems may
result. High frequency sources such as microwave ovens, broadcasting (radio and TV) systems and other
proliferating wireless communication systems have also increased daily exposure to EMI, particularly in
industrialized countries, all leading to more stress.
2.1.4 EMI and Global Positioning System (GPS)
The Global positioning System (GPS) is a space-based Global Navigation Satellite System (GNSS) which was
initially developed for the military purposes (location and targeting). Its use has now extended to civilian
applications such as maritime and aviation. Its applications therefore range from hand-held positioning and
personal navigation devices to precision surveying tools. A typical GPS receiver on earth’s surface (with builtin microprocessors) must lock onto signals from at least four satellites, of twenty-four GPS satellites, to give
full 3-D position (latitude, longitude and altitude), velocity (speed and direction) and time offset.
The signals broadcast by the satellites in the GPS constellation travel nearly 300,000 km towards the earth’s
surface through the atmosphere and are thus vulnerable to frequency-related effects while propagating
through the tropospheric and ionospheric layers. In addition, broadcast signals by GPS satellites are
extremely low power, hence vulnerable to EMI from sources such as broadcast TV, VHF transmitters,
Portable Electronic Devices (PEDs), UWB radar and mobile satellite satellites service (MSS) communication
systems. Intentional disruptions of GPS services are also possible through jamming and spoofing. A simple 14 Watt transmitter is known to be capable of disrupting GPS signals within an area of 100 nautical mile
radius [6]. These disruptions affect the reliability, availability, integrity and accuracy of the GPS.
The use of spread spectrum techniques (e.g. CDMA) in GPS allows multiple satellites to transmit on the same
frequencies without interfering with each other, thus providing a high level of resistance to noise and
interference. In addition, the GPS system uses a dual-frequency design that allows GPS receivers to
compensate for the frequency-related effects of tropospheric and ionospheric layers.
2.1.5 Residual Magnetism in Buildings
Static magnetic field has been confirmed to be the cause of EMI with cathode ray tube (CRT) which forms an
integral part of some medical equipment. Sources of such EMI are the electric welds of steel frames and
deck plates in building structures housing the medical equipment [ 11, 12]. This is the reason for hospitals
tocarry out residual magnetic field measurement; place electronic equipment away from strongly
magnetized points where strong magnetic fields are found; de-magnetize affected equipment; and,
magnetically shield such EMI vulnerable equipment. Wen and Wang [13] have reported on the effective use
of steel fibre cement (cement paste containing 0.72% 304 stainless steel fibres of diameter 8 μm and length
6 mm having a resistivity of 16 Ω-cm) as shielding material. A shield effectiveness of 70 dB at 1.5 GHz was
attained. Earlier shielding materials produced made use of polymer-matrix composites containing electrically
conductive filters.
7
2.2 EMI CONTROL TECHNIQUES AT THE COMPONENT, CIRCUIT, AND
EQUIPMENT LEVELS
- The previous design considerations dealt with topics that represent problems between sources and
receptors. There are also EMI control techniques that are applied at the component, circuit, and
equipment levels. The problem with resistors, inductors, and capacitors is that they do not behave at
their stated values, especially at high frequencies due to the effects of parasitic inductance and
capacitance. Under certain conditions, their performance degrades at frequencies as low as 1MHz.
Inductive devices like transformers, solenoids, and relays produce low-impedance fields that are
sources of EMI if they are uncontrolled. The main techniques available for controlling transientproducing devices involves using diodes and filters, and for controlling magnetic fields involves
shielding.
- Surface tracking is an insulator problem that is a source of EMI. Surface tracking (or leakage) is a
condition in which small currents creep across the insulator. It is caused by surface contamination of
the insulation by moisture or solid conductive particles. The EMI control technique is to protect from
contamination through the use of proper material and proper voltage design. Techniques used to
minimize EMI in conductors include coating with a high-permeability material and using hollow
conductors at higher frequencies to minimize external fields. There are many techniques for different
components which are not all listed here.
- Radio-frequency interference (RFI) is a serious EMI problem today due largely to the large number
of radio transmitters that exist. Radio transmitters range from large, high-power transmitters such as
broadcast, communications, and radar to small, low-power equipments such as handheld radios and
cellular telephones. The problem with radio transmitters is twofold, as equipment can cause
interference to nearby radio and television receivers, and as equipment can be upset by nearby
transmitters.
- Radio and television receivers can be very vulnerable to RFI pollution from nearby computers.
Repetitive digital signals contain harmonics that can extend into the GHz range. This unwanted
energy can be radiated through cables and wiring acting as antennas, or conducted through the ac
power system. If the levels are high enough, the receivers can be damaged. It was this emissions
problem that caused countries around the world to pass EMI regulations. In the U.S., complaints
from consumers about interference with television disruption in the 70's drove the FCC to initiate
mandatory EMI testing of personal and commercial computers in the 1980's. Digital circuits are
usually the primary source of emissions, and analog circuits are more vulnerable to RFI than digital
circuits. In protecting equipment against RFI, it is important to start at the circuit level.
- Filters can be used and sometimes multistage filters are needed. Slots and seams cause the most
problem in RFI shielding, so high-quality shields and connectors are needed for adequate RFI
protection. [Gerke94]
- Electrostatic discharge (ESD) is also an EMI problem. An ESD event starts with a very slow buildup
of energy, followed by a very rapid breakdown. It is this fast breakdown that causes EMI problems
in modern electronic systems. The energy discharge yields EMI frequencies in the hundreds of
megahertz. The high speed and frequency of the ESD energy can damage circuits, bounce grounds,
and cause upsets through electromagnetic coupling. The most common method of ESD generation is
triboelectric charging which is caused by stripping electrons from one object and depositing
electrons on another object. In an insulator, it may be a long time before charge recombination
occurs, so a voltage builds. If the voltage becomes large enough, a rapid breakdown occurs in the air,
creating the ESD arc or spark. Sources of triboelectric charging includes humans, furniture, and
material or device movement. Humidity also affects ESD as the lower the humidity, the higher the
likelihood of ESD problems. High humidity is helpful because the moisture reduces surface
8
impedance and allows charges to recombine at a faster rate. However, high humidity leads to surface
tracking or leakage at lower temperatures, so there is a tradeoff.
- ESD has several failure modes that are not completely independent of one another. These include
direct hit to circuit, ground bounce, electromagnetic field coupling, and pre-discharge electric field.
- Like RFI problems, good protection against ESD problems start at the circuit level through the use of
filters and multilayer boards. High-quality shields and connectors can be used for good ESD cable
protection. The length-to-width ratio for grounds should be less than 3 to 1. Thin materials are
adequate for shielding and special attention must be paid to slots and penetrations. [Gerke94].
- In addition to the design considerations above, there are other EMC issues in the design of embedded
systems. One is the compatibility among transmitters that are designed to work together. For
example, when every car has a forward-pointing smart cruise control radar, and they are either next
to each other or coming head-on at each other, the transmitters must be designed that there is not
interference. Another problem to consider is what happens when a component is inserted in an
integrated system and causes EMI. For example, computer motherboards are designed with empty
slots for different cards to be plugged into. In particular, video cards are FCC certified to ensure that
they are compatible with whichever motherboard they are plugged into.
3.0 Standards Compliance and Efforts toward Their Harmonization
The ability to sell electronic products depends upon the products being able to meet the
specifications contained in various regulations. Therefore, a brief study of the different emission
standards is necessary. In the United States, the Federal Communications Commission (FCC) Rules
and Regulations, Part 15 Subpart J deals with unintentional emissions from equipment that use
digital techniques and generate or use timing signals or pulses of frequencies in excess of 10kHZ, or
has a pulse rate of 10,000 pulses per second or higher. These specifications were first formed when
users of television and other radio receivers complained about the interference of radiation from
nearby operating digital devices. FCC 15J defines 2 classes of computing devices that must conform
to emissions specifications. Computing devices refer to any computer peripheral including modems,
printers, and other I/O devices. The 2 classes are defined as follows:
 Class A: "A computing device that is marketed for use in a commercial, industrial, or business
environment; exclusive of a device which is marketed for use by the general public, or which is
intended
to
be
used
in
the
home."
Class B: "A computing device that is marketed for use in a residential environment notwithstanding
use in commercial, business, and environmental environments."
A device that passes Class B limits may be used in a Class A environment. There are different tests
that are required for FCC compliance. There are 3 different types of FCC compliance as stated in the
FCC Rules and Regulations.


Type approval - Based on equipment examination and test by the FCC.
Type acceptance - Based on representation and test data for equipment to be used pursuant to a
station authorization. Testing is performed by the manufacturer and the data is not required unless
specifically requested by the FCC.
 Certification - Based on representation and test data for equipment designed to be operated without
individual license under Rules and Regulations Parts 15 and 18. Testing is performed by the
manufacturer and the test data is required by the FCC. [Violette87]
The International Special Committee on Radio Frequency Interference (CISPR) is an organization
sponsored by the International Electrotechnical Commission (IEC). CISPR is composed of each of
the national committees of the IEC, a United Nations commission, and other international unions,
commissions, and committees. It is responsible for setting uniform limits on electromagnetic
9
emissions from equipment so that trade would not be inhibited between member countries as a result
of different emissions specifications. CISPR publications deal with interference for the following
items:




Microwave ovens with power consumption below 5 kW.
Ignition systems.
Televisions, FM receivers, and AM receiver power-line susceptibility.
Conducted and radiated emission of household appliances, portable tools up to 2 kW, office
machines, dimmer regulators, and other electrical apparatus.
 Fluorescent lamps.
Compliance with CISPR usually varies from country to country and each country has its own
regulations regarding enforcement of the limits. [Violette87]
Currently, there is worldwide effort towards harmonizing various EMC standards to reduce the trade
barriers between countries and various sectors like Defense and Civilian. The lack of harmonization
of standards is a great burden on manufacturers of electrical and electronic systems because it
increases the duration of the product development cycle and the compliance evaluation costs. The
increased use of these products has made it absolutely necessary to harmonize various EMC
standards. In the Defense sector, the success of military missions is dependent on the trouble-free
field performance of the electronic and communication equipments used. In the Civilian sector, it is
necessary to protect the radio frequency spectrum from the electromagnetic noise emission of
electrical systems. CISPR has provided recommendations for the implementation of EMC. However,
each country can choose its own set of test instrumentation, test procedures, and test limits in their
own EMC standards. This causes any manufacturer wishing to supply electronic equipment to
different countries and the Defense and Civilian sector having to deal with a plethora of EMC
standards. [Sampath97]
In Europe, the market unification of 16 countries to form the European Union has affected the EMC
standards scenario. The national EMC standards of these countries are being combined to form a
harmonized EMC standard, called European Norms. This became known as the EMC Directive
which went into effect January 1, 1996. All products that complied to the EMC Directive would bear
a CE marking. This mark was required for any nation that wanted to sell electrical equipment in the
European Community.
3.1 Procedures Towards Achieving Compliance.
Compliance can be completed by the following three ways:

Self-certification by manufacturer - The manufacturer performs the tests using in-house test
equipment or a commercial test house. After the tests are completed and documented, the
manufacturer files for a declaration of compliance.
 Technical Construction File (TCF) - The manufacturer prepares a TCF which describes the
product, sets out the procedures used to ensure conformity of the product, and includes a technical
report or certificate from a Competent Body which are test facilities designated by member states as
able to make decisions regarding compliance with the EMC Directive. Once the TCF is completed,
the manufacturer files for declaration of compliance.
 Type acceptance - An EC type examination certificate issued by one of the Notified Bodies is
required. Notified Bodies are usually government agencies in member states.
10
In the United States, the MIL-STD-461D issued by the Department of Defense represents a
harmonized standard for military equipments and subsystems.
Even with all the work that has been done to harmonize EMC standards, there are still more than 20
European Norms on EMC, various MIL-STD-461 documents, different FCC Rules and Regulations
parts, and other EMC specifications from different industries. This still results in problems including
different test requirements and different limits and units of measurements. Currently, 5 certification
bodies in the world, North America's Underwriters Laboratories (UL), Germany's VDE, Italy's IMQ,
the UK's BABT, and the TUV Product Services have teamed up to issue an international EMC mark
to products that meet all of the standards followed by the major economies. Even though acquiring
this international mark requires product testing to comply to each standard and a high bill toward
testing charges, it is a good step toward achieving a global EMC compliance certificate for a product.
[Sampath97].
3.2 Available tools, techniques, and metrics.
EMI testing is needed because EMI predictions and analysis alone are inadequate to assure
compliance with EMI regulations. It is also necessary due to the complexity of design for EMC.
There are a number of methods and nomenclature used in measuring EMI emission and susceptibility
characteristics of equipment and subsystems. There are three levels of testing that exist and
generally, the higher the level of testing, the more difficult and expensive it becomes.

Low-level testing - Component, equipment, and subsystem testing. Basically, low-level testing
ensures that there will be very few EMI problems when testing at the next higher level.
 Intermediate-level testing - System and vehicle testing. This involves testing for EMI degradation
or malfunction due to self-jamming.
 High-level testing - Electromagnetic environment (EME) interaction with the test item. Even
after low-level and intermediate level testing, numerous problems can occur when the product is
operating in its natural environment. [Violette87]
EMI testing can also be divided into three categories - compliance, engineering, and audit testing.

Compliance tests - These tests are run to prove that the design meets appropriate EMI
requirements. These tests require very precise and absolute measurements, so expensive equipment
and experienced personnel is needed. Compliance testing is performed at the end of the design but
before sale of the product. Testing can be performed either using an independent EMI test
laboratory or an in-house EMI test laboratory.
 Engineering tests - The objective of these tests is to uncover potential problems early in the design
process. This is when you have the most time and flexibility in making design changes. Unlike
compliance testing, engineering testing does not require high precision and accuracy to obtain good
results, so simple tests with inexpensive equipment is satisfactory. EMI engineering tests are
performed in-house. Some tests include emission prescreening, ESD prescreening, RFI
prescreening, and power-disturbance prescreening.
 Audit tests - Audit tests are associated with manufacturing and quality, not with design. The goal
of audit testing is to ensure that the design stays intact through its product life. An example of audit
testing is statistical checks, where a unit is occasionally pulled off the production line and run
through a series of EMI tests. Screening tests on all production units can prevent faulty units from
leaving the production plant but it can be very expensive. [Gerke94].
4.0 Safety Measures
11
The need to identify sources, their frequencies and radiation intensities is to protect both the
user and the equipment. Therefore, safety measures are essential to visit for both humans and
equipment, considering all sources.
Humans: There is need for personal safety as well as safety of equipment. Power supplies, and
atmospheric and cosmic radiations are dangerous to people, who can be either electrocuted or
irradiated. Safety measures against these hazards are inescapably necessary.
Measures against Static Charges
When a computer is open either to repair, for example, to add RAM, upgrade your CPU or hard
drive, or plug in a new sound card or graphics in order to avoid static damage to your PC


Check your AC wiring: Before you can use the electrical ground in your home or office, you
need to make sure it's actually working. Old homes may have grounded outlets on the wall,
but they may not be grounded. And even new construction isn't necessarily safe, given the
time constraints of harried builders. The best way to check the wiring is to buy a wiring
checker. Sophisticated units can be expensive, but Radio Shack has a $20 tester (Catalog #
910-5501) that will tell you if the ground is working, and much more.
Use a wrist strap: The easiest way to dissipate static electricity is to use an antistatic wrist
strap, which connects to your AC ground. Follow the manufacturer's instructions carefully to
connect it. Wrist straps are available in a wide variety of models, from disposable units for
under $10 designed for one-time use , to $50 units designed for those who use them
regularly. Sources include ESD Systems, Radio Shack, and Visiflex Static Solutions. If you
don't want to deal with a ground, $39 cordless wrist straps, based on a technology that uses
the Corona principle to dissipate static without using a ground, are also available at
Directron.com. Industry experts say they're not as effective as a true grounded wrist strap,



but they're better than taking your chances.
Use additional antistatic components: If you work with computer upgrades regularly,
consider investing in additional antistatic measures, such as grounded pads that you can lay
your PC case on when you work with it. (You should still use a wrist strap.) The companies
listed above have a wide range of products to choose from.
Prepare your work area: Make sure the area where you're working on your upgrades isn't
full of other static-inducing components. A bare table is best. Keep plastic desk accessories,
wastebaskets, and telephones away from your work area. And one of the worst creators of
static charge is a rolling desk chair. Push it away, and stand up when you're working on your
PC.
Control the humidity: The lower the humidity, the more likely it is that damaging static
charges will build up quickly. If your ventilation system allows you to control it, a humidity
level between 35 and 50 percent is ideal. If you can't control your humidity, don't do upgrades
on a cold winter day when the humidity tends to be very low, or on a warm day with the air
12
conditioning turned up high. If you live in an area where the humidity is generally high, it's not
a bad idea to open the windows while you do your upgrades.
While the precautions above cannot guarantee prevention to static electricity discharge, they
will at least reduce the chances that your computer memory or hard drive upgrade being
permanently damaged.
 Measures against Surges
LEMP surges are directed to the ground by dedicated primary Lightning Protection Systems
(LPSs) comprising the aerial termination, down conductor and the earthing system. Fig. 4
shows such systems conducting lightning channels on buildings.
FIG.4: LIGHTNING INTO PROTECTED BUILDINGS.
Switching surges and surges induced into power supply systems and transmitted to equipment
are protected by equipotential bonding and earthing. The purpose of equipotential bonding is
to bring metallic objects to the same potential, thus reducing the shock hazard.
For coaxial cables used on antennas, devices such as the COAXTRAB and bonding in Figs.5 and
5 are used.
13
FIG.5: EARTHING OF A COAXIAL CABLE.
*Ground connections at the antenna – The black conductive grease that is visible around the connections is
Ideal brand Noalox and prevents deterioration of the electrical conductivity due to corrosion. This is
especially important when bonding two dissimilar metals as in this picture of copper wire bonded to a
galvanized steel antenna mast.
FIG.6: A COAXTRAB.[ 4,5]
For a metallic antenna tower, Fig.5 shows the earthing.
Fig.7: EARTHING FOR A METALLIC ANTENNA TOWER
14
Fig.8 A computer room requires both equipotentialization and earthing.
REFERENCES
1. Eushiuan Tran, Carnegie Mellon University, 18-849b Dependable Embedded Systems.
2. Safe Engineering and Technologies Ltd.
3. Peter B. Ladkin, et al. , Electromagnetic Interference with Aircraft Systems, why worry?,
http://www.rvs.uni-biefield.de/publications/
4. Violette, J.L. Norman, White, Donald R.J. and Violette, Michael F., Electromagnetic Compatibility
Handbook, New York: Van Nostrand Reinhold Company, 1987.
5. [Caruso96] Caruso, Hank, "An Overview of Environmental Reliability Engineering," Proceedings of
Annual Reliability and Maintainability Symposium, Las Vegas, NV, 1996, pp. 102-109.
6. [Gerke94] Gerke, Daryl and Kimmel, Bill, "ESD as an EMI problem ... how to prevent and fix,"
EDN's Designer's Guide to Electromagnetic Compatibility, vol. 39, no. 2, January 20, 1994, pp. 2332.
7. An overview of what is ESD, the EMI problems related to ESD, and how to prevent these problems.
8. [Gerke94] Gerke, Daryl and Kimmel, Bill, "Radio-frequency interference ... why computers and
radios hate each other," EDN's Designer's Guide to Electromagnetic Compatibility, vol. 39, no. 2,
January 20, 1994, pp. 33-40.
9. An overwiew of what is RFI, the EMI problems related to RFI, and how to prevent these problems.
10. [Gerke94] Gerke, Daryl and Kimmel, Bill, "EMI testing ... if you wait until the end, it's too late,"
EDN's Designer's Guide to Electromagnetic Compatibility, vol. 39, no. 2, January 20, 1994, pp. 101108.
11. The different categories of EMI testing which are compliance testing, engineering testing, and audit
testing.
12. [Sampath97] Sampath, K., Subramanian, C., and Das, Sisir K., "Harmonization of International
EMC Standards," Proceedings of the International Conference on Electromagnetic Interference and
Compatibility, Chennai, India, 1997, pp. 127-132.
13. [Siewiorek91] Siewiorek, Daniel P. and Koopman Jr., Philip John, The Architecture of
Supercomputers - Titan, A Case Study, San Diego, CA: Academic Press, Inc., 1991.
14. [Violette87] Violette, J. L. Norman, White, Donald R. J., and Violette, Michael F., Electromagnetic
Compatibility Handbook, New York: Van Nostrand Reinhold Company, 1987.
15. ECMA International Technical Report – ECMA TC20 2008 054 – Guide for assessment of human
exposure to electromagnetic fields from multimedia products in accordance with IEC/EN62311.
16. Feasibility study to apply total radiated power measurements for EMF assessments. EMC center
memorandum EMC-08-PAB-006-MEM, Pierre Beeckman, dated 2008-09-16.
15
17. D. B. O. Konditi, J.K. Makiche, H.A. Ouma, C.O. Adika, E.K. Koech and V.M. Dharmadhikary,
Practical and Theoretical Evaluation of EMC/EMI Problems of Metallic Enclosures with Apertures,
IJTPE, ISSN: 2077-3528, Nov. 2010.
18. Reverberation Chamber Calibration Process for EMF TRP measurements– EMC Center
Memorandum EMC-09-KB-MEM, Konika Banerjee, dated 2008-04-01.
19. IEC 61000-4-21 – International standard – Testing and measurement techniques – Reverberation
Chamber test methods.
20. TCN68-140:1995: Protection of telecommunication lines and equipment against over voltages and
over currents - Technical requirement.
21. TCN68-167:1997: The devices for protection against over voltages. Over currents from lightning
discharges and electric power lines - Technical requirement.
22. ITU-T (1978) : The protection of telecommunication lines and equipment against lightning
discharges, Chapters 6,7 and 8.
23. IEEE Emerald Book; IEEE STANDARD 1100-1999, Recommended Practice for Powering and
Grounding for Sensitive Electronic Equipment, IEEE Standards Department, Piscataway, NY.
Paul Frame, CHP, PhD,
24. http://openlearn.open.ac.uk/mod/oucontent/view.php?id=397533&section=2.2.1IEC
62311
–
International Standard – Assessment of electronic and electrical equipment related to human
exposure restrictions for electromagnetic fields (0 Hz – 300 GHz).
25.
26. http://www.williamson-labs.com/index.html
27. http://www.ecma-international.org/activities/Hardware/tc20-2009-019.pdf
28. http://pdf.directindustry.com/pdf/dehn-sohne/lightning-protection-main-catalogue/12397-88012_5.html
29. http://pdf.directindustry.com/pdf/dehn-sohne/safety-equipment-main-catalogue/12397-88014.html
29. http://www.lerdn.com/English/pdf/computerroom.pdf
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31. http://www.dehn.de/en/products/pdb_e.shtml
Appendix
List of equipment
The list of essential equipment and the associated frequency ranges are listed in Table 1.
Table 1 Equipment list
Version : 3.0 No. Description
1. Reverberation Chamber
2. LogPeriodic antenna
3. Horn antenna
4. LF Band Pass Filter
5. HF Band Pass Filter
6. Pre-amplifier
7. Power sensor
8. Power meter
Type/id Frequency range ETS Lindgren
(MSC14) 80 MHz – 18 GHz
ETS Lindgren 30 MHz – 2 GHz
EMCO 3050 1 – 18 GHz
Mini circuits 100 MHz – 1 GHz
SHP 100+ and SLP 1000+
Mini circuits 1 – 6 GHz
SHP 1000+ and VLF 6000+
Miteq CE 50359 100 MHz – 26 GHz
R&S NRV-Z2 10 MHz – 18 GHz
R&S URV5 9 kHz – 18 GHz
16
Appendix B: Fig 8 Anechoic Chamber Test Equipment Arrangement
About The Author
Dominic Bernard Onyango Konditi was born in Kochia, Homa - Bay County, in July 22, 1950. He received his
Master’s Degree in Electrical Engineering from Tottori University, Japan, in 1991 and Ph.D degree in
Electronics and Computer Engineering from Indian Institute of Technology (IIT) Roorkee in 2000. He was
awarded a Gold Medal for the best Application -Oriented paper published in The Institution of Electronics
and Telecommunications Engineers (IETE) Journal in 2001. He is Associate Editor of International Journal
on Measurement Technologies and Instrumentation Engineering (IJMTIE), 701 E. Chocolate Avenue Hershey,
PA 17033-1240, USA. He was Plenary Speaker delivered talk on A Review of the Biological Effects of
Extremely Low Frequency-Electromagnetic Fields Associated with Electric Power Systems, at Technical
and Physical Problems of Electrical Power Engineering (TPE-09) Conference held at Ibis Bilbao Centro,
Spain, Sept. 2009 and gave invited talk on Telemedecine:21st Century Innovative Technology at IEEEMultidisciplinary Aspects of Engineering IMAE 05, IEEE Bombay Section, held at Hotel Le Meridian, INDIA on
January 3-5, 2005. He has authored and co-authored over fifteen (15) papers in reputable journals and
over 10 papers in refereed conference proceedings. He has supervised two (2) PhD students and over
thirteen (13) MSc degree students successfully in the area of telecommunication engineering. He has been
a reviewer for RadioScience, World Scientific, Engineering Academy and Society (WSEAS), and JAGST
journals and Taylor & Francis Co. book chapters. He has been cited in The Marquis WHO’S WHO in Science
and Engineering, USA, and Cambridge Bibliographic Society, England. Konditi is Associate Professor of
Electrical & Communication Engineering and was the founding Dean of the Faculty of Engineering, and is
currently the Director for Centre for Sustainability and Sustainable Development Studies at Multimedia 17
University of Kenya.