Electronics Material Officer Course

MODULE NUMBER THREE

LESSON TOPIC TWO

ELECTROMAGNETIC INTERFERENCE CONTROL

LESSON TOPIC OVERVIEW

LESSON TOPIC TWO

ELECTROMAGNETIC INTERFERENCE CONTROL

This lesson topic presents information about your responsibilities concerning electromagnetic interference control, what it is, how it effects equipment, and program requirements.

The LEARNING OBJECTIVES of this LESSON TOPIC are as follows:

The student should review the "LIST OF STUDY RESOURCES" and read the Lesson Topic LEARNING OBJECTIVES before beginning the lesson topic.

LIST OF STUDY RESOURCES

ELECTROMAGNETIC INTERFERENCE CONTROL

To learn the material in this LESSON TOPIC, you will use the following study resources:

Written Lesson Topic presentations in the Module Booklet:

Additional Materials:

References:

LESSON TOPIC SUMMARY

ELECTROMAGNETIC INTERFERENCE CONTROL

This lesson topic introduces you to electromagnetic interference. Your will learn the definition, sources, and means of controlling EMI. You will also learn how to resolve EMI problems, where to seek assistance, and the content of applicable references. The lesson narrative is organized as follows:

NARRATIVE FORM

OF

LESSON TOPIC 3.2

ELECTROMAGNETIC INTERFERENCE CONTROL

The following is an excerpt from a CNO message to all Flag Officers: "EMI jeopardizes our Navy's warfighting ability. It degrades, even disables, the very electronic systems we depend on to provide a decisive edge. I am determined to restore lost combat capability, to prevent future degradation, and to give the fleet an organic capacity to control and cope with EMI. Correction of EMI is a top priority and requires both awareness and active intercession by all hands."

As more complex systems, with higher power and greater receiver sensitivity, are crowded into a restricted and corrosive environment, the environment itself becomes a major limitation to the effective employment of the ship's systems. The problem is further aggravated by the requirement that all systems operate simultaneously, while still performing to specifications. Thus, the ship must be treated as a combination of systems whose overall performance depends on system-to-system and platform-to-system compatibility. The ability of an equipment or system to operate in its intended electromagnetic environment (EME) without suffering degradation caused by EMI is known as electromagnetic compatibility (EMC). Another source of interference or degradation is an electromagnetic pulse (EMP). EMP is a brief, intense burst of EM energy created by the explosion of a nuclear weapon or by lightning. It can result in system and component damage or degradation.

Electromagnetic interference (EMI) is an electromagnetic or electrostatic disturbance that causes electronic equipment to malfunction or to produce undesirable responses or conditions. As EMO, you must be aware of the problems caused by EMI and solutions to these problems. A requirement for EMI certification was promulgated in 1988 for all ships in the fleet and new constructions, requiring backfit on the former. The program was actually implemented in 1991. The west coast is relying primarily on the Waterfront Corrective Action Program (WCAP) and the east coast on industrial/NAVSEA processes. Expect INSURV to include EMI certification as a requirement.

There are three elements to every EMI problem, comprising the EMI triangle: source, victim, and a means of transferring energy called the coupling path. Each EMI problem can be characterized by the use of the EMI triangle (Figure 3.2-1). Each side of the triangle represents an element of an EMI interference condition. When an EMI problem is encountered, resolution involves making a determination of which side(s) of this triangle can be most effectively removed or controlled.

Figure 3.2-1 EMI Triangle

SOURCES OF ELECTROMAGNETIC INTERFERENCE (EMI)

The key to reducing shipboard EMI is to first identify the source of the offending electromagnetic energy, then to determine a method of correction and, finally, to correct or minimize the effect. The sources of electromagnetic energy affecting shipboard systems fall into four broad categories:

Natural EMI is caused by natural phenomena, such as electrical storms, rain, particles, and solar and interstellar radiation. It is recognized by the following audible noises:

Incidental EMI can originate from manmade sources that are not designed specifically to generate electromagnetic energy, but which do, in fact, cause interference. Examples of incidental EMI sources include power lines, motors, and switches.

Functional EMI can originate from sources that are designed to radiate electromagnetic energy. These signals are potentially major sources of interference to receiving equipment. Interference may be unintentional, caused by other on board or adjacent platform systems, or intentional (EA).

Hull-generated EMI can be caused by the radiated energy interacting with elements of the ship's hull and rigging which can serve as efficient RF antennas. This interaction generally results in one of the following types of interference:

Interference that occurs as the result of mixing two signals (heterodyning) in a nonlinear element such as the first stage of a receiver or the final stage of a transmitter. The nonlinear element may also be external to the equipment, as in nonlinear junctions, or "rusty bolts." A nonlinear junction is the contact area between two metallic surfaces which exhibits nonlinear voltage-current transfer characteristics when subjected to an RF voltage, usually due to corrosion or other semi-conducting material in the contact area. Mixing may generate a new signal of sufficient amplitude to be detected as interference. The number of these signals depends on the number of transmitters "on the air." These new signals are called intermodulation products, and radiate into the environment from the same hull and superstructure elements that received the original RF signals. IMI occurs at discrete frequencies, and may appear as BBN under severe conditions.

Elements of the ship's superstructure are susceptible to high levels of induced RF voltage from nearby transmitter antennas. If the induced voltage levels are high enough, an electrical arc may be generated. This arc will, in turn, generate a broadband spectrum of electromagnetic energy, resulting in BBN. RF arcing may be continuous, depending on conditions, but it is usually intermittent, much like energy noises generated by nearby electrical storms. Frequently, such arcing occurs between loose or broken elements of an antenna. Other sources of broadband noise include various metallic structures in which RF currents are induced. These structures may include items such as lifelines with corroded sister hooks, broken corroded welds on liferails, loose metallic objects stored on deck such as pipes, ladders, and spare wire, and safety chains. When a ship is at sea, in constant motion because of pitch and roll, the movement of these structures in the topside area of the ship can increase BBN. If these same junctions are corroded as well as rubbing or touching each other, they can also produce IMI. BBN often proves to be from the same source as IMI. BBN levels may be of sufficient magnitude to mask IMI.

While little can be done to control natural interference, operational work-arounds (e.g., frequency management) may help to minimize its impact upon ship operations. However, much interference that is assumed to be natural is actually functional, incidental, or hull-generated.

Therefore, you need to investigate all interference to verify whether or not it is natural EMI, before selecting a corrective action. Incidental EMI usually can be eliminated, or effectively controlled, at its source by proper design, installations, and maintenance. Functional EMI poses a more difficult problem, since the source of the interference generally is essential to the operation of the equipment. In complex systems, such as communications, radar, or electronic warfare (EW) transmitters, the generation of the functional signal often results in generation of undesired electromagnetic energy at frequencies other than the operating frequency. These spurious outputs, which adversely impact total ship system performance, should be eliminated, or reduced to an acceptable level, by the application of proven EMI-reduction techniques. Many of these techniques are available to, and can be applied successfully by ship's force. Hull-generated EMI is of particular concern. The resulting intermodulation or broadband interference effects can easily mask a host of other EMI problems.

EMI is coupled between systems by a radiated path, a conducted path, or sometimes by a radiated and then conducted combination path. No interference condition can exist unless the EMI source is coupled to the EMI victim through a coupling path; therefore, elimination of this path provides another possible solution to resolving any EMI problem.

Radiated EMI is transferred through space to the EMI victim by an electromagnetic field. The radiated field escapes from or is radiated intentionally by an EMI source and spreads out in free space according to the laws of wave propagation. When this radiated field transfers energy to a EMI victim (susceptible device), it has followed a radiated coupling path.

Conducted EMI is transferred through conductors between an EMI source and an EMI victim. This requires a complete electrical path for flow of interference currents between them. The path can be made entirely of metallic conductors, or the return path may be through the earth or a common ground.

Any equipment or system capable of responding to electromagnetic fields or to electrical signals must be considered a potential victim. One of the basic objectives of the Department of Defense (DOD) is to provide equipment and systems whose performance will not be adversely affected by EMI. The effects of EMI on a system may be either permanent, during which the system will not operate until the problem has been corrected, or temporary, during which the system will operate in a degraded mode while EMI is present. Examples of the different effects that can be produced, depending on the victim, are:

RESOLVING EMI PROBLEMS

Several MRCs include checks for the presence of EMI sources and victims. These MRCs include visual and operational checks of equipment and systems.

During class A and C schools, technicians are taught to recognize and correct shipboard EMI problems.

Normally billeted to FTSCs, IMAs, and mission essential units, these technicians perform RADHAZ monitoring and perform tests, measurements and analyses of systems and equipments using a wide variety of electronic test equipment to determine the presence or severity of EMI. The NEC is acquired by attending course A-101-2050.

IMAs provide on-call assistance in matters related to EMC and RADHAZ. Assistance includes topside visual surveys, and EMI problem location and resolution using approved techniques.

The SEMCIP is a CNO sponsored, NAVSEASYSCOM managed program that identifies and develops fixes for EMI problems. SEMCIP provides the following:

This is the engineering, problem-solving, and R&D arm of SEMCIP. It provides teams of highly skilled technical personnel to test, evaluate, research, and develop corrections for individual shipboard EMI problems on a quick-response basis and provides full-scale EMC evaluation and total ship analysis. SEMCIP engineering teams provide shipboard testing and engineering analysis in all areas of ship operation affecting EMC and have trained experts in the following areas: communications, radar, electronic warfare, RADHAZ, sonar, and EMC problems encountered in belowdecks equipment, such as propulsion control systems.

This is the groom-and-fix-it area of SEMCIP that you will deal with continually. WCAP is responsible for locating, evaluating, and correcting known EMI problems on individual ships. WCAP provides the following:

SEMCIP Industrial Electromagnetic Compatibility Program

This portion of SEMCIP is targeted toward incorporating EMC corrective measures in ship construction, modernization, overhaul, and repair processes. IEMC preserves corrections made in

the field by SEMCIP engineering and WCAP as well as assuring that EMC has been included in

alteration and repair planning. The IEMC portion of SEMCIP also provides manufacturing capability for prototype development and testing of proposed EMC-correction devices or materials.

The STAN is an on-line database geared to provide the EMI engineers and technicians with access to the latest information on the status of EMI problems. It also provides ship administrative information to assist in all phases of SEMCIP and information on the development, installation, and verification of known fixes. Additionally, STAN contains Electromagnetic Control Topside Arrangement Drawings. STAN information is accessible by the fleet through the WCAP. The EMC Program Manager and WCAP Program Manager can be contacted at (703)602-2549/2597, DSN 332-2549/2597 at SEMCIP Headquarters (NAVSEA O6K23). SEMCIP publications can not be obtained through the supply system. To obtain publications, contract NAVSEA.

The U.S. Navy relies on radar, electronic warfare, and communications to make a battle group combat ready. A typical group of twelve ships has approximately eighty radars and twenty EW systems that can interfere with each other unless their frequencies are properly managed. The CSFMP provides information the fleet requires to achieve EMC. Additional frequency management tools are: frequency propagation charts, radio propagation forecasts, the Recommended Frequency Bands and Frequency Guide (NTP 6, Supplement 1), frequency prediction information from shore communications stations, Chirpsounder data, and EMCAP. The Chirpsounder AN/TRQ-35 Tactical Frequency Management System (TFMS) is composed of transmitters ashore and a receiver/spectrum analyzer on designated afloat units. Chirpsounder provides a display of HF frequencies that are propagating, signal strength, signal path, and multipath areas to be avoided. A cathode ray tube displays 110 kHz or 500 kHz in the 2-30 MHz range, centered on a chosen frequency. Additionally, a monitor displays up to the last thirty minutes of utilization of all frequencies. EMCAP is discussed in greater detail in the following paragraphs.

EMCAP is an automated frequency management tool for maximizing EMC among surface and airborne weapon systems. EMCAP products include the NAVSEA T9407-AA-GYD-010(C) Electromagnetic Compatibility Criteria for Surface Weapon Systems, EMCAP software, and the CSFMP newsletter. The EMC or EMCAP coordinator uses T9407 or EMCAP software on a AN/UYK-20 computer and inputs information on force composition, force-level information, and initial assignments of participants to identify and disseminate frequency and channel assignment information to force participants (e.g., battle group). T9407 is a primer on interference and propagation that provides:

EMCAP software is an automated tool to determine compatibility assignments. EMCAP software is executed on the ship's AN/UYK-20 computer. EMCAP software:

CSFMP News is a published semi-annually by the Combat Systems Frequency Management Program that includes frequency management information, current events, a question and answer section, and the next fleet distribution of EMCAP and T9407.

One of the keys to effective and long-lasting EMI reduction and control is the proper installation of EMI control measures. The following paragraphs will review a number of documents and procedures currently available to help you ensure that your ship's EMI control techniques are correct.

Shipboard Bonding and Grounding Methods and Other Techniques for EMC and Safety provides requirements for shipboard bonding, grounding, shielding, and the use of nonmetallic materials to reduce EMI and IMI, to protect personnel from electrical shock, and to protect electronic equipment from an EMP. The requirements specified in MIL-STD-1310 apply to all ships, including submarines and nonmetallic hull ships, during normal operational periods and during periods involving construction, overhaul, alteration, and repair. If you notice any conflicts between MIL-STD-1310 and other publications, specifications, standards, or drawings, notify either the SUPSHIP or NAVSEA. Electromagnetic control topside arrangement drawings are available to help you apply MIL-STD-1310 requirements. Due to cost impact, the EMP protection requirements specified by MIL-STD-1310 are not implemented routinely, but only when specifically authorized. To provide protection to solid-state electronics, MIL-STD-1310 provides additional requirements and details for EMI and EMP protection. Hardware to accomplish this protection has been developed and installation methods have been detailed. The bonding, grounding, and shielding requirements for both EMP protection and EMI reduction are

similar, since the intent in both cases is to keep electromagnetic radiations (EMP and HF antenna radiations) from coupling to equipment below deck. MIL-STD-1310 does not specify methods for achieving EMI reduction through equipment design, frequency selection, limits on operating power, equipment location, or use of multicouplers or blankers. These requirements are contained in other publications.

MIL-STD-1310 is augmented by the Handbook of Shipboard Electromagnetic Shielding Practices (S9407-AB-010). This handbook specifies cable spacing and shielding requirements and installation procedures that minimize the effects of EMI on installed electronic equipment.

The Commanding Officer's Guide to the Shipboard Electromagnetic Environment provides to the ship's commanding officer, executive officer, or other appropriate personnel a ready reference that describes the causes and effects of EMI problems typically found aboard ship. It identifies the following:

The Electronic Material Officer's Guide to Shipboard Electromagnetic Interference Control provides appropriate EMC information, based on SEMCIP "lessons learned," to EMOs afloat and to facilities that train prospective EMOs and other supervisory personnel involved in the maintenance of electronic systems. Its format allows you to use it as a management tool and as a guide for achieving EMC by coordinating EMI control actions. It recommends a plan for management controls and procedures for dealing with common problems.

Standard EMI Survey Procedure provides standardized EMI survey test requirements and methods for conducting all EMI surveys. Test philosophy is included so that planning and test personnel will know why as well as how tests are to be performed.

SEMCIP Standard Operating Procedures (SOP) provides comprehensive procedures for you to follow in complying with the directives and policies of navy EMC under the cognizance of the SEMCIP.

The EMI Reduction EIMB Handbook provides techniques for EMI reduction and elimination.

Electromagnetic Compatibility, Theory, and Concepts provides an overall review of the most current information available on EMC as it applies to U.S. Navy ships. It is intended to be the reference for modern-day electromagnetic interference (EMI) identification and reduction techniques. It also serves as a general reference guide for navy and civilian engineers, technicians, and technical supervisory personnel as the most current EMC information available. The "1779" is for use by all levels of personnel involved in EMC. It applies to both the day-to-day EMI reduction efforts conducted by ship's force personnel and to the EMI control functions carried out by the EMC engineer. The information applies to all U.S. Navy ships, including submarines and nonmetallic hull ships, during periods of normal operation and during ship construction, overhaul, alteration, and repair. Any conflict between this standard and other standards, drawings, publications, etc., should be reported to NAVSEASYSCOM, Code 06D44, Washington, D.C., for resolution.

This publication provides standardized procedures to be used for installing shipboard electrical and electronic systems. The IEMC WPI is intended for use as a working document for navy and industrial personnel involved with shipboard electrical and electronic systems. It is based on the information provided in MIL-STD-1310 and other formal navy specifications, standards, and current publications.

PROCEED TO ASSIGNMENT SHEET 3-2-1A IN THE ASSIGNMENT BOOKLET. UPON COMPLETION, TAKE THE ASSIGNMENT BOOKLET TO THE LEARNING CENTER INSTRUCTOR.