ABSTRACT The electromagnetic envi- ronment of today’s surface combatant is both extremely complex and dynamic in nature. The quantity, sophistication, and sensitivity of the installed communication systems have grown in concert with the techndogical advances of the electronics industry The evolution of new electronic systems has yielded not only new sources of electromagnetic interference (EMI) but also an increased susceptibil- ity to existing EMI. However, the traditional EM1 abatement efforts, though productive, have failed to keep pace with emerging EMI-induced prob- lems.

Those facts suggest the need for a new approach to EMI. This paper describes a new concept that enables us to intelligentlv predict EM1 impact and achieve a system configuration that maxi- mizes circuit effectiveness while minimizing the degradmg consequences of EMI. We discuss use of the enhanced data processing capabilities of today’s personal computers and the new genera- tion of automated test equipment to develop software and data coUection methods to obtain, quantlfy and reduce the diverse radio frequency spectrum variables. Once the data are accumulated in a common database, they can be tailored to a specific end user’s opera- tional requirements. The resultant frequency infonnation can be displayed in a simplified and informative manner suit- able for use at all levels of expertise from fleet operator to radio communications system (RCS) system design engineer.

Stephen Valvonis, La\ &John M. Krawchuk

EM1 Avoidanc A New Front in the

Introduction

lectromagnetic interefer- ence is perhaps one of the most s eve re concerns faced by the naval com-

munications community today. EMI and the attempts at EM1 resolution have been the primary causes of problems ranging from a minor com- munications circuit or system degra- dation to major tragedies. For ex- ample: H EM1 triggered an aircraft rocket

detonation that killed 134 crew- men aboard USS Fmrestal in the late 1960s. [l]

H Attempts at resolving the mutual EM1 between the anti-ship missile defense radar and satellite com- munications secure voice system included securing the ship’s anti- ship missile radar during satellite voice operation. This created a vulnerability that caused the loss of the HMS Sheffield during the Falklands War. The satellite com- munications secure voice system was being utilized; therefore, the missile defense radar was secured and unable to detect the inbound missile. [l] Additionally, the number of high-

powered emitters has grown to the point that tradeoffs must be made be- tween battle readiness and safety of personnel. The increase in the power and quantity of communications transmitters has yielded a dramatic

Siephen Valvonis is a project engi- neer at Naval Command, Control and Ocean Surveillance Center Inservice Engineering East Coast Division (NISE East Det). St. Inigoes, Md., in the Ship- board Communications Integration

NAVAL ENGINEERS JOURNAL

urence T. Nosek,

EM/ Battle

Division for DDG-51 AEGIS class destroyers. He graduated from Wilkes University in 1992 with a Bachelor of Science Degree in Electrical Engineering and a minor in physics. While at NEE East Det, he attended a class on electro- magnetic inte@-ence (EMI) and control at George Washingtan University’s Continuing Engineemg Education Program. He is current& a member of Sigma P i Sigma, Physics National Honw Society, and IEEE. John M. Krawchuk is ajieid engineer with the Electronic Systems Division (ESD) of Tracor Applied Sciences, Inc. A s a member of the ImpactlFeasibility Studies group, he provides engineering support to NISE East Det. After attend- ing the Communiiy College of Philadelphia, he entered the US. Nauy in 1969 as an electronics technician. He co- authored a course of instruction fm FFG- 7 Combat Systems maintenance and management while assi’d to the Naval Guided Missile School, Dam Neck, kh. At the Fleet Training Unit, Atlantic Fleet, he conducted combat systems training fm N a y and Coast Guard ships rangrng from airraft cam’ers to icebreakers. He retured from the N a y in 1990 while sm- ing as the station maintenance chief at the Naval Communications Unit, Cutlq Maine. Lawrence T. Nosek is also with ESD of Tracor Applied Sciences, Inc. As a senior engineer in the ImpactiFmibility Studies group of the Engineering Dtpart- ment, he provides enginem‘ng support to NISE East Det in the integration of radw communications systems on Arleigh Burke (DDG-51) class AEGIS destroys. During 22 years of Naval service as an electronics technician, he served as chief instructor at both Patrol Hydrofbil Missile Ship Squadron Two and the Electronics School at the Fleet Training Centq Ndolk , k. A graduate of the Senior Enlisted Academy, Newpwt, R.I., his last duty station was the USS Guadalcanal (LPH-7). He is pursuing an Electrical Engineering degree at Capitol College and is a member of the Antenna Measure- ment Techniques Association.

January 1995 63

€MI Avoidance

increase in the potential for crew members receiving radio frequency (RF) burns. [13 rn Manually operated hull, machin-

ery, and electrical (HM&E) sys- tems are being replaced with EMI- susceptible, automated systems. I t is a proven fact that EM1 to HM&E systems can stop a ship dead in the water. [2J Various programs such as the

Ship’s Electromagnetic Compatibility Improvement Program (SEMCIP) and the Waterfront Corrective Ac- tion Program (WCAP) have been im- plemented to resolve the identified EM1 problems. Yet increases in the quantity, sophistication, and com- mensurate susceptibility of new ship- board communication systems con- tinue to generate new EMI-related problems at a rate greater than so- lutions can be developed and imple- mented. Although individual equip- ment and systems may be designed and built to comply with MIL-STD- 461 (Electromagnetic Emission and Susceptibility Requirements for the Control of Electromagnetic Interfer-

The primary thrust of our proposed approach is the avoidance, rather than the elimination, of EM1 through man- agement. This innovative strategy en- tads employing current technology to quant& analyze and reduce the var- iables of the existing comunication system’s EM1 environment so that in- telligent, informed decisions concern- ing those variables can be made. These decisions, based on hard data rather than conjecture, permit safe and effective operation of the com- munication system through manage- ment of EMI. Thus, we learn to co- exist with EM1 while other programs work to eliminate it.

rnary thrust of posed approach

avoidance, rather than the elimination, of EM1 through ence), the synergistic effect pro-

duced when the equipment is inte- grated a s a radio communications system (RCS) frequentiy generates management. unforeseen EM1 problems. Gener- ally, these problems are discovered by trial and error during use or as a result of investigations to determine the cause of degradation or failure of other shipboard systems.

Data Collection Previous efforts to collect and quan- tify the data necessary to understand

Potential Solution While efforts to rid ourselves of EM1 problems through corrective design and maintenance persist, we must ac- knowledge that EM1 is a permanent element of the communication envi- ronment. Clearly, we must learn to manage it wisely and effectively to re- duce the effects of increased numbers of known and unknown EMI-related problems. We must afford both the design engineer and fleet operator alike the opportunity to analyze and forecast the impact of EM1 on a com- munication system.

and manage the EM1 environment were hampered by the sheer volume and complexity of the dormation to be captured and analyzed. Just col- lecting data from one particular ship to construct a comprehensive com- munications EM1 database is an im- posing task. For example, to capture the desired data on an AEGIS class cruiser as currently configured, we must take 24,276 distinct measure- ments to quantdy the mutual coupling between the communications anten- nas. This includes data from the four communications frequency bands spanning 2 MHz through 400 MHz:

high frequency (HF), very high fre- quency-low (VHF-LO), very high frequency-high (VHF-HI), and ultra high frequency (UHF). However, we can quickly collect this data using cur- rent technology personal computers (PCs) and new-generation test equip- ment that automatically records the measurements needed for the data- base. We have found that one person can operate the equipment and, using a PC and self-written software that automates a spec t rum analyzer/ tracking generator combination, col- lect the requisite system coupling data in approximately one week. The coupling data can then be merged with information gathered during sep- arate testing that incorporates the variances introduced by the mode of operation, whether teletype (TTY), data, or voice. Such an integration yields 218,484 distinct data items. With PCs and software, we are able to reduce and manipulate this vast amount of information to suit a spe- cific end user’s operational require- ments. The data can then be dis- played in an easy-to-use format.

Converting thls extensive data col- lection to useful information is not a complicated process. The number of possible applications to an end user’s requirements is lunited only by the user’s creativity NISE East Detach- ment, St. Inigoes engineers recently conceived two applications, wrote the necessary software, and successfully ran the programs for demonstration purposes. One program was devel- oped for use at the operator level whde the other may be employed dur- ing the system design phase.

Use at the Operator Level The .AEGIS RCS EM1 avoidance computer program, written in C + + on a 386 PC, allows the RCS operator to forecast and avoid potential EM1 from a proposed system configura- tion. This relatively simple to operate application is designed to be platform specific. Approximately two weeks is

64 January 1995 NAVAL ENGINEERS JOURNAL

EMI Avoidance

required to gather and process the mutual coupling data for a hull the size of an AEGIS cruiser. The program and associated data fit on a single floppy diskette and can be run on any 286 or faster PC.

During initial program installation aboard a given ship, transmitter, re- ceiver, multicoupler, and antenna RF coupling data are entered into the pro- gram along with the EM1 environ- mental data. Thereafter, for hulls presently configured with non-auto- mated RCS, the operator need only enter specific transmitter and re- ceiver frequency and circuit configu- ration information from the commu- nications plan to maintain a current EM1 avoidance data base. However, when used with the future automated RCS configurations, thls program will automatically collect information di- rectly from the equipment. No oper- ator data entry will be necessary. With either configuration, the data can be stored to virtually any form of media for future recall.

The EM1 avoidance computer pro- gram provides specific information concerning EMI-related problems re- sulting from a proposed configura- tion. In Figure 1, a sample printout of reduced data displays some of the in- formation available to the operator. In this case, the operator sees which specific transmitters and frequencies will cause interference; the re- ceiver(s1 and frequencies that will be affected, and the level of the interfer- ing signal in dB above the receiver’s threshold. Any proposed configura-

tions or frequencies that might result in radiation hazards (RADHAZ) or Hazards of Electromagnetic Radia- tion to Personnel (HERP) are re- jected and a warning message is dis- played to iden@ the safety problem. As presently designed, the program also rejects entries that do not prop- erly match transmit and receive fre- quencies to the requirements of as- sociated peripheral systems. The

rogram and iated data fit on a floppy diskette

and can be run on any

286 or faster PC.

operator may easily tailor the data- base to set up parameters to guide him in configuring a system. For in- stance, adding variables identified as producing EM1 detrimental to weap- ons, engineering systems and other combat systems could cause the pro- gram to highhght and reject circuit configurations and frequencies.

Use at the System Design Engineer Level The other application in use at NISE East Detachment, St. Inigoes is a

system-level engineering program written for Microsoft Excel. This pro- gram and its associated data also fit on one floppy diskette that can be run on any 286 or faster PC. It employs the EM1 environment database to give graphic feedback of problems that wdl be encountered when a given combination of frequencies and equip- ment is to be used. The system de- sign engineer may access more vari- ables with which to analyze the potential impact of EM1 from changes made to RCS parameters. For exam- ple, a design engineer enters data about the following proposed scena- rio: an ANNRT-23 transmitter d be energized at 29 MHz, transmitting 1,000 watts, and will be coupled to antenna 2-4 using an ANNRA-38 an- tenna coupler. Figure 2 presents the feedback received concerning poten- tial problem areas produced by the second through fifth harmonics of the fundamental frequency. As can be seen, an ANNRC-46 operating at 58 MHz, coupled to antenna 3-2, wdl ex- perience severe interference from the AN/URT-23 at a level over 70 dB greater than its sensitivity threshold. An ANIGRC-211 transceiver, coupled to antennas 3-3, 3-7, or 3-11, vvlll ex- perience interference at both 116 MHz and 145 MHz.

The reduced data indicate that se- lecting different frequencies or modi- fylng circuit configurations would de- crease the interference. For example, Figure 3 shows the results of couphg the ANNRT-23 antenna to antenna 2-3 using an AN/SRA-58 multicou-

POSSIBLE SELF-GENERATED EM1 ** dB ABOVE RECEIVER SENSITIVITY

TRANSMITTER FREQUENCY RECEIVER FREQUENCY ** AN/URT-2 3 AN/URT-2 3 AN/URT-2 3

5.7900 R-1051 23.1600 13.2 16.0720 AN/GRC-211 144.6500 51.7 16.0720 ?iN/WSC-3 SAT 257.1500 37.0

F I G U R E 1. Operator Forecast of Self-Generated EM1

NAVAL ENGINEERS J O U R N A L January 1995 65

EM1 Avoidance

70 60 50 40

30

80 70 60 50 40 30 20

g 10 - - 0 3 -10

-20 -30 -40 -50 60 -70 -80

-

2ND. HARMONIC

70 60 50

‘I

-30 -40 -50 -60 -70

SUSCEPneLE RECEIVER

a

80 70 80 50 40 30 20

- 0

-20 -30 -40 -50 60 -70 -80

6 10

E -10

2)

1s)

5RD. HARMONIC

29. MHr TRANSMITTER ANT2-4 URT-23AJRA36

1000 w I I

suscEniee RECEIVER

58. MHt vRo4(1 67. MHs NONE I I E N l E R I XMIT FREQII

-40 -50 -80 -70 -80

SUSCEPTIBLE RECEIVER

F I G U R E 2. EM1 Susceptibility, Antenna 2-3

pler, which reduces interference to the receivers to acceptable levels.

The challenge presented in today’s communication community is to man- age EMI, both at the RCS operator’s real-time level and at the design en- gineer’s future-systems level. To do so, we must be able to conceptualize and implement user-fnendly program applications that transform raw EM1 and frequency data to user-specific mformation on which to base config- uration and antenna location deci- sions. As illustrated by the examples above, the tools to quanw the EM1 environment now exist. Clearlx flexi- ble programs such as the two de- scribed may be specifically tailored to provide diverse end users with the data to make both short-term deci- sions concerning circuit configura-

tions and long-term decisions about antenna location problems.

SUMMARY AND CONCLUSIONS Attempts to resolve EM1 by correct- ing problems as they surface cannot keep pace with the difficulties pro- duced by the proliferation of sophis- ticated, sensitive, and susceptible electronic systems now being imple- mented aboard ships. While EM1 eradication efforts such as SEMCIP and WCAP must certainly continue, an alternative to problem resolution is required: development of a discipline that emphasizes avoidance of EM1 ef- fects by quan-g and managing the variables and parameters of the com- munications environment. The ad- vances in automated test equipment

and the availability and economy of powerful personal computers facilitate the capture and reduction of data that defme the EM1 environment. A truly significant decrease in the impact EM1 has on naval communications and other critical shipboard systems is possible. To accomplish that goal, we must continue to develop and im- plement innovative methods to man- age the EM1 spectrum using the tools and dormation available. + REFERENCES 113 Grich, R.J., RAdm., USN. and Cdr.

netic Environment Engineering-A Solution to the EM1 pandemic,” Na- val Engineers Journal, May 1987.

[2] Baron, N.T. and D.R. Cebulski. “EM1 The Enemy Within,” Naval Engineers Journal, March 1992.

R.E. B ~ ~ n i n g a , USN, “Electromag-

66 January 1995 NAVAL ENGINEERS JOURNAL

EM/ Avoidance

80 70 60 50 40 30 20

3RD. HARMONIC

58. MHz -

80 70 60 50 40 30 20

P 10 3 0 .

2ND. HARMONIC

-20 -30 -40 -50 -60 -70 -80 -I-- 8USCEPnBl.E RECEIVER

80 70 60 50 40 30 20

4TH. HARMONIC

5 10

3 -10 - 0 -

-20 -30 -40 -50 8 0

rs)

-70 1 -80

SUSCEPTl8LE RECEIVER

29. MHt TRANSMITTER ANT2-3 URT-23lSRA46

lo00 w I I

F I G U R E 3. EM1 Susceptibility, Antenna 2-4

NAVAL EN G I NEE R S JOU R N A 1 January 1995 67