A mining research contract report 

MAY 19%6 

INTERACTION OF RADIO 

TRANSMISSIONS ON MINE MONITORING 

AND CONTROL SYSTEMS 

Contract J0123038 

AmRmFm PRODUCTS, INCm 

BUREAU OF MINES 

UNITED STATES DEPARTMENT OF THE INTERIOR 
The views and conclusions contained in this document are 

those of the author and should not be interpreted as 

necessarily representing the official policies or 

recommendations of the Interior Department's Bureau of Mines 

or of the U.S. Government. 
I I i PAGE 

4. ria 8rd SUmtM LReuonOaa 1 

Interaction of Radio Transmissions on Mine Monitoring May 1986 

and Control Systems. I 

7. Aulhor(.) ~~-~CrpnUIflQn~ttQ 

Dr. Lamy G. Stolarczyk 1 

% ~rf.n~trt)ocr nunr and Wrou 1Q RaHa/T.~/Wort urdt no. I 

A.R.F. Products, Inc. 

Gardner Road 

Raton, New Mexico 87740 

U -n.g metiom Nama rnd Addm ~ILfyp.dRe~orl&hrW~ i Final - 30 Sept. 82 

This report deals with the creation of an efficient method to determine if 

cormand, control, cmunication and monitoring (3a) equipment in coal, metal 

and non-mtal mines is susceptible to Radio Frequency Interference (RFI) from 

the Medium Frequency (MF) radio communications system. A qualitative and 

quantitative RFT test plan was developed for in-mine and laboratory evaluation 

of the equipment. The laboratory testing was accomplished using the TEM Test 

Chamber. Detailed information on the Test Plan and the TEM Test Chamber is 

included. During in-mine testing of the MF System some underground equipment 

malfunctioned when the transmitter's radiating antenna was in close proximity. 

Electromagnetic Compatibility (EMC) testing was done on three levels; 

Component ( circuit or box) , subsystems and system. Nine tables are included 

which show the results of testing various eqilipmt for RFI. 

I 

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Mines; radio communications; communications; coal mines; metal/non metal mines; 

I radio propagation; tunnel mde , coal seam mde ; wave pmpagation ; underground 

I mine ; mine rescue radio ; trapped miners ; radio vest transceiver; undergmund 

I mines; medium frequency; existing wireplant; loop antennas, parasitic coupling; h mhw Tm line couplers; radio, health and safety enchancemat. 

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FOREWORD 

This report was prepared by A.R.F. Products, Inc., 

Raton, New Mexico, under USBM contract number J0123038. The 

contract was initiated under the Mine Health and Safety 

Program. It was administered under the technical direction 

of the Pittsburgh Reasearch Center with James R. Means Jr. 

acting as the Technical Project Officer. Gladys Barrerea 

was the contract administrator for the Bureau of Mines. 

This report is a summary of the work recently completed as a 

part of this contract during the period 30 September 1982 to 

6 June 1985. This report was submitted by the author on 

31 May 1986. 
CONTENTS 

Pase 

Abstract ................................................ 3 

I . Executive summary ............................... 9 

Objective .................................. 9 

Background information ........................ 9 

The MF communications system .................. 10 

MF equipment design ........................... 11 

Findings and conclusions ...................... 13 

Results of in-mine system tests ............. 13 

MF communications quality and range ......... 14 

Susceptibility measurement 

methodologies .................................. 15 

Characteristics of electromagnetic 

waves .................................... 15 

Free space wave equation .................... 15 

Underground wave eq~~ations .................... 18 

Coal seam propagation mode ......... ......... 19 

Tunnel propagation modes .................... 21 

Comparison of magnetic field levels on 

the surface and in underground mines ......... 22 

Measured magnetic fields ...................... 24 
Page 

IV. 

RFI susceptibility testing of mining 

equipment ................................ 25 

Test procedure ................................ 25 

Test plan ..................................... 26 

References.......,. ............................. 35 

Appendix A. - RF susceptibility test of hand held 

methane gas detectors.,.....,............ 38 

Appendix B. - Susceptibility of Hand-Held 

Methane Gas Detectors 

to Medium Frequency Signals ............. 41 

Appendix C. - RFI susceptibi1i.t~ test of 

aeronavigationa.1 beacons................. 59 
ILLUSTRATIONS 

Page 

The cellular repeater (seam mode) ................. 12 

Geometry of the transmitting loop antenna 

in free space (loop in Y-Z plane) ................ 16 

Seam mode field components ........................ 19 

Signal current (I) flow on conductors ......... .. 21 

Magnetic field strength of a tuned loop 

antenna ........................................ 23 

Planar alignment of antennas ...................... 24 

RFI test setup .................................... 26 

Test setup ........................................ 39 

Test setup ........................................ 42 

Planview of Raton Municipal Airport ............... 61 

Transmitter setup ................................. 62 

Surface AC power and telephone cable 

transmission system .............................. 63 

Measurement setup ................................. 64 

TABLES 

Free space wave length a:nd phase constants ........ 17 

Free space magnetic field strength versus 

distance of a magnetic dipole .................... 17 
TABLES .. Continued 

Paqe 

Antenna correction factors ........................ 25 

Atmospheric monitors .............................. 26 

Remote radio control^...........^................. 28 

Electrical power system monitors .................. 29 

Communications equipment .......................... 30 

Fire detection systems ............................ 31 

Electronic longwall controls ...................... 31 

Telemetry .......................................... 32 

Hoist controls .................................... 34 

RFI susceptibility test* .......................... 35 

Allocated radio spectrum in the 

LF and MF band ................................... 59 

Power line characteristics ........................ 60 

MF communication system signal 

levels radiated .................................. 64 

Power company power line with remote switching 

signal levels .................................... 64 
I. EXZCUTIVE SUMMARY 

OBJECTIVE 

The principle objective of this work was to create an 

efficient method to det-ermine if command, control, 

communication, and monitoring ( 3CM) equipment in the 

nation's coal and metal/non~-metal mines were susceptible to 

radio frequency interference (RFI) from the medium frequency 

(MF) radio communications system. The project would be used 

to: 

. decrease the possibility of RFI increasing the bit 

error rate and causing monitoring systems in 

underground mines to be unreliable, 

. speed up mine automation by preventing RFI from 

causing malfunctions in mining equipment, 

. provide the mining industry with information on an 

electromagnetic compatability (EMC) standard, 

. develop a frequency coordination plan for use in 

underground mining, and 

. make the Mine Safety and Health Administration 

(MSHA) along with the mining equipment manufacturers 

aware of the need to test and design for RFI 

suppression. 

A central part of the work was to identify classes of 

mining equipment that could potentially be susceptible to 

RFI. A list was made of suspect susceptible 3CM products 

and possible RFI induced failure modes. A qualitative and 

quantitative RFI test plan was then developed for in-mine 

and laboratory evaluation of the products. Upon evaluating 

the various 3CM equipment, the project centered around 

developing an EMC test standard to test the RFI 

susceptibility of the 3CM circuits. During the course of 

the work, the program was expanded to include evaluation of 

the effects of MF RFI on aircraft aeronavigational devices 

since non-directional beacons (NDB) use frequencies in the 

MF band. 

BACKGROUND 

In recent years, automation in the mining industry has 

resulted in advanced mine technology which features complex 

and sophisticated electronic circuits to communicate, 

command, control, and monitor vital functions in the mining 

process. 
To achieve the degree of automation required in todays 

competitive mining industry, MF communication links would 

be required in a wide variety of applications. Although the 

MF system is a quantum leap forward in underground mine 

communications, it is possible that the system's radio 

frequency (RF) waves could interfere with other 3CM circuits 

and result in the following safety and operational problems: 

1. Effect on atmospheric: monitoring systems - 

False readings on methane monitors, CO 

monitors and heat sensors could trigger false 

alarms and shut down mining equipment or 

allow dangerous levels of methane or CO to 

accumulate undetected. 

2. Effect on control systems - Interference 

with control systems could cause underground 

and hoist equipment to start and stop at 

unpredictable times, resulting in decreased 

safety and production. loss. 

3. Effect on other communications equipment - 

Interference with existing communications 

could affect safety and the orderly operation 

of the coal mine. 

If using the system would increase the susceptibility 

of other mining equipment to radio interference and thereby 

cause unexpected changes in the mining process, it could be 

exceedingly dangerous. 

Practical experience gained in the installation and 

testing of the MF [300-3000 kHz] communications system 

transmitters in underground mines clearly shows that the 

transmitters are a potential RFI threat to 3CM circuits. 

This problem of interference is expected to intensify as the 

whole mine radio communicati,ons systems are made operational 

in the nation's underground mines. 

THE MEDIUM FREQUENCY (MF) COMMUNICATION SYSTEM 

Excellent radio coverage by the Medium Frequency (MF) 

communications system in an underground coal and metal/nonmetal mine is due to the multiplicity of efficient (low 

loss) electromagnetic (EM) wave propagation modes in 

tunnels, layered formations, and directly through the ore 

body. 
Underground tests proved that electromagnetic signals 

in the MF band couple into and reradiate from continuous 

electrical conductors in such a way that these conductors 

become the transmission lines and antenna system for the 

signals, The existence of electrical conductors in the 

entryway provides the means for what is called the "tunnel 

mode" of radio signal propagation in an underground mine. 

Testing also showed that MF signals propagating on one 

conductor would, by magnetic induction, induce signal 

current flow on other nearby conductors. Thus all of the 

entryway conductors and the magnetic coupling mechanism 

between conductors provided a means of minewide signal 

distribution in an underground mine. Further Bureau testing 

showed that radio signal propagation was possible in 

"natural waveguides" (coal, trona, and potash seams that are 

surrounded by more conductive rock) existing in certain 

layered formations. Because of signal propagation in the 

waveguide (seam mode) , communication links can be 

established through coal pillars and can be extended to the 

"working face" (the focal point of most mining activity). 

Testing also showed that signal propagation was possible 

through rock and barricades in the mine. These MF modes 

result in excellent communication coverage in an underground 

mine. By way of contrast, very high frequency (VHF) and 

ultra high frequency (UHF) radio signals exhibit high 

attenuation rates down tunnels and through natural rock. 

Unless these signals are guided by a low loss transmission 

line, unacceptable radio coverage results. 

MF EQUIPMENT DESIGN 

The MF communications system design was based upon 

prior fundamental research in MF. The equipment was 

designed to operate in both the tunnel and seam modes. For 

the tunnel mode, radio coverage to all vehicle and personnel 

carried transceivers was provided by magnetic induction 

(inductively coupling) of radio signals into local 

electrical conductors. The electrical conductors include 

AC power cable, telephone cable, metal, water and air pipes, 

and wire rope. Base station signals are coupled to the 

conductors to produce local magnetic fields at distant . 

locations. The mobile personnel carried and vehicular 

transceivers communicate with the base via magnetic coupling 

to these conductors. The transceivers use tuned loop 

antennas to receive and generate the magnetic fields. The 

base station is centrally located in the radio coverage 

area. Passageway repeaters extend the operating range of 

the base station, vest and vehicular transceivers. RF line 

couplers are used to couple the repeaters and base stations 

to the conductors. The same repeater can be equipped with 

tuned loop antennas to radiate and receive seam mode signals 

as illustrated in figure 1. 
Pager phone line ( existing ) 

I 

- 

T/'f 1 

,R/'f 2 Transmitter b 

I transceiver I I transceiver I 

FIGURE 1. - The cellular repeater (seam mode). 

Since the repeater services a "cell" (local working 

area) in the mine, it is called a cellular repeater. This 

repeater may be connected to the local pager telephone 

system to enable communications with other distant miners 

and with the surface communications center. When repeaters 

are used to extend the operating range, a second operating 

frequency is assigned to the radio system. A transmission 

frequency of F2 causes repeater action to occur. The 

repeater retransmits the message at the frequency of F1 (a 

high power signal). All receivers are tuned to the F1 

frequency; base stations and the mobile transceivers are 

designed to transmit on F1 or F2 frequencies. A direct 

communications link between the base and mobile transceivers 

is created by a transmission frequency of F1; and repeater 

action extends the operating range by using F2 transmissions 

from the base or mobile transceivers. The repeaters are 

essential in large mines since they enable personnel carried 

transceivers to communicate over ranges which are similar to 

that achieved by the higher output power vehicular and base 

transceivers. 

The system has been designed to operate on several selectable frequencies in the MF band. Separate communication 

networks (cells) can be set up by assigning a unique set of 

frequencies (F1 and F2) to each network which may 

independently serve the com~nunication needs of maintenance, 

production, haulage and supervision. Additional networks 

are created by installing other base stations and repeaters. 

The base stations, repeaters and mobile transceivers are all 

tuned to the assigned unique network frequencies. Because 
digital frequency synthesizers are used in the equipment 

design, it is possible for mobile transceivers to monitor 

a-nd communicate with other networks in the mine. 

Underground evaluation of the radio system showed that it 

could be used in a wide variety of applications which 

include command, control, and monitoring of all types of 

mining equipment. Evaluation of the MF system in four mines 

determined that an RFI susceptibility problem exists in the 

automated underground mine. 

FINDINGS AND CONCLUSIONS 

Results of In--Mine System Tests 

The MF communications system was installed and 

evaluated in four underground mines. The mines ranged in 

size from small (500 tons/day) to large (67,000 tons/day) 

capacity and represented several different mining methods. 

Two of the mines were medium sized coal mines (approximately 

1 million tons per year - MT'PY). These mines use continuous 

mining equipment to develop longwall panels and belt haulage 

systems to transport coal out of the mine. The third mine 

was a small silver mine which uses the vertical crater 

retreat mining method. Diesel trucks haul approximately 500 

tons of silver ore per day up a 7,000 foot long decline to 

the adit. The fourth mine was a large copper mine which 

uses the multiple level bilock caving method to extract 

67,000 tons of ore per day. The mine uses an extensive rail 

haulage system to transport ore to the ore bins where hoists 

are used to lift it to the surface. 

These mines offered an excellent opportunity to evaluate numerous aspects of the system's features in a wide 

variety of mining conditions. In-mine tests were conducted 

to measure: 

(1) The MF signal carrier to noise ratio along the entire 

length of conductors in several entryways; (2) the signal 

attenuation rate of the MF signal along the conductors; (3) 

the receive and "talk-back" (transmit) range from mobile 

transceivers to the base station; (4) electrical and 

acoustical noise levels in the mine; and (5) receiver 

quieting. Additional experimental testing involved a 

simulated rescue and recovery operation and a simulated 

locating of a trapped miner. 

Analysis of the in-mime test results showed that the 

MF communication system performed equally well in each mine. 

Because the performance consistant and predictable in 

.these mines, underground radio system engineering can 

predict performance in other mines. Furthermore, the in- 
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During in-mine testing of the system, underground 

mining equipment malfunctioned when the transmitters 

radiating antenna was in clolse proximity. The first incidents occurred on operating longwall mining systems. Radio 

communications along the face caused interruption of the 

longwall mining system's power. The interruption was caused 

by the susceptibility of the methane monitor to the radio 

frequency waves. After being made aware of the EMC equipment problems, spot checks of other mining systems were 

made. These spot checks showed that carbon monoxide monitors 

were also susceptible to the radio frequency waves. These 

findings gave rise to the formal EMC investigation decribed 

in this work. 

11. SUSCEPTIBILITY MEASUREMENT METHODOLOGIES 

A test plan was developed for in-mine, open field, and 

laboratory RFI surveys of susceptible equipment. The test 

plan was designed to 1) develop qualitative procedures for 

identifying the RF susceptibility of an operating coal or 

metal/non-metal mine and 2) develop qualitative procedures 

to measure the RF levels tha,t cause malfunctions in underground mining equipment. 

CHARACTERISTICS OF ELECTROMAGNETIC WAVES 

The characteristics of the electromagnetic (EM) waves 

radiated by the MF communication system's transmitting loop 

antennas must be known in order to accurately simulate EM 

fields in the underground mine environment. Equations 

describing the EM waves produced by a tuned loop antenna in 

free space, within a coal seam, and through natural media 

have been previously developed in literature as well as in 

prior U.S. Bureau of Mines research. These equations were 

used to determine the radiated field strength in the 

vicinity of the transmitter's antenna. 

Free Space Wave Equation 

The electromagnetic fields produced by a transmitting 

loop antenna in free space will. be analytically presented in 

this section. Figure 2 illustrates the geometry of the 

antenna in full space (spherical. coordinate system). 
FIGURE 2. - Geometry of the transmitting loop antenpa 

in free space ( loop in Y-X plane) . 

The loop of small area A is enclosed by a conductor with an 

excitation current amplitude (I) of 1 ampere. The fields 

produced at the observation point P are given by: 

1 1 SIN 0 

where f3 = the phase constant, and 

M = the magnetic moment of the antenna. 

The above set of equations are noteworthy in several 

respects. When the radial distance (r) from the excited 

loop antenna exceeds X/2 , the terms involving l/r dominate 

the field equations. When 0 = 90 the He field strength is 

maximum. A companion receiver with a tuned loop antenna 

would receive a maximum signal level when the transmit and 

receiving loops lie in the same plane (coplanar). Terms 

with l/r2 identify the "induction" field components in the 

EM waves. The "static" field terms are identified by l/r3 

in equation 1. While power transfer to the distant point is 

associated with l/r components, a large amount of power can 

be transferred through the near field "induction" and 

"static" fields. Terms are in equations 1, 2, and 3. 
Equation (1) has been evaluated for a unit magnetic 

moment. Table A shows the free space wave length (A) and 

phase constant (6) at selected frequencies used in LF and MF 

communications. Table B gives the amplitude of the azimuthal 

component of the EM wave at different radial distances from 

the antenna, The tabular data in table B shows that the 

azimuthal field component is independent of the frequency 

near the loop antenna. 

TABLE A, - Free space wave length and phase constants. 

Frequency Wav~ Length Phase Constant 

(kHz) (Meters ) (Radians/Meters) 

------------------------------------------------------- 

60 5000 1.2566 x 10-3 

100 3000 2.094 x10-3 

200 1500 4.19 x 10-3 

300 1000 6.28 x 10-3 

350 857,143 7,330 x 10-3 

400 7.5 0 8-38 x 10-3 

520 5'76.9 10.89 x 10-3 

600 500 12.6 x 10-3 

TABLE B, - Free space magnetic field strength versus 

distance of a magnetic dipole (M=l) . 

Radial 

Distance Azimuthal Cc~mponent Field Strength (pA/m) 

Meters ReHe ImHe He ........................................................ 

Frequency 60,000 Hz 

Frequency 100,000 Hz 
TABLE B. - Free space magnetic field strength versus 

distance of a magnetic dipole (M=l) - Con. 

Frequency 350,000 Hz 

Frequency 400,000 Hz 

Frequency 520,000 Hz 

UNDERGROUND WAVE EQUATIONS 

Coal seam and tunnel signal propagation modes were 

evaluated in a series of underground tests conducted by the 

Bureau (, The test results indicated that the coal seam 

mode enabled maximum communications range in the frequency 

band extending from 400 to 700 kHz. This band is a subset 

of the medium frequency, (300 kHz to 3000 kHz) portion of 

the electromagnetic spectrum. Further, as predicted by 

theory (A), low loss signal propagation modes existed in 
entryways with electrical conductors. In-mine testing 

confirmed the existence of low loss signal propagation in 

the entries of both coal and M/NM mines. 

Coal Seam Propagation Mode 

The theory of electromagnetic wave propagation in 

layered formations has been rigorously developed by Wait 

(4). Figure 3 illustrates the model used to analytically 

determine the wave propagation characteristics in a coal 

seam. 

Coal 

or 

I 

J It- r -------4 

rock ////// , , / 

FIGURE 3. - Seam mode field components. 

The coal seam is bound by two conducting half spaces 

with the conductivity of the roof rock (or being several 

orders of magnitude more than the conductivity of coal 

(oC) Along the transmission path (r) , the vertical 

orientation of the transmitting loop antenna (source) 

produces a horizontal magnetic field He and a vertical 

electrical field E,. These fields are relatively constant 

over the height oz the coal seam. It has been sho n (5) 

that the fields die off exponentially in the rock Y - . At 

large radial distances (r) from the antenna, the fields 

decay exponentially. The rake of this exponential deca.y is 

determined by an effective attenuation constant (a) which 

depends on the conductivity of the coal and rock, and on the 

'skin depth in rock is 0.69 meter; (or, = 1 mho/m; 520 

k~z). 
coal's dielectric co~stant. There is also a r-4 factor at 

large radial distances because of the wave's cylindrical 

spreading. The zero-order TEM magnetic field Ha in the 

transmitting loop plane is given by: 

where ?I the magnetic of the transmitting loop 

antenna , 

be = b + 1/26, is the effective half-height of 

the coal seam3, 

6, the z direction skin depth in the rock, 

k=B-ia = the complex propagation constant in the 

radial direction, and 

~,(~)#(kr) = the derivation of the first-order 

Function for an outgoing wave. 

On taking the asymptotic form of the Hankel Function, the 

azimuthal component of the magnetic field4 is: 

The attenuation is mathematically represented by: 

a = ( (4) + q2)% + 14 

the phase constant by 

B = (4) [(p2 + q2)% - 1% 

and 

where 

f = the operating frequency 

h = the coal seam height 

3be may be complex. 

4~alid at ranges kr >> 1. 
0, = skin depth in coal 

EC = EO EF = dielectric constant of coal 

The zero-order TEM wave described by equation (4) has 

been compared with experimental measurements (6). These 

measurements were found to be in close agreement with 

equation 4. Equations 6, 8,, and 9 are useful in determining 

the dependence of the wave propagation constant on seam 

parameters. 

The attenuation rate in coal is approximately 4 dB/100 

ft (0, = 1.4 x 10 mho/m, E, = 7, OF, = of, = 1 s/m, 

h=lm, 350 kHz). The attenuation rate 1s expected to 

increase with decreased coal seam thickness and increased 

conductivity. The rate decreases with increased rock 

conductivity. The rate also depends upon frequency. 

Tunnel Propagation Modes 

Bifilar and monofilar signal propagation modes exist on 

a pair of wires in the wireplant. The current flow of each 

mode is shown in figure 4. 

A - Bif ilar ( differential ) mode 

FIGURE 4. - Signal current (I) flow on conductors. 5 

The excitation of monofilar and bifilar modes on a 

tunnel's transmission line have been examined (3). In the 

monofilar mode (also called the balanced, diTferentia1, 

5~he number of possible modes is n-1 where n is the number 

of electrical conductors in the entryway. One of the 

conductors may be the conducting wall of the tunnel. 
coaxial, or symmetrical mode) the current flows in the same 

direction in each conductor and returns as a surface current 

in the mine tunnel. In fact, only one conductor is actually 

needed. This mode is easily excited by a magnetic coupling 

from a loop antenna anywhere in the mine tunnel, but it 

suffers high attenuation because the return current flows in 

the lossy tunnel wall. 

In the bifilar mode which requires two conductors (also 

called the unbalanced, asymmetrical or differential mode), 

the forward current in one conductor returns through the 

other conductor. This tra~nsmission line mode has low 

attenuation because the ret-urn current flows on the second 

wire rather than through the surrounding rock. Excitation 

of this mode depends upon magnetic flux threading the area 

between the transmission line conductors. 

Random imperfections in the wireplant and mine tunnels 

cause mode conversion to occur on a two-wire transmission 

line. Non-uniformities in the tunnel cross section, cable 

sagging with respect to the roof, and incidental changes in 

conductor spacing cause the characteristic impedance (zO) of 

the cable to change along the line. Changes in this line 

characteristic impedance cau.se radiation and reflection of 

the signal energy thereby cawing monofilar and bifilar mode 

interchange conversions to occur all along a line. 

Radio coverage in conductorless entries can be provided 

by installing a dedicated cable such as two-wire telephone 

cable. It is easy to install and supports both the monofilar 

and bifilar modes of signal propagation. The MF antenna-tocable coupling efficiency is high due to monofilar coupling 

and the operating range is great due to the bifilar mode 

propagation. 

COMPARISON OF MAGNETIC FIELD LEVELS 

MEASURED ON THE SURFACE AND IN UNDERGROUND MINES 

The magnetic field data measured on the surface of the 

earth and in the drifts of a coal mine are illustrated in 

figure 5. The magnetic field strength is plotted versus 

radial distance (r) from the radiating antenna. For 

comparison purposes, the free space theoretical data is also 

plotted in figure 5. The data taken from table A was 

adjusted to account for an increase in magnetic moment from 

1 to 4.6 Ampere Turn Meter2 AT^^ ) . 
USTAM€ ( r) in feet 

FIGURE 5. - Measured magnetic field strength versus distance 

(r) from between excited transmitting antenna 

The plotted curves illustrate several characteristics. 

Curve a illustrates the free space values; curve b 

illustrates the values measured over a conductive free 

earth; curve c illustrates the effect of a nearby conductor 

(tunnel mode); and curve, d illustrates the magnetic field 

strength versus range in an underground coal mine. As can 

be seen in the figure, the free space values (curve a) are 

in close agreement with the values measured over a conductor 

free earth (curve b). The agreement improves as the radial 

separation distance decreases. In the case of curve c a 

single conductor pair (500 ft long) was placed along the 

propagation path. As expected the conductor aided in the 

propagation of the EM wave., Near the end of the conductor 

(last 200 ft), the induced signal current decreases 

resulting in smaller fields. The measurements for curve d 

were made in a uniform coal seam. The field strength values 

are greater than the free space values owing to the 

cylindrical spreading of the wave in the rock-coal 

waveguide. In the near vicinity (less than 20 ft) of a 

radiating loop antenna, the field strength approaches the 
free space values. In conclusion, a radiating loop antenna 

can be used in qualitative evaluation of mine equipment. 

MEASURED MAGNETIC FIELDS 

Magnetic field produced by excited loop antennas have 

been measured on the surface of the earth and in drifts in 

an underground coal mine. The test setup is illustrated in 

figure 6. 1 L I 

Transmitting 

antemna 

Receiving 

antenna 

mff 

Earth 

I . FIGURE 6. - Planar alignment of antennas. 

The MF transceiver efficiently drives the antenna. The 

magnetic moment (M) produced by the antenna is given by: 

where 

M = NIA (Ampere Turn ~eter~) (10) 

N = the number o:E turns in the loop, 

I = the peak current in amperes, and 

A = the area of the loop. 

The magnetic moments produced by the MF equipment 

antennas are: 

2.1 AT^^ personnel carried antenna 

(11) 

4.6 AT^^ vehicular antenna 

The transmitting and receiving antennas are positioned 

in a vertical plane (Horizontal Magnetic Dipole - HMD) 

Measurements are made with the coplanar orientation of the 

antennas. The field strength produced by the radiating 

antenna along the propagation path is mathematically 

represented by: 

Field Strength = Meter Reading + Antenna Correction 

Factor -51.5 dB* 
The field strength reading is in dB above 1 pA/M (dB re 

1 vA/M). The Field Strength Meter (FSM) reading is 

calibrated in dB above one microvolt (dB re 1) The 

antenna correction factors are given in table C. 

TABLE C. - Antennla correction factors, 

Frequency (kHz) Factor (dB) 

111. RFI SUSCEPTIBILITY TESTING OF MINE EQUIPMENT 

TEST PROCEDURE 

The main objectives of the test procedure were to 

determine possible effects in mining equipment and to set 

forth the appropriate test method. Manufacturers were for 

the most part unwilling to provide detailed drawings of the 

equipment; however, drawings of some of the equipment under 

test were obtained from the mine maintenance office. Prior 

to the test, schematic drawings were reviewed to determine 

circuitry that would be susceptible to either conducted or 

radiated RFI. The effects of the RFI and possible failure 

scenarios were studied before testing began. 

The procedures used in the examinations depended upon 

the prior RFI assessment of the schematic drawings and 

possible failure scenarios. In some notable cases, RFI 

testing could possibly cause severe damage to the mining 

equipment. For example, RFI examination of hoist controls 

could cause inner or outer control loop failure. This 

could lead to a possible runaway condition in the hoist 

sys tem. 

RFI examination requires that the EM wave source be 

used in near proximity to the mining equipment. The data 

presented in Table B and Figure 6 shows that in the 

neighborhood of a radiating antenna, the surface of the 

earth and the coal seam electrical parameters have 

negligible effects on the magnitude of the radiated EM wave 

field strength. Since the EM wave field strength can be 

accurately determined (analytically and by measurement), 

consistent RFI results can be obtained in the underground 

mine and on surface test ranges. 
TES'T PLAN 

Electromagnetic compatibility (EMC) testing was done 

on three levels: component (circuit or "box"), subsystem 

and system. Component level testing includes the testing 

of black boxes such as methane spotters, toxic gas 

detectors, etc. A subsystem, on the other hand, is any 

electronic or electrical entity that performs a specified 

function within an overall system and is usually 

characterized by having terminal leads - included in this 

category are SCR switching packages, vehicular speed 

controllers, etc. The system, by contrast, is the overall 

complex of equipment used to perform a specific function. 

Component testing can be carried out at surface facilities 

of the mine or an antenna test range. 

The testing was setup as illustrated in figure 7. - 

FIGURE 7. - RFI test setup. 

The radiating loop antenna is located on a tripod. 

The antenna is then connected to a battery powered MF 

transmitter. The antenna and transmitter have the capability of being tuned in the field to 300, 400, 500,. and 

600 kHz. The equipment under test is located a distance r 

from the antenna. Test instruments may be connected to the 

equipment under test to measure the effects of the radiated 

signals. 

Tables D through L list the mining equipment tested 

for RFI susceptibility and give the results of that 

testing. 

TABLE D. - Atmoslpheric monitors. 

Manufacturer Description Results Notes 

--------------------------

National Mine Methane remolte 

Service sensor module No effect 

Oxygen remote 

sensor module No effect 
TABLE D. - Atmospheric monitors -- Con. 

Mine Safety Methane moinitor 

Appliance Co . model VI No effect 

(MSA) 

Echolizer 

Bacharach 

NOTE A: 

Minico Company 

monitor 

Spotter ,methane 

detector 

Spotter QII-LEL 

combustible gas 

detector 

Model 245 

oxygen indicator 

Fluctuations 

Slight 

effect 

Fluctuations 

output 

decreased 

1% 

Model 245 I? output 

oxygen indicator increased 

by 1-2% 

Model 3000 

CO detector Failed 

See 

note A 

See 

note A 

See 

note A 

See 

note A 

See 

note A 

See 

note B 

Models 230-7285 

and 23-7288 See 

methane monitors Failed note C 

In-house tests were conducted at MSA's Ryan Lab, 

located in Pittsburgh, Pennsylvania, on five handheld monitor devices. All units were exposed to 

an excited 520 kHz loop antenna. The results 

were as follows: 

The MiniCO CO monitor has an LCD readout in 

parts-per-milli-on. When irradiated, this output fluctuated randomly between 0-400. 

The Spotter permissible methane detector has a 

meter movement. output. When irradiated, the 

output decreased in level readings by a slight 

amount. The en~vironment was methane free. 

The Spotter MIode1 QII LEL combustible gas 

detector has an LED readout. The level fluctuated randomly between 0-608 when irradiated. 
NOTE B: 

NOTE C: 

The MSA Model 245 oxygen indicator has a meter 

movement outpu,t. When irradiated, the output 

level decreased by 1%. 

The MSA Model 245R oxygen indicator is similar 

to Model 245, but has the sensor located on a 

remote wire assembly. This indicator showed a 

1-2% increase in readings when the sensor was 

laid on the loop. No change was detected when 

the unit itself was brought into proximity of 

the loop antenna. 

MSA Hand-held methane spotters (Models 23-7285 

and 23-7288) were highly sensitive to RFI. 

The instruments not only read high but they 

remained high for a long period. 

The Echolizer Moldel 3000 carbon monoxide monitor 

was installed in the MAGMA Copper mine San 

Manuel, Arizona, and was found to be extremely 

susceptible to RFI. The monitor went into alarm 

when radiated by an MF signal. The monitor was 

connected to an Outokompu telemetry system. The 

system, however, did not report an alarm. It may 

be that only the local alarm circuits were 

activated by the MF signal. 

The Bacharach methane monitor Models 23-7285 and 

23-7288 were tested at the York Canyon Mine and 

were found to be highly susceptible to MF 

signals. These signals caused the power system to 

trip. 

TABLE E. - Remote radio controls. 

Manufacturer Description Results Notes 

----.--.------------------.--.----------------------.--- 

Moog Inc. 

GLI Corp. 

NOTE D: 

NDL radio control system No effect 

Radio remote 

controls Failed 

Testing at Island Creek Coal Company's V.P. mine 

#6 showed that the Giangarlo 2002 telemetry 

system is suscept~ible to MF signals. The system 

is used to monitor methane levels in fresh air 

entries. The central station and three 
outstations communicate via a two-conductor 

shielded cable using FSK. The FSK signal level 

decreased substantially anytime the mine's 

carrier phone system, which operates at 100 kHz, 

was being used. At the same time, there was a 

definite increase in the noise level on the 

line. It was evident that the SCR controls for 

the shaft hoist also induced noise spikes on the 

telemetry lines. Mine personnel said they had 

witnessed communication failures in the telemetry 

system on past occassions. The failures were 

attributed to the carrier phone interference. 

The MF interference equipment was setup to directly irradiate the telemetry lines. A junction 

box located across the building from the central 

station was opened and transmitted into, The 

Giangarlo system immediately lost communications 

ability. A Kidd telemetry system was also tested 

in the V,P. Mine #6. The system is used to 

monitor methane levels in the return air entries, 

This system communicates from outstations to a 

central processing station using FSK on a coaxial 

line. Mine persnnnel indicated that this system 

was immune to failures of the type experienced in 

the Giangarlo system. The system was irradiated 

at an outstation point near the central processor 

location. No apparent effect to the system was 

detected. 

TABLE F, - Electrical power system monitors, 

Manufacturer Description Results Notes --------..--.-..--.------..--,-..-.----.--..-----..----.-- 

~ational Mine Ground sentinel 

Service I1 ground fault 

detector No effect 

GM-2001 ground 

fault detector No effect 

Pemco Corp, Modd CM-110 

ground fault 

detector No effect 

Ohio Brass Co, 0-B ground monitor ground 

fault detector No effect 

American Mine Model GM-200 

Research Inc, ground fault 

detector No effect 
TABLE F. - Electrical power system monitors -- Con. 

Line Power Ground monitor 

Manufacturing ground fault 

detector 

Westinghouse Type DS 

ground fault 

detector 

Type DSL 

ground fault 

monitor 

No effect 

No effect 

No effect 

Plains Electric Power line 

Co-op carrier current See 

signal No effect note E 

NOTE E: Measurements were made in the vicinity of the 

transmission liines near Kaiser Coal ' s York 

Canyon mine portal. The measurements showed that 

the underground MF communication system induces 

signals that are 17 dB below power line carrier 

current signals. It is unlikely that the MF 

signals will interfere with power lines since the 

power line carrier current receiver has a low 

sensitivity (-10 dBm) . 

TABLE G. - Communications equipment. 

Manufacturer Description Results Notes 

National Mine SBM-5000 

Service Co. trollyphone No effect 

CSE Mine 

Services 

American Mine 

Research Inc. 

Loudspeakirlg 

mine telephone 

Central amplifier audio 

system 

No effect 

No effect 

Model 170 

carrier communications system No effect 

TC-650 loop 

trolly communications unit No effect 
TABLE G. - Communications equipment -- Con. 

Control Corp. Loudmouth 

telephone No effect 

Motormouth 

trolly radio No effect 

Gai-Tronics 

Corp . 

Mine Safety 

Appliance Co. 

Model 490 mine 

pager phone No effect 

Mine dial/ 

page phone I1 No effect 

Pager I11 m~ine 

communications 

system No effect 

Pager IV mine 

communications 

system No effect 

Multiphone 

mine communications system No effect 

TABLE H. - Fire detection systems. 

Manufacturer Description Results Notes -----o----.----------------w----.-.---------.------.----- 

National Mine Belt head fire 

Service Co. suppression 

system No effect 

Mine Safety Belt fire dleAppliance Co. tection sys,tem No effect 

TABLE I. - Electronic longwall controls. 

Manufacturer Description Results Notes 

-----.---------------------.-.-------.--.----------.--.--- 

Dowty Corp. Electronic 

longwall ad-- 

vance controls 

Heinscheidt Entire longwall 

system 

No effect 

See 

note F 
NOTE F: Longwall controls are known to be susceptible to 

RFI signals in the Medium Frequency (MF) range. 

In previous MF testing in Kaiser Coal Corp's York 

Canyon mine, the methane monitor was found to 

read high when MF signals were present. The 

monitoring system was observed to turn off the 

longwall power; therefore, the longwall mining 

system was investigated for RFI susceptibility. 

After a gas level check, the entire longwall 

system was investigated using the equipment 

described for the test plan. The test included 

the shearer controls, chair conveyor belt 

controls and the methane monitor. The shearer 

was an Eickhoff Model 300L and the methane 

monitor was malnuf acturer by Bacharach. The 

methane monitor sensor was located at the 

tailgate and the indicator/control enclosure was 

located at the headgate. MF signals did cause 

the methane monistor to read high and interrupt 

the longwall. 

TABLE J. - Telemetry. 

Manufacturer Description. Results Notes ......................................................... 

National Mine R5000 central 

Service Co. control system 

Outokumpu Mine monitoring 

system 

Motorola Mine monitoring 

control system 

Slo-Electronics Procol 240 

telecontrol 

system 

Davis Derby 

Mine Safety 

Appliance Co. 

Walter Kidde 

Grancar lo 

Scientific Corp. 

Telecontrol 

sys tem 

Scada system 

Automated 

system 

No effect 

No effect 

No effect 

No effect 

No effect 

No effect 

No effect 

Fluctuations 

See 

note G 

See 

note D 
TABLE J. -- Telemetry - Con. 

Conspec 

Controls Inc. 

Aqua Trol 

Hawker Siddely 

DOE/Bituminous 

Coal Research 

Kidde 

Mundix 

RFL Industries 

San GauroWeston 

NOTE G: 

NOTE H: 

Telemetry 

system 

Telemetry 

sys tem 

Telemetry 

system 

Telemetry 

system 

No effect 

No effect 

No effect 

No effect 

No effect 

No effect 

No effect 

See 

note H 

The Outokompu telemetry system was extensively 

investigated for RFI susceptibility at the MAGMA 

Copper mine. The system includes a surface 

reporting and control center, subsurface outstations, and 1,ow current loops (ImA) . The 

system was not su~~ceptible to RFI. 

The RFI susceptibility of the Mundix telemetry 

system was evaluated at Occidental Oil Company's 

oil shale Logan Washsite. The Mundix telemetry 

system in the mine uses a daisy chain loop to 

monitor multiple outstations. The surface 

control room is located in the head frame, It 

includes the controls for a Canadian General 

Electric hoist system as we11 as the video 

terminal for the Mundix telemetry system, The 

Mundix system uses "off the shelf" hardware 

manufactured by Cutler-Hammer. This equipment 

features the use of an Intel computer and 

software program. The Mundix system features the 

use of polling at a baud rate of approximately 

500 kHz. The interrogation signal includes the 

address of the outstation. The outstation 

replies as a result of being addressed. Fast 

polling allows the system to provide surveillance 

without a needed vector interrupting the 

operating system. The outstations are located in 

fresh air. Intrinsically safe barriers are used 
on leadout wires to sensors located beyond seals 

in the retort area. The barrier strips are 

manufactured by Stahl, Inc. and TransAmeric 

Deleval. RFI susceptibility tests were conducted 

at the collar in accordance with the RFI test 

procedure. The Mundix system did not respond to 

the test signals at 150 kHz and 520 kHz. An RFI 

test was also conducted on the hoist control 

telemetry system cables located in the same 

raceway. No malfunctions were found in the hoist 

control cable. 

TABLE K. - Hoist Controls. 

Manufacturer Descriptiorl Results Notes 

..---------------.---------

General Electric Drives and 

controls 

Westinghouse Drives and 

controls 

See 

note I 

See 

note I 

Rexnord Controls See note J 

NOTE I: The RFI suscepti.bility of five hoist systems at 

the MAGMA Copper mine were investigated. The 

hoist network speed regulator, acceleration1 

deceleration rate controls, etc. were found not 

to be susceptible to signals in the MF band. 

This was true even when the radiating antenna was 

placed inside the control cabinets. By way of 

contrast, Very High Frequency (VHF) signals from 

handheld transmitters (Motorola brand) did cause 

the hoist system to trip-off. General Electric 

and Westinghouse static power supplies were used 

in the hoist system. Falkner gear boxes were 

used to drive the drum; and in the event of an 

unexpected trip, hydraulic breaking systems were 

used to bring the cage to a safe stop. Nuisance 

tripping may require that the maintenance man * 

enter and inspect the shaft. 

NOTE J : The RFI susceptibility of three hoist control 

systems were evaluated in a series of field 

tests. The hoist systems are located at Union 

Oil/Molycorp, Inc.'s mine near Questa, New 

Mexico. The mai:n mine hoist motor is a 500 HP 

500 volt DC shunt wound'motor. A 6-pulse 
thyrister power converter is used to supply power 

to the hoist system. The entire control-system 

includes more than 40 networks. The networks 

include speed regulators, acceleration/ 

deceleration rate control, etc. The control 

circuits were mounted in equipment cabinets. 

Sensors such as slack rope detectors, RPM 

monitoring, ground fault monitors, etc., were 

located at critical locations on the hoist 

system. A radiating loop antenna was used in near 

proximity to the control networks and the remote 

sensing points. The system was not susceptible 

to RFI. 

In addition to the above tests, an RFI susceptibility 

test of hand held methane gas detectors was made in a TEM 

mode test chamber (Crawford Cell) driven by a sweep 

generator. The results are given in table L. 

TABLE L. - RFI susceptibility test of hand held 

methane gas detectors. 

Manufacturer Description Results Notes 

-----------------------------.---------------------------- 

Mine Safety 

Appliance Co. Analog No effect 

Digital No effect 

Bacharach Digital No effect 

* A description of this test and the test data is given 

in Appendix A. 

Testing for the effect of RFI susceptibility to 

aeronavigational devices was also performed. These tests 

showed that MF signals from mine communications do not 

interfere with aerona~igat~onal devices. A description of 

the test along with the test results are given in Appendix 

B. 

IV. R.EFERENCES 

1. Lagace, R.L. Emsile, A.G. and Grossman, M.A. 

Modelling and Data Analysis of 50 to 5,000 kHz Radio Wave 

Propagation in Coal Mines. (Contract H0346045) BuMines OFR 

83-80 1980, 109 pp. Arthur Do Little, Inc. PB 80-209455. 
IV. REFERE:NCES -- Continued 

2. Cory, T.S. Propagation of EM Signals in Underground 

Mines. (Contract H0366028, Collins Radio Group). BuMines 

OFR 136078, 1977, 158 pp. Pl3289757/AS. 

3. Hill, D.A. and Wait, J.R. "Excitation of Monofilar 

and Bifilar Modes on a Transmission Line in a Circular 

Tunnel. Journal of Applied Physics", V. 45, No. 8, Aug. 

1974. 

4. Wait, J.R. Electromagnetic Waves in Stratifield 

Media, Pergamon Press, 1970. 

5. Emsile, A.G. and Lagace, R.L., "Propagation of Low and 

Medium Frequency Radio Waves in a Coal Seam", Radio 

Science, v. ii, No. 4, 253-26;l pp., April 1976. 

6. Cory, T.S. Summary Data Report No, 2 - Mine Wireless 

Propagation Test Program - Ireland Mine Test Data at Medium 

Frequency. Spectra Associates, Inc., Cedar Rapids, Iowa.. 

7. Crawford, M,L,, "Generation of Standard EM Fields 

Using TEM Transmission Cellsw, IEEE Transactions on 

Electromagnetic Compatibility, Vol, EMC-16, No, 4, November 
IV. REFERElNCES -- Continued 

8. Crawford, M.L., Improving the Repeatability of EM 

Susceptibility Measurements of Electronic Components When 

Using TEM Cells, SAE Technical Paper Series, 830607. 

9, Crawford, M.L., and Workman, J.L., "Using a TEM cell 

for EMC measurements of electronic equipment, NBS Technical 

Note 1013", Revised July 1981, 65 pp. National Bureau of 

Standards, Boulder, CO 80303, 
APPENDIX A 

TEST PLAN 

RP SUSCEPTIBILITY TEST OF MINING EQUIPMENT 

USING TEM CELL 

1. PURPOSE 

The purpose of the TEM Cell is to determine, using a 

repeatable quantitative method, failure condition in susceptible equipment, due to MF electromagnetic interference. 

The failure modes will be determined qualitatively 

- RE' frequency range of failures, 

- approximate field strength (if possible), 

- failure characteristics, 

- modulation of the RP frequency (if critical), 

- any other observations. 

2. THEORY 

Two suitable methods of evaluating susceptible electronic equipment to electroma~gnetic (EM) interference are: 

- Open field test range, where a known EM field is 

established in the vicinity of equipment under 

evaluation. 

- a TEM cell, where (s known constant field is established within an enclosure. 

The first method is widely used in equipment RFI 

susceptibility evaluations. Its main advantage is that it 

is relatively easy to setup the open field test range, 

Larger equipment can be evaluated with this method. Its 

disadvantage is that it is difficult to maintain calibration 

between different test sites. The TEM cell, on the other 

hand, is basically self-contained and can be set up at any 

convenient location, since it is self shielding, The 

desired fields are easily established within the cell and 

are comparatively uniform. The technical papers by Crawford 

describe the theory of operation in more detail (7,8). - - Additional information is also contained in NBS Technical 

Note 1013 (9). - 
3. EQUIPMENT AND TEST SETUP 

The following test equipment is necessary to perform 

the tests : 

- Signal Generator (covering the desired RF frequency 

range) . 

- TEM Cell (Model CC103) , 

- 50 ohm Load 

The test equipment setup is shown in Figure A-1. 

I I 

FIGURE A-1. -- ~est setup 

Place the equipment under test (EUT) in the chamber. 

The height of the equipment sh.ould not exceed 9 inches using 

the specified cell. 

4. CALIBRATION 

The TEM Cell relationship between the electric and magnetic fields is: 

In a TEM Cell the established electric field within its 

operating limits is mathematically given by: 
where 

Using 

V = input voltage 

b = the distance between the center conductor and 

the bottom of t.he cell. 

b = 0.22 meters for the specified cell: 

For instance to establish a magnetic field of 2000 microamperes per meter a signal input of: 

V = 83 X 2000 X lom6 = 0.166 volts 

or -2.6 d"Bm is required. 

5. PROCEDURE 

5.1 Record information on EM1 susceptibility in paragraph 2 

of the test data shelet. A blank and examples follow 

Appendix B. 

5.2 Also record value of used multiplier (Equation 4) on 

ddta sheet. 

5.3 Set. signal generator output to establish a field 

strength, H, of 2000 pA/rn. (Use equation 4) 

5.4 Slowly sweep the RF range of 80 kHz to 1.0 MHz and 

record all frequency ranges over which malfunction 

occurs. 

5.5 Over each frequency range recorded in 5.4, reduce field 

strength to a minimum value at which a malfunction 

still occurs. Record frequency (or frequency range) ' 

and field stength level. 

5.6 If failure modes are different at different frequencies 

and field strength levels, indicate this in the failure 

mode column. Note any other pertinent data in the otes 

column. 

5.7 In Paragraph 3 of the test data, note any pertinent 

information received with the test unit (comments, 

references, etc.) and any special observations and 

comments from the laboratzory testing. 
APPENDIX B 

RFI SUSCEPTIBILITY TESTING OF 

METHANE INSTRUMENTS 

SUSCEPTIBILITY OF HAND-HELD METHANE GAS DETECTORS 

TO MEDIUM FREQUENCY SIGNALS 

The RFI susceptibility tests were performed using a TEM 

Mode Test chamber (Crawford Cell) driven by a sweep 

generator. 

Subjecting the equipment under test to an E and H field 

of from 80 kHz to 1000 kHz at a predetermined level of H 

field level of 2000 pA/m (microamperes per Meter) and higher 

levels as specified. 

METHANE METER TESTS 

Three hand-held Methane Gas Detector Meters were 

evaluated, two by MSA and one by Bacharach as follows: 

MSA "Spotter" Model N, LED readout, SN 02325 

MSA Permissible Methane Spotter, Analog Meter, SN 20089 

Bacharach Methane Indicating Detector, Model 23-7600, SN 

550586 

Test equipment used: 

Voltmeter, AC Hewlett Packard 410C 

Timer, Counter, 

DVM Hewlett Packard 5326B 

Generator, Sweep Hewlett Packard 675A 

"TII Probe Hewlett Packard 11042A 

RF Power Amplifier A.R.F. Products 301D177 

Power Supply A.R.F. Products AAP- 12 

Load, 50 ohm Sierra 160-20FM 

TEM Cell instrument:^ for 

Industry, Inc. Model CC103 

SN 227 

Calibration Gas, Methane 2.5% as supplied by Bacharach with 

Calibration Kit. i 
Ffqumcy counter 

. . 

FIGURE B-1. - Test setup 

The signal generator was driven direct to the TEM Cell 

for output levels of -153 V and 1.0 V. The RF amplifier was 

placed in the setup only for the 30V tests. 

The sweep generator was set to the slowest sweep rate 

available for complete range coverage (80-1000 kHz) in 100 

seconds, 

The high impedance AC voltmeter monitored the actual 

input voltage to the cell. 

The frequency counter was monitored during the sweep 

tests to determine the exact frequency a failure might 

occur. 

The units-under-test were each tested in three 

orientations: Vertical, horizontal longitudal, and horizontal transverse. The test unit was placed on a styrofoam 

block center inside the TEM Cell. Each test unit "push on" 

switch was fixed "ON" during tests by the use of small block 

and tape, The readout of (each test unit was oriented for 

observation during each sweep test and position. 

CALIBRATION 

The TEM Cell relationship between the electric and 

magnetic fields is: 
In a TEM Cell the established electric field within its 

operating limits is: 

where V = Input voltage 

and b = distance between center conductor and bottom 

of the cell. 

Using b = 0.203 meters for the specified cell: 

or V (volts) = 76.5 H (AmperesIMeter) 

Example to establish a magnetic field of 2000 vV/m 

V = 76.5 X 2000 X = 0.153 volts 

TEST PERFORMANCE 

Each methane meter was tested at three different power 

levels and three orientations for each power level with methane gas and without methane gas. Initial tests performed 

at the level of 2000 UA/rn (.153V) revealed absolutely no 

interference in any test condition. Therefore, two higher 

levels were selected and cell tests re-run. The 1.0 volt 

level was the maximum output of the sweep generator directly 

and the 30 volt level was derived using a MF transceiver 

with transmitter operating at approximately 20 watts. 

The frequency was slowly swept from 80 through 1000 kHz 

in each power level and in each of the three orientations. 

Tests were performed with a continuous wave (CW) signal and 

with 30% AM modulation. 

The methane meters were closely and carefully monitored 

during every sweep test to observe for any possible 

momentary malfunction. 

TEST RESUGTS 

All three methane met.ers tested performed without 

malfunction during all tests with and without methane gas. 
CONCLUSION 

The test performed using the TEM Cell method revealed 

no failure conditions due to electromagnetic interference in 

all of the following conditio:ns: 

- RF frequency range of 80 to 1000 kHz. 

- Up to the maximum field strength (392156 vV/m). 

- Modulation of the RF carrier to 30% AM. 

- With and without methane calibration gas into the 

instruments under test. 

* 

These laboratory tests show no need to devise method to 

avoid EM1 as applies to these particular instruments. 
TEST DATA 

EM1 SUSCEPTIBILITY 

REFERENCE 

Test Plan, EM1 ~esting Using TEM Cell 

2, TEST INFORMATION 

Date Tqken by - 

Multiplier (See equation 4) V (volts) = 76.5 H(A/m) 

See data sheet attached, 

TEST SAMPLE 

Name 

Ser, No, 

Manufacturer 

Notes 
TEST DATA EM1 SUSCEPTIBILITY 

Frequency Leve 1 Failure Notes 

V,volts H,pA/m Mode 

80 - 1000 kHz ,153 2000 None Vertical Position 

80 - 1000 kHz 1.0 13070 None Vertical Position 

80 - 1000 kHz 30 392157 None Vertical Position 

80 - 1000 kHz ,153 2000 None Horizontal-Longitudal 

80 - 1000 kHz 1.0 13070 None Horizontal-Longitudal 

80 - 1000 kHz 30 392157 None Horizontal-Longitudal 

80 - 1000 kHz ,153 2000 None Horizontal-Transverse 

80 - 1000 kHz 1.0 13070 None Horizontal-Transverse 

80 - 1000 kHz 30 392157 None Horizontal-Transverse 
TEST DATA 

EM1 SUSCEPTIBILITY 

1. REFERENCE 

Test Plan, EM1 Testing Using TEM Cell 

2. TEST INFORMATION 

Date 7 March 1985 

Multiplier (See equation 4) 'V (volts) = 76.5 H(A/m) 

See data sheet attached. 

3. TEST SAMPLE 

Name Permissible Methane Indicating Detector 

Type Model 23-7660 

Ser. No. JJ0586 

Manufacturer Bacharach 

Notes Tested with NO Methane at zero level, 

zero modulation (CW) and 30% AM modulation. 
TEST DATA EM1 SUSCEPTIBILITY 

Frequency Leve 1 Failure 

V,volts H,vA/m Mode 

Notes 

80 - 1000 kHz .I53 2000 

80 - 1000 kHz 1.0 13070 

80 - 1000 kHz 30 392157 

80 - 1000 kHz .I53 2000 

80 - 1000 kHz 1.0 13070 

80 - 1000 kHz 30 392157 

80 - 1000 kHz .I53 2000 

80 - 1000 kHz 1.0 13070 

80 - 1000 kHz 30 392157 

None Vertical Position 

None Vertical Position 

None Vertical Position 

None Horizontal-Longitudal 

None Horizontal-Longitudal 

None Horizontal-Longitudal 

None Horizontal-Transverse 

None Horizontal-Transverse 

None Horizontal-Transverse 
TEST DATA 

EM1 SUSCEPTIBILITY 

1. REFERENCE 

Test Plan, EM1 Testing Using TEM Cell 

2, TEST INFORMATION 

Date 7 March 1985 

Multiplier (See equation 4) V (volts) = 76.5 H(A/m) 

See data sheet attached, 

3, TEST SAMPLE 

Name Permissible Methane Indicatins Detector 

TYPe Model 23-7660 

Ser, No, JJ 0586 

Manufacturer Bacharach 

Notes Tested with 2,5& Methane sas, zero modu- - - - - - - - -- - - - - - - 

lation (CW) and 30% AM modulation, 
TEST DATA EM1 SUSCEPTIBILITY 

Frequency Leve 1 Failure 

V,volts H,lJA/m Mode 

Notes 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

None 

None 

None 

None 

None 

None 

None 

None 

None 

Vertical Position 

Vertical Position 

Vertical Position 

Horizontal-Longitudal 

Horizontal-Longitudal 

Horizontal-Longitudal 

Horizontal-Transverse 

Horizontal-Transverse 

Horizontal-Transverse 
TEST DATA 

EM1 SUSCEPTIBILITY 

1. REFERENCE 

Test Plan, EM1 Testing Ulsing TEM Cell 

2. TEST INFORMATION - -- -- - - - - - 

Date 7 March 1985 

Multiplier (See equation 4) V (volts) = 76.5 H(A/m) 

See data sheet 2 

3. TEST SAMPLE 

Name Permissible Methane Spotter 

TYPe P/N 457167 Analog Meter Readout 

Ser. No. 20089 

Manufacturer Mine Safety Appliances 

Notes Tested with NO Methane at zero level, 

zero modulation (CW) and 30% AM modulation. 
TEST DATA EM1 SUSCEPTIBILITY 

Frequency Leve 1 Failure 

V,volts H,uA/m Mode 

Notes 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

80 - 1000 kHz 

,153 2000 None 

1 0 13070 None 

30 392157 None 

,153 2000 None 

1 0 13070 None 

30 392157 None 

,153 2000 None 

1.0 13070 None 

30 392157 None 

Vertical Position 

Vertical Position 

Vertical Position 

Horizontal-Longitudal 

Horizontal-Longitudal 

Horizontal-Longitudal 

Horizontal-Transverse 

Horizontal-Transverse 

Horizontal-Transverse 
TEST DATA 

EM1 SUSCEPTIBILITY 

1. REFERENCE 

Test Plan, EM1 Testing Using TEM Cell 

2. TEST INFORMATION 

Date 7 March 1985 

Multiplier (See equation 4) - V (volts) = 76.5 H(A/m) 

See data sheet attached. - 

3. TEST SAMPLE 

Name "SPOTTER" Model N Methane Detector 

TYPe P/N 465005 Digital LED Readout 

Ser. No. 02325 

Notes Tested with 2.5% Methane calibration gas, 

zero modulation (CW) and 30% AM modulation. 
TEST DATA EM1 SUSCEPTIBILITY 

Frequency Leve 1 Failure Notes 

V,volts H,PA/m Mode 

80 - 1000 kHz .I53 2000 None Vertical Position 

80 - 1000 kHz 1.0 13070 None Vertical Position 

80 - 1000 kHz 30 392157 None Vertical Position 

80 - 1000 kHz .I53 2000 None Horizontal-Longitudal 

80 - 1000 kHz 1.0 13070 None Horizontal-Longitudal 

80 - 1000 kHz 30 392157 None Horizontal-Longitudal 

80 - 1000 kHz -153 2000 None Horizontal-Transverse 

80 - 1000 kHz 1.0 13070 None Horizontal-Transverse 

80 - 1000 kHz 30 392157 None Horizontal-Transverse 
TEST DATA 

EM1 SUSCEPTIBILITY 

1. REFERENCE 

Test Plan, EM1 Testing Using TEM Cell 

2. TEST INFORMATION 

Date 7 March 1985 

Multiplier (See equation 4) V (volts) = 76.5 H (A/m) 

See data sheet attached. 

3. TEST SAMPLE 

Name . "SPOTTER" Model N Methane Detector 

TYPe P/N 465005 Digital LED Readout 

Ser . No. 02325 

Manufacturer Mine Safety Appliance 

Notes Tested with NO Methane at zero level, 

zero modulation (CW) and 30% AM modulation. 
TEST DATA EM1 SUSCEPTIBILITY 

Frequency Leve 1 Failure Notes 

V,volts H, pA/m. Mode 

80 - 1000 kHz -153 

80 - 1000 kHz 1.0 

80 - 1000 kHz 30 

80 - 1000 kHz ,153 

80 - 1000 kHz 1.0 

80 - 1000 kHz 30 

80 - 1000 kHz ,153 

80 - 1000 kHz 1,O 

80 - 1000 kHz 30 

None 

None 

None 

None 

None 

None 

None 

None 

None 

Vertical Position 

Vertical Position 

Vertical Position 

Horizontal-Longitudal 

Horizontal-Longitudal 

Horizontal-Longitudal 

Horizontal-Transverse 

Horizontal-Transverse 

Horizontal-Transverse 
TES'T DATA 

EM1 SUSCEPTIBILITY 

1. REFERENCE 

Test Plan, EM1 Testing Using TEM Cell 

2. TEST INFORMATION 

Date 7 March 1985 

Multiplier (See equation 4) V (volts) = 76.5 H(A/~) 

See data sheet attached, 

3, TEST SAMPLE 

Name Permissible Methane Spotter 

TYPe PIN 457167 Analoq Meter Readout 

Ser, No, , 20089 

Manufacturer Mine Safety Appliance 

Notes Tested with 2,5$ Methane calibration aas, - - - - - -- - 

zero modulation (CW) and 30% AM modulation, 
TEST DATA EM.1 SUSCEPTIBILITY 

Frequency Leve 1 Failure 

V,volts H, pA/m Mode 

Notes 

80 - 1000 kHz ,153 2000 None Vertical Position 

80 - 1000 kHz 1.0 13070 None Vertical Position 

80 - 1000 kHz 30 392157 None Vertical Position 

80 - 1000 kHz .I53 2000 None Horizontal-Longitudal 

80 - 1000 kHz 1.0 13070 None Horizontal-Longitudal 

80 - 1000 kHz 30 392157 None Horizontal-Longitudal 

80 - 1000 kHz ,153 2000 None Horizontal-Transverse 

80 - 1000 kHz 1.0 13070 None Horizontal-Transverse 

80 - 1000 kHz 30 392157 None Horizontal-Transverse 
APPENDIX C 

RFI SUSCEPTIIBILITY TESTS OF 

AERONAVIGATIONAL BEACONS 

RFI SUSCEPTIBILITY OF AERONAUTICAL NAVIGATION 

Aeronautical navigation, remote AC power transmission 

system switchings and MF communication systems employ 

carrier frequency signals in the LF and MF bands. Since 

these sytems use the same frequency bands, it is important 

that the radio signals in one service not interfere with 

normal operations of the other. 

To test if the MF system has an effect on aeronautical 

navigation, measurements were made in the vicinity of the 

transmission lines near Kaiser Coal Co.'s York Canyon mine 

portal and the Municipal Airport near Raton, New Mexico. 

The measurements at York Canyon mine show that the 

underground MF communications system induces signals that 

are 17 dB below power line carrier current signals. This 

would indicate that the MF system shouldn't have an effect 

on the aeronautical navigation system. The Federal 

Aviation Administration (FAA) has determined that no 

incidence of aeronautical navigation interface from 

powerline carries has been reported in the New Mexico 

regions. It is also un1ik:ely that the MF signals would 

interfere with remote power line switching since the power 

line carrier current receiver has a low sensitivity (-10 

dBm). Testing at the Raton Municipal airport also showed no 

interference between MF signals and navigational beacons. 

FREQUENCY BANDS AND SURFACE TRANSMISSIONS 

OF 

AERONAUTICAL NA.VIGATION BEACONS 

Non-directional Beacon (NDB) transmitters are used as a 

crosscountry aeronautical navigation aid. The signals are 

amplitude modulated (90-100%) with audio tones. The audio . 

tone modulation provides a Morris Code identification of the 

NDB location. Table C-A shows the frequency bands allocated 

for surface navigation. 

TABLE C-A. - Allocated radio spectrum in the LF and MF band. 

Frequency, MHz Service --------o--------------o--------------o------------o------- 

Radionavigation 

Fixed, Maritime Mobile 
TABLE C-A. - Allocated radio spectrum in the LF and MF band. 

Con. 

Frequency, MHz Service .--------.-.-----------------,----..-----------------------. 

Aeronautical 

Radionavigation 

Maritime Radionavigation 

Aeronautical 

Radionavigation 

Maritime Radionavigation 

Maritime Mobile 

Mobile 

Broadcasting 

Aeronautical 

Radionavigation 

Fixed, Mobile, 

Radiolocation 

Radionavigation 

Maritime Mobile 

Aeronautical Mobile 

Surface AC power tr,ansmission systems use single 

sideband (SSB) carrier current signals on power lines to 

monitor and remotely control substation switching. Table 

C-B illustrates the transmission characteristics of the 

radio control system. 

TABLE C-B. - Power line characteristics. 

Modulation SSB 

-----.-------.--------.------------------.----- 

Receiver Sensitivity 

Receiver Bandwidth (BW) 

Transmitter Power 

Frequency Range 

Leading Manufacturers 

-10 dBm 

16 kHz 

40 Watts 

60 to 300 kHz 

General Electric 

and Lynch 

Substation voltage and current levels are monitored and 

then analogue values are modulated on the SSB carrier. The 

SSB signal is coupled to a single conductor of the 

transmission system. The signals are received at 

dispatching centers and used to control and monitor the 

transmission system. A typical use of the carrier current 

communication system occurs when the dispatching center 

remotely switches the subst-ation breakers. Up to four 

digitally encoded signals can be encoded on a single 

suppressed carrier channel, 
RFI SUSCEPTIBILITY OF AERONAVIGATIONAL BEACONS 

Raton Municipa,l Airport Testing 

The susceptibility of aeronavigational beacons to ME' 

signals was evaluated during tests at Raton Crews Municipal 

Airport near Raton, New Mexico, 

The airport's non-directional beacon is located two 

miles south of Runway 20 alld operates on an assigned 

frequency of 284 kHz. The planview of the airport is given 

in figure C-1, 

r*' 

FIGURE C-1. - Planview of Raton Municipal Airport. 
The evaluation was made by placing the MF transmitter 

at locations 1 and 2 (arrow symbols) as shown in figure C-1. 

I Transmitter I 

FIGURE C-2. - Transmitter setup. 

The radiating antenna produces a magnetic moment of 6.0 

ampere turn meters. Its vertical plane heading is indicated 

by the arrow symbol. The automatic direction finding (ADF) 

receiver, which included a h~eading indicator, was located in 

a turbo'charged Lance aircraft. 

The test was started with the aircraft flying at an 

altitude of 11,500 ft on a, north heading 60 miles south of 

the airport. The pilot tuned. the ADF between 300 kHz and 284 

kHz during the test. The flight path included a 1000 ft 

(7350 ft) flyover as well as a ground check at the terminal 

location. During the test., the ADF, when tuned to 284 kHz 

was not affected by the 300 k,Hz test signal. 

In a second test, the aircraft was on a flight path set 

to intercept the 7350 ft flyover altitude. Approximately 5 

miles south of the airport, the flyover segment was heading 

in the direction of runway 20, During this test, the 

transmitter was located at the airport terminal. When the 

air craft was on a northerly flyover heading, the MF signal 

was detected at a radial range of approximately 1500 ft from 

the transmitter location, After landing, the aircraft was 

parked at the terminal and the transmitter was moved to the 

hanger location for a third test, 

In the third test, the ADF receiver monitored the MF a transmitter as it moved toward the hanger location. Beyond 

the 1/4 mile mark, the ADF receiver did not respond to the 

MF signal transmission but it did respond to the NDB beacon 

signal. The ADF receiver was also not affected by the MF 

transmission when the frequency separation was 16 kHz and 

the interference range was 1500 ft, 
York Canyon Mine Testing 

The MF communications system was tested at the York 

Canyon mine to determine if transmission of the MF signals 

over an AC power line would cause interference with 

aeronavigational beacons. 

An MF communications system was installed in the York 

Canyon mine. The system used .a multiple pair telephone 

cable for distribution of radio signals within the mine. 

These signals couple to the underground AC power system and 

induce carrier current flow in the electrical conductors. 

On the surface, the telephone cable and three phase 

conductors (and ground) are supported on the same wooden 

poles. Figure C-3 illustrates the surface AC power and 

telephone cable transmission system and figure C-4 

illustrates th'e measurement setup. , t' 1 

FIGURE C-3. 

Earth 

- 

&ace 

Surface 

- 

AC 

-?- 

power and telephone cable 

transmission system. 
South 

South 

South 

South 

North 

North 

North 

North 

Table C-D gives the power line carrier signal strength 

measured in the vicinity of the power transmission 

structure. The carrier current second harmonic level was 4 

dB below the fundamental carrier current level. 

TABLE C-D. - Power company power line with remote 

switching signal levels radiated from a surface 

AC power transmission line (167 kHz). 

Radial Distance Field Strength 

Along Surface (dB re lJA/m) Location 

South 

South 
TABLE C-D. - Power company power line with remote 

switching signal levels radiated from a surface 

AC power transmission line (167 kHz) -- Con. 

South 

South 

North 

North 

North 

North 

The level of carrier current signals arriving at the 

Kaiser substation was approximately 21 dB below the Kaiser 

substation output. This indicates that the signal 

propagating loss over 34 miles of power line is only 0.6 dB 

per mile. 

SUMIMARY OF TESTING 

Testing showed that M:F signals induced on AC power 

transmission lines will not interfere with aeronautical 

navigation and AC power line signals. 

The data indicated by the * indicates that the 

measurement signal level at 300 ft exceeds the FCC part 15.7 

limit by approximately 6 dB. The FCC limit at 400 kHz is - 

28 dB re 1 A/m.