ELECTROMAGNETIC NOISE IN ITMANN MINE 

W. D. Bensema 

M. Kanda 

J. W. Adams 

Electromagnetics Division 

Institute for Basic Standards 

National Bureau of Standards 

Boulder, Colorado 80302 

The views and conclusions contained in 

this document should not be interpreted 

as necessarily representing the official 

policies or recommendations of the Interior 

Department's Bureau of Mines of the U.S. 

Government 

June 1974 

Prepared for 

U. S. Bureau of Mines 

United States Department of the Interior 

Pittsburgh, Pennsylvania 15222 

Working Fund Agreement HO 133005 

U.S DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary 

NATIONAL BUREAU OF STANDARDS Rlchdrd W Robert5 D~rectcjr 
iii 
AMPLITUDE PSBABILITY DISTRIBUTION bEASUREP."Er\lTS---- 47 

4.1 Introduction and IJncertainties---------------- 47 

4 2 Results--------------------------------------- 48 

4.2.1 Introduction--------------------------- 4 8 

4.2.2 F4easurement Results-------------------- 49 

4.2.3 RYS and Average Values----------------- 5 1 

CONCLUSIONS---------------------------------------- 9 8 

RECOMMEhTDATIONS------------------------------------ 99 

ACKNOWLEDGMENTS------------------------------------ 100 

REFERENCES----------------------------------------- 101 

APPFNDIX------------------------------------------- 102 
LIST OF FIGURES 

Page 

Figure 2-1. 

Figure 2-2. 

Figure 2-3. 

Figure 3-1. 

Figure 3-2. 

Figure 3-3. 

Figure 3-4. 

Figure 3-5. 

Figure 3-6. 

Figure 3-7. 

Figure 3-8. 

Block diagram of portable instrumentation- 7 

System for field recording data to obtain 

amplitude probability distributions------ -- 8 

Block diagram of laboratory recording 

system modified for field use------------- 9 

Map of Itmann Mine where measurements were 

made, Cabin Creek panel------------------- 19 

Spectrum with mine in operation, measurements made 10 meters from end of longwall 

face, Cabin Creek panel. Spectral resolution of 78.1 Hz------------------------- 2 0 

Spectrum with mine in operation, measurements made 10 meters from end of longwall 

face, Cabin Creek panel. Spectral reso- lution of 3-91 Hz------------------------- 21 

Spectrum with mine in operation, measurements made 5 meters from end of longwall 

face, Cabin Creek panel. Spectral reso- lution of 78.1 Hz------------.------------- 22 

Spectrum with mine in operat ion, measure - ments made 5 meters from end of longwall 

face, Cabin Creek panel. Spectral resolution of 3.91 Hz------------------------- 23 

Spectrum with second shift in full operation, measurements made 5 meters from end 

of longwall face, Cabin Creek panel. 

Spectral resolution of 3.91 Hz----------- 24 

Spectrum of quiet time between shifts, 

measurements made 5 meters from end of 

longwall face, Cabin Creek panel. 

Spectral resolution of 78.1 Hz--------.--- 2 5 

Spectrum of quiet time between shifts, 

measurements made 5 meters from end of 

longwall face, Cabin Creek panel. 

Spectral resolution of 3.91 Hz----------- 26 
LIST OF FIGURES (continued) 

Page 

Figure 3-9. 

Figure 3-10. 

Figure 3-11. 

Figure 3-12. 

Figure 3-13. 

Figure 3-14. 

Figure 3-15. 

Figure 3-16. 

Figure 3-17. 1 

Figure 3-18. 

Spectrum with mine in operation, measure - 

ments made 10 meters from end of longwall 

face, Farley panel. Spectral resolution 

of 78.1 ljz-------------------------------- 2 7 

Spectrum with mine in operat ion, measure - 

ments made 10 meters from end of longwall 

face, Farley panel. Spectral resolution 

of 3.91 HZ-------------------------------- 2 8 

Spectrum with hydraulic pump operating, 

measurements made 10 meters from end of 

longwall face, Farley panel. Spectral resolution of 78.1 Hz ..................... 2 9 

Spectrum with hydraulic pump operating, 

measurements made 10 meters from end of 

longwall face, Farley panel. Spectral resolution of 3.91 HZ--------------------- 30 

Spectrum with conveyor belt starting up, 

measurements made 10 meters from end of 

longwall face, Farley panel. Spectral resolution of 78.1 Hz--------------------- 3 1 

Spectrum with conveyor belt start ing up, 

measurements made 10 meters from end of 

longwall face, Farley panel. Spectral resolution of 3.91 Hz--------------------- 32 

Vertical component of magnetic field 

spectrum about 3 meters from longwall machine--------------------------------- 33 

Vertical component of magnetic field 

spectrum at end of haulageway in Farley panel------------------------------------- 34 

Vertical component of magnetic field 

spectrum at end of haulageway in Farley 

Horizontal component of magnetic field 

spectrum at end of haulageway in Farley panel------------------------------------- 36 
Figure 3-26. 

Figure 3-27. 

Figure 3-28. 

Figure 3-29. 

Figure 4-1. 

Figure 4-2. 

Comparison of logarithmic average of 

magnetic field strengths of three mines 

at six frequencies-- ...................... 43 

Logarithmic average magnetic field strength 

summary----------------------------------- 44 

Comparison of EM noise levels near operating machinery from four mines------------- 45 

Comparison of EM noise levels along 

haulageways in four mines----------------- 46 

APD, 10 kHz, vertical component, Cabin 

Creek------------------------------------- 53 

APD, 30 kHz, vertical component, Cabin 

Creek------------------------------------- 5 4 
LIST OF FIGURES (continued) 

Page 

Figure 4-3. APD, 70 kHz, vertical component, Cabin 

Creek----------------------------------- 55 

Figure 4-4. APD, 130 kHz, vertical component, Cabin 

Creek----------------------------------- 56 

Figure 4-5. APD, 160 kHz, vertical component, Cabin 

Creek----------------------------------- 57 

Figure 4-6. APD, 250 kHz, vertical component, Cabin 

Creek----------------------------------- 58 

Figure 4-7. APD, 500 kHz, vertical component, Cabin 

Creek------------------------------------- 5 9 

Figure 4-8. APD, 1 MHz, vertical component, Cabin Creek 60 

Figure 4-9. APD, 2 MHz, vertical component, Cabin Creek 61 

Figure 4-10. APD, 6 MHz, vertical component, Cabin Creek 62 

Figure 4-11. APD, 14 MHz, vertical component, Cabin 

Creek------------------------------------- 6 3 

Figure 4-12. APD, 32 MHz, vertical component, Cabin 

Creek------------------------------------- 64 

Figure 4-13. APD, 10 kHz, vertical component, quiet time, Cabin Creek------------------------- 6 5 

Figure 4-14. APD, 30 kHz, vertical component, quiet 

time, cabin creek- -- - - -- - - - - - - -- - - -- - - -- - - 66 

Figure 4-15. APD, 130 kHz, vertical component, quiet time, cabin creek------------------------- 67 

Figure 4-16. APD, 500 kHz, vertical component, quiet time, cabin Creek------------------------- 68 

Figure 4-17. APD, 1 T\ltIz, vertical component, quiet time, cabin creek ......................... 69 

Figure 4-18. APD, 2 MHz, vertical component, quiet time, Cabin Creek------------------------- 70 

Figure 4-19. APD, 6 MHz, vertical component, quiet time, Cabin Creek------------------------- 71 

viii 
LIST OF FIGURES (continued) 

Figure 4-20. 

Figure 4-21. 

Figure 4-22. 

Figure 4-23. 

Figure 4-24. 

Figure 4-25. 

Figure 4-26. 

Figure 4-27. 

Figure 4-28. 

Figure 4-29. 

Figure 4-30. 

Figure 4-31. 

Figure 4-32. 

Figure 4-33. 

Figure 4-34. 

Figure 4-35. 

Page 

ApD, 10 kHz, roof bolts------------------- 72 

APD, 10 kHz, vertical component, Farley panel----------------------------------- 73 

APD, 30 kHz, vertical component, Farley panel------------------------------------ 74 

APD, 70 kHz, vertical component, Farley panel------------------------------------- 75 

APD, 130 kHz, vertical component, Farley panel------------------------------------- 76 

APD, 250 kHz, vertical component, Farley panel------------------------------------- 7 7 

APD, 500 kHz, vertical component, Farley panel------------------------------------- 7 8 

APD, 1 MHz, vertical component, Farley panel------------------------------------- 79 

APD, 2 MHz, vertical component, Farley panel------------------------------------- 80 

APD, 10 kHz, vertical component, Farley 

headpiece at the end of main belt haulage- 81 

RPD, 30 kflz, vertical component, Farley headpiece--------------------------------- 82 

APD, 70 kHz, vertical component, Farley headpiece--------------------------------- 83 

APD, 130 kHz, vertical component, Farley headpiece--------------------------------- 84 

APD, 160 kHz, vertical component, Farley headpiece--------------------------------- 85 

APD, 250 kHz, vertical component, Farley headpiece -------------- ------------------ 86 

APD, 500 kHz, vertical component, Farley headpiece--------------------------------- 8 7 
LIST OF FIGURES (continued) 

Page 

Figure 4-36. 

Figure 4-37. 

Figure 4-38. 

Figure 4-39. 

Figure 4-40. 

Figure 4-41. 

Figure 4-42. 

Figure 4-43. 

Figure 4-44. 

Figure 4-45. 

APD, 1 MHz, vertical component, Farley headpiece--------------------------------- 8 8 

APD, 2 MHz, vertical component, Farley headpiece--------------------------------- 89 

APD, 6 MHz, vertical component, Farley headpiece--------------------------------- 90 

APD, 14 ?Hz, vertical component, Farley headpiece--------------------------------- 9 1 

APD, 32 IWz, vertical component, Farley headpiece--------------------------------- 92 

Field strength excursions between 0.001% 

and 99% of the time as a function of 

frequency, vertical component, Cabin Creek 94 

Field strength excursions between 0.001% 

and 99% of the time as a function of frequency, vertical component, quiet time, Cabin Creek------------------------------- 95 

Field strength excursions between 0.001% 

and 99% of the time as a function of frequency, vertical component, Farley panel, ~pyil 17, 1973---------------------------- 96 

Field strength excursions between 0.001% 

and 99% of the time as a function of frequency, vertical component, Farley headpiece, April 19, 1973 ------------- - ---- --- 97 
ELECTROMAGNETIC NOISE IN ITMANN MINE 

Two different techniques were used to make 

measurements of the absolute value of electromagnetic noise in an operating coal mine, Itmann No. 3 

Mine, located near Mullens, West Virginia. The 

electromagnetic environment created by 250-volt-dc 

and 550- and 950-volt-ac machinery in two longwall 

panels was measured and is reported. One technique 

measures noise over the entire electromagnetic 

spectrum of interest for brief time periods. It 

is recorded using broadband analog magnetic tape, 

and the noise data is later transformed to give 

spectral plots. The other technique records noise 

amplitudes at several discrete frequencies for a 

sufficient amount of time to provide amplitude 

probability distributions . The specific, measured results are given in a 

number of spectral plots and amplitude probability 

distribution plots. 

Key words: Amplitude probability distribution; coal 

mine noise; digital data; electromagnetic communications; electromagnetic interference; electromagnetic 

noise; Fast Fourier Transform; Gaussian distribution; 

impulsive noise; magnetic field strength; measurement 

instrumentation; spectral density; time-dependent 

spectral density. 

1. INTRODUCTION 

This report gives data concerning electromagnetic noise 

in a coal mine that uses dc rail haulage power and ac-powered 

conveyor belt and longwall equipment. In this section, background information and a brief mine description are covered. 

In Section 2, measurement instrumentation is discussed. 

In Section 3, spectral plots of data are presented. In Section 

4, amplitude probability distributions (APD) of magnetic-field 

noise are given. 
g 

During operation, the machinery used in mines creates a 

wide range of many types of intense electromagnetic interference (EMI). This EM1 is a major limiting factor in the 

design of a communication system. The work reported. here 

gives the results of comprehensive measurements of this EM1 

in critical communication locations where miners extract coal 

as well as along haulageways. 

There are several EM1 parameters that can be measured: 

magnetic field strength, H; electric field strength, E; conducted current, I; and voltage, V, between two conductors. 

One parameter was emphasized, magnetic field strength. There 

are several reasons. First, electric field sensors are very 

insensitive at lower frequencies, and hence probably will not 
be useful in any practical mine communication system. Second, 

at any air-earth interface, only the magnetic field is essentially undisturbed, while the electric field is severely 

reduced. Third, any currents will induce magnetic fields, 

and hence measurement of the magnetic field will directly 

sense currents. Fourth, power line voltages are propagated 

as transmission line phenomena, are directly related to transmission line currents, and hence to magnetic fields induced. 

Thus, measuring magnetic field strength gives a representative 

composite picture of noise from currents and voltages from 

most sources. 

Although magnetic field strength measurements are emphasized here, even this one parameter is difficult to measure 

meaningfully. The IEEE definition [3] of magnetic field 

strength, H (magnitude of the magnetic field vector), is used 

in this report. The resultant magnetic field strength noise 

vector is a function of frequency, time, orientation, and 

location. Small variations in these parameters can cause 

several orders of magnitude difference in measured field 

strength. 

1.2 Mine Description 

The results and data presented in this report are based 

on measurements made on April 17 and 19, 1973, in the Itmann 

No. 3 Coal Vine located near Mullens, southwest of Beckley, 

West Virginia. The mine belongs to Consolidat ion Coal Company. 

The coal in this mine occurs in a narrow seam, approximately 

one meter thick, and is called "low-coal." The measurements 

were made in the two sections of the mine using the longwall 

mining technique. These sections were called Cabin Creek panel 

and Farley panel and were separated by about 1500 meters at 

the time of measurement. Overburden at Cabin Creek was 
290 meters and at Farley was 440 meters. The mine has seven 

conventional , room-and-pillar sect ions ; measurements were 

restricted to the longwall panels. 

The mine uses 250 V dc trolley 5aulage to carry coal out 

of the mine, and ac powered conveyor belt haulage from the 

section to the trolley. .A11 of the section longwall mining 

equipment is ac powered, with the exception of a dc-powered 

cable winch which was used occasionally to advance portions 

of the longwall equipment. The face and associated longwall 

equipment were 145 meters long. Each of the separate components 

of the lonpwall mining equipment was made by a different 

manufacturer, typically in England or Scotland. There were a 

total of six electric motors in the section ranging from 15 to 

300 F!P. The shear and face conveyor used 950 volts and the 

stage loader and hydraulic pumps used 550 volts. The stepdown transformer supplying these voltages is kept 45 to 230 

meters back from the face, and is sl,~pplied with 13,200 volts. 

Vertical clearance for personnel passage in Cabin Creek 

panel was limited to the 1.0 meter left by the extracted coal. 

In Farley panel, clearance was increased to 1.2 meters by the 

removal of some shale in the personnel passageways. 

Acoustical noise at the longwall face may be high enough 

to seriously degrade voice communication systems. 
2 . MEASUREMENT INSTRUMENTAT ION 

Two measurement techniques were used. In the first 

technique used a large portion of the spectrum is covered as 

a "snapshot" at one relatively short period of time. In 

three -dimensional form, several such "snapshots" can show how 

drastically a signal varies, not only with frequency, but 

also with time. In the second technique, variations over a 

20-minute time interval are measured at one frequency. 

Usually, a set of twelve different frequencies was used. 

Both techniques were used to measure two orthogonal components of magnetic field strength. This was done either by 

using two sys tems simultaneously or by varying the orientation 

of one system; both techniques were used in as many different 

locations as possible. 

With the exception of the electric dipole spectral plots 

and the roof-bolt APD's, all measured noise is reported in 

absolute quantities (instead of relative) to allow others to 

make effective use of the data. For the magnetic field strength 

measurements, the NBS field calibration site [4] was used with 

each complete measurement system to assure correct calibration. 

A complication to making these measurements is the mine 

environment, which is generally humid, dusty, poorly lighted, 

and potentially explosive. In Itmann Mine, the restrict ion 

caused by the one meter clearance in the passageways caused 

a significant reduction in the total number of locations where 

measurements could be made. Battery-operated, dust-protected, 

permissible gear was used for most of our portable measuring 

equipment. 

There are two types of noise recorded in the spectral plots, 

and hence two different magnetic field strength parameters are 

required, H and Hd. Results are given as the rms value of one 

component of magnetic field strength , H, versus frequency for 
discrete frequencies, or as one component of magnetic-fieldstrength spectrum density level [3] , Hd, versus frequency for 

broadband noise in the spectral plots. In the amplitude 

probability distributions, results are given as the rms value 

of one component of magnetic field strength versus percent of 

time this value is exceeded. The APD gives the distribution 

of the actual instantaneous values only as far as the 

measurement-system detector bandwidth will allow the detector 

to follow the time variations of the actual magnetic field. 

(In this context, noise envelope is sometimes used. ) Thus, 

the results are applicable for a communication receiver whose 

bandwidth is similar to the measurement -system detector 

bandwidth. 

Three measurement systems were used to make measurements 

underground. The three systems are described in the block 

diagrams shown in figures 2-1, 2-2, and 2-3. For a detailed 

description of these systems, see two previous reports [1,2]. 

There are some differences in the systems used in Itmann Mine 

from the systems used in Robena #4. The systems used in 

Itmann are the same ones used in Grace. 

The first system measures data for spectral plots and 

is fully permissible and portable. The second system meas - 

ures data for statistical cl.sscriptions of time variations, 

most commonly amplitude probability distribution; it is also 

permissible. The third system is not permissible but is 

portable (with considerable effort) ; it records data for both 

spectral plots and statistical presentat ions. 
SIGNAL MONITORS 

LOUD I SPEAKER I 1 OSCl LLOSCOPE 1 

SYSTEM 

#I 

LOOP I 

ANTENNA BROADBAND 

AMPLIFIER 

100-kHz 

MICROPHONE EDGE TRACK 

( VOICE) 

PORTABLE 

TAPE RECORDER 

(30 ips, record) 

Figure 2-1 Block diagram of portable instrumentation. FM 

tracks are used to record from 40Hz to 100 kHz; 

direct tracks are used from 3 kHz to 320 kHz. 

Systems 2 and 3 are identical to system 1. When 

the direct tracks are used, the 100-kHz low pass 

filters are eliminated, and the amplifier bandwidth is increased from 100 kHz to 300 kHz. The 

microphone is used for occasional vocal comments 

by the operator. 

TRACK 4 (DIR) 

TRACK 5 (FM) 

SYSTEM 

r 

ZOO-kHz CRYSTAL 

OSC l LLATOR 

TRACK I (FM) 

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

I 

lo METERS 

l MPEDANCE OF CABLE 

TRANSFORMER 

LOW PASS 

FILTER A 
Figure 2-2 System for field recording data to obtain amplitude 

probability distributions. 

SCOPE 
COLLAPSIBLE 

LOOP 

ANTENNA 

rn FIELD 

4- r 

BALUN . . STRENGTH 455kH7 MIXER 40kHz 

METER 

10 kHz - 2- 

1 10 kHz 

HIGH PASS 1 FILTER 

LOOP 

ANTENNA 

(SENSITIVE AXlS VERTICAL) 

COLLAPSIBLE 

LOOP 

ANTENNA EQUIPMENT 

SlMlLARTO3, 0- 

BUT WITH HORIZONTAL 

ANTENNA ORIENTATION 

FIELD I~H STRENGTH 

METER 

1455 HZ Fw 

1% kHz -32MHz 

4 

20 kHz 

LOW PASS -0- 

FILTER 

LOOP 

ANTENNA 

(SENSITIVE AXlS VERTICAL) 

RECORDER 

:HANNEL I (FM) 

IHANNEL 7 (FM) 

X> ips 

Figure 2-3 Block diagram of laboratory recording sys ten modified 

for field use. 
3. SPECTRUPI MEASIJREPlENT RESULTS 

3.1 Introduction and Uncertainties - -- 

In this section of the report, spectrum plots are 

presented and discussed. Most of these plots present magnetic 

field strength up to 100 kHz. Measurements were made at many 

different locations and results can be used to characterize 

electromagnetic noise levels generated by most fixed and 

mobile equipment used in this mine. Some plots give data 

to 3 kHz, 20 kHz, and 230 kHz. 

The spectra to 100 kHz, to 3 kHz, and to 20 kHz have 

uncertainties of + 1 dB over the following portions of the 

spectra. The 100 kHz spectra are valid either from 1 to 100 

ltHz or 10 kHz to 100 kHz as stated or shown. The 3 kHz spectra 

have the k 1 dB uncertainty from 100 Hz to 3 kHz. Between 40 Hz 

and 100 Hz the uncertainty is k 6 dB. The 20 kHz spectra 

have an uncertainty of + 1 dB from 750 Hz to 20 kHz. 

The spectra shown to 230 kHz have an uncertainty of + 2 dB 

from 3 kHz to 180 kHz. 

3.2 Antenna Sites 

Figure 3-1 is a map of Cabin Creek panel as it was on 

April 17, 1973, the first day measurements were made. The 

shear would operate back and forth across the face, as the 

mining operation advanced. The recording equipment was set up 

in the dinner man hole, and the antennas were deployed in the 

locations labeled A and R. 

On the second day measurements were made in Farley panel, 

which has similar equipment but was arranged in the mirror 

image of Cabin Creek panel. The layout can be determined by 

looking at figure 3-1 through the back side of the drawing. 

No separate map is given for Farley panel. 
3.3 Electromagnetic Noise Spectrum Results 

3.3.1 Interpretation 

When reading values from the spectra in this report, 

keep the following points in mind: 

1. Field strength values above the upper roll-off 

frequency and below the lower roll -off frequency are 

not calibrated and are therefore not shown on the spectra. 

2. The correct units for the spectral peaks are microamperes per meter (pA/m) . 3. The broadband noise between spectral peaks is as 

seen by a receiver having the same bandwidth as the Fast 

Fourier Transform (FFT) spectral resolution bandwidth 

used to compute the spectrum. The correct units for the 

background noise between peaks are microamperes per meter 

per square root x hertz [(p~/m)//s], where x is the 

spectral resolution of the FFT (x equals 78.1 Hz for the 

1-to-100 -kHz graphs) . An easy way to obtain the spectral density per (one) 

root hertz for .broadband noise is to subtract the required 

number of dB, remembering that the units have now changed to 

(p~/m)//K. For spectra with a resolution bandwidth of 78.1 

Ilz, subtract 10 loglO (78.1) or 18.93 dB. 

The Appendix gives the code key used in determining the 

meaning of the numbers in the header block at the top of 

each spectrum. The resolution bandwidth is also given on the 

ordinate of the plots. 

3.3.2 Cabin Creek Panel 

Figure 3-2 upper curve, shows the magnetic field noise 

spectrum from 1 kHz to 100 kHz received at the antenna location identified as A (in figure 3-1). The antenna sensitive 
axis was vertical. Location A is near the dinner man hole, 

10 meters from the end of the face, and is a busy area in the 

section. The lower curve in this, and in following figures, 

is the receiving system noise. It is included to indicate 

frequency ranges in which system noise may predominate. The 

lower curve is obtained by replacing the loop antenna with a 

dummy antenna. This figure shows data from 1 kHz to 100 kHz 

from one system and from 10 kHz to 100 kHz from another system 

that had lower system noise. An obvious feature in figure 3-2 

is a signal at 17.8 kHz. This is from the U.S. Navy transmitter NAA located in Cutler, Maine. With the exception of one 

shallow location in a hardrock mine, this is the only underground mine location where reception of a distant VLF station 

occurred. This strong signal from NAA in a coal mine under 

this large overburden (290 meters) is very unusual. The minegenerated noise shown on figure 3-2 extends to 100 kHz at the 

-20 dB relative to 1 pA/m level. Between 60 and 75 kHz, there 

is a dip in amplitude of 8 dB or more. Figure 3-3 shows the 

expanded spectrum at location A, ten meters from the end of 

the longwall face, with the mine operating. Figure 3-3 shows 

a noise spectrum dominated by powerline harmonics of 60 Hz. 

Figure 3-4 was measured at location B, five meters from 

the end of the longwall face, with the mine in operation. 

The noise spectrum at location B, with the antenna axis vertical, has about the same shape as the spectrum at location A, 

but is 4 to 10 dB higher. The spectra recorded at B, as at 

location A, shows a rise in noise level from about 80 kHz to 

100 kHz. Figure 3-5 shows the expanded spectrum at location 

B. The spectrum taken with the antenna sensitive axis horizontal gives 4 to 10 dB less noise than with the sensitive 

axis vertical. Figure 3-6 shows the expanded spectrum at loca 

tion B later, during the second shift, with the mine in full 

operation. Figure 3-6 is included because of the high level 

(108 dB relative to 1 pA/m) of 60 Hz noise. 
Figure 3-7 shows the noise spectrum measured at Cabin 

Creek panel during the quiet time between shifts at location 

B. This spectrum is about 10 to 20 dB quieter than when the 

mine is in full operation. Figure 3-8 shows the expanded 

spectrum measured at location B between shifts. The 60 Hz 

noise here is 46 dB lower than when the mine was in full 

operation during the second shift. 

3.3.3 Farley Panel 

Figure 3-9 shows the spectrum measured ten meters from 

the end of the longwall face in Farley panel. Farley panel 

was the mirror image of Cabin Creek. The measurement location for figure 3-9 corresponds to location A on figure 3-1. 

While the noise in Farley between 10 kHz and 20 kHz is sometimes as much as 10 dB higher than in Cabin Creek, generally, 

the noise in Farley may be considered lower than the noise in 

Cabin Creek panel. Neither the signal from NAA nor the increase in noise between 80 and 100 kHz show up in Farley. 

Figure 3-10 shows the expanded spectrum at location A, Farley 

panel, with the mine in operation. In Farley, the 60 Hz noise 

is 24 dB lower, the 360 Hz noise is the same amplitude, and 

most other harmonics are lower by as much as 15 dB, than at 

Cabin Creek. 

Figure 3-11 shows the spectrum measured at Farley panel, 

ten meters from the end of the longwall miner, during the quiet 

time at lunch hour. Only the hydraulic pump, associated with 

the 134 roof jacks, was running. This pump was left running 

much of the time. The spectrum is essentially the same as 

shown in figure 3-9 when the mine was in operation. Figure 

3-12 shows the expanded spectrum at Farley during lunch hour. 

The noise at 60 Hz is 4 dB lower during lunch hour. With some 

minor variation, the remainder of the expanded spectrum is 

about the same during lunch hour as during mine operation. 
Figures 3-13 and 3-14 show the spectrum recorded in 

Farley panel, ten meters from the end of the longwall face. 

The ac-powered conveyor belt was just starting up. Evident 

on figure 3-13 is powerline related noise out to 100 kHz, 

occurring with broad peaks about every 20 kHz. This noise 

signature is probably associated with an ac motor starting, 

and is probably of correspondingly short duration. Figure 

3-14 shows 7 dB higher 60 Hz noise than with the mine in 

operat ion (figure 3 -10) . Induction motors typically require 

about 2.5 times (8 dB) more current to start than to run. 

Probably the increased 60 Hz noise comes from the increased 

starting current being drawn by the starting of the conveyorbelt motor. 

Data taken with the third system in Farley Panel are 

shown in the following figures. Figure 3-15 shows a spectrum 

from 0.8 to 20 kHz taken about three meters from an operating 

shear on the longwall machine. Figure 3-16 shows typical 

noise at the end of the rail haulage, about 200 meters from 

the longwall face. Figures 3-17 and 3-18 show two components 

of noise generated by an unidentified piece of machinery. 

Figure 3-19 shows an expanded (to 20 kHz) spectra of figure 

3-17. There were strong cw signals at frequencies higher than 

our sys tems were normally operated; however, two illustrations 

are shown at frequencies higher than the system's calibration 

is valid. One signal shown in figures 3-20 and 3-21 is 

at 202.5 kHz; it may be a control signal specific to this 

mine. It did generate higher harmonics that were detected 

with other equipment. 

3.4 Miscellaneous Measurements 

3.4.1 Electric Field 

An active dipole, 1.93 meters long, was used as a sensor 

on the second day while in Farley panel. This dipole has not 
been calibrated, nor have any system nonlinearities in gain 

vs. frequency been removed by a correction curve. Therefore, 

all field strength information is only qualitative. Figure 

3-22 shows unprocessed data results obtained with the dipole 

ends pointed parallel with the drift and 0.75 meters from the 

phone line. Measurements taken with the dipole pointed across 

(perpendicular to) the drift gave fields that were 10 to 20 dB 

stronger than those shown in figure 3-22. Fields were 20 to 

30 dB weaker when the dipole was 4 meters from the phone line. 

This indicates the noise was coming from the phone line. The 

electric field data shown in figure 3-22 was taken simultaneously with the magnetic field data in two previous figures, 

3-13 and 3-14. The mine conveyor belt was just starting up. 

There is some similarity in the general shape of the two 1 kHz 

to 100 kHz spectra shown in figures 3-13 and 3-22. 

Because of the relative nature of the electric field 

measurements, the principal conclus ions that can be drawn 

are restricted to: (1) an electric noise field exists in 

Farley panel; (2) it is primarily powerline related, similar 

to the magnetic field noise; (3) the electric noise field is 

maximum for horizontal dipole orientat ion across (perpendicular to) the drift; and (4) the source of the electric 

field noise appears to be the phone line. 

3.4.2 Measurements of Voltage Between Roof Bolts 

A s ingle roof -support -bolt measurement was performed at 

Farley panel on the second day. The separation between the two 

bolts was 15.2 meters, and the voltage was measured using nonshielded copper wire clipped to the bolts. Figures 3-23 

and 3-24 show the resulting spectra. No receiver system noise 

curves are available for these spectra. It is not possible to 

say that the voltage measured between bolts was induced by any 
single mechanism. It may be any combination of electric field 

and magnetic field acting on the copper wires connected to the 

bolts, as well as by any potential produced by current flow 

between the bolts. 

3.5 Intercomparison of Different Mines 

3.5.1 Roof Bolt Voltage Intercomparison 

Figure 3-25 shows a summary table of the rms noise voltage 

measured between roof bolts of various spacings, in four mines. 

Logarithmic 

Frequency Roof Bolt Voltage Aver age 

Mine 

-- (Hz) dB Relative to 1 Vrms Volt age 

I tmann 1080 

(coal) 2160 

McE lroy 1080 

(coal) 2160 

Grace 1080 

(hardrock) 2160 

Rob ena 10 80 

(coal) 2160 

Figure 3-25. Summary of the rms noise voltage measured 

underground between r o o f - s u p p o r t -bolts in four mines. 

The logarithmic average is the arithmetic average of the dB 

values. Two frequencies within the voice baseband were chosen 

for comparison: 1080 Hz, the third harmonic of 360 Hz, and 

2160 Hz, the sixth harmonic of 360 Hz. The results show that 

the logarithmic averages for these two frequencies give the 

highest voltage (-53 dB with respect to 1 V rms) for Itmann, 

and the lowest value for Robena (-81.5 dB with respect to 

1 V rms) . Possibly a factor contributing to the low roof 

bolt voltage in Robena, is the fact that the bolts were on a 
line perpendicular to the haulageway. In Itmann, the bolts 

were on a line along the haulageway. In McElroy and Grace 

this distinction could not be made. 

3.5.2 Summary of 1 kHz to 3 kHz Data 

Figure 3-26 is a summary of magnetic field strength at 

powerline harmonic frequencies observed within Itmann (acpowered longwall), Robena (all 600 v dc) and the Grace (dieselpowered haulage) mines. Plotted are the dB averages of six 

powerline harmonics. This logarithmic average masks the 

highest single value. Average fields at five locations in 

Itmann are plotted as a function of distance from the nearest 

current-carrying cable or wire. The six frequencies chosen 

, are between 1020 Hz and 2940 Hz and are either the third 

through eighth harmonic of 360 Hz, or the highest adjacent 

powerline harmonic. 

The logarithmic average of noise from 1 kHz to 3 kHz in 

Cabin Creek panel of Itmann was 40 dB relative to 1 pA/m with 

the mine in operation. The noise was 7 dB less between shifts. 

The noise in Farley panel was 28 dB (as measured with the 

third system, first day) and 29 dB (as measured with the first 

system, second day) relative to 1 pA/m during operation, and 

was also 29 dB during lunch hour. The noise in Farley was 

5 dB higher during the time the conveyor belt was starting up 

than while running, and 8 dB higher measured 70 meters back 

from the face, near the end of the dc-powered rail haulage. 

This last finding is consistent with the observation that, in 

general, dc machinery is noisier than ac machinery. 

Figure 3-27 is a summary of magnetic field strength over 

the same frequency region as measured in the McElroy Coal Mine 

[7.] (ac-powered continuous miner and head loader, dc-powered 

shuttle cars and trolley) . 
A comparison of the magnetic noise from 1 kHz to 3 kHz 

in the four mines shows: 

1. Robena is noisiest, McElroy is next, followed by 

Grace and Itmann, which are about equal. 

a. The highest logarithmic average of section noise 

measured one meter from a cable in McElroy is 15 dB 

relative to 1 uA/m (at the power center). The noise 

is 16 dB higher at the "air split" on the haulageway 

in Robena, and 21 dB higher at the car pull in 

operation in Robena than the 15 dB value in McElroy. 

b . The highest logarithmic average of haulageway 

noise measured 2 meters from a cable in McElroy is 

7 dB stronger than the noise measured 2 meters from 

a load-haul-dump in Grace. The Grace noise is equal 

to the noise measured in Cabin Creek panel in Itmann. 

c. For a given constant distance from the currentcarrying cable in each of the four mines measured, 

the maximum logarithmic average noise between 1 kHz 

and 3 kHz varies over a rather small range. For 

example, at the 2 meter distance from the cable (or 

noise source), the highest noise was 48 dB (in McElroy) , 

and the lowest was 40 dB (in Grace and Itmann). 

The range of values is only 8 dB. Part of the 

reason for this low spread may be due to the parameter 

chosen for measurement, the logarithmic average. 

This average masks the peak value, which is dominant 

in causing interference to a broadband system. 

3.5.3 Intercomparison of 3 kHz to 200 kHz Data 

Comparative spectra from 3 kHz to 200 kHz from four mines 

are s'1own in figures 3'-28 and 3-29. The Robena curve is only 

calibrated to 100 kHz. 
roof jacks Conveyor 0 0 0 0 0 0 0 0 0 7 000 ?ace conveyor 

\O 0 0 0 0 0 0 0 0 0 0 0 010 

1111111111111111111IIIl1IIII1I11111 111 

# +pa 

face 2 shear 2 

dinner 

man hole main 

4 145 m m conveyor 

*-belt 

__etC 

main belt headpiece 

approximately 1000 meters 

direction of 

mine 

advancement 

Figure 3-1 Map of ltmann Coal Mine, Cabin Creek panel long-wall 

mining section. Farley panel is a minor image of 

this .sect ion. 
, LIIL G

-30 -- - - 

0 10 20 

- - 

=z 

0;: 

Figure 3-2 Compo

obtain

Itmann 

the en

antenn

April 
d d ma, 

0.4 .r 3 b 0.4 

a'cdrcc, 

a, u .4 d am 1r-i "hyd d M cd a,C, a,b 

C,d mcn a.4w rl 

or, 0 cd 

d - 

ca cb c, d d 04 

bGcd a,C, 

dE a,C, a, cd-4 dd 

kHrd k c, c, -a m - 64 

NEO az 0.4 - 

d&4kc, 

a, WcdE 

~4.r k 

W ma,= 

Oba 

UC, a, 00 -4 C, 4 

c,Na,dw* 

a3= E.4P-l 

c d mo 0 Qj 

cd-d F: - md 4 

-Ed 

wdd U 

0 d a, -.d 

a, 6 a,c, 

Ec,cdUk 

3 d acd a, kcd w3 

C, &4 

U aa,d m a, 0 Q4.d a0 k cd X 

C/)dU 3 cd 
12 0 0 2048 20 1 54-001 7.8l~00l 10104175 18.51.24 22 102 * I 95-00 -5.90+00I O.QO+OOO 0.00+000 20 43008 43008 

21 88 4 17 73~oin corr , rec.= -14 tot const.= 38.4 

C=25RG= 500(-14d81 DG= OFG= 0 AG-52 

0004008 

0.3086 1. 0224007. 

FREQUENCY, kHz 

Figure 3-4 Spectrum of magnetic field strength obtained 

loop antenna 1 kHz to 100 kHz, Itmann Mine, 

Creek panel, 5 meters from the end of the lo

face, mine in operation, antenna sensitive a

vertical, 3:17 p.m., April 17, 1973. Spectr

resolution is 78.1 Hz. 
HlCROAblPERE ONE TO RELA,TlVE dB I, STRENGTH, FIELD MAGNETIC RR 

OR FREQilE;lClES; DISCRETE FOR KETER, PER 

TO FtELRTlVE dB Hd, LEVEL, DEIiSlTY SFECTRUM I!,AGNETIC-FIELD-STRENGTH El8 

!2lsE EX:D 843YJ FOR , PER METER PER- MICROh:4PERE- ONE 

om 0 W 

3 W'a3 - 

- 

0 Crr CDCD3:CD 'ao 1-'3~r+~cr 

YPOP~ 

PX3e 

0 P' rm5Q I-' 

I-' 

0 

hru 

uro U 

":: d 

al - 11 J - 
ucco 

Y:u w .. ' 0 g. . ...a , . , - ' 0 

6; .: L. .L. L I1 -.; 0 

. , u cA 

::xc - 

of .,'.- m s::; 2 

o'm ' <> r- - w-- 

9- *- z r. rJ 

zm-a 

<~. - NI 11 

nM L9 ' 

< > -- c> z 1- + .°, 3 g .. N-- *"a7 
0 kW 

W> 

a ps 70 W 

g 22 

" CT "~60 0 -z r -Om 

a GO wo ==d 50 s&- -a= 

OW W 

aw 

9 2 ' - 20 

sg EE ;a B 

zg s 10 z - w ==% CT 5s gk a S? 0 1s ha" 

W -= AE -C.L &s -10 - 

= ?-&2 

FZ-20 4 

r E 0 c7 W 

zz3 cT - 30 5 -- 

a 

12 0 0 204# 20 1.34-001 7.#1*001 1010417¶ I#:¶8:02 32 I52 j.,%-!{ 322iO;O 7$~0+000 0.00*000 20 49008 43001 

oln corr., rec.= -20 tot const.= 32.4 

C=25 RG= 10001-20dBl DG= 0 FG= 0 AG= 52 

0 10 20 30 10 50 60 70 

FREQUENCY, kHz 

Figure 3-7 Spectrum of magnetic field strength obtain

loop antenna 1 kHz to 100 kHz, Itmann Mine

Creek panel, 5 meters from long-wall face, 

between shifts, antenna sensitive axis ver

357 p.m., April 17, 1974. Spectral resol

78.1 Hz. 
; 

.c. irc c:.- c. L 

5 .i",y L i a) r tct L. 

M? Er 2 0. C b? ro in ': . 
Figure 3-9 Spectrum 

loop an

panel, 

mine in 

11 : 50 a

is 78.1 

I 0 0 2 2 .Ol 7 810 IOfOf l:8 

1% 2I0 00.000 0.00.000 20 4BO0 

0 r 58 84 4 19 7k~ain corr.. rec.: -20 tot conY C'25 RG= 10001-20dB1 DG= 0 FG= 0 AG= 52 Z =I 60 W -m - 53 

Y -- 

1. 000+006 , 0.3086 

S 2 50 .t 0 -0- & IS 0 40. =&- ;z 

30 . 

N 4 

- 5 4 -20 ., y- wu 

+- w 

0% 

F zi -30 y w L 52% 

g 

.. 

e 

%? 

-40 

B ii 10 ;J 30 
3 

O 

ED- 

-- 
12 0 0 2041 20 1 34-001 7.11.001 10/04/71 1¶:01:56 

;o%-l{ -6~iO~l ,f~O+,OOO 0.00-000 20 41188 

aln cotr.. rec.= -20 tot c

C-25 RG= 1000l-2OdBl DG= 0 FG= 0 At= 52 

t 000+007 , 0 $086 

L 10 2: 3~ 

Figure 3-11 Spectru

loop an

panel, 

face, olunch h1:03 p.

is 78.1 
:2 0 C 2048 2: 2.69tttC 3.9:t::: 

1.95.CC3 -4.25tC:: 2,;:t;C; :.;:t::: 

61 113 4 17 73Gain corr., r

cc 0 500 1,000 

Figure 3-12 Spectrum of mag

antenna 40 Hz t

neters from the 

hydraui lc pxrp 

serisitlve axis 

Spectral resolu
I2 0 0 2041 20 1.14-001 7.11.001 10/04/71 1@:57:5@ U 102 

i.,%-O# -5$l;O(l 7$$0*000 0 00*000 20 4100@ 4100@- 

oln corr., rec.= -20 tot conrt. - 32.4 

C=25 RG= 10001-20dB) DG= 0 FG= 0 AG= 52 

,. 000+007 . 0.3086 2.5134006. 

40 50 60 

FREQUENCY, kHz 

Figure 3-13 Spectrum of magnetic field strength ob

loop antenna 1 kHz to 100 kHz, Itmann 

panel, 10 meters from the end of the l

face, conveyor belt starting up, anten

axis vertical, 12:42 p.m., April 19, 1

resolution is 78.1 Hz. 



." . . 

, _,. 

. . 

' < . .(; 

0 20 40 60 80 

Figure 3-17 Vertical 

in Farley 

Calibrati
CIJ 

m 

' 0 

Figure 3-18 Ho

in 

ca
UHrl 

d 

aJ 

8; "I a d .TI 

I2 (d 

oad 

L) 0 h *TI rlau 

cdrl rd 

L)kk 

.TI cd p U Fr .TI 

k rl 

d .a 2 

Figure 3-21 Horizont

in Farle

Calibrat

1 0 0 I 2 6 2 52 2 8 3 ' U 69 . 

1 5-003 -5 01.110 : OC.01: ' ....... '. "' 1: 43111 IIPPI 

S 89 92 A :' -3Go n co-. .cc : -26 :o; cons[ - 26.4 - 

Y -- r- :; y 5; - r- .I? 2 2F >., 

2 -a, .' -.. - * 22 

= 0- '- FZ 2~ d - 9 ' - .:. -a rg 

~ 

W P3: a ;z 22 d, 

,; u ;: = - <.. ",* 

. , . - i. -.- =g , .-, - ,. zcc ::z * e * :;., 3% -- '" 4 24 z- -2 .: 

5 48 

,- >- .. 3 s; =r3 - 1J. 

C.! Y 2" 

c . !$ y' . 

. . ('33 RG: 2::: -?;c5 I) . . , . :;: 52 

0001005 . 5:9: 1. !46+004, 

"' o 20 40 60 80 

FREQUE
k 5 0 

ad *d 

3Q)Q)Q) dd 3 

a.dd GM 

or, cd Oh 

d kUrn 

arldcd d 2%"; m 

a E dm 

oc,a.dr( 

H dd 

Q) 5 - a-d 

MN Q) c k 

dZd Q)r oa 

OJ!d; 

k aa c, 0.d -+Z woa E 

Fi OEFi 

a -+k 

Fi 0Fiw a03 

Q)C,Q) b 

.rl dvlh] 

WNcdk*, 

z a a, ...r( 

Ur C,h] 

.d %.add 

kFiQ)E 0 C, Fi -.d 

UQ) kmaQ ad cdb 3 3 

do& d 

0 MO . - c, 

w a a -+.d Q) 

0 CWQk 

a> 3w k 

E 3 0.d cdd 

3.d k kc, cd 

kc,~arnk 

C, U k c, UcdQ)&C,U 

Q) ac,d~) 

avrcu 

2:sdo u a-rl 
120- 

110 

g looW 

?u, 90- 

FZ 

4a 

W~ 80- 

aw 

%L 70- 

I I I I 1 1 I 1 I 

- 

-Z 

s MINING MACHINE 

(ROBENA) APPROXIMATE DATA TREND AWAY 

PRIMARY MINE SUPPLY CABLES (

40- 

FARLEY PANEL 

(ITMAN) .. 

--- 

1 

WO 

z 10- 

1 

3 PANEL APPROXIMATE DATA TREND \ 

= 0- 

-10 

(ITMAN) (GRACE) 

- 

1 I 1 I 1 I 1 1 I 

- 20' 

I 2 3 45 I0 20 30 4050 

DISTANCE TO NEAREST CURRENT CARRYING CABLE (ROBENA), M

DISTANCE TO CRUSHER ROOM NOISE SOURCE (GRACE), METE

Figure 3-26 Comparison of the logarithmic average of 

magnetic field strengths at six frequencies 

between 1 kHz and 3 kHz of Itmann, Grace, 

and Robena Mines as a function of distance 

from noise source. 
I I I I I ,\A I 1 I I I I 

~000o~~~~g"o" 

-gmcor- I 

SWU 'U313W Eld 3U3dWWOU31W 3N0 

01 3AllW13U BP 'H 'Hl9N3UlS 0131j 3113N9VW 
2s own r Prt r. (D m 3 (D 

m(D 

MICROAMPERE ONE TO RELATIVE dB H, STRENGTH, FIELD MAGNETIC RMS 

OR FREQUENCIES; DISCRETE FOR PER METER, 

TO RELATIVE dB Hd, LEVEL, DENSITY SPECTRUM MAGNETIC-FIELD-STRENGTH RMS 

NOISE BAND BROAD FOR ,/- PER MICROAMPERE-PER-METER ONE 

4. AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS 

4.1 Introduction and Uncertainties 

Statistical representations are required since the variations of field strength are, in general, random. The amplitude 

probability distribution (APD) of the received noise envelope 

is one of the most useful statistical descriptions of the 

noise process for the design and evaluation of a telecommunications system operating in a noisy environment [5,6,8] . 

By plotting the cumulative APD on Rayleigh graph paper, 

one can show clearly the fraction of time that noise envelope 

exceeds various levels. Rayleigh graph paper is chosen with 

scales such that a Rayleigh distribution (i .e. , envelope dis - 

tribution of Gaussian noise) plots as a straight line with 

slope of -1/2. Noise with rapid large changes in amplitude 

(e.g., impulsive noise) then has a much steeper slope, 

typically -4 or -5, depending on the impulsiveness of the 

noise and the receiver bandwidth. 

With the exception of the roof-support bolt measurements, 

all APJI measurements are reported in absolute quantities. 

The estimated limits of error for the APD noise measurements are ? 5 dB. Several sources of error that are critical 

to the overall accuracy of our measurements are listed below: 

1. Use of a discrete, digital level counter (levels are 

6 dB apart) contributes ? 1-dR quantization error limit. 

One -decibel step attenuators are used to achieve the 

+ one decibel. 

2. The system, i .e . , recording, data transcribing, and 

data processing, has a calibration uncertainty of 

? 0.5 dB [4]. 

3. The estimated uncertainty involved in using the portable and the laboratory tape recorders for record and 

playback is r 0.5 dB due to harmonic distortion, flutter, 

dropout, cross-talk, etc. 
4. The gain ins tab ili ty during measurements, gain 

changes between measurements and calibration, and the 

non-linearity of electromagnetic interference and field 

strength (EIFS) meters and mixers, all combined, contribute + 0.5 dB uncertainty. 

5. The gain instability and non-linearity of the digital 

level counter, the tuned frequency converter, the amplifier, and attenuators, all combined, contribute k 0.5 dB 

uncert ainty . 6. Connector losses and BNC cable losses, particularly 

at higher frequencies above 100 kYz, contribute 2 2.0 dB 

uncertainty . 

Some additional uncertainty beyond the stated measurement 

system uncertainty is caused by the in-mine environment. Care 

was taken to provide at least one meter separation from 

metallic objects wherever possible. However, coal, rock, or 

earth was sometimes immediately adjacent to a loop antenna. 

In all observed cases, this had no effect at frequencies up 

to 1 ?lHz. Above 1 MHz, earth and other reflections did in 

some cases cause k 1 dB variations, even with a shielded, 

balanced loop antenna. An estimate is that an additional 

+ 5 dB uncertainty might be advisable. However, due to the 

complexity of the shielded loop in the mine environment, this 

uncertainty cannot be rigorously bounded without substantial 

additional analysis. 

4.2 Results 

4.2.1 Introduction 

APD measurements were made on April 17 and 19, 1973, 

during operation in the Itmann #3 Coal Mine located near 

Mullens, southwest of Beckley , West Virginia. Descriptions of 

this mine are given in section 1.2. APD measurements were 
made at three locations. The first set of APD measurements 

was made on April 17, 1973, at Cabin Creek panel. Here, APD 

measurements were made both during the operation of the mine 

and during a period when the mining equipment was turned off. 

In addition, APD measurements between r o o f - s u p p o r t bolts were 

performed. The second set of APD measurements was made on 

April 17 at Farley panel, and the third set of measurements 

was made on April 19 at the headpiece for the main conveyor 

belt for Farley panel beside the mainline rail haulage. In 

these sets of APD measurements, only the vertical components 

of magnetic field were measured. In addition, APD measurements between roof -support bolts were performed at the Farley 

headpiece on April 19, 1973. 

4.2.2 Measurement Results 

Figures 4-1 through 4-12 show the APD's of the vertical 

component of the magnetic field noise measured during operation of the mine at Cabin Creek panel, location A, figure 3-1, 

on April 17, 1973. APD's measured during a period when mining 

equipment was not operating are shown in figures 4-13 through 

4-19. In these "quiet" measurements (with levels that are 

sometimes higher than during normal operation), the vertical 

components of magnetic noise were measured at frequencies 

ranging from 10 kHz to 6 MHz. Above 100 kHz, the magnetic 

field strength levels are not substantially different during 

quiet time compared to normal operation. The harmonics of 

88 kHz trolley phones extend to 8 MHz, and there are other 

higher frequency carriers, e . g. , 202.5 kHz. 

Figure 4 -20 shows the r o o f - s u p p o r t bolt measurement made 

at Cabin Creek panel, location A in figure 3-1, on April 17, 

1973. The separation between the two roof-support bolts was 

1.5 meters, and the APD's were measured using non-shielded 

copper wire connected between the roof -support bolts and 
the electromagnetic intensity and field strength (EIFS) meter. 

The dc resistance measured with a dc ohmmeter connected to 

these roof-support bolts was 30kQ. The RF impedance measured 

at 10 kHz using a CW generator, RF voltmeter, and RF current 

meter was 8 kQ. It is not easy to analyze what was measured 

through non-shielded copper wires. It is a combination of 

electric field coupled through a dipole with a lossy surrounding medium (i.e., coal) and of magnetic field through a lossy 

loop antenna, and of voltage induced by current flowing through 

the medium between the roof bolts. Therefore, relative volt - 

age is the parameter given. The rms value is arbitrarily 

assigned the value 0 dB. 

Figures 4-21 through 4-28 show APD measurements of the 

vertical component of magnetic field noise measured about 70 

meters (230 ft .) from the longwall face in Farley panel on 

April 17, 1973. Figures 4-29 through 4-40 show APD's of the 

vertical component of magnetic field noise measured at the 

headpiece for Farley main conveyor belt on April 19, 1973. 

Generally, the levels at the headpiece are about 20 dB higher 

than the levels 70 meters from the face. The length of time 

for each APD measurement is nominally 20 minutes; for the 

relatively long work cycle in a longwall mine, 20 minutes is 

insufficient time to provide statistical validity. Also, 

along main haulageways, the time required may be much longer 

than 20 minutes. 

Figure 4 -41 shows the roof -support bolt measurements 

made at the Farley headpiece on April 19, 1973. The separation between the two roof-support bolts was one meter, the dc 

resistance between these roof bolts was 30 kQ, whereas the RF 

impedance at 10 ktlz was 5.5 kQ. Again, the units are relative 

voltage, with the rms value arbitrarily assigned the value 

0 dB. 
4.2.3 RMS and Average Values 

The APD1s are integrated to give rrns and average values 

of the field strength, according to the equations 

H = - H dp (H) 

avg 0 

H 

rms = [-l H~ dp(H)]', 

where H represents the magnetic field strength of the noise, 

and p is the probability that the measured field strength 

exceeds the value H. These quantities are also dependent on 

the measurement bandwidth, the length of the data run, and 

possibly other parameters. Finite series are actually used 

for the numerical integration. The rrns and average values so 

arrived at are identified on each graph and are time averages 

(23 minutes) of these time-dependent parameters. If the tapes 

are played into ordinary rrns -reading meters , the meter readings will vary 10 to 20 dB over fractions of a second. The 

rrns value is directly relatable to noise power. With these 

wide variations of field strength with time, the most suitable 

presentations are statistical. 

Excursions of field strength between 0.001 and 99 percent, 

as well as rrns and average values, are summarized in figures 

4-42 through 4-45. The predetection bandwidth for these APD 

measurements either is 1 kHz or is normalized to 1 kHz. Figure 4-42, vertical component, Cabin Creek, is the summary 

figure for curves shown in figures 4-1 through 4-12. Figure 

4-43, vertical component, quiet time, Cabin Creek, is the summary 

figure for curves shown in figures 4-13 through 4-19. Figure 

4-44, vertical component, Farley Panel, is the summary figure 

for curves shown in figures 4-21 through 4-28. Figure 4-45, 
vertical component, Farley Headpiece, is the summary figure 

for curves shown in figures 4-27 through 4-40. 

Magnetic field strength generally decreases monotonically 

with increasing frequency at 20 dB per decade. A significant 

exception occurred during "quiet" time. Possibly due to the 

heavy use of 88 kHz trolley phones (with their attendant 

harmonics), during this period, the levels from 100 kHz to 

6 ?@Iz were freq-uency independent, and higher than during 

normal operation at the higher frequencies. 
Percent of Time Ordinate is Exceeded 

Figure 4-1 APD, 10 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 11:40 a.m., Cabin Creek, Itmn 13. 
4001 .OM Dl i .5 1 5 K) 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-2 APD, 30 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 12:20 p.m., Cabin Creek, Itmann #3. 
Percent of Time Ordinate is Exceeded 

Figure 4-3 APD, 70 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 12: 50 p.m., Cabin Creek, Itmann 13. 
.0001.001.01 .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-4 APD, 130 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 1:30 p.m., Cabin Creek, Itrnann #3. 
!I001 .OM Ol .I 5 1 5 I0 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-5 APD, 160 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 2:20 p.m., Cabin Creek, Itmann #3. 
Percent of Time Ordinate is Exceeded 

Figure 4-6 APD, 250 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 3:00 p.m., Cabin Creek, Itmann t3. 
Percent of Time Ordinate is Exceeded 

Figure 4-7 APD, 500 kHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 11:40 a.m., Cabin Creek, Itmann 13. 
Percent of Time Ordinate is Exceeded 

Figure 4-8 APD, 1 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 12: 20 p.~. , Cahin Creek, Itmann 63. 
-50 

-60 

-m 

,0001 .OM .OI .1 .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-9 APD, 2 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 12:50 p.m., Cabin Creek, Itmann 13. 
Percent of Time Ordinate is Exceeded 

Figure 4-10 APD, 6 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 1:30 p.m., Cabin Creek, Itmann 13. 
Percent of Time Ordinate is Exceeded 

Figure 4-11 APD, 14 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 2: 20 p.m., Cabin Creek, Itmann 13. 
Linear by - - in p) 

0 

- I0 

0 

w 5 -20 

L 

QI 

C 

E 

L 

-30 

t' 

QI 

P 

E 

0 

-40 . - 

E - 

0 

C 

Q, 

> .z -50 

- 0 

2 

m 

-0 

V 

I -60 

r: 

C 

0, 

C 

L ' -70 

0 

a8 .- 

LA 

0 

.- 

C 

a8 

g -80 

S 

-90 

-100 

.0001 .OM .OI .I .5 1 5 I0 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-12 APD, 32 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 3:00 p.m., Cabin Creek, Itmann 83. 
Percent of Time Ordinate is Exceeded 

Figure 4-13 APD, 10 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 3:40 p.m., Quiet Time Measurement, Cabin Creek, 

Itmann W3. 
Percent of Time Ordinate is Exceeded 

'igure 4-14 APD, 30 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 3: 50 p.m., Quiet Time Measurement, Cabin Creek, 

I tmann #3. 
Linear by - log,,(-~n p) 

0001 .001 .01 .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-15 APD, 130 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 4 :05 p.m., Quiet Time Measurement, Cabin Creek, 

Itmann 13. 
Percent of Time Ordinate Is Exceeded 

Figure 4-16 APD, 500 kHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 3:40 p.m., Quiet Time Maaeuranent, Cabin Creek, 

Itmann #3. 
Percent of Time Ordinate ir Exceeded 

Figure 4-17 APD, 1 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 3: 50 p.m., Quiet Ti- Meeeurement, Cabin Creek, 

Itrnann #3. 
Percent ot Time Ordinate is Exceeded 

Figure 4-18 APD, 2 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 4:00 p.m., Quiet Time Measuranent, Cabin Creek, 

Itmann 13. 
Percent of Time Ordinate is Exceeded 

Figure 4-19 APD, 6 mz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 4: 05 p.m., Quiet Time Meaeurement, Cabin Creek, 

Itmann #3. 
DO01 .OM .Ol I .5 1 5 10 20 30 40 50 60 10 80 85 90 95 98 99 

Percent of Time Ordinate in Exceeded 

Figure 4-20 APD, 10 kHz, roof bolt measurement, 1.0 kHz predetection bandwidth, 

April 17, 1973, 5:00 p.m., Cabin Creek, Itmann 1113. 
Percent of Time Ordinate is Exceeded 

Figure 4-21 APD, 10 kHz, vertical coraponent, 1.0 kHz predetection bandwidth, 

April 17, 1973, 12:30 p.m., Farley Panel, Itmann 1/3. 
Percent of Ti me Ordinate is Exceeded 

Figure 4-22 APD. 30 kHz, vertical component, 1.0 Idlz predetection bandwidth, 

April 17, 1 -7. 1.15 p.m., Farley Panel, Itmann 83, 
Percent of Time Ordinate is Exceeded 

Figure 4-23 APD, 70 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 2:00 p.m., Farley Panel, Itmann $3. 
Percent ot Time Ordinate is Exceeded 

Figure 4-24 APD, 130 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 17, 1973, 2:45 p.m., Farley Panel. Itmann #3. 
Magnetic Field St
Percent of Time Ordinate is Exceeded 

Figure 4-26 MD, 500 kHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 1:15 p.m., Farley Panel, Itmann 63. 
Percent of Time Ordinate is Exceeded 

Figure 4-27 APD, 1 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 17, 1973, 2: 00 p.m., Farley Panel, Itmann #3. 
10'100'1006 1' IS' S 01 OZ OF Ob E 09 01 08 S8 06 S6 66 86 

001- 

06- 

08- 

01- 
Linear by -+ loglo(-In p) 

ine Generated Noise 

i 1 Y 

I / I IiII j I 

I I 

t 

I --- 

I I---- ( 

I 1 --------- 

-. I I . .- - - -- - -- -. . 

1 

Percent of Time Ordinate is Exceeded 

Figure 4-29 APD, 10 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 19, 1973, 10: 20 a,&, Farley Headpiece, Itmann a3. 

81 
- 73 

(I, 

. - 

LL 

0 .- 

C 

al 

C 

CI1 

0 

r 

Percent of Time Ordinate is Exceeded 

Figure 4-30 APD, 30 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 19, 1973, 10:50 a.m., Farley Headpiece, Itmann f3. 

8 2 
Percent of Time Ordinate is Exceeded 

Figure 4-31 APD, 70 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 19, 1973, 11:25 a.m., Farley Headpiece, Itmann 83. 
4001.OM .OI .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-32 APD, 130 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 19, 1973, 12:00 p.m., Farley Headpiece, Itmann #3. 

84 
El, 

C 

aJ 

C 

El, 

-30 

- 40 

- 50 

-60 

D001.001.01 .I .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-33 APD, 160 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 19, 1973, 12:30 p.m., Farley Headpiece, Itmann $3. 
Percent of Time Ordinate is Exceeded 

.gum 4-34 APD, 250 kHz, vertical component, 1.0 kHz predetection bandwidth, 

April 19, 1973, 1:00 P.m., Farley Headpiece, Itmann 13. 

86 
Percent of Time Ordinate is Exceeded 

Figure 4-35 APD, 500 kHz, vertical component, 1.2 kHz predetection bandwidth, 

April 19, 1973, 10:20 a.m., Farley Headpiece, Itmann 83. 
9001.001.01 .I .5 1 5 10 20 30 40 50 60 TO 80 85 90 95 98 99 

Percent of Time Ordinate is Exceeded 

Figure 4-36 APD, 1 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 19, 1973, 10:50 a.m., Farley Headpiece, Itmann 113. 

88 
Magnetic Field Strength, H (dB relative to 1 microampere per meter R

I I I I 

0 I 

0 a = 0 
Perctn t of Time Ordinate is Exceeded 

Figure 4-38 APD, 6 MAz, vertical component, 1.2 kHz predetection bandwidth, 

April 19, 1973, 12:OO p.m., Farley Bcadpicce, Itmanu 13. 
Percent of Time Ordinate is Exceeded 

Figure 4-39 APD, 14 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 19, 1973, 12:30 p.m., Farley Headpiece, IhPann 13. 

9 1 
Percent of Time Ord~nate is Exceeded 

Figure 4-40 APD, 32 MHz, vertical component, 1.2 kHz predetection bandwidth, 

April 19, 1973, 1: 00 p.m., Farley Headpiece, Itmann #3. 

92 
Linear by - log,&-In p) 

30 

Percent of Time Ordinate is Exceeded 

Figure 4-41 APD, 10 kHz, roof bolt measurement, 1.0 kHz predetection bandwidth, 

April 19, 1973, 1:30 p.m., Farley Headpiece, Itmann #3. 

9 3 

I0 kHz 

60 

40 

20 

X 

l MHz 

Frequency 

Figure 4-43 Field strength excursions between 0

of the time as a function of freque

component, quiet time, Cabin Creek. 

- 1 I I IIII

-40 

1 

- 

- 

- 

i 

-60 

-80 

A - 

-. 1i1 I I I III

0- 

X 
a 6 

.d '+I 0 

LOU 


In Itmann, in addition to the lower than usual powerline-harmonic noise and the average impulsive noise, there are 

more intermittent cw carriers and harmonics of these carriers 

than in any other mine visited. Therefore, longer intervals 

of interference may be present at more discrete frequencies, 

and design of communication equipment should take this into 

account. 

8. REFERENCES 

Bensema, W.D., Kanda, M., Adams, J.W., Electromagnetic 

Noise in Robena No. 4 Coal Mine, NBS Tech. Note 654, 

April 1974. 

Adams , J. W. , Bensema, W. D. , Kanda, ?4. , Electromagnetic 

Noise in Grace Hardrock Mine, NBSIR 74-388, June 1974. 

The Institute of Electrical and Electronic Engineers, Inc., 

IEEE Dictionary of Electrical and Electronic Terms, 

Std. 100, 1972. 

Taggart , H.E. and Workman, J. L. , Calibration Principles 

and Procedures for Field Strength Meters (30 Hz to 1 GHz), 

NBS Tech. Note 370, March 1969. 

Crichlow, W.0. , et al. , Amplitude-probability distributions 

for atmospheric radio noise, NBS Monograph 23 (1960b). 

Thompson, W.1 . , 111, Bibliography of ground vehicle communications and control. AKWIC index, Report No. DOTTSC-UWA-71-3, July 1971. 

Kanda, bbtohisa, Adams, J.W., Bensema, W.D., Electromagnetic Noise in ?lcElroy Coal Mine, NBSIR 74-389. 

Spaulding, A.D., and Disney, F..T., Man-Made Radio Noise, 

Part I: Estimates for Business, Residential, and Rural 

Areas, OT Report 74-38, June 1974. 
9. APPENDIX 

Decoding of Spectrum Captions - 

Spectrum captions are generally organized into the following format : 

First line: MP NDT NZS NDA NPO RC DF date, time, frame, serial, 

where 

MP = Two's power of length of Fourier transform, example, 

2MP where MP = 12 

NDT = Detrending option, example, 0 (dc removed) 

NZS = Restart spectral average after output, example, 0 

(restarted) 

NDA = Data segment advance increment, example, 2048 

NPO = Number of spectra averaged between output calls, 

example, 20 

RC = Integration time in seconds per spectra, example, 0 .I68 

DF = Resolution bandwidth, spectral estimate spacing in 

hertz, example, 62.5 

Date = Date of computer processing, example, 03/21/73 

Time = Time of computer processing, example, 15:06:34 

Frame= Frame set number, example, 10 

Serial = Film frame serial number, example, 42. 

Second line : DTA DA(1) DA(2) DA(3) NSA NRP NPP, where 

DTA = Detrending filter parameter a, example, 0.00195 

DA(1) = Detrending filter average, K=l, example, 59.4 

DA(2) = - Detrending filter average, K=2, example, 0 

DA(3) = Detrending filter average, K=3, example, 0 

NSA = Number of periodograms averaged, example, 20 

NRP = Number of data points processed since spectrum 

initialization, example, 43008 

NPP = Number of data points processed since data initialization, example, 43008. 
Third line: RUN, SESSION, DAY, MONTH, YEAR Gain corr., rec. = 

tot. constr. =, where 

Run and Session = the title of the portrayed frame identifying 

the digitizing session and run number, 

example, 21-83 

Month, Day, Year = date data were recorded in the mine, 

example, 8 25 73 

Gain corr. rec. = receiver gain correction, example, 0 

tot. const. = constant gain correct ion of entire sys tem, 

example, 46.4 

Fourth line: C =, RG =, DG =, FG =, AG =, where 

C = correction curve used with data, example, 25 

RG = receiver gain and accompanying correction in dB added to 

the data, example, 200 (-6 dB) 

DG = digitizer gain, example, 0 

FG = filter gain in dB, often rounded to nearest single digit, 

example, 0 

AG = absolute gain correction added to data, example, 52 

Fifth line: Top of Scale, Standard Error, Spectral Peak, where 

Top of Scale = largest scale marking for computer drawn 

4 graph, example, 1.000+004 (1.0 x 10 ) 

Standard Error = standard error of curve, example, 0.316 2 

Spectral Peak = largest spectral peak observed, example, 

4.108+003 (4.108 x lo3) 
The specific, measured results are given in a number of spectral plots and amplitu e 

probability distribution plots. 4 

I 

17. KEY WOKIIS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper 

name; separated by semicolons) Amplitude probability distribution ; coal mine noise, digital 

electromagnetic communications; electromagnetic interference; electromagnetic noise; 

Fast Fourier Transform; Gaussian distribution; impulsive noise; magnetic field strength; 

measurement instrumentation; spectral density; time-dependent spectral density. 

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