ELECTROMAGNETIC NOISE IN LUCKY FRIDAY MINE 

W. W. Scott, NBS 

J. W. Adams, NBS 

W. D. Bensema, NBS 

H. Dobroski, U. S. Bureau of Mines 

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. 

October 1974 

Prepared for 

U. S. Bureau of Mines 

Pittsburgh Mining and Safety Research Center 

4800 Forbes Avenue 

Pittsburgh, Pennsylvania 15213 

Working Fund Agreement HO 133005 

- - -- 

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

NATIONAL BUREAU OF STANDARDS R~chard W Roberts Dtrector 
CONTENTS 

Page 

3.1 Introduction- - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - 13 

3.2 Surface Noise Measurements---------------------- 13 

3.2.1 Hoist House------------------------------ 13 

3.2.3 Noise Near Business District, Center of 

Town------------------------------------- 15 

3.3 Spectra at Levels Within the Mine--------------- 16 

3.3.1 The 1450 Level-- -----,------ -------------- 16 

3. 3.2 The 3650 Level---- - ------ --.------ -- --.---- 17 

3.3.3 The 4050 Level--------------------------- 17 

3.4 Spectra Obtained from Cage Runs, Loop Antenna- - - 21 

3.4.1 Mine Not in Operation----------.---------- 21 

3.4.2 Mine in Operation------------------------ 2 2 

AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS------ 74 

4.1 Introduction and Uncertainties------------------ 7 4 

NOISE AND ATTENUATION MEASUREMENTS ALONG THE HOIST 

ROPE ----- ------------- -------------- ----- ---- -------- 114 

5.1 Noise Measurements------------------------------ 114 

5.2 Attenuation Measurements------------ ------------ 115 

6. CONCLUSIONS- - - - -- - - -- - - -- - - -- -- -- -- -- ---- ---- -- - - --- - 126 

7. RECOMMENDATIONS- - - - - - -- - - - - - - -- - - - - - - - - - - - - - - -- - - - - - - 126 

8. ACKNOWLEDGMENTS-------------------------------------- 126 

9. REFERENCES- - - - - - - - - - - -- - - -- - - --- - --- - -- - -- - --- - - - - -- - 127 

10. A~~ENDIX--------------------------------------------- 128 

iii 
Figure 3-3. 

Figure 3-4. 

Figure 3-5. 

Figure 3-6. 

Figure 3-7. 

Figure 3-8. 

Spectrum of magnetic field strength, headframe - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 26 

Spectrum of magnetic field strength, headframe ----------------------------------- ---- 27 

Spectrum of magnetic field strength, headframe--------------------------------------- 2 8 

Spectrum of magnetic field strength, head- frame - - -- - - - - - - - - - - - - - - - - -- -- - - - - - - - - -- - - - - - 29 

Spectrum of magnetic field strength, headframe- -- --- - -- - - -- - - -- -- - - --- - -- -- -- - - ----- - 30 

Spectrum of magnetic field strength, headf Tame - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 31 
LIST OF FIGURES (Continued) 

Figure 3-9. Spectrum of magnetic field strength, headframe- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 32 

Figure 3-10. Spectrum of magnetic field strength, headframe--------------------------------------- 33 

Figure 3-11. Spectrum of magnetic field strength, Cedar 

Street, Wallace, Idaho-- - -- -- -------- - -- --- - 34 I 

Figure 3-12. Spectrum of magnetic field strength, Cedar 

Street, Wallace, Idaho--- ------------- -- -- -- 35 

Figure 3-13. Spectrum of magnetic field strength, Cedar 

Street, Wallace, Idaho---------------------- 

Figure 3-14. Spectrum of magnetic field strength, 1450 

level-- - - ---- ------ ---- -------- -- ------- ---- 37 

Figure 3-15. Spectrum of magnetic field strength, 1450 

level-- ---------.---------------- ------------ 38 

Figure 3-16. Spectrum of magnetic field strength, 3650 

level ---------------- --.--------------------- 39 

Figure 3-17. Spectrum of magnetic field strength, 3650 

level ------------------------- -------------- 40 

Figure 3-18. Spectrum of magnetic field strength, 3650 

level ------ - ------------------------- ------- 41 

Figure 3-19. Plan view of portion of 4050 level, Lucky Friday Mine--- ---------------- -------------- 4 2 

Figure 3-20. Spectrum of magnetic field strength, 4050 

level-- --------------- ---------------------- 4 3 

Figure 3-21. Spectrum of magnetic field strength, 4050 

level------------------- ----- - ----- --------- 44 

Figure 3-22. Spectrum of magnetic field strength, 4050 

level--------------------------------------- 4 5 

Figure 3-23. Spectrum of magnetic field strength, 4050 

level--------------------------------------- 46 
Figure 3-33. 

Figure 3-34. 

Figure 3-35. 

Figure 3-36. 

Figure 3-37. 

Figure 3-38. 

Spectrum of magnetic field strength, 4050 

1 eve 1 - - - -. - - - - - - - - - - - - - - - - -, - -, - - - - - - - - - - 5 7 

Spectrum of magnetic field strength, zero 

level-----------------------------,---------- 5 9 

Spectrum of magnetic field strength, 4050 

level--------------------------------------- 60 

Spectrum of magnetic field strength, zero 

level-----.---------------------------------- 6 1 
LIST OF FIGURES (Continued) 

Page 

Figure 3-39. Spectrum of magnetic field strength, 150 

level-.-------------------------------------- 62 

Figure 3-40. Spectrum of magnetic field strength, 1450 

level-- -------------- ---- ------ -- ---- -- ----- 63 

Figure 3-41. Spectrum of magnetic field strength, 3400 

level --------------- ------------------------ 64 

Figure 3-42. Spectrum of magnetic field strength, 4250 

level-------------------------.-------------- 65 

Figure 3-43. Spectrum of voltage across a 50 ohm load, 4250 level---------------------------------- 66 

Figure 3-44. Spectrum of magnetic field strength, 4250 

level ---------- - ------ ...................... 67 

Figure 3-45 Spectrum of voltage across a 50 ohm load 

(comparison of strong unknown source and 

typical noise) --- ------- - ---- ---- - --- ---.- -- - 68 

Figure 3-46. Spectrum of magnetic field strength, 4250 

level-- ----- - ---- - -------- ------------------ 69 

Figure 3-48. Spectrum of voltage across a 50 ohm load 

(unknown narrowband sources) - - - - - - --- -- -- --- 7 1 

Figure 3-49. Spectrum of voltage across a 50 ohm load 

(unknown narrowband sources) - - - -- - - - - - - - - - - - 7 2 

Figure 3-50. Spectrum of magnetic field strength, 1800 

level ------ --- -------- - --------- ------------ 73 

Figure 4-1. APD, 30 kHz, headframe---------------------- 78 I I 

Figure 4-2. APD, 70 k~~, headframe---------------------- 7 9 

Figure 4-3. APD, 150 kHz, headframe--------------------- 8 0 I 

Figure 4-4. APD, 250 kHz, headframe--------------------- 81 
LIST OF FIGURES (Continued) 

Page 

Figure 4-5. 

Figure 4-6. 

Figure 4-7. 

Figure 4-8. 

Figure 4-9. 

Figure 4-10. 

Figure 4-11. 

Figure 4-12. 

Figure 4-13. 

Figure 4-14. 

Figure 4-15. 

Figure 4-16. 

Figure 4-17. 

Figure 4-18. 

Figure 4-19. 

Figure 4-20. 

Figure 4-21. 

Figure 4-22. 

Figure 4-23. 

Figure 4-24. 

Figure 4-25. 

Figure 4-26. 

Figure 4-27. 

APD, 150 kHz, 1450 level-------------------- 88 

APD, 250 kHz, 1450 level-------------------- 89 

APD, 250 kHz, 1450 level-------------.------- 93 

APD, 150 kHz, 3050 level-------------------- 96 

APD, 150 kHz, 3050 level-------------------- 99 

APD, 200 kHz, 3650 level-------------------- 102 

viii 
LIST OF FIGURES (Continued) 

Page 

Figure 4-28. 

Figure 4-29. 

Figure 4-30. 

Figure 4 -31. 

Figure 4-32. 

Figure 4-33. 

Figure 4-34. 

Figure 4-35. 

Figure 4-36. 

Figure 5-1. 

Figure 5-2. 

Figure 5-3. 

Figure 5-4. 

Figure 5-5. 

Figure 5-6. 

Summary curves, headframe, horizontal 

(north-south) component--------------------- 106 

Summary curves, headframe, vertical component-------------------------------------- 107 

Summary curves, 1450 level, vertical component-------------------------------------- 108 

Summary curves, 1450 level, horizontal 

(north-south) component-- - -- -- ------ ---.----- 109 

Summary curves, 3050 level, horizontal 

(north-south) component--------------------- 110 

Summary curves, 3050 level, vertical component-------------------------------------- 111 

Summary curves, 3650 level, horizontal 

(north-south) component--------------------- 112 

Summary curves, 3650 level, vertical component- - -- - - - - - - -- - -- - - - - -- - - - - -- - - - - - - -- - - - 113 

EM noise in mine shaft, mine not in operation, 49 kHz- - -- - - -- ---- - - - - - -- - --.- - -- - - - - - - 116 

EM noise in mine shaft, mine not in opera- tion, 49 k~z-------------------------------- 117 

EM noise in mine shaft, mine not in opera- tion, 35 k~z-------------------------------- 118 

EM noise in mine shaft, mine not in opera- tion, 35 kHz ---------- ---------------------- 119 

EM noise in mine shaft, mine in operation, 75 kHz and 100 kHz-------------------------- 120 

EM noise in mine shaft, mine in operation, 52 kHz and 75 kHz--------------------------- 121 

ELECTROMAGNETIC NOISE IN LUCKY FRIDAY MINE 

Measurements of the absolute value of electromagnetic noise and attenuation along a hoist rope were 

made in an operating hard-rock mine, Lucky Friday Mine, 

located near Wallace, Idaho. Spectra of electromagnetic 

noise generated by various pieces of equipment, spectra 

of specific noise signals at various depths, and noise 

and attenuation on the 4250 foot (1295 meter) hoist, 

were measured. Three techniques were used to make the 

measurements. First, noise was measured over the entire electromagnetic spectrum of interest for brief 

time periods. Data were recorded using broadband analog 

magnetic tape for later transformation to spectral plots. 

Second, noise amplitudes were recorded at several dis - Crete frequencies for a sufficient amount of time to 

provide data for amplitude probability distributions. 

A third technique gave attenuation data through the 

direct measurement of field strength at various depths. 

The specific measured results are given in a number 

of spectral plots, amplitude probability distribution 

plots and amplitude curves as a function of depth. 

Key words : Amplitude probability distribution; digital 

data; electromagnetic interference; electromagnetic 

noise ; emergency communications ; Fast Fourier Transform; 

Gaussian distribution ; impulsive noise; magnetic field 

strength ; measurement instrumentation ; mine noise ; 

spectral density; time-dependent spectral density. 

1. INTRODUCTION 

This report gives data concerning electromagnetic noise 

in a hard-rock mine. 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. In Section 5, the results of direct measurements of 

field strength are given, from which attenuation may be 

computed. The last two sections (6 and 7) cover conclusions 

and recommendations. 
Only representative samples of the total data measured 

are given in this report, and only a limited set of datapresentation formats have been used. If additional data, or 

data presentation in other formats, are required, please 

contact any of the authors. With the specific permission 

of the Bureau of Mines, we will supply the additional data. 

A more complete description of the measurement systems used 

is given in the Robena Mine report [I]. 

1.1 Background 

The lack of reliable communication systems in mines is 

a long-standing problem. For emergency use, when all power 

in a mine is off, the residual electromagnetic noise is no 

problem. However, if a communication system were designed only 

for emergency use, it would have three serious drawbacks. First, 

it would not be ready for immediate use in an emergency; second, 

it would not be of any value during normal operations; and 

third, even during emergencies, some power must usually be 

present. Therefore, the Bureau of Mines decided to design a 

communication system that could be used for both emergency and 

normal operational conditions. 

Also, two-way communication to personnel in a moving 

hoist is desirable for normal operating conditions, and is 

necessary in emergency conditions. 

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, 

particularly along the hoist path at various depths. 
Several EM1 parameters can be measured: magnetic field 

strength, H; electric field strength, E; conducted current, i; 

and voltage, v, between two conductors. Two parameters were 

emphasized: magnetic field strength measured with loop antennas and noise currents on the hoist cable measured with a 

clamp-on toroid. (Hoist cables will be referred to a 'ropes' 

hereafter .) 

There are several reasons for emphasizing the measurement 

of the magnetic field strength. First, at any air-earth interface, only the magnetic field is essentially undisturbed, while 

the electric field is severely reduced. Second, any currents 

will induce magnetic fields, and hence measurement of the 

magnetic field will directly reflect currents. Third, power 

line voltages are propagated as transmission line phenomena, 

and are directly related to transmission line currents and the 

magnetic fields induced. Thus, measuring magnetic field strength 

gives a representative composite picture of noise from currents 

and voltages from most sources, including arcing equipment. 

Voltage from the toroid is measured to determine signal 

strength, noise, and hence signal-to-noise ratios for design 

information for a specific system, a two-way hoist-phone. 

Although magnetic field strength measurements are 

emphasized here, even this one parameter is difficult to 

measure meaningfully. The IEEE definition [2] of magnetic 

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

is used in this report. Since there are a multitude of different sources that generate all known types of noise, 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 August 25, 26, and 27, 1973, and on 

February 8, 1974, in the Lucky Friday Mine and other locations 

near Wallace, Idaho. The mine, shown in figure 1-1, belongs 

to Hecla Mining Company and produces ore containing lead, 

silver, and zinc. Access is by way of a single, double-drum 

hoist, using the No. 2 shaft. There are two hoists on the 

No. 2 shaft. Ore is removed from the stopes via raises and 

drifts and then is removed from the mine by the same hoist 

personnel use. Somem~t is_dcC~,,o-wered: the 5-ton, 90 

cell, battery-powered locomotives, and the 1250 horsepower 

motor used to raise the hoists. Much equipment uses ac power 

at 120, 440, and 2400 volts: air-conditioners, ventilation 

systems, compressors, lighting, and battery chargers. Other 

equipment uses compressed air. 

Shifts run to 3:00 p.m., 4:00 p.m., 11:OO p.m., 12 a.m., 

and 7:00 a.m.; blasting is scheduled at 2:20 p.m., 11:20 p.m., 

and 6:20 a.m. 

The temperature and humidity are high, although not 

excessive in most places. 

Of particular interest in this measurement effort is how 

signals and noise propagate along the shaft, with and without 

hoist ropes. Power cables and compressed-air pipes, as well 

as sand-transport pipes, run in this same shaft, so there is 

always a composite, single conductor present to serve as one 

wire of a two wire transmission line. The presence of either 

hoist rope strongly affects transmission characteristics along 

the shaft by providing a second wire of a two-wire transmission 

1 ine . 
4sFigure 1-1 Isometric Projection of Lucky Friday Mine. 
2. MEASUREMENT INSTRUMENTATION 

Three measurement techniques were used. The first covers 

a large portion of the spectrum as a "snapshot" at one instant 

of time. In three-dimensional form, several such "snap-shots" 

can show how drastically a signal varies not only with frequency but also with time. The second technique gives variations over a 20-minute time interval as a view over a narrow 

frequency window. Usually, noise was measured at a set of 

four different frequencies. Both techniques were used to 

measure two orthogonal components of magnetic field strength 

by either using two systems simultaneously or by varying the 

orientation of one system. Both techniques were used in as 

many different locations as possible. Whether the noise signal 

tends to be Gaussian or impulsive depends on the number of 

sources and the distance to each source. With the third technique, values of field strength at various levels under various 

conditions were recorded. These measurements gave attenuation 

values, complicated mainly by severe standing-wave patterns. 

Noise levels were recorded also, but values taken this way 

cannot meaningfully relate the time variations of the noise 

parameter. The values given are within the bounds indicated 

in the 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 is used with each complete measurement 

system to assure correct system calibration [3]. 

The mine environment is generally humid, dusty, hot, and 

poorly lighted. This complicated the measurement process. 

Most of our portable measuring equipment was battery-operated, 

dust-protected, and permissible. 
Two types of noise are 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; it is given as one component of magneticfield-strength spectrum density level [2], 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. 

Two measurement systems were used to make measurements 

underground. One system was configured four different ways. 

Five block diagrams are shown in figures 2-1 through 2-5. 

For a detailed description of these systems, see previous 

reports [I, 41. The systems used in Lucky Friday are the ones 

used in previous mine measurement but are configured differently 

in some cases. 

The first system measures data for spectral plots and 

is fully permissible and portable. The second system is not 

permissible but is transportable; it records data for both 

spectral plots and statistical presentations, e.g., amplitude 

probability distributions. 
MICROPHONE EDGE TRACK 

(VOICE) 

Figure 2-1 Block diagram of portable instrumentation, first system. 

FM tracks are used to recard frnm..100 Hz to 100 kHz; 

direct tracks F -. 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. 
LOOP ANTENNA, 

SENSlTlV E AXlS VERTl CAL 

OSCl LLOSCOPE '+ 

CHANNEL 

SIMILAR TO 3, 

BUT WITH ANTENNA 

SENSITIVE AXlS 

ANALOG 

TAPE RECORDER 

Figure 2-2 Second field recording system, first configuration. 

Figure 2-4 Second field recording system, third configuration; it 

recorded data for APD'S on 3650 level. 

11 
Figure 2-5 Second field recording system, fourth configuration; it 

was used on hoist runs up and down shaft. 

TO TOROID 

AROUND HOIST ROPE 

A 

1) BALUN -05 (DIR) 

FIELD STRENGTH 

METER i 

20 kHz 

LP FILTER 07 (FM) 
3. SPECTRUM MEASUREMENT RESULTS 

3.1 Introduction 

In this section of the report, spectrum plots are presented and discussed. Most of these plots present magnetic 

field strength to either 100 kHz or 200 kHz. The curves to 

100 kHz or less have an uncertainty of + 1 dB. The curves 

to 200 kHz have an uncertainty of + 2 dB from 3 kHz to 200 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. 

3.2 Surface Noise Measurements 

3.2.1 Hoist House 

The hoist house contains a 1250 hp, direct current, 

double-drum hoist with dc current supplied by a motorgenerator. Figures 3-1 and 3-2 show the noise measured in 

the hoist house. The antenna sensitive axis was vertical 

and about two meters from the electrical cables supplying 

the dc current to the hoist motor. The cables were below 

the concrete floor. For figure 3-1 the hoist was lifting a 

load (8.2 metric tons) of waste rock at 1300 feet/minute 

(396 m/min.), and for figure 3-2 at 1700 feet/minute (518 m/min.). 

This noise is one of the higher levels measured at Lucky 

Friday. Figures 3-1 and 3-2 are typical of several spectra 

taken in the hoist house, on Monday, August 27, 1973, a typical working day at the mine. This group of spectra (including 

figures 3-1 and 3-2) differs from other spectra taken around 

other machinery in that (1) noise in figure 3-2 is not dominated by powerline harmonics, (2) there are no obvious 
commutator-produced spectral lines, which might normally be 

expected to occur around dc commutated machinery, (3) the 

spectral lines at 300 Hz and 925 Hz are the only lines that 

appear regularly; also, they are not harmonically related, 

and (4) other lines at non-harmonically related frequencies 

appear irregularly. The line at 1090 Hz is typical; it appears 

only in the spectrum shown in figure 3-2 and in none of the 

other spectra taken in the hoist house. Note that on figure 

3-1, the spectrum has a minor increase centered around 19 kHz. 

Later in this report, other spectra taken elsewhere will show 

a similar increase. The inference will be drawn that the 

hoist house noise is propagating down the 1 1/2 inch (3.8 cm) 

steel hoist cable (rope) to some extent. 

3.2.2 Head Frame 

The head frame was 75 m away and uphill 40 m from the hoist 

house. The steel head frame stood about 20 meters high and 

supported two large sheaves, which in turn supported wire ropes, 

one each for the north and south shafts. Figures 3-3 and 3-4 

show the noise measured on the surface 0.7 m from the open 

north shaft, with the antenna sensitive axis horizontal EW 

(pointed toward the wire rope). These measurements were made 

on August 27, 1973, a typical working day. The minor increase 

at 19 kHz seen in the hoist house does not show up here; however, it may have been masked by a sferic impulse. The same 

type of noise as heard on the audio monitor in the hoist 

house could also be heard at the head frame. However, at 

the head frame, there was a regular periodicity to the noise 

that probably can be correlated to the rotation of the main 

hoist drum. Finally, figure 3-3 shows the 18.6 kHz signal from 

the Navy Jim Creek transmitter, NLK Washington. 
Spectra of three components of magnetic field noise at 

the head frame are shown in figures 3-5, 3-6, and 3-7. The 

noise levels are much lower than might be expected near operating 

machinery. Either distant sferics or arcs from the hoist house 

(where dc motors were operating) raise the noise levels slightly 

and in unpredictable ways. This is shown in figures 3-8, 3-9, 

and 3-10. The two hoist ropes leading from the hoist house 

to the head-frame serve as two-wire transmission lines, but 

the increase or decrease in impulsive noise does not seem to 

be related to rope movement. Compare figures 3-9 and 3-8. 

3.2.3 Noise Near Business District, Center of Town 

Three components of surface noise were measured on the 

sidewalk along a row of buildings with 'Leon signs): This is 

representative of surface noise over a mine that is under a 

town or city. The noise was predominantly at 60 Hz or its 

odd harmonics, and was quite strong, approaching 90 dB above 

a microampere per meter at 300 Hz, and 80 dB above a microampere per meter at 180 Hz. At frequencies above 2.5 kHz, 

all harmonics were of nearly equal amplitude. Valleys between 

the power line harmonics are about 40 dB above one pA/m up to 

2.5 kHz, but are down to 10 dB above one pA/m from 5 to 10 kHz. 

The vertical and horizontal (N-S) components of magnetic 

field strength were both strong, while the horizontal (E-W) 

component was about 20 to 30 dB lower. The component which 

is strongest or weakest will be different in each location 

depending principally on the direct ion (s) of the strongest 

source(s) . The magnetic field noise spectra are shown in figures 

3-11, 3-12, and 3-13. 
3.3 Spectra at Levels Within the Mine 

3.3.1 The 1450 Level 

The levels within the mine are named by the depth, and 

correspond to the depth below the zero level in feet. The 

zero level is 40 meters below the headframe located on the 

surface. The depth in meters is obtained by multiplying the 

depth in feet by 0.3048 and adding 40 meters; the 1450 level 

is therefore 482 meters deep. 

The 1450 level contained a 300 hp water pump. The 

motor used 67 amperes at 2300 V, three phase. Figures 3-14 

and 3-15 show the noise measured at this level with the pump 

not operating. There is no longer any mining activity at 

this level. The measurement was made on Saturday, August 25, 

1973, a non-working day in the mine. The antenna was one 

meter from the shaft with the sensitive axis horizontal N-S, 

tangent to the opening to the shaft. Figure 3-14 shows the 

same minor increase in the spectrum around 19 kHz that was 

noted in the hoist house. The noise, as heard on the audio 

monitor, had the characteristic sound of "grease-frying," 

but was too regular for atmospherics. The noise from the 

hoist house is similar to noise at the 1450 level. With the 

300 hp pump turned on, the only change was a 20 dB increase 

in the 60 Hz noise. 

While the teams from NBS were in the mine making noise 

measurements, another team from a communications firm was 

making rope transmission and impedance tests by injecting 

a single frequency signal into the north rope. The signal 

was coupled into the wire rope using a ferrite ring, and was 

nominally at a frequency of 50 kHz. Figure 3-14 shows a cw 

signal as it was received at the 1450 level. The frequency 

of this signal was 44.6 kHz, but this was not one of the 
frequencies used in their tests. The transmitter might 

have been detuned at the time of our measurement, or there 

may have been some other source present. For example, see 

noise signals as shown in figure 3-49. 

3.3.2 The 3650 Level 

Noise measurements were made at a working level on 

February 8, 1974. Activity was very low at the time, so 

the noise levels measured may be somewhat lower than occur 

normally. A spectrum of the vertical component is shown in 

figure 3-16; a horizontal (N-S) component is shown in figure 

3-17. Each covers time intervals during a transient of noise. 

Antenna location was about two meters east of the hoist doors. 

Figure 3-18 shows the spectrum of typical machine noise. 

3.3.3 The 4050 Level 

The 4050 level (1274 meters below the surface) was the 

deepest level at which normal mining was being carried on in 

August, 1973. The mine extended about a hundred meters lower 

to some mine development workings. The 4050 level contained 

a complex array of wires and switchboxes controlling pumps, 

fans, battery chargers, lights, etc. Figure 3-19 shows a 

plan view of the area near the shafts. 

Figures 3-20 and 3-21 show the noise measured at location 

A (shown on figure 3-19) on Saturday, August 25, 1973, a nonworking day in the mine. The antenna was 0.6 meters in front 

of the open shaft door, with sensitive axis horizontal N-S. 

Figure 3-20 shows the low noise level present at the 4050 level 

with most of the mine shut down. Figure 3-20 also shows what 

we believe is a strong test signal; the frequency was 48.6 kHz. 

It is significant that this test signal (if such it is) has 

penetrated the mine from the surface along metallic paths. 
load is increased. These and other spectra in this report show 

harmonic structure that could probably be traced to other 

rotating machinery. 

With the antenna in the above position (sensitive axis 

vertical, 0.6 m in front of the open south shaft door), during 

lunch, the 48.6 kHz (nominally 50 kHz) signal was transmitting 

into the north rope, with the north cage at the zero level 

(40 m below the surface). Measurement results at the 4050 

level showed a 48.6 kHz signal strength of -12 dB relative to 

1 uA/m for the south cage at the bottom of the shaft (about 

50 meters below the 4050 level), 0 dB re 1 pA/m for the cage 
at the 4050 level, -16 dB re 1 pA/m for the cage 6 meters 

above the 4050 level, and -15 dB for the cage 40 meters above 

the 4050 level. A possible explanation for these results is 

that the cage acts as a moving transmission line termination. 

When the cage is at the 4050 level, the antenna picks up the 

current in the termination. 

Figures 3-26 and 3-27 show the noise measured at location 

B in figure 3-19. The antenna was then 10 meters away from 

the north shaft with the sensitive axis vertical. A large 

number of harmonically related spectral lines can be seen 

from 1 kHz to 15 kHz on figure 3-26. These lines are generally 

present on most spectra taken while at this level. The lines 

arising from the water pump previously pointed out in figure 

3-24 appear here also and are marked by arrows. The noise 

at 4.2, 8.4, 11.2 and 14.2 kHz also appears on the spectra 

taken with the antenna axis horizontal N-S. For the horizontal orientation, the noise is about the same at the upper 

three frequencies mentioned, and is as much as 12 dB lower 

at other frequencies. 

Three large fans, one 20 hp, and two 40 hp, 440 volt 

three phase, were turned on and spectra were taken. The 

spectra are not shown,as very little difference in the magnetic noise was noted. The noise at 8.6 kHz on figure 3-26 

was 6 dB higher. These fans were acoustically very noisy. 

A fourth 20 hp fan remained operating at all times at a 

level below 4050 (possibly accounting for some of the 8.6 kHz 

noise in figure 3-26). 

Measurements made at 4050 with the cage ascending or 

descending showed a series of weak impulses, probably 

originating in the hoist house. At the 4050 level they were 

not a serious problem. 
Figures 3-28 and 3-29 were taken with two rotary battery chargers operating, 4 meters distant from antenna location B. One of the battery chargers was relatively quiet, while 

the other contributed almost all the noise observed in the 

two spectra. This battery charger was the noisiest piece of 

equipment encountered at the 4050 level. Figure 3-29 shows 

a fine structure to the noise spectrum, with lines separated 

by about 28 Hz. 

The mine used 5-ton, 90 cell, battery-operated electric 

locomotives. The battery chargers mentioned above were used 

for recharging these locomotive batteries. Spectra taken with 

the antenna at location B while the locomotive was running 

back and forth across the ore dump produced no measurable 

spectral lines. An impulse was received every time the locomotive motor contactor engaged or disengaged. In an attempt 

to determine the effective noise field near a cap-mounted 

receiver worn by the locomotive operator, spectra were taken 

with the antenna around the operator, sensitive axis vertical, 

while the locomotive was operating. Figures 3-30 and 3-31 

show the resultant spectra. Figure 3-30 looks like noise 

received from the hoist house. Listening to the audio monitor 

during this recording reveals a low frequency, low amplitude 

commutator brush-noise whenever the battery was connected to 

the motor and the locomotive was accelerating. Note the strength 

of the 48.6 kHz test signal. Figure 3-31 shows an impulse 

that has been produced by the locomotive. The impulse is as 

much as 30 dB above the steady mine power-line harmonics and 

is at least 50 dB above background levels between 100 Hz and 

1000 Hz. 

At the 4050 level, measurements were made close to the 

working face area, at an area known as the "Y of 99 and 95Y." 

This location was a hundred meters or so from the shaft area. 
There was no mining activity in progress (measurements 

were made on Saturday). Figure 3-32 shows the spectrum obtained with the antenna axis horizontal, perpendicular to the 

drift, and the tracks in the drift. The 4.2 and 8.4 kHz noise, 

as previously seen in figure 3-26, appear clearly here also. 

The spectrum taken with the antenna axis vertical showed about 

6 dB less noise than figure 3-32. For the antenna axis horizontal and parallel to the tracks, the noise was below the 

measurement system noise. Figure 3-33 shows the expanded 

spectrum measured with the antenna axis vertical. Transients 

were still in evidence at this location, possibly from the 

hoist. 

At this location near the face, it was clear that the 

source of noise was primarily the two steel rails, and 

secondarily, any other metal pipe in the drift. To demonstrate this, a measurement was taken with the antenna directly 

adjacent to one of the rails. Figures 3-34 and 3-35 show 

the result. Immediately apparent on figure 3-34 is the very 

strong 48.6 kHz test signal inserted on the north rope at the 

surface with a few watts of power. 

3.4 Spectra Obtained from Cage Runs, Loop Antenna 

3.4.1 Mine Not in Operation 

To measure the fields on top of the cage as it traveled 

the entire length of the shaft, a loop antenna was secured 

to the top of the cage, next to the supporting hoist rope and 

associated hardware. Because of the proximity of this rope, 

levels of fields measured are not accurate field strength 

values, but due to close coupling between antenna and hoist 

rope, the values do reflect (on a relative basis) current 

levels in the hoist rope. 
cated the noise source was at or below the 4050 level. Laboratory replay of the analog recordings showed that this noise 

has the following characteristics : 

(1) The noise is made up of groups of about 4 to 8 

individual impulses. 

(2) The groups of impulses occur 120 times per second. 

(3) The impulses within a group are not time synchronized. 

(4) Alternating groups appear to have some similarity. 

From the above characteristics, we speculate that this noise 

source is an arc of some sort and is produced by 60 Hz single 

phase, ac voltage. 
On a second visit to this mine on February 8, 1974, this 

same type of noise was received. Gains were set low enough 

that saturation of the measurement system was avoided. The 

spectra are similar in shape, and in the following figures, 

absolute levels can be determined. This unknown source causes 

noise many orders of magnitude stronger than any other source 

of interference in this mine. It is not a transient, but 

lasts seconds or minutes, and hence must be considered as 

intermittent. Spectra are shown in figure 3-42 as recorded 

from a loop antenna on top of a hoist cage. Another spectrum 

of the same noise from the output of a ferrite loop around 

the hoist rope into a 50-ohm load is shown in figure 3-43. 

The spectral distribution varies with time as is shown by 

comparing figure 3-44 with 3-42. 

This source raises the noise level at least 40 to 60 dB 

above background noise as shown in figure 3-45 over a wide 

frequency range (50-100 kHz); figure 3-46 shows this noise 

signal to be above system noise from 10 kHz to 200 kHz. 

Transient events such as shown in figures 3-47, 3-48, and 

3-49 are also present, but only for relatively short durations of time. Figure 3-50 shows a 20 kHz spectrum; it may 

indicate a ground station at 18.6 kHz, but at the 1800 foot 

level, this is doubtful. 
I2 0 0 2048 20 1 34-001 ' 81.15' '3/041'5 2' 5' t2 3' 2 -0 

I 95-005 2 6-,041 o 00.000 c 00.03C 2: ASJOB rs008 

36 82 8 25 '3Go1n corr , rcc = 6 101 con31 = 88 4 

C=25 RG= 50( 6dB) DG= 3 Fix 35 A&= 52 

80 1 OOOt008 , ; 3086 6 396456'. 

1 

Figure 3-1 Spectrum of magnetic field strength obtained on a l

antenna 1 kHz to 100 kHz, Lucky Friday Mine, locate

at hoist house, two meters from motor cables, hoist

waste rock, antenna sensitive axis vertical, 9:30 a

August 27, 1973. Spectral resolution is 78.1 Hz. 

70 ., 

60 .. 

50 .. 

40 .. 

30 

20 .t 

I0 

0 

-10 

-20 

.. 

.* 

.. 

0 I0 20 30 40 53 60 70 

80 

FREQUENCY, kHz 
k-w 

mas 

I w 60 DCL 

12 0 0 2O4B 20 2.69t000 3.91 tC2C 36/$4/.4 23:59::: 55 26' +t 

1.95-003 -2.79+001 0.00+000 0. OOtOOG 2C 45000 43000 

54 118 8 25 74Gain cotr., roc.= 6 tot const.= 88.4 

/MINE GENERATED NOISE 

0 500 1,01?0 1,500 2,000 

FREQUENCY, HZ 

Figure 3-2 Spectrum of magnetic field strength obtained on a loop 

antenna 40 Hz to 3 kHz, Lucky Friday Mine, located 

at hoist house, two meters from motor cables, hoisting 

waste rock at full speed, antenna sensitive axis verti

9: 54 a.m., August 27, 1973. Spectral resolution is 3.
12 0 0 204s 20 1 51-011 181.001 10105113 13.SY 21 22 

0 r I f5-001 .I 11.001 0 OO~ODO 0 00.000 20 IYOOl 1100# W 

21 83 B 25 73Goin corr.. rcc.= -6 101 conrl.: 4

W=- GZ C=25 RG; 2001 -6dBl DG= 0 FG= 0 AG= 52 

a 000+004 , 0.3006 . 4. 10

40). 

d -=o "L 

u %g 30. 

=, Go 

-a =s g &- ;s 20.. 

-10 .. 

= 2 -20 .. SYSTEM NOISE" 

Figure 3-3 Spectrum of 

antenna 1 k

frame by hsensitive a

Spectral re

22 Ga LI1 W ==W *L s- 

, , -30 .. Y Y'E GZ Pa 

d= 

+ 5 -40 zz 

4 -50 ro dE 

I I 

c2z 

Y -60 

.. 

,. 

- 

u 

0 10 20 30 
12 o o 2040 20 2.69t0~3 3.911~;~ :a;l/:r :~:29 6 5 3:0 

1.95-003 -3.04t001 0.00t000 t. 201::: 2 43S;B 43;36 

63 118 8 25 74Galn corr.. rec. = -6 tot const." 46.4 

FREQUENCY, Hz 

Figure 3-4 Spectrum of magnetic field strength obtained on a loo

antenna 40 Hz to 3 kHz, Lucky Friday Mine, at head 

frame by hoist cable operating at full speed, antenna 

sensitive axis horizontal, 11: 02 a.m., August 27, 197

Spectral resolution is 3.91 Hz. 

tI1ICROA!4PERE OHE TO RELATIVE dB H, STRENGTH, FIELD IglAGNETIC RMI 

OR FREQUENCIES, DISCRETE FOR FdETER, PER 

TO RELATIVE dB Hd, LEVEL, DENSITY SPECTRUM !\ACI;FTIC-FIELD-STRENGTH P,'.IS 

NOISE BAND BROAD FOR PERJmz, MICR0A:IFERE-PER-METER ONE 

MICROAMPERE ONE TO RELATIVE dB H, STRENGTH, FIELD MAGNETIC 4llS 

OR DISCRETE FREQUENCIES; FOR METER, PER 

TO RELATIVE dB Ed, LEVEL, DENSITY SPECTRUM \II~'ILTIC.FIELD-STRENGTH P'iS 

KOISE BAND ,FOR BROAD JgTFz PER MlCfiOAl4PERE-PER-METER CHE 
we -- c> 

In.. 0 

<.;:- 

In 

<O 

-- -a 

I w .. r r.l I1 - - r, - .. U I - .. Q 

c. *>*. .,'. - c ., r- c ' 

r ..'. L 

m .; 0 

. . u 0.. 

.z, <, '= m- c , .- <, ', 0 

.' 

me 

0 

+ 

m 

m 

CV 

(D 

N. 

Ln " 

I I 

w 

4 

0 

II 

2 g 0 g. ., 

< > 

II 

c3 

a 

- 

m 

-0 

0 

-a 

I - 

0 ', 

0 

0 

0 - 

$ -a 

u", 

-3 + 

2': u 

- . c;.oo~oooooo 

- n > cw - , C.. r CT W I 

0 

- 0" 

0 

LL-2 0 

" zn 

0 Q) - E= 

0 

.. " 0 

g;2 r-- 0 - 0 "2 fdszz 

EQ)k 

0 MhI_ 

k E= 4-r fd hnl 

0 

Lo a krY: -- 

CD s hq .d 2 r' M 

*Q)Q)g 

rJ 

I 

$ $54 

U4-r - 

kO. G- 

- n '"E" m4E; e f-, fd fd - 'C)UkO 

m-$4-(0 

2 a)>@ :4& 0 G *&Z " .d Q) 0 z- -2 x s a ,Ad-fd 

-- 

&5fdM fd :s .5 

Ern;$ 

0 

u'- 0 3::~ CU E *+c, -0 

gi,c 

k c 

sgg; a0 E 

m fd- k 0 

lJ7 m 

-!. I 

m 

Q) 

k 

3 

M 

.d 

h 

0 

3SICN Ohil'B OYOIja 804 'z~!/" 83d 6313iri-H3d-3Y3dlVOrl3Ili 3!:3 

. 3A!lV131 BP ''\I '13A31 IlISN30 N08133dS H13H3~1S-O131~-3111iiIr\~~i 5ilU 

80 '~313~3n83H4 313U3Sl0 UO4 'U313N U3d 

383dKV083IN 3N0 01 3h11V138 0P 'H 'H13N3rllS 01314 3113133VW SWtl 
MICROAI4PERE ONE TO RELATIVE dB H, STRENGTH, FIELD RMS MAGNETIC 

OR FREQUENCIES; DISCRETE FOR METER, PER 

TO RELATIVE dB Hd, LEVEL, DENSITY SPECTRUl IJAGIIETIC-FIELD-STRENGTH !S 

NOISE BAND FOR BROAD dm', PER MICROAh\PEP.E-PER-t11ETER OtiE 

. a::. 

-1- g 

LR 11 - 

ale& a 

0 

y:; g ra - - .I r- 

-1 . 

Y WP' 

3 

G 

I-'- 

c%; (,g 

0 gz; c :.'-'' 2, rF 

sE 0 

;gCI.,w & OP' g 

- CI 2. x 

~"l~;.n 

rZ N .. • A: 

e- E rro 

e Y. 0 

;tgLn 

a-0: 

n)m3 ego 

P' 3 n-9 o 

2.p: 

Os'Dwd 

arr;rg e5' O; n) en) e H.rm 3 

Ye- " 

P'?? P' 

g!'-''o 

P' 

3 : 0 

'-"a 5 

"2% 

0 

O 2 on) a w 
:2 S 0 2049 1. 39t:03 9. ?7tOO: ;7/;:/?4 :6:44:39 32 3: 

1.95-003 -Z.55tOEfC C. 2EtSCJ ;.OCt12? 2: 43109 43539- 

31 07 8 26 73Galh corr. , roc. = 0 tot const. - 52. 0 

FREQUENCY, Hz 

Figure 3 - 1 1 Spectrum of magnetic field strength obtained from 

antenna, sensitive axis vertical, frequency range 56

10 kHz, located on Cedar Street in Wallace, Idaho, 

6:00 p. m. , August 26, 1974. Neon lights are abou

meters distant. 
--. we

(0 - - 0 

I-N * ,. 

> 1' I1 . . 

. . 

.... 

!=l 

a," O 

:g ; 

"3 
'.,A q 

"I" 2 'U. .M . . 
12 0 0 20ll 20 I 34-00: ' 81.0:: :01:4l-J '6 2C.:Y 

0 ,-- 195-OOJ 2 7'*00' C '*,O:O C 1:.1:: 2' 4300a 

:O 02 R25-3CLin corr rcc :'-26 tor con

Figure 3-14 Spectrum of ma

antenna 1 Hz t

pump off, anten

August 25, 1973

Figure 3 - 16 Spectru

antenna, 

the freq

at the 3 

10:OO a. 

. . 

!f si-.f, file2 ,,?: .0..2::Ii . ,7i:ii2 :"':/-4 .. 'a 'I ... "5

.... . ...... . ..*... 2: As::# I

0 e- 50 1b'l 2 8 7L;oin co--. . rcc. = -2; tot con.tw C=37 RG= 1002'-2ide' ,.i= : 'i= C AG= 52 

2 ;o w g 2s 

4 sz 0 

sz 10.. 

=z ,g =&S = .- s 0. 

-Lo Jm 

,. 005*002 . 3086 

, 

-= zg =- U& -$g.. 52 -a 

r 

k--e %E 0 0 

w 5 " = .. 

1 

Y, Ek-& 

u.p EE a LU J .c3 

2 CL 

w *s GZ 9% 2 - 5e 4 $3 '?s =.z 20 Z"-lO. - 

.,? g LC --0 

z-- 

; -:I 

" .. 

-- ~ C $ 20 40 60 

'2 9;..i, 21'8 -,:: 3: ,;,:2:;ji , ,!a: j;: :-. "/-r :? :2 25 r? 

48 2' -h2.+ ,... . .:... . Z3::8 d3:;

uasn co--. . -ec.= -2; tot con¶

Figure 3 - 18 Spectru

antenna, 

the frequ

at the 36

10:OO a. 
Figure 3-19 Plan view of portion of 4050 level, Lucky Friday Mine. 

Antemas were located at A and Be 
Figure 3-20 Spectrum of 

antenna 1 k

open south 

axis horizo

Spectral re

I2 0 0 211) 20 ! 74-10: ' ll.OC! !:1141'7 2: 1- 35 2- 12s 

1 5-001 -2 24.001 0 1J.CLC C PO.::$ 2: IlOOB 15CO) 

e 41 81 8 25 73Goin corr rec : -43 tor const.: 12.w 

30 F% Jq d Sa2J 

g ez ' 

z 

a &a 10 . 2 z- z- g 

zg 2% 0 bJz 2- " cs gz 3% m- i 2- =y -10. -20,. 

3z- CO - 

-a 8 %g -30 ZE =% 

g; G& cn w 9 -40 +- ow E; J= ,a 

5 Z -50 ,- =a FS 5 "U +- zs -60 

sw ', 5% g = " -70 

"7 

C=25 RG=10000(-ACdB) DL= : FG: 3 hG= 52 

.000+003 , C. 3586 4.601+

.. 

.. .. 

.. 

z 3C: 

0 \2 :3 
I2 0 0 2049 20 2.69+000 3.91+000 06/04/74 21:34:59 24 112 r 

1.95-003 -3.60+001 0.00+000 O.OO+OOO 20 43009 43009 

23 118 8 25 74Galn corr., roc.= -40 tot const.= 12.4 

C=42 RG=10000(-4OdB) DG= 0 FG= 0 AG= 52 

0.7086 3.567+005. 

MINE GENERATED NOISE 

l poo 

-- 

2,000 

FREQUENCY, Hz 

Figure 3-21 Spectrum of magnetic field strength obtain

antenna 40 Hz to 3 kHz, Lucky Friday Mine, 

open south shaft doors, 4050 level, antenn

axis horizontal (N-S), 11:09 a.m., August 

Spectral resolution is 3.91 HZ. (Location A
12 0 0 2048 20 ' 34 20 ' E +3: :I:dl'3 2 49 34 29 11) - 0 t-- I %-003 -3 16.001 0 00.CC3 + 22.::: 2: 4~000 4n0( 

43 81 0 25 '3Gcjn cbvr .ec -23 rot cons! = 12 4 W 

- CT - C=25 RG=10000 1-4000) CGr iG= AG= 52 

w a2 20 L 000+002 C 3C86 1 499*001. z &P 

u 

0 %Z 10. 

L"-~o., 

25% 0 4- 5 =o u 0 -OIJ 

1 CT 

0 10 20 30 40 3 F 0 10 EO 

FREQUENCY, kHz 

Figure 3-22 Spectrum of magnetic field strength obta

antenna 1 kHz to 100 kHz, Lucky Friday M

open south shaft doors, 4050 level, wate

antenna sensitive axis vertical, 11:25 a

1973. Spectral resolution is 78.1 Hz. 
- 

U U 

00 

0-C: 

-0- 

ul- coo 0 

,"0 

o* 

- 

~~~X~""~?

0 

ISION ONVB 01018 804 'ZH \fi.$ ad 1313W -)13d-383dWV0831W IN0 

3AllV131 BP 'P~ ' 1~31 MISN30 Wn1133dS H13N3l1S-Oi31A-311313VW 

Orw " Kl rcr3 
I2 0 0 Poll 20 ! 3&-00. ' @:.:: .:!:1/-3 2' 19 4' 30 

1 5-009 -3 c0.001 C 10.2:: : :1.::: 2. 43004 43001 44 81 8 25 -JGo,n corr, rec : '-4; 101 con,t.= 

CG= ; ;&= : AG= 52 

: !:as 1.7

-70 .. 

-60 . 

C It 20 3C 

Figure 3-24 Spe

ante

ope

wat

11:2
I2 0 0 2048 20 2.69t000 3

1.95-003 -4.50i001 0. OOtOOC 3.0

26 118 0 25 74Galn co

I 

0 500 

Figure 3-25 Sp

an

op

wa

11
- - -- 

CO 

B 13 20 30 

Figure 3-26 
zzc - +o, m 

zza .'IS 0 0 FL 

-- 0 

",In , 

&'V 0 

Z (VI II 

ma3 C3 00, a 0 

I - 0 (U 9n (V- - U 
Figure 3-28 
12 0 0 2040 20 2.69tOOO 3.91tOOO 06/04/74 23:27:53 !S 67 4 

1.95-003 -3.90tOOl 0. OOtOOO 0. OOtOOO 20 43000 43000 

14 I18 8 25 73Galn corr., roc.= -34 tot const.= 18.4 

- 

z= 

aE 0' 

E22 

g& 

W E -10 * a= I 

t-w 

IW 

&z -20 * 

LO 

I = 00 

F 1. -30 * W 

Z 

252 

' " -40 - - 

k 

MINE GENERATED NOISE 

SYSTEM NOISE' 

FREQUENCY, HZ 

Figure 3-20 Spectrum of magnetic field strength obtai

antenna 40 Hz to 3 kHz, Lucky Friday 

level, 10 meters from shaft, battery cha

antenna sensitive axis horizontal (N-S), 

August 25, 1973. Spectral resolution is 
12 0 0 2041 20 ! 31~00: '81100: !O/CI/73 :12! 23 I 

195.003 2 71.001 C $0.000 0 30.000 20 43008 410

F 3 82 8 25 73Gnin covr . rec -14 IOI con11 

Y 

w C.25 RG. 500 !-:4d81 3G: C FG' 3 AG' 52 

2 3G, 000+003 . 0.3086 

a 

r dP 

==a 

MINE GENERATED NO

Ln W 

0 -5 60 .. 

W 

2 zs Oz 7G . 

=E 

0 10 20 30 

Figure 3-30 Sp

an

lo

is 

11
12 0 0 2048 20 2.69t003 3.91*C,C ;6/C4/-4 23:42:20 3: :4: 0 

* 1.95-003 -4.06t001 0. 00t000 0. 00*0Cf 2: 43::8 43C50 

30 118 0 25 74Gain corr., rec.= -14 tot const.= 30.4 

0 560 l,OOb i $0 2,500 

FREQUENCY, Hz 

Figure 3-31 Spectrum of magnetic field strength obta

antenna 40 Hz to 3 kHz, Lucky Friday Min

loop antenna around driver of locomotive 

is pulling an ore car, antenna sensitive 

11: 59 a.m., August 25, 1973. Spectral r
t-' m 

E: 

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

OR FREQUEt,CIES; DISCRETE FOR METER, PER 

TO RELATIVE dB Hd, LiVEL, DENSITY SPECTRUM MAGNETIC-FIELD-STRENGTH RXS 

t:OISE BAND BROAD FUR flz, PER MICROAMPERE-PER-METER ONE ,,,I1111 

*m CO - g"o&oo 
m P, 

x rY 

El N an, 

P, 2"m 

03 

n, P, wr) 3 

8:~: 

Fm 5 a 

r* r)Wu 

n, Y 

rr cn P, 

a t rn, n =I 

Rcn cn Y r) re* n, Y cnrt r-elm 0 

3 Y rC 

r-m n, t ar) r) 

9 P, r-P, 

an*. B 8:: ," 

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

OR DISCRETE FREQUENCIES; FOR METER, PER 

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

NOISE BAND BROAD FOR J~z, PER MICROAMPERE-PER-METER ONE 
IS . , o - Q .-Tasqe o 

3SiOfl lFV9 OVC!IR HCI IzHISI/L M!(I illi3?1 \IId-!HI.I#YO~l?lW 3t10 

Oi 3hllV13i 01' "H '13h31 AllS#JU lrinMl33dS H1.3EiitllP3-1113li-3\1IM3bIi SWN 

10 !S31343n0314 313DSl0 804 '8313W M3d 

3H3dWVO131W 3N0 01 3hIlV131 8P 'ti '~13~311S 01314 3113N3VW SVIM 
12 0 0 2048 20 2.69tOOO 3.91t

1.95-005 -3.52t001 0. OOtOOO 0. OOt

21 118 8 25 74Galh corr

Figure 3-35 Spectr

anten

near 

maximu

resol
238 2; 39 rt 

$$g$Sr 

rte'd e 't 

pl plc IU 

mm;- 

v rn 1-0 Y (

3

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

PER METER, FOR DISCRETE FREQUENCIES, OR 

RiS E!.ACCETTIC-FIELD-STRENGTH SFECTRUM DElSlTY LEVEL, Id, dB RELAlIVE TO 

CYIE M;CROAMPERE-PER-METER PER flz, FOR BROAD BAND NOISE 
12 c c 2048 ?i : 14-OCI I.UI+OCI u1/03/74 .e 55:3~ 26 

1.95-or3 2. ?T+COI -O.OC.,~CC e.co+ace i3 rW6 43

25 82 B 25 .3ioln corr.. rec. = -2C tot con

o C=Z7 RG= I000 (-20dB) PG= 0 FC= C AG= 52 

0 3086 

Y 0 

o\ %= 20 

0 -o= 5= 

sg e2 

-a - Fe gf5 13. 2" -2 

- r,a 0.. L?g se 5% E& -13.. 25 2+ 

e= 5s .IY -M c3 ,-z< -4; :; - .. 

,. - s.; :.:_s -30 - . 

C< 

C: 

- -. 

C 10 20 3C 

'. . 

Figure 3 -37 Spectrum of m

antenna, 10 k

on top of ele

antenna sens

August 25, 19
I2 0 0 2041 20 I 34-00! ' 111001 10/05/~1 I! 01 34 23 

I.%-00 2 45.001 O.VOtOO0 0 00.000 20 4lOOD 1W0@ 28 83 8 25 73Gain ccrr.. rcc.= -20 tot tonst.= 

I SYSTEM COlSE 

Figure 3-38 S

a

r

s

o

r
g; 

7 rd 

&G -x t; Cd-rd 

u a'? u+>c 

ac u om 

ad- Nr- 
0 

I2 0 0 204e 20 I 54.00: - e..::. .:,:5,-1 .. .5 13 19 

+- 1 15-00 2 41.001 J JC.80: : ?:a;:: 2: 4lDCl 4!O)I w 38 85 82573Gomn corc ?rc = -2: 101 con9t = 

Db= : :;= : AG= 52 

Z 

: ?:$A 3 3

- =ez 

Figure 3 -40 Spectrum 

antenna 

(47Q me

axis hor

resoluti

*-g z s- 20.. -a w Eg %5 k? - 

= 22 10 ., s -z& z25 sz 32 E& 

Y 7'5 0 .. $2 2% 

ZO 

, e -10.. W 00 4 L' 

g $ -20 ., CO 

ZE zo 0: 

LO -30- 

0 10 20 30 
1 7 E! (00: :O/CS/-J !! 22 49 0 OO+GJO 20 43001 corr,, rec.= -23 tot c 

DG= 0 FG= 0 AG= 52 

0.3086 

FREQUENCY, kHz 

Figure 3-41 Spectrumof magnetic field strength obtained on a lo

antenna 10 kHz to 100 kHz, Lucky Friday Mine, 3400 l

(1080 meters deep) , mine in operation, antenna sens

axis horizontal (E-W), August 27, 1973. Spectral 

resolution is 78.1 Hz. 
Z 

w 25 2g Z 

O&- 2 -= eg zg 

gg 

sE g,K ,LA- sz ZCT -I.; mw O 

-OL zCT 

=-g zE k- 

;a Y zg %g z LA- W =% CL GE- & 

aL 2: 25: me 

EE AaW 

,,- &Z = "B z c;.U - k-r 4 

5 s 

UW y 2s cT5 c.7 

-- 

t . SYSTEM NOISE / 

0 20 40 60 80 100 120 140 

FREQUENCY, kHz J 

Figure 3 -42 Spectrum of magnetic field strength obtained from 

antenna, sensitive axis horizontal (East-West), loca

top of cage adjacent to hoist rope, Lucky Friday M

Time is about 11:OO a. m. , February 8, 1974. Cal

is valid over the frequency range from 3 kHz to 20

Cage is at 4250 level. Signal is from a strong unknow
0 M%jW QFc 

rd 0 ~~~ Ere Egz: 50dO 

S>[IIZx g U a,--' Id .o 

~Cp,2~*~ a- 0" 

mwOrd o\~ 

04 >6(d=' 
KlCR3AKPERE OF;E TO RELATIVE dB H, STRENGTH, FIELD MkGMETIC iil:IS 

OR FREQUENCIES; DISCRETE FOR METER, PER 

Tij RELCTIVE dR lid, LEVEL, DENSITY SPECTRUFl TIC-FIELD-STRENGTH !!!!?!L 1C1:; 

Ilb!jE @AYE BROA1) FOR , HZ PER I*lICRDA!~PERE-PER-METER PUL 
Figure 3 -45 Spectrum of voltage across a 50 ohm load. The 

of the voltage is a ferrite loop around the hoist rop

loop is about 2 meters above the cage. The calib

valid from 3 kHz to 200 kHz. Location is the L

Friday Mine. Time was about 11:OO a. m., Feb

1974. The upper curve is a strong unknown source a

lower curve is typical noise during mining operatio

'2 : : 2:AO 2: 6 -2-::2 ' 55.;:2 :T/'E/-A 2: '0 20 6: 292 . : 95.:;5 -5 Js.::: 9 -" '.- " -, .a63 t"' 2: AS:;8 4S::E iu. 2 8 -ii;;l':nv cb;;'':. rec, = 2: :O; con,t. =-29 : 

:=36 RG= 10: 2:d9: 3G= : F&= : Aiz-49 

a - 60 r G 10 

0 Z 

0 

a 52 50 '0 s 0 u' 0 ur ;z 40. 

+- mz s >='ye 

?+->z 

g2 * r - 30 52 '2 Cn 

i 

>-zE= 

gggz 20- OIlr13 

zzzmz 

O3 ~l-lt;aw,w 10.. 2 0: UJ 

L;g&z 

1 0,. CaOOV 

0'--0 

- Cnz 

Zk, -10.. 4 b -.. 

.J 0 

c> > e v, -20.. /. - Lirn Y v fiJ u -30 .. 

-40 

: 

, 

:30-:C6 :. 3C8L - 9-6-; :- 

MINE GENERATED NOISE ' 

.' 

.* 

. . 

fi MINE 6ENERATED NOISE 

0 20 40 60 80 

100 120 140 160 

FREQUENCY, kHz 
W 

!+ =,A w a- 2 c 40 .' ds 

-,z 50. = - g =&Z 

Z 

0;;;s 20. OW W zg 5s 

7 2 -- IC . ~rn 5- zg -20 , E& z= .OF 52 2 y EY; -30 .. W '?5 xs Oa- 2 =E =a- W4 , --40 . g c9 FZ 

4 - z y -:o 0 22 

E T 0 20 40 60 = 17 

-- A

- 

Figure 3 -46 Spect

antenna

top of c

Time i

is valid 

Cage is 

. . 

. . . ::1- : & -. ; .n.:,: ., :< -' '? ,. '- 

-c ::? .; - ;1 

L. .. : .. .:: 

-7 .:: > C-L?. . 4:::8 15:

-. L . 0- -?I - ; :',: ro*,: 

- - , 

.- -.? 0.' . . . 

~. - 

-7,-. -: . : .,' : 1., L:. 

- 5 69 ; ;:: .:; . -.- =z . ; .8? r 0 Z 

c. n 

2 z 53 fn o 

LT -4 

- : 

W 9 %g 

C a -10. 

-2 

C;. 0 

> +- 

'" 'id - Z -8 .. CT ,-- cC 

2 - 

2 -30 ' 

V 

-40 ' 

P, 20 40 60 

Figure 3-48 Spectr

of the v

loop is 

valid fr

Friday 

1974. C

narrowba
:2 ; ; ;; i-L, ;;: . c- ... 

. . . '2.2 22 

:.55.::5 -: :5.::: . ;:.:.; ; I;.:.: :. t5::e ‘3:;E 21 97 2 8 7AGoin corr , rec = -& to: const.=

0 20 40 60 

Figure 3-49 Spectru

of the vo

loop is a

valid fro

Friday M

1974. C

narrowban
ad 

0 2 qcf cd " 

%I ho' E 3- 02 y "A 

%Id400 

> 

a Wh s.22; 

'$cast 

WO?" $a>% cd &I "Oh 

-2g - ?;;; - 

:u,i 
4. AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS 

4.1 Introduction and Uncertainties 

The amplitude probability distribution (APD) of the received noise signal magnitude 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 [5,6,7]. 

By plotting the cumulative APD on Rayleigh graph paper, 

one can show clearly the fraction of time that noise exceeds 

various levels. Rayleigh graph paper is chosen with scales 

so that Gaussian noise (e.g., thermal 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 

receiver bandwidth. 

All APD 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-dB quantization error limit. 

One-decibel step attenuators are used to achieve the 

5 one decibel. 

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

data processing, has a calibration uncertainty of 

+ 0.5 dB [3]. 

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

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

dropout, cross-talk, gain instability, etc. 
4. The gain instability 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 f 0.5 dB 

uncertainty. 

6. Connector losses and BNC cable losses, particularly 

at higher frequencies above 100 kHz, contribute + 2.0 dB 

uncertainty. 

4.2 Results 

APD measurements were made on August 27, 1973, and on 

February 8, 1974, during operation in the Lucky Friday Mine 

located near Wallace, Idaho. Descriptions of the Lucky 

Friday Mine are given in section 1.2. APD measurements were 

made at four locations. The first set of APD measurements at 

four frequencies was made on August 27 at the head-frame on 

the surface. APD's are shown in figures 4-1 through 4-9 for 

two antenna orientations. The second set of APD measurements 

at four frequencies was made on August 27, 1973, at the 1450 

foot (427 m) level. These APD's are shown in figures 4-9 

through 4-16. The third set of APD measurements at three 

frequencies was made on August 27, 1973, at the 3050 foot 

(930 m) level. APD's are shown in figures 4-17 through 4-22. 

In these sets of APD measurements, both the vertical and 

horizontal components of magnetic field were measured. The 

fourth set of APD measurements at three frequencies was made 

on February 8, 1974, at the 3650 foot (1113 m) level, during 

operation. The 3650 level was a working level with light 

activity. APD's are shown in figures 4-23 through 4-28. 
II = - I H dp (H) 

avg 0 

and 

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 

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

and possibly other parameters. finite series are us-pr 

the numerical integration. The rms 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 rms-reading meters, the meter 

readings will vary 10 to 20 dB over fractions of a second. 

The rms value is directly relatable to noise power. With 

these wide variations of field strength with time, the most 

suitable presentations are statistical ones. 

4.4 Summary Curves 

Excursions of field strength between 0.001 and 99 percent, 

as well as rms and average values, are shown in figures 4-29 

through 4-36. The predetection bandwidth for these APD 

measurements is either 1 kHz or is normalized to 1 kHz. 

Figure 4-29 is a summary of the figures 4-1 through 4-4, 

at the headframe, the horizontal (N-S) component. Figure 4-30 

is a summary of figures 4-5 through 4-8, at the headframe, 

vertical component. Figure 4-31 is a summary of figures 4-9 

through 4-12, at the 1450-foot level, vertical component. 

Figure 4-32 is a summary of figures 4-13 through 4-16, at the 

1450-foot level, horizontal (N-S) component. Figure 4-33 is 

a summary of figures 4-17 through 4-19, at the 3050-foot 

level, horizontal (N-S) component. Figure 4-34 is a summary 

of figures 4-28 through 4-22, at the 3050-foot level, vertical component. Figure 4-35 is a summary of figures 4-23 

through 4-25, at the 3650-foot level, horizontal (N-S) component. Figure 4-36 is a summary of figures 4-26 through 4-28, 

at the 3659-foot level, vertical component. 
Figure 4-1 APD, Magnetic field strength, 30 kHz, Horizontal 

(North-South) component, Headframe, Lucky Friday Mine, 

1 kHz predetection bandwidth. Time was 11:OO a. m. , 

August 27, 1973. 

Magnetic Field 

;I urn 

@'ZY K" a 

P 2. x.., 9 s ;- 

a E'+ " "o ? !, 2- 5 

a Fr 

: Oxx +- : + g. a ,, 0 oaz 

PI 

P* K 
Percent of Time Ordinate is Exceeded 

Figure 4-4 APD, Magnetic field strength, 250 kHz, Horizontal 

(North- South) component, Headframe, Lucky Friday M 

1. 2 Me predetection bandwidth. Time was 1 1 :00 a. m 

August 27, 1973 
Figure 4-5 APD, Magnetic field strength, 30 kHz, Vertical component, Headframe, Lucky Friday Mine. 1 kHz predetection bandwidth. Time was 10:30 a. m. , August 27, 1973. 
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 4-6 APD, Magnetic field strength, 70 kHz, Vertical component, 

Hesdframe, Lucky Friday Mine, 1 kHz predetection 

bandwidth. Time was 10:30 a. m. , August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-7 APD, Magnetic field strength, 150 kHz, Vertical component, Headframe, Lucky Friday Mine, 1.2 kHz predetection bandwidth. Time was 10:30 a. m., August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-8 APD, Magnetic field strength, 250 Me, Vertical component, Headframe, Lucky Friday Mine, 1.2 kHz predetection bandwidth. Time was 10:3 0 a. m., August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-9 APD, Magnetic field strength, 30 kHz, Vertical component, 1450 level, Lucky Friday Mine, 1 kHz predetection bandwidth. Time was 1:00 p.m., August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-10 APD, Magnetic field strength, 70 kHz, Vertical corn 

nent, 1450 level, Lucky Friday Mine, 1 kHz predetec - 

tion bandwidth. Time was 1:00 p.m., August 27, 1973 
Percent of Ti me Ord i na te is Exceeded 

Figure 4- 11 APD, Magnetic field strength, 150 kHz, Vertical compo-- 

nent, 1450 level, Lucky Friday Mine, 1.2 kHz predetection bandwidth. Time was 1 :00 p. m. , August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4- 12 APD, Magnetic field strength, 250 kHz, Vertical component, 1450 level, Lucky Friday Mine, 1.2 Wz predetection bandwidth. Time was 1 :00 p. m. , August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-13 APD, Magnetic field strength, 30 kHz, Horizontal 

(North-South) component, 1450 level, Lucky Friday Mine, 

1 kHz predetection bandwidth. Time was 1 :30 p. m. , August 27, 1973. 
.0~01.001.01 .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- 14 APD, Magnetic field strength, 70 kHz, Horizontal 

(North-South) component, 1450 level, Lucky Friday Min 

1 Hz predetection bandwidth. Time was 1 :3 0 p. m., 

August 27, 1974. 

9 1 
Percent of Time Ordinate is Exceeded 

Figure 4-15 APD, Magnetic field strength, 150 kHz, Horizontal 

(North -South) component, 1450 level, Lucky Friday Mine, 

1. 2 kHz predetection bandwidth. Time was 1 :3 0 p. m. , August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-16 APD, Magnetic field strength, 250 kHz, Horizontal 

(North-South) component, 1450 level, Lucky Friday Mine, 

1.2 kHz predetection bandwidth. Time was 1 :3 0 p. m. , 

August 27, 1973. 

93 
Percent of Time Ordinate is Exceeded 

Figure 4-17 APD, Magnetic field strength, 30 kHz, Horizontal 

(North-South) component, 3 050 level, Lucky Friday Mine, 

1 kHz predetection bandwidth. Time was 3 :00 p. m. , 

August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-18 APD, Magnetic field strength, 70 kHz, Horizontal 

(North-South) component, 3 050 level, Lucky Friday Mine, 

1 kHz predetection bandwidth. Time was 3:00 p.m., 

August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-19 APD, Magnetic field strength, 150 kHz, Horizontal 

(North-South) component, 3050 level, Lucky Friday Mine, 

1. 2 kHz predetection bandwidth. Time was 3 :00 p. m. , 

August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-20 APD, Magnetic field strength, 30 kHz, Vertical component, 3050 level, Lucky Friday Mine, 1 kHz predetec - 

tion bandwidth. Time was 2:30 p. m. , August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-21 APD, Magnetic field strength, 70 kHz, Vertical component, 3050 level, Lucky Friday Mine, 1 kHz predetection bandwidth. Time was 2:30 p. m., August 27, 1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-22 APD, Magnetic field strength, 150 kHz, Vertical component, 3050 level, Lucky Friday Mine, 1.2 kHz predetection bandwidth. Time was 2:30 p. m. , August 27, 

1973. 
Percent of Time Ordinate is Exceeded 

Figure 4-23 APD, Magnetic field strength, 35 kHz, Horizontal 

(North-South) component, 3 650 level, Lucky Friday Mine, 

1 kHz predetection bandwidth. Time was 10:OO a. m. , February 8, 1974. 

100 
D001.001.01 I 5 1 5 I0 20 30 40 50 60 70 85 90 95 9a 99 

krcent of Time Ordinate is Exceeded 

Figure 4-24 APD, Magnetic field strength, 75 kHz, Horizontal 

(North- South) component, 3650 level, Lucky Friday Mine, 

1 kHz predetection bandwidth. Time was 10:OO a. m. , February 8, 1974. 
Percent of Time Ordinate is Exceeded 

Figure 4-25 APD, Magnetic field strength, 200 kHz, Horizontal 

(North-South) component, 3650 level, Lucky Friday Mine, 

1.2 kHz predetection bandwidth. Time was 10:OO a. m., 

February 8, 1974. 
Percent of Time Ordinate is Exceeded 

Figure 4-26 APD, Magnetic field strength, 35 kHz, Vertical component, 3650 level, Lucky Friday Mine, 1 kHz predetection 

bandwidth. Time was 10:30 a. m., February 8, 1974. 
Percent of Time Ordinate is Exceeded 

Figure 4-27 APD, Magnetic field strength, 75 kHz, Vertical component, 3650 level, Lucky Friday Mine, 1 kHz predetection 

bandwidth. Time was 10:30 a. m., February 8, 1974. 
Percent of Time Ordinate is Exceeded 

Figure 4-28 APD, Magnetic field strength. 200 kHz. Vertical component, 3650 level, Lucky Friday Mine, 1.2 MIz predetection 

bandwidth. Time was 10:30 a. m. , February 8, 1974. 
MAGNETIC FIELD STRENGTH, H 

(dB RELATIVE TO I MICROAMPERE PER METER RMS) 
x'f 


Figure 4-33 Summar

between 0.0

3050 level, component, 

40 

20 

0 

-20 -40 

-60- 

- 80- 

- - - 

- 

- 

I I I I I I Ill 

1 10 
(SWd U13W 8d 3d3dWVOd31W 1 01 3AllV13d UP) 

H '~13~311~ 013U 3113N3VW 
Figure 4-3 5 Summ

between 0

3650 leve

component

60 

40 

20 

-20 -40 

-60 

- 80 

I I I I I 1111 

x MAXIMUM (0.001 %) 

- RMS 

0 AVERAGE 

A MINIMUM (99%) 

- 

0- 

- 

- 

- 

I I I I I I 111 

I 10 
a (I) * 
The noise data for the time when the mine was not operating are shown in figures 5-1, 5-2, 5-3, and 5-4; data taken 

when the mine was in operation are shown in figures 5-5, 5-6, 

5-7, and 5-8. Noise is somewhat higher during operation, but 

the variations indicate the basic problem with this type of 

measurement -- the cw measurement system is responding to the 

time variations, but in a way that masks the statistical range 

of values caused by transients and intermittents. The APD 

section gives data at some levels, but APD's were not recorded 

on the hoist. 
5.2 Attenuation Measurements 

Discrete-frequency signals were inj ected at the headframe, 

and signal strength measurements were made of the current at 

the cage at a number of levels. The plots show standing wave 

patterns. Either the short has some inductance, or the open 

has some capacitance, or both, as the equal-amplitude mark is 

at about 3600 feet (- 1100 meters) for 50 kHz, and if there 

were no stray effects, the equal amplitude (2 X/8) point 

should be at about 2500 feet (750 meters). 

Actual attenuation is relatively low, only a few dB over 

the 4000 foot (1200 meter) length of cable. The standing 

waves due to an unterminated transmission line are clearly a 

more serious problem. Up to 20 dB variation may be expected 

from maxima to minima. 

The signal-to-noise ratio looks very encouraging, unless 

the intermittent noise from the strong unknown source (plus 

60 dB noise) combines with a minimum in a standing wave pattern (minus 20 dB signal). Even this worst case may be handled, 

but the margin is significantly reduced, especially near the 

working levels when the mine is in operation and where noise 

levels are highest. 
Figure 5- 1 EM 

an49 

10- 

0- 

I 

w 

c: short 

m m 0 

> open 

=l. - 

Q) > 

0 

n 

a -30- m 

u 

-40- 

~&:,73<t\ 

-50- ' I 

(.3=2'+,. :+?t\ 1,000 

. ,, 

I \ 

z- ! ' : i" r-+< 

c/ 

q ,ar-(. ) 

-40 I 

A 

1 0 1,000 

- . , .-, .q4 \ 

_I _ 1. \ d 5.-' 

J- v\ 

Figure 5-3 EM Noi

3 5 kHz


8 

Tf0 

0 

0- 

Tf 

0 

0 

%- 

0 

0 

0' 

m - 

E 

a 

0 e 

s: 9 

cu- 0 

II 

t 

Y- - 

u 

0 + 

8- $ 

cuC .- 

f 

a 

0 8 

0 'c -

0 

0 

0- - 

0 

8 

0 

I 


Pool 'CTOS SSOJW A+ l ahoqtl 8P 
Depth in Feet (lft.=0.3048m) 

Figure 5- 10 Received signal at cage from 50 kHz source a

1 kHz predetection bandwidth. 
8. ACKNOWLEDGMENTS 

Those making significant contributions to this program 

are as follows: laboratory development and field use of measurement equipment, Ed Neisen, Doug Schulze, and Tom Bremer; 

data processing, Anne Rumfelt, Nancy Tomoeda, Frank Cowley, and 

David Stearns. Those making valuable but less time-consuming 

contributions are Gerry Reeve, Bob Matheson, Don Spaulding, 

John Chukoski, Lorne Matheson, Dave Lewis, and Sharon Foote. 

Sharon Foote and Janet Jasa typed tirelessly through 

many versions. Jocelyn Spencer and Barbara Bolton provided 

drafting assistance. 

Finally, none of this would have been possible without 

excellent cooperation from various people in the Hecla Mining 

Company. For arrangements we thank Wallace Crandall , George 

Wilhelm, and Art Brown; for much special assistance we thank 

Don Beck. 

126 
9. REFERENCES 

[l] Bensema, W.D., Kanda, M., Adams, J.W., Electromagnetic 

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

(April 1974). 

[2] IEEE Dictionary of Electrical and Electronic Terms, 

The Institute of Electrical and Electronic Engineers, 

Inc., Std. 100 (1972). 

[3] 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). 

[4] Adams, J.W., Bensema, W.D., Kanda, M., Electromagnetic 

Noise in Grace Hardrock Mine, NBS Tech. Note 657 (June 

1974). 

[5] Crichlow, W .Q., et al. , Amplitude-Probability Distributions for Atmospheric Radio Noise, NBS Monograph 23 

(1960b). 

[6] Thompsom, W.I., 111, Bibliography of Ground Vehicle Communications and Control, AKWIC index, Report No. DOTTSC-UMTA-71-3 (July 1971). 

[7] Spaulding, A.D. and Disney, R.T., Man-Made Radio Noise. 

Part 1: Estimates for Business, Residential, and Rural 

Areas, OT Report 74-38 (June 1974). 
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, MONTH, DAY, YEAR Gain corr., rec. = I 

tot. cons tr. = , where 

Run and Session = the title of the portrayed frame identifying 1 

the digitizing session and run number, I 

example, 21 83 

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

example, 8 25 73 

Gain corr. rec. = receiver gain correction, example, -6 

tot. const. = constant gain correction of entire system, 

example, 46.4 

C = correction curve used with data, example, 25 

RG = receiver gain and accompanying correction in dB added to I 

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 1 

graph, example, 1.000+004 (1.0 x lo4) I 

Standard Error = standard error of curve, example, 0.3162 1 

Spectral Peak = largest spectral peak observed, example, 1 
corded using broadband analog magnetic tape for later transformation to 

spectral plots. Second, noise amplitudes were recorded at several discrete frequencies for a sufficient amount of time to provide data for 

amplitude probability distributions. A third technique gave attenuation 

data through the direct measurement of field strength at various depths. 

The specific measured results are given in a number of spectral 

plots, amplitude probability distribution plots and amplitude curves 

as a function of depth. 

instrumentation; mine noise; spectral density: time - de 

18. A\'AII.AI~II.I'I'Y t-- rx linlimited 

17. RllY U'0KI)S (six to twclve entries; alphabetical order; capitalize only Ule first letter of t h e f i r s t k e y word unless a proper 

rleme; separated by semicolons) Amplitude probability distribution; digital data, electromag2etic interference; electromagnetic noise; emergency communications; Fast Fourier 

Transform; Gaussiam distribution; impulsive noise; magnetic field strength; measurement 

[, - 1-or Official 1)isrribution. I)o Not Keleasc to N'I'IS 

UNCL ASSIF IED 

[ Orclrr I;rclnl Sup. <>i l)uc., U.S. Governmenr l'rinting Office 

U'JS~III~I~I~, I).(:. 2U iU2, 511 Cat. No. (:I3 (THIS PAGE) 

+,, . 

i : Order I:rvm National Technical Informnrion Service (NI'IS) 

Springiicld, Virg~n~a 22151 UNCI.ASSIFIE1) 

,. , USCOMM-DC 29042-P74