Electromagnetic Noise in Lucky Friday Mine · 100 kHz and 75 kHz-----.--- 123 Figure 5-9. Received signal at cage from 35 kHz source at headframe----- 124 Figure 5-10. Received signal

ELECTROMAGNETIC NOISE IN LUCKY FRIDAY MINE

W. W. Scott, NBS J. W. Adams, NBS W. D. Bensema, NBS H. Dobroski, U. S. Bureau o f Mines

Electromagnet ics Div is ion Ins t i t u te fo r Basic Standards Nat iona l Bureau o f Standards Boulder, Colorado 8 0 3 0 2

The views and conclusions con ta ined in t h i s document should no t be i n te rp re ted as necessar i ly represent ing t h e o f f i c i a l po l ic ies or recommendat ions o f t h e In te r io r Depar tment ' s Bureau o f Mines o f t h e U. S. Government .

October 1974

Prepared for U. S. Bureau o f Mines Pi t tsburgh Min ing and Safety Research Center 4800 Forbes Avenue Pi t tsburgh, Pennsylvania 15213 Work ing Fund Agreement HO 133005

- - --

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

NATIONAL B U R E A U OF S T A N D A R D S R ~ c h a r d W Roberts Dtrector

CONTENTS Page

3 . 1 I n t r o d u c t i o n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 3

3 .2 S u r f a c e Noise M e a s u r e m e n t s - - - - - - - - - - - - - - - - - - - - - - 1 3 3 . 2 . 1 H o i s t H o u s e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 3

3 . 2 . 3 Noise Near B u s i n e s s D i s t r i c t , C e n t e r o f T o w n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 5

3 . 3 S p e c t r a a t L e v e l s Wi th in t h e M i n e - - - - - - - - - - - - - - - 16 3 . 3 . 1 The 1450 Leve l - - - - - - - , - - - - - - - - - - - - - - - - - - - - 1 6 3. 3.2 The 3650 L e v e l - - - - - - - - - - - - - . - - - - - - - - - - . - - - - 17 3 . 3 . 3 The 4050 L e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - 17

3 . 4 S p e c t r a Ob ta ined from Cage Runs, Loop Antenna- - - 2 1

3 . 4 . 1 Mine Not i n O p e r a t i o n - - - - - - - - - - . - - - - - - - - - - 2 1 3 . 4 . 2 Mine i n O p e r a t i o n - - - - - - - - - - - - - - - - - - - - - - - - 2 2

AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS------ 74

4 . 1 I n t r o d u c t i o n and U n c e r t a i n t i e s - - - - - - - - - - - - - - - - - - 7 4

NOISE A N D ATTENUATION MEASUREMENTS ALONG THE HOIST ROPE - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 114 5 . 1 Noise M e a s u r e m e n t s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 114

5 .2 A t t e n u a t i o n M e a s u r e m e n t s - - - - - - - - - - - - - - - - - - - - - - - - 115

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

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

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

9 . REFERENCES- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 127 1 0 . A ~ ~ E N D I X - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 128

iii

LIST OF FIGURES

Page

F igure 1-1.

Figure 2 - 1 .

F igure 2 - 2 .

F igure 2-3.

F igure 2 - 4 .

Figure 2-5.

Figure 3-1 .

Figure 3 -2 .

Figure 3-3 .

F igure 3-4 .

F igure 3 - 5 .

Figure 3 -6 .

Figure 3 -7 .

Figure 3 -8 .

I somet r ic p r o j e c t i o n of Lucky Fr iday Mine--- 5

Block diagram o f p o r t a b l e i n s t rumen ta t i on , f i r s t s y s t e m - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8

Second f i e l d record ing system, f i r s t c o n f i g u r a t i o n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9

Second f i e l d record ing system, second con- f i g u r a t i o n ; used t o record d a t a f o r A P D ' s - . - - 10

Second f i e l d record ing system, t h i r d con- f i g u r a t i o n ; it recorded d a t a f o r A P D t s on 3650 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11

Second f i e l d record ing system, f o u r t h con- f i g u r a t i o n ; it was used on h o i s t runs up and down s h a f t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 2

Spectrum of magnetic f i e l d s t r e n g t h , h o i s t h o u s e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24

Spectrum of magnetic f i e l d s t r e n g t h , h o i s t house-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - . - - - - - - - 25

Spectrum of magnetic f i e l d s t r e n g t h , headframe - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 26

Spectrum of magnetic f i e l d s t r e n g t h , headframe - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 7

Spectrum of magnetic f i e l d s t r e n g t h , head- f r a m e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 8

Spectrum of magnetic f i e l d s t r e n g t h , head- f r a m e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 29

Spectrum o f magnetic f i e l d s t r e n g t h , headframe- -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 30

Spectrum of magnetic f i e l d s t r e n g t h , head- f Tame - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 31

LIST OF FIGURES (Cont inued)

F i g u r e 3 - 9 . Spectrum o f magne t i c f i e l d s t r e n g t h , headframe- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 32

F i g u r e 3 - 1 0 . Spec t rum o f magne t i c f i e l d s t r e n g t h , head- f r a m e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 33

F i g u r e 3-11 . Spectrum o f magne t i c f i e l d s t r e n g t h , Cedar S t r e e t , Wal l ace , Idaho-- - - - - - - - - - - - - - - - - - - - -

34 I F i g u r e 3 -12 . Spec t rum o f magne t i c f i e l d s t r e n g t h , Cedar

S t r e e t , Wal l ace , Idaho-- - - - - - - - - - - - - - - - - - - - - 35

F i g u r e 3 -13 . Spec t rum o f magne t i c f i e l d s t r e n g t h , Cedar S t r e e t , W a l l a c e , I d a h o - - - - - - - - - - - - - - - - - - - - - -

F i g u r e 3 -14 . Spectrum o f magne t i c f i e l d s t r e n g t h , 1450 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 37

F i g u r e 3 - 1 5 . Spectrum o f magne t i c f i e l d s t r e n g t h , 1450 l e v e l - - - - - - - - - - - . - - - - - - - - - - - - - - - - - - - - - - - - - - - - 38

F i g u r e 3 - 1 6 . Spectrum o f magne t i c f i e l d s t r e n g t h , 3650 l e v e l - - - - - - - - - - - - - - - - - - . - - - - - - - - - - - - - - - - - - - - - 39

F i g u r e 3 - 1 7 . Spectrum o f magne t i c f i e l d s t r e n g t h , 3650 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 40

F i g u r e 3 -18 . Spec t rum o f magne t i c f i e l d s t r e n g t h , 3650 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 41

F i g u r e 3 - 1 9 . P l a n view o f p o r t i o n o f 4050 l e v e l , Lucky Fr iday Mine- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 2

F i g u r e 3 - 2 0 . Spectrum o f magne t i c f i e l d s t r e n g t h , 4050 level-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 3


F i g u r e 3-22. Spectrum o f magne t i c f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 5


LIST OF FIGURES (Continued)

Page

F igure 3-24.

Figure 3-25.

Figure 3-26.

Figure 3-27.

Figure 3-28.

Figure 3-29.

F igure 3-30.

F igure 3-31.

Figure 3-32.

F igure 3-33.

F igure 3-34.

Figure 3-35.

F igure 3-36.

Figure 3-37.

F igure 3-38.

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4 7

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - . - - - - - - - - - - - - - 48

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 49

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - SO

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - -- - - - - - - - - - - - - -- - - - - -- - - - - - - - - 5 1

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 53

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - . - - - - - - - - - 54

Spectrum of magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - -- - - - - - --.- - - - - - - - - - - - - - - - - - - - - - - - - - - 55

Spectrum of magnetic f i e l d s t r e n g t h , 4050 1 eve 1 - - - -. - - - - - - - - - - - - - - - - -, - -, - - - - - -- - - - - 5 7

Spectrum of magnetic f i e l d s t r e n g t h , zero l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - , - - - - - - - - - - 5 9

Spectrum o f magnetic f i e l d s t r e n g t h , 4050 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 60

Spectrum of magnetic f i e l d s t r e n g t h , zero l e v e l - - - - - . - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 6 1

LIST OF FIGURES (Cont inued)

Page

F i g u r e 3 - 3 9 . Spectrum o f magne t i c f i e l d s t r e n g t h , 150 l e v e l - . - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 62

F i g u r e 3-40 . Spec t rum o f magne t i c f i e l d s t r e n g t h , 1450 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 63

F i g u r e 3-41 . Spectrum o f magne t i c f i e l d s t r e n g t h , 3400 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 64

F i g u r e 3 -42 . Spectrum o f magnet ic f i e l d s t r e n g t h , 4250 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - . - - - - - - - - - - - - - - 65

F i g u r e 3 - 4 3 . Spectrum o f v o l t a g e a c r o s s a 50 ohm l o a d , 4250 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 66

F i g u r e 3 - 4 4 . Spectrum o f magnet ic f i e l d s t r e n g t h , 4250 level - - - - - - - - - - - - - - - - - . . . . . . . . . . . . . . . . . . . . . . 67

F i g u r e 3 -45 Spectrum o f v o l t a g e a c r o s s a 50 ohm l o a d (compar ison o f s t r o n g unknown s o u r c e and t y p i c a l n o i s e ) - - - - - - - - - - - - - - - - - - - - - - - - - - . - - - - 68

F i g u r e 3 - 4 6 . Spectrum o f magne t i c f i e l d s t r e n g t h , 4250 l e v e l - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 69

F i g u r e 3-48 . Spectrum o f v o l t a g e a c r o s s a 50 ohm l o a d (unknown narrowband s o u r c e s ) - - - - - - - - - - - - - - - - 7 1

F i g u r e 3 - 4 9 . Spectrum o f v o l t a g e a c r o s s a 50 ohm l o a d (unknown narrowband s o u r c e s ) - - - - - - - - - - - - - - - - 7 2

F i g u r e 3 -50 . Spectrum o f magne t i c f i e l d s t r e n g t h , 1800 level - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 73

F i g u r e 4 - 1 . APD, 30 kHz, h e a d f r a m e - - - - - - - - - - - - - - - - - - - - - - 78 I I F i g u r e 4 - 2 . APD, 70 k ~ ~ , h e a d f r a m e - - - - - - - - - - - - - - - - - - - - - - 7 9

F i g u r e 4 - 3 . APD, 150 kHz, h e a d f r a m e - - - - - - - - - - - - - - - - - - - - - 8 0 I F i g u r e 4 - 4 . APD, 250 kHz, h e a d f r a m e - - - - - - - - - - - - - - - - - - - - - 8 1


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

L I S T OF FIGURES (Continued)

Page

F igure 4-28.

Figure 4 -29 .

Figure 4-30.

F igure 4 -31.

F igu re 4-32.

F igure 4-33.

F igure 4-34.

F igure 4-35.

F igu re 4-36.

F igure 5-1 .

F igure 5-2 .

F igure 5 -3 .

F igure 5-4 .

F igure 5 -5 .

F igure 5-6 .

Summary c u r v e s , headframe, h o r i z o n t a l ( no r th - sou th ) componen t - - - - - - - - - - - - - - - - - - - - - 106

Summary cu rves , headframe, v e r t i c a l com- p o n e n t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 107

Summary cu rves , 1450 l e v e l , v e r t i c a l com- p o n e n t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 108

Summary c u r v e s , 1450 l e v e l , h o r i z o n t a l ( no r th - sou th ) component-- - - - - - - - - - - - - - - . - - - - - 109

Summary c u r v e s , 3050 l e v e l , h o r i z o n t a l ( no r th - sou th ) c o m p o n e n t - - - - - - - - - - - - - - - - - - - - - 1 1 0

Summary cu rves , 3050 l e v e l , v e r t i c a l com- p o n e n t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 111

Summary c u r v e s , 3650 l e v e l , h o r i z o n t a l ( no r th - sou th ) c o m p o n e n t - - - - - - - - - - - - - - - - - - - - - 1 1 2

Summary cu rves , 3650 l e v e l , v e r t i c a l component- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 113

EM n o i s e i n mine s h a f t , mine no t i n ope ra - t ion, 49 kHz- - - - - - - - - - - - - - - - - - - - - - . - - - - - - - - - - 116

EM n o i s e i n mine s h a f t , mine no t i n ope ra - tion, 49 k ~ z - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 117

EM n o i s e i n mine s h a f t , mine n o t i n ope ra - tion, 35 k ~ z - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 118

EM n o i s e i n mine s h a f t , mine n o t i n ope ra - t ion, 35 kHz - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 119

EM n o i s e i n mine s h a f t , mine i n o p e r a t i o n , 75 kHz and 100 k H z - - - - - - - - - - - - - - - - - - - - - - - - - - 120

EM n o i s e i n mine s h a f t , mine i n o p e r a t i o n , 5 2 kHz and 75 k H z - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 2 1


Page

F igure 5-7. EM n o i s e i n mine s h a f t , mine i n o p e r a t i o n , 52 kHz and 35 kHz------- . -------------------- 1 2 2

F igure 5-8. EM n o i s e i n mine s h a f t , mine i n o p e r a t i o n , 100 kHz and 75 kHz- - - - - - - - - - - - - - - - - - - - - - - . - - - 123

F igure 5-9. Received s i g n a l a t cage from 35 kHz source a t headf rame- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 124

Figure 5-10. Received s i g n a l a t cage from 50 kHz source a t head f r ame- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 125

ELECTROMAGNETIC NOISE I N LUCKY FRIDAY MINE

Measurements o f t h e a b s o l u t e v a l u e o f e l ec t romag- n e t i c n o i s e and a t t e n u a t i o n a long a h o i s t rope were made i n an o p e r a t i n g ha rd - rock mine, Lucky F r i d a y Mine, l o c a t e d n e a r Wal lace , Idaho. S p e c t r a o f e l e c t r o m a g n e t i c n o i s e g e n e r a t e d by v a r i o u s p i e c e s o f equipment , s p e c t r a o f s p e c i f i c n o i s e s i g n a l s a t v a r i o u s d e p t h s , and n o i s e and a t t e n u a t i o n on t h e 4250 f o o t (1295 mete r ) h o i s t , were measured. Three t e c h n i q u e s were used t o make t h e measurements. F i r s t , n o i s e was measured o v e r t h e en- t i r e e l e c t r o m a g n e t i c spectrum o f i n t e r e s t f o r b r i e f t ime p e r i o d s . Data were recorded u s i n g broadband ana log magnet ic t a p e f o r l a t e r t r a n s f o r m a t i o n t o s p e c t r a l p l o t s . Second, n o i s e ampl i tudes were recorded a t s e v e r a l d i s - C r e t e f r e q u e n c i e s f o r a s u f f i c i e n t amount o f t ime t o p r o v i d e d a t a f o r ampl i tude p r o b a b i l i t y d i s t r i b u t i o n s . A t h i r d t echn ique gave a t t e n u a t i o n d a t a through t h e d i r e c t measurement o f f i e l d s t r e n g t h a t v a r i o u s d e p t h s .

The s p e c i f i c measured r e s u l t s a r e g iven i n a number o f s p e c t r a l p l o t s , ampl i tude p r o b a b i l i t y d i s t r i b u t i o n p l o t s and ampl i tude c u r v e s a s a f u n c t i o n o f d e p t h .

Key words : Amplitude p r o b a b i l i t y d i s t r i b u t i o n ; d i g i t a l d a t a ; e l e c t r o m a g n e t i c i n t e r f e r e n c e ; e l e c t r o m a g n e t i c n o i s e ; emergency communications ; F a s t F o u r i e r Transform; Gaussian d i s t r i b u t i o n ; impuls ive n o i s e ; magnetic f i e l d s t r e n g t h ; measurement i n s t r u m e n t a t i o n ; mine n o i s e ; s p e c t r a l d e n s i t y ; t ime-dependent s p e c t r a l d e n s i t y .

1. INTRODUCTION

This r e p o r t g i v e s d a t a concern ing e l e c t r o m a g n e t i c n o i s e

i n a ha rd - rock mine. I n t h i s s e c t i o n , background i n f o r m a t i o n

and a b r i e f mine d e s c r i p t i o n a r e covered . I n S e c t i o n 2 ,

measurement i n s t r u m e n t a t i o n i s d i s c u s s e d . In S e c t i o n 3 ,

s p e c t r a l p l o t s o f d a t a a r e p r e s e n t e d . I n S e c t i o n 4 , ampl i tude

p r o b a b i l i t y d i s t r i b u t i o n s (APD) o f m a g n e t i c - f i e l d n o i s e a r e

g i v e n . In S e c t i o n 5 , t h e r e s u l t s o f d i r e c t measurements o f

f i e l d s t r e n g t h a r e g i v e n , from which a t t e n u a t i o n may be

computed. The l a s t two s e c t i o n s (6 and 7 ) cover c o n c l u s i o n s

and recommendations.

Only r e p r e s e n t a t i v e samples o f t h e t o t a l d a t a measured

a r e g iven i n t h i s r e p o r t , and o n l y a l i m i t e d s e t o f d a t a -

p r e s e n t a t i o n fo rmats have been u s e d . I f a d d i t i o n a l d a t a , o r

d a t a p r e s e n t a t i o n i n o t h e r f o r m a t s , a r e r e q u i r e d , p l e a s e

c o n t a c t any o f t h e a u t h o r s . With t h e s p e c i f i c pe rmiss ion

o f t h e Bureau o f Mines, we w i l l supp ly t h e a d d i t i o n a l d a t a .

A more complete d e s c r i p t i o n o f t h e measurement systems used

i s g iven i n t h e Robena Mine r e p o r t [ I ] .

1.1 Background

The l a c k o f r e l i a b l e communication systems i n mines i s

a l o n g - s t a n d i n g problem. For emergency u s e , when a l l power

i n a mine i s o f f , t h e r e s i d u a l e l e c t r o m a g n e t i c n o i s e i s no

problem. However, i f a communication system were des igned o n l y

f o r emergency u s e , i t would have t h r e e s e r i o u s drawbacks. F i r s t ,

i t would n o t be ready f o r immediate u s e i n an emergency; second,

it would n o t be o f any v a l u e d u r i n g normal o p e r a t i o n s ; and

t h i r d , even d u r i n g emergencies , some power must u s u a l l y be

p r e s e n t . T h e r e f o r e , t h e Bureau o f Mines dec ided t o d e s i g n a

communication system t h a t cou ld be used f o r b o t h emergency and

normal o p e r a t i o n a l c o n d i t i o n s .

Also , two-way communication t o p e r s o n n e l i n a moving

h o i s t i s d e s i r a b l e f o r normal o p e r a t i n g c o n d i t i o n s , and i s

n e c e s s a r y i n emergency c o n d i t i o n s .

During o p e r a t i o n , t h e machinery used i n mines c r e a t e s a

wide range o f many t y p e s o f i n t e n s e e l e c t r o m a g n e t i c i n t e r -

f e r e n c e (EMI). Th i s EM1 i s a major l i m i t i n g f a c t o r i n t h e

d e s i g n o f a communication sys tem.

The work r e p o r t e d h e r e g i v e s t h e r e s u l t s o f comprehensive

measurements o f t h i s EM1 i n c r i t i c a l communication l o c a t i o n s ,

p a r t i c u l a r l y a long t h e h o i s t p a t h a t v a r i o u s d e p t h s .

S e v e r a l EM1 paramete r s can be measured: magnetic f i e l d

s t r e n g t h , H ; e l e c t r i c f i e l d s t r e n g t h , E; conducted c u r r e n t , i ;

and v o l t a g e , v , between two c o n d u c t o r s . Two paramete r s were

emphasized: magnetic f i e l d s t r e n g t h measured w i t h loop an-

t e n n a s and n o i s e c u r r e n t s on t h e h o i s t c a b l e measured w i t h a

clamp-on t o r o i d . ( H o i s t c a b l e s w i l l be r e f e r r e d t o a ' r o p e s '

h e r e a f t e r .)

There a r e s e v e r a l r e a s o n s f o r emphasizing t h e measurement

o f t h e magnet ic f i e l d s t r e n g t h . F i r s t , a t any a i r - e a r t h i n t e r -

f a c e , o n l y t h e magnetic f i e l d i s e s s e n t i a l l y u n d i s t u r b e d , w h i l e

t h e e l e c t r i c f i e l d i s s e v e r e l y reduced. Second, any c u r r e n t s

w i l l induce magnetic f i e l d s , and hence measurement of t h e

magnet ic f i e l d w i l l d i r e c t l y r e f l e c t c u r r e n t s . T h i r d , power

l i n e v o l t a g e s a r e p ropaga ted a s t r a n s m i s s i o n l i n e phenomena,

and a r e d i r e c t l y r e l a t e d t o t r a n s m i s s i o n l i n e c u r r e n t s and t h e

magnet ic f i e l d s induced. Thus, measuring magnet ic f i e l d s t r e n g t h

g i v e s a r e p r e s e n t a t i v e composi te p i c t u r e of n o i s e from c u r r e n t s

and v o l t a g e s from most s o u r c e s , i n c l u d i n g a r c i n g equipment .

Vol tage from t h e t o r o i d i s measured t o de te rmine s i g n a l

s t r e n g t h , n o i s e , and hence s i g n a l - t o - n o i s e r a t i o s f o r d e s i g n

in fo rmat ion f o r a s p e c i f i c sys tem, a two-way h o i s t - p h o n e .

Although magnet ic f i e l d s t r e n g t h measurements a r e

emphasized h e r e , even t h i s one parameter i s d i f f i c u l t t o

measure mean ingfu l ly . The IEEE d e f i n i t i o n [ 2 ] o f magnetic

f i e l d s t r e n g t h , H (magnitude o f t h e magnet ic f i e l d v e c t o r ) ,

i s used i n t h i s r e p o r t . S ince t h e r e a r e a m u l t i t u d e of d i f -

f e r e n t s o u r c e s t h a t g e n e r a t e a l l known t y p e s o f n o i s e , t h e

r e s u l t a n t magnetic f i e l d s t r e n g t h n o i s e v e c t o r i s a f u n c t i o n

o f f r e q u e n c y , t i m e , o r i e n t a t i o n , and l o c a t i o n . Small v a r i a -

t i o n s i n t h e s e pa ramete r s can cause s e v e r a l o r d e r s o f magnitude

d i f f e r e n c e i n measured f i e l d s t r e n g t h .

1 . 2 Mine D e s c r i p t i o n

The r e s u l t s and d a t a p r e s e n t e d i n t h i s r e p o r t a r e based

on measurements made on August 25 , 26 , and 27, 1973 , and on

Februa ry 8 , 1974 , i n t h e Lucky F r i d a y Mine and o t h e r l o c a t i o n s

n e a r W a l l a c e , Idaho . The mine , shown i n f i g u r e 1-1, b e l o n g s

t o Hecla Mining Company and p roduces o r e c o n t a i n i n g l e a d ,

s i l v e r , and z i n c . Access i s by way o f a s i n g l e , double-drum

h o i s t , u s i n g t h e No. 2 s h a f t . There a r e two h o i s t s on t h e

No. 2 s h a f t . Ore i s removed from t h e s t o p e s v i a r a i s e s and

d r i f t s and t h e n i s removed from t h e mine by t h e same h o i s t

p e r s o n n e l u s e . S o m e m ~ t is_dcC~,,o-wered: t h e 5 - t o n , 90

c e l l , b a t t e r y - p o w e r e d l o c o m o t i v e s , and t h e 1250 horsepower

motor used t o r a i s e t h e h o i s t s . Much equipment u s e s a c power

a t 1 2 0 , 440 , and 2400 v o l t s : a i r - c o n d i t i o n e r s , v e n t i l a t i o n

s y s t e m s , c o m p r e s s o r s , l i g h t i n g , and b a t t e r y c h a r g e r s . O the r

equipment u s e s compressed a i r .

S h i f t s run t o 3:00 p.m. , 4:00 p .m. , 1 1 : O O p .m. , 1 2 a .m. ,

and 7:00 a .m. ; b l a s t i n g i s s c h e d u l e d a t 2:20 p.m. , 11 :20 p .m. ,

and 6 :20 a.m.

The t e m p e r a t u r e and humid i ty a r e h i g h , a l t h o u g h n o t

e x c e s s i v e i n most p l a c e s .

Of p a r t i c u l a r i n t e r e s t i n t h i s measurement e f f o r t i s how

s i g n a l s and n o i s e p r o p a g a t e a l o n g t h e s h a f t , w i t h and w i t h o u t

h o i s t r o p e s . Power c a b l e s and c o m p r e s s e d - a i r p i p e s , a s w e l l

a s s a n d - t r a n s p o r t p i p e s , run i n t h i s same s h a f t , so t h e r e i s

a lways a c o m p o s i t e , s i n g l e c o n d u c t o r p r e s e n t t o s e r v e a s one

w i r e o f a two w i r e t r a n s m i s s i o n l i n e . The p r e s e n c e o f e i t h e r

h o i s t r o p e s t r o n g l y a f f e c t s t r a n s m i s s i o n c h a r a c t e r i s t i c s a l o n g

t h e s h a f t by p r o v i d i n g a second w i r e o f a two-wire t r a n s m i s s i o n

1 i n e .

4 s -

Figure 1-1 I some t r i c Project ion of Lucky Fr iday Mine.

2 . MEASUREMENT INSTRUMENTATION

Three measurement t echn iques were used . The f i r s t covers

a l a r g e p o r t i o n of t h e spectrum a s a "snapshot" a t one i n s t a n t

o f t ime . I n th ree -d imens iona l form, s e v e r a l such "snap-shots"

can show how d r a s t i c a l l y a s i g n a l v a r i e s no t on ly w i t h f r e -

quency bu t a l s o w i th t ime . The second t echn ique g ives v a r i a -

t i o n s over a 20-minute t ime i n t e r v a l a s a view over a narrow

frequency window. Usua l l y , n o i s e was measured a t a s e t of

f ou r d i f f e r e n t f r e q u e n c i e s . Both t echn iques were used t o

measure two or thogona l components of magnetic f i e l d s t r e n g t h

by e i t h e r u s ing two systems s imul taneous ly o r by va ry ing t h e

o r i e n t a t i o n o f one system. Both t echn iques were used i n a s

many d i f f e r e n t l o c a t i o n s a s p o s s i b l e . Whether t h e n o i s e s i g n a l

t ends t o be Gaussian o r impuls ive depends on t h e number of

sou rce s and t h e d i s t a n c e t o each sou rce . With t h e t h i r d t e c h -

n i q u e , va lue s of f i e l d s t r e n g t h a t va r i ous l e v e l s under v a r i o u s

c o n d i t i o n s were recorded . These measurements gave a t t e n u a t i o n

v a l u e s , compl ica ted mainly by s eve re s tanding-wave p a t t e r n s .

Noise l e v e l s were recorded a l s o , bu t va lue s t aken t h i s way

cannot meaningful ly r e l a t e t h e t ime v a r i a t i o n s of t h e n o i s e

parameter . The va lue s g iven a r e w i t h i n t h e bounds i n d i c a t e d

i n t h e APD's.

A l l measured n o i s e i s r e p o r t e d i n a b s o l u t e q u a n t i t i e s

( i n s t e a d of r e l a t i v e ) t o a l low o t h e r s t o make e f f e c t i v e use

o f t h e d a t a . For t h e magnetic f i e l d s t r e n g t h measurements, t h e

NBS f i e l d c a l i b r a t i o n s i t e i s used w i t h each complete measurement

system t o a s s u r e c o r r e c t system c a l i b r a t i o n [ 3 ] .

The mine environment i s g e n e r a l l y humid, d u s t y , h o t , and

poo r ly l i g h t e d . This compl ica ted t h e measurement p roce s s .

Most o f ou r p o r t a b l e measuring equipment was b a t t e r y - o p e r a t e d ,

d u s t - p r o t e c t e d , and p e r m i s s i b l e .

Two t y p e s o f n o i s e a r e recorded i n t h e s p e c t r a l p l o t s ,

and hence two d i f f e r e n t magnetic f i e l d s t r e n g t h pa ramete r s a r e

r e q u i r e d , H and Hd. Resu l t s a r e g iven a s t h e rms v a l u e of one

component of magnetic f i e l d s t r e n g t h , H , v e r su s f requency f o r

d i s c r e t e f r e q u e n c i e s ; it i s g iven a s one component of magnetic-

f i e l d - s t r e n g t h spectrum d e n s i t y l e v e l [ 2 ] , H d , v e r su s f requency

f o r broadband n o i s e i n t h e s p e c t r a l p l o t s . In t h e ampl i tude

p r o b a b i l i t y d i s t r i b u t i o n s , r e s u l t s a r e g iven a s t h e rms va lue

o f one component of magnetic f i e l d s t r e n g t h ve r su s p e r c e n t of

t ime t h i s va lue i s exceeded. The APD g ive s t h e d i s t r i b u t i o n

of t h e a c t u a l i n s t an t aneous va lue s on ly a s f a r a s t h e

measurement-system d e t e c t o r bandwidth w i l l a l low t h e d e t e c t o r

t o f o l l ow t h e t ime v a r i a t i o n s of t h e a c t u a l magnetic f i e l d .

( I n t h i s c o n t e x t , n o i s e envelope i s sometimes used . ) Thus,

t h e r e s u l t s a r e a p p l i c a b l e f o r a communication r e c e i v e r whose

bandwidth i s s i m i l a r t o t h e measurement -system d e t e c t o r

bandwidth.

Two measurement systems were used t o make measurements

underground. One system was conf igured f o u r d i f f e r e n t ways.

Five b lock diagrams a r e shown i n f i g u r e s 2 - 1 through 2-5.

For a d e t a i l e d d e s c r i p t i o n of t h e s e sys tems , s e e p r ev ious

r e p o r t s [ I , 41 . The systems used i n Lucky Fr iday a r e t h e ones

used i n p r ev ious mine measurement b u t a r e con f igu red d i f f e r e n t l y

i n some c a s e s .

The f i r s t system measures d a t a f o r s p e c t r a l p l o t s and

i s f u l l y p e r m i s s i b l e and p o r t a b l e . The second system i s no t

p e r m i s s i b l e b u t i s t r a n s p o r t a b l e ; it r eco rds d a t a f o r bo th

s p e c t r a l p l o t s and s t a t i s t i c a l p r e s e n t a t i o n s , e . g . , ampl i tude

p r o b a b i l i t y d i s t r i b u t i o n s .

SIGNAL MON

LOUD I SPEAKER I loscl LLoscopE 1

SYSTEM #I

LOOP ANTENNA BROADBAND n AMPLIFIER I

IMPEDANCE TRANSFORMER

TAPE RECORDER (30 ips, record)

TRACK I (FM)

SYSTEM # 2

SYSTEM # 3

MICROPHONE EDGE TRACK (VOICE)

200.kHz CRYSTAL OSC l LLATOR

Figure 2-1 Block diagram of portable instrumentation, f i r s t system. F M t racks a r e used to r eca rd frnm..100 Hz to 100 kHz;

TRACK 4 (DIR)

di rec t t racks F - . a r e - - used *--.... f r o m 3 .kHz to 320 kHz. Systems 2 and 3 a r e identical to sys tem 1. When the direct t racks a r e used, the 100-kHz low pass f i l ters a r e eliminated, and the amplifier bandwidth i s increased f rom 100 kHz to 300 kHz. The microphone i s used for occasional vocal comments by the operator.

- - - - - TRACK 5 (FM)

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 f i e l d r e c o r d i n g system, f i r s t c o n f i g u r a t i o n .

Figure 2-4 Second f i e l d recording system, t h i r d conf igura t ion ; i t recorded d a t a f o r APD'S on 3650 l e v e l .

11

TO RIGID LOOP ANTENNA ON TOP OF HOIST CAGE

BALUN + TO COLLAPSIBLE LOOP ANTENNA ON TOP OF HOIST CAGE

FIELD STRENGTH I METER I

Figure 2-5 Second f i e l d record ing system, f o u r t h conf igura t ion ; i t w a s used on hoist runs up and down shaft.

0

. 25 kHz

OSC

TO TOROID AROUND HOIST ROPE

ANALOG TAPE RECORDER

CHANNEL a3

a 4 (DIR)

A 1 ) BALUN -05 (DIR)

FIELD STRENGTH METER

i

20 kHz LP FILTER 07 (FM)

3. SPECTRUM MEASUREMENT RESULTS

3.1 In t roduc t ion

In t h i s s e c t i o n of t h e r e p o r t , spectrum p l o t s a r e p re -

s en ted and d iscussed . Most of t h e s e p l o t s p re sen t magnetic

f i e l d s t r e n g t h t o e i t h e r 100 kHz o r 200 kHz. The curves t o

100 kHz o r l e s s have an unce r t a in ty of + 1 dB. The curves

t o 200 kHz have an u n c e r t a i n t y of + 2 dB from 3 kHz t o 200 kHz.

Measurements were made a t many d i f f e r e n t l o c a t i o n s and r e s u l t s

can be used t o c h a r a c t e r i z e e lectromagnet ic no i se l e v e l s

generated by most f i xed and mobile equipment used i n t h i s

mine.

3.2 Surface Noise Measurements

3 .2 .1 Hoist House

The h o i s t house con ta ins a 1250 hp, d i r e c t c u r r e n t ,

double-drum h o i s t w i th dc cu r ren t suppl ied by a motor-

gene ra to r . Figures 3-1 and 3-2 show t h e no i se measured i n

t h e h o i s t house. The antenna s e n s i t i v e a x i s was v e r t i c a l

and about two meters from t h e e l e c t r i c a l cab le s supplying

t h e dc c u r r e n t t o t h e h o i s t motor. The cab le s were below

t h e concre te f l o o r . For f i g u r e 3-1 t h e h o i s t was l i f t i n g a

load ( 8 . 2 met r i c tons) of waste rock a t 1300 fee t /minute

(396 m/min.), and f o r f i g u r e 3-2 a t 1700 fee t /minute (518 m/min.).

This no i se i s one of t h e h igher l e v e l s measured a t Lucky

Fr iday. Figures 3-1 and 3-2 a r e t y p i c a l of s e v e r a l s p e c t r a

taken i n t h e h o i s t house, on Monday, August 2 7 , 1973, a t y p i -

c a l working day a t t h e mine. This group of s p e c t r a ( inc lud ing

f i g u r e s 3 - 1 and 3-2) d i f f e r s from o t h e r s p e c t r a taken around

o t h e r machinery i n t h a t (1) no i se i n f i g u r e 3-2 i s no t domi-

na ted by powerline harmonics, (2) t h e r e a r e no obvious

commutator-produced s p e c t r a l l i n e s , which might no rmal ly be

e x p e c t e d t o o c c u r a round dc commutated machinery , (3) t h e

s p e c t r a l l i n e s a t 300 Hz and 925 Hz a r e t h e o n l y l i n e s t h a t

a p p e a r r e g u l a r l y ; a l s o , t h e y a r e n o t h a r m o n i c a l l y r e l a t e d ,

and (4) o t h e r l i n e s a t n o n - h a r m o n i c a l l y r e l a t e d f r e q u e n c i e s

a p p e a r i r r e g u l a r l y . The l i n e a t 1090 Hz i s t y p i c a l ; i t a p p e a r s

o n l y i n t h e spec t rum shown i n f i g u r e 3-2 and i n none o f t h e

o t h e r s p e c t r a t a k e n i n t h e h o i s t house . Note t h a t on f i g u r e

3 - 1 , t h e spec t rum h a s a minor i n c r e a s e c e n t e r e d around 19 kHz.

L a t e r i n t h i s r e p o r t , o t h e r s p e c t r a t a k e n e l sewhere w i l l show

a s i m i l a r i n c r e a s e . The i n f e r e n c e w i l l be drawn t h a t t h e

h o i s t house n o i s e i s p r o p a g a t i n g down t h e 1 1 / 2 i n c h (3 .8 cm)

s t e e l h o i s t c a b l e ( r o p e ) t o some e x t e n t .

3 .2 .2 Head Frame

The head frame was 75 m away and u p h i l l 40 m from t h e h o i s t

house . The s t e e l head frame s t o o d about 2 0 m e t e r s h i g h and

s u p p o r t e d two l a r g e s h e a v e s , which i n t u r n s u p p o r t e d w i r e r o p e s ,

o n e each f o r t h e n o r t h and s o u t h s h a f t s . F i g u r e s 3 - 3 and 3 -4

show t h e n o i s e measured on t h e s u r f a c e 0.7 m from t h e open

n o r t h s h a f t , w i t h t h e a n t e n n a s e n s i t i v e a x i s h o r i z o n t a l EW

( p o i n t e d toward t h e w i r e r o p e ) . These measurements were made

on August 2 7 , 1 9 7 3 , a t y p i c a l working d a y . The minor i n c r e a s e

a t 19 kHz s e e n i n t h e h o i s t house does n o t show up h e r e ; how-

e v e r , i t may have been masked by a s f e r i c impu l se . The same

t y p e o f n o i s e a s h e a r d on t h e a u d i o moni to r i n t h e h o i s t

house c o u l d a l s o be h e a r d a t t h e head f r ame . However, a t

t h e head f r ame , t h e r e was a r e g u l a r p e r i o d i c i t y t o t h e n o i s e

t h a t p r o b a b l y can be c o r r e l a t e d t o t h e r o t a t i o n o f t h e main

h o i s t drum. F i n a l l y , f i g u r e 3 -3 shows t h e 1 8 . 6 kHz s i g n a l from

t h e Navy J i m Creek t r a n s m i t t e r , NLK Washington.

S p e c t r a o f t h r e e components o f magnet ic f i e l d n o i s e a t

t h e head frame a r e shown i n f i g u r e s 3 - 5 , 3 -6 , and 3-7 . The

n o i s e l e v e l s a r e much lower t h a n might be expec ted n e a r o p e r a t i n g

machinery. E i t h e r d i s t a n t s f e r i c s o r a r c s from t h e h o i s t house

(where d c motors were o p e r a t i n g ) r a i s e t h e n o i s e l e v e l s s l i g h t l y

and i n u n p r e d i c t a b l e ways. This i s shown i n f i g u r e s 3 -8 , 3-9 ,

and 3-10. The two h o i s t ropes l e a d i n g from t h e h o i s t house

t o t h e head-frame s e r v e a s two-wire t r a n s m i s s i o n l i n e s , b u t

t h e i n c r e a s e o r d e c r e a s e i n impuls ive n o i s e does n o t seem t o

b e r e l a t e d t o rope movement. Compare f i g u r e s 3-9 and 3-8 .

3 .2 .3 Noise Near Business D i s t r i c t , Cen te r o f Town

Three components of s u r f a c e n o i s e were measured on t h e

s idewalk a long a row o f b u i l d i n g s w i t h 'Leon signs): This i s

r e p r e s e n t a t i v e o f s u r f a c e n o i s e o v e r a mine t h a t i s under a

town o r c i t y . The n o i s e was predominant ly a t 60 H z o r i t s

odd harmonics , and was q u i t e s t r o n g , approaching 90 dB above

a microampere p e r meter a t 300 Hz, and 80 dB above a micro-

ampere p e r meter a t 180 Hz. A t f r e q u e n c i e s above 2 . 5 kHz,

a l l harmonics were o f n e a r l y equal a m p l i t u d e . V a l l e y s between

t h e power l i n e harmonics a r e about 4 0 dB above one pA/m up t o

2.5 kHz, b u t a r e down t o 10 dB above one pA/m from 5 t o 1 0 kHz.

The v e r t i c a l and h o r i z o n t a l (N-S) components of magnetic

f i e l d s t r e n g t h were b o t h s t r o n g , w h i l e t h e h o r i z o n t a l (E-W)

component was about 20 t o 30 dB lower . The component which

i s s t r o n g e s t o r weakest w i l l be d i f f e r e n t i n each l o c a t i o n

depending p r i n c i p a l l y on t h e d i r e c t i o n ( s ) o f t h e s t r o n g e s t

s o u r c e ( s ) . The magnet ic f i e l d n o i s e s p e c t r a a r e shown i n f i g u r e s

3-11, 3-12, and 3-13.

3 . 3 S p e c t r a a t L e v e l s Wi th in t h e Mine

3 . 3 . 1 The 1450 Level

The l e v e l s w i t h i n t h e mine a r e named by t h e d e p t h , and

c o r r e s p o n d t o t h e d e p t h below t h e z e r o l e v e l i n f e e t . The

z e r o l e v e l i s 40 m e t e r s below t h e headframe l o c a t e d on t h e

s u r f a c e . The d e p t h i n m e t e r s i s o b t a i n e d by m u l t i p l y i n g t h e

d e p t h i n f e e t by 0.3048 and a d d i n g 40 m e t e r s ; t h e 1450 l e v e l

i s t h e r e f o r e 482 m e t e r s deep .

The 1450 l e v e l c o n t a i n e d a 300 hp w a t e r pump. The

motor u s e d 67 amperes a t 2300 V , t h r e e p h a s e . F i g u r e s 3-14

and 3-15 show t h e n o i s e measured a t t h i s l e v e l w i t h t h e pump

n o t o p e r a t i n g . There i s no l o n g e r any mining a c t i v i t y a t

t h i s l e v e l . The measurement was made on S a t u r d a y , August 25 ,

1973, a non-working day i n t h e mine. The a n t e n n a was one

me te r from t h e s h a f t w i t h t h e s e n s i t i v e a x i s h o r i z o n t a l N-S,

t a n g e n t t o t h e open ing t o t h e s h a f t . F i g u r e 3-14 shows t h e

same minor i n c r e a s e i n t h e spec t rum around 1 9 kHz t h a t was

n o t e d i n t h e h o i s t house . The n o i s e , a s h e a r d on t h e a u d i o

m o n i t o r , had t h e c h a r a c t e r i s t i c sound o f " g r e a s e - f r y i n g , "

b u t was t o o r e g u l a r f o r a t m o s p h e r i c s . The n o i s e from t h e

h o i s t house i s s i m i l a r t o n o i s e a t t h e 1450 l e v e l . With t h e

300 hp pump t u r n e d on , t h e o n l y change was a 20 dB i n c r e a s e

i n t h e 60 H z n o i s e .

While t h e teams from NBS were i n t h e mine making n o i s e

measurements , a n o t h e r team from a communicat ions f i r m was

making r o p e t r a n s m i s s i o n and impedance t e s t s by i n j e c t i n g

a s i n g l e f r e q u e n c y s i g n a l i n t o t h e n o r t h r o p e . The s i g n a l

was c o u p l e d i n t o t h e w i r e r o p e u s i n g a f e r r i t e r i n g , and was

n o m i n a l l y a t a f r e q u e n c y o f 50 kHz. F i g u r e 3-14 shows a cw

s i g n a l a s i t was r e c e i v e d a t t h e 1450 l e v e l . The f r e q u e n c y

o f t h i s s i g n a l was 44 .6 kHz, b u t t h i s was n o t one o f t h e

f r e q u e n c i e s used i n t h e i r t e s t s . The t r a n s m i t t e r might

have been detuned a t t h e t ime of our measurement, o r t h e r e

may have been some o t h e r s o u r c e p r e s e n t . For example, s e e

n o i s e s i g n a l s a s shown i n f i g u r e 3-49.

3 .3 .2 The 3650 Level

Noise measurements were made a t a working l e v e l on

February 8 , 1974. A c t i v i t y was ve ry low a t t h e t i m e , s o

t h e n o i s e l e v e l s measured may be somewhat lower t h a n occur

normal ly . A spectrum of t h e v e r t i c a l component i s shown i n

f i g u r e 3-16; a h o r i z o n t a l (N-S) component i s shown i n f i g u r e

3 -17 . Each c o v e r s t ime i n t e r v a l s d u r i n g a t r a n s i e n t of n o i s e .

Antenna l o c a t i o n was about two mete r s e a s t of t h e h o i s t d o o r s .

F igure 3-18 shows t h e spect rum of t y p i c a l machine n o i s e .

3 . 3 . 3 The 4050 Level

The 4050 l e v e l (1274 mete r s below t h e s u r f a c e ) was t h e

d e e p e s t l e v e l a t which normal mining was b e i n g c a r r i e d on i n

August , 1973. The mine extended about a hundred mete r s lower

t o some mine development workings . The 4050 l e v e l c o n t a i n e d

a complex a r r a y o f w i r e s and swi tchboxes c o n t r o l l i n g pumps,

f a n s , b a t t e r y c h a r g e r s , l i g h t s , e t c . F i g u r e 3-19 shows a

p l a n view of t h e a r e a n e a r t h e s h a f t s .

F i g u r e s 3-20 and 3-21 show t h e n o i s e measured a t l o c a t i o n

A (shown on f i g u r e 3-19) on S a t u r d a y , August 25, 1973, a non-

working day i n t h e mine. The an tenna was 0 .6 mete r s i n f r o n t

o f t h e open s h a f t d o o r , w i t h s e n s i t i v e a x i s h o r i z o n t a l N-S.

F igure 3-20 shows t h e low n o i s e l e v e l p r e s e n t a t t h e 4050 l e v e l

w i t h most o f t h e mine s h u t down. F igure 3-20 a l s o shows what

we b e l i e v e i s a s t r o n g t e s t s i g n a l ; t h e f requency was 48.6 kHz.

I t i s s i g n i f i c a n t t h a t t h i s t e s t s i g n a l ( i f such it i s ) has

p e n e t r a t e d t h e mine from t h e s u r f a c e a long m e t a l l i c p a t h s .

Figures 3-22 and 3-23 show t h e n o i s e i n t h e same l o c a t i o n

w i t h t h e antenna s e n s i t i v e a x i s v e r t i c a l . A t t h a t t ime both

t h e t e s t s i g n a l and a 30 hp, 7 0 ampere, 440 v o l t water pump

below t h e 4050 l e v e l were o f f . The nex t f i g u r e s show s p e c t r a l

f e a t u r e s t h a t appear whenever t h i s p a r t i c u l a r pump was ope ra t i ng .

Figures 3-24 and 3-25 show t h e no i se measured i n t h e same

l o c a t i o n when t h e pump was ope ra t i ng . I n f i g u r e 3-24 arrows

i n d i c a t e t h r e e s p e c t r a l f e a t u r e s t h a t appear whenever t h e

pump i s o p e r a t i n g . These f e a t u r e s a r e t h e fundamental , second

and t h i r d harmonic of 2.86 kHz. Because of t h e i r a s s o c i a t i o n

w i t h t h i s pump, t h e s e f e a t u r e s can be a t t r i b u t e d t o , and

c a l l e d , t h e s i g n a t u r e of t h i s water pump. Other s p e c t r a , no t

inc luded i n t h i s r e p o r t , o c c a s i o n a l l y show h igher o rde r h a r -

monics. Figure 3-25 shows s p e c t r a l l i n e s (marked by arrows)

above 2050 H z , a l s o from t h i s water pump, t h a t a r e s epa ra t ed by

approximately 1 1 7 . 5 Hz i n s t e a d of 1 2 0 H z ( t h e second harmonic

o f 60 Hz). Pos s ib ly t h e 117.5 Hz l i n e s a r i s e from t h e pump

induc t ion motor s q u i r r e l cage r o t o r " s l i pp ing . " Induc t ion

motor r o t o r s i n c r e a s i n g l y " s l i p " ( i . e . , run slower than t h e

synchronous e l e c t r i c a l r o t a t i o n of t h e f i e l d ) a s t h e mechanical

l o a d i s i nc rea sed . These and o t h e r s p e c t r a i n t h i s r e p o r t show

harmonic s t r u c t u r e t h a t could probably be t r a c e d t o o t h e r

r o t a t i n g machinery.

With t h e antenna i n t h e above p o s i t i o n ( s e n s i t i v e a x i s

v e r t i c a l , 0.6 m i n f r o n t of t h e open sou th s h a f t d o o r ) , dur ing

lunch, t h e 48.6 kHz (nominally 50 kHz) s i g n a l was t r a n s m i t t i n g

i n t o t h e n o r t h rope , wi th t h e n o r t h cage a t t h e zero l e v e l

(40 m below t h e s u r f a c e ) . Measurement r e s u l t s a t t h e 4050

l e v e l showed a 48.6 kHz s i g n a l s t r e n g t h of - 1 2 dB r e l a t i v e t o

1 uA/m f o r t h e s o u t h cage a t t h e bottom of t h e s h a f t (about 50 meters below t h e 4050 l e v e l ) , 0 dB r e 1 pA/m f o r t h e cage

a t t h e 4050 l e v e l , -16 dB r e 1 pA/m f o r t h e cage 6 meters

above t h e 4050 l e v e l , and -15 dB f o r t h e cage 4 0 meters above

t h e 4050 l e v e l . A p o s s i b l e exp l ana t i on f o r t h e s e r e s u l t s i s

t h a t t h e cage a c t s a s a moving t r an smi s s ion l i n e t e r m i n a t i o n .

When t h e cage i s a t t h e 4050 l e v e l , t h e antenna p i c k s up t h e

c u r r e n t i n t h e t e r m i n a t i o n .

F igures 3-26 and 3 - 2 7 show t h e n o i s e measured a t l o c a t i o n

B i n f i g u r e 3-19. The antenna was t hen 10 meters away from

t h e n o r t h s h a f t w i t h t h e s e n s i t i v e a x i s v e r t i c a l . A l a r g e

number of ha rmonica l ly r e l a t e d s p e c t r a l l i n e s can be seen

from 1 kHz t o 15 kHz on f i g u r e 3 -26 . These l i n e s a r e g e n e r a l l y

p r e s e n t on most s p e c t r a t aken whi le a t t h i s l e v e l . The l i n e s

a r i s i n g from t h e wa te r pump p r e v i o u s l y po in t ed ou t i n f i g u r e

3-24 appear he r e a l s o and a r e marked by ar rows. The n o i s e

a t 4 . 2 , 8 . 4 , 1 1 . 2 and 1 4 . 2 kHz a l s o appears on t h e s p e c t r a

t aken w i t h t h e antenna a x i s h o r i z o n t a l N-S. For t h e h o r i -

z o n t a l o r i e n t a t i o n , t h e n o i s e i s about t h e same a t t h e upper

t h r e e f r e q u e n c i e s mentioned, and i s a s much a s 1 2 dB lower

a t o t h e r f r e q u e n c i e s .

Three l a r g e f a n s , one 2 0 hp , and two 40 hp, 440 v o l t

t h r e e phase , were t u rned on and s p e c t r a were t aken . The

s p e c t r a a r e no t shown,as ve ry l i t t l e d i f f e r e n c e i n t h e mag-

n e t i c n o i s e was no t ed . The n o i s e a t 8 .6 kHz on f i g u r e 3-26

was 6 dB h i g h e r . These f a n s were a c o u s t i c a l l y ve ry n o i s y .

A f o u r t h 2 0 hp f an remained o p e r a t i n g a t a l l t imes a t a

l e v e l below 4050 ( p o s s i b l y account ing f o r some of t h e 8 .6 kHz

n o i s e i n f i g u r e 3 - 2 6 ) .

Measurements made a t 4050 w i th t h e cage ascending o r

descending showed a s e r i e s of weak impulses , p robab ly

o r i g i n a t i n g i n t h e h o i s t house. A t t h e 4050 l e v e l they were

n o t a s e r i o u s problem.

F i g u r e s 3-28 and 3 - 2 9 were t a k e n w i t h two r o t a r y b a t -

t e r y c h a r g e r s o p e r a t i n g , 4 me te r s d i s t a n t from an tenna l o c a -

t i o n B . One of t h e b a t t e r y c h a r g e r s was r e l a t i v e l y q u i e t , w h i l e

t h e o t h e r c o n t r i b u t e d a lmost a l l t h e n o i s e observed i n t h e

two s p e c t r a . Th i s b a t t e r y c h a r g e r was t h e n o i s i e s t p i e c e of

equipment encoun te red a t t h e 4050 l e v e l . F igure 3 - 2 9 shows

a f i n e s t r u c t u r e t o t h e n o i s e spect rum, w i t h l i n e s s e p a r a t e d

by about 28 H z .

The mine used 5 - t o n , 90 c e l l , b a t t e r y - o p e r a t e d e l e c t r i c

locomot ives . The b a t t e r y c h a r g e r s mentioned above were used

f o r r e c h a r g i n g t h e s e locomotive b a t t e r i e s . S p e c t r a t a k e n w i t h

t h e an tenna a t l o c a t i o n B whi le t h e locomotive was running

back and f o r t h a c r o s s t h e o r e dump produced no measurable

s p e c t r a l l i n e s . An impulse was r e c e i v e d every t ime t h e l o c o -

motive motor c o n t a c t o r engaged o r d i sengaged . I n an a t t empt

t o de termine t h e e f f e c t i v e n o i s e f i e l d n e a r a cap-mounted

r e c e i v e r worn by t h e locomotive o p e r a t o r , s p e c t r a were t a k e n

w i t h t h e an tenna around t h e o p e r a t o r , s e n s i t i v e a x i s v e r t i c a l ,

w h i l e t h e locomot ive was o p e r a t i n g . F igures 3-30 and 3-31

show t h e r e s u l t a n t s p e c t r a . F igure 3-30 looks l i k e n o i s e

r e c e i v e d from t h e h o i s t house. L i s t e n i n g t o t h e audio monitor

d u r i n g t h i s r e c o r d i n g r e v e a l s a low f requency , low ampl i tude

commutator b r u s h - n o i s e whenever t h e b a t t e r y was connected t o

t h e motor and t h e locomot ive was a c c e l e r a t i n g . Note t h e s t r e n g t h

o f t h e 48.6 kHz t e s t s i g n a l . F igure 3-31 shows an impulse

t h a t has been produced by t h e locomot ive . The impulse i s a s

much a s 30 dB above t h e s t e a d y mine power - l ine harmonics and

i s a t l e a s t 50 dB above background l e v e l s between 100 Hz and

1 0 0 0 H z .

A t t h e 4050 l e v e l , measurements were made c l o s e t o t h e

working f a c e a r e a , a t an a r e a known a s t h e "Y of 99 and 95Y."

Th i s l o c a t i o n was a hundred mete r s o r so from t h e s h a f t a r e a .

There was no mining a c t i v i t y i n p r o g r e s s (measurements

were made on S a t u r d a y ) . F igure 3-32 shows t h e spect rum ob-

t a i n e d w i t h t h e an tenna a x i s h o r i z o n t a l , p e r p e n d i c u l a r t o t h e

d r i f t , and t h e t r a c k s i n t h e d r i f t . The 4.2 and 8 . 4 kHz n o i s e ,

a s p r e v i o u s l y seen i n f i g u r e 3-26, appear c l e a r l y h e r e a l s o .

The spect rum taken w i t h t h e an tenna a x i s v e r t i c a l showed about

6 dB l e s s n o i s e t h a n f i g u r e 3 - 3 2 . For t h e an tenna a x i s h o r i -

z o n t a l and p a r a l l e l t o t h e t r a c k s , t h e n o i s e was below t h e

measurement sys tem n o i s e . F igure 3 - 3 3 shows t h e expanded

spect rum measured w i t h t h e an tenna a x i s v e r t i c a l . T r a n s i e n t s

were s t i l l i n evidence a t t h i s l o c a t i o n , p o s s i b l y from t h e

h o i s t .

A t t h i s l o c a t i o n n e a r t h e f a c e , i t was c l e a r t h a t t h e

s o u r c e o f n o i s e was p r i m a r i l y t h e two s t e e l r a i l s , and

s e c o n d a r i l y , any o t h e r meta l p i p e i n t h e d r i f t . To demon-

s t r a t e t h i s , a measurement was t a k e n w i t h t h e an tenna d i r e c t l y

a d j a c e n t t o one o f t h e r a i l s . F igures 3-34 and 3-35 show

t h e r e s u l t . Immediately a p p a r e n t on f i g u r e 3-34 i s t h e v e r y

s t r o n g 48.6 kHz t e s t s i g n a l i n s e r t e d on t h e n o r t h rope a t t h e

s u r f a c e w i t h a few w a t t s o f power.

3 .4 S p e c t r a Obta ined from Cage Runs, Loop Antenna

3 . 4 . 1 Mine Not i n Opera t ion

To measure t h e f i e l d s on t o p o f t h e cage a s i t t r a v e l e d

t h e e n t i r e l e n g t h of t h e s h a f t , a loop an tenna was s e c u r e d

t o t h e t o p of t h e cage , n e x t t o t h e s u p p o r t i n g h o i s t rope and

a s s o c i a t e d hardware. Because o f t h e p r o x i m i t y o f t h i s r o p e ,

l e v e l s o f f i e l d s measured a r e n o t a c c u r a t e f i e l d s t r e n g t h

v a l u e s , b u t due t o c l o s e c o u p l i n g between an tenna and h o i s t

rope , t h e v a l u e s do r e f l e c t (on a r e l a t i v e b a s i s ) c u r r e n t

l e v e l s i n t h e h o i s t rope .

On Sa turday , August 2 5 , 1973, t h e mine was no t i n opera -

t i o n . Figure 3-36 shows t h e no i se measured a t t h e zero l e v e l ,

and f i g u r e 3-37 shows t h e no i se measured a t t h e 4050 l e v e l .

The no i se l e v e l s shown a r e r e l a t i v e l y low, and c o n t a i n t h e

minor i n c r e a s e around 19 kHz which a s p rev ious ly no t ed , probably

comes from t h e h o i s t motor.

3 .4 .2 Mine i n Operation

On Monday, August 2 7 , 1973, when t h e mine was i n f u l l

o p e r a t i o n , t h e measurement of f i e l d s on top of t h e cage was

r epea t ed . Figure 3-38 shows t h e spectrum taken w i t h t h e cage

s t a t i o n a r y be fo re s t a r t i n g down. Figure 3-39 shows t h e spectrum

j u s t a f t e r s t a r t i n g down. Figure 3-40 shows t h e spectrum a t

about 4 7 0 meters of dep th . Figure 3-41 shows t h e spectrum

a t about 1080 meters o f dep th . Immediately apparent from t h e

l a s t f ou r f i g u r e s i s t h e presence of a severe no i se source

t h a t was n o t p r e s e n t on Saturday when t h e mine was no t ope ra t i ng .

This no i se i s from an unknown source and seemed t o i n c r e a s e

w i th dep th . Figure 3-41 i s t h e l a s t spectrum taken be fo re

t h e record ing equipment s a t u r a t e d . The s i g n a l monitors i n d i -

c a t e d t he no i se source was a t o r below t h e 4050 l e v e l . Labora-

t o r y r ep l ay of t h e analog record ings showed t h a t t h i s no i se

has t h e fol lowing c h a r a c t e r i s t i c s :

(1) The n o i s e i s made up of groups of about 4 t o 8

i n d i v i d u a l impulses.

(2) The groups of impulses occur 120 t imes pe r second.

(3) The impulses w i t h i n a group a r e no t time synchronized.

(4) A l t e r n a t i n g groups appear t o have some s i m i l a r i t y .

From t h e above c h a r a c t e r i s t i c s , we s p e c u l a t e t h a t t h i s n o i s e

source i s an a r c o f some s o r t and i s produced by 60 H z s i n g l e

phase , a c v o l t a g e .

On a second v i s i t t o t h i s mine on February 8 , 1974, t h i s

same t y p e o f n o i s e was r e c e i v e d . Gains were s e t low enough

t h a t s a t u r a t i o n of t h e measurement sys tem was avo ided . The

s p e c t r a a r e s i m i l a r i n shape , and i n t h e f o l l o w i n g f i g u r e s ,

a b s o l u t e l e v e l s can be de te rmined . This unknown s o u r c e c a u s e s

n o i s e many o r d e r s o f magnitude s t r o n g e r t h a n any o t h e r s o u r c e

o f i n t e r f e r e n c e i n t h i s mine. I t i s n o t a t r a n s i e n t , b u t

l a s t s seconds o r m i n u t e s , and hence must be c o n s i d e r e d a s

i n t e r m i t t e n t . S p e c t r a a r e shown i n f i g u r e 3-42 a s r ecorded

from a loop an tenna on t o p of a h o i s t c a g e . Another spect rum

o f t h e same n o i s e from t h e o u t p u t of a f e r r i t e loop around

t h e h o i s t rope i n t o a 50-ohm l o a d i s shown i n f i g u r e 3-43.

The s p e c t r a l d i s t r i b u t i o n v a r i e s w i t h t ime a s i s shown by

comparing f i g u r e 3-44 w i t h 3-42.

T h i s s o u r c e r a i s e s t h e n o i s e l e v e l a t l e a s t 40 t o 60 dB

above background n o i s e a s shown i n f i g u r e 3-45 o v e r a wide

f requency range (50-100 kHz); f i g u r e 3-46 shows t h i s n o i s e

s i g n a l t o be above sys tem n o i s e from 10 kHz t o 200 kHz.

T r a n s i e n t e v e n t s such a s shown i n f i g u r e s 3 -47 , 3-48, and

3-49 a r e a l s o p r e s e n t , b u t o n l y f o r r e l a t i v e l y s h o r t dura -

t i o n s o f t i m e . F igure 3-50 shows a 20 kHz spect rum; i t may

i n d i c a t e a ground s t a t i o n a t 1 8 . 6 kHz, b u t a t t h e 1800 f o o t

l e v e l , t h i s i s d o u b t f u l .

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3

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pe

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3

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of

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a d 0 2 q c f cd "

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cd &I " O h

- 2 g - ?;;; - : u , i

4 . AMPLITUDE PROBABILITY DISTRIBUTION MEASUREMENTS

4 . 1 I n t r o d u c t i o n and U n c e r t a i n t i e s

The ampl i tude p r o b a b i l i t y d i s t r i b u t i o n (APD) of t h e r e -

c e i v e d n o i s e s i g n a l magnitude i s one of t h e most u s e f u l

s t a t i s t i c a l d e s c r i p t i o n s of t h e n o i s e p r o c e s s f o r t h e d e s i g n

and e v a l u a t i o n of a te lecommunicat ions system o p e r a t i n g i n a

n o i s y environment [ 5 , 6 , 7 ] .

By p l o t t i n g t h e cumula t ive APD on Rayle igh graph p a p e r ,

one can show c l e a r l y t h e f r a c t i o n of t ime t h a t n o i s e exceeds

v a r i o u s l e v e l s . Rayleigh graph paper i s chosen w i t h s c a l e s

so t h a t Gaussian n o i s e ( e . g . , thermal n o i s e ) p l o t s a s a

s t r a i g h t l i n e w i t h s l o p e of - 1 / 2 . Noise w i t h r a p i d l a r g e

changes i n ampl i tude ( e . g . , impuls ive n o i s e ) t h e n has a

much s t e e p e r s l o p e , t y p i c a l l y -4 o r - 5 , depending on t h e

r e c e i v e r bandwidth.

A l l APD measurements a r e r e p o r t e d i n a b s o l u t e q u a n t i t i e s .

The e s t i m a t e d l i m i t s of e r r o r f o r t h e APD n o i s e measure-

ments a r e + 5 dB. S e v e r a l s o u r c e s o f e r r o r t h a t a r e c r i t i c a l

t o t h e o v e r a l l accuracy of our measurements a r e l i s t e d below:

1. Use of a d i s c r e t e , d i g i t a l l e v e l c o u n t e r ( l e v e l s a r e

6 dB a p a r t ) c o n t r i b u t e s . + 1-dB q u a n t i z a t i o n e r r o r l i m i t .

One-decibel s t e p a t t e n u a t o r s a r e used t o ach ieve t h e

5 one d e c i b e l .

2 . The sys tem, i . e . , r e c o r d i n g , d a t a t r a n s c r i b i n g , and

d a t a p r o c e s s i n g , has a c a l i b r a t i o n u n c e r t a i n t y o f

+ 0 . 5 dB [ 3 ] .

3 . The e s t i m a t e d u n c e r t a i n t y invo lved i n u s i n g t h e p o r -

t a b l e and t h e l a b o r a t o r y t a p e r e c o r d e r s f o r r e c o r d and

p layback i s + 0 . 5 dB due t o harmonic d i s t o r t i o n , f l u t t e r ,

d r o p o u t , c r o s s - t a l k , g a i n i n s t a b i l i t y , e t c .

4 . The g a i n i n s t a b i l i t y d u r i n g measurements, g a i n

changes between measurements and c a l i b r a t i o n , and t h e

n o n - l i n e a r i t y o f e l e c t r o m a g n e t i c i n t e r f e r e n c e and f i e l d

s t r e n g t h (EIFS) mete r s and m i x e r s , a l l combined, con-

t r i b u t e + 0.5 dB u n c e r t a i n t y .

5 . The g a i n i n s t a b i l i t y and n o n - l i n e a r i t y o f t h e d i g i t a l

l e v e l c o u n t e r , t h e tuned f requency c o n v e r t e r , t h e ampl i -

f i e r , and a t t e n u a t o r s , a l l combined, c o n t r i b u t e f 0 .5 dB

u n c e r t a i n t y .

6 . Connector l o s s e s and BNC c a b l e l o s s e s , p a r t i c u l a r l y

a t h i g h e r f r e q u e n c i e s above 100 kHz, c o n t r i b u t e + 2.0 dB

u n c e r t a i n t y .

4 .2 R e s u l t s

APD measurements were made on August 2 7 , 1973, and on

February 8 , 1974, d u r i n g o p e r a t i o n i n t h e Lucky Fr iday Mine

l o c a t e d n e a r Wallace, Idaho. D e s c r i p t i o n s o f t h e Lucky

F r i d a y Mine a r e g iven i n s e c t i o n 1 . 2 . APD measurements were

made a t f o u r l o c a t i o n s . The f i r s t s e t of APD measurements a t

f o u r f r e q u e n c i e s was made on August 2 7 a t t h e head-frame on

t h e s u r f a c e . A P D ' s a r e shown i n f i g u r e s 4-1 through 4-9 f o r

two antenna o r i e n t a t i o n s . The second s e t of APD measurements

a t f o u r f r e q u e n c i e s was made on August 2 7 , 1973, a t t h e 1450

f o o t (427 m) l e v e l . These APD's a r e shown i n f i g u r e s 4-9

through 4 - 1 6 . The t h i r d s e t o f APD measurements a t t h r e e

f r e q u e n c i e s was made on August 2 7 , 1973, a t t h e 3050 f o o t

(930 m) l e v e l . A P D ' s a r e shown i n f i g u r e s 4-17 th rough 4-22.

I n t h e s e s e t s o f APD measurements, bo th t h e v e r t i c a l and

h o r i z o n t a l components of magnet ic f i e l d were measured. The

f o u r t h s e t o f APD measurements a t t h r e e f r e q u e n c i e s was made

on February 8 , 1974, a t t h e 3650 f o o t (1113 m) l e v e l , d u r i n g

o p e r a t i o n . The 3650 l e v e l was a working l e v e l w i t h l i g h t

a c t i v i t y . A P D ' s a r e shown i n f i g u r e s 4-23 through 4-28.

In a l l c a se s except f o r t h e 3650 working l e v e l , t h e

h o r i z o n t a l component i s about 1 0 dB s t r o n g e r than t h e v e r t i c a l

component. This i s probably because t h e h o r i z o n t a l o r i e n t a t i o n

of t h e antenna coupled more s t r o n g l y t o t h e nearby h o i s t ropes

( t h e apparent source o f n o i s e ) than d i d t h e v e r t i c a l o r i e n t a -

t i o n . A t t h e working l e v e l , t h e s t r o n g e s t no i se source was

n o t t h e h o i s t ropes bu t was machinery a t t h e l e v e l . Somewhat

h ighe r l e v e l s were a l s o measured a t t h e 3650 l e v e l than a t

o t h e r l e v e l s . Whether t he 2 0 minute time i n t e r v a l f o r each

record ing was s u f f i c i e n t f o r s t a t i s t i c a l v a l i d i t y needs t o be

determined from f u r t h e r a n a l y s i s .

Also, a t t he 3650 l e v e l , t h e no i se ampli tude tended t o

i n c r e a s e wi th i n c r e a s i n g f requency, whi le a t a l l o t h e r l o c a -

t i o n s a t t h i s mine, it tended t o decrease wi th i n c r e a s i n g

f requency.

4 .3 RMS and Average Values

The APD's a r e i n t e g r a t e d t o give rms and average va lues

of t h e f i e l d s t r e n g t h , according t o t h e equa t ions

II = - I H dp (H) avg 0

and

where H r e p r e s e n t s t h e magnetic f i e l d s t r e n g t h of t h e n o i s e ,

and p i s t h e p r o b a b i l i t y t h a t t h e measured f i e l d s t r e n g t h

exceeds t h e va lue H. These q u a n t i t i e s a r e a l s o dependent

upon t h e measurement bandwidth, t h e l e n g t h of t h e d a t a run ,

and p o s s i b l y o t h e r paramete rs . f i n i t e s e r i e s a r e us-pr

t h e numerical i n t e g r a t i o n . The rms and average va lues so

a r r i v e d a t a r e i d e n t i f i e d on each graph and a r e t ime averages

(23 minutes) of t he se t ime-dependent paramete rs . I f t h e

t apes a r e played i n t o o rd ina ry rms-reading me te r s , t h e meter

read ings w i l l vary 1 0 t o 20 dB over f r a c t i o n s of a second.

The r m s va lue i s d i r e c t l y r e l a t a b l e t o no i se power. With

t h e s e wide v a r i a t i o n s of f i e l d s t r e n g t h w i th t ime, t h e most

s u i t a b l e p r e s e n t a t i o n s a r e s t a t i s t i c a l ones .

4 . 4 Summary Curves

Excursions of f i e l d s t r e n g t h between 0 . 0 0 1 and 99 p e r c e n t ,

a s we l l a s r m s and average v a l u e s , a r e shown i n f i g u r e s 4-29

through 4-36. The p r e d e t e c t i o n bandwidth f o r t h e s e APD

measurements i s e i t h e r 1 kHz o r i s normalized t o 1 kHz.

Figure 4-29 i s a summary of t h e f i g u r e s 4 -1 through 4 -4 ,

a t t h e headframe, t h e h o r i z o n t a l (N-S) component. Figure 4-30

i s a summary of f i g u r e s 4-5 through 4-8, a t t h e headframe,

v e r t i c a l component. Figure 4-31 i s a summary of f i g u r e s 4-9

through 4-12, a t t h e 1450-foot l e v e l , v e r t i c a l component.

Figure 4-32 i s a summary of f i g u r e s 4-13 through 4-16, a t t h e

1450-foot l e v e l , h o r i z o n t a l (N-S) component. Figure 4-33 i s

a summary of f i g u r e s 4-17 through 4-19 , a t t h e 3050-foot

l e v e l , h o r i z o n t a l (N-S) component. Figure 4-34 i s a summary

o f f i g u r e s 4-28 through 4 - 2 2 , a t t h e 3050-foot l e v e l , v e r -

t i c a l component. Figure 4-35 i s a summary of f i g u r e s 4-23

through 4-25 , a t t he 3650-foot l e v e l , h o r i z o n t a l (N-S) compo-

n e n t . Figure 4-36 i s a summary of f i g u r e s 4-26 through 4-28,

a t t h e 3659-foot l e v e l , v e r t i c a l component.

F i g u r e 4 -1 APD, Magnetic f ie ld s t rength , 3 0 kHz, Horizontal (North-South) component, Headframe, Lucky F r iday Mine, 1 kHz predetect ion bandwidth. T ime w a s 11:OO a. m . , August 27, 1973.

Ma

gn

eti

c F

ield

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tre

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th ,

H (

dB

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eter

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urn

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5 a

Fr

: Ox

x +

- :

+

g.

a ,,

0

oa

z

PI

P*

K

Percent of Time Ordinate is Exceeded

Figure 4-4 APD, Magnetic f ie ld s t rength , 250 kHz, Horizontal (North- South) component, Headframe, Lucky F r iday M 1. 2 M e predetect ion bandwidth. T ime was 1 1 :00 a. m August 27, 1973

Figure 4 -5 APD, Magnetic field s t rength , 3 0 kHz, Vert ica l component , Headf rame , Lucky F r i d a y Mine. 1 kHz prede tec- t ion bandwidth. T ime was 10:30 a. m . , August 2 7 , 1973.

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


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 T ime Ordinate is Exceeded

Figure 4-7 APD, Magnetic field s t rength , 150 kHz, Vert ica l component, Headf rame , Lucky F r iday Mine, 1.2 kHz prede tec- t ion bandwidth. T ime was 10:30 a. m . , August 27, 1973.


Figure 4-8 APD, Magnetic field s trength, 250 M e , Vert ica l component, Headframe, Lucky F r iday Mine, 1 .2 kHz predetec- t ion bandwidth. T ime was 10:3 0 a. m. , August 27, 1973.

Percent of Time Ordinate is Exceeded Figure 4-9 APD, Magnetic field s t rength, 30 kHz, Vert ica l compo-

nent, 1450 level , Lucky F r iday Mine, 1 kHz prede tec- t ion bandwidth. Time was 1:00 p.m., August 27, 1973.

Percent of Time Ordinate is Exceeded Figure 4-10 APD, Magnetic field s t rength, 70 kHz, Vert ica l corn

nent , 1450 level , Lucky F r iday Mine, 1 kHz predetec - t ion bandwidth. T ime was 1:00 p . m . , August 2 7 , 1973

Percent of Ti me Ord i na te is Exceeded

Figure 4- 11 APD, Magnetic field s t rength, 150 kHz, Vert ica l compo-- nent, 1450 level , Lucky F r iday Mine, 1 .2 kHz predetec- t ion bandwidth. T ime was 1 :00 p. m. , August 27, 1973.


Figure 4- 12 APD, Magnetic field s trength, 250 kHz, Vert ical component, 1450 level , Lucky F r iday Mine, 1.2 W z predetec- t ion bandwidth. Time was 1 :00 p. m. , August 27, 1973.


Figure 4-13 APD, Magnetic field strength, 30 kHz, Horizontal (North-South) component, 1450 level, Lucky Fr iday Mine, 1 kHz predetection bandwidth. Time was 1 :30 p. m. , August 27, 1973.

Linear by -+ log,,(-lnp)

.0~01.001.01 .1 .5 1 5 10 20 30 40 50 60 70 80 85 90 95 98 99


Figure 4- 14 APD, Magnetic field strength, 70 kHz, Horizontal (North-South) component, 1450 level, Lucky Friday Min 1 H z predetection bandwidth. Time was 1 :3 0 p. m., August 27, 1974.

9 1


Figure 4-15 APD, Magnetic f ie ld s t rength, 150 kHz , Horizontal (North -South) component, 1450 level , Lucky F r iday Mine, 1. 2 kHz predetect ion bandwidth. T ime was 1 :3 0 p. m. ,

August 27 , 1973.


Figure 4-16 APD, Magnetic field s trength, 250 kHz, Horizontal (North-South) component, 1450 level, Lucky Fr iday Mine, 1 . 2 kHz predetection bandwidth. Time was 1 :3 0 p . m. , August 27 , 1973.

93


Figure 4-17 APD, Magnetic field s t rength, 3 0 kHz, Horizontal (North-South) component, 3 050 level , Lucky Fr iday Mine, 1 kHz predetect ion bandwidth. T ime was 3 :00 p. m. , August 27 , 1973.

Linear by - log,,(-In p)


Figure 4-18 APD, Magnetic field s t rength , 70 kHz, Horizontal (North-South) component, 3 050 leve l , Lucky F r iday Mine, 1 kHz predetect ion bandwidth. T ime was 3:00 p . m . , August 27 , 1973.


Figure 4-19 APD, Magnetic field s t rength , 150 kHz, Horizontal (North-South) component, 3050 level , Lucky F r iday Mine, 1. 2 kHz predetect ion bandwidth. T ime was 3 :00 p. m. , August 27, 1973.


Figure 4-20 APD, Magnetic field s t rength, 30 kHz, Vert ica l component, 3050 level , Lucky F r iday Mine, 1 kHz predetec - t ion bandwidth. T ime was 2:30 p. m . , August 27, 1973.


Figure 4 -21 APD, Magnetic field s t rength, 70 kHz, Vert ica l component, 3050 level , Lucky F r iday Mine, 1 kHz prede tec- t ion bandwidth. T ime was 2:30 p. m . , August 27, 1973.


Figure 4 -22 APD, Magnetic field s t rength, 150 kHz, Vert ica l component, 3050 level , Lucky F r iday Mine, 1 . 2 kHz p r e - detect ion bandwidth. T ime was 2:30 p. m. , August 27, 1973.

Percent of Time Ordinate is Exceeded Figure 4-23 APD, Magnetic field s t rength , 35 kHz, Horizontal

(North-South) component, 3 650 level , Lucky F r iday Mine, 1 kHz predetect ion bandwidth. T ime was 10:OO a . m . , F e b r u a r y 8, 1974.

100

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

k r c e n t 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.


Figure 4-26 APD, Magnetic field strength, 35 kHz, Vert ical component, 3650 level, Lucky Fr iday Mine, 1 kHz predetection bandwidth. Time was 10:30 a. m., February 8, 1974.


Figure 4-27 APD, Magnetic field s t rength, 75 kHz, Vert ica l component, 3650 level , Lucky F r iday Mine, 1 kHz predetect ion bandwidth. Time was 10:30 a. m . , F e b r u a r y 8, 1974.


Figure 4 - 2 8 APD, Magnetic field strength. 200 kHz. Vert ical component, 3650 level, Lucky Fr iday 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

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5. NOISE AND ATTENUATION MEASUREMENTS ALONG THE HOIST ROPE

5 .1 Noise Measurements

Measurements were made on two d i f f e r e n t d a y s . On one day

t h e mine was i n o p e r a t i o n ; on t h e o t h e r day it was n o t . On

t h e day t h e mine was i n o p e r a t i o n , measurements were made

w h i l e t h e cage was i n mot ion ; when t h e mine was n o t i n o p e r a -

t i o n , measurements were made w i t h t h e cage s t o p p e d a t a number

o f l e v e l s . The cage was s h o r t e d t o wa te r p i p e s , and bo th

"open" and " s h o r t " measurements were made. A t 35 kHz, t h e

r e a d i n g s were r a t h e r e r r a t i c , i n d i c a t i n g e i t h e r s u b s t a n t i a l

v a r i a t i o n s w i t h t i m e , o r nea rby s o u r c e s . The 50 kHz d a t a

showed s t a n d i n g wave p a t t e r n s s i m i l a r t o t h o s e o b t a i n e d i n

t h e a t t e n u a t i o n measurements .

Values a r e i n dB w i t h r e s p e c t t o one m i c r o v o l t a c r o s s

50 ohms; t h e u n c e r t a i n t y i s e s t i m a t e d a s + 5 dB. The a i r -

c o r e loop v a l u e s c o u l d be c a l i b r a t e d i n t e rms o f microamperes

p e r m e t e r , b u t t h e f i e l d s t r e n g t h i s r e a l l y c o n t r o l l e d by t h e

c u r r e n t i n t h e h o i s t rope ( a l t h o u g h c o u p l i n g i s n o t a s t i g h t

a s w i t h t h e f e r r i t e c o r e ) , s o o n l y v o l t a g e u n i t s w i l l be g i v e n .

The n o i s e d a t a f o r t h e t ime when t h e mine was n o t o p e r a t -

i n g a r e shown i n f i g u r e s 5 - 1 , 5 - 2 , 5 - 3 , and 5 - 4 ; d a t a t a k e n

when t h e mine was i n o p e r a t i o n a r e shown i n f i g u r e s 5 - 5 , 5 - 6 ,

5 - 7 , and 5 - 8 . Noise i s somewhat h i g h e r d u r i n g o p e r a t i o n , b u t

t h e v a r i a t i o n s i n d i c a t e t h e b a s i c problem w i t h t h i s t y p e o f

measurement - - t h e cw measurement sys tem i s r e spond ing t o t h e

t ime v a r i a t i o n s , b u t i n a way t h a t masks t h e s t a t i s t i c a l r ange

o f v a l u e s caused by t r a n s i e n t s and i n t e r m i t t e n t s . The APD

s e c t i o n g i v e s d a t a a t some l e v e l s , bu t APD's were n o t r e c o r d e d

on t h e h o i s t .

5.2 A t t e n u a t i o n Measurements

D i s c r e t e - f r e q u e n c y s i g n a l s were i n j e c t e d a t t h e headframe,

and s i g n a l s t r e n g t h measurements were made of t h e c u r r e n t a t

t h e cage a t a number of l e v e l s . The p l o t s show s t a n d i n g wave

p a t t e r n s . E i t h e r t h e s h o r t h a s some i n d u c t a n c e , o r t h e open

h a s some c a p a c i t a n c e , o r b o t h , a s t h e e q u a l - a m p l i t u d e mark i s

a t abou t 3600 f e e t (- 1100 m e t e r s ) f o r 50 kHz, and i f t h e r e

were no s t r a y e f f e c t s , t h e e q u a l a m p l i t u d e ( 2 X/8) p o i n t

s h o u l d be a t a b o u t 2500 f e e t (750 m e t e r s ) .

A c t u a l a t t e n u a t i o n i s r e l a t i v e l y low, o n l y a few dB o v e r

t h e 4000 f o o t (1200 m e t e r ) l e n g t h o f c a b l e . The s t a n d i n g

waves due t o an u n t e r m i n a t e d t r a n s m i s s i o n l i n e a r e c l e a r l y a

more s e r i o u s problem. Up t o 20 dB v a r i a t i o n may be e x p e c t e d

from maxima t o minima.

The s i g n a l - t o - n o i s e r a t i o l o o k s v e r y e n c o u r a g i n g , u n l e s s

t h e i n t e r m i t t e n t n o i s e from t h e s t r o n g unknown s o u r c e ( p l u s

60 dB n o i s e ) combines w i t h a minimum i n a s t a n d i n g wave p a t -

t e r n (minus 20 dB s i g n a l ) . Even t h i s w o r s t c a s e may be h a n d l e d ,

b u t t h e margin i s s i g n i f i c a n t l y r e d u c e d , e s p e c i a l l y n e a r t h e

working l e v e l s when t h e mine i s i n o p e r a t i o n and where n o i s e

l e v e l s a r e h i g h e s t .

Fig

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6 . CONCLUSIONS

The e l e c t r o m a g n e t i c i n t e r f e r e n c e i n Lucky F r i d a y Mine i s

somewhat lower t h a n many o t h e r m i n e s , most o f t h e t i m e . How-

e v e r , t h e r e i s some unknown s o u r c e o f n o i s e t h a t i s p r e s e n t

on a n i n t e r m i t t e n t b a s i s , and d u r i n g t h e s e t i m e s , t h e spec t rum

from 10 kHz t o 200 kHz i s s u b j e c t t o l e v e l s 60 dB above

ambient from 50 t o 100 kHz. T h i s n o i s e may l a s t seconds o r

even m i n u t e s ; i t i s n o t s i m i l a r i n n a t u r e t o n o i s e from v e r y

s h o r t - d u r a t i o n t r a n s i e n t s .

Noise n e a r neon l i g h t s such a s a r e common i n c i t i e s c a u s e

c o n s i d e r a b l y h i g h e r p o w e r - l i n e harmonics t h a n occur i n most

r u r a l a r e a s . We have now o b t a i n e d a b s o l u t e d a t a on t h i s t y p e

o f n o i s e .

Un te rmina ted t r a n s m i s s i o n l i n e s formed by h o i s t ropes

g i v e s t r o n g s t a n d i n g waves.

7 . RECOMMENDAT IONS

E f f o r t s h o u l d be made t o d e t e r m i n e t h e s o u r c e o f t h e

h i g h - l e v e l n o i s e . On h o i s t phones , s t a n d i n g wave v a r i a t i o n s

must be t a k e n i n t o account i n d e s i g n s .

8 . ACKNOWLEDGMENTS

Those making s i g n i f i c a n t c o n t r i b u t i o n s t o t h i s program

a r e a s f o l l o w s : l a b o r a t o r y development and f i e l d u s e o f meas-

urement equipment , Ed Ne i sen , Doug S c h u l z e , and Tom Bremer;

d a t a p r o c e s s i n g , Anne Rumfe l t , Nancy Tomoeda, Frank Cowley, and

David S t e a r n s . Those making v a l u a b l e b u t l e s s t ime-consuming

c o n t r i b u t i o n s a r e Gerry Reeve, Bob Matheson, Don S p a u l d i n g ,

John Chukoski , Lorne Matheson, Dave Lewis, and Sharon Foo te .

Sharon Foote and J a n e t J a s a t y p e d t i r e l e s s l y th rough

many v e r s i o n s . J o c e l y n Spence r and Barba ra Bo l ton p rov ided

d r a f t i n g a s s i s t a n c e .

F i n a l l y , none o f t h i s would have been p o s s i b l e w i t h o u t

e x c e l l e n t c o o p e r a t i o n from v a r i o u s p e o p l e i n t h e Hecla Mining

Company. For a r r angement s we thank Wallace C r a n d a l l , George

Wilhelm, and A r t Brown; f o r much s p e c i a l a s s i s t a n c e we thank

Don Beck. 126

9 . REFERENCES

[ l ] Bensema, W . D . , Kanda, M . , Adams, J . W . , E l e c t r o m a g n e t i c

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

( A p r i l 1 9 7 4 ) .

[ 2 ] I E E E D i c t i o n a r y o f E l e c t r i c a l and E l e c t r o n i c Terms,

The I n s t i t u t e o f E l e c t r i c a l and E l e c t r o n i c E n g i n e e r s ,

I n c . , S t d . 100 (1972) .

[ 3 ] T a g g a r t , H . E . and Workman, J . L . , C a l i b r a t i o n P r i n c i p l e s

and P rocedures f o r F i e l d S t r e n g t h Mete r s (30 H z t o 1 GHz),

NBS Tech. Note 370 (March 1 9 6 9 ) .

[ 4 ] Adams, J . W . , Bensema, W . D . , Kanda, M . , E l e c t r o m a g n e t i c

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

1 9 7 4 ) .

[5] Cr i ch low, W . Q . , e t a l . , A m p l i t u d e - P r o b a b i l i t y D i s t r i b u -

t i o n s f o r Atmospheric Radio N o i s e , NBS Monograph 23

(1960b) .

[ 6 ] Thompsom, W . I . , 111, B i b l i o g r a p h y o f Ground V e h i c l e Com-

m u n i c a t i o n s and C o n t r o l , AKWIC i n d e x , Repor t No. DOT-

TSC-UMTA-71-3 ( J u l y 1 9 7 1 ) .

[ 7 ] S p a u l d i n g , A . D . and Di sney , R . T . , Man-Made Radio No i se .

P a r t 1: E s t i m a t e s f o r B u s i n e s s , R e s i d e n t i a l , and Rura l

A r e a s , OT Repor t 74-38 ( June 1 9 7 4 ) .

1 0 . APPENDIX

Decoding of Spectrum Captions

Spectrum c a p t i o n s a r e g e n e r a l l y organized i n t o t h e f o l -

lowing format :

F i r s t l i n e : MP NDT NZS NDA NPO RC DF d a t e , t ime , frame, s e r i a l ,

where

MP = Two's power of l e n g t h of Four ie r t rans form, example,

zMP where MP = 1 2

NDT = Detrending o p t i o n , example, 0 (dc removed)

NZS = R e s t a r t s p e c t r a l average a f t e r o u t p u t , example, 0

( r e s t a r t e d )

NDA = Data segment advance increment , example, 2048

NPO = Number of s p e c t r a averaged between ou tpu t c a l l s ,

example, 20

RC = I n t e g r a t i o n time i n seconds per s p e c t r a , example, 0.168

DF = Resolu t ion bandwidth, s p e c t r a l e s t ima te spacing i n

h e r t z , example, 62.5

Date = Date of computer p roces s ing , example, 03/21/73

Time = Time of computer p roces s ing , example, 15:06:34

Frame= Frame s e t number, example, 1 0

Ser ia l ' = F i l m frame s e r i a l number, example, 4 2 .

Second l i n e : DTA DA(1) DA(2) DA(3) NSA NRP NPP, where

DTA = Detrending f i l t e r parameter a , example, 0.00195

DA(1) = Detrending f i l t e r average , K = l , example, 59.4

DA(2) = Detrending f i l t e r average, K = 2 , example, 0

DA(3) = Detrending f i l t e r average, K=3, example, 0

NSA = Number of periodograms averaged, example, 20

NRP = Number of d a t a p o i n t s processed s i n c e spectrum

i n i t i a l i z a t i o n , example, 43008

NPP = Number of d a t a p o i n t s processed s i n c e d a t a i n i t i a l -

i z a t i o n , example, 43008.

T h i r d l i n e : R U N , SESSION, MONTH, DAY, YEAR Gain c o r r . , r e c . = I t o t . cons t r . = , where

Run and S e s s i o n = t h e t i t l e o f t h e p o r t r a y e d f rame i d e n t i f y i n g 1 t h e d i g i t i z i n g s e s s i o n and run number, I e xample , 2 1 8 3

Month, Day, Year = d a t e d a t a were r e c o r d e d i n t h e m i n e ,

example , 8 25 73

Gain c o r r . r e c . = r e c e i v e r g a i n c o r r e c t i o n , example , -6

t o t . c o n s t . = c o n s t a n t g a i n c o r r e c t i o n o f e n t i r e s y s t e m ,

example , 46.4

C = c o r r e c t i o n c u r v e u s e d w i t h d a t a , example , 25

R G = r e c e i v e r g a i n and accompanying c o r r e c t i o n i n dB added t o I t h e d a t a , example , 200 ( - 6 dB)

D G = d i g i t i z e r g a i n , example , 0

FG = f i l t e r g a i n i n dB, o f t e n rounded t o n e a r e s t s i n g l e d i g i t ,

e x a m p l e , 0

AG = a b s o l u t e g a i n c o r r e c t i o n added t o d a t a , example , 52

F i f t h l i n e : Top o f S c a l e , S t a n d a r d E r r o r , S p e c t r a l Peak , where.

Top o f S c a l e = l a r g e s t s c a l e mark ing f o r computer drawn 1 g r a p h , example , 1 .000+004 ( 1 . 0 x l o 4 ) I

S t a n d a r d E r r o r = s t a n d a r d e r r o r o f c u r v e , e x a m p l e , 0 .3162 1 S p e c t r a l Peak = l a r g e s t s p e c t r a l peak o b s e r v e d , example , 1

Elec t romagne t i c Noise i n Lucky F r iday Mine

U.S . DEPT. O F COMM.

BIBLIOGRAPHIC DATA SHEET

I - 7. AU'I IIOR(S) 18. P e r f o r m ~ n n Organ. Report No.

1. I'III3I.I(.Al'ION OR I<I~I'OK1' NO.

NBSIR 74-391

NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE WASHINGTON, D.C. 20234

4. 7'1'I'l.I< ANIj 511 111'11'1.1:

W . W . S c o t t , J . W . Adams, W.D. Bensema, H . Dobroski 9. I'I<I<1;ORMIN(; 0KC;ANIZATION NAME AND ADDRESS

11. Contract /Grant No. r

5. Pub l i ca t ion Date

2. C;ov't Acc-chsion No.

.. .

10. Pro-ect /Task/Work Unit No. i768412

3. Rec ip ien t ' s Access ion No.

I

16. Al{Sl'KA(''l' (A 200-word o r l e s s f ac tua l summary of mos t s ign i f i can t information. If document i nc ludes a s ign i f i can t bibliography o r l i tera tur? su rvey , mention i t here . )

Measurements of t h e a b s o l u t e v a l u e of e l e c t r o m a g n e t i c n o i s e and a t - t e n u a t i o n a long a h o i s t rope were made i n an o p e r a t i n g h a r d - r o c k mine, Lucky F r i d a y Mine, l o c a t e d nea r Wal lace , Idaho. S p e c t r a o f e l ec t romag- n e t i c n o i s e gene ra t ed by v a r i o u s p i e c e s o f equipment , s p e c t r a of s p e c i f i c n o i s e s i g n a l s a t v a r i o u s d e p t h s , and n o i s e and a t t e n u a t i o n on t h e 4250 f o o t (1295 mete r ) h o i s t , were measured. Three t e c h n i q u e s were used t o make t h e measurements. F i r s t , n o i s e was measured ove r t h e e n t i r e e l e c t r o magne t ic spec t rum o f i n t e r e s t f o r b r i e f t ime p e r i o d s . Data were r e - corded u s i n g broadband ana log magnet ic t a p e f o r l a t e r t r a n s f o r m a t i o n t o s p e c t r a l p l o t s . Second, n o i s e amp l i t udes were r eco rded a t s e v e r a l d i s - c r e t e f r e q u e n c i e s f o r a s u f f i c i e n t amount of t ime t o p rov ide d a t a f o r amp l i t ude p r o b a b i l i t y d i s t r i b u t i o n s . A t h i r d t e chn ique gave a t t e n u a t i o n d a t a t h rough t h e d i r e c t measurement of f i e l d s t r e n g t h a t v a r i o u s d e p t h s .

The s p e c i f i c measured r e s u l t s a r e g iven i n a number of s p e c t r a l p l o t s , amp l i t ude p r o b a b i l i t y d i s t r i b u t i o n p l o t s and ampl i tude cu rves a s a f u n c t i o n o f d e p t h .

12. S onsor ing Orgilnizat ' n Nsmc and C:onipletr Address (Street, Ci ty , S t a t e , ZIP)

P i t t s b u r g h Mining and S a f e t y Research Cente r 4800 Forbes Avenue P i t t s b u r g h , Pennsy lvan ia 15213

13. Type of Report & Period

14. Sponsor ing Agency Code

ins t rumenta t ion; mine no i se ; s p e c t r a l dens i ty : time - de 18. A\'AII.AI~II.I'I'Y t-- rx l inlimited

1 . 8. Bureau OF Mlnes Covered

17. RllY U'0KI)S (six to twc lve en t r i e s ; a lphabe t i ca l order; c a p i t a l i z e on ly Ule f i rs t l e t t e r of t h e f i r s t k e y word u n l e s s a proper rleme; s e p a r a t e d by s e m i c o l o n s ) Amplitude p r o b a b i l i t y d i s t r i b u t i o n ; d i g i t a l d a t a , electromag-

2 e t i c i n t e r f e r e n c e ; e lec t romagnet ic n o i s e ; emergency communications; Fas t Four ier Transform; Gaussiam d i s t r i b u t i o n ; impulsive noise ; magnetic f i e l d s t r e n g t h ; measurement

[ , - 1-or Official 1)isrribution. I)o Not K e l e a s c to N'I'IS UNCL ASSIF I E D

[ Orclrr I;rclnl Sup. <>i l)uc., U.S. Governmenr l'rinting Off ice U ' J S ~ I I I ~ I ~ I ~ , I) . ( : . 2U iU2, 511 Ca t . No. (:I3 ( T H I S P A G E )

+,, .

i : Order I:rvm Nat ional T e c h n i c a l Informnrion Se rv ice (NI'IS) Spr ingi ic ld , V i r g ~ n ~ a 2 2 1 5 1 UNCI.ASSIFIE1)

, . , USCOMM-DC 29042 -P74

Electromagnetic Noise in Lucky Friday Mine · 100 kHz and 75 kHz-----.--- 123 Figure 5-9. Received signal at cage from 35 kHz source at headframe----- 124 Figure 5-10. Received signal

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