ELECTROMAGNETIC PROPAGATION IN 

LOW COAL MINES AT 

MEDIUM FREQUENCIES 

Prepared for 

UNITED STATES DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

Collins Communications Switching Systems Division 

Commercial Telecommunications Grou~ 

Cedar Rapids, Iowa 52406 

Rockwell International 

FINAL REPORT 

Contract No. H0377053 12 JUNE 1978 
REPORT DOCUMENTATION PAGE, 

1 3. Recipient's Accession No. I 

I 

4. T~lt and Subtitle 

Electromagnetic Propagation in Low Coal 

Mines at Medium Frequencies 

7. Aulhor(9) 

Terry S. Cory 

Department of the Interior 

Washlngton, D.C. 20241 14. 

5. Report Date 

12 June 1978 

- 6. 

8. Performing Orgnniration Report No. 

523-07691 30-001 31M 

9, Performing Organization Name and Address 

Coll ins Communications Switching Systems Division 

Commercial Tel ecomnunications Group 

Rockwell International 

Cedar Rapids, Iowa 52406 

12. Sponsoring Orgmiznrbn Name and Addreu 

Office of the Assistant Dlrector - Mining 

Bureau of Mines 

- 

15. Supplemenlary Notes 

Prior related work - Propagation of EM Signals In Underground Mines 

USBM Contract H0366028 

10. Projrcr/Tark/Work Unit No. 

20-1308/93-6527 

11. Contract or Grant NO. 

H0377053 

13. ~yp, of Report 

Final Report 

16. Abrrrsct 

This report covers magnetlc fleid strength measurements vs range and frequency 

in low-medium coal mines. Both quasi-conductor-free and conductor-proximity 

areas were investigated. The program covered 5 mines, 4 seams, 6 measurement 

sets, and 3 geographic areas. The results have been summarized in terms of 

maximum comnunication range expected per seam and noise condition. Scatter 

gain is further explored as a simple measure of energy coupled to conductors. 

17. Orilinatoc'r Key Words 18. Availability Stacemen1 

MF wireless radio propagatlon; maximum 

communication range; conductor-free areas; 

conductor-proximity areas; set limited noise; 

median mine noise 

1 iccurity Classif. of rhr Report 

IJ..~! ~sified 

21. No. of Pagn 

94 

20. U.S. Security Classif. of This Page 

Unclassified 

22. Price 
FOREWORD 

This report was prepared by Terry S. Cory, P.E., for Collins 

Communications Switching Systems Division, Commercial Telecommunications Group, Rockwell International , Cedar Rapids, Iowa, under 

USBM Contract H0377053 and Terry S. Cory, P.E., Subcontract 

C-651672. The contract was initiated under the Coal Mine Health 

and Safety Program. It was administered under the technical direction of Bruceton Research Center with Mr. Harry Dobroski acting 

as the Technical Project Officer. The Bu Mines Contracting Officer 

was Alan G. Bol ton, Jr. 

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

this contract during the period October 19, 1977 to May 31, 1978. 

This report was submitted by the author on June 12, 1978. 

For clarity, this report contains equipment brand names as being 

generically representative of equipments which may be available 

to implement medium frequency systems in coal mines. Reference to 

specific brands, equipment, or trade names in this report is made 

to facilitate understanding and does not imply endorsement by the 

Bureau of Mines. No patentable techniques or items of equipment 

have been developed or otherwise used during the course of this 

program. 
Table of Contents 

Page 

Report Documentation Page---------------- Forewor&-------------------------------- 

1.0 Introduction------------------------ 

1.1 Program Background------------------ 

1.2 Program Overview-------------------- 

1.3 Report Contents--------------------- 

2.0 Executive Summary------------------- 

2.1 Results Summary--------------------- 

2.2 Transmission Characterization------- 

2.2.1Computatlon Criteria 8 Techniques--- 

2.2.2Utility of the Characterization----- 

Technique 

2.3 Recomendations--------------------- 

3.0 Technical Approach------------------ 

3.1 Empirical Technique----------------- 

3.2 System Calculations----------------- 

3.3 Scatter Galn Comparisons------------ 

4.0 Individual Mine Test Descriptions--- 

4.1 Margaret #II Mine------------------- 

4.2 Adrian Mine------------------------- 

4.3 Nanty Glo Mlne #31------------------ 

4.4 Ehrenfeld #38D Mine----------------- 

4.5 Stinson #3 Mine--------------------- 

Append i x 

A-l Margaret #11 Test Data at Medium---- 

Frequency 

A-2 Adrian Mine Test Data at Medi urn----- 

Frequency 

A-3 Nanty Glo #3I Mine Test Data at----- 

Med i um Frequency 

A-4 Ehrenfeld #38D Mlne Test Data at---- 

Mad l um Frequency 

A-5 Stinson #3 Mine Test Data at-------- 

Medium Frequency 

References------------------------------- 

Special Technical Report----------------- 

In-Situ Measurement of Coal Seam 

Conductivity Using a Parallel Wire 

Transmission Line Method 
L l s t o f Illustrations 

Figure Page 

I Maximum Communl cation Range vs Operating 

Frequency In Conductor-Free Areas of Coal 

Mines - Set Noise Limit------------------------ 10 

2 Maximum Communication Range vs Operating 

Frequency In Conductor-Free Areas of Coal 

Mines - Median Mine Noise ..................... 11 

3 Maximum Communication Range vs Operating 

Frequency In Coal Mines In Proximity to 

Conductors - Tx Located Remotely - Median 

Mi ne No 1 se------------------------------------- 12 

4 Maximum Communication Range vs Operating 

Frequency in Coal Mines In Proximity to 

Conductors - Tx Located Remotely - Set 

~~i~~ ~imit------------------------------------ 14 

5 Required Field Strength Sensitivity Levels 

for Mine Wireless Radios Based on the CollinsDeveloped Mine W I re less Prototype Radios at 

520 KHZ------------------------------------- 16 
1 .0 I NTRODUCT I ON 

This is the Final Report covering work performed by Collins Divisions, 

Rockwell International Corporation under Bureau of Mines Contract 

H0377053 entitled Electromagnetic Propagation in Low Coal Mines at 

Medium Frequencies. 

The technical work was performed by Terry S. Cory, P.E. under 

Subcontract C-651672 with administrative direction and technical 

support provided by Collins and uslng Collins' facllltles. 

The primary work consisted of performing measurements of magnetic 

field strength in five (5) mines and four (4) coal seams coordinated 

with a concurrent theoretical study performed by Arthur D. Little, 

Inc. (ADL) under separate contract* to the Bureau. The measurements 

were taken in such a manner as to enable the reduced results to 

characterize the wireless radio transmission properties of each 

mi ne/coa l seam; both in areas without conductors and wi th conductors. 

This program was a technological extension of a previous program 

entitled Propagation of EM Slgnals in Underground Mlnes ( performed 

under Bureau of Mines Contract H0366028 herein referred to as the 

"EM Signal l ing Program". This current program has appl led an establ ished 

technique for transmission characterization, to selected highly 

productive low-coal areas. The test equipment, furnished GFE, was 

developed and/or configured under this previous fy?gram and the reader 

is referred to the final report for that program for a detal led 

description of the technique and the measurement system. 

The magnetic field strength measurement data sets from each mine 

were separately reported in each of five (5) interlm Summary Data 

Reports. The data summaries in the form of families of curves of 

magnetic field strength vs range and frequency and the mine map 

topological descri ption of the measurement traverses have been 

compended and are given in the Appendix to this report. The further 

summarizing of this data in terms of maximum communlcatlon range 

with a technique which can be used to apply the results to system 

designs for particular mines is the subject of this report. 

Secondarily, a technique was developed under the contract funding 

for the independent in-sltu measurement of coal seam conductivity 

and pre l imi nary measurements using this technique were performed 

in two mines. This work was beyond the original scope of this 

Ysqgrarn and has been reported separately in a Special Technical Report 

which is not a part of this Final Report. For convenience, this 

Special Technical Report is submitted concurrently as an Attachment 

to this Final Report. 

All program measurements were perfoned by a team consisting of the 

Subcontractor and Principal Investigator Terry S. Cory, a Bureau of 

Mines furnished technician, and a Collins furnlshed technician. 

*Task Order #4, Basic Ordering Agreement H0346045. 

5 
I. I PROGRAM BACKGROUND 

The viability of wireless radio transmission in coal mines has been 

established; largely as a result of the Bu Mines sponsored EM 

Signalling Program, the companion ADL program, and prior Bu Mines 

sponsored research in thls area dating back to 1973. The baseline 

studles and measurements were performed largely in high-coal in 

West Virginia and Illinois and in DC mines, Renewed national emphasis 

on coal production, largely underground, has spurred the here-to-fore 

embryonic and somewhat antiquated mine electronics technology into 

a major arena offering -substantially increased capabilities for 

production efficiency, control, and for enhanced mine safety. A large 

portion of the U.S. coal reserves reside in low-coal ( seams nominally 

36 - 48 Inches thick . Newer AC mines do not provide the trolley wlre 

transport mechanism for implementation of the carrier phone 

comnunication systems prevalent in older mines for handling vehicle 

traffic. Pager phone systems alone, especially in low-coal where 

physical mbility is difficult, are not sufficient to regulate vehicle 

traffic, personnel movement, and to efficiently supervise production 

related activities in large working section panels. 

Within the last year, sources of medium frequency portable radios 

have been identified and within the next one to two years, these radios 

are expected to have been certified and to become available in the 

marketplace. ( RACAL Model TR58 frm South Africa and a U.S. 

manufactured radio now in the productlon prototype stage sponsored 

by CONSOL via Lee Engineering 1. 

The Bureau of Mines currently has an RbD program underway to define 

mine wireless system configurations adaptable to trackless haulage 

mines ( H0366056 ) and planned research relating to portable and 

vehicular antenna development and coupling to existing mine wiring 

conductor configurations. 

This program accomplishes the wireless transmission characterlzatlon 

of low-coal mines and provides a data base which may be used for 

prel iminary estimates of wireless transmission system requirements. 

1.2 PROGRAM OVERVIEW 

Measurements were performed in five (5) mines in chronological order 

as follows: 

(I) Decsmberl977, Helvetia Coal Co. Margaret #11 Mine In 

Armstrong Co., Pennsylvania - Upper Freeport seam 

(a) Field strength vs range and frequency in I-Butt 

Sect ion - quasi -conductor-f ree 

(b) Field strength vs range at 900 KHz in 2-Butt Section 

- conductor-proximi ty 

(2) January 1978, Upshur Coal Corp. Adrian Mine in Upshur Co., 

West Virginia - Upper Freeport seam 
(a) Fleld strength vs range , and frequency in area paral lel 

to Road 8X between 1st Right and 2nd Right - quasiconductor-f ree 

(3) February 1978, Bethlehem Steel Coal Mlne #31 ( Nanty Glo ) 

in Cambria Co., Pennsylvania - Lower Kittanning seam 

(a) Fleld strength vs range and frequency In Main-N area 

- quas I -conductor-f ree 

conductor-proximi ty 

(b) Field strength vs range and frequency In 5-Cross area 

- quas I-conductor-f ree 

conductor-proximi ty 

(4) February 1978, Bethlehem Steel Coal Mine #38D ( Ehrenfeld 

in Cambria Co., Pennsylvania - Lower Freeport seam 

(a) Fleld strength vs range and frequency in I-Right Main-B 

area - quasi-conductor-f ree 

conductor-proximi ty 

(5) May 1978, National Mine Corp. Stlnson #3 Mlne In Knott Co., 

Kentucky - El khorn #3 seam 

(a) Field strength vs range and frequency in C-Section area 

- quasi-conductor-free 

conductor-proximity 

1.3 REPORT CONTENTS 

Section 2.0 presents an Executive Summary consisting of an overview of 

the results in terms of maximum communication range vs frequency plus 

specific observations, conclusions, and recomnendaTlons. 

Section 3.0 presents the Technical Approach consisting of a description 

of the new two-turn receive antenna used, details of the data reduction 

process including calibration, and details concerning the comparison of 

measured and computed scatter gains and derivation of the simple scatter 

gain formulas. 

Section 4.0 presents l ndi vidual Mine Test Descriptjoss lncl uding a 

sumnary of results for each of the five (5) mines visited. 

Appendix presents the compended field strength curves and mine map 

traverses for each set of measurement results obtained. These have been 

extracted from the individual Summary Data Reports. 
2.0 EXECUTIVE SUMMARY 

The primary goal for this program has been to expand the mine/seam 

wireless radio transmission data base into additional low-coal mines/ 

seams, while comparing the results for consistency with the prevlous 

EM Signalling program results. The program work exceeded the origlnal 

expectation of four mines, four seams, and one measurement sample 

per mine by providing data from flve mines, four seams, and six 

measurement samples. Qualitative observations of noise were made along 

the way during the program, 'sewchlng for noise conditions which had 

not previously been experienced in high-coal. Quantitative noise 

measures in operating mines were not possible during the program time 

frame as mst measurements were made during the mine strike. This 

shift of emphasis away from quantitative nolse tests made it possible 

to gather additional field strength data, especially in close 

proximity to conductors, as we1 i as expanding on the mine/seam/ 

measurement set format. 

A secondary goal for this program has been to define simple-toimplement measures for characterizing particular mines and to expand 

on the technique(s1 for using the data base results, confidently, to 

obtain system performance estimates based on the mine/seam 

characterizations. An important part of obtaining this goal has been 

to validate the concept of scatter gain and to establish a simple 

means for measuring it. Once validated, scatter gain provides an 

easy-to-use empirically based way to estimate conductor coupling 

to radio fields. Also an important part of obtaining this goal has 

been to obtain conductor proximity data useful to ADL in their 

more rigorous analysis of conductor coupling and of the transmission 

modes associated with current travellns along multi-conductor 

ensembles. 

To provide the mst complete "total sumnary" of transmlsslon effects, 

this report includes the use of data from the prpy{oy;i,EM Signal l lng 

Program and conducti vlty data derived from AOL's ' modei ing 

evaluation of the measured field strengths. 

2.1 RESULTS SUMMARY 

From the measured magnetic field strength vs range and frequency data, 

maximum comnunication ranges were computed both In quasi-conductorfree mine areas and in conductor-proximity situations for each seam 

under assumptlons of both set-limited nolse and median mine noise. 

Specific criteria upon which these computatlons were based are 

summarized in the next subsection. 
As was characteristic of all seams except, perhaps, the Pittsburgh 

seam, all measurements ( and, thus,ihe expected performance of actual 

radios ) were set-noise-llmlted when the receiver was removed one or 

more entries away from an entry containing conductors. Conversely, 

the received noise levels in conductor entrles are expected to conform 

approximately to median mine nolse. The very few estimates of noise 

made close to energized conductors verl fled this; however, due to the 

strike, determination of typical operational nolse levels was not 

possible. 

The maximum comnunication range in quasi-conductor-free environments 

for the total data base of seven seams for set-limited noise and for 

median mine noise are given respectively in Figures I and 2. The 

comnunication ranges obtained were fairly tightly grouped; being 

greater in value than those for the Herrin #6 seam and less in value 

than those for the Pocahontas #3 seam. 

In set-limited noise, the low-coal mines exhibited maximum ranges of 

180-260 meters at frequencies lylng between 200 and 300 KHz. 

In median mine noise, the low-coal mines exhibited maximum ranges of 

115-140 meters at frequencies lylng between 400 and 800 KHz wlth the 

optimum frequency/range conditions being quite broad. 

These range curves clearly show the Pittsburgh seam to be the exception 

rather than the rule for range performance with the range being 

approximately twice that for the other seams in the data base. 

The maximum comnunication range in proximity to conductors for six of 

the seven seams ( ADL data for the Elkhorn #3 seam was not available 

at the time of this writing ) for median mine noise is given In 

Figure 3. The transmitter is assumed to be located one entry away from 

conductors and the receiver is assumed to be located in the conductor 

entry. Here, there is considerable difference between the values of 

range for the three displayed low-coal seams. The Upper Freeport seam 

gives the best range of 890 meters at 900 KHz and the Lower Kittanning 

gives the poorest range of 570 meters at 1150 KHz. With the exception 

of the Pittsburgh seam, the Upper Freeport seam gives the best 

performance of the total seam set; all other seams are fairly tightly 

grouped at between 570-670 meters at from 900-1150 KHz. The range 

shown is obstensibly the range along the conductor string with the 

conductor attenuation assuming a single transmission line mode ( or 

single dominant mde ). 

- - 

> 9 

0 

?? w 

WZ 

3 - 

s= 

E 5 - 

a 0 

Eg 

WLO 

a w 

0 z - 

LO I 

> 

-I 

wa 

a 0 

3: 

Z 

0 

2 2 

ia K 

0 - 4 

Z W 

2 w 

E K 

ILL 

0 1 

5 & 7 

.c - 0 

X Z 

2 8 
FIGURE 3 

MAX l MUM COMMUN l CAT l ON RANGE VS OPERAT l NG FREQUENCY I N COAL M l tJES 

IN PROXIMITY TO COtJDUCTOR(S) - TX LOCATED REMOTELY - MEDIAN MINE NOISE 

100 

FREQUENCY - I(HZ 
The maximum communication ranges in proxlmlty to conductors for the 

three low-coal seams for which data was available are given in Figure 4 

for set-limited noise. These ranges were not previously computed in 

high-coal as the utility of this situation was at the time questionable. 

Recently, the possibility of an entry carrying only an AC power cable 

or the cable plus a phone line with low nolse in newer AC nines has 

arisen so as to make this a reasonable limiting case. The data is 

shown assuming the transmitter located both one entry and two entries 

removed from the entry carrying the conductor(s). Just as the optimum 

frequency for coupling when both the transmitter and recelver are 

close to the conductors is known to be lower; so the optimum frequency 

for lower noise ( ie greater margin to accmodate conductor attenuation) 

is also lower. For one-entry remoting of the transmitter, the maximum 

comnunication ranges are between 2400-5000 meters at optimum frequencies 

ranging between 220 and 350 KHz. For two-entry remoting of the 

transmitter, the maximum conununicatlon range lies between 470-1050 

meters at optimum frequencies ranging between 220 and 700 KHz. In each 

case, the Lower Freeport seam provides the best range performance. 

2.2 TRANSMISSION CHARACTERIZATION 

2.2.1 COMPUTATiON CRITERIA 8 TECHNIQUES 

The summaries of maximum comnunicatfon range presuppose values of 

receiver sensitivity and transmit NIA. The following criteria have 

been assumed for these summaries based on the Collins mine wireless (51 

prototype fm radios developed for the Bureau and the NBS noise study 

( Bu Mines Contract ti0133005 1: 

NIA = 2.5, the transmit magnetic current moment of the 

radlo using a loop antenna 

Receive sensitivity of 0.02 microamps/meter for 12 dB SlNAD 

for 12 KHz noise bandwidth 

Set-nolse-limited magnetic field strength level for I2 dB 

SlNAD given by 

where, Af is the 12 KHz bandwidth 

Q is the antenna "Q" made as narrow 

as posslble to be consistent with 

transmission; Q = 44 for the Collins 

prototype fm radlo ?, 

A is the antenna area = 0.217 mL 

N is the nolse figure of the receiver 

= 2 dB for the Collins Prototype fm radlo 

Median mine noise magnetic field strength level for 12 dB 

SlNAD ( 13.51 dB signal-noise-ratlo, Hamshur 1 

is given by 
FIGURE 4 

YAXlMUM COMMUNICATION RANGE VS OPERATING FREQUENCY IN COAL MINES 

IN P:WXIMITY TO CONDUCTOR(S) - TX LOCATED REMOTELY - SET LJOlSE LII.?IT 

TX IJIA = 2.5 

RX SENSITIVITY 

0.02 uAMP/M 

12 DB SI NAD, BW = 12 KHZ 

CONDUCTOR Zo = 50 OHMS 

- TX 30 METERS 

TX 60 METERS 

. . 

. ~ '0 

100 I 3n0 

FREQUENCY - KHz 
H~~ = 175.8 - 32.5 loglO f(hz) 

dB above one microamp/meter in a 12 KHz band 

The ranges are then derived by picking off the ranges from the 

measured data corresponding to the receive noise criteria given 

above. The formula results shown above are given in convenient form 

in Figure 5. 

The sumnaries of maximum cmunicatlon range in proximity to conductors 

further presuppose a coup! ing to the conductors of the radlo fields 

and an attenuation rate of the coupled carrier current along the 

conductor strings as well as specific distances of the transmit and 

receive antennas from the conductors. The attenuation constants used 

are those appropriate for a single line source in close pro~&~it~)to 

the roof ( ar flow ). Usi~q the ADL derived conductivities ' 

of the overburden/underburden; the attenuation constants glven in 

Table I were obtained. Other line parameters assumed were: 

where, a is the spacing from the conductor 

center to the rock 

ai is the conductor radi us 

Z = 50 ohms, the surge impedance of 

tRe ~ossy transmission I I ne 

The estimate of conductor coupling is based on the scatter gain ratlo, 

which is that of the field strength atlhe receiver with the conductor 

present to the field strength at the receiver in absence of the 

conductor. Scatter gain has been determined during this program to be 

a valid way of specifying the coupling. For each seam, the computation 

of scatter gain has been reduced to the simple formulas given in 

Table 2. These formulas give values within 3 dB on average of measured 

scatter gain samples. 

To obtain the field strength at the receiver, the computation proceeds 

as fo l lows; 

(1) Choose ranges of the transmit and receive antennas from 

the conductor(s) 

(2) Obtain the magnetic field strength at the closest range 

between the transmitter and the conductor assuming the 

conductor is absent from measured field strenqth curves 

( or from ADL mdel calculations ) for a conductor-free 

environment 
METER PER *A 1 GREATERTHAN DB MAGNETIC FIELD STRENGTH IN 

0 2 0 0 II, 0 

& k b .& < 0 0 0 

I 1 I I I I 

- 

N A 

0 0 0 - 

1 I I 

- 

- 

- 

- 

- 

2 

0- 

O 

N- 

- 0 

- P 

"7- 

m- 

- -4 

m- 

- (0 

2 

8- 

0 

- 

- 
SUMMARY OF SHORT FORMULAS FOR CONDUCTOR ATTENUATION VS 

COAL SEAM ( BASED ON SINGLE CONDLCTOR GEOMETRY 1 

- SEAM FORMULA 

PI TTSBURGH d = 0.02665 DB/M @ I MHz 

POCAHONTAS #3 = 0.02277 DB/M @ I MHz 

HERRIN #6 * = 0.02916 DB/M @ I MHz 

LOWER FREEPORT = 0.02130 DB/M @ 1 MHz 

UPPER FREEFORT = 0.02171 DB/M @ I MHz 

LOWER KI TTANN I NG 4 = 0.02171 DB/M @ I MHz 
TABLE 2 

SUMMARY OF SHORT FORMULAS FOR SCATTER GAIN CALCULATION VS COAL SEAM 

- SEAM 

PITTSBURGH 

POCAHONTAS #3 

LOWER FREEPORT 

UPPER FREEPORT 

LOWER KITTANNING 

FORMULA 
(3) Multiply the field strength of (2) by the scatter gain 

( or add dB ) as computed from Table 2 

(4) Subtract the result of (3) in dB from the sensitivity 

level obtained from Figure 5 for the appropriate type 

of noise 

(5) Divide the dB magln of (4) by the conductor attenuation 

as computed from Table I. This gives the range along 

the conductor string. 

2.2.2 LlTlLlTY OF THE CHARACTERIZATION TECHNIQUE 

The arrangements of conductors encountered in mine environments are 

highly variable. These impact both the coupling of transmitted radio 

fields into the conductors and the propagation of the induced carrier 

currents along the conductors. Usually, the coupling can be measured; 

ie measured scatter gain, by transmittinq from a known useful location, 

measuring the field strength at a desired distance away from the 

conductor with a receive loop ( but along the shortest dlstance 

between the transmitter and the conductors ) and then measuring the 

received field strength again at the same spacing from the conductors 

but at a considerable distance "down" the conductor ( ie, beyond the 

direct field range ) where the current attenuation rate flattens out. 

During the program, the strongest field strength was observed along 

the shortest path from the transmitter to the conductor even though 

the transmit loop was oriented parallel to the conductors. The 

coupling to the conductors was near optimum because of the relatively 

good agreement between measured and computed scatter gains. This does 

not infer that the optimum orientation of the transmit antenna for 

best coupl ing is known, however. To assure optimum coupi ing when 

measuring scatter gain one should begin with the "distant1' measurement 

orienting the transmit antenna for optimum coupling; then, keeping 

this transmit antenna orientation constant, nave in close and obtain 

the "in-l ine" measurement orienting the receive antenna again for 

optimum coupling. This simple technique for assessing coupllng will 

work and provide meaningful results providing the mine wiring topology 

does not change between receive measurement locations. 

Conductor attenuation may be difficult to determine if the configuration 

is complex. Measurement may be required of the attenuation in !@eciflc 

mines rather than computation to obtain accurate resulrs. ADL has 

computed the complex propagation constant for typical multi-conductor 

configurations which lend insight to these particular situations. ADL 

is currently formulating a conductor coupling model from which to 

determine optimum antenna orientations for conductor coupling. A 

particular set of conductor-proximity measurements made In the 

Stinson #3 Mine showed that the VMD orientation produced the greatest 

coupling at low frequencies of 200-300 Khz or less, VMD and both 

principal HMD orientations produced nearly equal coupling at 400-500 
KHz, and at 800-900 KHz the HMD orientation with the loop plane 

perpendicular to the conductors was predominant. 

2.3 RECOMMENDATIONS 

From the results of this program and the EM Signalling Program, the 

quasi-conductor-free transmission performance of wireless radio in 

most seams is fairly well bounded to a small region of optimum 

ranges and frequencies. Whl le scatter gain seems to work in def inlng 

rough coupling estimates from a remotely located portable transmitter, 

more accdrate coupling definition from practical mineworthy antenna 

mountings to a variety of useful mine wiring topologies should be 

made. This is particularly true for transmit locations in close 

proximity to the conductor ensembles. In addition, measurements of 

attenuation along a variety of useful mine wiring topologies should 

be made and correlated with ADL theory. 

The trpggmission along mine wiring conductor strings has been shown 

by ADL to be aided by the presence of a dedicated wire. 

Alternatively, a mine wi re less radio ystem could operate wi th the 

aid of a leaky feeder specially designed to provide optimal coupling 

from a transmitter in a particular worklng area, carry the current 

from this area a long distance and then "reradiate" most of the 

energy over another predetermined working area. The local coupling 

from a remote transmitter Into this type of conductor should be 

investigated. 
3.0 TECHNICAL APPROACH 

3.1 EMPIRICAL TECHNIQUE 

The measuring equipment arrangement was Identical to that used during 

the EMp$jgnal l ing program and described in Section 3.0 of that f lnal 

report . Again, Singer NM-12 and NM-25 field strength me3ers were 

used for reception. The single-turn shielded coaxial 0.73 m loop 

antenna was rewound into two-turns on easy-to-assemble wooden frames 

to facilitate physical maneuvering in low-coal. The new design preserved 

the antenna reactance so that the same coarse tuning networks could 

be used. The two-turn loop usage resulted in an approximate 6 dB 

decrease in System sensitivity. Calibration data comparlsons between 

the one-turn and two-turn loops are given in Table 3. These comparison 

dl fferentials were used to adjust the cal ibratlon data obtained 

during the EM Signalling Program to obtain new absolute calibrations. 

The two-turn loops were used to obtain most of the measurements during 

this program. 

The NM-12 field strength meters were calibrated so that a known incldent 

field strength will produce a readlng of +25 dB on the instrument 

panel meter with the attenuator in the -20 dB position. The NM-25 field 

strength meters were calibrated so that a known incldent fleid strength 

will produce a reading of +I0 dB on the instrument panel meter with 

the attenuator in the -20 dB position. These known fleld strengths 

are in terms of microvol ts/meter ( the plane wave equivalent electric 

field strength ). As the actual calibration was performd using loop 

antennas, the true H calibration field strength is obtained by dlvidlng 

the equivalent electric field strength by 377 ohms. 

In reducing the field strength data, the field strength at each location 

in dB greater than I microamp/meter was found as the sum of the meter 

reading as determined in dB minus the field strength calibration point 

in dB ( +I0 for the NM-25, +25 for the NM-12 plus the attenuator 

range setting in dB plus 20 dB plus the calibration fleld strength in 

dB greater than I microamp/meter plus the NIA nonallzatlon factor. 

In equation form, this is expressed as 

Field Strength = analog meter readlng - ( 10 or 25 

+ attenuator range setting +20 + 

calibration fleld strength + 

2.5 

20 loglo Tx current x NIA 

NIA = 2.04 for 7-turn loop below IOOOKHz 

1.17 for 4-turn loop above 1000 KHz 

This equation normalizes the NIA to a standard of 2.5 which is 

representative of the Collins fm prototype radio and the older ECAM 

am radlo. 

The absolute calibrations in terms of equivalent electric fleld strengths 

used to eeduce the data taken during this program are given in Table 4. 
TABLE 3 

COMPARISON OF ONE-TURN AND TWO-TURN LOOP W ANTENNAS 

500 

500 

500 

500 

1000 

I 000 

1000 

1000 

1500 

1500 

2000 

2000 

2000 

2000 

3000 

MOO 

MOO 

3000 

4000 

4000 

4000 

4000 

RX ANTENNA RELATIVE 

ANT TYPE (TU WS ) BAND SET # FIELD STRENGTH(DB1 
TABLE 4 

CALI BR4TION Fl ELD STRENGTHS USED DURl NG THE PROGRAM 

RX ANTENNA 

BAND SET # 

FREQUENCY 

KHz 

98- 100 

2 18-220 

252-258 

420 

440 

470-486 

470 

440 

880-900 

1750 

1850- 1860 

1890- 1900 

3620-37 I0 

3620 

3750 

4050 

Fl tLD STRENGTH 

bII CROVOLTS/M 

549.6 

144.0 

139.0 

128.0 

123.9 

115.7 

88.8 

82.8 

73.3 

43.4 

41.4 

37.5 

22.4 

13.3 

12.8 

11.8 
3.2 SYSTEM CALCULATIONS 

The criteria used to prepare the maximum communication range summaries 

are presented in Section 2.0 and will not be repeated here. The 

comparison of the criteria used with that expected for other radios is, 

however, of interest. The Collins fm radio criteria were used in this 

report for consistence with the EM Signalling Program results which, 

when prepared, were representative of the radlo parameters expected 

to be available. 

The transmit NiA has, in all cases, byen assumed to be 2.5. This 

corresponds to 20 watts into a 0.22 m antenna of 7 turns with an NA 

of 1.52 ( typlcal for a portable man-carried antenna 1. Newer radios 

are expected to be in the 1-5 watt range for portables and probably 

SSB where the power rating is in PEP. Normally we think of SSB having 

an approximate 9 dB advantage over am and being aporoximately equal 

to fm on a PEP basis under low but intelligible signal-to-noise 

conditions. The receive system sensitivlty of the Collins fm receiver 

and the new RACAL SSB unit are roughly equal using the Hamshur criteria 

of 12 dB SlNAO which was the basis for the report summary calculations. 

This Is shown as 

Sensitivity, dB above I ua/m 

(I) Collins fm radio for 12 dB 

SlNAD 8 2 dB noise figure 

@ 520 KHz, 12 KHz BW (a) Hamshur -34.0 

(b) Shimbo -37.6 

(c) measured -35.5 

(2) RACAL SSB radio 

0.2 uv for 15 dB S/N For 10 dB S/N -34.9 

The conclusion is that the PEP SSB power rating ratioed to 20 watts 

gives the NIA reduction factor and, hence, the total system comparison 

of the Collins fm system as analysed herein and new SSB radio systems 

using the same antenna. 

3.3 SCATTER GAIN COMPARISONS 

Measured scatter gains for the Upper Freeport and Lower Kittanning seams 

have been given to the Bureau in mnthly progress reports under this 

program. These were based on the fleld strength in absence of the 

conductor being that taken directly from the quasi-conductor-free curves 

in the saw manner as if the scatter gains were being analytically 

calculated. Analysis has shown these previously reported values to be 

incorrect as the actual measured field strength at the receiver via 

the shortest path between the transmitter and the conductor should have 

been used. Using these actual measured values of the dominant dlrect 

field strength at the receiver on the "in-line" path, there is good 

agreement between measured and computed scatter gains. This also shows 

that the "in-l inel' measured values were near optimum for the orientation 

of the transmit antenna employed ( loop plane parallel to the conductors 1. 

For actt~al system estimates, the field strength on theftin-line" path 

was assumed to be that between coplanar loop antennas. Based on the 

Stinson #3 results, this polarization will probably produce optimum 

24 
coupling from at least 500 KHz upward in frequency and this is in 

agreement with periodic observations made over the term of this 

program and the EM Signal l ing Program for elther the transmitter 

or the receiver located at least one entry removed from the 

conductors. 

The scatter gain computations in the data summaries used simple 

"short formula" expressions for scatter gain. These were derived 

via correcting the "ful l formula" scatter gain expression sl lghtly 

to be consistent with the measured scatter gain frequency dependence. 

The "ful l formula " Scatter gain is given by 

The scatter gain was calculated using coal seam and rock conductivity 

va l ues deri ved from ADL mode I i ng and comput ing oc and (3 from 

where, K is the dielectric constant = 6 

C 

. dr Is the rock conduct1 vity 

4, is the coal seam conductivity 

h is the seam height 

The simple "short formula" scatter gains were derived using the form 

G = Fl F2 

where F expresses the frequency dependence of the "ful l formula" and 

F2 expresses the frequency dependence correction to make the overall 

frequency dependence agree with the measured data. 
Comparisons of the measured and computed scatter gains for the 

Upper Freeport, Lower Freeport, and Lower Kittanning seams are given 

respectively in Tables 5, 6, and 7. These comparisons show good 

agreement between measured and computed results except in the case 

of the AC power cable in the Upper Freeport seam ( Margaret 811 1 

case. Oddly enough, the complex phone line and belt support cabling 

configuration gave good results whereas the simple conductor did not. 

The only conclusion to be drawn is that the AC power cable must have 

been open circuited somewhere in the vicinity of the measurements so 

as to create a high surge impedance. 
TABLE 5 

COMPARISON OF MEASURED 8 COMPUTED SCATTER GAINS 

MARGARET #I1 MINE - UPPER FREEPORT SEAM 

FULL FOR4 SHORT FORM 

MEASURED 

y(M) RR(M) GS(DB) CALCULATED MEAS/CALC GS( DB) CALCULATED 

FREQ(KHZ) - GS(DB) - A(DB) 

900 4.3 0.25 -26.0 -15.6 10.4 NOTE: AC POWER CABLE 

AC POWER 14.0 0.25 -41.5 -20.7 20.8 BEEN OPEN ClRC

CABLE ,, 

THE MEASUREMEN

ONLY 10.4 3.7 -57.5 -42.8 14.7 

I1 28.4 0.25 -18.0 -23.8 5.8 -18.5 

PHONE LINP 25.0 3.0 -39.5 -44.8 5.3 -39.5 

8 BELT ,, 

w SUPPORT 9.8 0.25 -22.0 -19.1 2.9 -13.9 

.I 

NOTE: CALCULATION ASSUMPTIONS 

Zo = 50 OHMS, FULL FORMULA 

25 OHMS, SHORT FORMULA 
COMPARISON OF MEASURED 8. CWPUTED SCATTER GAINS 

EHRENFELD #38 MINE - LOWER FREEWRT SEAM 

FULL FOR4 SHORT FORY 

MEASURED CALCULATED MEAS/CALC CALCULATED 

y(M) RR(M) FREQ4KHZ) GS( DB) GS(DB) A(DB) G~(DB) 

NOTE: CALCULATION ASSLMPTIONS 

h = 1.12 M 

4c = 6.3 x ?4iO/M 

4 r = 5.4 x MHO/M 

Zo = 50 OHMS 
TABLE 7 

COMPARISON OF MEASURED 8 COMPUTED SCATTER GAINS 

NANN GLO #31 MINE - LOWER KITTANNING SEAM 

FLJLL FORM SHORT FORM --- - 

MEASURED CALCULATED MEAS/CALC CALCULATED 

R+M) RR(M) GS(DB) GS(DB) GS(DB) - - A (DB) 

NOTE: CALCULATION ASSUMPTIONS 

h = 1.04 M -5 

dc =6.2 x 10 MHO/M 

4 r = 7.2 x WO/M 

Zo = 50 OHMS 
4.0 INDIVIDUAL MlNE TESTS DESCRIPTIONS 

4.1 .,MARGARET #I I MlNE 

The Margaret #11 Mine is in low-medium coal in the Upper Freeport seam. 

In the area used for testing, the seam was approximately 48-54 inches 

thick. In haulage entries, the overburden and underburden have been 

trenched out to give entry heights of approximately 6 feet. 

This mlne is the most productive one Helvetia/R&P Coal Cos. has and is 

a "punch mine" with an expected l i fetime of rough1 y 5-10 years. At 

this location, the Upper Freeport seam is about 100-120 feet beneath 

the surface. The mine employs only two working sections and three 

mining machines. The mine is AC with belt haulage using tracked 

support vehicles in the mains and rubber tired vehicles In the sections. 

In this mine, the AC power cable is run in the entry adjacent to the 

haulage entry. The AC power is 7200 VAC. Both the miner(s) and the 

shuttle cars operate from stepped-down 480 VAC. 

The entries are nominally 18-20 feet wide and the coal pillars are 

nominal l y on 60 foot centers. There are pager phones only at the 

section head and tail pieces. 

Most of the measurements were performed in the conduct~r-free !-Butt 

and in the conductor-proximity 2-Butt sections with supplemental 

measurements being performed In the #I malns. The mlne traverse 

topology and the measured field strength data plotted vs range and 

frequency are given in Appendix A-I. 

Selected observations based on the reduced data include: 

(1) The field variation near the phone line/beltway from a transmitter 

located 32 feet away due to interaction of the direct and scattered 

fields was about 5 dB and the ripple due to SWR was about 2 2.5 dB. 

(2) The coupled current in the phone line/belt support cabling from a 

transmitter located 32 feet away was about 15 dB greater in the 

direction toward the face than in the direction toward the mains. 

(3) In an entry containing the phone line and belt support cabling, the 

VMD and HMD field components in the opposite rib plane were of 

near-equal amplitue. The rib plane field strengths were about 15 dB 

less than those at close proxlmity to the conductors when the 

transmitter was 32 feet away and about 25 dB less when the transmitter 

was located 88 feet away. 

(4) In an entry containing only the AC power cable, the cable "carrier" 

current was about 12 dB greater when the transmitter was located 

14 feet away than when it was located 46 feet away. The rib plane 

field strength was about 15 dB less than the close proximity field 

strength when the transmitter was located 46 feet away. 
4.2 ADRIAN MlNE 

The Adrian Mine is in high coal in the Upper Freeport seam. In the area 

used for testing, the seam is approximately 72 inches thick. 

This mine, established in 1965, is of small-to-moderate size, and is 

scheduled for another 18-20 years of l i fe. This is one of the farthest 

south mines in the Upper Freeport seam. Although the overburden in the 

test area was approximately 300 feet, the seam outcrops In the nearby 

area. The mine employs continuous miners and belt haulage, working 

three sections with a production of approximately 94 tons per man shift. 

The mine uses the room and pillar technique wlth the pi llars being on 

70 foot centers in length and on 50 foot centers in width. The entry 

crossectlonal widths are nominally 17 feet. The overburden material 

is metawhasized shale wlth no draw slate adjacent to the seam. No 

top coal is left in mining. The mine employs track and trolley for 

service vehicles. The continuous miners are AC operated at 2480 or 

1575 volts stepped down from the 4160 VACline. The shuttle cars are 

DC operated and the roofbolter Is AC operated. 

All measurements were performed In the area parallel to Road 83C between 

1st-Right and 2nd-Right with the transmit ,antenna oriented HMD with 

the loop plane coplanar in the entry crossection. The mine measurement 

traverse topology and the measured field strength data plotted vs 

range and frequency are given in Appendix A-2. Only frequencies of 

90 and 220 KHz were used in this mine. 

The data taken In the two entries compared within 2 dB at 90 KHz and 

within 5 dB at 220 KHz at the same range with the transmitter entry 

having the advantage over the entry two entries remved from the 

transmitter entry. 

4.3 NANTY GLO MlNE #31 

The Nanty Glo #31 Mine is in low-medium coal in the Lower Kittanning 

( "B" ) seam. In the area used for testing, the seam was approximately 

39-43 inches thick. 

This is a large old mine ( approximately 50 years ); the Main-N and 

5-Cross areas of the mine being approximately 16 miles apart underground. 

This shaft entry mine maintains 600-900 feet of overburden with a 

substantial variation in the seam elevation. The Leidy Portal, in a 

valley, marks the low point of the seam and the Maln-N area is 

relatively near this portal. The 5-Cross area is approximately 900 feet 

higher in elevation than Main-N and is near where the seam outcrops 

on a mountain top. 

The mine uses entries driven on 60-foot centers ( crosscuts every 120 

feet in the old area ) in Main-N and on 70-foot centers ( crosscuts 

every 100 feet ) in 5-Cross. The entry widths are 18 feet. The roof 

is hard rock and is flat; the best roof the author has ever experienced. 

No top coal is left in mining. 
This mine provided the equivalent of two mines worth of data due 

to the wide separation of measuring locations. Although both 

quasi-conductor-free and conductor-proximity data were taken in 

the Main-N area, only the quasi-conductor-free data was conclusive. 

This data was "dearly won" for the floor had heaved and the data 

was gathered with only 2-3 feet of head clearance. Both quaslconductor-free and conductor-proximity data were oathered in the 

5-Cross area. The test traverse and reduced data are given in Appendix A-3. 

Selected observations based on the reduced data include: 

(I) The limited conductor proximity data taken in the Main-N area show 

comparable coupled field strength levels along entry centers 

at 218 KHz in both power cable and belt entries. In the power 

cable entry, the coup led field strength is about 5 dB more at 

480KHz than at 218 KHz and about 22 dB more than at 3620 KHz. 

(2) In the 5-Cross area very close to the power cable, the optimum coupled 

field strength appears to be in the 1860-4050 KHz range (approximately 

10 dB greater than at 890 KHz ) while In the rlb plane, the field 

strengths seem to be much lower with the purely coupled field 

strength condition not being obtained. 

(3) Pursuant to (2), there appears to be an effect at higher frequencies 

which produces a periodic variation In field strength with distance 

along the power cable entry rib plane. 

4.4 EHRENFELD #38D MINE 

The Ehrenfeld #38D Mine is in low-medium coal In the Lower Freeport 

( "D" ) seam. In the area used for testing, the seam was approximately 

42-46 inches thick. 

This drift mine, established in the late 1950ts, is of mderate size 

with several seams being mined. Currently, most of the production 

comes from the "D" seam; an operation to mine the Upper Freeport ( "E" 

seam is just beginning. This mine employs conventional mining sections 

with belt haulage. In the test area, the overburden level was 

approximately 250 feet. 

The mine uses the room and plllar technique with the pillars being on 

100 foot centers In length and on 70 foot centers In width. The entry 

crossectional widths are nominally 18 feet. The power cable entry used 

for the conductor-proximity testing contained only the 4160 VAC cable 

suspended beneath a 3/8 " stranded steel messenger cable. 

All measurements were performed in the I-Right Main-B area wlth the 

transmitter in a fixed location. Quasi-conductor-free measurements 

were made in the entry containing the transmitter. Conductor-proximity 

measurements were made in the adjacent power cable entry. The test 

traverse topology and the measured field strength data plotted vs 

range and frequency are given in Appendix A-4. 
Selected observations based on the reduced data lncl ude: 

(I) The optimum coup1 lng frequency observed in the rib plane was 

about 470 KHz. 

(2) Optimum coupling immediately adjacent to the AC power cable 

appears to be between 470 and 880 KHz. 

(3) At 200 KHz, the coupled field strength is 10-15 dB below the 

optimum coup led results. 

4.5 STINSON #3 MINE 

The Stinson #3 Mine is in low-medlum coal in the Elkhorn #3 seam. 

In the area used for testing, the seam was approximately 50-56 

inches thick. 

This is a small drift mine and is one of a connected set of mines 

in the imediate area; serviced via separate power systems and 

separate portals to faci l itate operation us In@ battew operated 

service veh icles, accomodate the mountainous 'to~ography, and 

minimize belt-to-tipple runs. This seam is one of seven Elkhcrn 

seams ( numbered from the bottom up ) and stacked approximately 

60 feet apart. Existing leases In the area will permit National 

Mine Corp. to continue operation In the highly productive #3 

seam alone for 20-30 years. This mine employs conventional mining 

sections w(th belt haulage. In the test area, the overburden was 

approximately 500 feet thick and about 100 feet thick at the C 

Section face ( outcropped Just before our trip ), 

The mlne uses the room and pillar technique with the pillars 

being on 60 foot centers ( nominally 38 foot pillar widths and 

are roughly square. The mine is not pl llared In retreat mlning 

due to the intended mining of the other seams. The pillars in 

these future mines will be made to coincide vertically with the 

pillars in the currently mined areas. 

The overburden/underburden consists of approximately l i feet of 

shale on the roof/floor followed by sandstone. 

This mine runs all conductors in the belt entry: the 4160 VAC 

power cable lies on the floor. All service vehicles are battery 

operated and are of the articulated variety. 

All measurements were performed in C-Section of this mlne. The 

quasi-conductor-free measurements were made in an entry three 

entries removed from the conductor entry. Conductor-proxlmlty 

measurements were made both from a remote transmltter ( same 

location as for the quasi-conductor-free tests ) and from a 

tightly coupled transmitter for the coupled field polarization 

measurements. The test traverse topology and the measured field 

strength data plotted against range and frequency are given 

in Appendix A-5. 
Selected observations based on the reduced data include: 

(I) Conductor-proximity measurements show: 

VMD polarization to be predominant at low frequencies 

HMD polarization with the loop plane perpendicular to the 

conductors to be predomi nant at higher frequencies 

All polarizations produce nearly equal field strengths at 

486 KHz 

A pronounced null, just off the loop-plane-parallel direction 

in the HMO polarization 

The best coupling frequency to be.the highest used; 890 KHz. 
APPEND l X 

--- MINE TEST DATA 
This Appendix gives the mine maps and summary field strength reduced 

data sets from each of the five Sumnary Data Reports prepared during 

this program. For additional information regarding a particular mlne, 

the reader is referred to the particular Summary Data Report for that 

mlne. 

The information in this Appendix is organized as: 

A- 1 Margaret "I I Mine 

A-2 Adrian Mine 

A- 3 Nanty Glo #31 Mine 

A-4 Ehrenfeld #38D Mine 

A- 5 Stinson #3 Mine 

The particular references for the five Summary Data Reports are given 

as References ( 10) th'rough ( 14). 
A- l 

MARGARET #II TEST DATA AT MEDIUM FREQUENCY 
W 

z W 

WZ 

K - 

5 ZE ul 

a - 4 FZ G 

0 

0- IZt- W 

W a0 K 

LL wa 

S - Ot- 2" a 

LL -t- z + 3 

am - 

01 0 

0- 0 2 

z --I LL- a 

WO 

t-a 0 

k2 a 

zo - 2 L 

a > 

LL -I 

t- W 

I . 

> 

a 

0 

J 

0 

a 

0 

t- 

TRANSMLTTER L0CATI:ON TN CROSSCUT BETWEEN 

BELT AND POWER CABLE. ENTRIES 

TRANSMLTTER LOCAT [,ON AT BARRIER ADJACENT 

TO POHER CABLE ENTRY 

OWER CABLE ENTRY 

FlGURE A3 

MI~NE !IAF SHOWLNG TOPOLOGY, TRANSMI.TTER LOCATIONS, AND MEASUREMENT STATIONS ALWc 

FOR CONDUCTOR-PROXIMITY MEASUREM.ENTS IN 2-BUTT SECTION AND #I. MAI.NS - TOWARD POR

HELVETI'A COAL CO. MARGARET #I1 MINE 
MAGNETIC FIELD 

COFIDUCTOR-FREE 

HELVETIA COAL C

DATA TAKEN IN E

COFLANAR HMD OR

0 20 40 60 80 100 120 I40 

RANGE FROM TRANSMITTER - METERS 
MAGNETIC FIEL

CONDUCTOR-FRE

HELVETIA COA

DATA TAKEN ON

FROM ENTRY CO

COPLANAR HMD 

0 20 40 60 80 100 120 1 40 

RANGE FROM TRANSMITTER - METERS 
FIGURE 

MAGNETIC FIELD STRENGTH Y$ RA

IN 24TT SECTION OF HELVETIA 

MINE @ 900 KHz WITH TRANSMIT 

AWAY NIA = 2.5 

DATA TAKEN ALONG PHONE LINE/B

FOR MAXIMUM FIELD STRENGTH AD

TX ANTENNA LOOP PLANE ORIENTE

CABLE CROSSES 

RY @ WWER CENTER 

0 100 200 ;OO 400 500 

DISTANCE ALONG BELT ENTRY -. METERS 
PP 

METER PER MICROAMP 1 GREATER THAN 08 IN STRENGTH FLELD MAGNETIC 

+ 

- I - + + + + + 

(3, cn e w N o 0 0 0 0 0 0 CI 

? 0 0 0 0 in M N - 0 

+ 7 + + 0 + 

t1313W t13d dWVOtl31W I NVHl t131V3t13 Ba NI H13N3HlS 01314 3113N3VW 

46 
A-2 

ADRIAN MINE TEST DATA AT MEDIUV FREQUENCY 

MAGNETIC FIELD STRENGTH VS RANGE IN CONDUCTOR-FREE AREA PARALLEL TO R

BETWEEN IST-RIGHT AND 2ND-RIGHT 63 90 KHZ FOR NIA = 2.5 ......................................

UPSHUR COALS CORP. ADRIAN MINE 

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

RECEIVE ANTENNAS ORIENTED HMD WITH LOOP PLANE OF TRANSMIT 8 RECEIVE A

RANGE FROM TRANSMITTER - METERS 

A- 3 

NANTY GLO #31 MINE TEST DATA AT MEDIUM FREQUENCY 


0 5: 3 $I 0 0 - 0 - 0 

Ip N 0 N + + + + + I I 

$: 

I 

t1313W t13d dWVOt131W I NVHl t131V3t13 €la NI H13N3HlS a131d 3113N3WW 

54 
FIGURE A16 

MAGNETIC FIELD STRENGTH VS RANGE ALONG CENTER OF POWER CABLE OR BELT ENTRI

AS NOTED, TRANSMITTER LOCATED ONE ENTRY REMOVED FROM POWER CABLE ENTRY AND 

TWO ENTRIES REMOVED FROM BELT ENTRY, TRANSMIT ANTENNA LOOP PLANE PARALLEL 

.................... BETHLEHEM STEEL COAL MINE NANTY GLO #31 MAIN-N AREA .................... RECEIVE ANTENNA ORIENTED WITH LOOP PLANE HMD AND PARALLEL 7 ;O ENTRY Dl HECT I

DISTANCE ALONG POWER CABLE OR BELT ENTRIES - METERS 
2 4 "I 

- 9 4 

G Z 

IW1 

Z 

W 0 W 

WO > + 

Z I- Z 

a > IZI raw a 

a 

IZI 

> W a1w1 

% 

2 x E 2lZl ? 5 

=I--< 

- 151 - J Iz II a 

V W x "Y141 

a V) 

Ia z 

I- a $181 - w In V 0 Z - 

I IJI LT 

own w 

-1 W IWI 

0 

Wa - I- n -La "Y I 

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UOI- W - CL 

I- - 4 LS55 z 

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t-ZI 

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A-4 

EHRENFELD #38D MINE TEST DATA AT MEDIUM FREQUENCY 

FIGURE 

MAGNETIC FIELD STRENGT

CONDUCTOR-FREE I-RIGHT 

ENTRY CONTAINING TRANS

- -----

BETHLEHEM STEEL COAL M

------

NIA = 2

COPLANAR HMD ORIENTAT

0 20 40 60 80 100 

RANGE FROM TRANSMITTER - METERS 
m LT 

LL1? Z 

ON, 

W 

> I1 

0 x4 I-- 

W- I Irz 2 * rr 

(L 1 

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z J 

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43a I 

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I 4 1x1 

t- W 

a I--1x1 

2- W 

t3 I-- 

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LT 

LL W 

U E - - 

kt 5 

Z Z 

I- 
FIGURE A23 

MAGNETIC FIELD STRENGTH VS RANGE ALONG RIB PLANE OF POWER CABLE ENTRY, ONE ENTRY 

REMOVED FROM TRANSMITTER; TRANSMIT ANTENNA LOOP PLANE PARALLEL TO CABLE NIA = 2.5 

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

BETHLEHEM STEEL COAL MINE EHRENFELD #38(D) I-RIGHT MAIN B 

0 20 40 60 80 100 120 140 160 

DISTANCE ALONG POWER CABLE ENTRY - METERS 
A-5 

STINSON #3 MINE TEST DATA AT MEDIUM FREQUENCY 
Z - 

a 

5" 

3k- mu) W 

PII- 5 

z ,= [La 

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WZ [L 

4 

WJ 

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2'- 

0 (3 

z 0g-I a - 

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C = 

0 0 985 ou 
0 20 40 60 80 100 120 140 160 180 

RANGE - METERS 
MAaJETlC FIELD STRENGTH VS RANGE AWAY FROM CONDUCTORS ( REFERENCED TO VIRTUA

TRANSMIT ANTENNA LOCATION ) ON TRAVERSE PERPENDICULAR TO CONDUCTOR ENTRY - 

8 258 KHz FOR THREE ORTHOGONAL RECEIVE ANTENNA POLARIZATIONS NIA = 2.5 

10 20 30 

RANGE - METERS 
MAGNETIC FIELD STRENGTH VS RANGE AWAY FROM CONDUCTORS ( REFERENCED TO VIRTU

TRANSMIT ANTENNA LOCATION ON TRAVERSE PERPENDICULAR TO CONDUCTOR ENTRY 

@ 486 KHZ FOR THREE ORTHOGONAL RECEIVE ANTENNA POLARIZATIONS NIA = 2.5 

20 30 

RANGE - METERS 
MAGNET lC Fl ELD STRENGTH VS RANE AWAY FROM CONDUCTORS ( REFERENCED TO Vl 

TRANSMIT ANTENNA LOCATION ) ON TRAVERSE PERPENDICULAR TO CONDUCTOR ENTRY 

@ 890 KHz FOR THREE ORTHOGONAL RECEIVE ANTENNA POLARIZATIONS NIA = 2.5 

20 30 

RANGE - METERS 
REFERENCES 

(I) T.S. Cory, " Propagation of EM Signals in Underground Mines", 

Collins Radio Group, Rockwell International Corporation, 

Final Report, Bureau of Mines Contract H0366028, September 1977. 

(2) T.S. Cory, "In-Situ Measurement of Coal Seam Conductivity Using 

a Paral le l Wi re Transm1.ssion Line Method", Col l ins Groups, 

Rockwell International Corporation, Special Technical Report, 

Bureau of Mines Contract H0377053, 18 May 1978. 

(3) R.L. Lagace, A.G. Emslie, M.A. Grossman, "Vodelling and Data 

Analysis of In-Mlne Electromagnetic Wave Propagation", Arthur 

D. Little, Inc., Interim Report, Task Order #4, Bureau of Mlnes 

Contract H0346045, May 1978. 

(4) R.L. Lagace, A.G. Emsl ie, "Analysis of MF Propagation Data from 

Margaret #I I, Nanty Glo, Ehrenfeld, And Adrian Coal Mines", 

Arthur D. Little, Inc., Working Memorandum, Task Order 64, 

Bureau of Mines Contract H0346035, May 1978. 

(5) R.P. Decker, "Research and Development Contract for Coal Mlne 

Communication System, Vol. 3 Theoretical Data Base", Collins 

Radio Co., Final Report, Bureau of Mines Contract H0232056, 

Section 6 pp 6-1 to 6-30, 15 November, 1974. 

Summarizing: 

(A) W. Bensema, M. Kanda, J.W. Adams, "Electromagnetic Noise 

in Robena #4 Coal Mine, NBS Technical Note 654, April 1974, 

( work performed under Bureau of Mlnes Contract H0133005 ). 

(0) J.W. Adams, W.D. Bensema, M. Kanda, Electromagnetic Nolse 

in Grace Mlne", NBSlR 74-388, June 1974, Bureau of Mines 

Contract H0133005. 

(C) M. Kanda, J.W. Adams, W.D. Benserna, "Electromagnetic Noise 

in McElroy Mine", NBSlR 74-389, June 1974, Bureau of Mlnes 

Contract H0 133005. 

(D) W.D. Bensema, M. Kanda, J.W. Adams, "Electromagnetic Noise 

in ltmann Mine", NBSlR 74-390, June 1974, Bureau of Mines 

Contract H0 133005. 

(El W.W. Scott, J.W. Adams, W.D. Bensema, H. Dobroski, 

"Electromagnetic Noise in Lucky Friday Mine", NBSlR 74-391, 

October 1974, Bureau of Mlnes Contract H0133005. 
(6) Loc. Ci t. R.L. Lagace, A.G. Ems l le, M.A. Grossman. 

(7) Loc. Cit. R.L. Lagace, A.G. Emslie. 

(8) A.G. Emslie, R.L. Lagace, R.H. Spencer, P.F. Strong, "Theory of 

the Dedicated Wire as a Means of Alding Propagation on a Trolley 

Wire", Arthur D. Little, Inc., Working Memorandum 1-8, Bureau of 

Mlnes Contract H0346045. 

(9) Loc. Cit. A.G. Emslie, et.al. 

( I0)T.S. Cory, "Electromagnetic Noise 8 Propagation In Low-Coal Mlnes, 

Sumnary Data Report - I, Helvetia Coal Co. Margaret #!I Mine", 

Collins Groups, Rockwell lnternatlonal Corporation, Bureau of 

Mi nes Contract H0377053. 

(1I)T.S. Cory, "Electromagnetic Noise & Propagation In Low-Coal Mines, 

Sumnary Data Report - 2, Upshur Coals Corporation Adrian Mine". 

Collins Groups, Rockwell International Corporation, Bureau of Mines 

Contract Ho377053. 

(12)T.S. Cory, "Electromagnetic Noise & Propagation in Low-Coal Mines, 

Sumnary Data Report - 3, Bethlehem Steel Coal Mine #31 Nanty Glo", 

Collins Groups, Rockwell International Corporation, Bureau of Mines 

Contract H0377053. 

(13)T.S. Cory, "Electromagnetic Noise & Propagation in Low-Coal Mines, 

Sumnary Data Report - 4,Bethlehem Steel Coal Mine #38D Ehrenfeld", 

Collins Groups, Rockwell lnternatlonal Corporation, Bureau of Mines 

Contract H0377053. 

(14)T.S. Cory, "Electromagnetic Noise & Propagation In Low-Coal Mines, 

Sumnary Data Report - 5, National Mine Corp. Stlnson #3 Mine", 

Collins Groups, Rockwell lnternatlonal Corporation, Bureau of Mines 

Contract H0377053. 
PREPARED FOR: 

SPECIAL TECHNICAL REPORT ....................... 

IN-SITU MEASUREMENT OF COAL SEAM CONDUCTIVITY 

USING A PARALLEL WIRE TRANSMISSION LINE METHOD 

Technlque Development 

Technique Application in Two Mines 

PREPARED BY: 

Col l i ns Groups 

Rockwe I I International Corporation 

400 Collins Road N.E. 

Cedar Rapids, Iowa 52406 

Under: Bureau of Mines Contract ~0377053 

Terry S. Cory, P.E. Subcontract C-651672 

Terry S. Cory, P.E. 

2857 West. Mount Vernon Road S.E. 

18 May 1978 
1.0 INTRODUCTION 

The conductivity of coal seams greatly affects the ability to transmlt 

radio waves underground to any significant distance. Recent Fieldstrength 

measurements and testing of two-way radios at medium frequency in coal 

mines under Bu Mines sponsershi p have demonstrated comnun lcatl on ranges 

as great as 1600 feet ( in the Pittsburgh seam ) and as little as 400 feet 

( in the Herrin #6 seam and others ) in areas without conductors. The 

difference in range is due in part to differences in coal seam conductlvlty 

in the "para1 le l plate wavegul de " formed by the seam sandw l ched between 

the overburden/underburden rock. 

Two-way radio transmission at medium frequency is expected to have a 

significant impact on future underground coal mine operations In some 

mines. The design of systems embodying this type of transmisslon will 

require a knowledge of coal seam conductivlty ( as well as, for that 

matter, overburden/underburden conductivity and a means to simply 

obtain it in particular mines. 

This report presents the results of in-situ conductivity measurements 

in two seams employing a simple empirical technique which may have wide 

appl icabi l ity in the future. The results of these measurements confirm 

the low conductivity values expected based on computer model ing analysis 

of extensive fieldstrength measurements by ADL. 

Previous measures of coal seam canductlvity have been made largely on 

samples anaiysed in thellaboratory following removal frm the mine. 

These results suggest that the conductivity is a strong function of 

frequency down to at least I MHz, is strongly affected by water and ash 

content, and could be in the lo-* to mho/meter range. The in-situ 

estimates of coal seam conductivity derived from the field strength 

measurements suggest that the conductivlty i s a t mst weakly dependent 

on frequency in the medium frequency range. The resuits reported herein 

support this suggestion. 
The technique for conductivity determination involves measurement of 

the open and short circuit impedance magnitudes of a parallel wire 

transmission line in close proximity to the coal using two pieces of 

simple battery operated equipment, a current probe, and the transmission 

line. This data is easily reduced to provide a measure of the normallzed 

phase constant along the line as a function of frequency. The 

conductivity is then determined by fitting the measured data with a 

computed curve; the algorithm, for which, is a function of conductivity. 

The accuracy of the results are not signlflcantly dependent on the 

precise spacing of the test line from the coal. 

The technique has been demonstrated to be effective for use in both 

conventional and continuous mining sections. 

The results reported herein were obtained in March, 1978 in the 

Bethlehem Steel Coal Mine( Ehrenfeld)#38D ( Lower Freeport seam ) In 

Cambria County Pennsylvania, and in May 1978 in the National Mine Corp. 

Stinson #3 Mine ( El khorn 13 seam ). 
2.0 SUMMARY 

The results of the testing reported herein are signlflcant in two 

areas; namely, the technique - its applicability and accuracy, and 

the results themselves - their values and frequency dependence. 

2.1 MEASURED RESULTS 

(I) The conductivity in the Lower Freeport seam data sample is 

estimated to be 1.05 x mho/meter 2 10% and essentla l ly 

Independent of frequency. The coal seam relative dielectric 

constant is estimated to be about 2.3. 

(2) The results of (I) are applicable over the frequency range of 

at least 100-600 KHz. 

(3) The conductivity in the Elkhorn #3 seam data sample is estimated 

to be ).7 x mho/meter - + 10% and essential ly independent of 

frequency. The coal seam relative dielectric constant Is 

estimated to be about 2.0. 

(4) The results of (1) are applicable over the frequency range of 

at least 100-800 KHz. 

2.2 MEASUREMENT TECHNIQUE 

(1) The dynamic frequency range of measurement is between some low 

frequency ( typical ly 80-100 KHz for mho/meter conductivity 

where the conductivity dependence of the normalized phase 

constant becomes weak, and the frequency at which the relative 

dielectric constant predominates over the conductivity, d/wso 

( for mho/meter and relative dielectrlc constant of 2-2.5, 

the range is typically 600-800 KHz ). 
(2) The technique Is relatively independent of the precise spacing 

of the test line from the coal. For the smoother continuously 

mined Lower Freeport data sample, the low frequency normalized 

phase constant was about 1.88 for an average spacing of the 

wires from the coal of 9.5 wire radii ( 0.3 inches ). For the 

rougher conventionally mined Elkhorn #3 data sample, the low 

frequency normal ized phase constant was about 1.55 for an average 

spacing of the wires from the coal of about 22.2 wire radii 

( 0.71 inch ). 

(3) The phase constant accuracy based on the low frequency Iimlt 

of impedance measurement is a function of line length. To 

obtain accurate measurements below 100 KHz, a line length of 

at least 200 feet is required. 

(4) The quasi-frequency independence of the conductivity was 

establ ished by observing the "goodness of f i t" of computed 

and measured results curves having the same shape and by 

observing the difference in shape of curves where the 

conducti vity is changing with frequency. If the conductivity 

Increased substantial l y wi th frequency, Instead of gl vlng 

an abrupt rolloff with frequency and a monotonic decrease 

in phase constant, the plot of B/Po with frequency would 

either be nearly linear ( decade lncrease in conductivity 

for decade frequency Increase ) or exhibit a region of 

increased negative slope between regions of lesser negative 

slope. 
FIGURE I 

GEOMETRY OF PARALLEL WIRE LINE NEAR COAL FOR CALCULATIONS 
3.0 TECHNICAL APPROACH 

The technique consists of measuring short and open circuit impedance 

magnitudes on a balanced-fed parallel wire line with frequency using 

simple instrumentation from which the normalized phase constant with 

frequency is derived, and then fitting a computed curve to the measured 

data using an algorithm where the normalized phase constant is a 

function of conductivity. 

3.1 COMPUTATION ALGORITHM 

The formal derivation for the phase constant of the parallel wire line 

is beyond the intended scope of this report. The expression was 

derived considering the lowest order TM mode on a coaxial line with a 

lossy outer conductor. The determinental equation for the complex 

propagation constant was reduced to a form containing logarithms by 

making small angle approximations to the Hankle functions. Then, using 

static field mapping, the geometry was successively mapped to a single 

conductor over a lossy halfspace ( assuming that the spacing from the 

halfspace was much greater than the conductor radius I and then to a 

balanced line pair over the lossy halfspace ( assuming that the 

conductor spacing was much greater than the wire radii ). The geometry 

of the line over the lossy halfspace is illustrated in Figure I. 

The resulting expression for the normalized phase constant is implicit. 

The expression was solved on an HP-67 iteratively assuming a startlng 

value for the phase constant, conputing the result explicitly, and 

then adjusting the starting value each time until convergence was 

obtained. 
The expression for the normalized phase constant is: 

where, 

4- 2aS 

[.-jaee][n ( -) - In ( A I] 

at 

where, 

a is the spacing of each conductor from the haifplane s 

ad is the spacing of the parallel conductors 

al is the conductor radius 

6,Gr are the conductivity and relative dielectric constant 

of the ha1 f~lane 

The expression is of the form 

solving iteratively on an HP-67 with a starting value ofF = fi for 

@/(lo 

a60 

and modified in each step as 

within a specified degree of accuracy. 
The normal i zed phase constant is taken to be the magnitude of the 

complex result. 

3.2 EMPIRICAL TECHNIQUE 

The line parameters were chosen to confine the transverse fringing 

fields of the line to the coal seam so that the much higher overburden/ 

underburden conductivity would not influence the results. A line 

spacing of 6 inches was chosen with the line conductors being #I4 

wire. The line was attched as close as possible to the rough coal rlb 

face using nails or spads through spacers supporting the iine. The 

line was driven balanced from an HP-204C signal generator. The 

impedance magnitude data was obtained by separate measurement of the 

input line voltage and the input line current ( and then, of course, 

taking the r a t i o o f voltage to current ). The current was measured 

using a Stoddard current probe with a prior calibrated relationship 

between the line current and the probe output voltage. The probe 

output voltage and the balanced line voltage were both measured using 

an HP-4038 voltmeter. The arrangement of the measuring equipment is 

illustrated in Figure 2. The current and voltage were measured for 

both open circuit and short circuit conditions of the transmission 

line. The calibration curves for the Stoddard current probe are 

given in Figure 3. 

3.3 REDUCTION OF MEASURED DATA 

The normalized phase constant was determined from the measured 

impedance data through the use of a Smith Chart. The open clrcult 

and short circuit impedances always lie on opposite sldes of the 

chart such that they are joined by a straight edge through the chart 

center. For a given data point, and using a normalized Smlth Chart 

( unity Zo at the center 1, the straight edge is rotated until alignment 

is obtained between a normal ized short circuit reactance value ( on 

the right-hand edge of the chart ) and a normalized open circult 

reactance value equal to the short circuit value multiplied by the 
HP-204C SIGNAL GENERATOR 

NOMINAL RANGE 20-1000 KHZ 

600 OHM BALANCED OUTPUT 

STODDARD CURRENT PROBE 

PARALLEL WlRE TRANSMISSION L

200-300 FEET #I4 WlRE SPACED 

L lNE END EITHER SHORT 

O

OPEN C

FIGURE 2 

MEASUREMENT EWIPMNT ARRANGEMENT FOR DETEIWINING THE MAGNITUDE OF 

THE OPEN AND SHORT CIRCUIT LlNE IMPEDANCE OF PARALLEL WlRE TEST LlNE 
000 1 

008 

OOL 

009 

00s 

OOP 

OOE 
ratio of the measured open circuit-to-short circuit Impedance 

magnitudes. Once this alignment is obtained, the line electrical 

length is given either as the wavelengths from the chart top ( short 

circuit to the right-hand alignment point or as the wavelengths 

frm the chart bottom ( open circuit ) to the left-hand alignment 

point. The normalized phase constant is then this electrical length 

divided by the calculated free space electrical length knowing the 

physical length of the line and the frequency. The Smith Chart 

alignment process is i l l ustrated in Figure 4. 

It should be noted that only the r a t i o o f the open circuit-to-short 

circuit impedance magnitudes Is required to implement the technique. 

If the same value of driving current can be maintained for both 

short and open circuit conditions, then a simplification of the 

empirical and data reduction methods results. Under this condition, 

this ratio is just the ratio of open circuit-to-short circuit line 

vo I tage. 

In obtaining a computed fit, a low frequency plus an arbitrary 

conductivity and dielectric constant in the expected range are 

taken first and the ratio of as/ai is varied .unti I computed and 

measured values match. The conductivity is then varied until a fit 

is obtained over the central portion of the frequency range. The 

dielectric constant is then varied for best fit over the high 

frequency portion. The final fit is obtained considering small 

incremental changes in both a /ai and conductivity. s 
OPEN CIRCUIT 

FIGURE 4 

ILLUSTRATION OF THE USE OF THE SMITH CHART TO OBTAIN THE 

TRANSMISSION LINE ELECTRICAL LENGTH FOR A RATIO OF Zoc /ZSC 

OF 25 
4.0 PRESENTATION OF DATA 

The raw data for each of the two sets of measurements are given in 

the Appendix to this report. 

Summaries of the reduced data in tabular form for the two measurement 

sets are shown in Tables I and 2. 

The Ehrenfeld #38D reduced data is shown only for 80-600 KHz although 

data was measured from 20-1200 KHz. This is because this was the first 

set 03 data reduced and the frequency "edges" result in smal l electrical 

lengths on the Smith Chart which are hard to read accurately unless 

extreme care is taken. For this first set, a very close fit was obtained 

using only the "easy-to-reduce" data. The Stlnson #3 data was reduced 

from 40-800 KHz exercising greater carewith the Smith Chart as the 

measured data sample was more scattered. 

The Ehrenfeld #38D data is given in Figure 5 showing both the nominal 

fit assuming the conductivity was frequency invariant plus the fit wlth 

small excursions in conductivity from nominal. The accuracy of the 

nominal fit was, thus, estimated to be 2 10%. 

The Stinson 83 data is given in Figure 6 showing both the nominal fit 

assuming the conductivity was frequency invariant plus the fit with 

small excursions in the conductivity from nominal. The accuracy of the 

nominal fit was, again, estimated to be + 10%. 

To illustrate the effect of conductivlty which increases llnearly wlth 

frequency, computations were made for comparison with the Ehrenfeld #38D 

nominal fit assuming linear increases of x 10 and x 5 for a decade in 

frequency matched to the geometric mean frequency of the 80-600 KHz 

range. This data is given in Figure 7. By noting the shapes of the x 10 

and x 5 curves and the fact that the measured data was very closely fit 

with the mdel on a frequency invariant basis, the conductivity was 

judged to be quasi-frequency independent. 
REDUCED DATA FOR CONDUCTIVITY MEASUREMENTS IN BETHLEHEM STEEL COAL MINE 

#38D EMPLOYING ME PARALLEL WIRE TRANSMISSION LINE TECHNIQUE 

SHORT C I RCU I T 

FREQ( KHz) I(MA) V(V0LTS) IZI I(MA) - -- 

80 8.25 0.77 93.3 3.20 

100 7.85 0.99 126.1 3.43 

200 8.60 2.15 250.0 5.65 

400 6.75 4.8 711.1 7.20 

600 0.90 4.0 4444 8.50 

OPEN CIRCUIT 

V(V0LTS) IZI Iz~~/z~~$ - 

4.8 1500 16.08 0.0382 0.0

4.6 1341.1 10.634 0.0475 0.0

3.4 601.8 2.407 0.0905 0.0

1.7 236.1 0.332 0.1670 0.1

0.33 38.8 0.0087 0.2350 0.1
F REQ (KHz) 

REDUCED DATA FOR CONWCTIVITY MEASUREMENTS IN NATIONAL MINE CORP. 

STINSON #3 MINE EMPLOYING THE PARALLEL WIRE TRANSMISSION LINE TECHNIQUE 

SHORT CIRCUIT (PEN CIRCUIT 

I (MA) V(V0LTS) IZ( I (MA) V(V0LTS) IZI IZOC/ZSC( @ - -- - Po 
FZ W 89 W. 

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t--J 

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WSJ 

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iLU 

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FIGURE 7 

COMPUTED RESULTS BASED ON EHRENFELD #38D DATA ILLUSTRATING THE SHAPE OF T

NORMALIZED PHASE VELOCITY CURVES WITH FREQUENCY FOR THE FREQUENCY INVARIA

NCMINAL FIT AND FOR ASSUMED LINEAR IiiCREASE IN CONDUCTIVITY WITH FREQUEN
RAW DATA FROM COAL SEAM CONDUCTIVITY MEASUREMENTS VIA OPEN 8 SHORT 

CIRCUIT IMPEDANCE MEASUREMENTS ON PARALLEL WIRE TRANSMISSION LlNE 

A DATA FROM BETHLEHEM STEEL COAL MINE #38D EHRENFELD IN LOWER 

FREEPORT SEAM 

250.3 FEET OF LlNE DEPLOYED AROUND COAL PILLAR 

SHORT CIRCUIT HP-4038 READING 

CURRENT PROBE Ll NE VOLTAGE 

0.066 VOLTS 0.7 VOLTS 

0.042 1.55 

0.0225 2.60 

0.0037 4.0 

0.0 14 5.0 

0.020 4.8 

0.019 3.40 

0.0135 2.15 

0.0068 0.99 

0,0054 0.77 

0.0040 0.57 

0.0028 0.38 

0.00044 0.295 

OPEN CIRCUIT HP-4030 READING 

CURRENT PROBE LlNE VOLTAGE 

0.03 VOLTS 3.4 VOLTS 

0.068 4.62 

0.057 1.90 

0.037 0.33 

0.030 1 ,oo 

0.022 1.70 

0.013 2.55 

0.008 3.40 

0.0024 4.60 

0.0016 4.80 

0.00095 5.0 

0.00043 5.2 

0.00010 5.3 
B DATA FFEDM NATIONAL MINE CORP. STINSON #3 IN ELKHORN #3 SEAM 

201 FEET OF LlNE DEPLOYED ALONG RIB 

SHORT CIRCUIT HP-4030 READING 

CURRENT PFEDBE LlNE VOLTAGE 

0.020 VOLTS 2.20 VOLTS 

0.007 3.15 

0.002 2.63 

0.009 3.40 

0,010 2.55 

0.020 3.70 

0.020 3.15 

0.020 2.85 

0.020 2.60 

0.010 1.21 

0.0060 0.70 

0.0050 0.58 

0.0031 0.36 

0.0020 0.235 

0.0010 0.1175 

OPEN CIRCUIT HP-4038 READING 

CURRENT PROBE LlNE VOLTAGE 

0.100 VOLTS 

0.060 

0.050 

0.040 

0 030 

0.020 

0.020 

0.010 

0.010 

0.0050 

0.0010 

0.00090 

0.00050 

0.00020 

0.00015 

2.80 VOLTS 

0.540 

0.205 

0.73 

1.10 

1.25 

2.22 

2.00 

3.6 1 

4.40 

3.50 

4.90 

4.90 

4.70 

5.35