Propagation of EM Signalss in 

Underground Mines 

Prepared for 

UNITED STATES DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

Collins Commercial Telecommunications Group 

Circuit Switching Systems Division 

Cedar Rapids, Iowa 52406 

Rockwell International 

FINAL REPORT 

Contract No. H0366028 September 1977 
DISCLAIMER NOTICE 

The views and conclusions contained in this document are those of the authors and 

should not be interpreted as necessarily representing the official policies or recommendations of the Interior Department's Bureau of Mines or of the US Government. 
I. Tide and Subtitle 

Propagation of EM Signals In Underground Mines 

REPORT DOCUMENTATION PAGE 

5. Report Dace 

22 August 1977 

6. 

I. Report No. 2. 

I. Author(r) 

Terry S. Cory 

I. Supplemenrary Notes 

3. Recipient's Accerrnon No. 

8. Performing Organization Report No. 

I. Performing Organization Name and Address 

Rockwell International 

Commercial Telecommunications Group 

1200 North Alma Road 

Richardson, Texas, 85080 

12. Sponsoring Organization Name and Address 

Office of The Assistant Director of Mining 

Bureau of Mines 

Department of the Interior 

Washington, D.C. 20241 

6. Abstract 

This report is a comprehensive summary of the results of the propagation measurements program 

conducted for the US Bureau of Mines under Contract H0366028. Data was gathered in the MF 

frequency range from a cross sample of six mines representative of the industry having typical 

wireless requirements. From the raw data which was gathered, a logical method of data reduction 

is presented which culminates in a set of average attenuation characteristics for all mines visited. 

These characteristics define a typical MF wireless system when the communication range 

requirements are known. Direct through-the-earth propagation and the range enhancement 

mechanism due to coupling on and off conductors are evaluated and related to the planning of a 

typical wireless MF communications system. 

10. ProjecrlTarklWork Unit No. 

93-7890 

11. Contract or Grant No. 

H0366028 

13. Type d Report 

Final Report 

14. 

propagation characteristics; conductors; overburden 

and underburden conductivities; communication range; 

MF frequencies. 

7. Originaror's Key Words 18. Availability Statemenr 

I 

9. U.S. Securiry Clarrif. of the Report 

Unclassified 

1/2 

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

Unclassified 

21. No. of Pages 

174 

22. Price 
FORE WORD 

This report was prepared by Collins Commercial Telecommunications Group, Rockwell International, Cedar Rapids, Iowa under USBM Contract Number H0366028. The contract was initiated under the Coal Mine Health and Safety Program. It was administered under the technical 

direction of PM&SRC with Mr. Harry Dobroski acting as the Technical Project Officer. Mrs. 

Pearl A. Shapert was the contract administrator for the Bureau of Mines. 

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

period August 2, 1976 to September 30, 1977. This report was submitted by the authors on 

April 26, 1977. 
Table of Contents 

Report Documentation Page ........................................... Foreword .................................................................... 1.0 Introduction .......................................................... 1.1 Program Background ............................................. 1.2 Summary of Program Goals and Technical Objectives .. 1.3 Program Overview ................................................ 1.4 Report Contents .................................................... 2.0 Executive Summary ............................................... 2.1 Overview of Results ............................................... 2.1.1 Results Summary ................................................ 2.1.2 Correspondence of Results to Program Goals .......... 2.1.3 Summary of Evaluation Criteria ............................ 2.2 Specific Observations and Conclusions ...................... 2.3 Recommendations .................................................. 3.0 Technical Approach ............................................... 3.1 Empirical Techniques ............................................ 3.1.1 General Measurement System Redesign .................. 3.1.2 Transmit Antenna and Antenna Coupler Design ......... 3.1.3 Receive System Calibration .................................. 3.1.4 Deployment of Measurement Equipment .................. 3.2 Data Reduction and Display Methods ......................... 4.0 Compended Results and Analysis .............................. 4.1 Reduction of Measured Field Strengths to Maximum 

Communication Range-Presentation of Reduced 

Data .................................................................... 37 

4.2 Analysis . and Development . of System Application 

of Data ................................................................ 4.2.1 Quasi-Conductor-Free Maximum Communication 

Range Vs Frequency ............................................ 4.2.2 Conductor Proximity Maximum Communication 

Range Vs Frequency ............................................ 4.2.3 Range Variability Assessment ............................... 5.0 Individual Mine Tests Descriptions ........................... 5.1 Ireland Mine ......................................................... 5.2 Inland Steel Coal Mine No . 1 (Sesser) ........................ 5.3 Consolidation Coal Mine No . 5 (Robinson Run ). ............ 5.4 Eastern Associated Coal Mine Federal No . 1 .............. 5.5 Virginia Pocahontas No . 1 Mine ...................... ...... 5.6 Peabody Coal Company Mine No . 10 .......................... 6.0 Conclusions and Recommendations ........................... 6.1 State of Knowledge of Propagation Effects .................. 6.2 Usability of Program Results .................................. 6.3 Potential MF Wireless Communication Applications .... 
Table of Contents (Cont) 

6.4 Recommendation for Further Measurements 

and Analysis ..................................................... 6.5 Typical System Performance Considerations ............ 6.6 Effect of an Ideal Repeater in Conductor-Free 

Areas ............... ................ ........ ......................... 6.7 ~ffect ofan Ideal Repeater in Proximity to 

Conductors. ... .... . . .. .. .. . ... . ... . . .. .... .... . . .. . ... . ... . . .. .... . Appendix A Mine Test Data ........................................ Appendix A1 Ireland Mine Test Data at Medium 

Frequency ....... . . .. .. .. .. . . . . .... . . .. .... .... . ... . ... . Appendix A2 Sesser Mine Test Data at Medium 

Frequency and UHF ................................. Appendix A3 Consolidation Coal Mine No. 95 

(Robinson Run Portal) .................... .... ..... Appendix A4 Eastern Associated Coal Federal No. 1 

Mine (Eddy Portal) .................................. Appendix A5 Island Creek Coal Co. Virginia 

Pocahontas No. 1 Mine ............................. Appendix A6 Peabody Coal Co. Mine No. 10 .............. ..... Appendix B Errata and Added Calibration Information..... 

Appendix C Magnetic Field Strength Sensitivity of an 

FM Receiver ........................................... References ....... . ... . ... . . .. ... . . . .. .. .. .... . ... . . .. ... . . ... .. .. .. .. . ... . 
List of Illustrations 

Figure ~ 

1 Maximum Com Range Vs Operating 

Frequency in Areas of Coal 

Mines - All Data Sets ............. 2 iliaximum ~omrnunication-~an~e Vs Operating 

Frequency in Proximity to Conductor's RX 

From Conductor(s), TX 

- Pittsburgh Seam ....................... 3 Maximum on Range Vs Operating 

ity to Conductor's RX 

Antenna 2 Me 

nductor.. .................................... 6 Measureme Configurations ............ 

.................. 

Frequcncy Antennas ............................................. 13 Maximum Communication Rangc Vs @crating 

Frequency in Areas of 

Coal Mines - ................... 

................ 
List of Illustrations (Cont) 

Figure page 

15 Maximum Communication Range Vs Operating 

Frequency in Conductor-Free Areas of Coal 

Mines - Pocahontas No. 3 Seam Data Sets ................... 41 

16 Required Field Strength Sensitivity Levels for 

Mine Wireless Radios Based on the CollinsDeveloped Mine Wireless Prototype Radios 

at 520 kHz ............................................................. 44 

17 Estimated Noise Magnetic Field in Coal 

Mines Extrapolated Beyond 200 kHz 

From NBS Data ..................................................... 61 
1.0 INTRODUCTION 

This is the Final Report covering work performed by Collins Telecommunications Group, 

Rockwell International under Bureau of Mines Contract H0366028 entitled Propagation of 

EM Signals in Underground Mines. 

The technical work was performed by Epectra Associates, Inc. personnel under Subcontract 

C-651333 with administrative direction provided by Collins Telecommunications Group, 

Mine Electronics Department, and with technical assistance provided by Collins Telecommunications Group personnel using Collins Telecommunications Group facilities. The technical 

work was directed by the Principal Investigator, Terry S. Cory, P. E. under Spectra 

Associates, Inc. Subcontract 002607. 

The primary program work consisted of performing measurements of magnetic field strength 

in six underground coal mines coordinated with a concurrent theoretical study, performed by 

the Arthur D. Little Co. (ADL) by action of a Goal Setting Committee. The Goal Setting Committee members included personnel from the Bureau of Mines, ADL, Collins Telecommunications Group, Spectra Associates, Inc., and the Principal Investigator. 

The test equipment was furnished by Collins Telecommunications Group and the Bureau of 

Mines, except for special antennas and antenna matching assemblies designed during this 

program. The magnetic field strength measurement sets from each mine were separately 

reported in each of six interim Summary Data Reports. The analysis and assessment of the 

measured data together with a summary of the specific work performed is the subject of this 

report. 

The measurements were performed by a team consisting of Bureau of Mines personnel, a 

Collins Telecommunications Group furnished technician, and the Principal Investigator. 

1.1 PROGRAM BACKGROUND 

Bureau of Mines (Bu Mines) investigations during 1973-74 identified a possible need for face 

area communications forward of the section phone toward improving operating efficiency in 

some mines. The coverage area required for this communication could extend forward at 

least 750 feet from the section phone and, if the miner(s) was driving, say, 12 parallel entries 

(characteristic of mains and submains in some mines) on 90- to 100-foot centers, the required 

communication range could be as great as 1,300 feet. 

In December of 1974 and January of 1975 as part of Phase 1 of a subsequent Bu Mines contract 

with Collins Telecommunications Group (H0346067) for development of prototype portable and 

base station mine wireless radio equipment, field strength measurements were made in 

Consolidation Coal Company's Rose Valley (I)* and Ireland mines (2) by Spectra Associates, 

Inc. under Collins Telecommunications Group Subcontract C-615171. These measurements 

were made to determine maximum communication range and to select the operating frequency 

for the prototype radios. 

Previous theoretical work performed in 1974 under Bu Mines Contract H0232056 to Collins 

Telecommunications Group by Spectra Associates, Inc. under Subcontract C-696447 using 

homogeneous earth theory (3) predicted maximum communication ranges of the order of 750 

feet (depending on the electrical ground parameters) employing VMD orientation of both 

transmit and receive loop antennas. In August of 1974, Bu Mines personnel range tested mine 

*Numbers in parentheses refer to References at the end of this report. 

9 
wireless portable radios made by ECAM Ltd. of Braamfontein, South Africa, in the 

conductor-free 8-north escapeway area of the Ireland mine. They were able to communicate 

to a range of 1,200 feet which, at the time, was thought to be an anomaly. The late 1974/ 

early 1975 testing under the Mine Wireless program not only confirmed the 1,200-foot range 

in Ireland, but also postulated the HMD orientation of both antennas to be optimum; meaning 

the possibility that transmission had occurred via a seam waveguide mode. The Rose Valley 

data was tahen to be inconclusive as the transmission path was only one entry removed from 

a 7,200 V ac power cable. That the 1,200 feet achieved in Ireland almost matched the desired, 

1,300 feet was only coincidental. 

ADL, using a 3-layer (5) wave equation formulation was able to "matcht1 the measured Ireland 

data, but only by using a seam conductivity of the order of 10-4 mho/meter (at that time considered unthinkably low) and an overburden/underburden conductivity approaching 1 mho/ 

meter (which seemed very high). The Ireland mine measurements resulted in the selection of 

nominally 500 kHz for the Mine wireless operating frequency. 

The validity of the Ireland data was suspect in terms of being representative of a number of 

mines. The concern over these results engendered this current measurement program. As 

initially conceived, this program was to investigate wireless radio propagation in both mf and 

uhf frequency ranges (low coal) and also in hard rock and metal mines. Subsequent planning 

limited the measurements to the mf region in medium-to-high coal. 

This program came under contract effective in July 1976, and has continued through the time 

of this writing. 

1.2 SUMMARY OF PROGRAM GOALS AND TECHNICAL OBJECTIVES 

The major thrust of this program from the onset has been verification (or nullification) of the 

1975 Ireland results as being representative of, at least, the Pittsburgh seam and to develop 

a more complete understanding of the radio propagation mechanism(s) involved. 

As the program planning developed, the consensus of the Goal Setting Committee was to investigate and characterize the radio propagation in as many seams representing as many 

high-production coal areas as possible. As it occurred, these were the Pittsburgh seam in 

northern West Virginia, the Pocahontas #3 seam in southern West Virginidvirginia panhandle, and the Herrin #6 seam in central-to-southern Illinois. 

~mphasis was placed, during the measurements, on obtaining field strength vs range and 

frequency in quasi-conductor-free areas in sufficient detail to enable ADL to fit the measured 

data with computed data using their model. This, then, permitted estimates of seam and 

overburden/underburden conductivity for each test area to be made. 

As the particular sets of field strength measurements are summarized in the Summary Data 

Reports with the data from each of the mines given in the appendix to this report, it was 

decided not to simply resummarize this data in field strength form for this report. The data 

is compended in terms of maximum communication range vs frequency, thus leading back to 

results that can be used directly in the solution of communications problems. This same 

form for compending the measured field strength data was used with the Ireland Mine data (4) 

from the previous program which led to the selection of 500 kHz as the operating frequency. 

The program structure was configured to permit redirection of both the goals and the particular data taking objectives in particular mines as the work progressed. The preliminary 

planning for the first two mines was determined at the program kick-off meeting in August by 

the Goal Setting Committee. During the first two mine visits, the character of the data taken 
was discussed day-by-day either in face-to-face working sessions (when Bu Mines and ADL 

representatives were present) or verbally by telecon. After each set of mine measurements, 

the raw data and the preliminary reduced data were sent informally to both Bu Mines and 

ADL within a week, followed by an unedited draft of the Summary Data Report within two 

weeks. 

The selection of, and revised technical objectives for, the second two mines were determined 

without a face-to-face Goal Setting Committee meeting by a series of telecons. A second 

Goal Setting Committee meeting was held in December to plan the remaining two sets of 

mine measurements. The format for forwarding preliminary datddata reduction and draft 

report material continued, intermixed with frequent telecons. 

The measurements were performed at a rate of approximately one mine per month. 

1.3 PROGRAM OVERVIEW 

Measurements were performed in six mines in chronological order as follows: 

a. September 1976, Ireland Mine, Ohio Valley Division, Consolidation Coal Co, Moundsville, 

West Virginia- Pittsburgh Seam 

1. Field strength vs range and frequency in $-north submain -- quasi-conductor-free 

and conductor dilute 

2. Field strength mapping of $-north 3-right working section -- conductor-dense 

b. October 1976, Inland Steel Coal Mine #1 (Sesser), Sesser Illinois - Herrin #6 Seam 

1. Field strength vs range and frequency in 1-main east -- quasi-conductor-free 

2. Field strength mapping of 1-main east 5- and 6:left and 9-right working sections -- 

conductor dense 

3. Comparative testing of South African and our mine wireless prototype radios -- 

quasi-conductor-free 

c. November 1976, Consolidation Coal Mine #95 (Robinson Run), Mountaineer Division, 

Consolidation Coal Co., Shimston, West Virginia - Pittsburgh Seam 

1. Field strength vs range and frequency in main-north 2-west -- quasi-conductor-free 

2. Field strength vs range and frequency in main-north 2-west -- conductor proximity 

3. Noise near conductors @ 1000 kHz in main-north 2-west 

d. November 1976, Federal #1 Mine, Eastern Associated Coal Co., Grantown, West Virginia, 

- Pittsburgh Seam 

1. Field strength vs range and frequency in $-main north -- quasi-conductor-free 

2. Field strength vs range and frequency in 3-main left working section -- conductordense 

e. January 1977, Virginia Pocahontas #1 Mine (VP #I), Island Creek Coal Co., Grundy, 

Virginia - Pocahontas #3 Seam 

1. Field strength vs range and frequency in 3-south -- quasi-conductor-free 

2. Field strength vs range and frequency in 2-north #1 plow -- quasi-conductor-free 

3. Range testing Collins mine wireless prototype radios -- quasi-conductor free 
f. February 1977, Peabody Coal Mine #lo, Peabody Coal Co., Pawnee, Illinois - Herrin 

#6 Seam 

1. Field strength vs range and frequency in 1-south 1st west 2nd north working section -- 

quasi-conductor-free 

2. Field strength vs range and frequency in 1-south submain -- quasi-conductor-free 

3. Field strength and noise vs range in 5-l/2-east/l-south junction -- conductor dense 

1.4 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 and conclusions, 

and recommendations all based on the maximum communication range data. 

Section 3.0 presents the technical approach to the program including a program description 

(expansions on paragraphs 1.1 and 1.2), a description of the measurement test equipment, a 

description of the measuring technique(s), and details of the data reduction process. 

Section 4.0 presents the technical formulation of methods used in summarizing the report 

results in terms of maximum communication range and optimum frequency and in estimating 

maximum communication range and optimum frequency in the presence of conductors. 

Section 5.0 presents a description of the tests conducted and a summary of results for each 

of the six mines visited, 

Section 6.0 presents the program conclusions and recommendations, including several 

strawman system calculations to further illustrate the use of the data. 

Appendix A presents complete summary data sets from the Summary Data Reports. 

Appendix B presents a list of "tracks" including any errata and corrections to data previously 

published in the Summary Data Reports. 

Appendix C presents Magnetic Field Strength Sensitivity of an FM Receiver. 

2.0 EXECUTIVE SUMMARY 

Wireless radio transmission at medium frequency is feasible for both section and haulage 

communications in underground coal mines. The radio wave propagation occurs via either a 

coal seam waveguide mode or electromagnetic coupling into and out of mine wiring, or both. 

The capabilities of battery operated portable and base station radios being developed by the 

Bureau of Mines are compatible with this wireless transmission means. The results of this 

measurement program provide a starting point for design and implementation of radio systems for coal mines. Further refinement beyond these results will be necessary to design 

radio systems predictively and to formulate performance requirements for sophisticated 

applications employing multiple radios and repeaters in disciplined operation. 

This report stresses mine wireless communications at medium frequency using the measured 

results rather than dealing only with the intricacies of the measured results themselves. To 

this end, performance measures have been derived in part directly from the measured data 

and in part from simple analyses verifiable from the data. These analyses embody some 

aspects of the Arthur D. Little Co. (ADL) radio propagation analysis method (6) which separately has served toward defining the basic propagation mechanisms and providing the 

theore!3cal data base for this work. The philosophy developed in this report is to define 
typical performance characteristics, using these above measures based on reasonable 

estimates of noise (7), (a), and a simple conductor geometry defined in section 4.0 of this 

report. The performance characteristics defined are in the form of graphs of maximum 

communication range vs frequency. 

2.1 OVERVIEW OF RESULTS 

2.1.1 Results Summary 

The communication range depends primarily on the particular seam electrical characteristics, 

the local radio noise, the proximity to mine wiring, and the operating frequency. Based on the 

typical performance characteristics presented in this report, maximum ranges will generally 

exceed 600 meters with radios located within one entries' distance from a conductor-carrying 

entry and 100 to 300 meters with radios located beyond 2-3 entries' distance from this 

conductor-carrying entry. 

Of the three seams tested (Pittsburgh, Pocahontas No 3, and Herrin No 6) the greatest range 

was achieved in the F'ittsburgh seam and the least range in the Herrin No 6 seam. If both 

radios are located in the same entry as conductors (or in any entries containing connected 

conductor strings), the particular seam characteristics become less important. The greatest 

range differences between seams occur when communicating in areas where at least one radio 

is well removed from conductors. 

Mine wiring conductors extend the communication range well beyond that achievable in their 

absence. Ranges of several miles are obtainable for haulage service if both radio units are 

in entries containing connected conductors. Similarly, complete section radio coverage is 

obtained if one of the radios is close to any conductor leading toward the face. If one or both 

radios are two or more entries away from conductors (three entries in the case of the 

Pittsburgh seam), the communication range is not extended. Elevated suspended conductors 

are better for radio transmission than conductors lying on the floor or closely strapped to 

the roof. 

An examination of the measured data reveals that the frequency range of 700 to 1000 kHz is 

optimum for achieving the optimum communication range in proximity to conductors; and is 

roughly independent of the type of coal seam involved. 

This frequency range is higher than that obtained for transmission along conductors where 

both radios are closely coupled to the conductors. For this latter case, the communication 

range improved with decrease in frequency over the test frequencies considered which varied 

between nominally 100 and 5000 kHz. The optimum area coverage frequency range is largely 

independent of the characteristics of the particular seam and is governed largely by the 

coupling characteristics of radio waves to conductors and by radio noise. 

Radio noise limits the communication range and influences the optimum frequency range for 

maximum area coverage. The greatest communication range occurs when the external noise 

is so low that the radios are set-noise limited. This noise condition occurs in remote areas 

of the mine or in sections and especially when the power is down. Based on the typical performance characteristics of this report, the optimum frequency range for maximum communication coverage is 200 to 500 kHz remote from conductors and 500 to 700 kHz near conductors. 

Noise floors in quiet areas of mines have never been measured at medium frequency. 

The communication range is secondarily dependent on the mine topology, excluding conductors. 

The maximum communication range in areas remote from conductors is shorter when the 

transmission path is through a solid coal block than it is in a room and pillar area. 
Transmission paths through coal pillars at discrete frequencies exhibit a standing wave in 

field strength with range due to the periodic path discontinuities presented by the coal pillars. 

This latter effect has limited practical significance and was only occasionally observed during 

the measurement prograin. 

2.1.2 Correspondence of Results to Program Goals 

Extended lateral through-the-earth transmission, compared to that expected using homogeneous 

earth theory, was first observed in testing in two mines in the Pittsburgh seam in 1975 (9). The 

limited test sample was insufficient upon which to base a technology. The results of this measurement program have confirmed the extended range phenomenon and have provided the basis 

for categorizing mine wireless radio propagation, in six mines comprising 3 seams in 

medium-to-high coal. Concurrent analytical modeling by ADL has enabled the categorization 

of the electrical parameters of major importance in the waveguide transmission mode in 

conductor-free areas using this bask Modeling to account for topological effects remains to 

be accomplished but is of secondary impbrtance at the time of this writing in establishing 

wireless radio feasibility and in providing initial system design guidelines. 

Of significance is the analytical marcage of measured field strength data in quasiconductor-free areas with a conductor coupling and transmission model. A simple model for 

doing this is presented in section 4.0 of this report. This model has permitted reasonable 

computations to be made of combined through-the-coal and conductor-carried transmission 

effects on communication range and operating frequency. 

We have fallen short of the original program goal of measuring the radio noise floor and 

radio noise values in operationally important areas of mines at frequencies above 200 kHz due 

to emphasis in obtaining high quality quasi-conductor free field strength data. Noise in 

particular areas uf a mine can always be measured, however, and thus can easily be made a 

part of particular future system design analysis. Of perhaps more concern is the fact that 

much of the time the measurement receiving equipment was set-noise limited. Knowledge of 

the noise floor is necessary for effective design of base stations and repeaters using large 

antennas. 

Overall, between the measured results of this program and the accompanying theoretical 

analysis of ADL, substantial progress has been made toward predictive modeling of mine wireless performance, although this modeling is not a specific goal of either this program or the 

companion ADL program. The model(s) is simple and imperfect in many respects as a purely 

predictive tool, but it has enabled characterizing the electrical properties of the coal seams 

(and nearby overburden/underburden) with accuracies commensurate with the measurement 

accuracy and the statistical size of the total measurement sample to date. 

2.1.3 Summary of Evaluation Criteria 

Criteria for evaluating communication performance have been based on characteristics and 

specifications for mine wireless portable radio performance put forth by the Bureau of Mines 

and which have evolved as a result of the mine wireless prototype radio development by 

Collins Telecommunications Group; and also on noise performance previously determined by 

the National Bureau of Standards (10) and as summarized by Collins Telecommunications 

~roup/Spectra Associates (11). These characteristics and specifications were known to the 

author prior to performing the mine measurements. The measured results were gathered 

largely using test equipment with a dynamic range encompassing that of portable radio 

designs. Periodic tests were performed using actual mine wireless prototype radios and 

similar radios developed by ECAM, Ltd. in South Africa. 
The criteria for performance evaluation basbd on the portable radio equipment include the 

following: 

a. NIA = 2.5, the transmit magnetic curre moment of the radio using a loop antenna 

b. Receive sensitivity of 0.02 p~/meter 

c. Receive noise bandwidth of 12 kHz. 

The above are applicable to any operating fr quency from nominally 100 to 5000 kHz. i 

The noise criteria used included the followi : "k 

a. Radio set noise limit 

b. Median mine noise, based on the NBS w rk, and defied by Decker (12) 

HN = 121.5 - 32.5 loglO f (HZ) 

in dB greater than 1 pA/meter/ H I 

2.2 SPECIFIC OBSERVATIONS AND CONCL SIONS I' 

The frequency dependence of the 

summarized for the three seams 

environmellts in figure 1. These summary mean of all applicable data sets and include the Ireland 

Specific observations that may be drawn fro figure 1 include the following: 'r 

a. The increase in optimum frequency withincrease in noise; from 400 kHz to 800 kHz in 

the Pittsburgh seam being typical 

b. The decrease in optimum frequency in from the Pittsburgh seam results to 

the Pocahontas no. 3 seam results to 6 seam results; from 800 to 500 kHz 

c. The progressive range going from the Pittsburgh 

seam results to Herrin no. 6 seam results; 

from 300 being typical 

The maximum range obtained using the mine wireless prototype radios in Sesser and VP no. 1 

mines are representative of performqce in he median-mine-noise case. Range tests performed with the South African radios in the I eland mine resulted in roughly 400 meters which 

is between set-noise and median-mine-noise i 

Considering the variation of optimum freque cy with seam type and noise and the fairly broad 

optimum frequency peaking; the choice of 52 kHz for mine wireless prototype radios was 

wise if the radios were always expected to o erate in quasi-conductor-free transmission 

situations. The Bu Mines desire to achieve 1 1,300-foot range in a conductor-free area 

(assumed to be near the face) may be possibl/e in many Pittsburgh seam mines as the face 

areas are generally the quietest. I 

The frequency dependence of the maximum range with radios located in varying proximity to conductors is typified for and median mine noise in figures 

2, 3, and 4. These figures consider the receiver is located two meters 

away from an elevated conductor (or having a surge impedance 

of 50 ohms in the presence of a rock The transmitter is 

assumed located 1, 2, or 3 entries centers. 
- SET-NOISE LIMITED 

- -- MEDIAN MINE NOIS

TX N1A = 2.5 

PITTSBURGH SEAM 

FREQUENCY - KHZ 

Figure 1. Maximum Communication Range Vs Operating Frequency In Conductor-Free 

of Coal Mines - Geometric Average of All Data Sets. 
I2O0 r 

Tx NIA = 2.5 

RX SENSITIVITY 

0.02 rA/METER FOR 

12 DB SINAD. BW = 12 KHz 

MEDIAN MINE NOISE 

ENTRY SPACING 30 METERS 

CONDUCTOR SURGE IMPEDANCE 

50 OHMS 

TX LOCATED 

1 ENTRY AWAY 

CONDUCTOR-FREE 

TX LOCATION 

I Ill 111 I I I ill I I I I I I I 

789 2 34 5 6 789 2 3 45 6 

100 1000 

FREQUENCY - KHZ 

Figure 2. Maximum Communication Range Vs Operating Frequency in Proximity 

to Conductor's RX Antenna 2 Meters From Conductor(s), TX Located 

Remotely - Pittsburgh Seam. 
TX NlA = 2.5 

RX SENSITIVITY 

0.02 pAlMETER FOR 

12 DB SINAD. BW = 12 KHz 

MEDIAN MINE NOISE 

ENTRY SPACING 30 METERS 

CONDUCTOR SURGE IMPEDANCE 

50 OHMS 

Le 

W + 

W POCAHONTAS #3 " S '0° 1 SEAM 

I 

TX LOCATED 

1 ENTRY AWAY 

CONDUCTOR-FREE 

TX LOCATION 

Ill I I I Ill I I I I I I I 

789 234 5 6 789 2 3 45 6 

100 1000 

FREQUENCY - KHz 

Figure 3. Maximum Communication Range Vs Operating Frequency in Proximity 

to Conductor's RX Antenna 2 Meters From Conductor TX 

Located Remotely - Pocahontas #3 Seam. 
RX SENSITIVITY 

0.02 vA/METER FOR 

12 DB SINAD. BW = 12 KHZ 

MEDIAN MINE NOISE 

ENTRY SPACING 30 METERS 

CONDUCTOR SURGE IMPEDANCE 

50 OHMS 

TX LOCATED 

1 ENTRY AWAY 

HERRIN #6 SEAM 

CONDUCTOR-FREE 

TX LOCATION 

111 I 1 I Ill I I I I I I J 

7 89 234 5 6789 2 3 45 8 7 

100 1000 

FREQUENCY - KHZ 

Figure 4. Mdmum Communication Range Vs Operating Frequency in Proximity 

to Conductor's RX Antenna 2 Meters From Conductor TX 

Located Remotely - Herrin #6 Seam. 
Specific observations that may be drawn from figures 2, 3, and 4 include the following: 

a. The increase in optimum frequency with increased distance away from conductors; from 

700 to 1000 kHz to 20'00 kHz are typical for the Pittsburgh seam, respectively, 1, 2, and 

3 entries away. 

b. For seams other than Pittsburgh, the communication ranges for transmitter distances 

greater than one entry away from conductors are determined by direct through-the-earth 

transmission. 

c. The communication range and optimum frequency for a transmitter located two entries 

away in the Pittsburgh seam and one entry away for either the Pocahontas no. 3 or 

Herrin no. 6 seams are near constant at 600 meters and 1000 kHz. 

d. The decrease in communication range with distance of one of the radios from a 

conductor-carrying entry; from 1070 meters to 600 meters to 360 meters in the 

Pittsburgh seam are typical progressively 1, 2, and 3 entries away. 

Considering most communication paths to be in proximity to conductors, 520 kHz (chosen on 

the basis of conductor-free data only) is too low a frequency to take full advantage of nearby 

conductors, particularly in the Herrin #6 seam. 1000 kHz seems to be the best overall 

choice of operating frequency based on figures 2, 3, and 4. 

In areas with dense conductor groupings in several adjacent parallel entries (such as are 

found in typical four-parallel-entry section headings) the range achieved is governed by the 

superposition of the individual entry conductor grouping fields excited at the receiver. The 

excitation of the individual groupings from an arbitrarily located transmitter is not a simple 

problem, however. Mapping of field strength shows that the section coverage is adequate to 

ensure communications in both the Pittsburgh and Herrin no. 6 seams. 

Of interest in the dense conductor grouping data is the case in the Ireland mine with a track 

entry sandwiched between a belt entry and a power cable/phone line entry. Of the three 

mapping frequencies 488, 954 and 4220 kHz, 954 kHz was the only frequency producing 

significant current in the track and trolley wire. 

The frequency dependence of the maximum communication range with both radios in the 

conductor-carrying entry (or both in entries carrying conductors which are connected) for 

the three seams in median mine noise is illustrated in figure 5. These curves assume 

transmit and receive antennas located two meters away from and oriented coplanar with 

respect to elevated conductor(s) (or dilute conductor groupings) having 50-ohm surge 

impedance in the presence of rock conductivity as determined by ADL. Also assumed are 

no conductor branch points or unusual shunting impedances to ground. 

Specific observations that may be drawn from figure 5 include the following: 

a. Within the frequency limits shown, the maximum communication range increases with 

decrease in frequency exhibiting the effect of lower line attenuation; showing a range of 

about 6 miles at 100 kHz and a range of 2 miles at 1000 kHz. 

b. The differences in communication range with seam type are relatively minor with the 

least difference occurring between the Pittsburgh and Herrin no. 6 data. 

There will be an optimum frequency range for this type of transmission with the low frequency range reduction eventually occurring due to the increase in noise. Perhaps the 

optimum frequency range roughly agrees with the trolley phone frequency band, although no 

quantitative data is available to support the conclusion. 
TX NIA = 2.5 

RX SENSITIVITY 

0.02 rAIMETER FOR 12 DB SINAD 

BW = 12 KHZ 

MEDIAN MINE NOISE 

CONDUCTORSURGElMPEDANCE

PITTSBURGH SEAM \% 

---- - POCAHONTAS #3 SEAM 

- .-. HERRIN #6 SEAM \ 

111 I I I1 I1 I IIIII I I I Il

2 3 4 5 6 789 2 3 4 56

100 1000 

FREQUENCY - KHZ 

Figure 5. Maximum Communication Range Vs Operating Frequency, Both TX and RX An

Located 2 Meters From Conductors. 
2.3 RECOMMENDATIONS 

Recognizing the limited resources available for gathering additional related measured data, 

future measurement goals should be prioritized according to the degree to which the data 

base will be enhanced. Accordingly, a list of recommendations for further measurements 

and accompanying theoretical modeling includes, in priority: 

a. Performing measurements and modeling in additional high-productivity seam/region 

areas including low coal. 

b. Investigating conductor proximity modeling plus verification measurements including 

characterizing important conductor groupings and topological strings of conductors. 

c. Performing additional higher frequency mf noise measurements including characterizing 

noise sources and their coupling into mine power, control, and phone wiring. 

d. Investigating topological variations in mf propagation with emphasis on comparing solid 

coal block and room and pillar paths. 

e. Performing measurements and modeling at lower frequencies than 100 kHz including 

optimum frequency identification for long-range transmission conductors from closely 

coupled radios. 

f. Performing measurements to assess location variability in coal mines. 

The results of this measurement program have also influenced the mine wireless equipment 

development activities. The following recommendations are included in this area: 

a. Change the operating frequency to about 1000 kHz. 

b. Reconfigure the portable units to make them smaller and more portable (including a 

flexible antenna); in doing so, the NIA could be reduced to the order of 0.7 to 1.0. 

c. For the portable radios, provide an optional "clip-on" shielded loop probe for coupling 

tightly into insulated conductors in coal mines. 

Sufficient information is available to permit a simple computerized predictive model to be 

prepared including conductor proximity. This development would be particularly helpful 

in evaluation of transmission characteristics in the presence of conductors for future measurements. The analysis in this report provides a starting point for this effort, but the work 

needs to be put on a sound theoretical basis where variation of many parameters can be 

included. 

As nearly all real transmission paths in coal mines involve conductor proximity, any predictive 

model must include these effects. ADL's model in quasi-conductor-free areas has served as a 

tool to define seam plus overburden/underburden electrical parameters. The author suggests 

using the ADL propagation model plus one or more simple models for conductor configurations 

and include the possibility of branches in conductor runs and the simultaneous excitation of 

conductors in more than one entry by electromagnetic coupling. 

3.0 TECHNICAL APPROACH 

Magnetic field strength measurements made during Phase 1 of the Mine Wireless program 

were limited in dynamic range. Also, the HP467A transmit amplifier driving the antenna was 

limited to approximately 1 MHz and tended to produce an unstable output for antenna currents 

of about 1 ampere. In addition, the antenna tuning circuitry used consisted only of a 

resonating capacitor rather than an L matching section. 

The dynamic range was limited partly due to the transmit NIA achievable with the 31-turn 

8-inch loop antenna due to higher antenna resistance (NIA of 0.7 was achieved for an antenna 

current of 1 ampere) and partly due to the sensitivity of the EMC-25. The noise figure of the 
EMC-25 was determined to be about 18 dB and the single-turn receive antenna only had an 

area of 1/4 square meters. 

As will be discussed in the next subsection, the selection of a wideband solid-state amplifier 

was instrumental in increasing transmit equipment operational stability and in increasing 

the usable measurement frequency range toward higher frequencies. 

The selection of Singer NM-12 and NM-25 field strength meters and the use of a receive 

antenna of increased area (0.73 m)2 were instrumental in improving the receive system 

sensitivity. 

The use of discrete L-section matching networks, while limiting the tuning to rather discrete 

ranges in frequency, resulted in improved transfer of amplifier power output into antenna 

current. 

The assembly and implementation of the test equipment into a viable measuring system was a 

joint effort between Spectra Associates, Collins Telecommunications Group, and the Bureau 

of Mines. The signal generator used was provided from the Collins Telecommunications 

Group test equipment pool. The amplifier, battery packs, and the field strength meters were 

furnished GFE. For each mine visit, both the Bu Mines and Collins Telecommunications 

Group technicians on the measurement team brought along backup pieces of equipment, hand 

tools, repair equipment, power supplies for recharging batteries, and other items. 

The technical approach to the performance of the measurements at a particular mine was one 

of evaluating the character of the data after each day of measurements and using this evaluation as a guide in determining the next day's measurement effort. This evaluation involved 

the nature of the test area (proximity to conductors), range achieved vs frequency, the 

uniformity of the test results, and other factors. The procedure for quick dissemination of data 

and preliminary summary results was that outlined in section 1.0. 

3.1 EMPIRICAL TECHNIQUES 

3.11 General Measurement System Redesign 

The main objective in designing the test equipment configuration was to obtain a transmit NIA 

and receive system sensitivity as high or higher than that of the mine wireless prototype 

portable radio at 520 kHz and further to sustain as high values of NIA and sensitivity as 

possible over the frequency range of nominally 100 to 5000 kHz. This was so the dynamic 

range of the test equipment would encompass that for the prototype radio at 520 kHz, plus 

encompassing the expected range of NIA and sensitivity with change in frequency. The size of 

the test antennas had to be constrained to values useful in a mine environment. 

A block diagram illustrating the test equipment configuration is shown in figure 6. 

The receive equipment consisted of Singer NM-12 (10 to 250 kHz) and NM-25 (150 kHz to 32 

MHz) field strength meters. The available Singer receive antennas for these instruments 

were square shielded loops of the same size (0.73 m2) but with separate low frequency and 

high frequency coarse "tuning headst1 (vlf type 929380-2 and mf/hf type 92943-1). These 

antennas, consisting of 1 turn each, were judged to be of the largest practical size for use in 

the mine. The initial design question was whether or not the receive sensitivity of the field 

strength meters using these antennas would be adequate. The receive system sensitivity 

measurement of the NM-25 was made in the environmental screen rooms at Collins Telecommunications Group. In addition, the NM-25 noise figure was measured and found to be 1.9 

dB. The NM-25 sensitivity values are shown in table 1. The sensitivity of the NM-12 wasn't 
- - - - . . - . . 

MATCH UNIT -I--- 

- 

CUSTOM BUILT 

FOR PROGRAM 

v CUSTOM BUILT 

12VDC GATES CELLS 

BATTERY I PACK I OR -AUTO BATTERY 

TRANSMITTING TEST SETUP 

FOR PROGRAM 

GENERATOR 

HP-8640B 

SIGNAL 

- 

651 B 

0 1-TURN ANTENNA 

FIELD STRENGTH 

METER H TKF 1 SlNCiER-T~~Xl~f 

SINGER NM-12 

-25 

- 

RECEIVING TEST SETUP 

POWER 

AMPLIFIER 

ENI-300P 

Figure 6. Measurement Test Equipment Configurations. 

24 

measured due to the difficulty in making measurements at 50 and 100 kHz in the Collins 

Telecommunications Group environmental area. 

These sensitivities were judged to be adequate as the value at 520 kHz exceeds that for the 

mine wireless radio (-34 d~/ above 1 pA/meter for 12 dB SINAD). The sensitivities given 

in the table are given in terms of four numbers; "easy and quick" minimum useful level, 

minimum useful level if care was exercised in taking the reading (4 dB more sensitivity than 

"quick and easy"), the minimum detectable signal level (taken to be 10 dB below "quick and 

easy") and the minimum detectable signal density. 

The transmit equipment consisted of either an HP-8640B or an HP-651B signal generator 

driving an EN1 Model 300P broadband amplifier (150 kHz to 30 MHz, 3 watts, maximum 

output at 50 ohms) in turn driving either of two loop antenna and special matching circuitry 

designed as part of this program. The loop antennas were nominally 2 feet in diameter. One 

loop antenna was designed for frequencies below 1000 kHz and having 7 turns. The other 

loop antenna was designed for a frequency range of 1000 to 5000 kHz and having 4 turns. The 

nominal antenna current available from the amplifiers was 1 ampere. With this value of 

current, the achievable NIA's were respectively 2.04 at lower frequencies and 1.17 at higher 

frequencies. Actual values of antenna current achieved during measurements were 0.7 to 1.0 

A at all frequencies except above 3000 kHz where the antenna current was typically 0.4 A. 

The transmitting equipment was powered from two separate battery packs. The amplifier 

(requiring 0.9 A at 25 V dc) was driven from one of two available 5 A hour, 25 V dc Gates 

cell packs. The signal generator was powered from a 150-watt inverter, in turn driven by a 

12 V dc Gates cell pack or from a 12-volt automobile storage battery. A single 2.5-A hour 

Gates cell is capable of powering the generator for one hour. A pack of 4 such cells in 

parallel was normally used. 

Early in the program, the HP-8640B generator was used exclusively with the HP-651B 

provided as backup plus for use at 50 and 100 kHz. Due to bulk and increased power drain 

of the HP-8640, the HP-651B was used exclusively later in the program. 

3.1.2 Transmit Antenna and Antenna Coupler Design 

The antenna and matching circuitry design is shown schematically in figure 7. The main antenna design criterion was that of keeping the antenna resistance as low as possible with 

increase in frequency so that, when tuned, maximum current could be driven into the antenna. 

Additionally, the maximum reactance was designed to be less than about 700 to 800 ohms so 

that with 1.0 A of current flowing, the maximum voltage stress across capacitors could be 

kept less than 1000 volts. The impedance curves for the low frequency and high frequency 

antennas are given in figures 8-a, b, c and 9. 

The antenna tuning circuitry was designed to tune the antennas at the following discrete frequency ranges (matching the antenna to 50 ohms resistive): 

95 to 100 kHz 

225 to 240 kHz 

465 to 500 kHz 

980 to 1100 kHz 

1800 to 2300 kHz 

3800 to 4600 kHz. 

The particular frequency for optimum antenna current varied from mine to mine according 

to details of the antenna mounting and the length of the antenna tuning leads. In the last two 
Figure 7. Schematic Diagram of Transmit Antenna Tuning Unit. 

\w4 SMALL AIR VARIABLE 

LARGE AIR VARIABLE 

/I - F 

\I 

/I 

0.001 PF 

\I 

O.QO7 PF 

\I 

.. c 

0 B 

A 

0.0347 pF 
0 200 400 600 

FREQUENCY - KHz 

Figure 8-a. Input Resistance of Low Frequency 

Transmit Antenna. 
FREQUENCY - KHz 

Figure 8-b. Input Reactance of Low Frequency 

Transmit Antenna. 
FREQUENCY - KHZ 

Figure 8-c. Input Resistance of Low Frequency 

Transmit Antenna. 
1 2 3 4 5 

FREQUENCY - MHZ 

Figure 9. Input Impedance of High Frequency Transmit Antenna. 
mines, antenna leads 6 to 7 feet in length were employed and the highest frequency to which 

the antenna would tune slipped to approximately 2900 to 3800 kHz. 

An additional feature of antenna tuning is that of ensuring a "cleanft transmit frequency 

spectrum; particularly at lower frequencies of nominally 50 and 100 kHz. (During the fifth 

mine visit, a tuning circuit was added to permit tuning to 50 kHz) where the 300P amplifier 

was operated below its design limit. The transmit spectra of the antenna current is shown 

in figure 10. In each case, the 2nd harmonic component is seen to be at least 20 dB below the 

fundamental. 

3.1.3 Receive System Calibration 

The receive system was calibrated for field strength in the Collins Telecommunications 

Group environmental area. This calibration was performed several times during the course 

of the program, serving to both expand the calibration baseline and also to pinpoint changes in 

the condition of the equipment due to the relatively hard use experienced during this program. 

The field strengths resulting in the analog meter reading on the instrument calibration mark 

with the attenuator in the -20 dB position were used (calibration marks were at +10 dB on the 

NM-25 and at +25 dB on the NM-12). The field strength calibration obtained was in terms of 

p~/meter. Table 2 gives the magnetic field and plane-wave-equivalent electric field strength 

values at frequencies actually used during the program. Figure 11 shows an average curve 

of all the calibration data (assuming the high frequency antenna tuner only is used) and is 

within 2 dB of all particular calibration readings taken. The calibration data in reality does 

not follow a perfectly continuous curve due to switching of the antenna tuners in roughly 3:l 

bandwidth segments. 

Figure 12 shows the measured comparison between the low frequency and high frequency tuners 

used with the 0.73-square-meter shielded loop antenna. 

3.1.4 Deployment of Measurement Equipment 

The transmitting power amplifier, tuner, rf ammeter and test leads were carried in a metal 

suitcase. Similarly, the signal generator(s) were (each) carried in another metal suitcase(s). 

The antennas were both carried in a heavy duty cardboard box just made to fit. The battery 

packs were carried into the mine separately. Each field strength meter and both antennas 

were transported in separate portable cases. The antennas were assembled on-site for use. 

Typically, the transmit antenna was positioned in an entry/crosscut cross-section geometric 

center. The antenna was almost always suspended from a roof bolt by a piece of nylon cord. 

The transmitting equipment was deployed on the floor immediately beneath the antenna. 

The transmitting equipment was set up on a particular frequency, tuned for maximum antenna 

current, and was left on continuously while the field strengths were being measured at 

locations on a particular measurement traverse. 

3.2 DATA REDUCTION AND DISPLAY METHODS 

During the measurements, particular measurement locations or stations were designated by 

counting crosscuts (or half crosscuts). These stations were located on a mine map and the 

actual ranges from the transmitter to the receiver in each case were determined from the 

map. Field strength readings were recorded in terms of the analog meter reading and the 

attenuator setting from the field strength meter. For each set of readings, the receive 

antenna band switch position, the frequency, and the transmit antenna current were recorded. 
HARMONIC 

0.05 1 AMP MHz INTO PER ANT DIV. L!A@J 0.6 0.1 AMP MHz INTO PERANT DIV 

0.5 MHz PER DIV 

0.8 AMP INTO ANT 

1 MHz PER DIV 

1 AMP INTO ANT 

I"" MHz 

Ia~~~.naasI 

2 MHz PER DIV 

0.5 AMP INTO ANT 

0.5 MHz PER DIV 

1 AMP INTO ANT 

- 

-35 DB - 

2 MHZ PER DIV 

0.92 AMP INTO ANT 

I......l 

2 MHz PER DIV 

Figure 10. Swept Spectrum of Transmit Antenna Current Showing Harmonics. 

33 
Table 2. Field Strength Calibration Factors Used in Data Reduction. 

RX ANTENNA 

BAND SET 

3 lf tuner 

1 hf tuner 

1 hf tuner 

1 hf tuner 

1 hf tuner 

1 hf tuner 

2 hf tuner 

3 hf tuner 

3 hf tuner 

3 hf tuner 

3 hf tuner 

4 hf tuner 

4 hf tuner 

4 hf tuner 

4 hf tuner 

3 hf tuner 

FREQUENCY 

@Hz) 

83 

92 to 100 

228 to 250 

42 0 

470 to 485 

935 

910 to 1047 

940 

1800 to 1840 

1940 to 2030 

2750 

3100 to 3200 

3400 

3800 

3960 to 4120 

4750 

FIELD STRENGTH 

MICROVOLTS/METER 

103 

251.2 

7 1 

62 

56 

22 

34.9 

46.5 

20.5 

16.6 

13.5 

11.5 

10.5 

9.5 

8.9 

5.6 
2 3 

FREQUENCY - MHZ 

Figure 11. Average Calibration Data for Singer NM-12 and NM-25 Field Strength 

Meters Using Singer 0.73 Meter Antennas. 
I I I I I I I 

200 600 1000 1400 1 BOO 

FREQUENCY - KHZ 

Figure 12. Comparison of High Frequency Vs Low 

Frequency Antennas. 

In reducing the field strength data the field strength at each location in dB greater than 1 PA/ 

meter was found as the sum of the reading as determined in dB, minus the field strength 

meter calibration point in dB (exp: for NM-25 + 10 dB with -20 dB attenuation setting), the 

calibration factor in dB and the factor to convert the actual transmitted NIA to a common 

NIA of 2.5 in dB. In equation form, this is expressed as: 

Field strength = (analog meter reading -10) + (attenuator range setting +20) 

2.5 + +20 Loglo Tx current x (2.04 or 1.17) 

in dB greater than 1 pA/meter. 

The data display most commonly used during the program in the summary Data Reports consisted of field strength in dB greater than 1 pA/meter vs range in meters plotted on linear 
paper. As the attenuation in the conductor medium goes as dB per lineal distance (except for 

a (range)-112 variation), the field strength curves then plot as straight lines. 

Another display, used to present the field mapping data, was a contour map of field strength 

(in dB greater than 1 pA/meter) with approximately 6-dB contour intervals. These contours 

were overlayed on an appropriate mine map section. 

4.0 COMPENDED RESULTS AND ANALYSIS 

4.1 REDUCTION OF MEASURED FIELD STRENGTHS TO MAXIMUM COMMUNICATION 

RANGE-PRESENTATION OF REDUCED DATA 

Each of the quasi-conductor-free field strength data sets, consisting of magnetic field 

strength vs range for several frequencies between nominally 100 and 5000 kHz, were converted to a maximum communication range vs frequency curve. This was accomplished by 

identifying the range at which a minimum required field strength level was obtained for each 

of two noise criteria; set-noise-limited and median-mine-noise-limited as defined in paragraph 4.2.1 using the characteristics and specifications of the mine wireless prototype portable 

radios developed by Collins Telecommunications Group for the Bureau of Mines as a model. 

The detailed technique for compending the measured results in this manner is described in 

the next subsection. The technique was first employed during the previous measurement 

program (14) where it was found to be the most direct and useful way of summarizing a large 

amount of radio propagation data. Results in the form of maximum communication range vs 

frequency for an assumed 12-dB SINAD condition of the mine wireless portable receiver 

permit conclusions to be drawn directly from the results regarding the performance of radio 

systems. 

The Pittsburgh seam maximum communication range vs frequency data are given in figure 13 

for four data sets in three mines (Ireland mine data from current and previous programs (15), 

Federal no. 1 data (16), and Consolidation Coal Mine no. 95 (17)). There is an optimum 

operating frequency for achieving maximum range. 

The,optimum operating frequency for set-noise-limited operation is lower than that for operation in the presence of median-mine-noise. The optimum frequency for the set-noise-limited 

case varies from 300 kHz for Consolidation Coal Mine no. 95 to 400 kHz for the Ireland mine 

results from this program. The data for the previous Ireland mine testing is limited in the 

number of frequencies considered and there is no clear cut optimum in this case. 

When limited by median-mine-noise, the optimum frequency for Federal no 1 and Consolidation Coal Mine no. 95 are clearly defined as being about 600 kHz for Consolidation Coal Mine 

no. 95 and 940 kHz for Federal no. 1. The Ireland mine data from the previous program 

follows the Federal no. 1 data closely and the optimum frequency is probably about 1000 kHz. 

For the Ireland mine data taken during this program, the optimum frequency is not clearly 

defined, but is probably about 2000 kHz. 

The geometric mean summary curves of the four data sets of figure 13 shown in figure 1 place 

the set-noise-limited optimum frequency at 400 kHz and the median-mine-noise-limited 

optimum frequency at 800 kHz. These summary curves were obtained by arranging the form 

data sets according to the relative 

Range (R1 R2 R3 R4) 1/4 

Where R1 R2 R3 R4 on the individual data set maximum ranges. 
- FEDERAL #I .-.- - - - - CONSOLIDA

MINE #95 

U--- -- - - - IRELAND, PR

. . . . IRELAND, CU

d,'. - % TX N1A = 2.

'\@. \ RX FOR SENSITIV12 DB S

BW = 12 KH

SET-NOISE LIMIT 

d 

NOISE LIMIT 

I I IIII I I I I I IIII I I I 

100 2 3 4 5 6 7 891000 

RANGE - KHZ 

Figure 13. Maximum Communication Range Vs Gperating Frequency in Conductor-Free 

of Coal Mines - Pittsburgh Seam Data Sets. 
An analysis of the range variability is presented in the next subsection. The geometric mean 

ranges for these data sets show roughly 500 meters for the set-noise-limit and 300 meters for 

the median-mine -noise -limit. 

The Herrin no. 6 seam maximum communication range vs frequency data is given in figure 14 

showing results from three data sets in two mines (Sesser mine, and sets in two areas of the 

Peabody no. 10 mine). For the set-noise-limited case, no optimum frequencies are clearly 

defined except along the coal block in the 1-south 1st west, 2nd north area of Peabody no. 10 

where the optimum frequency is probably about 250 kHz. The optimum frequencies for Sesser 

and for the 1-south submain area of Peabody no. 10 will be below 100 kHz. 

In the presence of median-mine-noise, the optimum frequencies are clearly defined except 

through the coal block in the 1-south 1st west 2nd north area of Peabody no. 10. The optimum 

frequencies vary from 240 kHz for the 1-south submain area of Peabody no. 10 to about 600 

kHz for Sesser. 

The geometric mean summary curves of the figure 13 data sets in figure 1 place no optimum 

frequencies on set-noise-limited data and a broad optimum frequency of about 250 kHz on 

the median-mine-noise-limited data. 

The mine wireless portable prototype radio maximum communication range was tested in 

Sesser and was found to agree closely with the median-mine-noise-limited range at about 

105 meters. 

Figure 14 also shows a partial data set in the 1-south 1st west 2nd north area through a solid 

coal block. This set is not extensive enough to show the optimum frequencies in either the 

set-noise-limited or median-mine-noise-limited situations. 

The Pocahontas no. 3 seam maximum communication range vs frequency data is given in 

figure 15 showing results from three data sets in the VP no. 1 mine. For the set-noiselimited case, optimum frequencies are clearly defined at about 240 kHz in the 3-south area 

(54-inch seam) and at about 480 kHz in the lower coal 2-north no. 1 Plow area (48-inch seam), 

both of which are at least one entry removed from a coal block or from conductors. The data 

set in the 3-south area along a coal block exhibited a slightly lower optimum frequency of about 

200 kHz. 

In the presence of median-mine-noise, the optimum frequencies were clearly defined and 

were somewhat higher than those for the open-entry cases. These frequencies were about 

330 kHz in the 3-south area and 700 kHz in the 2-north no. 1 Plow area. Correspondingly, 

along the coal block in the 3-south area, the optimum frequency was about 400 kHz. 

The figure 1 geometric mean summary curves of the data sets place the optimum frequency 

for the set-noise-limited case at about 230 kHz and the optimum frequency for the medianmine-noise-limited operation at about 500 kHz. 

The mine wireless portable prototype radio maximum communication range was tested 

through a solid coal block in VP no. 1 with the maximum communication range experienced 

at 520 kHz of 140 meters being a little greater than that expected for median-mine-noiselimited operation. 

Partial data sets were taken during the mine measurements showing the effect of proximity to 

conductors with the transmitter remotely located from the conductors. In addition, quasiconductor-free data occasionally exhibited a decrease in attenuation slope at low field strength 

levels due to the presence of conductors. Sufficient measured data to show range vs frequency 
SET-NOISE-LIMIT 

\ 

\ PEABODY #I0 

\ 

'A 

- - - - SESSER 

\ 

\ RX SENSITIVITY 0.2 

FOR 12 DB SINAD 

1-SOUTH \ AREA 

\ BW = 12 KHZ 

\ 

\ 

THROUGHCOALBLOCK 

I I I 1 1 1 11 I I I I IIIII 

100 2 3 4 5 6 7 891000 

FREQUENCY - KHz 

Figure 14. Maximum Communication Range Vs Operating Frequency in Conductor-Free A

Coal Mines - Herrin No. 6 Seam Data Sets. 
380 - 

360 - 

340- 

320- 

300 - 

280 - 

260 - 

240 - 

ul 

u 

W 

I220- 

I 

W 

200- 

4 

0: 

180- 

160- 

140- 

120- 

100- 

80- 

60 - 

40 

TX NIA = 2.5 

RX SENSITIVITY 0.2 yAlM 

FOR 12 DB SINAD 

BW = 12 KHz 

ALONG COAL BLOCK VP #I MlNE 

3-SOUTH AREA 

1 ENTRY AWAY 

FROM COAL BLOCK 

ALONG COAL BLOCK 

MEASURED MINE 

WIRELESS RANGE 

IN &SOUTH 

THROUGH COAL BLOCK 

MEDIAN-MINENOISE-LIMIT 

I I I II I I I I IIIII I I I 1 

100 2 3 4 5 6 7891000 

FREQUENCY - KHz 

Figure 15. Maximum Communication Range Vs Operating Frequency In Conductor-Free 

Areas of Coal Mines - Pocahontas No. 3 Seam Data Sets. 

41 
effects was not taken due to the exhaustive testing required to obtain this data. Instead, the 

existing conductor proximity data has been used in this report to gain insight into possible 

modeling in the presence of conductors and, finally, as a check on the accuracy of an 

elementary model at discrete points. 

Complete magnetic field strength mappings were taken in worldng sections in the Ireland and 

Sesser mines during the measurement program. This data speaks for itself in showing that 

a complete section can be covered with communications via mine wireless radios with dense 

groupings of conductors. There is little summarizing or data refinement which is practical 

to perform with regard to these mappings. Consideration of this type of data in this report 

is limited to the observations that can be drawn directly from these maps as shown in 

sections 2.0 and 5.0. 

4.2 ANALYSIS AND DEVELOPMENT OF SYSTEM APPLICATION OF DATA 

4.2.1 Quasi-Conductor-Free Maximum Communication Range Vs Frequency 

This subsection develops the basis for obtaining the maximum communication range in quasiconductor-free areas from the measured magnetic field strength data. 

The set-noise performance limit at the mine wireless prototype operating frequency comes 

directly from the specification 

Sensitivity = 0.02 fiA/meter for 12-dB SINAD 

This specification is taken to be the minimum incident field strength to obtain a usable 

received signal from the radio. At 520 kHz this corresponds to -34 dB greater than 1 MA/ 

meter. The complete sensitivity expression for the 12-dB SINAD condition is given by 

where, Af is the bandwidth of 12 kHz 

Q is the antenna "Q" made as narrow as possible to be 

consistent with transmission; this Q is 44 for the 

prototype radio unit 

A is the antenna area = 0.217 meter" 

N is the noise figure of the receiver, = 2 dB for the mine 

wireless prototype 

The above expression for sensitivity makes allowance for an input signal-to-noise ratio to 

produce 12-dB SINAD. The absolute accuracy of this expression is dependent on the loop 

conductors being given by the form 

1/2 2 L=KA n 

Where K is proportionately constant 

Appendix C provides an alternate analysis method that affects somewhat improved results for 

purely FM systems. 
For the mine wireless receiver, HSN computes to be 0.021 pA/meter which is very close to 

the specification. 

The frequency dependence of HSN is needed to perform evaluations with frequency. For this 

purpose, it is assumed that the Q varies directly wlth frequency so that HSN varies directly 

with frequency. 

For median mine noise, HN (1-Hz bandwidth) the formula given in section 2.0 was 

H = 121.5 - 32.5 loglO f (Hz) in dB greater than 1 p~/meter/ a N 

The 12-dB SINAD condition for the mine wireless prototype radio corresponds to a signal-tonoise ratio of 13.51 dB. At 520 kHz, computing HN in a 12-kHz bandwidth and adding 13.51 dB, 

the sensitivity corresponding to that given for the set noise limit is -9.97 dB greater than 1 

pA/meter. The frequency dependence is derived from the HN formula. 

The above two field strength sensitivity conditions used in summarizing the magnetic field 

strength data are Hven in figure 16. The maximum communication range vs frequency data 

was developed by taking the level at a particular frequency from one of the two curves in this 

figure, finding this level on a particular measured field strength curve corresponding to this 

frequency, and recording the range at which this field strength level was developed. The 

measured field strength data sets for the mine measurements are given in appendix A to this 

report. 

4.2.2 Conductor Proximity Maximum Communication Range Vs Frequency 

All conductor proximity range computations, except those where both radios were assumed 

to be very close to conductors, were determined as follows: 

a. Select fixed transmitter and receiver ranges away from the conductor. 

For the cases developed in this report, the receiver range was 2 meters and the transmitter ranges were 30, 60, or 90 meters corresponding to 1, 2, or 3 entries away from 

the conductors. 

b. Select measured field strength curves to be used which are representative of the seams. 

For the cases developed in this report, the Federal no. 1 mine data was used for the 

Pittsburgh seam, the Sesser mine data for the Herrin no. 6 seam, and the VP no. 1 data 

for the Pocahontas no. 3 seam. 

c. Compute the scatter gain, which is the ratio of the field strength at the receiver in the 

presence of the conductor to the field strength in absence of the conductor. Multiply the 

scatter gain by the field strength at the conductor determined from b at the range 

determined from a. 

d. Divide the result of c, which is the scattered field at the receiver, by the sensitivity field 

strength for median mine noise which gives the margin ratio to accommodate attenuation 

along the conductor. 

e. Compute the conductor attenuation per unit length. Divide the field strength margin ratio 

of d by the conductor attenuation per unit length to get range. 
t1313W t13d V" NVHl t131V3UE) 80 NI HlDN3tllS 01313 3113NE)VW 
These steps are illustrated in the following equation: 

HT (GS) 

1 = , in field form with ap in nepers/meter 

H~ e 

where ap is in d~/meter. 

To illustrate the concept of scatter gain, this gain will be computed for free space, 

homogeneous earth, and in-mine situations. 

The scattered field from an infinite sheathed conductor in a nonmagnetic conducting medium 

excited by a small transmitting loop is 

30 (a + p . ,112 (IAN) HS = R R , A/meter 

4n '0s T R 

where 

a, 0 are the attenuation and phase constants of the 

Mtransmission line" formed by the conductor and 

the medium 

(IAN) is the transmit loop magnetic moment 

zo~ is the 'lineft surge impedance 

R R are respectively the transmit and receive ranges T' R 

in meters. 

The direct field in homogeneous earth is given by: 

or, in free space for a = 0, 

For free space, the scatter gain ratio is given by: 
For homogeneous earth where, in a conducting medium, 

a 1 

la1 = IflI = 6 , 6 being the skin depth = with o being the conductivity of the medium. vxjiz 

the scatter gain is given by: 

For the in-mine situation, we assume the direct field is given by expression used by ADL (18): 

(a2 + f12 ) 3/4 (IAN) 

where h is the seam height in meters 

6, is the skin depth of the rock 

overburden/underburden 

and the scatter gain is given by: 

From the equation for the complex propagation constant used by ADL (20), calculations of a 

and p were made over a wide range of frequency, seam and overburden/underburden conductivities, and dielectric constant. Using values of conductivity and dielectric constant 

obtained by private communication with R. Lagace of ADL values of a and 6 were selected 

from the values calculated as being representative of the three seams. These values are 

given in the paragraphs to follow where specific approximate formulas for scatter gain are 

derived. 

For the Pittsburgh seam, assume a = 0.02, fl= 0.03 at 316 kHz so that (a2 t f12)1/4 = 0.19; 

also h = 2 meters. 

2 From computations of a and fl for various frequencies, (a t fl2)'I4 is approximately 

proportional to V'f. Then, as the skin depth is inversely proportional to fl, the Pittsburgh 

seam scatter gain is approximately frequency independent and given by: 
2 2 1/4 = For the Herrin no. 6 seam, assume a = 0.145, fl = 0.10 at 1 MHz so that (a + 0 ) 

0.420; also, h = 3 meters. 

From computations of a and fl for various frequencies, (a2 + fl ')'I4 is approximately 

proportional to f1/4 and the Herrin no. 6 scatter gain is given approximately by: 

For the Pocahontas no. 3 seam, assume a = 0.16, B = 0.175 at 1 MHz so that 

(a2 + p2)'I4 = 0.488; also, h = 1.5 meters. 

From computation of a and p for various frequencies, (a2 + fl ')'I4 is approximately 

to f0.425 and the Pocahontas no. 3 seam scatter gain is given approximately by: 

Verification of these formulations for scatter gain was obtained for the Pittsburgh and 

Pocahontas no 3 seams by comparison with measured data where signal "plateau" levels were 

observed in the measured field strength. These comparisons are given in table 3. 

Table 3. Comparisons of Measured and Computed Scatter Gains. 

The line attenuation is determined considering the lowest order TM mode on a transmission 

line formed by a conductor a distance away from a lossy conducting medium with a plane 

interface. For this case, the normalized attenuation constant is given by: 

MINE/SEAM 

Consol Mine No. 95 

Pittsburgh 

Federal No. 1 

Pittsburgh 

VP No. 1 

Pocahontas No. 3 

FREQUENCY 

&Hz) 

935 

236 

520 

CONDUCTOR 

TYPE 

Water line 

Water line 

buried 

Water line 

ZOS 

50Q 

10Q 

50Q 

RT 

46M 

55M 

62.6 

R~ 

1M 

1/2M 

1M 

MEAS 

G~ 

-28 dB 

-13.5 dB 

-35 dB 

CALC 

G~ 

-31 dB 

-11.8 dB 

-35.5 dB 
where, 

a is the distance from the conductor center to the interface 

ai is the conductor radius 

the computations used in this report assumed a ratio of a/ai = 9. 

For the Pittsburgh seam, assuming or = 0.085 mho/meter 

a 

- = 0.14652 at 1 MHz k 

For the Herrin No. 6 seam, assuming or = 0.22 mho/meter 

a 

-= 0.16030 at 1 MHz k 

For the Pocahontas No. 3 seam, assuming or = 0.01 mho/meter 

a = 0.12518 at 1 MHz k 

Taldng k = 2 rr/A and multiplying by 8.686 to change nepers to dB, these attenuation constants 

are easily exprbssible in dB/meter at any particular frequency of interest. 

A check is afforded from field mapping data in the Ireland mine in the 8-north 3-right section 

at 4220 kHz in the Pittsburgh seam. The measured attenuation constant along the belt entry 

is 0.09612 d~/meter and the computed attenuation constant is 0.11248 d~/meter. 

The coupled (scattered) field strength when both transmit and receive antennas are close to 

the conductor in the same entry (or in separate entries with conductors which are connected) 

is given by: 

HS = wp (IAN) , A/meter 

(2n) ZOS RR T R 

assuming no line attenuation when there are no conductor branch points or unusual shunting 

impedances and with antennas oriented for maximum coupling. For the computations performed in this report, 

ZOS = 50 ohms 

R , R = 2 meters T R 

and the field strength is: 

H = 55.9 + fMHz dB greater than 1 hA/meter S 
In a manner similar to that used for the remote transmitter calculations, the maximum communication range is found by subtracting the sensitivity field in dB for median mine noise 

from HS and then dividing the answer (which is the margin ratio for attenuation) by the 

attenuation constant in dB/meter, or: 

where HS, HN, ap are expressed in dB. 

4.2.3 Range Variability Assessment 

The assessment of range variability will be constrained in this report to the variability values 

afforded by comparison of ranges derived from the field strength measurement sets obtained 

during this program plus the previously obtained Ireland data. The statistical sample of data 

in various mines and vs location in each mine is not large enough to allow estimation of the 

true location variability. 

The assessment also considers on the quasi-conductor-free data as there is no real way to 

estimate the variability of the conductor proximity data. 

The results of comparing the variability of data sets on a per-seam basis are shown in table 4. 

These results show variations between data taken in open entries, with topological range differences being considered separately. The comparison between four data sets in the Pittsburgh seam gives the least average variation, while the comparison between the two Herrin 

No. 6 seam data sets gives the greatest average variation. Considering maxima and minima 

with frequency, the Herrin No. 6 provides the least variation over frequency while the 

Pocahontas No. 3 seam gives the greatest variation. 

Variations with topology are also important; the most significant of which are those encountered in comparing paths away from (open room and pillar areas), along (adjacent to), 

and through a solid block of coal. Data supporting these comparisons was taken in the 

Pocahontas No. 3 seam in the VP No. 1 mine and in the Herrin No. 6 seam in the Peabody 

No. 10 mine. The only Pittsburgh seam data of this kind was taken in the Ireland mine during 

the previous program with the field strengths between open-entry and through-coal-block 

paths being within 3 dB of one another on average and, thus, showing essentially a negligible 

range decrease in going through the coal block. 

Considering the Peabody No. 10 data first, the main effect of transmission through the coal 

block compared with transmission in an open entry was an amplitude offset in the field 

strength (the attenuation slopes were nearly identical) vs range data with the offset varying 

from about 10 dB at 480 kHz to about 20 dB at 3400 kHz. This offset resulted in a range 

decrease in going through the coal block which varied between 19.7 percent at 480 kHz and 

35.8 percent at 1800 kHz when set-noise-limited, and 17.8 percent at 480 kHz, and 35.5 

percent at 1800 kHz when median-mine-noise-limited. Comparing the data along the coal 

block with the data one entry away from the coal block (assumed to be representative of the 

open entry case data), the range on paths along the coal block decreased with respect to the 

range away from the coal block. With frequency, this decrease varied between 18.6 percent 

at 240 kHz to 3.4 percent at 600 kHz to 14.3 percent at 1800 kHz when set-noise-limited, and 

16.1 percent at 240 kHz to 1 percent at 600 kHz to 15.1 percent at 1800 kHz when median mine 

noise limited. 
Table 4. Maximum Communication Range Variability From Mean Values Based on 

Measured Magnetic Field Strength Data Sets Converted to Maximum 

Communication Range. 

PITTSBURGH SEAM - 4 DATA SETS 

FREQUENCY 

@Hz) 

100 

200 

400 

800 

2000 

4000 

SET-NOISE-LIMITED 

RANGE VARIABILTI'Y 

111.1% 

15.5 

16.8 

+13.5 

16.4 

113.6 

MEDIAN-MINE-NOISE-LIMITED 

RANGE VARIABILITY 

i14.9% 

120.4 

48.0 

i17.1 

H.8 

111.5 

Average 19.5% 115.0% 

HERRIN NO. 6 SEAM - 2 DATA SETS 

FREQUENCY 

@Hz) - 

250 

500 

1000 

2000 

SET-NOISE-LIMITED 

RANGE VARIABILITY 

122.2% 

i25.2 

131.9 

126.7 

MEDIAN-MINE-NOISE-LIMITED 

RANGE VARIABILITY 

115.8% 

+22.8 

127.7 

e0.1 

Average 126.5% 121.6% 

POCAHONTAS NO. 3 SEAM - 2 DATA SETS 

FREQUENCY 

@Hz) 

100 

200 

400 

800 

2000 

3000 

Average +18.7% 115.1% 

- 

SET-NOISE -LIMITED 

RANGE VARIABILITY 

123.9% 

i31.1 

*25.2 

13.0 

19.8 

119.1 

MEDIAN-MINE-NOISE-LIMITED 

RANGE VARIABILITY 

il4.0% 

+38.9 

d0.9 

11.8 

16.1 

H8.7 
For the VP No. 1 mine data, there was only a single point "through the coal block" which 

represented the tests with the mine wireless prototype radios. For this case, at 520 kHz, 

there was a range reduction of 72 percent. 

Comparing the data along the coal block with the data one entry away from the coal block, the 

range along the coal block was decreased (as in Peabody No. 10 mine). With frequency, this 

decrease varied between 31.2 percent at 240 kHz to 16.4 percent at 600 kHz to 21.6 percent 

at 1800 kHz when set-noise-limited, and 20.8 percent at 240 kHz to 8.9 percent at 600 k~z to 

12.3 percent at 1800 kHz when median-mine-noise-limited. 

The large decrease in going through the coal block in VP No. 1 could be due to the fact that 

the roof and seam conductivities were much closer together (possibly within an order of 

magnitude) whereas, these conductivities were at least two orders of magnitude or more apart 

in the other seams. This particular result should be confirmed with additional data. 

5.0 INDIVIDUAL MINE TESTS DESCRIPTIONS 

All test areas in the six underground mines at which testing was conducted were in mediumhigh coal with seam thickness varying between 54 and 108 inches except for the northern 

43-inch-seam area in the VP No. 1 mine. Half the mines used belt haulage from the section 

to the surface excluding Ireland, Federal No. 1 and Consolidation Coal Mine No. 95. All mines 

employ tracked support vehicles except for Sesser. All mines were shaft-entry mines except 

for Consolidation Coal Mine No. 95. All mines used continuous mining (or long wall mining) 

exclusively except for Peabody No. 10 where conventional mining was still used in sections on 

the north side of the mine. 

Summary characteristics and measurement results are presented for each of the mines in 

the subsections to follow. 

5.1 IRELAND MINE 

The Ireland mine is in high coal in the Pittsburgh seam located 500 to 1000 feet beneath the 

surface. The coal is soft bituminous; so soft that working sections cannot be "pillaredf' in 

retreat mining. A typical entry/crosscut crossection was 16 feet wide and 6 to 7 feet high. 

The seam was approximately 5 feet thick covered (in sequence) with 6 to 18 inches of 

drawslate, 6 to 12 inches of additional coal, and additional drawslate. 

The 8 north submain and 8 north 3 right working section test areas were very close to the 

conductor-free 8-north escapeway area in which the original mine wireless testing was 

accomplished. In the submain, the testing was always within one entry of a conductor 

(7200-V ac line on floor). In the section, which was mapped, each of the three fresh air 

entries contained conductors. The transmitter was closely coupled to the wiring near the 

section headpiece. 

Mine maps and both the quasi-conductor-free/conductor-dilute and the mapping magnetic 

field strength data are given in appendix Al. Key results of the testing include the following: 

a. The maximum communication range in a quasi-conductor-free area continued to be in 

excess of 1,000 feet in the Pittsburgh seam. South African radios were used. 

b. A field strength level adequate for communication coverage of an entire 2,000-foot 

4-parallel-entry working section panel was demonstrated for a portable transmitter 

located at the section headpiece. 
5.2 INLAND STEEL COAL MINE NO. 1 (SESSER) 

The Sesser mine is in high coal in the Herrin No. 6 seam located nominally 725 to 750 feet 

beneath the surface. The seam is thick, varying between 9 and 14 feet. The mining process 

leaves top coal with the result that entry/crosscut heights were 6-1/2 to 7-1/2 feet. Entry 

widths were normally 14 feet. The underburden is fire clay. The overburden contains no 

draw slate but supposedly shale in the dry area and sandstone in the wet area. "Domed-out" 

areas from roof falls to heights of 30 to 40 feet revealed limestone overburden which was 

laminated near the seam and homogeneous near the 30- to 50-foot level. 

The 1-main east main and 1-main east left, 6-left and 9-right working section test areas were 

in the flat/dry area of the mine. In the main, the testing was conducted two entries away from 

conductors (which were located in the belt haulageway); and, due to the highest seam attenuation, the test environment was truly conductor free. In the sections, which were mapped, two 

of the three fresh air entries contained conductors (no track and trolley wires in the mine). 

The fixed transmitter for the mapping was located approximately in the middle of a 2,000-foot 

working section panel, closely coupled to the 7,200-V ac power cable. 

Mine maps and both the quasi-conductor-free and free mapping magnetic field strength data 

is given in appendix A2. 

Key results of the testing include the following: 

a. The maximum communication range in a quasi-conductor-free area was roughly 500 feet 

in the Herrin No. 6 Seam for Rockwell-Collins Mine-Wireless Prototype radios and 440 

feet for the South African radios. 

b. A field strength level adequate for communication coverage of an entire 2,000-foot 

working section panel was demonstrated for a portable transmitter located close to the 

7,200-V ac power cable in the approximate center of the panel. 

c. A field strength level adequate for communications coverage between adjacent working 

section panels and between adjoining panels separated by a 13-parallel-entry main line 

was demonstrated (for the transmit location of b above). Ranges of 3,800 feet between 

adjacent panels and 5000 feet between adjoining panels were achieved (and these were not 

maximum ranges). 

5.3 CONSOLIDATION COAL MINE NO. 5 (ROBINSON RUN) 

The Consolidation Coal Mine No. 95 is in medium high coal in the Pittsburgh seam. In the 

quasi-conductor-free test area, the seam was approximately 5 feet thick. With nominally 6 

inches of top coal, the entry/crosscut heights in this area averaged 54 inches. In haulage 

entries, the underburden was "trenched-out" giving entry heights of approximately 6 feet. 

Entry widths averaged 14 feet. The overburden consisted of 10 to 15 feet of unconsolidated 

shale (no draw slate was observed) above which was grey sandstone of undetermined thickness. 

The main north 2-west submain area used for both quasi-conductor-free and conductor 

proximity measurements consisted of 9 parallel entries. The quasi-conductor-free measurements were made three entries removed from conductors. The transmitter location remained 

unchanged for both sets of measurements. The conductor-proximity measurements were made 

largely in the main haulage entry (the entry with conductors closest to the transmitter). 

Mine maps and both the quasi-conductor-free and conductor proximity data are given in 

appendix A3. 
Key results of the testing include the following: 

a. A field strength level adequate for a maximum quasi-conductor-free communication 

range exceeding 1,000 feet in the Pittsburgh seam was demonstrated. The greatest 

usable test range was approximately 1,300 feet. 

b. The measured noise field strength levels along the main haulage conductors were as 

much as 27 dB greater near conductors than away from conductors with the noise levels 

near the trolley wire being the greatest (this compares with 30 dB predicted in comparing 

the median-mine-noise and trolley noise data). 

c. As range increases, the field strength at the receiver eventually is determined by 

reradiation from nearby conductors as evidenced by a very pronounced plateau in field 

strength with range. 

5.4 EASTERN ASSOCIATED COAL MINE FEDERAL NO 1 

The Federal No. 1 mine is in high coal in the Pittsburgh seam. In the 8-main north and 3- 

left main areas used respectively for quasi-conductor-free and conductor proximity testing, 

the seam height was 7 to 7-1/2 feet with 11 to 14 inches of top coal so that the entry/crosscut 

heights averaged 6 to 6-1/2 feet. Entry widths averaged 13 feet. The overburden consisted 

of approximately 60 feet of unconsolidated shale and no draw slate. An occasional 16- to 18- 

inch "wild" seam approaching as close to the main seam as 2 feet existed. 

The 8-main-north and 3-left-main area employed respectively 7-parallel-entry and 10- 

parallel-entry patterns. The quasi-conductor-free testing was performed 2 entries removed 

from a water line (partially buried) lying on the floor. The 3-left-main area, being mined as 

two adjacent and adjoining sections (10 and 22) contained conductors in nearly every entry. 

In the conductor-proximity measurements, the transmitter was located approximately 90 to 

100 feet from the nearest conductor. 

Mine maps and both the quasi-conductor-free and conductor proximity measurements are 

given in appendix A4. 

Key results of the testing include the following: 

a. A field strength level adequate for a maximum quasi-conductor-free communication range 

of 1,300 feet was demonstrated. The greatest usable test range was approximately 

1,200 feet. 

b. In an entry with conductors, fields strengths representative of conductor-free areas can 

be measured out to a range of several hundred meters if the transmitting antenna is 

located well away from conductors. At 236 to 238 kHz in this mine, this range was 

approximately 200 meters for an approximate 27-meter separation between the transmit 

loop and the nearest (7200-V ac cable) conductor. 

5.5 VIRGINIA POCAHONTAS NO. 1 MINE 

The VP No. 1 mine is in low-medium coal in the Pocahontas No. 3 seam. This seam is at a 

depth ranging between 1,100 to 1,200 feet in the valleys to 1,850 to 2,400 feet under hill crests. 

Mines in this seam are quite gassy. The seam height extremes in this mine ranged between 

38 inches in the north and 66 inches in the south. The 3-south and 2-north No. 1 plow test 

areas respectively had 54- and 48-inch seam heights. 

No top coal is left. The entry/crosscut width averages 29 to 22 feet. The overburden and 

underburden close to the seam consists of grey shale with a few inches of draw slate immediately above the seam. In the overburden above the gray slate is hard gray sandstone. 
The 3-south submain and 2-north No. 1 plow access to a nearby longwall section were both 

used for quasi-conductor-free tests and these areas were separated by about 2-1/3 miles. In 

the 3-south submain, field strength data was taken at two entries away from an air line lying 

on the floor; also, data was taken through a solid coal block. In the 2-north No. 1 plow area, 

the measured path was only one entry away nearest conductors, but the transmitter was 

located two entries away from the conductors. 

Mine maps and the quasi-conductor-free measurements for both areas are given in appendix 

A5. 

Key results of the testing include the following: 

a. The path attenuation through a solid coal block is greater than that along open entries. 

b. The maximum communication range through a solid coal block is 460 to 490 feet in the 

Pocahontas No. 3 seam. Collins Mine Wireless Prototype portable radios were used. 

The open entry maximum range is roughly 900 feet (as determined by comparison with 

field strength data. 

5.6 PEABODY COAL COMPANY MINE NO. 10 

The Peabody Coal Co. Mine No. 10 is in high coal in the Herrin No. 6 seam. This averages 

350 feet in depth in this part of Illinois. In the 1-south main test area, the seam height 

averaged 6-1/2 feet (no top coal) and the entry/crosscut width was 15 feet. In the 1-south 

1st west 2nd north section, the seam height averaged 7 feet (no top coal) with the entry/ 

crosscut width averaging 20 feet. The underburden close to the seam consisted of 1 to 2 feet 

at siltstone grading into claystone. The overburden consisted of gray shale near the seam 

(no draw slate) grading into hard limestone. 

The 1-south 1st west 2nd north section area was truly conductor-free and permitted multiple 

direction conductor-free transmission paths from a fixed transmitter location including 

through a solid coal block. The 1-south submain test area was 1 and 2 entries removed from 

conductors with the transmit being 2-1/2 entries removed from test conductors. 

Mine maps and both the quasi-conductor free data sets from both test areas are given in 

appendix A6. 

Key results of the testing include the following: 

a. Field strengths adequate for maximum quasi-conductor free communication ranges of 

330 feet for frequencies below 1000 kHz and 165 feet for frequencies above 1000 kHz 

were demonstrated. 

b. The range achievable through a solid coal block was less than that achievable in open 

entries. The attenuation rates were similar for these two cases but the coal block field 

strengths experienced an amplitude offset varying from 10 dB at 430 kHz to 20 dB at 

3400 kHz. 

c. A "periodic loading" effect was observed at 240 kHz on a path through coal pillars 

appearing as a standing wave in field strength with range. The maximum variation from 

the open entry field strength curve observed was *10 dB. 
6.0 CONC 

6.1 STAT 

This meal 

character 

has been I 

important 

(except fo 

particular 

for the se 

has been ( 

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(Herrin Nl 

strength d 

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fading, an1 

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USIONS AND RECOMMENDATIONS 

OF KNOWLEDGE OF PROPAGATION EFFECTS 

rement program has primarily provided magnetic field strength data toward 

ing mf radio wave propagation in conductor-free areas. This characterization 

~de according to seam type in three important seams (corresponding to three 

3ographic production regions) and in two or more locations per seam/region 

;he Pocahontas seam in Virginia). The extent of this data has shown that a 

leasurement set of field strength vs range and frequency was at least not atypical 

l/region. Secondarily, magnetic field strength data in proximity to conductors 

iained toward demonstrating area coverage between portable radios in conductorng section environments for seams giving the greatest (Pittsburgh) and the least 

6) communication ranges when away from conductors. Also, a few magnetic field 

a samples were gathered along conductor runs, developed in the process of check- 

~w "conductor-free" particular measurement paths ackally were. 

3e gathered during this program constitutes the first step toward designing wireystems for coal mines. The data base enables an estimate of "mean" propagation 

ics per seam/region and the test area deviations from this mean to be put forth. 

insufficient, however, for enabling a statistical propagation prediction analysis 

:ation performance to be made similar to those which can be made for hf, vhf, and 

round systems. In particular, these above-ground analyses predict the probability 

:ating (service probability) based on known statistics of location variability, signal 

ioise. The in-mine data base is not large enough to accurately access location 

that is, local variations in field strength in terms of nonuniformity of seam thickmogeneities in overburden/underburden and in terms of topological variations due 

pration of the mined areas. 

of noise data in mines has been gathered by NBS at lower frequencies (generally 

32). Above 200 kHz the best available estimate is an extrapolation of this lower 

ita. Also, the NBS data is not characterized according to its being carried by 

which becomes increasingly important at higher frequencies. The few times that 

ss prototype portable radios were tested in mines during this program, the noise 

. seemed to be characteristic of median-mine-noise. The majority of the time in 

?ee areas, however, the measuring equipment was set-noise-limited. We do not 

le noise floor(s) in quiet mine areas is (are). For tracked haulage communicans, the noise needs to be characterized according to proximity to dc power 

the ways in which these sources are tied into the trolley feeder system. 

data was available to permit defining the maximum range below about 100 kHz. 

.ta summarized in figure 14 shows that frequencies below 100 kHz are important 

maximum communication range in quiet areas of the Herrin No. 6 seam. Also, 

Losely coupled to conductors, frequencies below 100 kHz are important for obtainmum communication range. We cannot be sure that simple extrapolation to lower 

than were measured using the ADL 3-layer model will predict performance 

[hen using the higher-frequency-determined conductivities. This is because the 

; greater at lower frequencies. A theory embracing more than 3 layers may 

ie is lacking when the propagation paths are in proximity to conductors. Practical 

ss communication paths will invariably involve conductor proximity and the curinsufficient in extent to support a conductor proximity model of more sophisticat used in this report. Of most practical importance is the case where one of the 
radios is located remotely from conductors by one or more entries. The signal attenuation on 

the portion of the transmission path along the conductors will be very much a function of the 

conductor grouping configuration(s). The transmission performance will also be influenced 

by conductor branching and by shunting impedances along conductor strings. 

The measured data has consisted of field strength amplitude only and has not considered 

phase. While phase knowledge may be of secondary importance in characterizing communication range/coverage (multipath null field areas have not shown up during the measurement 

program) it is of importance in the development of mathematical models for computing 

propagational performance. A simple technique for measuring phase in a mine environment 

has not yet emerged. 

6.2 USABILITY OF PROGRAM RESULTS 

While the program results provide only guidelines toward predictive modeling synthesis of 

communication system designs, the data base in its current form is sufficient for system 

design if a more direct approach is taken for a particular mine. The more direct approach 

involves measuring certain propagation characteristics in particular mines for which a system 

is designed. The results can readily be used to determine what is to be measured and where 

it should be measured during the survey phase of the system design for a particular time. 

Knowing the conductor types and topology and the operational requirements for the system, 

estimates of maximum communication range can be made from the results in this report for 

a particular mine. This may require a reasonable assumption on current splitting at branch 

points, etc. These estimates will show locations in range where measurements of both signal 

and noise should be made. The calculations can then be modified using the measured results 

to extend the analysis to a larger operating area. Again, if not exposed by the first survey 

measurements, additional survey data can be obtained to positively identify the marginal signal areas and to assess the field strength location variability which occurs in these areas. 

6.3 POTENTIAL MF WIRELESS COMMUNICATION APPLICATIONS 

Originally conceived to serve communication needsin developing face areas forward of the 

section phones, ME wireless communication development activities and application concepts 

have been extended by the Bureau of Mines to include the following (some of which have 

evolved into separate programs): 

a. Haulage communications to and from a central dispatch point in trackless areas where 

trolley phone communications is not possible. 

b. Telemetry of data from methane sensors mounted on continuous miners to a remote 

monitoring location near the section power center; with the capability of shutting down 

the section power if necessary. 

c. Fire boss communications to serve safety and maintenance needs, particularly along 

extended belt haulage ways having limited pager phone capabilities. 

d. Telemetry of airflow data from remotely located air shafts to a central monitoring location to facilitate quick assessment of ventilation system failures. 

e. "Snapper" communications in tracked haulage applications for communicating between 

the locomotive operator and the man coupling strings of coal cars near the section headpiece tipple for example. 

Additional applications in section communications emerged from discussion with Peabody 

Coal Mine No. 10 personnel. These involved communications to expedite logistics over the 

entire section and communications to permit the face boss to control section operations 

efficiently. 
6.4 RECOMMENDATION FOR FURTHER MEASUREMENTS AND ANALYSIS 

Typical areas for further measurements and analysis have been alluded to in paragraphs 6.1 

and 6.2 which would lead toward a broader data base for system design applications. These 

have been data base expansions in seams/regions already visited. Additional areas for further measurements include low coal seams and possibly area coverage throughout longwall 

sections whose topologies depart significantly from room and pillar mining and which are 

characterized by large roof falls. 

For current energy resource reasons, coal mine communications has been emphasized during 

this program. EM signal propagation in mine types other than coal remains virgin research 

territory. 

Particular areas for further measurements and analysis, arranged in descending order of 

priority by the author, include the following: 

Performing measurements and modeling in additional high-productivity seam/region 

areas including low coal 

Investigating conductor proximity modeling plus verification measurements including 

characterizing important conductor groupings and topological strings of conductors 

Performing additional higher frequency mf noise measurements including characterizing 

noise sources and their coupling into mine power, control, and phone wiring. 

Investigating topological variations in mf propagation with emphasis on comparing solid 

coal block and room and pillar paths 

Performing measurements and modeling at lower frequencies than 100 kHz, including 

optimum frequency identification for long-range transmission conductors from closely 

coupled radios 

Performing measurements to assess location variability in coal mines 

Performing mf field strength vs range and frequency measurements in mine types other 

than coal 

Performing field mapping in conductor-dense section areas from a remotely located 

transmitter near the face. 

6.5 TYPICAL SYSTEM PERFORMANCE CONSIDERATIONS 

Consider the Pittsburgh seam as represented by the Federal No. 1 mine data for quasiconductor-free propagation shown on page A4-3 in the appendix. Let us choose the 479-kHz 

curve to represent nominal 500-kHz operation. The attenuation slope as determined from this 

curve is approximately 0.143 d~/meter. 

If the base station equipment were set-noise-limited, the increase in the base station sensitivity compared to that of the portable (from the equation given in section 4.0) is given by: 

base station antenna sensitivity increase = 20 loglO portable antenna area 
Using the attenuations slope defined above for the Pittsburg seam at 500 kHz, the set-noiselimited sensitivity (if it could be realized) would give a range increase of 

range increase = 27'1 dB = 190 meters. 0.143 dB/m 

If the noise level is median-mine noise, both the portable and base stations receiving 

equipments will be external noise limited so that no advantage is achieved with increased 

base stations receive sensitivity. 

The increased base station NIA over that of the portable is 

base station MA = 14 = 14.4 dB, 20 loglo portable NIA = 2.5 

which corresponds to a range extention over that of the portable of: 

14.4 dB 

range extention = 0.143 dB/m = 105 meters 

in a conductor-free area. Or, in proximity to conductors with the base station transmitter 

and portable transmitter assumed located at the same distance away from the conductor so 

that the increased base station MA corresponds purely to overcoming attenuation along the 

conductors; 

using the equation for attenuation, constant in section 4.0; at 520 kHz 

so that the range extention along the conductor is: 

= 1111 meters. 

6.6 EFFECT OF AN IDEAL REPEATER IN CONDUCTOR-FREE AREAS 

Now, consider the base station to be an ideal repeater (not limited by transmit noise spectrum 

at the receive frequency or limited by receiver desensitization) extending range of portableportable operation in a conductor-free environment. If the portables are both set-noise 

limited, the maximum communication range of 495 meters as determined from figure 1 for 

the Pittsburgh seam at 500 kHz is extended to: 

495 meters: the range from a portable assumed to be transmitting to the repeater 

if the repeater receive sensitivity were the same as that of the portable. 
plus 190 meters: The range increase due to the increased base station/repeater 

sensitivity over that of the portable, 

plus 495 meters: The range from the repeater assumed to be transmitting to the 

other portable if the transmit NIA of the repeater were the 

same as that of the portable, 

plus 105 meters: The range increase due to the increase base statiodrepeater 

NIA over that of the portable, 

which gives: 

495 + 190 + 495 + 105 = 1285 meters. 

Similarly, if the portables are both medium-mine-noise-limited, the maximum communications range of 290 meters as determined from figure 1 for the Pittsburgh seam at 500 kHz 

is extended to: 

290 meters: The range from a portable assumed to be transmitting to the 

repeater which is the same as that to another portable (both are 

external-noise-limited) , 

plus 290 meters; The range from the repeater assumed to be transmitting to the 

other portable if the NIA of the repeater were the same as 

that of the portable, 

plus 105 meters: The range increase due to the increased base station of repeater 

NIA over that of the portable, 

which gives: 

290 + 290 + 105 = 685 meters. 

6.7 EFFECT OF AN IDEAL REPEATER IN PROXIMITY TO CONDUCTORS 

Consider the base station to be configured as an ideal repeater to extend the portable-toconductor range while achieving a desired maximum range along a conductor. As a baseline 

reference, consider the minimum range along the conductor to be 1020 meters, (the range 

determined from figure 2 in the Pittsburgh seam at 500 kHz in median-mine-noise) with the 

receiver located 2 meters from the conductor and the transmitter located 30 meters from 

the conductor for assumed portable-portable operation. 

Consider the repeater to be located near the transmit end of the path at a range so as to 

permit the maximum range extention of the portable away from the conductor. The portable 

transmitter range of 30 meters is extended to: 

30 meters: The original range without the aid of the repeater, 

plus 290 meters: The range from the portable transmitter to the repeater, assuming 

the same INA for portable and repeater noted in paragraph 6.6, 

plus 105 meters: The range increase due to the increased base station/repeater 

NIA over that of the portable noted in section 6.5. 
which gives, 

30 + 290 + 105 = 425 meters if the repeater is located 30 + 105 = 135 meters away 

from the conductor. 

If the repeater were located at the original portable transmitter location 30 meters away 

from the conductor, the range extention would be 

30 + 290 = 320 meters 

and the distance along the conductor could be increased to 

1020 meters: The original desired maximum range along the conductor, 

plus 1111 meters: The increased range along the conductor if the increased NIA of 

the base station/repeater over that of the portable were used to 

overcome conductor attenuation 

which yields: 1020 + 1111 = 2131 meters. 

If the repeater, located at 30 meters from the conductor, were haulageway-noise-limited instead of median mine-noise-limited, the maximum range of the portable away from the 

conductor would be reduced to: 

320 meters: The range computed above, 

minus 70 meters: The range reduction due to a lO-dB increase in noise above 

median-mine-noise as determined from figure 17 and computed 

from 

10 dB = 70 dB 

0.143 d~/inch 

which gives: 

320 - 70 = 250 meters. 

Similarly, if the repeater (located at 30 meters from the conductor) were trolley-noiselimited, the maximum range of the portable away from the conductor would be further 

reduced to: 

250 meters, the range computed above for the haulage -noise-limit 

Minus 140 meters: The range reduction due to a 20 dB increase in noise above haulagenoise as determined from figure 17 and computed from 

20 dB = 140 dB 

0.143 d~/inch 

which gives 

250 - 140 = 110 meters. 

60 

APPENDIX A 

A1 - A6 

MINE TEST DATA 
APPENDIX A 

This appendix gives the mine maps and summary reduced field strength plotted data sets from 

each of the six Summary Data Reports prepared during this program. For additional information regarding a particular mine, the reader is referred to the particular Summary Data 

Report for that mine. 

The information in this appendix is organized as: 

Appendix A 1 Ireland Mine 

A2 Inland Steel Coal Mine No. 1 (Sesser) 

A3 Consolidation Coal Mine No. 95 (Robinson Run) 

A4 Eastern Associated Coal Mine Federal No. 1 

A 5 Virginia Pocahontas No. 1 Mine 

A 6 Peabody Coal Company Mine No. 10 

The particular references for the six Summary Data Reports are given as references (23) to 

(28). 
APPENDIX A1 

IRELAND MINE TEST DATA AT MEDIUM FREQUENCY 
IRELAND MINE DATA 

BELT ENTRY 

RETURN AIR ENTRY 

SUPPLY TRACK ENTRY 

POWER CENTER 
IRELAND MINE DATA 
IRELAND MINE DATA 

POWER CENTER 
I I I 

100 2 3 4 5 6 7 8 91000 

RANGE IN FEET 

Figure A1-4. Field Strength Data From Previous Testing in Ireland Mine -- Conductor-Free 8-

Normalized to a Transmit NIA = 2.5 (Performed Under Bu Mines Contract H034606
NOTE: PARALLEL COMPONENT DE

ORIENTATION COPLANAR W

PERPENDICULAR COMPONE

ORIENTATION PERPENDICU

TRANSMIT ANTENNA HMD O

IS PARALLEL TO CABLE 

A 493 KHZ 

950 KHz 

I I I I I I11 I 

100 2 3 4 5 6 7 8 1000 

RANGE IN FEET 

Figure A1-5. Field Strength Data Taken in the 8-North Submain Cable Entry Adjacent to the Fa

Fresh Air Entry With Transmitter Located at 31 + 85 Crosscut Proceeding South 

Line -- Data Normalized to a Transmit NIA = 2.5. 
NOTE: PARALLEL COMPONENT DENOTES HMD 

ORIENTATION COPLANAR WITH CABLE 

PERPENDICULARCOMPONENT DENOTE

ORIENTATION PERPENDICULAR TO CAB

TRANSMIT ANTENNA HMD ORIENTATION 

IS PARALLEL TO CABLE 

.ABOVE 8 BELOW 

SLACK IN CABLE 

0 I00 KHZ 

0 1988 KHZ 

(0) DENOTED PARALLEL F

(1) DENOTES PARALLEL F

COMPONENT 1 FOOT A

(2) DENOTES PERPENDICU

COMPONENT 1 FOOT A

(3) DENOTED PARALLEL F

COMPONENT 6 FEET F

(4) DENOTES PERPENDICU

COMPONENT 6 FEET F

(5) DENOTES PARALLEL F

COMPONENT 12 FEET 

I 

100 2 3 4 5 6 7 8 1000 

RANGE IN FEET 

Figure A1-6. Field Strength Data Taken in the 8-North Submain Cable Entry Adjacent to the Farth

Fresh Air Entry With Transmitter Located at 31 + 85 Crosscut Proceeding South To

Line -- Data Normalized to a Transmit NIA = 2.5. 
I 

Ia 

W NOTE: FIELDS FOR HMD ORIENTATION OF 

I- LOOP ANTENNA WITH LOOP PLANES 

2 PARALLEL TO PATH DIRECTION 

a EXCEPT AS NOTED 

I PERPENDICULAR I- COMPONENT 

P 

W 

-20 - 

(I) 

9 

W 

Y 

0 

-40- 0 ------ 

1 ant I I 

100 2 3 4 5 6 7 8 1000 

RANGE IN FEET 

a 

4 

I 

Figure A1-7. Field Strength Data Taken in 8-North Submain in Farthest Left-Hand Fresh Air Entry 

Located at 31 + 85 Crosscut Proceeding South Toward Main Line -- Data Normalized t

NIA = 2.5. 

A --- 

- -- 
NOTE: THE SOUTH AFRICAN RADIOS WERE USED F

THE TRANSMITTING AND REClEVlNG HMS'S 

DATA TAKEN IN THE CABLE ENTRY WAS 

ESSENTIALLY INDEPENDENT OF PARTICULA

PROXIMITY TO THE CABLE 

0 335 KHZ IN FARTHEST LE

AIR ENTRY 

335 KHZ IN CABLE ENTRY 

THE FARTHEST LEFT HAN

t t t t 

ACTIVE CABLE INACTIVE CABLE INACTIVE CABLE INACTIVE CABLE 

LEAVES CABLE BEGINS (OPEN CKRT) CABLE ENTERS STOPS (OPEN CKRT) 

ENTRY IN CABLE ENTRY LEFT HAND ENTRY IN LEFT HAND ENTRY 

I I III I I I 

100 2 3 4 5 6 7 8 91000 

RANGE IN FEET 

Figure A1-8. Field Strength Data Taken in the 8-North Submain With Transmitter Located at 2

Proceeding North Toward Grave Creek -- Data Normalized to a Transmit NIA = 
PARALLEL 

COMPONENT 

re I \ -\ NOTF. FIFI na Fna urrn nmrusastnn nc A.,~~.,.,... -. . .----. . -.. ..... ' ",.'L'.'"""I. "r .-.,"ICl"l"n

WITH LOOP PLANES PARALLEL TO PATH 

DIRECTION EXCEPT AS NOTED 

DATA TAKEN DOWN CENTER OF ENTRY, CABL

RUNS DOWN LEFT SIDE OF ENTRY 

PERPENDICULAR 

COMPONENT 

0 1988 KHZ PA

A 1988 KHZ PE

COMPONEN

I 1 111 

100 2 3 4 

I 

5 6 7 8 91000 

RANGE IN FEET 

Figure A1-9. Field Strength Data Taken in the %North Submain in Farthest Left-Hand Fresh A

Transmitter Located at 24 + 40 Crosscut Proceeding North Toward Grave Creek 

Normalized to a Transmit NIA = 2.5. 
NOTE: THE SOUTH AFRICAN RADIOS 

WERE USED FOR THIS TESTING 

a335 KHz. RECEIVE ANTENNA 

SPACING FROM CABLE WAS 1 FOOT 

AND COPLANAR WITH CABLE 

RANGE IN FEET ALONG CABLE 

Figure A1-10. Field Strength Data Taken in the 8-North Submain With Transmitter Located at 24 

Proceeding North Toward Grave Creek -- Data Taken in Close Proximity to Inact

Distance Normalized to Cable End Closest to Transmitter - Data Normalized to N
IRELAND MINE DATA 

ADJACENT CABLE ENTRY TRANSMITTER LOCATION 24+40 FOR 

FARTHEST LEFT HAND r FRESH AIR ENTRY /'- 

\\, RQUTE OF PORTION OF TERMINATED 7200 

VOLT CABLE SfGNIFtCANT TO MEASUREMENTS 
IRELAND MINE DATA 

TOWARD 

FACE 

AIR SCREEN FOR 

IMRiNSlC SAFETY 

SHUTTLE CAR PATH 

WITH DC TRAILING CABLES 

BELT CONVEYOR TAIL PIECE 

SUPPLY TWK 

TOWARD LEFT TOWARD LEFT HAND EDGE 

IN MEASUREM OF ENTRY IN MEASUREMENT 

TRAVERSE DlRECTlON 

POWER CENTER - CONVERTS 

7200 VAC TO 440 VAC FOR 

MINER AND 330 VOC FOR SHUTTLE CARS 

AC AN0 DC CABLES 

SUSPENDED FROM ROOF 
APPENDIX A2 

SESSER MINE TEST DATA AT MEDIUM FREQUENCY AND UHF 
I I SCALE: 1 INCH = 655 FEET 

Figure A2-1. Overall Perspective of Area in Which EM Measurements Were Made Inland Ste

No. 1 (Sesser) in Main East Section. 
SCALE: 518 INCH = 100 FEET 

Figure A2-2. Location of Quasi-Conductor-Free Range Vs Frequency Tests. 

9 0 

SCALE: 270 FEET = 1 INCH 

Figure A2-4. Topology of 1-Main East 9-Right Working Section and Measurement Traverse U

the Magnetic Field Strength Mapping. 
Figure A2-5. Magnetic Field Strength Coverage Map of 1-Main East 5-left and 6-Left 

Working Sections at 952 kHz With Transmitter Located Adjacent to the AC Power 

Cable in 1-Main East 5-Left With the 

Transmit Loop Antenna Oriented 

Parallel to the Cable -- The Field 

at Any Point is the Maximum 

Field in dB Greater Than 1 PA 

Per Meter Normalized to a 

Transmit NIA of 2.5. 

Figure A2-6. hlagnetic Field Strength Coverage Map of 1-Main East 5-Left and 6-Left 

Working Soctions at 1950 kHz With Transmitter located Adjacent to the AC Power 

Cable in 1-Main East 5-Left 'With the 

Transmit Loop Antenna Oriented 

Parallel to the Cable - The Field 

at Any Point is the Maximum 

Field in dB Greater Than 1 PA 

Per i\.leter Normalized to a 

Transmit NLA of 2.5. 

METER PER *A 1 THAN GREATER DB STRENGTH IN FIELD MAGNETIC 

+ 2 'a + 

Q UI 

0 

L= 

fi3 

I 

-a 
Figure A2-8. Magnetic Field Strength Coverage Map of 1-Main East 5-Left and 6-Left 

Working Sections at 265 kHz With Transmitter Located Adjacent to the AC Power 

Cable in 1-hIain East 5-Left With the 

Transmit Loop Antenna Oriented 

Parallel to the Cable - The Field 

at Any Point is the Maximum Field 

in dB Greater Than 1 pA Per Meter 

Normalized to a Transmit NIA of 

2.5. 

. ". , , , ,- . . . . . .. - .. . . . . 

.. . .. 

THE CONTOUR INTERVAL IS 6 DS SCALE: 
NNNNN 

11111 

YYYYY 

t1313t4 tl3d V" 1 NVHl tl31V3tlD Ba NI HlDN3UlS a1314 3113NDVW 
METER PER PA 1 GREATER THAN DB STRENGTH IN FIELD MAGNETIC 

+ 

(D 
LOT 

METER PER pA 1 THAN GREATER DB MAGNETIC FIELD STRENGTH IN 

in $gg$z mmm 00 

XXX xx 

I11 I1 

N NN N N 
NNNNN 

ILTXI 

YYYYY 

V)V)vIOO 

V)O)V)OINP~OV) 

5 

z 

I I I I I 1 

0 0 0 0 g 0 0 lo L? * 0 N 0 N 1 .* 

+ + + + + k 

tl313W t13d V"L NVHH t13lV3tlO 8a NI HlON3MlS a13U 3113NOVW 
ROOF 

FLOOR 

1 I I I I I I I 

0 20 40 60 80 100 120 140 160 

RANGE - METERS 

Figure A2-14. Magnetic Field Strength Vs Range in Quasi-Conductor-Free Area of 1 Main E

Transmit and Parallel HMD Receive Antenna Orientations. 
ROOF 

+ 255 KHz 

0 495 KHz 

0 955 KHZ 

a 2000 KHZ 

0 4570 KHZ 

I I 1 I I I I I I 

0 20 40 60 80 100 120 140 160 

RANGE - METERS 

Figure A2-15. Magnetic Field Strength Vs Range in Quasi-Conductor-Free Area of 1 Main Ea

Orientation of Transmit and Receive Antennas. 
APPENDIX A3 

CONSOLIDATION COAL MINE NO. 95 (ROBINSON RUN PORTAL) 


H313W tl3d VQ NVHl tl31V3tlD 8(1 NI HlDN3tllS a1314 3113NE)VW 

117 
METER PER #A 1 THAN GREATER DB STRENGTH IN FIELD MAGNETIC 
I I I 

m 

0 

I 

0 

I 

0 0 0 

L 0 'C 

8 V) + + * 0 :' z + + + + 0 N 

U313YY tl3d V" 1 NVHl tl3lWtlO 80 NI HlDN3UlS 01314 3113NOVW 
Figure 

Range 

Pardle

Locate

Conduc

Antenn

to Cond

Orlent

+60 

2 '5a. 

e 

x 

3 

.. 

2 +4oE 

a 

2 a -30. .m 

m 

I 

I 

k 

'20. 

Y) 

3 

Y 

". 

g*,o. 

Z 

C1 

I 

0. 

-10. 

- 

n o 

45"0\ AREA OF CONSOL

N1A -25 

0- 

A 

\ 

lo 

0 40 80 120 760 2W 240 

RANGE - METERS 

APPENDIX A4 

EASTERN ASSOCIATED COAL FEDERAL NO. 1 MINE (EDDY PORTAL) 

33 2 0 

gvw 53 .$ 

x.2 0 Agaa* m-02 'dq!%, k 

m E2332 

;*ma, 0f3:a $mm&g g 2?.2'"&~P, 

ON* gC.4 $3 ,z 

bT3ZQg 

Ej 5:E.is 

l0Olrn~ t*l"Z k a& * 22s &4 

gokwa 

%Zf%r; - 0 6 Q &4+ 

-GC%~~BN!~ 
TCT 

METER PER MA 1 THAN DB GREATER IN FIELD STRENGTH MAGNETIC 
tl313W tl3d V" 1 NVHl H31V3tlD 80 NI HlDN3tllS a1313 3113NDVYU 
Ftgure A

Range in 

North Ar

Federal 

meet of 

and Path

Wlz Incl

Une in E

+WC 

-50 

= +10 

! 

E 

D 

4, 

- 130 

3 

t 

3 

g *m8 

z 

z -1DE 

LL 

C m 

a 

0 

g 

.*a 

30 

p. 

- 

- 

- 

N1A-2

D OUASl-C

(SAME A

Q DATA FR

- a DATA F

0 DATA FR

" t DATA F

2s WWt

- 

4 - I I I I 

0 M 80 120 180 m0 240 

RANOE - METERS 
FIELD STRENGTH 18 INCHES FIELD 

/FROM 300 V DC WIRE IN TRACK ENTRY FROM 

POWE

Figure A4-6. Magnetic Field Strength Vs Range in 3 Left Main Section 10 Area of Eastern Asso

Federal No. 1 Mine (Eddy Portal) in Power Cable and Track Entries for Transmi

Antenna Located 27 Meters From 7200 V AC Cable and With Transmit Antenna 

Loop Plane Oriented HMD Parallel With Entries at 236 kHz. 

-30 I I I I I I I 

0 

40 80 120 160 -- 200 240 280 320 360 

RANGE - METERS 
-3J :o I I I I 6 I I I 

80 120 160 200 240 280 320 360 

RANGE - METERS 

Figure A4-7. Magnetic Field Strength Vs Range in 3 Left Main Section 10 of Eastern Associated 

No. 1 Mine (Eddy Portdl in Belt Entry for Transmit Antenna Located 27 Meters F

7200 V AC Cable and With Transmit Antenna Loop Plane Oriented HMD Parallel 

Wth Entries at 236 kHz. 

a 

W 

t; 

AMPLITUDE SHOWING EFFECT 

OF COSINE TRANSMIT ANTENNA 

Z 

PATTERN 

4 

I 

; t20 

W 

I9 FIELD STRENGTH 18 

a 

0 

m 

+I0 z 

F 

CL w m s w (I: I-

" 0- 

9 

W 

Y 

I! 

b 

Z 

0 -10- 

4 

z 

0 FROM BELT SUPPO

AALA-A\ 

FIELD STRENGTH NEAR CROSSCUT 

BARRIERS OFF THE BELT ENTRY 

"\ 0 
NIA = 2.5 

AMPLITUDE SHOWING EFFECT 

OF COSINE TRANSMIT ANTENNA 

PATTERN 

-300 I I I I I 

40 80 120 160 200 240 280 320 

RANGE - METERS 

Figure A4-8. Magnetic Field Strength Vs Range in 3 Left Main Section 22 of Eastern Associated 

No. 1 Mine (Eddy Portal) in Power Cable Entry for Transmit Antenna Located 27 

7200 V AC Cable in Section 10 and With Transmit Antenna Loop Plane Oriented HM

Parallel with Entries at 236 kHz. 
NIA = 2.5 

0 238 KHz 8 MAlN NORTH QUASI-CONDUCTOR-FREE 

236 KHz 3 LEFT MAlN SECTION 10 BELT ENTRY 

236 KHz 3 LEFT MAlN SECTION 10 POWER CABLE ENTRY 

Q 236 KHz 3 LEFT MAlN SECTION 22 POWER CABLE ENTRY 

-301 I I I I I I 

0 

I 

40 

I 

80 120 160 200 240 280 320 

RANGE - METERS 

Figure A4-9. Comparison of 236 and 238 kHz Magnetic Field Strength Vs Range Data in Eastern 

Federal No. 1 Mine (Eddy Portal) in Both Quasi-Conductor-Free and Conductor-Pr

Environments: Quasi-Conductor-Free Curve Segments Only. 
APPENDIX A5 

ISLAND CREEK COAL CO. VIRGINIA POCAHONTAS NO. 1 MINE 
WATER LINE 

SCALE: 1 INCH = 324 FEET 

* 

Figure A5-1. Topology of 3-South Area of Island Creek Coal Co. Virginia Pocahontas No. 1 Mine 

Locations for Quasi-Conductor Free Measurements. 


LOWER FREQUENCIES 

COPLANAR ORIENTATION OF BOTH ANTENNAS 

! ENTRY A ENTRY B 

\ ./ ---- 51 KHZ 

- 

12 - KHL ---- 95 KHz 

\ 

\ ./ 

/ '. 

\ \.' 

RELATIVE / \ 

AMPLITUDE SCALE ONLY 

1 'A 

\.I 

I I 1 I I 

40 80 120 160 200 240 

1 

RANGE - METERS 

Figure A5-4. Magnetic Field Strength Vs Range in 3-South Area of Island Creek Coal Co. 

Virginia Pocahontas No. 1 Mine Comparing Two Paths Along Adjacent 

Entries (TX Located in Measurement Entry for Both Paths) NIA = 2.5. 
HIGHER FREQUENCIES 

COPLANAR ORIENTATION OF BOTH ANTENNAS 

MEASURED IN ENTRY A; ONE ENTRY 

AWAY FROM AIR LlNE (TO THE LEFT PROCEEDING 

AWAY FROM TRANSMITTER) AND ONE ENTRY AWAY 

FROM SOLID COAL BLOCK (TO THE RIGHT 

PROCEEDING AWAY FROM TRANSMITTER) - - - MEASURED IN ENTRY B ADJACENT TO 

SOLID COAL BLOCK AND TWO ENTRIES AWAY 

FROM AIR LlNE (TO THE LEFT PROCEEDING 

AWAY FROM TRANSMITTER) 

ENTRY A ENTRY B 

A 920 KHz ---- 920 KHZ 

0 1840 KHz. 

0 ---- 2720 KHZ 

El 3200 KHz 

0 3800 KHz 

RANGE - METERS 

Figure A5-5. Magnetic Field Strength Vs Range in 3-South Area of Island Creek Coal Co. 

Virginia Pocahontas No. 1 Mine Comparing Two Paths Along Adjacent 

Entries (TX Located in Measurement Entry for Both Paths) NIA = 2.5. 
COPLANAR ORIENTATION OF ANTENNAS 

-25 I I I I 1 1 

0 40 80 120 160 200 240 

RANGE - METERS 

Figure A5-6. Magnetic Field Strength Vs Range in 2-North No. 1 Plow Area of Island 

Creek Coal Co. Virginia Pocahontas No. 1 Mine (TX Located 1 Entry 

Away From Measurement Entry) NIA = 2.5. 
520 KHZ 

COPLANAR ORIENTATION OF ANTENNAS 

LAB MEASURED 20 DB - - - - 

QUIETING LEVEL T----- 

\ 

\ TEST STATION 9 TWO ENTRIES 

FROM WATER LINE, TONE WITHIN 

3 DB OF TANGENTIAL NOISE 

-40 I I I I I i 

0 40 80 120 160 200 240 

RANGE - METERS 

Figure A5-7. Magnetic Field Strength Vs Range in 3-South Area of Island Creek Coal Co. 

Virginia Pocahontas No. 1 Mine for Collins Mine - Wireless Radio on 

Path Around and Through Solid Coal Block NIA = 2.5. 
APPENDIX A6 

PEABODY COAL CO. MINE NO. 10 


0 ALONG COAL BLOCK 

PARALLEL TO COAL BLOCK a ONE ENTRY OVER 

-30 I I I 1 

0 

1 

20 40 60 80 100 

RANGE - METERS 

Figure A6-3. Magnetic Field Strength Vs Range in Room and Pillar Area of 1-Main South 

1st West 2nd North Working Section of Peabody Coal Co. Mine No. 10 at 

240 kHz for Coplanar Antenna Orientation and NIA = 2.5 Comparing 

Paths. 
Figure A6-4. Magnetic Field Strength Vs Range in Room and Pillar Area of 

South 1st West 2nd North Working Section of Peabody Coal Co. 

Mine No. 10 at 480 kHz for Coplanar Antenna Orientation and 

NIA = 2.5 Comparing Paths. 

+so- 

+40- 

+30- 

+20- 

+loo - 

-10- 

-20- 

-30 

a ALONG COAL BLOCK 

a THROUGH COAL BLOCK 

UBMAIN, PARALLEL 

0 

A 

0 

0 I I I I 1 

20 40 60 80 100 

RANGE - METERS 
Figure A6-5. Magnetic Field Strength Vs Range in Room and Pillar Area of 1-Main 

South 1st West 2nd North Working Section of Peabody Coal Co. Mine 

No. 10 at 910 and 920 kHz for Coplanar Antenna Orientation and 

NIA = 2.5 Comparing Paths. 
0 ALONG COAL BLOCK 

0 PARALLEL TO COAL BLOCK 

ONE ENTRY OVER 

RANGE - METERS 

Figure A6-6. Magnetic Field Strength Vs Range in Room and Pillar Area of 1-Main 

South 1st West 2nd North Working Section of Peabody Coal Co. Mine 

No. 10 at 1800 kHz for Coplanar Antenna Orientation and NIA = 2.5 

Comparing Paths. 
0 ALONG COAL BLOCK 

Figure A6-7. Magnetic Field Strength Vs Range in Room and Pillar Area of 1-Main 

South 1st West 2nd North Working Section of Peabody Coal Co. Mine 

No. 10 at 3100 kHz for Coplanar Antenna Orientation and NIA = 2.5 

Comparing Paths. 
0 ALONG COAL BLOCK 

ATHROUGH COAL BLOCK 

a TOWARD SUBMAIN, PARALLEL 

TO TRACK 

RANGE - METERS 

Figure A6-8. Magnetic Field Strength Vs Range in Room and Pillar Area of 1-Main 

South 1st West 2nd North Working Section of Peabody Coal Co. Mine 

No. 10 at 3400 kHz for Coplanar Antenna Orientation and NLA = 2.5 

Comparing Paths. 
0 FRESH AIR ENTRY 

ADJACENT TO RETURN AIR 

0 ONE ENTRY OVER, TOWARD 

MAIN CENTER 

-30 1 I 1 

0 20 40 60 80 100 

RANGE - METERS 

Figure A6-9. Magnetic Field Strength Vs Range in l-South Conductor-Free Entries Near 

the 5-1/2-East/l-South Junction of Peabody Coal Co. Mine No. 10 at 

83 kHz for Coplanar Antenna Orientation and NIA = 2.5 Comparing 

Paths. 
0 FRESH AIR ENTRY 

ADJACENT TO RETURN AIR 

fER, TOWARD 

+so - 

B L +40 - 0 FRESH AIR ENTRY 

I ADJACENT TO RETURN AIR 

5 

P ONE ENTRY OVER, TOWARD 

P MAIN CENTER 

z 

a 2 +30 - 

0 

z 

7 

Z 

2 + 

rr. +20 - 

w 

u 

CI 

m 

0 

z +lo - 

E 

n 

W 

E 

V, 0- 9 

W 

Y 

I! 

ki 

Z 2 -10 - 

I 

-20 - 

-30' I I 1 

0 20 40 60 80 100 

RANGE - METERS 

Figure A6-10. Magnetic Field Strength Vs Range in 1-South Conductor-Free Entries 

Near the 5-1/2-~ast/l-south Junction of Peabody Coal Co. Mine 

No. 10 at 245 kHz for Coplanar Antenna Orientation and 

NIA = 2.5 Comparing Paths. 
0 FRESH AIR ENTRY 

ADJACENT TO RETURN AIR 

ONE ENTRY OVER. TOWARD 

MAIN CENTER 

RANGE - METERS 

Figure A6-11. Magnetic Field Strength Vs Range in 1-South Conductor-Free Entries 

Near the 5-1/2-~ast/l-South Junction of Peabody Coal Co. Mine 

No. 10 at 420 kHz for Coplanar Antenna Orientation and 

NIA = 2.5 Comparing Paths. 
PATH THROUGH COAL PILLAR 

PATH THROUGH COAL PILLAR CORNER 

PATH ALONG COAL PILLAR 

PATH THROUGH COAL PILLAR 

PATH THROUGH COAL PILLAR 

CORNER 

PATH ALONG COAL PILLAR 

-20 loo 0 20 RANGE 40 - METERS 60 80 100 

Figure A6-12. Magnetic Field Strength Vs Range in 1-South Conductor-Free Area Near 

the 5-1/2-~ast/l-South Junction of Peabody Coal Co. Mine No. 10 

at 420 and 1800 kHz for Coplanar Antenna Orientation and 

NIA = 2.5 on Paths Generally Perpendicular to Entries 

From a Fixed Transmitter Location. 
APPENDIX B 

ERRATA AND ADDED CALIBRATION INFORMATION 
APPENDIX B 

The NM-25 calibration data at nominally 500 and 1000 kHz used in reducing the Ireland Mine 

data was in error. The field strength at 500 kHz should be increased 8.2 dB and the field 

strength at 1000 kHz should be decreased by 1.1 dB. The correct calibration factors were 

used in reducing the data taken in the other five mines. 

The frequency of 100 kHz was the most difficult at which calibration of the receive system 

was accomplished. This was due to the transition region at about 100 kHz which occurred 

between sets of equipment used to make the calibration measurements. The calibration level 

of 251.2 pV was determined by extrapolating the antenna factor for the reference antenna used 

in the screen room as checked by plotting a smooth curve through successive calibration points 

above 100 kHz from 150 kHz up. .The absolute accuracy of this calibration level is unknown 

but expected to be within &3 dB. 

A calibration level was developed for 50 kHz, but was not used during the program due to 

equipment failures and lack of backup test equipment in this frequency. This calibration level 

was 230 p~/m using the low frequency antenna tuner on band 3 or, correspondingly, 1293 

p~/m using the high-frequency antenna on band 1. 

Early calibration data of the receive system was made over small frequency ranges about 

fixed frequencies. Later in the program, additional calibration information was gathered 

which enabled the average curve shown in figure 11 to be drawn. The earlier fixed frequency 

calibrations were used for all frequencies close to these points, however, in reducing the 

measured data for this program. The error incurred in this way of using the calibration data 

is estimated to be less than 1 dB at any particular frequency. 
APPENDM C 

MAGNETIC FIELD STRENGTH SENSITIVITY OF AN FM RECEIVER 
APPENDIX C 

As an alternative approach to the determination of the magnetic field strength sensitivity of an 

FM receiver, the following analysis is offered which is based on the'measured loop resistance 

rather than loop Q. 

Let Y = 4noNA x 

Where o= 2 nf 

N = number of turns 

A = loop area in meters 2 

The matched output voltage of a loop, transformed to an impedance Z is 

H 

E = Ys volts 2 RL 

where RL is the loop resistance; 

where Hs = magnetic field strength in A/m. 

The 12-dB SINAD noise figure relationshig for a 50-ohm FM receiver with a 12-kHz IF 

bandwidth, using EIA test procedures is ( ). 

where NF, can be considered to be the system noise figure in dB. 

Now, if there is no external noise field Hn, the equivalent external noise figure = 1, and 

NTs = 10 log Fr, the receiver noise figure. In general, however, since the external noise 

power Pn, injected at the receiver input terminal is 

The equivalent external noise figure Fx, can be derived from 

Pn = (Fx - 1) k To 

*"FM Noise Figure and 12 dB SINAD Sensitivity", R. P. Decker, Spectra Associates 

Internal Memo, 4-15-76 
The system noise figure Fs is 

Fs = Fx - 1 + Fr (ratios) 

Converting equation (2) to volts, and allowing for an input impedance Z other than 50 ohms 

(but requiring a match between loop and receiver), we have 

+F xlO -7.836985 volts 

4RL k To r 

Combining equations (1) and (6), we have 

Hs = 3686.8484 PA/^ 

fnA 

Using equation (8) and assuming 

2 

y2 Hn 

4RL k To >> Fr (set noise limited sensitivity) 
For the Collins mine wireless radio: 

f = 520 kHz 

RL = 5.0 ohms 

Fr = 1.59 (2 dB) 

N = 7 turns 

we find 

It is interesting to note that the effective noise power of the above receiver is equal to the 

external noise power when the external noise field is -84.8 dB below 1 pA/meter/ mz 

The sensitivity of the base station receive system is 

or 19 dB greater than the portable system. 

The increase in base station communication range mentioned in sections 6-6 and 6-9, then 

become 133 meters in lieu of the 190 meters computed by the loop Q method. 
REFERENCES 

Summary Data Report, "Rose Valley Mine Measurementst1, Mine Wireless Propagation 

Test Program, Spectra Associates, Inc., Bureau of Mines Contract H0346067, Phase 1, 

Collins Groups Subcontract C-65171, 7 January 1975. 

Summary Data Report-2, "Ireland Mine Measurements", Mine Wireless Propagation 

Test Program, Spectra Associates, Inc., Bureau of Mines Contract H0346067, Phase 1, 

Collins Groups Subcontract C-65171, 12 March 1975. 

Report, Research and Development Contract, Volume 3, Theoretical Data Base, Section 

7.5, Theoretical Predictions for In-Mine Propagation, pp 7-16 through 7-36, Spectra 

Associates, Inc., (R. Decker principal contributor) Bureau of Mines Contract H0232056, 

Collins Groups Subcontract C-696447, 15 November 1974. 

Op Cit Summary Data Report-2, 'IIreland Mine Measurements," p 26. 

R. Lagace and F. Emslie (Arthur D. Little Co.), "Theory of the Propagation of Low and 

Medium Frequency Radio Waves in a Coal Seam, Radio Science," Vol. 11 No. 4, 

pp 253-262, April 1976. 

Loc Cit R. Lagace & F. Emslie. 

W. Bensema, M. Kandu, I. W. Adams, 'lElectromagnetic Noise in Robena No. 4 Coal 

Mine," NBS Technical Note 654, April 1974. 

Op Cit Report, Research and Development Contract, Vol 3, Theoretical Data Base, 

Section 6; "The Application of Recent NBS Noise Data to Mine Communications, p 6-30. 

Ibid, Ref (2), Summary Data Report-2, "Ireland Mine Measurements." 

Loc Cit W. Bensema, et al. 

Ibid, Ref (a), Report, Research and Development Contract, Vol 3, Theoretical Data Base, 

p 6-30. 

Ibid, Ref (a), Report, Research and Development Contract, Vol 3, Theoretical Data Base, 

o 6-30. r- --- 

(13) Ibid, Ref (2), Summary Data Report-2, "Ireland Mine Measurements." 

114) Ibid. Ref (4). Summary Data Report-2. "Ireland Mine Measurements," p 26. 

Ibid, Ref (2); Summary Data ~eport-2 j "Ireland Mine Measurements." ' 

Summary Data Report-4, Eastern Associated Coal Federal No. 1 Mine (Eddy Portal), 

"Propagation of EM Sgnals in Underground Mines," Spectra Associates, Inc., Bureau 

of Mines Contract H0366028, Collins Groups, Subcontract C-651333, p 3-5, 

December 1976. 

Summary Data Report-3, Consolidation Coal Mine No. 95 (Robinson Run Portal), 

tlPropagation of EM Signal in Underground Mines," Spectra Associates, Inq., Bureau 

of Mines, Contract H0366028, Collins Groups Subcontract C-651333, p 3-5, 

December 1976. 

R. P. Decker, "FM Noise Figure and 12-dB SINAD Sensiti~ity,'~ Spectra Associates, 

Inc. Internal Memorandum, April 15, 1976. 

Loc Cit, R. Lagace and F. Emslie. 

Loc Cit, R. Lagace and F. Emslie. 

W. Weeks and R. Fenwick, Engineering Report, Submerged Antenna, Collins Groups, 

CER-T1477, pp 12-13, May 1962. 

Ibid, Ref (a), Report, Research and Development Contract, Vol 3, Theoretical Data Base, 

p 6-30. 

The following six reports were prepared under Bureau of Mines Contract H0366028, Collins 

Groups Subcontract C-651333, Spectra Associates Inc., Subcontract 002607 entitled "Propagation of EM Signals in Underground Mines." 

(23) T. Cory, Summary Data Report-1, "Ireland Mine Test Data at Medium Frequency," 

1 October 1976. 
(24) T. Cory, Summary Data Report-2, "Sesser Mne Test Data at Medium Frequency and 

UHF," November 1976. 

(25) T. Cory, Summary Data Report-3, "Consolidation Coal Mine No. 95 (Robinson Run 

Portal), December 1976. 

(26) T. Cory, Summary Data Report-4, "Eastern Associated Coal Federal No. 1 Mine 

(Eddy Portal)," December 1976. 

(27) T. Cory, Summary Data Report-5, "Island Creek Coal Co. Virginia Pocahontas No. 1 

Mine," February 1977. 

(28) T. Cory, Summary Data Report-6, "Peabody Coal Co. Mine No. 10,11 March 1977.