HOME OFFICE AND MANUFACTURINO PLANT - RATON, NEW MEXICO 

RESEARCH AND DNELOPMENT LABORATORY - BOULDER, COLORADO 
som - to1 

REPORT DOCUMENTATION 2 3 Reclplent'r Arcesr~on NO 

PAGE I iI. ___ -__ *. __ _. _ -- 2 -. --- 

4. Tttle and Subt~tle 

A Medium Frequency Wireless Communication -- 1983 (Submi: - 

System For Underground Mines -- -- 

7. Author(3 I. Padormlng Or8an1zat1on Rcgt. No 

Dr. Larry_G.Stolarczyk 9. Pertormtng Organ~zat~on Name and Address 

A.R.F. Products, Inc. 

Gzrdner Road 

Raton, New Mexico 87740 

- -- - - - -- - 11. Contract(C) or Cranl(C) No. 

12. !$ponuxing Or anizalion Name and Address 

Jnlted 5?tates Department of Interior 

Bureau of Mlnes 

4800 Forbes Avenue 

13. Typ. of Report L Period Covered 

Final 28 Dec 79 . 

. . 

31 Jan 83 , - - - - - -- - - - - -. . 

Pittsburgh, Pennsylvania 15213 - -- 1% Supplementary Not~ 

An underground medium frequency radio communications system ha 

been developed and demonstrated in both coal and metal/non met 

mines. 

I The principal advantage of the system are its low cost, ease c 

installation and the ability to provide radio communications t 

any vehicle or roving miner in the underground mine. The syste 

provides high quality radio coverage in work areas and along 

manways with existing "wireplant" conductors. The conductors 

include AC power cable, telephone cable, metal water and high 

pressure air pipes, etc. The measured communications range 

from the base station to mobile transceive~ exceeded 12,500 ft 

without the use of repeaters. A cost/benefit analysis shows 

that the in-itial cost of the equipment can be returned 2-6 

times in the first year. The mine productivity increases by 

approx. 13 percent. 5 

17.. Document kulrls t!. huriptorr 

Mlnes ; radlo communications ; communications ; coal mines ; metal, 

lnon metal mines; radio propagation; tunnel mode, coal seam mode 

I wave propagat ion ; underground mine ; mine rescue radio ; trapped 

miners ; radio vest transceiver. 

c COSAft Field/Group 

1L AwilabilrTy %atemen( 1 19. Secur~ty Class Cfh~s ReoorO 1 21. No. of Pages 

Iunclassif ied 

Release Unlimited 20. !hcur~ty class CT~TS. ~~~r) 22. Pncm Unclassif led 

(See ANSCZ39.18) Sea Instruct~ons on R.v~rse 

--i -- 

OPTIONAL FORM 272 (4-7 

(Formerly NT1535) 

Department of Comrnwme 

ion 

1 
USBM H0308004 

FINAL REPORT 

A MEDIUM FREQUENCY WIRELESS COMMUNICATION 

SYSTEM FOR UNDERGROUND MINES 

HARDWARE DESIGN AND PRELIMINARY 

PERFORMANCE TESTS 

INSTALLATION AND PERFORMANCE 

IN UNDERGROUND MINES 

Dr. Larry G. Stolarczyk--Program Manager 

Mike Sepich, Kurt Smoker 

A.R.F. PRODUCTS, INC. 

RATON, NEW MEXICO 87740 

The views and conclusions contained in this document 

are those of the author and should not be interpreted 

as necessarily representing the official policies or 

recommendations of the Interior Department's Bureau 

of Nines or of the U.S. Government. 

JANUARY 19 8 3 

UNITED STATES 

DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 
24 January 1983.. 

Applications for inventions developed in the course of the 

work have been filed with the Patent Office under Public Law 

96-517. 
TABLE OF CONTENTS 

PAGE 

Foreward 

List of Tables 

List of Figures 

I. INTRODUCTION AND PROGRAM SUMMARY 

A. OBJECTIVE 

B. APPROACH 

C. FINDINGS AND CONCLUSIONS 

11. SYSTEM DESIGN PLAN 

A. SUMMARY 

B. INTRODUCTION 

C. TYPICAL ORGANIZATIONAL STRUCTURE 

D. INFORMATION FLOW 

BENEFIT ANALYSIS 

F. SYSTEM ARCHITECTURE 

111. DESCRIPTION OF THE WHOLE MINE RADIO 

COMMUNICATIONS SYSTEM 

A. SUMMARY 

B. INTRODUCTION 

C. EF EQUIPMEIJT 

1. Mobile Transceivers 

a. Vest Transceiver 

b. Vehicular Transceiver 
TABLE OF CONTENTS (CONT'D) 

PAGE 

2. Fixed Location - Repeater 

3. Base Station 

4. Coupling Devices 

a. RF Line Coupler 

b. Antenna 

FIELD MAINTENANCE 

INSTALLATI ON 

1. Keyman Meeting 

2. Define Communication Needs 

and Coverage 

3. Selecting Needed Networks 

4. Mine Map 

5. Installation Plan 

6. Insuring System Usage 

IV. THE SYSTEM DESIGN 

A. SUMMARY 

B , INTRODUCTION 

C. HISTORY 

D, NOISE GENERATED IN MINE POWER SYSTEM 

E. SIGNAL PROPAGATION MODES 

1, Seam Mode Propagation Theory 

2 . Transmis s ion Line Propagat ion Modes 
TABLE OF CONTENTS (CONT'D) 

PAGE 

Fu COUPLING MF SIGNALS TO THE 

"WIREPLANT" 

1. Transmitting Loop Antenna and TwoWire Transmission Line Coupling 

2. Transmitting Loop Antenna To Receiving 

Loop Antenna Via Transmission Line 

Coupling 

3. Attenuation Rate 

G. LOOP ANTENNA DESIGN CONSIDERATIONS 

Design Optimization Process 

2. Antenna Area Constraints 

a. Vest Antenna Area Constraint 

b. Vehicular Antenna Area Constraint 

3. Design For Operation In Hazardous 

Atmosphere 

4. Theoretical Basis For Loop Antenna 

De s ign 

H. RF LINE COUPLER DESIGN 

I. MODULATION PROCESSES 

ACOUSTICAL NOISE PROBLEMS 

1. Overview of Microphone Noise 

Cancelling Theory 

2. Evaluation of Noise Cancelling 

Microphones 

3. Evaluation of Vest Microphones 
TABLE OF CONTEJTTS (CONT'D) 

PAGE 

4. Evaluation of Vest Speakers 

5. Evaluation of Acoustical Transducers 

on Mine Vehicles 

K. FREQUENCY PLAN AND PRESELECTOR FILTER 

DESIGN REQUIREMENTS 

1. Preselector Filter Network Discrimination 

Loss Specification 

2. Calculating The Discrimination Loss of 

Bandpass Filter Networks 

3. Discrimination Loss of Couplers and 

Antenna Filter Networks 

4. Discrimination and Dissipation Loss 

of the Preselector Network 

5. Designing Filter Networks 

a. Designing Low Pass Filters 

b. Designing A High Pass Filter From 

. A Low Pass Prototype Network 

c. Designing Bandpass Filters From 

Low Pass Prototype Filters 

d. Designing Band-Elimination Filter 

Networks From Low Pass Prototype 

Filter Networks 

e. Determination of the Discrimination 

Loss of Actual Bandpass and BandElimination Filters From the 

Discrimination Loss of a Low Pass 

Prototype Filter 
TABLE OF CONTENTS (CONT'D) 

PAGE 

SYSTEM DESIGN SPECIFICATIONS 

A. SUMMARY 

B. INTRODUCTION 

C. GENERAL SYSTEM SPECIFICATION 

D. BASE STATION AND VEHICULAR TRANSCEIVER 

SPECIFICATIONS 

1. Standard Transceiver 

2. Remote Control Terminal (RCT) Unit 

3. Remote Audio Head (RAH) 

E. REMOTE CONTROL CONSOLE 

F. VEST TRANSCEIVER SPECIFICATIONS 

1. Permissible Battery Pack 

2. ART-29 Vest Transceiver 

G. REPEATER TRANSCEIVER SPECIFICATIONS 

1. Repeater Block Diagram 

H. STANDARD MODULE SPECIFICATIONS 

LINE COUPLER AND ANTENNA SPECIFICATIONS 

VI. FIELD DEMONSTRATION 

A. MAGIW COPPER COMPANY, SAN MANUEL DIVISION 

1. Magma s Cornmunicat ion System 

2. The MF Communication System 

3. Test Results 

a. Test 1 - Vest Communications To Audio 

Room Base Station from Grizzly and 

Product ion Levels 
TABLE OF CONTENTS (CONT'D) 

PAGE 

b. Test 2 - Vehicular and Vest 

Communications To Audio Room Base 

Station Via Audio Conductors On 

Production Level 

c. Test 3 - Vehicular Communication To 

Base Station Relocated To 5 Shaft 

(Via Dedicated Wire on 2375 Level) 

d. Test 4 - Hoist Communications Test 

Base Station In Hoist Control Center 

e. Test 5 - Hoist Communication Test 

Base Station At The Collar 

4. Conclusion 

PLATEAU MINING COMPANY 

1. Installation of MF Equipment 

2. Installation of Repeaters 

3. Test Results 

4. Quality and Performance 

5. Lessons Learned 

6. Demonstration Results 

YORK CANYON COAL MINE 

1. Installation of MF Equipment 

2. Measurement Results 

3. Mine Rescue Communications 

4, Demonstration Results 
TABLE OF CONTENTS (CONT'D) 

RANCHERS EXPLORATION AND DEVELOPMENT CORP. 

1. Escalante Communication System 

2. Installation of MF Equipment 

3. Field Test 

VII. RECOMMENDATIONS 

A. BIDIRECTIONAL AMPLIFIER 

B. REDUCE LOSS ACROSS AC POWER TRANSFORMERS 

AND SWITCHES 

C. BETTER WAYS TO DEPLOY TWIN-LEAD CABLE 

D . TELEPHONE SYSTEM INTERFACE NETWORKS 

E. PAGING AND EMERGENCY COMMUNICATIONS 

F. RESCUE TEAM COMMUNICATIONS 

G . HOIST COMMUNICATIONS 

H. NATIONAL EMERGENCY FREQUENCY 

I. EMERGENCY COMMUNICATIONS 

J. TRAINI-NG MINE MANAGERS 

APPENDIX A NORMALIZED DISCRIMINATION LOSS 

(NORMALIZED ATTENUATION) OF THE 

LEGENDRE TRANSFER FUNCTION 

APPENDIX B DISSIPATION LOSS OF THE LEGENIIRE 

TRANSFER FUNCTION 

APPENDIX LEGENDRE FILTER ELEMENT VALUES 

PAGE 

LIST OF EFERENCES 
LIST OF TABLES 

Table Page 

Productivity Multiplier Worksheet 

Overlay Frequency Plan 

Cooperating Mines 

Typicai Equipment List 

RF Line Coupler Transfer Impedance (1 Inch) (omitted) 

Induced Line Current (omitted) 

Comparison of Measured and Calculated 

Twin-Coil Loop Vehicular Antenna Parameters 

RF Line Coupler Transfer Impedance 

(1 Inch) 

RF Line Coupler Induced Line Current 

Measured Sound Pressure Level Of 

Mining Machines 

Measured Articulation Index 

Recommended Microphone and Speakers For 

Use In Underground Mines 

Signal Path Power Level and Discrimination 

Loss 

Standard Transceiver Specifications 

Remote Control Terminal (RCT) Specifications 

Remote Control Head (RCH) Specifications 

Remote Control Console (RCC) Specifications 
LIST OF TABLES (CONT'D) 

Table Page 

Vest Transceiver Specifications 

RF Line Coupler Specifications 

Antenna Specifications 

Vest Transceiver Communications To 

Audio Room Base Station (Via 2315 and 

2375 Level Audio Cables) 

Vehicular and Vest Cornmunicat ions To Audio 

Room Base Station (Via Main Haulageway 

Audio Conductors) 

Vest and Vehicular Communications To 5 

Shaft Base Station 

Hoist Communications Signal Level Cage To 

Base At The Drum 

Hoist Communications Signal Levels Cage To 

Base At The Collar 

Signal To Noise Ratio Measurements At Base 

Station From Repeater Locations 
LIST 

Figure No. 

FIGURES 

Page 

1 Formulation of the System Design 

Specifications 

2 Typical Organization Chart 

3 Typical Production Profile 

4 System Architecture 

5 Radio Coverage Cells in an Underground 

Mining Complex 

The "Near" Magnetic Field Radio 

Cornmunicat ions System 

Use of Base Station and Repeater 

Radio Coverage Cell at the Face 

Fl/F2 Signalling 

Vest Transceiver 

Vest Control Head 

Vehicular Transceiver 

Repeater Transceiver 

Remote Control 

Remote Control Console 

RF Line Coupler 

Tuned Loop Antenna 

System Planning Guide 

RF Line Coupler Installation 

Base Station and Repeater Control 

Cable Installation Diagram 
LIST OF FIGURES (CONT'D) 

Figure No. Page 

2 1 Seam Mode Field Components 

2 2 Signal Current (I) Flow on 

Conductors (n=2) 

Geometries For a Vertical Transmission 

Line and Transmitting Loop Antenna 

Equivalent Transmission Line Network For 

Induced Voltages and Currents 

(Z1=Z2=Z0) 

Signal Coupling to a Receiving Loop 

Antenna 

Set Up For Measuring Induced Line Current 

Induced Line Current Versus Vehicular 

Transceiver Distance From Base Station 

Transmitting Loop Antenna Excitation 

Current and Magnetic Moment 

Collins Prototype Portable MF Transceiver 

South African Portable Transceiver 

Twin Coil Transmitting Loop Antenna 

Parallel Equivalent Circuit of a 

Single Coil Loop Antenna 

Unloaded Q Versus Frequency for a Flexible 

Rectangular Tubular Lexan Antenna 

Unloaded Q Versus Frequency for a Flexible 

Rectangular Planar Lexan Antenna 

Typical Matching Network 

Inductive Coupling in the Twin-Coil 

Loop Antenna 
LIST OF FIGURES (CONT'D) 

Figure No. Page 

3 7 Equivalent Circuit of the Twin-Coil 

Loop Antenna 

3 8 RF Line Coupler 

3 9 Signal Coupling From the "Wireplantl' 

(Cylindrical coordinates r, z, Q 

Test Set-Up for Measuring Induced Current 

as a Function of Line Resistance (RL) 

Over the Earth Multiple Wire Coupling 

Typical Modulation Process Gain 

Acoustical Noise Comparisons 

The Vought Second.Order Microphone Technique 

Normalized Noise Frequency Response At A 

Gradient Microphone 

PVFP Noise Cancelling Microphone and 

Circum-Aural Ear Cup Speakers Mounted On 

Miners Cap 

Hard Hat Mounted Speakers 

Digital Frequency Synthesizer Tuning 

Elements 

Transmitter To Receiver Isolation 

Comparison Of The Discrimination Loss Of 

Well Known Transfer Functions (5th Order) 

Low Pass Prototype Filter 

Legendre Band Pass Filter Discrimination 

Loss For Orders n=3,5,7 and 9 
LIST OF FIGURES (CONT'D) 

Figure No. Page 

5 3 Legendre Band Elimination Filter 

Discrimination Loss For Orders 

n=3,5,7, and 9 

5 4 Base Station And Vehicular Transceiver 

Block Diagram 

5 5 Block Diagram Of Remote Control Terminal 

(RCT) Unit 

5 6 Remote Audio Head (RAH) Block Diagram 

5 7 Remote Control Console (RCC) 

5 8 Vest Transceiver Block Diagram 

5 9 Block Diagram Of Permissible Battery Pack . 

6 0 Front and Rear Views Of Vest Transceive~ 

6 1 Repeater Block Diagram 

6 2 Grizzly And Production Level Drifts 

6 3 Illustration Of Loader And Motorman 

Loading Train 

6 4 Magma Communications Resources 

6 5 Mine Map Of Production Level 

6 6 Mine Map Of GrizzlyLevel 

6 7 Illustration Of Hoist Communications System 

6 8 Simplified Drawing Of The Plateau Mine 

6 9 Photograph Of Vehicular Transceiver 

Installation 

70 Photograph Of Vehicular Antenna 

Installation 
LIST OF FIGURES (CONTtD) 

Figure No. Page 

71 Simplified Plan View Drawing Of The 

York Canyon Mine 

Cross Section Of Manway (Looking Inby) 

Installation Of RF Line Coupler 

Photograph Of The Tera Jet Jeep Antenna 

Installation 

Induced Line Current Versus Vehicular 

Transceiver Distance Froin Base Station 

Radio Coverage Area At Cross Cut 31 Along 

Manway (3100 Feet From Base Station) 

Radio Coverage Area At Cross Cut 91 Along . Manway (9100 .Feet From Base Station) 

Plan View Of Transmission Line Aided Radio 

Coverage (Pair of Insulated #16 Conductors) 

Redco Silver Ore Body 

Plan View And Entry Cross Section Of The 4970 

Level Drill Sub-Level North Undercut 

B-B' View Of The Ore Body (VCR Mining) 

System Block Diagram 

Redco Silver Mine Haulage Drifts 

Emico Truck Showing Vehicular Antenna 

Circum-Aural Ear Cups 

Induced Line Current Versus Vehicular 

Transceiver Distance From Base Station 

8 7 Use Of Cap Lamp Receiver For Emergency 

Communications 

Location And Rescue By Medium Frequency 

Techniques 

89 Basic MF Communications Between Rescue 

Team Members 
INTRODUCTION AND PROGRAM SUMMARY 

OBJECTIVE 

The objective of this work was to design, develop and 

construct Medium Frequency (MF) communications equipment's 

for demonstration in operating underground mines. 

Recent theoretical and experimental radio wave propagation work conducted under the sponsorship of the U.S. 

Bureau of Mines (USBM) determined that low loss electromagnetic wave propagation modes exist in MF frequency band 

(300 to 1000 kHz). Using these modes, cells of radio coverage 

can be provided along the entries and in the working areas of 

an underground mine. Since the wave propagation modes take 

place because of the natural physical configuration of the 

mine, the transmission medium is already in place in the 

nation's underground mines. 

In previous work the USBM determined that commercially 

available VHF and UHF radio communicaticns equipment either 

was limited in coverage or required the installation of 

leaking feeder cable and repeaters. Although the leaky 

feeder communications system provided acceptable coverage 

along the entries (with leaky feeder cable), it failed 

around corners, through barracks, rock falls, etc. 
The principal advantage seen by the USBM for the MF 

system was its low cost, ease of installation and the ability 

to provide radio communications to any vehicle or roving 

miner in the underground mine. 

Because the necessary MF radio equipments needed to 

construct a whole mine communication system were not available 

on the market, the USBM initiated this program. 

Be APPROACH 

First, radio communication needs of coal and metal/ 

non-metal (M/NM) mining organizations were determined by 

systematically analyzing the structure, functioning, performance of organizations and the behavior of groups and 

individuals within them. Drawing together this background 

information and synthesizing the conclusions as to how the 

organization efficiency could be improved with radio cornrnunications, a system design plan meeting the present and future 

needs was formulated. This plan was used in developing block 

diagrams and specifications for each equipment needed in 

the system. 

Upon completion of the system design plan, the effort 

was directed in two related areas. First, the work focused 

on solving problems related to environmental and human factors 

and involving the use of electronic equipment in mining. 
Since the environmenta1,human factors and communications 

problems are so unique in mining, new thinking was required 

in the equipment design approach to realize an acceptable 

system. Lessons learned in developing radio equipment for 

military applications were sought out, evaluated and applied, 

where practical in the design of the equipment. Secondly, 

breadboards for each MF equipment were designed and built. 

As an extension of our laboratory evaluation, breadboards 

were evaluated in nearby mines. Weak points in the design 

. were resolved, resulting in a final design specification. 

Next, prototype equipments were manufactured and laboratory tested for compliance with the specifications. 

Finally, the MF equipment was installed and made operational in four (4) mines. The four Western mines that agreed 

to participate in the system demonstration program were: 

Ranchers Exploration and Development Corp., Redco Silver 

Mine, Enterprise, Utah; Kaiser Steel Corp. , York Canyon Coal 

Mine, Raton, New Mexico; Getty Oil Company, Plateau Coal 

Mine, Price, Utah; and the Magma Copper Company, San Manuel 

Division, San Manuel, Arizona. The size of the mines ranged 

from small (500 tons/day) to large (67,000 tons/day) and 

represented mining methods in common use in the U.S. mining 

industry. The performance of the whole mine communications 

system was evaluated in each of the mines during many months 

of field testing. 
C. FINDINGS AND CONCLUSIONS 

The MF communication systems that were installed in the 

demonstration mines provided high quality radio coverage in 

work areas and along manways with existing "wireplant" conductors. The conductors include AC power cable, telephone 

cable, metal water pipe and high pressure air pipe, etc. 

Excellent system performance was due in part to technological improvements achieved in the design of radio equipment for use in underground mining environment. Field testing 

lead to new discoveries about the characteristics and use of 

radio cornrnunications in mining. The discoveries will increase productivity, improve management performance and 

organizational team work, and reduce maintenance cost. Use 

of radio will make the mine a safer place to work. Radio 

will also revolutionize mine search (trapped miner location), 

and rescue team methods. 

Many important technological contributions to underground radio technology occurred in this work. First, highly 

efficient antennas and electrical conductor coupling devices 

were developed and evaluated in each mine. A unique antenna 

design featuring a twin-coil planar antenna structure achieved 

high magnetic moment, a fundernental requirement for inducing 

high level carrier currents in nearby electrical conductors. 

The optimized antenna design was also shown to be a highly 

sensitive device for receiving weak underground radio signals. 
The air-core toroidal RF line couple- achieved high coupling 

efficiency to the existing mine conductors. The efficient 

antenna and coupler designs are partially responsible for the 

excellent performance of the communications systems in the 

mines. Secondly, the use of high sensitivity superhetrodyne 

receiver design, that performed well in the high acoustical 

and electrical noise environment of the mine, was a major 

factor in receiving MF signals at great range from a base 

station location. Finally, the development of a small light 

weight transceiver that can be sewn into the miners' work 

clothing solved an important human factor problem .associated 

with the use of personnel carried transceivers in mining. 

From the point of view of comfort and convenience, the 

transceiver was sewn into a vest garment. The transceiver 

modules were distributed on the vest to reduce bulkyness. 

The vest did not in anyway restrict the miner's movement in 

tight quarters. The vest design features unique circuit to 

enable use in hazardous atmosphere encountered in both coal 

and some metalhon-metal mines. The vest design has been 

approved by the Mine Safety and Health Administration. 

The radio communication systems were installed in mines 

with the principal goal of solving a wide variety of communications related problems. The problem ranges from those 

associated with equipment installation and survivability 
in the mine environment to providing radio coverage in 

varying situations likely to be found in mining practice. 

Another goal was to determine the benefit of radio in the 

mining process. 

The communications range from the base station location 

(usually at the mine portal) to mobile transceivers in the 

manways (with conductors) was measured in miles. The same 

range was found to exist between mobile transceivers. A 

remarkable discovery was observed in the "listing" (receiving) 

range of a transceiver. MF signals can be received everywhe~e conductors exist in the mining complex. Transceivers 

in the surface office complex can listen to MF radio transmissions occurring in the underground mine. This occurred 

even when the conductors were not intentionally "illuminated" 

by the antennas and couplers. Thus, MF signals are distributed by natural coupling existing between conductors in the 

mine wiring. This discovery will have broad implications in 

trapped miner and rescue technology. In a layared formation 

like coal, the talk-back (transmitting) range included adjacent conductor less manways. It is difficult to make accurate radio signal propagation measurements in any mine, 

none the less measurements were made in every mine. The MF 

signal to noise ratio was measured at the base station 

location. The measured ratio frequently exceeded 50 dB 
when a mobile transceiver was a mile or more from the base. 

Since a 20 dB ratio provides good intelligibility, voice 

quality was remarkable. The attenuation rate measured along 

the AC power cable and telephone cable was less than 

4 dB/1000 feet. Considering the ratio and the MF signal 

attenuation rate, operating range from a base will be greater 

than 12,500 feet. AC power transformers add approximately 

10 dB to the transmission lcss. AC switches and transformer 

loss makes AC power cable a lower quality and less reliable 

MF signal distribution network. 

High quality and reliable MF signal distribution can be 

provided by installing low cost twin-lead cable in conductorless or AC power cable manways. Communications range will 

exceed 15,000 feet along the cable. Another extremely important aspect of the MF system is its ease of installation. 

Preliminary demonstrations to mining companies required less 

than 5 minutes of installation time. Permanent installation 

of all equipment and any twin-lead cable can be accomplished 

in a few hours. 

In every mine, unique communication problems were encountered and easily solved with the MF equipment. The 

multiple level Magma Copper Mine uses the block caving mining 

process. Mucking occurs on the grizzly level. Trains are 

loaded on the production level. Radio communications were 
extended to battery powered service vehicles and off-train 

men. Roving miners with vest transceivers were able to 

communicate from the grizzly and production levels to the 

surface control center. The use of radio enabled front line 

production foreman to better coordinate mucking activities. 

Hoist communications were also evaluated. Instead of 

"illuminating" the hoist wire rope at the sheave wheel 

location, as is common practice with the commercally 

available equipment, the highly efficient vehicular antenna 

was used to "illuminate" the wire rope at the collar. The 

RF coupler was clamped (like a current probe) around the 

wire rope just above the cage. The signal to noise ratio 

was measured as the cage traveled in the shaft. The signal 

to noise ratio exceeded 100 dB. 

The medium sized York Canyon coal mine employs conventional as weil as longwall mining technology. The Plateau 

Coal Mine uses conventional mining methods. Both mines use 

conveyor belt haulage. Vehicular transceivers were installed 

on diesel and battery powered service vehicles. Maintenance 

personnel and beltmen were assigned vest transceivers. 

Radio coverage included all manways and the entire longwall 

in the York Canyon Mine. The base was located at the portal. 

The talk-back (transmitting) range was limited to manways 
with telephone cable or AC power cable. The range exceeded 

15,000 feet. In some instances, the talk-back range extended to drifts adjacent to the manways. The listening 

(receiving) range included all manways with conductors. 

Repeaters were not required in the mine. The Plateau Mine 

working faces are more than three miles from the portal. The 

base station was located at the one mile point and repeater 

transceivers were installed near the working faces. In 

this mine, the primary MF distribution signal network was 

AC power cable. Some of the manways did not include AC 

cable. Radio coverage in manways with cable was excellent 

(exceeded 50 dB). However, twin-line cable was required in 

the conductorless manways. 

The Redco Silver Xine uses a modified vertical crater 

retreat (VCR) mining method developed in Canaia. Articulated 

rubber tired vehicles transport muck out of the mine. Radio 

communications to the motormen was excellent. 

The primary conclusion to be drawn from this work is 

that the MF radio communications system is a productivity 

and safety multiplier. Actual experience with the system 

in these mines shows that the keyman "reach" time has been 

reduced from an average of 35 minutes to seconds. 
Keymen receive first hand information instead of second 

hand information. More importantly, radio significantly 

improves team work, a factor of significant importance in 

improving productivity and safety. Our studies show that 

the existing telephone system, by its inherent limitation, 

isolates keymen from the main mine communications resource 

most of the time. By being isolated, roving miners retain 

their independence. The price paid for independence by the 

mining company is low productivity. Things do not have to 

be as they are in underground mining. Experience in the 

field tests show that radio improves information flow rate, 

replacing independence with team work in the working group. 

The availability of vital information, through the radio 

communications resource, will enable miners to better coordinate their activities and instantly reorder work 

priorities when required during a working shift. An exceedingly important organizational benefit is that the use 

of radio creates a definite sense of "belongingnessu in the 

working groups and in the mine organization. Because of 

"belongingnessM, miners affiliate more closely with the 

organization - this permotes team work. 

Cost/benefit analysis shows that the initial cost of 

equipment can be returned 2.6 times in the first year. Total 

mine productivity will increase by approximately 13 percent. 
the 

Mines wishing to install and use radio can following 

step step planning guide given Chapter Section 

D, of this report. Lessons learned in the demonstrations 

included the fact that management must be active in the 

initial planning of the system and must insure its initial 

use. Bear in mind that miners are accustomed to working independently. They will prefer to keep it that way. Trained 

maintenance personnel are required to keep the system in 

top working order. The equipment used in the system has been 

designed for high reliability and ease of troubleshooting by 

anyone with previous radio experience. The radio equipment 

was designed around a standard set of plug-in modules. Troubleshooting skill level only the board level. 
11. SYSTEM DESIGN PLAN 

A, SUMMARY 

The system design plan was formulated during Phase I 

time period of this project. The design plan included a 

definition of the system architecture, operating features 

and performance specifications. The plan was formulated 

by an iterative process of market and system research, 

The process is illustrated in Figure 1. 

PRELIMINARY 

I I 

DRAFT 

FIGURE 1 FORMULATION OF THE SYSTEM DESIGN 

SPECIFICATIONS (1) 
The first step in the iterative Trocess was the formulation of a preliminary draft of the system design plan 

by the program Research and Engineering (R and E) group. 

R and E group developed seminar materials (35rnrn slides of the 

system concept, mock-up models of personal transceivers, etc.) 

for presentation to different levels of management and operating personnel in both small and large coal and M/NN mining 

organizations. In all, twelve seminars were conducted at 

mines across the United States. The seminars succeeded in 

correctly defining the communications needs, equipment installation constraints, human factor problems, and the hostile 

mine environment conditions. During each seminar, forecast 

of the economic benefit of using radio were made with the 

cooperation of mine personnel. Production rates (tons/hour) 

were determined for each component of the mining process. 

Components that exhibited significant differences in maximum 

to actual (prior 12 month average) rate were examined to 

determine how radio could be used to improve the actual rate 

and reduce mining cost. With this vital information, the 

R and E group was able to tailor the system design to maximize 

benefit. 

Finally, as an extension of the laboratory aspect of 

the R and E work, breadboard models of the radio equipments 

were evaluated in nearby mines. 
Users indicated that the communication needs in coal 

and metal/non-metal (M/NM) mining organizations are different. 

However, there also exist many common needs. The most important 

common communications need was to create a radio comrnunications 

link between the maintenance foreman and his crew. Radio 

communications must be provided to the point of equipment 

break-down and to service vehicles that transport vital repair 

parts. The second most important need was to improve communications between keymen to better coordinate the production 

task. Production supervisors must have the capability of 

altering work priorities as conditions change in the mining 

process during the working shift and to communicate with the 

maintenance foreman. Radio links must exist between the superintendent, front line foremen and other keymen. Maintenance 

and production comrnunications networks are required in every 

mine. It was found that these networks should exhibit a party 

line characteristic so that all members of the working group 

have the same information. Separate networks are required 

for coordinating and directing haulage traffic and hoist 

operations. 

The communication networks must be distributed in the 

sense that each network can be operated independently of the 

other networks. The design of radio equipment must withstand 

the hostile mine environment and not be onerous to roving 

miners. 
INTRODUCTION 

Mine managers and engineers are driven in their thinking 

by production and safety concerns. They know that a safe 

mine is a productive mine. Attitudes are forged by the 

realization that more must be attempted than can be done with 

existing methods in any eight (8) hour shift. Further, they 

perceive that productivity and safety are greatly influenced 

by the geology of the formation, the mining process, type and 

maintainability of the mining equipment, the attitudes of the 

work force, effectiveness of the communication resources used 

in the mining organization, etc. Within their individual 

training experience and organizational constraints, managers 

do all that they can do to minimize mining cost. 

Methods of enhancing productivity in modern day industry 

have been ex~ensively studied and evaluated by researchers 

in many different disciplines. Researchers in the field of 

organization theory are concerned with structure, functioning, 

and performance of organization and the behavior of groups 

and individuals within them (2). Successful managers tend 

to equally concentrate their attention on three (3) productivity factors: 

1. The application of advanced technology and improvement 

skills. 
2. The systematic ordering of operations to minimize 

overall production cost. 

3. The organization of team work. 

The first factor tends to capture the interest of most 

managers. Managers and engineers by training and experience 

are able to relate technology improvements to improved 

productivity. In order to be informed of latest technological 

advances, they eagerly attend shows of mining equipment and 

read trade publications. They spend a great deal of time 

evaluating improvements in their mining process. The second 

factor is well developed in almost every organization. In 

general, managers are able to organize the physical plant 

and processes for near optimum operations. The third (team 

work), by comparison with the other two, is almost wholly 

neglected. Yet it remains true that if the three key factors 

are out of balance, the organization as a whole will not be 

successful. The first two operate to make an organization 

effective, the team work makes it efficient. 

The organization of team work and its effect on productivity was studied by Mayo (4) in the now famous Hawthorne 

Case. This study showed that a close relationship of the 

working group with management was a key factor in improving 

productivity. As management worked more closely with members 

of the working group, productivity increased. In 1948, 

Bavelas (5) considered the relationship between the behavior 
of small working groups within an organization and the 

patterns of communications (6). The group structure consisted of cells connected one to the other. What defines a 

pattern is the way cells are connected. The purpose of the 

work was to consider the psychological conditions that are 

imposed upon the group members by various communication 

patterns and the effects of these conditions on the organization and the behavior of its members (7) . The concept of 

centrality became the chief determinant of behavioral differences because centrality reflects the extent to which a 

miner is strategically located relative to his source of 

information in the pattern. Centrality derives from the 

belief that the availability of information necessary for the 

solution of the problem will be of prime importance in 

affecting the miner's behavior. Centrality is a measure of 

a person's closeness to all other group members, and hence is 

a measure of the availability of information necessary for 

solving problems. It is quite easy to see how the availability of information affects behavior within a working 

group. An individual who can ra2idly collect information 

will be seen by others in a different way from an individual 

to whom vital information is not accessible in a reasonable 

time period. 
The study of how information flows through a mining 

organization is interesting since it affects the design of 

a whole mine radio communications system. Further, the study 

will show how the system is to be designed to improve centrality in the mining organization. 

C. TYPICAL ORGANIZATIONAL STRUCTURE 

Through the years, mining companies have organized 

into pyramidal type of organizational structures. The 

structure is similar in many ways to organizational charts 

found in industrial firms producing a constant product over 

a long period of time. 

I GENERAL MANAGER I 

MAINTENANCE 

SUPERINTENDANT 

MECHANICAL 

1 CREW I 

FIGURE 2. 'L'YYlCHL UKbHlU~~tnllun ~nnnl 
Underground miners are organized into small semiautonomous working groups (crews) (4). The groups accomplish 

specific tasks necessary in the mining process. The location 

of the crews in the mining complex depends upon the task. 

For example, production crew members spend most of their time 

in the working section (face, stope, etc.). By way of contrast, maintenance crew members may be anywhere in the mining 

complex. 

Keymen are responsible for a smooth running mine. The 

superintendent coordinates and directs mining activity 

through his foremen. The foreman directs the working group. 

The efficiency of organization is measured in terms of 

product tonage produced per man-shift. 

D . INFOR?WTION FLOW 

It is well known that the communication resources 

employed in the Nation's underground mines have remained 

relatively unchanged over the past two decades. It is 

interesting to observe that this occurred during a period of 

high rate of technological change in new extractive technology and equipment. The reason fcr this is threefold. 

First, management and mine equipment manufacturers understand that bigger-better-automated mining equipment improves 

the machine component of productivity. Secondly, managers 

percei-ve ghat the)! have maximized the human component of 

productivity (in some cases, "beat the union horse to 
death"). Finally, most managers are not radio communications 

specialists. They f a i l t o perceive how radio can be a - productivity multiplier. 

In the present day mining organizations, information 

flows by several communication methods. At the beginning of 

each shift, the superintendent and foremen meet to outline the 

work task, objectives and priorities. Foremen relay vital 

information to members of their crews. During the working 

shift, the pager telephone system becomes the primary communications resource. 

Based upon the work of Bavelas, centrality is expected 

to be a measure of productivity. This has been confirmed in 

the course of this work by observing group management activities during shift changes in several coal and M/NM mines. In 

high productivity coal mines (greater than 25 ton/man-shift), 

meetings were held at the beginning of each shift. The meeting 

included all superintendents and foremen belonging to the inand-out-going shifts. Some of the crew members were also 

present. Members of the management team freely discussed 

problems encountered on the prior shift. The likelihood of 

the problems emerging again on the next shift were also 

discussed. By their presence, maintenance crews were 

apprized of possible problems. Repairs were scheduled to 

avoid production down time. In one mine a "crash" vehicle 

containing emergency repair parts was stationed underground 
and used in emergencies by the maintenance crew. It was 

interesting to note that the face production crew on the outgoing shift left the mining equipment in position to reduce 

start up time for the next crew. In lower productivity mines, 

the meetings at the beginning of a shift were noteworthy in the 

sense that they tend to be "by chance" one-on-one encounters 

between the superintendent and his own foremen. Thus, lower 

centrality occurs in a low productivity mine. 

Although management and other mine personnel have wished 

to use radio to improve production rate, the pager telephone 

system remained the only available communications resource. 

Lack of coverage in the mining complex was management's most 

frequent criticism of the system. Timely messages needed for 

adequate coordination fail to reach keymen. The lack of good 

communications in the developing years of modern mining processes, has contributed to many unsound mine management 

practices. Interviews with mine supervisory personnel 

emphasizes some of the problems. One superintendent said 

"I don't need radio, I have the Bell System - if my foreman 

doesn't know what he is doing, 1'11 fire him1'. Another said, 

"We have gotten along without radio so far, we don't need 

it. The reason I work underground is that I am not hastled 

by managementv. 
These statements are noteworthy in several respects. First, 

they confirm the fact that experienced miners (the ones that 

have not been fired!) know how to do their job - they only 

need to communicate when unexpected events occur. Secondly, 

cornmunicat ion from the superintendent to the foreman tends 

to be autocratic. "Go fix. . . If, etc. Since no one likes to 

receive autocratic messages, miners in working groups are 

"satisfied" with the poor telephone coverage. By being 

isolated from the information source most of the time, roving 

miners retain their independence. The price paid for independance is low centrality and productivity. Things do not 

have to be as they are in underground mining. Radio can be 

used to increase centrality, replacing independence with 

(1) synergism ln the working group. The availability of vital 

infcrmati~n, through the radio comrr~unication resource, will 

enable the miners to coordinate their activity and create a 

definite sense of "belongingness" in the working group and 

the mining organization. 

(1) Synergism - Cooperative action of individual working 

groups such that the total effect is greater than the 

sum of the two effects taken independently. 
E. BENEFIT ANALYSIS 

Users indicated that the communication needs in coal 

and M/NM mining organizations are quite different. However, 

there also exists many common needs. 

In coal, production depends strongly on the availability 

of face equipment. Potentially more coal can be mined than 

can be transported out of the mine. 

The Jet Propulsion Laboratory (JPL) and others have 

extensively studied the effects of equipment down time on 

productivity (8) (9). Their work shows that the down-time 

period tends to increase with the complexity of the mining 

equipment. Increased complexity also requires greater proficiency on the part of the maintenance crew members. In 

some mines, the proficiency of new maintenance crew members 

is suspect and repair burdens have been found to be shifted to 

others (skilled repairmen and supervisors). The average 

availability time of 35 continuous miners studied in the JPL 

work was 73% of the face time (production shifts less travel 

time). The availability of the longwall section was found 

to be near 76%. These figures exclude time lost to travel, 

scheduled maintenance, moving equipment, etc. Hence the 

availability is often less than 50%. In metal/non-metal 

mining, productivity is also dependent upon the equipment 

breakdown factor. In this case, the factor is the availability of the haulage system. The effect of mining equipment down-time on productivity is shown in the figure below. 
A 

ENTER 

HOURS 

FIGURE 3. TYPICAL PRODUCTION PROFILE 

Productivity is naturally lost during scheduled startups, lunch breaks and shift change activities. As Figure 

3 shows, unscheduled down time has a significznt effect on 

productivity. The cost of down time depends upon the 

failure point in the mining process. Failure in a working 

section may range from a few thousand dollars per hour to 

tens of thousands of dollars per hour on the main haulageway 

system. Thus the system cost can be justified by saving only 

a few production hours. 

The use of radio will enhance productivity and safety 

in the following ways: 
1. The average time to reach a keyman with the pager 

telephone system in both coal and M/NM mines is 35 minutes. 

This statistic was established by placing a call (paging) 

to both superintendents and foremen in the mine and measuring 

the reply time interval. 

Breakdowns occurring at the face or on the haulageway 

require communications between keymen to resolve the matter. 

As a result, mining equipment down time depends upon the 

"reach time'! Assuming that at least one breakdown occurs per 

shift, radio communications between maintenance and production 

keyrnen will reduce down time by 35 minutes per shift. 

2. Because of the'beach time'; critical telephone messages 

must frequently be relayed by others. Thus keymen frequently 

receive inaccurate information. This costs more than most 

mine managers realize. 

In one mine clean-up operation, wayside litter was 

gathered and shipped out of the mine on two coal cars. 

Seventy-five percent of the litter was in fact vital repair 

parts. Frequently, a wrong part is ordered from the warehouse and delivered to the point of equipment breakdown. 

Sometimes the part is delivered to the wrong location. 

Thus, the use of radio will lower the real cost of repairs. 
3. The single channel audio paging telephone system has 

been upgraded in recent years. Direct dial multiple channel 

(star and branch networks) telephone systems have been installed in mines to improve comrnunications. Maintenance crew 

members preferred the single channel party line pager telephone system. By listening to audio pagings, crew members 

were able to determine status of breakdown problems in the 

entire mine. Although this change is viewed by management to 

be Hgoodv, it actually decreased centrality in the maintenance 

group. Radio will dramatically increase centrality in the 

maintenance group. 

4. Serious accidents and fatalities occur in underground 

mining because of poor communications. Radio links must be 

established between all vehicular motormen and off-vehicle 

personnel. In the seminar activities, miners related how 

radio could have been used to prevent accidents: 

. The snapper expected the train to pull forward, instead 

of backwards resulting in serious injury to the snapper. 

. In a rail haulage system, the dispatcher cannot effectively communicate with motormen of battery-powered 

service vehicles. In one incident, a service vehicle 

was operating on the main haulageway immediately ahead 

of a loaded train. The service vehicle motorman was 

under pressure to clear the main line so that the 

train could proceed unimpeded to the dump. The 
motorman entered a turn-out to clear the track; 

however, he failed to switch the track back so that 

the train could continue to the dump. The loaded 

train entered the turn-out slamming into the waiting 

service vehicle. The service vehicle motorman could 

have used radio to inform the dispatcher that the 

service vehicle was on the track immediately ahead 

of the train. The dispatcher could have slowed the 

train to enable the timely exit of the service vehicle 

from the main line. It is a fact that rail traffic 

safety procedures cannot be implemented without the 

use of radio links to off- trainmen and notormen of 

battery powered service vehicles. 

. When a serious accident occurs, a great deal of time 

is required to inform management and sumon help. 

Many accidents require one to two hours before the 

injured miner can be removed from the mine. The use of 

radio will significantly reduce this time. 

. Haulage communications must be restricted to only 

traffic matters. During a field test, the haulage 

communications system was used during an operating 

shift to evaluate voice transmission quality of the 

new radio equipment. The test transmissions confused 

the train motormen. 
5. The communications technology used in hoist systems is 

in urgent need of improvement. 

In deep shafts, electronic equipments installed in cages 

are subjected to rapid changes in environmental conditions. 

High vibrations, rapid changes in temperature and condensation 

forming inside of enclosures degrades the reliability of the 

available radio equipment. Antennas coupling the signals to 

the wire rope are located on the head frame near the sheave 

wheel. Similar antennas are located on top of the cage. 

Shaft inspection is performed without the benefit of radio. 

Maintenance exposes the crew members to excessive risk. 

Efficient antennas and couplers are needed. The antenna 

must be capable of illuminating the wire rope at the collar 

or in the hoist room. This will permit maintenance to be 

performed at ground level. 

Radio equipment must be specifically designed for this 

application and include means for reliable electronic 

signalling. 
6. In the event of a mine disaster such as an explosion, 

cave-in, fire, etc., where miners may be trapped underground, 

efficient rescue efforts are essential. Rapid and efficient 

operations not only enhanee the possibility of achieving a 

successful rescue, but also reduce the risk to the rescue 

team. 

Teams equipped with personal radios will revolutionize 

mine rescue. In practice, rescue teams from surrounding mines 

cooperate during a disaster. To insure communications compatability among rescue teams, a common national rescue 

frequency (400 kHz) will be assigned. To insure that the 

rescue radio equipment will be properly maintained, the rescue 

radios will also be used in the maintenance net. 

7. Production foremen need to coordinate the underground 

mining activity. 

In coal mining, transportation of supplies must be coordinated with production needs. The foreman needs to comunicate with service vehicle motormen to insure timely delivery of supplies. Frequently, the foreman must adjust the 

production rate to match the belt haulage rate to avoid product 

spills along the belt line. 
In vertical crater retreat (VCR) and blockcaving mining 

processes, it is necessary to coordinate haulage and mucking 

operations. These operations occur on different levels of 

the mine. If the production foreman can be made aware of 

"full" transfer raises draw po int s mucking can eff iciently directed. 

As a practical matter, roving mucking and production 

foremen cannot use the telephones to efficiently coordinate 

haulage. Use of personal radio is expected to increase 

haulage by five percent. 

The radio productivity multiplier for any mining organization can be determined by considering the above factors. 

Table A illustrates the expected production improvement in a 

medium sized coal mine. Line Item B shows the average face 

production and belt haulage in a typical one million ton per 

year (1MTPY) mine. The data follows from the actual production statistics (prior 12 mo.). Line Item C shows the 

downtime cost in tons/hour. In coal and M/NM mining, haulageway disruption is exceedingly expensive. The expected production increase due to the use of radio is shown in Line 

Item D data. It is assumed that equipment breakdowns will 

occur in at least one section during. a shift. Product flow 

along the haulageway will be disrupted. Radio will eliminate 

the keymanttreach timett(35 minutes) associated with each 

production disruption. 
TABLE A 

PRODUCTIVITk MULTIPLIER 

WORK SHEET 

Example 

A. Actual Production Statistics 

Annual Production (Tons) 

Production Days 

Shifts Per Day 

Operating Sections 

B. Production Tonage Per Shift 

Each Face 

Haul ageway 

Feeder 

Main 

C. Down Time Cost Per Hour (Tons/Hour) 

Face 

Haulageway 

Feeder 

Main 250 

D. Increase In Production Per Shift (~ons/Shift) 

Reduced Breakdown Time 

Face 

Haulage 

Better Coordination 

Total 

E. Increase In Production 

(Per Year 

Mine 

Forecast 
Face and haulage system production rate will increase 

as shown. Use of radio by supervisors is expected to increase mining efficiency by five percent. The radio productivity multiplier for an empty coal mine significantly increases productivity by 13.5 percent (135,000 ton/year). 

The expected return on investment is remarkable. The 

cost of the radio equipment including maintenance and replacement cost is $53,900. Assuming a $35/ton revenue with a 3 

percent operating margin, the first year return on investment 

ROI = $141,800 2.63 

53,900 

The cost of the equipment can be recovered 2.63 times in one 

year. The present value (PVi=12%) of the 5 year production 

increases are 

(3.91) x $141,800 = $511,900 

The above productivity and financial analysis are conservative in the sense that safety enhancement expectations 

were not included. Poor cornmunications is a factor in many 

accidents. Cost includes damaged equipment, disruption in the 

mining process, and most of all, the loss of an injured 

employee's services (minimum cost of $60,000 per year). It 

is not unreasonable to expect an even greater ROI. 
SYSTEM ARCHITECTURE 

Following recommendations of Bavelas, cells of radio 

coverage are created enabling roving miners within a working 

group to communicate in a party line sense. Every miner 

within the group receives the same information. Cells are 

interconnected permitting information flow in the organization. 

The architecture of the whole mine radio communications system 

is shown in Figure 4. 

SURFACE 

FIGURE 4. SYSTEM ARCHITECTURE 
Each cell of radio coverage provides coverage in the 

working group's area. In the case of the maintenance group, 

the work area extends throughout the entry drifts and the 

face area. A communication path extends from the point of 

equipment breakdown to the surface shop and supply areas. 

Production coverage includes the work area as well as entry 

drifts. This enables key production personnel to coordinate 

haulage of critical supplies and production product (muck, 

coal, etc.). Haulage coverage includes the loading and 

dumping areas as well as along the haulageway coverage. 

Motormen (drivers) can communicate with the dispatcher and 

off-train men. 

In most mines, the maintenance and production nets can be 

merged into a single net. Production supervisors can 

communicate with maintenance supervisors. 

The cells of radio coverage will overlay each other. 

Messages in one cell are not heard in other cells. The cells 

are created by assigning a specific operating frequency to 

the radio equipment assigned to the working group. A typical 

operating frequency plan is shown in Table B below. 
TABLE B 

OVERLAY FREQUENCY PLAN 

MAGMA COPPER COMPANY 

SAN MANUEL DIVISION 

SAN MANUEL, AZ. 

CELL 

Haulage Net (F3) 

2075 Level 

2375 Level 

2600 Level 

Loading 

Maintenance/Production Net 

F1 

F2 (Aquisition of Repeater) 

Hoist Net 

Shaft 1 

Shaft 2 

Shaft 3 

FREQUENCY (kHz) 
111. DESCRIPTION OF THE WHOLE MINE RADIO COMMUNICATIONS 

SYSTEM 

A. SUMMARY 

The features and principles of operation of the whole mine 

radio system are described in this section. The system permits underground personnel to maintain communications almost 

anywhere in the mine, and with the surface complex. As a 

consequence, in case of a breakdown of mining equipment communication with the location of breakdown is possible. This is 

a significant feature, in that it improves productivity by 

reducing down time. 

Random inductive coupling into existing mine conductors 

proves to be desirable and insures extensive coverage. No 

special communications cable need be installed. Base stations 

and repeaters can be installed in minutes in locations of 

prime mine power. Backup batteries are included for additional 

reliability. 

Mobile transceivers consist of vehicular and personnel 

transceivers. The vehicular transceivers utilize a newly 

designed antenna of exceptional efficiency and durability. 

The personnel transceivers utilize a unique vest concept that 

permits a low profile and affords excellent user convenience. 

B . INTRODUCTION 

The radio coverage cells created by the system in a 

typical coal mine are illustrated in Figure 5. 
Cellular 

communications 

MEDIUM FREQUENCY 

WIREL ESS COMMI/NICATlON SY

FIGURE 5 RADIO COVERAGE CELLS IN AN UNDERGROUND MINING COMP
The maintenance cell (maintenance network; F-4~400 kHz) 

extends from the shop throughout the passageways. The haulage 

cell (haulageway network F-3) covers the entire haulageways 

and loading/unloading areas. 

Roving miners communicate by coupling electromagnetic 

signals to the existing electrical conductors in the passageways as illustrated in Figure 6. 

'INDUCED 

LINE CURRENT 

TUNED LOOP 

ANTENNA 

BASE 

STATION 

.TRF LINE COUPLER 

FIGURE 6. THE "NEAR" MAGNETIC FIELD RADIO COMMUNICATIONS 

SYSTEM 
Electrical conductors in the passageways provide a 

means of distributing radio signals in the mine. Research 

and field demonstrations have shown that medium frequency 

(MF) signals (300 kHz to 1.0 NHz) can couple to and from 

nearby conductors in the mine tunnels. These conductors 

(called a "wireplantft) include electrical power wiring, 

control lines, telephone cable, metal water and air pipes, 

and I-beams. Since mines include these electrical conductors, 

MF signal distribution networks are already in place in most 

mines in the U. S. The communication range between roving 

miners is measured in miles. 

Signal coupling to the "wireplant" occurs when the tuned 

loop antenna (transceiver A) produces a "near" magnetic field 

(Hl) , signal that illuminates the "wireplant". In effect, the 

signal magnetically couples to the "wireplant" creating induced line current flow in the electrical conductors. The 

current flows along the "wireplant" producing a local magnetic 

field (H2) as it travels (propagates) on the "wireplant". At 

a distant location, the local field inductively couples the 

MF signal to the tuned loop antenna associated with transceiver 

B. 
The emf signal produced in the antenna is applied to 

the input circuit of the "9" transceiver- receiver. Thus, 

personnel with "nea~~' magnetic field equipment can communicate when in near proximity to the "wirepiant". 

The use of base stations and repeaters is illustrated 

in Figure 7. The base station enables the roving miners with 

mobile transceivers to communicate with the shop or dispatchers 

office. The global repeater extends the operating range of 

the system in two ways. First, by transmitting on the frequency (F2), the base is able to acquire the global repeater 

and reach a distant mobile transceiver . Secondly, by transmitting on the frequency (F2), a mobile transceiver can acquire 

the repeater and reach a distant mobile transceiver. 

I RXFl , 

TRANSCEIVER 

STATION 

*F LINE COUPLER 

9 TUNED LOOP ANTENNA 

FIGURE 7. USE OF BASE STATIOFJ AND REPEATZR 
The base can be controlled remotely by a single pair of lines. 

The control console can be placed in a surface building for 

convenience, while the actual base transceiver is placed in 

the mine where it can more efficiently couple signals to the 

"wireplant". 

In addition to the tuned loop antenna illustrated in 

Figures 6 and 7, RF line couplers are used to couple signals 

to the tlwireplant" conductors. Like a current probe, the RF 

line couplers have been designed to be easily clamped around 

"wireplant" conductors. The level of line current induced by 

a coupler is greater than that produced by the illumination 

of the "wireplant" by an antenna. Couplers increase the 

operating range by miles. 

The system may use repeaters to increase the range between 

mobile transceivers. The radio coverage cell 7 (Figure 5) is 

created with the cellular repeater illustrated in Figure 8. 

It is known as a "cellular repeater" because it illuminates a 

"cell" or area of the mine, such as a working section only. 
FIGURE 8. RADIO COVERAGE CELL AT THE FACE 

The cellular repeaters use dual-loop antennas (for 

transmitting and receiving) attached to the rib or posts. 

The lltransmittinglt antenna produces a large magnetic moment 

that provides the signal for local cellular coverage, which 

is usually aided by random inductive coupling effects. The 

llreceiving" antenna is similar. 
Wireless signal paths exist between the section repeater and 

roving miners. Miners (production foremen and maintenance 

crew) wear vest transceivers in order to communicate with the 

cellular repeater. Figure 8 illustrates the mobile telephone 

nature of the working section communications system. 

TELEPHONE PAIR I I 

PAGER 

TELEPHONE 

TRANFCEIVER TRANSCEIVER 

FIGURE 9. Fl/F2 SIGNALLING 
The cellular repeater is connected to the mine telephone 

system through the pager telephone. The cellular repeater 

relays the telephone message to the vest transceiver using 

the transmission frequency (Fl). The vest transceivers are 

always tuned to receive the frequency (Fl). The vest can 

transmit on (F2) to acquire the cellular repeater and communicate with the host telephone network. The cellular repeater can also operate in the simplex/half duplex mode so 

that a calling vest transceiver (using F2) can reach a distant 

vest transceiver in the working area. The vest can create a 

local mobile-to-mobile network by transmitting on (PI). A 

distinguishing feature of the cellular repeater is that it 

uses loop antennas to excite the coal seam propagation mode 

in the working area. The existence of the coal seam mode was 

discovered and investigated in U.S.B.M. research (26) (27). 

This mode exists because the coal seam is bounded above and 

below by rock (shale) that is significantly more conductive 

than the coal. In the 300 to 700 kHz frequency range, the 

signal range reaches a maximum. Field testing in the Kaiser 

Steel Corp. York Canyon Mine near Raton, New Mexico, showed 

that voice quality communications could be established between 

the section power center and the continuous miner (approximately 500 feet 1. 
MF EQUIPMENT 

MF equipment designed for "near" magnetic field communications are shown in the table below: 

Mobile 

Vest Transceiver 

Vehicular Transceiver 

Fixed Location 

Base Station 

Global Repeater 

- Coupling Devices 

RF Line Coupler 

Antennas 

Remote Control Console 

Mobile Transceivers - - 

Two different types of mobile transceivers have been 

developed for use in the system. Transceivers consist of 

vest units for individuals and a vehicular units for use in 

underground vehicles. Functionally the two are identical, 

differing only in output power levels and physical configurat ion. 

a. Vest Transceiver -- .- 

The vest transceiver has been designed for operation in 

a gassy atmosphere (CFR, Title 30, Part 23-Telephones and 

Signalling Devices). The vest transceiver is shown in 

Figure 10. 
An important human factor problen was solved in the vest 

design. By distributing the bulk and weight of the transceiver over the surface of the vest, the radio becomes an 

integral part of the user's garmet (10). He is free to move 

in tight quarters and perform normal mining tasks without 

catching the radio on obstructions. Sound is directed toward 

the ears from epaulet speakers on each shoulder. A hinged 

control head is conveniently located on the front. 
FIGURE 11. VEST CONTROL HEAD 

The vest transceiver can communicate with other mobile 

units as illustrated in Figure 6. Depressing the push to 

talk (PTT) switch keys the vest transinitter to produce the 

carrier signal frequency (Fl). By speaking into the microphone, voice message frequency modulate the carrier signal. 

Depressing the signalling (signal) switch causes modulation of 

carrier signal with a 1000 Hz audiable tone. This can be used 

for emergency signalling in the event that a miner is unable 

to speak. 

The cellular repeater design includes switching circuitry 

to allow the vest to operate like a mobile telephone. Depressing the paging (page) switch keys the vest transmitter 

to the carrier frequency (F2). This signal is modulated with 

a 100 Hz subaudible tone. The tone signal is decoded in 

the cellular repeater causing the vest voice signal to be 

switched onto the host telephone network. Telephone network 

messages key the repeater to the carrier frequency (F1) for 

return message transmissions int~ the radio coverage cell. 

The tuned loop antenna is sewn onto the back of the vest. 

This construction retains the loop firmly keeping its area 

constant and avoids its detuning during use. 

The vest is supplied with nickel-cadmium battery packs. 

Sufficient capacity is provided in the battery pack for eight 

hours of normal operation (90% of time in receive and 10% of 

the time in transmit). 

b. Vehicular Transceiver 

The vehicular transceiver can be conveniently placed on 

any mine vehicle. It is used in con junction with a special 

loop antenna of advanced design that produces high magnetic 

moment. Mechanically, the antenna is enclosed in high 

strength lexan and is attached to the vehicle via special 

brackets. 
FIGURE 13. REPEATER TRANSCEIVER 

The repeater can stand alone; that is, operate as 

illustrated in Figure 7. The repeater can also be operated 

as part of the pager telephone system as shown in Figures 

8 and 9. The receiver section of the repeater demodulates 

the received carrier signals (F2), recovering the F2 message 

and the 100 Hz subaudible tone. The recovered message signals 

may be used for two purposes. First, the message signal keys 

the transmitter section of the repeater producing a high power 

retransmission signal at the F1 frequency. The message appears 

as FM modulation on the F1 signal. Secondly, when the subaudible tone is present the repeater decodes the 10.0 Hz tone 

and switches the message to the mine telephone network enabling telephone communications. 

The repeaters and the base station can be operated from 

remote control console(s) in the mining complex. Consoles 

can be located anywhere in the mining complex. A pair of 

wires connects the console to the repeater as shown in Figure 

14. 

The repeater design includes filter networks to prevent 

r e c e i v e r d e s e n s i t i z a t i o n . ------- - 
FIGURE 14. 

BASE 

OR 

REPEATER k 

REMOTE CONTROL CABLE 

REMOTE CONTROL 

Multiple Remote Control Consoles (RCC) units base stations 

and repeaters can be connected to the Remote Control (RC cable 

REMOTE 

CONTROL 

CONSOLE 

REMOTE 

CONTROL 

CONSOLE 

(wire pair). The maximum control signalling distances over 

MAINTENANCE SHOP 

OFFICE 

I 

the RC cable is 5 miles. The RCC unit is shown in Figure 15. 

FIGURE 15. REMOTE CONTROL CCNSOLE 

FIGURE 16. RF LINE COUPLER 
FIGURE 17. TUNED LOOP ANTENNA 

The antenna may be mounted on a vertical or horizonal 

mounting surface. 
FIELD MAINTENANCE 

The radio equipment is designed around a standard set 

of interchangeable plug-in circuit modules. The standard 

receiver, synthesizer, exciter and transmitter modules are 

used in the vehicular transceiver, base station and repeaters. 

The vest transceiver modules have been designed exclusively 

for use in the hazardous atmosphere per Underwriters Laboratory 

Document UL913 (MSHA requirements). The vest modules perform 

similar functions to standard modules; however, the actual 

design is substantially different. Maintenance requires 

troubleshooting to the module level. Module servicing is 

strictly prohibited other than by factory certified electrical 

technicians. Since the equipment uses similar performing 

modules, the specifications of all transceivers are identical. 

The modular design insures that the equipment can be 

maintained in the field at minimum cost. Servicing only 

requires troubleshooting to the module level. 
E. INSTALLATION 

The MF radio communications system features maximum 

installation versatility as well as simplicity and reliability in actual operation. The system has been successfully installed and demonstrated in four underground mines. 

The mines, identified in Table C , were selected because 

they are representative of mining process in common use in 

the U.S. mining industry. In the course of the installation 

work, a wide spectrum of problems were encountered and solved. 

Lessons learned in the successful installations have been 

developed into a planning guide that can be followed by a 

mining company wishing to take advantage of radio in mining. 

The planning guide is illustrated in Figure 18. 
TABLE C 

COOPERATING MINES 

ORGANIZATION 

Magma Copper Company 

San Manuel Division 

San Manuel, AZ 

Ranchers Exploration E Development 

Revco Silver Mine 

Interprise, Utah 

Kaiser Steel Corporation 

York Canyon Mine 

Raton, New Mexico 

Getty Oil Company 

Plateau Mining Company 

Price, Utah 

MINING PROCESS 

Block Caving 

Vertical Crater 

Retreat 

Conventional and 

Longwall 

Covent ional 
TRACE TELEPHONE 

AND AC POWER 

CABLE ON MAP 

MAINTENANCE 

FIGURE I8 SYSTEM PLANNING GUIDE 
1. Keyman Meeting 

Planning the cornrnunications system in advance of the 

installation is important in several respects. First, the 

primary goal is to involve management and other keymen, at 

the earliest possible time, in the planning process. Keyrnen 

must be familiar with the principal and operating features so 

that they may accurately define the required radio coverage 

areas. The material presented in Chapter I11 (Section B) 

can be used to acquaint keymen with the system concept. 

Secondly, planning insures that the cornrnunications system 

will contribute to team work and improve efficiency in the 

mining process. 

2. Define Communication Needs and Coverage 

Keymen must communicate to insure a smooth running mine. 

Communications must be provided in all work areas, and frequently traveled passageways. The needs can be determined by 

considering the following questions : 

. Which keymen must communicate (net together)? 

How will they communicate (from vzhicles or on foot)? 

What kind of communications problems must be solved 

with radio? 

. How can the system be used to reduce mining cost? 
The latter can be evaluated by using a benefit analysis 

similar to that presented in Table A . Line items to be 

considered can be expanded to include other specific tasks. 

For example, the cost of loading or drawing muck without 

using radio can be determined. The train loading process 

frequently employs light signalling to command the motorman 

to move the train (two blinks of a light to move forward, etc.). 

Radio will enable more exact train movement, thus minimizing 

loading time. 

The benefit analysis is useful as a guide in designing 

the communications system in the near and far term; In the 

near term, equipment can be installed to realize the greatest 

improvement in productivity expected in the benefit analysis. 

At a later date, additional equipment may be added to realize 

lessor improvements in productivity. 

The MF system provides natural radio coverage near 

"wireplant" conductors. If a frequently traveled passageway 

is "free1' of electrical conductors, a low cost two-wire cable 

must be installed to provide reliable radio coverage in these 

areas. 

In M/NM and coal mines, the operating range from the 

base station is dependent upon the type of electrical conductors in the "wireplant". Telephone cable provides the 

lowest signal propagation loss (4 dB/1000) and range along 

the cable will exceed 20,000 feet. AC power cables also 
provide excellent coverage; however, each power transformer 

along the cable absorbs signal energy. Each power transformer 

decreases the range by approximately 2000 feet. Bearing in 

mind, that if AC switches are encountered along the AC power 

cable, an open switch will dramatically reduce operating 

range. In coal, MF signals can be received almost everywhere 

in the mine; however, the talk-back range may be limited to the 

same entry with the ttwireplantv or at r.l.ost an adjacent entry. 

3. Selecting Needed Networks 

The following networks should be considered for use in 

a mine: 

Supervision Network, 

Maintenance Network, 

Production Network, 

Haulage Networks, and 

Hoist Systems Network. 

The use of radio will relieve the existing telephone system 

of most of the critical message traffic. In most mines, 

some of the networks will merge together. For example, the 

maintenance and production networks can be operated as a 

single network to improve team work. The "nerve" centers 

for this network are the shop, warehouse, and supervision 

(production and maintenance) offices. A remote control console(~) should be installed in each critical location. 
In very large mines, a separate supervision network may 

be considered for the transmission of sensitive information 

(union labor matters, etc.). However, in most mines, the 

direct dial telephone System serves this communication need. 

A separate network is mandatory for serving the comrnunication needs in a rail haulage system. Vehicular transceivers 

must be assigned to all rail service vehicles. Vest radios 

must be assigned to all off-train men (loader, snapper, 

chute tappers, etc.). In small mines, the systems are nost 

efficiently self-dispatched. The "nerve" centers are usually 

the shop, and the production superintendents o f f i c e . In 

larger mines, the dispatchers office is the comrnunications 

"nerve" center for the haulage and maintenance networks. In 

belt haulage systems, beltmen must be assigned vest transceivers to communicate in the maintenance network. 

It is necessary to install vehicular transceivers on all 

service and "keyman" vehicles. If the "keyman" is frequently 

on foot during the course of his work, a vest transceiver 

must be assigned. 

Since MF signals propagate so well in a mine, MF will 

revolutionize mine rescue and provide emergency comrnunications 

to trapped miners. The maintenance netwo~k will be used in 

emergency situations. Underground ambulances should be 

equipped with a vehicular transceiver and communicate in the 

maintenance network (400 kHz). 
The amount of radio equipment recommended for use in 

the networks depends upon the size of the mine. Table D 

describes the equipment used in maintenance and production 

networks in a medium sized coal mine. 
TABLE D 

TYPICAL 

EQUIPMENT LIST 

(1MTPY COAL MINE) 

NETWORK 

B(~) VST 

Foreman 

Roving Mechanic 

Roving Electrician 

Fire Boss 

Service Vehicle 

Longwall Crew 

Mechanic 

Head Gate 

Shear Operator 

Train Gate 

Chockmen 

Haulageway 

Belt 

Beltmen 

Rail 

Mot ormen 

Off Train Men 

Service 

Total 

B - Base Station CR - Cellular Repeater 

VST - Vest Transceiver GR - Global Repeater 

(1) Bar symbol indicates recommended equipment quantity in an 

lMTPY coal mine using belt haulage and conventional mining 

techniques. (2) Requires vehicular antennak). (3) Requires 

RF line coupler (s 1. 
4. Mine Map 

The mine map is the key installation document. Use the 

map to lay out the needed cells of radio coverage. Include 

on the map the telephone and AC power cable entries. Bear 

in mind, that coverage along the AC power cable will depend 

upon the number of installed power transformers. Radio 

coverage reliability will depend upon AC switch locations. 

The base station(s) and repeater(s) can be located on the 

map. The base station should be located at the portal or the 

mid-point of the tfwireplant" in larger mines. It must be 

located near 117 V AC power to enable charging of the standby 

batteries in the base. The operating range along telephone 

cable is typically 20,000 feet from the base. Along AC power 

cable the range is reduced by 2,000 feet for each transformer 

along the cable. Additional base stations can be installed 

to increase radio coverage to mobile transceivers. Single or 

multiple base stations in the network can be controlled from 

the remote control console(s) located in the mine "nerveu 

centers. 

As shown in Figure 7, the repeater has the advantage over 

the base in increasing operating range between mobile transceivers. This requires that the mobile transceivers operate 

in the Fl/F2 signalling mode. This is contrasted to only the 

F1 signalling required if multiple base stations are used to 

extend the base to mobile transceiver operating range along 

the llwireplantll. 
The RF line cou~ler and base station are installed as * 

illustrated in Figure 19. 

FIGURE 19. RF LINE COUPLE R INSTALLATION 
The coupler is simply clamped around every conductor ic the 

"wire plantn. The installat ion is completed by connecting the 

coupler to the base station. 

The Remote Control Console (RCC) unit(s) is located in 

the "nerveM center(s) for the communications network (shop, 

warehouse, etc.). RCC unites) is connected to the base station 

by Remote Control (RC) cable (single pair of wires). In most 

installations, a telephone pair has been used as RC cable. 

In manway entries without electrical conductors, a low 

cost twin-lead cable must be installed. The installation of the cable is diagramed in Figure 20. 

BRANCH 

J 

I I I 

I , RF 

----I 

I LINE 

I COUPLER C --- I/ LA 

FIGURE 20. BASE STATION AND REPEATER CONTROL CABLE 

INSTALLATION DIAGRAM 
The RC cable is installed like a pager telephone wire 

pair. The cable carries DC commands, signalling tones and 

voice signals to and from the RCC unit(s). By threading the 

RF line coupler with the RC cable (as illustrated in Figure 

201, the RC cable also serves to improve MF radio coverage 

in manways. Branch lines needed to extend radio coverage in 

manways are connected through passive power dividers. The 

branch lines are always terminated in the line characteristic 

impedance (Zo). This has several advantages, first, because 

the RC cable is properly branched and terminated, the standing 

waves caused by impedance mismatch conditions along-the lines 

are minimized. Communication "dead spotsn in the passageway 

are eliminated. Secondly, the RC cable extending from the 

mine portal to the surface "nerve" centers provide a communication means when the mobile transceivers are out of the 

mine. 

Radio coverage is greatly increased in practice by MF 

signal coupling between cables. Cables that route through 

the same drifts are magnetically coupled. MF signal current 

flow in one cable induces current flow in the other. 

Certain installation precautions must be observed in 

the installation of the equipment: 
The installation of an RF line coupler on telephone 

or AC power cables must observe specific high voltage 

insulation precautions. The coupler name plate must 

show adequate dielectric withstanding voltage (DWV) 

rating. If the name plate rating is inadequate, 

esophagus tubing with sufficient dielectric withstanding 

voltage rating may be placed over the cable before installation of the RF line coupler. 

In coal, roving miners that go inby must use permissible 

vests. 

Transceivers and repeaters used in the mine must be 

grounded to the vehicle frame ground or the mine safety 

ground system. Transceivers that are installed on 

vehicles that operate from high voltage batteries or 

trolley cable must be grounded to the vehicle frame 

ground. This requires the mandatory use of DC to DC 

converters with sufficient DC input to convert DC 

output isolation. 

Transceivers that are installed vehicles that operate 

from floating (ungrounded) batteries must be grounded 

to the vehicle frame ground. This requires the mandatory use of DC to DC converters with sufficient DC to 

input output isolation. 
Insuring System Usage 

Once the system is installed and checkedout, management 

must insure that it increases centrality. They should assist 

in training keymen to use the radio system effectively. 

Bear in mind that miners are accustomed to working independently. They will prefer to keep it that way. Management must require in and out shift meetings of all keymen to 

coordinate the mining activity. Radio should be used to 

assist the keymen and their crews in their assigned task. 

The radio system reliability will depend upon adequate 

maintenance. The mines shown in Table C have excellent 

maintenance policies and personnel. At the beginning of the 

sys-tem planning in each of the mines, radio maintenance responsibility was assigned to one maintenance crew member. He 

was trained to troubleshoot the system equipment to the board 

level. 

In all of the mines, the trained maintenance personnel 

were able to adequately maintain the radio system. As a back 

up contractor's personnel were made available to assist the 

maintenance crew member by telephone. 

Since the system uses plug-in modules, they required only 

two sets of plug-in boards for the transceivers and repeaters 

are maintained at the mine site. 
It is important to insure good radio maintenance policies. 

Crawley (30) of the U.S.B.M. has studied the five year performance of a leaky feeder communications system in the U.S. 

mining industry. After five years only one system remained 

in an operational condition. System failures were partly 

caused by the difficulty of maintaining coaxial cable in an 

operating mine. 

Lack of interest and effectiveness of the maintenance 

crew was also a strong factor in the failure of the radio 

equipment. 

RADIO EQUIPMENT SHOULD NOT BE INSTALLED IN MINES THAT HAVE 

POOR MAINTENANCE POLICIES. 
IV. THE SYSTEM DESIGN 

A. SUMMARY 

The operating range of a medium frequency (MF) underground communications system is dependent upon many technical 

factors, including the characteristics of the noise generated 

in electrical power systems, signal propagation modes, 

selection of the optimum modulation-demodulation process, the 

efficiency of the couplers and the susceptibility of the 

receiver to desensitization by impulsive mine noise. 

Considerations of the many factors provide additional 

insight into the expected system performance and a'conclusion 

that narrow-band FM is the preferable modulation process. 

INTRODUCTION 

This chapter deals with theoretical methods used in the 

design of the,underground radio communications system. Some 

of the problems which arise in the design of this system are, 

in many cases, similar to those encountered in surface radio 

systems. Therefore, solutions to these problems follow from a 

vast body of telecommunications knowledge developed over the 

past few years. Others require new thinking. 
Today's advanced radio communication technology is largely 

based upon the propagation of radiated field wave signals that 

travel great distances through atmospheric constituents. 

While it is true that these signals provide reliable communications over free space paths, waves encountering a contrasting 

medium are subjected to change in the wave propagation constant 

causing reflection, diffraction, and absorption of the signal 

energy. The subterranean environment is extremely hostile to 

these signals. It is found that the signals from VHF and UHF 

handheld transceivers are severely attenuated when passing 

near rail haulage equipment, around corners or through ventilation barricades in the mine. As a result, communications 

fail (go below threshold) exactly where quality voice communications are needed the most. "Leakytt transmission lines 

excited by high power transmitters improve tunnel comnunications; however, old problems persist and new problems have 

emerged. Communications through ventilation barricades and 

to the point of equipment breakdown were still not reliable. 

Further, the practicability of installing coaxial cable in the 

working area of the mine seems questionable. 

C. HISTORY 

Every since the emergence of radio for practical terrestrial radio cornmunications, attempts have been made to apply 

it to underground mining. As early as 1922, U.S.B.M. experiments showed that radio propagation in mines was possible but 

not practical. 
Equipment was bulky and insensitive, and only very large 

antennas could be used. By 1948 the Chambers of Mines 

of South Africa had programs in place to develop radio systems 

for deep mines, primarily gold mines (19). The result was 

that by 1973, advanced 1 Watt single sideband (SSB) portable 

radios were in use (17). The U.S.B.M. procured several of 

these units for evaluation. Performance in U,S. coal mines 

was not satisfactory. There were several reasons for this. 

First, U.S. mines are highly electrified, producing considerable 

electromagnetic interference (EM11 not normally found in the 

South African mines, which completely desensitized SSE radios. 

Second, the power of 1 Watt proved insufficient. U.S. mines 

are mostly composed of rooms and pillars which means that any 

radio system would have to have reasonable range from local 

conductors. Third, geological electrical parameters were less 

favorable in the United States. For these reasons, the South 

African system was not acceptable in the United States. 

The Bureau's approach was to first determine the actual 

propagation characteristics of MF in U.S. mines, and then to 

relate the propagation to the underground environment such as 

the geology, entry size, existing conductors, and EMI. 

Several exhaustive in-mine measurement and analysis programs 

were conducted (20) (21). These programs formed the foundation for the first true understanding of how MF propagates 

in mines, 
Theoretical and experimental work monitored by Sacks 

and Chufo (12) of U.S.B.M. have shown that MF "near" magnetic 

field signals propagate through natural media (water, rock, 

coal, etc.) and great distances down passageways in the 

underground mining complex. Emslie and Lagace (13) (14) 

established that a loop antenna would excite a coal seam mode 

enabling the propagation of MF signals through a coal seam. 

The cellular coverage in a typical working section is shown 

in Figure 8. 

The work of Hill and Wait (15) considered the excitation 

of monofilar and bifilar propagation modes on a transmission 

line in a passageway. Low loss transmission line propagation 

modes were discovered leading to the passageway coverage 

shown in Figure 6. 

Whole mine radio signal transmission and distribution 

depends upon the modal excitations described above. One of 

the advantages of MF "nearv magnetic field signals over 

VHF/UHF planar wave signals is that MF-"near" magnetic field 

signals are not subjected to extremely high path loss when 

passing near mining equipment, through ventilation barricades 

and around corners. This is especially important when comrnunicating in a long wall section or repairing mining equipment 

at the point of equipment breakdown. 
The operating range of an underground radio communication 

system depends upon many factors including: 

antenna magnetic moment (transmitted output power), 

characteristics of electrical noise generated in the 

mine electrical system, 

the signal propagation mechanism (modes), 

carrier signal coupling efficiency , 

the system modulation-demodulation processes, and 

susceptibility of the receiver to desensitization by 

electrical noise and other interfering/jarnming 

signals. 

In a lfnearv magnetic field communication system, operating 

range is a strong function of the signal propagation mechanism 

and medium, and antenna coupling efficiency between other 

antennas and transmission lines in the signal distribution 

system. These factors have been extensively studied in the 

context of the subterranean communication problem (14) as 

well as in the related terrestrial communication literature. 

With respect to these factors, range optimization procedures 

are well known. 

* 
D. NOISE GENERATED IN MINE POWER SYSTEM 

In the highly mechanized U.S. mining industry, radio 

frequency interference (RFI) generated in the mine electrical 

system is a dominating factor in the design of the cornmunication system. A review of the measured noise date (16) (17) 

reveals that the noise field strength varies over an enormous 

range (by several orders of magnitude - 60 to 100 dB variation). 

The noise is greatest near AC to DC converters (rectifiers) 

and along the trolley conductor in a rail haulage system. 

Away from the haulageways, the electrical noise level is as 

much as 40 to 50 dB below the haulageway level. The noise 

level also changes over a large range during a typical working 

shift. The magnitude of the noise spectrum decreases rapidly 

with frequency. For frequencies below 50 kHz its magnitude 

increases with decreasing frequency at an average rate of 

approximately 14 dB per octave. Above 100 kHz, the noise 

density decreases at the rate of 6 dB per octave. 

The high noise level influences the design of the RF 

section in the communications receiver. The receiver design 

is somewhat more critical than the transmitter design, mainly 

because of the presence of interfering signals before the 

signal processing stage. The RF section must discriminate 

against the noise as much as possible and then amplify the 

modulated signal and noise in a linear way before converting 

the signal and noise to the proper intermediate frequency 

(IF) and subsequent signal processing. 
E. SIGNAL PROPAGATION MODES 

The coal seam and transmission line signal propagation 

modes were evaluated in a series of underground mine tests 

conducted by the U.S.B.M. researchers. Cory's (21) (22) 

test results indicated the coal seam mode enabled maximum 

communication range for operating frequency in the 400 to 700 

kHz band (MF band - 300 to 3000 kHz). Further, as predicted 

by Hill and Wait (151, Cory found the propagation loss on the 

"wireplant" to decrease with decreases in operation frequency. 

1. Seam Mode Propagation Theory 

The theory of electromagnetic wave propagation in stratified media has been rigorously developed by Wait (23). 

Electromagnetic waves can propagate laterally via highly resistive layers in the earth (25). Wait (24) has analyzed the 

case of the coal seam using the simplified model shown below. 

ROCK 6, ER 

//////////I///////////// 

(SOURCE) 

COAL 

SEAM 

(RECEIVER) 

FIGURE 21, SEAM MODE FIELD COMPONENTS 
The coal seam is bounded by two conducting half spaces 

with the conductivity of the rock (6,) greater than the 

conductivity of coal (6c). The conductivity of the coal is 

several orders of magnitude less than the conductivity of 

the rock. The vertical orientation of the transmitting loop 

antenna (source) produces, along the transmission path (r), 

a horizontal magnetic field H and a vertical electrical field tJ 

Ez* The fields are almost constant over the height of the 

coal seam. Emslie and Lagace (26) have shown that the fields 

die off exponentially in the rock. ") At large radial distances (r) from the antenna, the fields decay exponentially 

at a rate determined by an effective attenuation constant 

which depends on losses both in the coal and in the rock and 

on the dielectric constant of the coal. There is also a 

l/r 'I2 factor at large radial distances due to cylindrical 

spreading of the wave. The zero-order TEM magnetic field 

H in the plane of the transmitting loop is given by: 4) 

(1) With perfectly conducting boundaries, when 6, is finite , the zero-order mode field varies with z, o, and r owing 

to wave propagation across the boundaries. 

(2) Skin depth in rock is 0.69 meter, 6, = 1 mho, 520 kHz. 
where M is the magnetic moment of the transmitting 

loop antenna, 

be = b+1/2 6, is the effective half-height of 

the coal seam. (1) 

6, = z direction skin depth in the rock. 

k=B it is the complex propagation constant in 

the radial direction, and 

H1 ('I' (kr) = derivative of the first-order 

Hankel Function for an outgoing wave. 

(1) Wait has noted the be may be complex. 
On ta'king the asymptotic form of the Hankel Function, the 

azimuthal component of magnetic field (1) is 

The attenuation and phase constants are given by Emslie 

and Lagace (26) are 

where 

2(6,-2nf&,) P - 4n2fZuO& , and 

b C 

(1) Valid at ranges kr< 1 
The zero-order TEN wave described by Equation (1) has been 

compared with experimental measurements by Cory (27). Emslie 

and Lagace have determined that the measured results are in 

close agreement with Equation (1). The attenuation rate in 

coal is approximately 4 dB/100 feet (6,=1.4 x ~O-~MHO/~, 

cC=7, 6r=1 MHO/m, b=lm, 350 KHz). 

Equations (3) (5) and (6) are useful in determining the 

dependence of wave propagation constant on seam parameters. 

The attenuation rate is expected to increase as the coal seam 

thickness decreases and conductivity increases. The attenuation rate decreases as the rock conductivity increases. The 

rate also depends upon frequency. 

2. Transmission Line Propagation ?lodes 

Theoretical research and actual field results confirm 

that two signal propagation modes exist on a pair of wires 

in the l1wireplantW. The modal current flows are shown below - ROOF - - 

I -r(k CONDUCTORS 

-lV fi 

0 

:in7 FLOOR 

A) 81 FILAR (DIFFERENTIAL) B)MONOFILAR (DIFFERENTIAL) 

MODE MODE 

FIGURE 22. SIGNAL CURRENT (I) FLOW ON CONDUCTORS (n-2 l1 

Footnote: The number of possible modes is n-1 where n is the 

number of electrical conductors in the wireplant. 
Hill and Wait (15) have examined the excitation of 

monofilar and bifilar modes on a transmission line in a 

tunnel. In the monofilar mode (also called the balanced, 

differential, coaxial, or symmetrical mode) current flows in 

the same direction on both conductors and returns as surface 

current in the mine tunnel. This mode is readily excited by 

magnetic coupling from a loop antenna anywhere in the mine 

tunnel but suffers high attenuation because the return current 

flows in the lossy tunnel wall. In the bifilar mode (also 

called the unbalanced, asymetrical or differentialmode), the forward current in the upper conductor returns through the lower 

conductor. This transmission line mode has low attenuation 

because the return current flows on the second wire rather 

than through the surrounding rock. Excitation of this mode 

depends upon magnetic flux threading the area between the 

transmission line conductors. Mode conversion naturally occurs 

on a two-wire transmission line because of random imperfections 

in the "wireplant" and mine tunnels. Non-uniformities in 

tunnel cross section, sag in cable with respect to the roof 

and incidential changes in the spacing between conductors 

cailse the characteristic impedance (Zo) of the cable to change 

along the line. Changes in the line characteristic impedance 

cause radiation and reflection of the signal energy. As a 

result, monofilar and bifilar mode interchange conversions 

occur all along a line. Researchers in Belgium were the first 

to develop mode converters to transform monofilar mode to bi- 
filar mode signals (33) (34). The Belgium converters were 

realized by a series of inductances inserted in one line and 

a capacitances in the other. 

Two-wire cable that is added to the "wireplant" to increase radio coverage in manways without "wireplant" should 

be designed to take full advantage of efficient monofilar mode 

coupling and bifilar mode low attenuation rate. Untwistedpair cable should be used because fields from twisted pair 

cable are reduced by 50 dB at a distance R = 1.5 p from the 

cabLe where p is the pitch of the twisted pair (35). 

F. COUPLING MF SIGNALS TO THE "WIREPLANT" 

The coupling of signals between transmitting loop antennas 

and the "wireplant" will be examined in this section. The 

equations define bifilar mode coupling to cables in free 

space. Monofilar coupling also occurs; however, monofilar 

signal level depends upon the tunnel surface impedance. The 

nature of this coupling was previously examined by Hill and 

Wait (15 1. 

1. Transmitting Loop Antenna and Two-Wire Transmission 

Line Coupling 

Theoretical equations that relate to the bifilar current 

signal level induced in a "wireplant" transmission line to the 

transmitting loop antenna magnetic moment (MT), operating 

frequency (f), loop to line distance (R) and conductor 

separation (b) in the line are exceedingly useful in planning 

the design of the communications system. The equations show 
that coupling improves with the first power of magnetic moment, 

frequency and increased separation between line conductors. 

Coupling improves with the second power by distance from the 

loop to the line as the loop is brought nearer to the line. 

Coupling depends upon the geometrical relationships 

between the transmitting loop antenna and the two-wire transmission line. Some of the possible geometrical relationships 

are illustrated in Figure 2 3. 

a.) ALIGNED 

C.) ALIGNED ; 

EDGE ON 

b.) COPLANAR 

d.) 

sEDGE ON 

FIGURE 23. GEOMETRIES FOR A VERTICAL TRANSMISSION LINE 

A 0 
In the aligned case shown in Figure 23, the loop and the 

line conductors lie in a vertical plane. The planes are 

separated by the distance R. The coaxial configuration occurs 

when the center line of the transmission line coincides with 

the axis of the transmitting loop antenna. This geometry 

is frequently encountered when vest and vehicular transceivers 

are in a manway. The axis of the loop may also be below the 

center line of the transmission line. The coaxial alignment 

induces strong bifilar current in the line and weaker monofilar elements. The aligned, edge-on, case of Figure 23 (c) 

induces stronger monofilar currents and weaker bifilar currents. 

The edge-on situation produces unfavorable coupling. The coplanar case shown in Figure 2 3 (b) produce both monofilar and 

bif ilar currents . 

Smith (28) has developed equations that define the induced current and voltage in a transmission cable. The twowire signal transmission medium is represented as a transmission line terminated at both ends by load impedances 

(Zland Z2) equal to the characteristic impedance of the line. 

The line is shown in Figure 24. 
- 

v + 

CENTER 

f LINE 

R 

1 

I 

FIGURE 24. EQUIVALENT TRANSMISSION LINE NETWORK FOR 

INDUCED VOLTAGES AND CURRENTS (Z1=Ze=Zo) 

The line is long and the conductor spacing is b. The 

field produced by the loop threads the area enclosed by the 

conductor spacing and a length L along the line. Because 

the field is non-uniform, it is assumed to be constant over 

the length L-R and zero elsewhere. When 2aR<< A, then the 

induced voltage is given by 

where f is the operating frequency, 

u, is the magnetic permeability of free space 

(4~ x loo7 henrys/meter) , and 

M is the loop magnetic moment. T 

The curren-t: flowing in the line is given by 
Equations (7) and (8) are useful in several ways. First, the 

voltage and current signals induced in the line are directly 

proportional to the magnetic moment of the transmitting loop 

antenna. Maximizing the loop moment for a given transmitter 

power will also maximize the induced signal and system operating range. Increasing the transmission line conductor 

spacing will increase the line characteristic impedance 

and decrease line current. Since the voltage (V) depends on 

the first power of conductor separation b and Z, on. its 

logarithm. There is some improvement in operating range 

obtainable by maximizing b given the constraint of cable cost. 

Secondly, coupling efficiency increases with the first power 

of operating frequency (f) . However, the attenuation rate of 

signals on the line also increases with frequency. Because of 

transmission loss, it is better to use lower operating 

frequencies. As described in Section E, the mine generated 

electrical noise also increases with decreases in operating 

frequency. Thus, although transmission losses are lower at 

lower operating frequency, increase in mine generated noise 

level causes the signal-to-noise ratio to degrade. Mine tests 

indicate that the signal to noise ratio (S/N) is optimized 

in the region of 250 to 500 kHz operating frequency band. 
Transmitting Loop Antenna. To Receiving Loop Antenna 

Via Transmission Line Cou~ling 

At a distant receiving site, the signal magnetic field 

couples to the receiving loop antenna as illustrated in 

Figure 25. 

PLANE OF 

TWIN-LEAD 

CABLE 

H~ 

ECE LOOP 

FIGURE 25, SIGNAL COUPLING TO A RECEIVING LOOP ANTENNA 
The magnetic field produced by the bifilar line current along 

the cable near the receiving loop is mathematically represented 

by 

The electromotive force (emf) produced in the receiving loop 

is given by Maxwell's first equation as 

where B in the flux density threading the loop+area AR, 

n is unit vector of surface threaded by B, and 

NR is the number of turns in the receiving loop. 

The equation reduces to 

emf = mu0 HSARNR 

Combining equations (10 ) and (12 , the direct relationship 

between the transmitting antenna moment (MT) and the receiving 

loop voltage (VL) is obtained as 
This equation is of fundamental importance in considering 

loop to loop via line coupling in the radio system. From 

the system design point of view, the voltage induced in a 

distant loop increases with the second power of the transmission line conductor separation (b) . Transmission lines 

that are installed for the purpose of increasing radio coverage 

in manways should have the greatest possible conductor separation distance. Twin lead transmission lines used in TV 

lead-in applications exhibit greater conductor separation than 

typical twisted pair pager telephone cable. Ruggedized twin 

lead cable is recommended. Given the antenna physical mounting 

constraints (height and length), receiving loop voltage increases with the number of turns. Therefore, increasing the 

number of turns increases the coupling efficiency of the 

antenna. Coupling increases with the second power of operating 

frequency . 

3. Attenuation Rate 

The attenuation rate untwisted telephone cable and 

AC power cable was measured in coal and M/NM mines. Xeasurements are extremely difficult (impossible) to accurately make 

in an operating mine owing to many well known factors. The 

principal factor is the natural variation of distance between 

the transmitting/receiving loop antennas and the signal transmission line in the manways. This causes uncontrollable 

second power of distance change effects in induced line 

current. Mining operations limit vehicular transportation 
and prohibit disruption of the mining processes by measurement procedures. Even with these difficulties, average 

attenuation rates were measured in the mines shown in 

Table C. 

The attenuation rates measured in coal and M/NM mines 

were found to be similar. The induced monofilar current 

flowing on the transmission line at the base station location 

was measured with a calibrated current transformer (probe). 

CURRENT PROBE 

OR RF LINE 

TELEPHONE 

8' CEIVER CALIBRATED 

\ VOLTMETER 

SINGER 

MODEL NM-25T 

/ / / /, // /- // / /I///, 

FIGURE 26. SET-UP FOR MEASURING INDUCED LIME CURRENT 

Figure 26 shows that the source (transmitting loop antenna) 

was mounted on a mine service vehicle. The induced current 

was measured as the vehicle moved away from the base station 

location. The measured data is shown in Figure 27. The 

attenuation rate was approximately 2.4 dB/1003 feet. 
I 2 3 4 5 6 7 8 9 10 11 

MAN WAY DISTANCE FROM BASE (THOUSAND FT
With a vehicle-to-base-station separation range of 5000 feet 

the induced line current was approximately 707 microamperes. 

The mine generated noise was also measured during each field 

test. The induced noise level typically measured 2.2 

microamperes in a medium sized coal mine with conveyor 

haulage. The signal to noise ratio was found to exceed 50 

dB. The horizontal dashed line (C/N=20 dB) represents the 

induced line current level communications. The intersection 

of the dashed and the protection of induced line current 

(not shown) curves forecast that the maximum cornmunications 

range along telephone cable will exceed 18,000 feet. at 

520 kHz. 
G. LOOP ANTENNA DESIGN CONSIDERATIONS 

The underground cornmunicaticn range depends upon the 

ability of the transmitting and receiving antennas to 

efficiently couple coal seam and transmission line signals. 

Equations (1) and (14) show that the level of signals induced 

on a transmission line or at the receiving antenna output 

terminal depends upon the first power of transmitting antenna 

magnetic moment (MT). The receiving signal also depends upon 

the first power of turns-area product (NRAR) of the receiving 

antenna. The transmitting loop magnetic moment (MT) is 

produced by an excitation current (I) flowing through the 

transmitting coil shown in Figure 2 8. 

n 

FIGURE 28. TRANSMITTING LOOP ANTENNA EXCITATION CUXRENT AND 

MAGNETIC MOMENT(^) . 

(1) The direction of the magnetic moment can be determined by 

the "right hand rule" whereby the fingers of the right hand 

point in the direction of the magnetic field when the conductor is grasped such that the right thumb points in the 

direction of the current. 
The magnetic moment is defined as 

I MT I = NIA 

where A is the area of the loop in square meters, 

I is the level of the excitation current, and 

N is the number of turns in the transmitting loop. 

The moment is a vector orthognal to the plane of the loop. 

The transmitting loop turns-current-area product (NIA) is 

a scaler quantity. The loop antenna produces a horizontal 

magnetic dipole (HMD) when the transmitting loop antenna lies 

in a vertical plane and a vertical magnetic dipole (VMD) 

when in the horizontal plane. 

1. Design Optimization Process 

Coupling can be optimized by maximizing the products 

(NIA) and (NRAR) for the transmitting and receiving antennas, 

respectively. Like all optimization problems, constraints 

placed upon the individual variables of the product significantly increases the design task. The optimization process 

to be described in this work examines each independent 

antenna design variable (Xi) to define its upper bound A 

(Bi). The upper bound for each of the variables may be 

written as 

where the subscripts i = 1, 2, 3, ... identifies the variables 

and constrained values. 
If separate antennas are used for receiving and transmitting 

functions, then the optimum feasible design will require 

different upper bounds for the antenna area and turns. If 

the functions are combined in a single antenna design, the 

same upper bounds apply. Antennas that operate in a hazardous 

atmosphere must necessarily have upper bounds on the transmitting antenna magnetic moment. 

Physical reliability of the antenna structure imposes 

additional mechanical and electrical design constraints. 

The materials selected for use in construction of the antenna 

must allow the antenna to survive extreme physical abuse. 

The electrical component reliability must not be adversely 

affected by: 

. High circulating current in the loop, 

. High localized electric fields that can produce 

corona effects, and 

. High voltages that can break down dielectrics used 

in the construction of the loop components. 

The antenna design constraints will be examined in the 

following paragraphs. 
Antenna Area Constraints 

Constraints placed upon the maximum antenna areas may 

be represented as 

h 

A1 2 B1 (vest), and 

A2 5 B2 (vehicular) . 

The upper bounds (B1, B are determined by straight forward 2 

examination of the antenna mounting limitations on the roving 

miners and many different types of underground vehicles. 

a. Vest Antenna Area Constraint 

In execution of the contract work covered by this 

report significant improvements in the design of the 

"vest" type loop antenna worn by the roving miner 

were accomplished. These improvements were based on 

certain factors evident from earlier similar work of 

others. A short summary of technical requirements 

and historical developments leading to the present 

design follows. 

The vest antenna must "fitn on the miners body, be 

of light weight construction and be conveniently 

worn by the roving miner. Any change in area of the 

antenna that results from the wide range of miner's 

physical body size or their movement during work will 

also change the inductance of the antenna coil. Any 

change in inductance will detune the antenna result ing in lower transmitting loop magnetic moment. 
In the course of the extended laboratory field work, 

rigid oval tubular, flexible strap (bandolier) and 

sewn garment antennas were examined for use by 

roving miners. The rigid oval tubular antenna A 

(B1 = 0.25 m2) used on the Collins Radio Prototype 

MF Transceiver (FM) design was found to be onerous 

to roving miners. 

FIGURE 29. COLLINS RADIO PORTABLE MF TRANSCEIVER 

FIGURE 30. 

An important feature of the Collins Radio rigid 

tubular loop antenna design was that the area did 

not change with the miners' body size or movement. 

Because this loop design encumbered the miner, it 

was rejected for use in mining. 

The strap-type bandolier antenna used in the South 

African transceiver (SSB) design satisfied many 

problems caused by human factor problems. Roving 

miners were not encumbered when "wearingrr the 

antenna. 

SOUTH AFRICAN PORTABLE MF TRANSCEIVER 

The area depended upon the physical body size of the 

miner and his range of movement. Because of the 

antenna detuning affects, it cannot be used in a 

high performance comunications system. 

The Lee Engineering prototype transceiver (SSB) n 

2 employed a sewn garment circular loop (B1 = 0.15 m 1. 

The loop was positioned over the miner's shoulder 

(14) . Like the bandolier antenna, the area depended 

upon the body size of the miner. 

Finally, as a result of tests conducted during this 

project a sewn garment antenna capable of being 

placed upon the front or back of the miner's work 

clothing was developed. The sewn garment antenna 

was found to maintain a constant area. For convenience of use, the antenna was sewn onto the back 

of a vest garment. The upper bound for the area 

of the vest loop antenna was found to be 
b. Vehicular Antenna Area Constraint 

The vehicular antenna must be of a low profile 

mechanical design. Tests show that the antenna coil 

must be situated at least five inches away from any 

metal surfaces to avoid the effects of detuning. 

Examination of available mounting surf ace on various 

types of underground vehicles revealed that the 

available mounting surface area amounts to about 

four inches by fifteen inches. The maximum length 

of the antenna is twenty-eight inches. The height is 

fourteen inches. 

The antenna surface finish must not reflect light. 

The antenna must include provision for vertical and 

horizontal mountings. 

The antenna must be sealed to prevent sulfide ore 

body ground water drip from contacting the internal 

loop components. 

In the field work, rigid rectangular tubular metal, 

flexible rectangular tubular ~exan(l) and flexible 

rectangular planar Lexan antennas were evaluated on 

many different types of underground vehicles. 

(1) General Electric trade name for polycarbonate. 
resonant frequency of all the structures investigated. 

Lexan laminated planar structures were found to 

withstand high impact abuse in mine usage. This 

antenna structure was adopted for use in the program. 

3. Design For Operation In Hazardous Atmosphere 

The vest and in some circumstances, the vehicular antennas 

must be designed to operate in hazardous atmospheres. As a 

result there are two types of design constraints that necessarily occur. The first is that the stored energy within the 

antenna inductances and capacitances must be less than 0.3 x 

joules. The second is that localized electric fields 

developed in the structure not be of sufficient strength to 

cause corona discharge effects or dielectric breakdowns. 
The first constraint has been examined by Lagace (14). 

The maximum intrinsic safe transmitting loop magnetic moment 

may be represented as 

MT = B3 (vest), and 

MT = B4 (vehicular). 

A 

For the vest, B3 = 2 -5 ampere turns meter2 (ATM'). This 

limit follows from an analysis of Underwriters Laboratory 

Document 913, In mines that have hazardous environments 

anywhere in the mining complex, the vest transceiver design 

(including the antenna) must be approved by the testing and 

certification center, Mine Safety and Health Administration 

(MSHA) . In fresh air and in non-gassy M/NM mines, the antennas 

may have greater moment. 

In emergency situations, when ventilation is lost in a 

gassy mine, the use of non-approved radio equipment is prohibited. The design precautions related to the avoidance of 

excessive local electric fields causing corona effects or 

discharges through or on the surface of dielectrics must be 

very rigorously observed in order to obtain MSHA approval. 

Corona discharges were in fact observed during some preliminary 

experiments. Damage of the surface of dielectric used in 

structural components also did occur before safe design was 

realized. Relatively high RF voltages across the antenna loops 

may occur, as well as high RF circulating currents in the 

loops. Approximately 10 Amps and 1800 V peak-to-peak may be 
cited as upper-bound limits of these data. It is important 

to bear in mind that high RF voltage per se does not cause 

corona effects, nor dielectric strain. The electric field, 

associates with RF voltage causes these effects. It is 

possible, by proper design, to limit these fields for a given 

value of RF voltage by avoiding sharp points and edges and, 

in general, low radii of curvature in construction. Printed 

circuit boards must be coated by dielectric coating, capable 

of withstanding high values of electric stress. Circulating 

RF currents must be limited in order to reduce the stored 

energy in the tuned antenna circuit, the safe value'being 

less than 0.3 joules, as before mentioned. The rationale 

for the above precautions is that ionization (corona) is 

caused by excessive electric field and sustained by the stored 

energy the circuit. 
4. Theoretical Basis For Loop Antenna Design 

The theoretical basis for the design and optimization 

of a tuned loop antenna will be reviewed in this section. 

It will be shown that the use of a twin parallel connected 

coil instead of a conventional single coil occupying the 

same constrained antenna area offers some important advantages. 

First, since the twin-coil is physically smaller, its selfresonant frequency is greater than a larger single coil 

design. Secondly, the unloaded Q of the twin-coil is greater 

enabling the receiving response to a given magnetic field 

strength to be greater than in single coil loop. Finally, 

because the twin coils are connected in parallel, the terminal 

inductance of the coil is less than a single coil antenna 

with the same number of turns. Thus, the transmitting twincoil loop produces less electric field stress across the 

structural components of the antenna. 
The magnetic moment of any conceivable system of current 

loops in any given geometrical configuration is mathematically 

represented by 

where vectorial integration is conducted for each coil (i) 

and all its turns. The symbols are: 

i = running subscript identifying the coils, 

Ii = current in the ith coil, 

$ = position vector with respect to any selected orgin. 

The result does not depend on the selection of the 

orgin, provided each loop is geometrically closed, 

and 

+- 

dl = incremental vector, tangential to the loop of each 

coil in the direction of current flow. 

The concept of magnetic moment can be used to compute electric and magnetic fields at remote locations. The definition 

of "remote1' is a distance large as compared with the dimensions 

of the coil. For coplanar coils, the moment simplified to 

where 5 is a unit vector perpendicular to the plane of the 

ith loop. Its direction is determined by the "right hand" 

rule. 
The excitation currents flowing in a twin-coil transmitting 

loop antenna are shown in Figure 31. 

FIGURE 31. TWIN-COIL TRANSMITTING LOOP ANTENNAS 

The twin-coil magnetic moment is mathematically represented 

by: 

3 -+ 3 

= PJN~I~A~ + N212A2); = P2 (21) 

The equivalent circuit of a single coil loop antenna is shown 

in Figure 32. 

FIGURE 32. EQUIVALENT CIRCUIT OF A SINGLE-COIL LOOP ANTENNA 
The inductance (L) represents the apparent inductance of the 

coil used in the construction of the loop antenna. It is an 

apparent inductance because distributed capacitance (not 

shown) between coil turns tune out some of the real inductance. The inductance of a planar air-core coil is 

mathematically approximated by: 

where A is the area in square meters, 

N is the number of turns, and 

KO is the form factor. 

The inductance form factor depends on the ratio of the diameter 

(dl to the width (W) of a single layer winding. The incidental dissipation loss associated with the coil is represented as the AC ohmic resistance 

where Qu is the unloaded Q of the coil. The capacitance 

(Co) and loop inductance are resonant at the operating 

frequency 
100 200 406 

FREQUENCY IN KILOHERTZ 

- 

I20 

I 1 FIG

UNLOADE

FOR A F

.TUBULAR 

SINGLE 

- 

The typical unloaded Q of tubular and planar antenna coils 

are shown in Figures 33 and 34. Comparison of the figures 

shows that the planar coil has significantly greater unloaded Q. Figure 33 shows the family of unloaded Q curves 

for a tubular single-coil antenna structure. The unloaded 

Q in the MF band degrades as turns are increased. 

The ohmic value of the coil resistance (rl) is frequency dependent. It increases at higher fre-quency because 

of skin effects associated with current flowing in the coil 

conductor. When a single-coil loop antenna transmits at high 

power level, high electric fields between turns can produce 

corona effects. This also causes the apparent rl to increase. The resistance (rc) represents the dissipation 

loss associated with the tuning capacitance (Co) depending 

upon the type of tuning capacitor, the loss resistance (re) 

may decrease with increases in operating frequency and the 

level of current flowing through the capacitance. The 

transmitter to loop matching network may be realized by 

using two capacitors as shown in Figure 35. 

RESONANT 

M 

NETWORK 

FIGURE 35. TYPICAL MATCHING NETWORK 
The transmitter output impedance (ZT) is transformed by the 

matching network and becomes part of the resonant network. 

The transformation ratio (n) is given by 

Impedances are transformed by the second power of n and 

voltage by the first power of n. 

The resistance Ro is the impedance of the resonant network at 

the antenna operating frequency Cwo) and is given by 

The circuit Q for the antenna structure is 

where BW is the 3 dB radian frequency bandwidth of the 

antenna, 

Because low dissipation loss porcelain capacitors are 

used in the structure, the ohmic value of r, (shown in Figure 

32) is much greater than Ro. Under this condition, the 

resistance (R ) represents only the parallel combination of 

0 

the transformed transmitter output impedance and the ohmic 

value of the coil loss given by 
When R is large and I1 < I, then 

0 - 

I = nV1, and 

wCo 

The circuit capacitances are mathematically represented by 

, and 

when n is large, then Co C1. Under this condition the 

upper capacitor primarily determines the resonance frequency 

of the antenna structure. When the loop is transmitting, the 

capacitor (C1) must withstand the RF voltage developed across 

the coil. 
In our case the transmitting loop antenna is also used for 

receiving (as a receiver input circuit). The matching to the 

receiver input, with the aid of the capacitive voltage divider 

of the ratio (n) must represent a good design compromise with 

the transmitting application. It must safeguard an acceptable 

value of receiving input bandwidth. The higher the unloaded 

Q value of the loop winding, the better will be the efficiency 

of signal power transition to the receiver input. 

The RF voltage (V) appearing across the inductances and 

capacitances in a transmitting antenna structure is mathematically represented by 

v = Iw,LII. (33) 

When considering the antenna design problem, the question of 

whether to use separate antennas for transmitting and receiving or to combine the functions into a single structure 

naturally arises. Receiving antennas are optimized by rnaximizing the number of turns (NR) in the loop. A transmitting 

loop can have fewer turns. Regardless of how the antennas 

are used, the self-resonant frequency must be above the 

operating frequency range of the communications system. A 

ferrite core antenna cannot be used for a transmitting loop. 

Ferrite antennas are significantly more lossy (lower QU) than 

are air-core loops and change inductance at high power level. 

As a result, they produce significant smaller magnetic moments. 

The lower QU of the ferrite loop degrades the magnetic field 

sensitivity of the receiving loop (i.e., requires greater n). 
From the stand point of realizing the highest selfresonant frequency in the loop antenna design, the optimum 

loop shape is planar. This coil configuration minimizes the 

self-capacitance between turns. Capacitance can be reduced 

further by spacing adjacent turns. Spacing adjacent turns 

reduces the electric field gradient between turns. It should 

be noted that the gradient can be partially canceled in a 

coil by crossover winding techniques. 

When the antenna area is constrained (as it is in this 

design problem), Dr. Hupert (38) has shown that transmitting 

loop magnetic moment may be represented by 

r 

where P is the power dissipated in the loop, and 

kl is a constant that depends on area. 

Equation (34) is relevant in the antenna optimization problem. The moment depends only on power and bandwidth and 

not on turns(N). Equation (14) shows that receiving sensitivity of an antenna increases with turns. Thus the receiving function of a combination transmittingheceiving 

loop can be optimized by increasing turns. As a practical 

matter, turns can be increased until the self-resonant 
frequency of the coil approaches the operating frequency band 

from above. Another limit on turns is implied in Equation 

(33). Since L increases with the second power of turns, 

maximum turns is also determined by the dielectric withstanding voltage of the capacitors and coils used in the 

structure. 

The principal objectives in the antenna design are: 

. To optimize the design of a combination transmitting 

and receiving loop antenna, and 

. To optimize the available area in order to design loop 

antenna capable of highest magnetic moment with the 

lowest RF voltage across it. 

The last objective led to the solution involving twin parallelloops forming the antenna in preference to an antenna using a 

single loop. The reduction in voltage between single and twincoil loop antenna designs will be examined on the basis of 

equal power dissipation and loaded circuit Q. Both antenna 

designs will be assumed to have the same number of turns and 

occupy the same total surface area. The area of each twin-coil 

is one-half of that of single coil area. The inductance given 

by Equation (22) of the twin-coil is assumed to be proportional 

to the square root of the applicable area. In addition, besides 

the area difference , the twin-coils are mutually coupled and 

their mutual coupling should be taken into account. 
The power (PI dissipated in the single coil loop with an 

inductance (L) and ohmic loss resistance (rl) is given by 

In a twin-coil loop, the dissipated power is mathematically 

represented by 

where ITt is the inductance of a single coil in the twin-coil 

structure. The inductance includes the effects of mutual 

coupling and smaller area of the coil. By equating Equations 

(35) and (361, the relationship between current flowing in 

a single coil and in each coil of the twin-coil structure is 

given by 

 he RF voltages are to be compared at resonace. The RF voltage 

( VS ) appearing across a single coil and the voltage 

( VT ) appearing across a twin-coil structures are 

VS -11 woLI (single coil) 

vT = /IT WoL+~ =I Ib,JLL'~ (twin coil) (39) 2 
The voltage developed across the twin-coil is clearly less 

than that developed across the single-coil. 

The currents and inductances in the mutually coupled 

twin-coil loop will be determined in the following coupled 

circuit analysis. 

The mutual coupling (M) in the twin-coil loop antenna 

is illustrated in Figure 36. 

u.) MUTUAL COUPLING b.) DEPENDENT SOURCES 

FIGURE 36. INDUCTIVE COUPLING IN THE TWIN-COIL LOOP ANTENNA 

The dependent voltage sources (shown in Figure 36 (b ) have 

been substituted for mutual coupling. Assuming that the coils 

are identical, the branch impedances are 
where S is the Laplace operator and (rlr2) represents the 

ohmic value of the dissipation loss associated with each 

coil as well as the equivalent load. 

FIGURE 37. EQUIVALENT CIRCUIT OF THE TWIN-COIL LOOP ANTENNA 

The voltage common to both loops can be expressed as 

from these equations 

and 

then v -- + VSM - I1 ( SM) 

I1 ZIZq 
The branch current becomes 

Since 

that 

then 

SEI = k \/SZL~L~ and 

where the inductance (LT1) is given by 

Equation (50) allows the twin-coil loop antenna structure to 

be considered as composed of two uncoupled coils of inductance LTt. The range of coil coupling is 
PARAMETER 

Frequency (kHz) 

TABLE G 

COMPARISON SINGLE AND TWIN-COIL 

VEHICULAR ANTENNA CHARACTERISTICS 

Bandwidth (kHz) 

Turns (N) 

Inductance (pH) 

Area (m2) 

Unloaded Q (QU) 

Capacitance 

woL (ohms) 

RF Voltage (Vpp) 

V1 Voltage (Vpp) 

Loop Current (each co ill 

I (App) 

Moment ( ATM* peak 

SINGLE-COIL TWIN-COIL 
The tabular results are noteworthy in several respects. 

First of all, even though the circuit Q of both antennas are 

identical, the unloaded Q of the individual coils are not. 

This follows from the fact that the smaller planar twincoil exhibits a higher self-resonance frequency (2.8 as 

compared to 1.5 MHz in the single coil). Secondly, the RF 

voltage appearing across the twin-coil structure is less 

than the voltage appearing across a single coil structure. 

The relative ratio of 0.55 compares closely with the value 

of predicted by Equation (55). The magnetic moments were 

found to be almost identical in the single and twin-coil 

loop antennas. This was attributed to the non-linear 

behavior of the source impedance. In summary, the twin-coil 

loop antenna RF voltage for a given magnetic moment is less 

than in a single coil design. Because of the lower operating voltage, the dielectric withstanding voltage requirements are less severe. 
The magnetic moments of single-coil ( I gS I and twin-coil 

+ 

structures ( 1~~1 ) are 

11 = NIA (single coil) 

I~$I = (twin-co il ) 

In the case of the planar twin-coil structure, the mutual 

coupling coefficient is negative and approximately 

Then, the uncoupled inductance of each coil of the twin-coil 

follows from Equation (50) as 

LT1 = 0.9L1 and 

since L1 = L/JT , then 

LT' - 0.64L. (54) 

By substituting Equation (54) into Equation (39) and Equation 

(531, a direct comparison of RF voltage and magnetic moment 

can be made between a single and twin-coil antenna as 

and 
Single and twin-coil planar loop antennas were constructed 

and evaluated in our laboratory. The antennas were each 

driven from a vehicular transceiver. The loop design parameters and measured results are shown in Table G. 

During the test, the DC power applied to the vehicular 

transceiver power amplifier was 26.4 watts. When the transceiver was terminated by a 50 ohm power meter, the power 

meter reading was 20 watts. The capacitances C1 and C2 are 

used to couple the transmitter (source) to the loop antenna 

coils. The transmitter output impedance (antenna source 

impedance ZS) is known to be non-linear. The capacitance 

values were selected to produce an apparent circuit bandwidth 

of 12 kHz centered about the operating frequency (400 kHz). 

When the loop antenna is used as a receiver, it is terminated 

by vehicular transceiver receiver input impedance ( 5 0 ohms 1 . 

The measured receiving bandwidth is approximately 12 kHz. 
RF LINE COUPLER DESIGN 

Many of the considerations which are important in the 

design of loop antennas are also important in the design of 

RF line couplers. The RF line coupler is a multiple-turn 

toroidal air-core current transformer. 

Equivalent circuit of the RF line coupler is shown 

! couolet / 

EQtllVALE NT 

NETWORK ACTUAL NETWORK 

FIGURE 38. RF LINE COUPLER 
The "wireplant" conductor becomes a single turn on the 

secondary. of the transformer. The transfer impedance of the 

coupler is given by 

where V1 is the coupler output voltage and 

IL is the line current flowing in any "wireplantfl 

conductor. 

If the coupler exhibits a higher transfer impedance (ZT), 

the output voltage applied to the receiver is greater. Thus, 

coupler efficiency can be characterized by its impedance. 

Coupling of "wireplant" signals to the toroidal coupler 

is illustrated in Figure 39. 

I -7 WIREPLANT 

CONDUCTORS 

FIGURE 39. SIGNAL COUPLING FROM THE WIREPLANT 

(CYLINDRICAL COORDINATES r, Z, 4) 
The time dependent line current flowing through the center of 

the toroidal coil along the Z axis is 

IL(t) = I SINwot L (57) 

From Amperes Law, the magnetic field at a radial distance (r) 

from the line current is given by 

where a@ is the azimuthal unit vector in the cylindrical coordinate system. The magnetic flux densitity in free space 

The magnetic flux (a) passing through the area enclosed by 

each turn of the toroidal coil is 

-+ -+ 

Q = /B$* da = dr dz. 

The voltage induced in N turn is given by Paraday's Law: 

Substituting Equation (60) into (61) and differentiating 

with respect to time, the induced voltage is mathematically 

given by 

emf = poNILfWLn(b/a). 
When a capacitance matching network is used in the coupler 

design (see Figure 35 1, the transfer impedance of the coupling 

structure may be mathematically represented by 

The transfer impedance increases with the first power of turns, 

current level, operating frequency and length (W) of the 

coupler. It decreases with the first power of n. It increases with the logrithm of the ratio of inside to outside 

diameter of the coil. 

The operating range between transceivers along a transmission line pair (which supports the bifilar mode) will 

exhibit an optimum value with respect to frequency. This 

occurs because both the coupling efficiency and signal attenuation rate increases with frequency. 

The transfer impedance of a 1 inch coupler was measured 

and the results are shown in the following table. 

TABLE H 

RF LINE COUPLER 

TRANSFER IMPEDANCE 

(1 INCH) 

Test Frequency 

350 kHz 

5.20 kHz 

Transfer Impedance (ohms) 
The induced current flow in the I1wireplant" by a 

transmitting coupler is dependent upon the resistance 

(impedance) of the conductors. The induced current was 

measured in the test set-up shown below. 

FIGURE 40. TEST SET-UP FOR MEASRUING INDUCED CURRENT AS A 

FUNCTION OF LINE RESISTANCE (RL) 

Y 

IL 

t 

TRANSCEIVER 

20 W 

b 

(1 

SINGER 

FS M 

NM-25T 6 

RF 

LINE 

COUPLER . 

? 

CURRENT 

PROBE 
On A.R.FWts antenna range, multiple conductors were 

placed in the RF line coupler as illustrated below. 

I TRANSCEIVER 

FIGURE 41. OVER THE EARTH MULTIPLE WIRE COUPLING 

The circle symbols show the location where the standard 

current probe was used to measure induced line current. As 

expected the line current in a remaining conductor did not 

change when other conductors were removed from the RF line 

coupler. In this test, the coupler can be modeled as a tuned 

primary transformer with a multifilar secondary winding. 
At 530 kHz, the induced current was measured to be 

approximately 3.9 mz in each wire. Data presented in Table I 

indicates that the apparent line and earth circuit resistance 

is greater than 2000 ohms. In mine tunnels, the apparent 

resistance of telephone cable is also approximately 2000 ohms. 

I. MODULATION PROCESSES 

The practical quality of a communication system is judged 

by the human ear. Listeners judge quality by the naturalness 

of the speaker's voice, background noise level and the like. 

In the laboratory, quality is judged by analyzing the recovered 

audio signal at the output of the receiver. The measurement 

of recovered audio signal to noise ratio (S/N), has come into 

being as a reliable measurement standard. 

The recovered audio output signal to noise ratio may be 

maximized by enhancing the signal in the presence of noise. 

Predetection filtering is useful in discriminating against 

noise that occurs outside of the occupied bandwidth of the 

modulated signal. Noise discrimination improves by selecting 

higher operating frequencies (FO) and by using the narrowest 

post detection bandwidth that is compatible with the modulated 

signal. 
Spread spectrum modulating processes have the ability 

of increasing the recovered output signal to noise ratio by 

providing process gain in the cornmunicat ion channel. Process 

gain is the result of subsequent bandwidth spreading and 

de-spreading operation. One of the most familiar of the 

spread spectrum modulation processes is seen in conventional 

frequency modulation ( FM) where the modulation process produces a much wider occupied bandwidth than the information 

bandwidth. 

Figure 42 shows the process gain characteristics for 

FM, SSB, and AM modulation processes. FM process gain increases with the modulation index (B) given by 

where Af is the peak frequency deviation and fm is the 

highest frequency in the modulating signal spectrum. 

The break in the slope of the FM characteristics marks 

the threshold in process gain. For carrier to noise (S/N) 

ratios below the threshold value, the recovered signal to 

noise (S/NIo ratio rapidly degrades. 

Single sideband (SSB) characteristic is noteworthy in 

that it does not exhibit a threshold. 
FIGURE 42 

20 - 

CARRIER TO NOISE RAT10 (s/N) 

TYPICAL MODULATION PROC ESS GAIN 
By considering only process gain, FM has an advantage 

in a communication system that can be operated with a large 

carrier to noise ratio. The advantage, of course, depends 

upon the modulation index and the carrier signal to noise 

ratio. In the "nearw field communication system, the combined 

effects of "near" field propagation loss and noise, force the 

carrier to noise ratio to be low some of the time. Because 

SSB does not exhibit a threshold, it might be preferable in 

some cases. 

In today's congested-band terrestrial radio services, 

SSB is favored because the RF occupied bandwidth is. the same 

as the information bandwidth. This means that many more user 

service channels can co-inhabit the assigned service channel. 

On the other hand, the occupied bandwidth of an FM signal as 

given by 

BW = 2 Af where B < 1 

is much greater than the information bandwidth. 
Since the communication system does not operate by means 

of a radiated field, but rather by an induction field, the 

magnetic moxent (MI of the antenna is to be maximized. For 

a given transmitter output power and loop area, reducing the 

bandwidth (BW) of the loop increases the magnetic moment as 

shown in Equation ( 33 1 . 

1% la /% (33) 

The occupied bandwidth of the loop current signal must 

be within the bandwidth (BW) of the tuned loop. The tuned 

loop antenna attenuates signal components that occur near the 

band edge frequencies of the loop passband. The loop antenna 

will not faithfully reproduce magnetic moments for these band 

edge signal components. When loop bandwidth is less than the 

occupied bandwidth, the modulation index B is reduced in the 

carrier signal. The modulated carrier signal occupied bandwidth determines the circuit Q(QCKT) of the loop antenna as 

In practice, QCKT is bounded by realizability considerations. The lower bound is determined by the available 

transceiver power supply voltage and the current drive capability of the power amplifier. The higher bound is determined by unloaded Q (Qu) of the antenna structure. The lower 

QCKT bound militates against the use of wideband FM in the 

communication system. 
SSB and narrowband FM can be compared on the basis of 

occupied bandwidth. The SSB circuit bandwidth can be onehalf that required for narrowband FM. With respect to . 

equivalent magnetic moment generated by the transmitting 

loop antenna, the SSB transmitter power can be 3 dB less than 

the FM transmitter power. On the other hand, an SSB loop 

antenna matching network will require a higher transfer ratio 

(n). The higher ratio makes the SSB antenna more sensitive 

to loading caused by nearby metal objects. Loading will cause 

the terminal impedance of the antenna to change. The Automatic 

Level Control (ALC) associated with the SSB transmitter will 

cause output power to vary with loading. By way of contrast,a 

FM transmitter final amplifier can be designed to produce 

almost constant load plane power over a wide range of impedance. 

Thus a narrowband FM transmitter is expected to produce constant power over a range of incidential antenna loading conditions. 

From the standpoint of received noise, narrowband FM 

would appear to have an advantage over SSB because of limiting 

in the FM receiver. It turns out that repetitive impulselike behavior of the mine noise causes the predetection 

circuits, including the limiter network in the FM receiver, 

to ring, degrading the recovered (S/N), ratio. As long as 

the carrier level exceeds the noise by 10 dB, the quality of 

the recovered voice signal is acceptable. On the other hand, 

impulsive noise causes the SSB automatic gain control (AGC) 

circuit to immediately desensitize the receiver with each 
noise burst for the release period (time constant) of the 

AGC. Because of the way AGC control signals are developed, 

decreasing the release period below a certain value causes 

instability in the AGC control circuit. While impulse noise 

degrades the FM receiver recovered audio signal quality, an 

SSB receiver is desensitized for the AGC release period which 

dramatically reduces the intelligibility of the voice signal. 

The operating range of prototype 1 Watt FM transceivers 

was compared to 1 Watt S3B transceivers in the York Canyon 

mine near Raton, New Mexico. Before the field test, laboratory measurements were made on the FM and SSB transceivers 

to ensure that the output powers were identical. 

Along the longwall the FM and SSB medium frequency 

(520 kHz) transceivers provided excellent coverage. In the 

entryways, the SSB transceiver range was over 400 feet while 

the FM transceiver provided entryway coverage exceeding one 

mile. 

The narrow-band FM modulation process is preferable for 

use in the underground wireless communication system. 
ACOUSTICAL NOISE PROBLEMS 

The measured acoustical noise ranges from the threshold 

of hearing (0.0002 ~~nes/~rn') to more than 104 dBA-(158,489 

times the threshold of hearing) in the reverberant surroundings of the longwall. Table J shows typical noise levels 

measured in the near vicinity of mining equipment (39). Noise 

levels of 108 dBA have been measured near mining equipment. 

For comparison purposes, Figure 43 shows the noise spectra 

measured near an operating longwall and inside of the M-60A 

military tank. 

FIGURE 43. ACOUSTICAL NOISE COMPARISONS 

v, 

a 

3 

IIO* I I I I 1 I I 1 i ,I 0 B 

ACOUSTICAL NOISE - L 

COMPARISONS -I 2 

0 m 

o LONGWALL MINER 

J 100- 

0 

=CU m 

WZ I ;;

c w90- 

a F 

z_ 0 

2 cli 

880- 

9 

9 O 

ow 

$" 

-32 I 

3 

-64 Z 

X 

I I I I I I I I I I 1~1282 

4 150 300 500 1000 2000 3000 4000 

T) THIRD-OCTAVE BAND CENTER FREQ., HZ 
TABLE J 

MACHINE 

MEASURED SOUND PRESSURE LEVEL 

OF 

MINING MACHINES 

SOUND LEVEL IN dBA 

Diesel Powered Locomotive 

Joy lORU Cutting Machine 

Wagner HMTT-410 Ram Hauler 

Joy Loader 

Exhaust Fan 

Wagner Loader 

Wagner MTT-108 Truck 
1. Overview of Microphone Noise Cancelling Theory - - - 

Comparison of the M-60A tank and longwall acoustical 

noise levels is noteworthy in several respects. The longwall 

noise level is approximately 8 dB greater than the acoustical 

noise level measured inside the M-60A tank! Military research indicated that intelligibility scores of voice modulated radio signals from inside of a moving tank is below the 

minimum acceptable limit (40). This is caused by the ambient 

acoustical noise mutilation of the speech pressure wave on 

the microphone diaphragm . By the same mechanism, voice radio 

communications near an operating mining equipment are expected to also be below the minimum intelligibility score. 

During the early years microphones were designed using 

resistance responding and controlled reluctance techniques. 

The carbon microphone is an example of the resistance responding microphone. Controlled reluctance microphones were 

designed with either a coil or magnetic armature mounted on 

a diaphragm. The telephone headset receiver is a good example of the later technology. 

Microphones have also been constructed with piezoelectric 

materials such as quartz, rochell salt crystals, and PZT/ 

BaTiO ceramic materials. 

In recent years, the piezoelectric properties of fluorocarbon polymers films have been investigated for using in the 

design of "thinf1 microphones. 
In general microphones are broadly classified by their 

order. A zero (0) order microphone reproduces speech without inherent noise cancelling properties. That is, both 

speech and background noise cause the microphone to produce 

an output signal. The speech and noise pressure waves can 

impinge on both sides of the diaphragm. That is, the microphone responds to the pressure ttdifference" across the 

diaphragm. Microphones of this design are called first order 

pressure gradient microphones. First order gradient microphones can be connected in arrays to improve noise suppression 

and are called second order gradient microphones.. 

There are two (2) factors that make the gradient microphones effective in s'uppressing background noise. These 

factors are: 

(1) The ttProximity effectu whereby spherical speech 

pressure waves produces a greater pressure gradient 

across the microphone diaphragm than do planar wave 

noise signals which are generated at distant points. 

(2) The cos or directional response of the microphone due to acoustical access to both sides of the 

diaphragm and the diffraction effects of the microphone 

in relation to the wavelength. 
Noise cancellation occurs because the phase and amplitudes of the far field noise signal sum to zero on the PZT 

diaphragm. 

Several methods are available to obtain noise reduction 

in the design of a microphone. They are summarized as 

(1) Direction Zero (0) order microphone 

(2) Contact microphones, and 

(3) Gradient microphones. 

In principal, a directional microphone will provide noise 

rejection. When ambient noise is a problem, these microphones have not been found to be effective in many applications. 

"~esearchers have found that a microphone attached to the 

front tooth has exceptionally good noise cancelling properties. 
First order gradient microphones are commonly available 

in the commercial art. Multiple order gradient microphones 

have superior noise cancelling properties; however, they are 

supercritical with respect to variations in air path length 

caused by lip action. 

The Department of the Navy is sponsoring the development 

of a second order noise cancelling microphone (42). Electro 

voice is exploring the adaptation of the electret noise cancelling technique whereas Vought is exploring the use of 

PZT ceramic technology (41). 

The Vought design uses a single PZT ceramic diaphragm 

with a specially designed acoustical entrance to obtain noise 

cancelling (41 . 

DIAPHRAGM 1 I 

FIGURE 44. THE VOUGHT SECOND ORDER MICROPHONE TECHNIQUE 
Contact microphones are sometimes called "BoneN or 

"Skull" microphones. Contact microphones offer little, if 

any, improvement in noise reduction. Further, contact microphones provide considerable discomfort to the users. It 

turns out, the skull bone itself becomes a conductor for 

noise and therefore does not inherently produce noise cancelling. Moving vehicular vibrations may be conducted through 

the body causing the contact microphone to respond to unwanted 

noise signals. The U.S. Marine Corp recently supported 

development work on the llskullv microphone for use in amphibian vehicles (landing craft 1. This work terminated when the 

marine radio operator complained about the microphone compression discomfort and resulting headaches. As one miner 

stated "How would you like to wear either the skull or throat 

microphone during a shift?" 

First and second order gradient air path microphones do 

offer theoretically predictable noise cancelling possibilities. 

From a circuit theory point of view, a high pass filter 

can be used as an analogy for the gradient microphone. Using 

the high pass filter analogy, the noise discrimination capability is shown in Figure 45. 
- Fc - Fc Fc 

4 2 FREQUENCY 

FIGURE 45. NORMALIZED NOISE FREQUENCY RESPONSE OF A GRADIENT 

MICROPHONE. A) VOICE SIGNAL, B) FAR FIELD NOISE, 

FIRST ORDER GRADIENT MICROPHONE, AND C)' SECOND 

ORDER GRADIENT MICROPHONE. 

The ordinate or y axis is labled Attenuation in dB. 

The attenuation represents the noise cancelling capability of 

the microphone relative to a reference - curve a. 

The abscissa or x axis is "scaled1' or normalized in 

terms of the cut off frequency (Fc) also called "cross over" 

frequency by microphone technologists. 

The cut off frequency of the noise cancelling microphone represents the noise frequency below which cancellation 

occurs. Curve a represents the theoretical output signal 

produced by a noise cancelling microphone to spherical wavefront speech signals. In practice, the microphone response 

will not be flat (constant) and will exhibit considerable 

frequency dependence. In the case of a first order gradient 

microphone, the noise cancelling microphone attenuation 

increases by 6 dB each time the noise 
frequency is halfed. For a second order microphone, the 

attenuation increases by 12 dB for each halfing of the noise 

frequency. In general, the asymptotic rate of attenuation is 

given by 

dB = n6 per octave reduction 

where n is the order of the gradient microphone. 

With this background, the limitation of noise attenuation can be readily assessed. First of all, if the amplitude 

spectrum of the noise source has principal components below 

the cut off frequency (fc), noise cancelling does occur. 

Also, the higher the cut off frequency, the better will be 

the noise cancelling attenuation for a particular noise source 

(same amplitude spectrum). As it turns out, the cut off 

frequency is dependent on the "thickness" of the microphone 

diaphragm. Thinner diaphragms have higher cut off frequencies 

and are therefore better noise cancelling microphones. 

It may rightfully be concludedthat higher order microphones would also be important in this application. A second 

order microphone design offers much greater attenuation. This 

conclusion may not be correct. First of all, changes in air 

path length occur during utterances. The apparent source 

position changes with lip movement (even if the microphone 

is stationary). Changes in air path length cause "phase1' distortion to occur and this phenomenon will be described below. 

The instantaneous pressure for a spherical wave is given by 
p = pkcA sin k (ct - r) 

where k = w/c is the free space propagation constant, 

c is the speed of sound in air, 

0 is the radiant speech frequency, 

r is the air path length, and 

P is the air density 

Po = ewA. 

Equation (67) may be rewritten as 

P P = o sin (wt - kr). 

The argument of the sine term includes the propagation 

constant (k) and the path length (r) . Changes in path 

length (r) cause changes in phase (kr) or phase modulation. 

In a filter network, the non-linear phase response of the 

filter transfer function causes distortion to occur in the 

speech signal as it "flows" through the network. The "degree" 

of the distortion is dependent upon the type of transfer function and the asymptotic behavior of the attenuation characteristic. That is, the greater the rate of change of asymptotic attenuation in the stop band, the greater is the speech 

distortion. Increasing the attenuation characteristic of a 

microphone can be expected to increase "phase distortionM 

problems. 
One can expect small changes in air path length to 

vmodulatefl the speech signal in higher order noise cancelling 

microphones. 

Noise cancelling microphones are positioned to the side 

of the mouth to reduce the ''puff" sounds. 

Expanding the noise cancelling problem to speaker devices, 

other problems emerge. For example, a single earphone does 

not work well in a high level voiceband noise environment. 

Noise is readily transferred through the head and on the skull 

bone. Further, research has shown that the ear "muff" must 

be large to achieve low frequency attenuation. That is to 

say, that an ear plug speaker does not work as well as a 

large ear muff speaker. 

The AVADT microphone and audio system study (40) is the 

most recent and extensive research into intelligibility scores 

achieved by many different types of acoustical devices in a 

wide range of background acoustical noise levels. 

Inside of the M-60A tank, the military M-138 noise cancelling microphone is used with circum-aural earphones to 

achieve an intelligibility score of better than 87% (72% is 

the minimum acceptable limit). To attain this score, a high 

pass filter with cut-off frequency of 300 Hz is designed into 

the audio processing path. This discriminates against the 

lower octave noise shown in Figure 43. 
In summary, the following conclusions have been reached: 

Bone and skull microphones will not be considered in 

this work. 

Thin diaphragm noise cancelling microphones must be 

used in high acoustical noise areas. 

A noise cancelling airpath microphone must be positioned 

on the radial line (to the side of the mouth) within a 

distance of 4 inch or less from the lip. This requires 

the use of a boom microphone located on the miners cap. 

A noise cancelling microphone cannot be built into the 

control head enclosure because the "apparenttT microphone 

diaphragm would be thick yielding a design with a low 

cut off frequency (Fc). The enclosure would also always 

need to be placed within f inch of the lip. 

2. Evaluation of Noise Cancell ing Microphones 

The acoustical noise and its effect on voice transmission 

quality was studied in each mine. However, more extensive 

series of tests were conducted in the York Canyon Mine. The 

purpose of the tests were to evaluate various types of noise 

cancelling microphones and earphones in the underground mine 

environment. The poly (vinylidene fluride) (PVF2) polymer 

film microphone, a military M-138 noise cancelling microphone, 

and a standard dynamic non-noise cancelling microphone were 

evaluated by voice recordings near an operating longwall. 

The voice recordings were made using ANSI phonetically 

balanced word lists. The results are shown in Table K. 
TABLE K 

MICROPHONE 

Quiet Area 

Standard 

M-138 

PVF2 

Longwall 

Standard 

M-138 

PVF2 

MEASURED 

ARTICULATION INDEX 

INTELLIGIBILITY SCORE 
Averages of the test in quiet environments show the microphone intelligibility to be very much alike. However, when 

subjected to higher background noise the difference becomes 

quite evident. 

In the vicinity of an operating longwall, the "standard" 

non-noise cancelling microphone scored below the minimum 

acceptable level of 72%. Although the M-138 microphone 

performance was acceptable, performance degraded from the 

quiet value. The tfthinll PVF2 microphone scored well above 

the M-138 microphone intelligibility score. The score did 

not change from the quiet area score. 

3. Evaluation of Vest Microphones - -- - 

Many different micmphone configurations were evaluated 

during the design of the vest transceiver. A prerequisite 

for the microphone is that it be convenient to use and not 

be onerous to the miner. A hand held microphone was found 

to be unacceptable because the microphone cord could accidentially become entangled in mining equipment causing subsequent serious injury to the miner. 

A boom microphone mounted on the minersf cap was found 

to be necessary in specific situations. In high acoustical 

noise areas, the PVFZ boom microphone and circum-aural ear 

cup speakers must be used to achieve an acceptable intelligibility score. The acoustical transducer mounting is 

illustrated in Figure 46. 
FIGURE 46. PVF2 NOISE CANCELLING MICROPHONE AND CIRCUMAURAL EAR CUP SPEAKERS MOUNTED ON THE MINERS CAP 

The PVFP boom microphone can be positioned near the miners 

lips. Speakers are installed in the circum-aura.1 ear cups. 

Working miners expressed concern that the boom microphone 

would be damaged doing work. The microphone is constructed 

with tough plastic and survived mine testing. Evaluation in 

miners indicated that these acoustical transducers are required when the noise level is greater than 86 dBA. 

Working miners perferred the control head microphone (shown in 

Figure 11) over the PVF2 boom microphone and built-in microphone in the South African Transceiver shown in Figure 30. 

The control head ceramic microphone achieved an acceptable 

score when the noise level was less than 86 dBA. However, in 

fresh air entries, the ventilation air flowing across the 

control head produced an unacceptable level of "windv noise. 
The "wind" noise problem was solved by mounting the ceramic 

microphone element in acoustical wind screen foam material. 

4. Evaluation of Vest Speakers 

When the acoustical noise exceeds 86 dBA, circum-aural 

earphones are required; however, these earphones may pose a 

safety problem in quiet areas. In quiet areas (or near idle 

machinery) miners are accustomed to listening to local "roof 

talk" caused by shifts in the layered formation. This peculiar noise may provide early warning to an experienced miner 

of a rock fall hazard. 

A satisfactory solution to the "roof talk" problem was 

found by the use of a combination of vest speakers. Speakers 

are designed into circum-aural ear cups and the epaulets on 

each shoulder of the vest. The vest transceiver is designed 

to simultaneously drive the combination of speakers. In 

quiet areas, the ear cups are folded up on the miners cap and 

the epaulet speaker sound waves are directed upward along the 

miners' neck to his ears. Evaluation in the mine indicates 

that the geometry of the miners' cap aids in directing sound 

waves to the ear. Since the ears are not covered, the miner 

can also listen to "roof talkv when the radio is not receiving 

messages. 
FIGURE 47. HARD HAT MOUNTED SPEAKERS 

The performance was similar to the epaulet speaker system. 

Both fail in high noise areas. 

"SetCom Corporation, 1400 Stierlin Road, Mountain View,CA. 
Evaluation of Acoustical Transducers on Mine Vehicles - -- 

Acoustical noise suppression on vehicular equipment 

required two different approaches. On trolley powered locomotives, the conventional practice of use of a standard hand 

held microphone and a remote audio head (with a loudspeaker 

up to 10 watts) was satisfactory. However, on diesel powered 

trucks and tractors (Kubuta, John Deere, etc.), the conventional practice simply fails. On diesel haulage trucks, a 

hand-held noise cancelling microphone (M-138) and circumaural ear cup (with speakers) was found to be satisfactory 

in every report. The ear cup speakers were connected to the 

remote audio head via a cord with a quick-disconnect connector. This enabled the motorman to get out of the truck 

without always remembering to unplug his earphones. 

On diesel powered tractors, a handset (without noise 

cancelling properties) was found to be satisfactory. A 

hand-held noise cancelling microphone and a remote audio 

head with a message lamp was also satisfactory. 

The mine tests indicate that a wide variety of microphones and speaker systems must be provided with a commercial 

radio system. 
TABLE L 

RECOMMENDED 

MICROPHONE AND SPEAKERS 

FOR USE IN 

UNDERGROUND MINES 

WORK AREA OR 

VEHICULAR EQUIPMENT 

Manways 

Longwall 

VEST TRANSCEIVER 

TYPE OF MICROPHONE 

AID SPEAKERS 

Vest control head with 

ceramic microphone and with 

epaulet speakers. 

PVF2 noise cancelling microphone and with speakers in 

circum-aural ear cups. 

VEHICULAR TRANSCEIVER 

Trolley locomotives and 

battery powered service 

vehicles 

Conventional dynamic hand 

held microphone and remote 

audio speaker (10 watts) 

Diesel Powered Noise cancelling hand-held 

Haulage Trucks 

Diesel Power Tractors 

Microphone with speakers in 

circum-aural ear cups 

(quick disconnect connector 

in speaker cord). 

Noise cancelling handset 

with microphone and speaker. 

(Message light on remote 

speaker) . 
K. FREQUENCY PLAN AND PRESELECTOR FILTER DESIGN 

REQUIREMENTS 

Communication networks that will be created and used in 

the nations' underground mines will require the use of many 

operating frequencies. To avoid radio frequency interference problems in the system, specific frequencies must be 

assigned in accordance with a frequency plan. The goal of 

the plan is to insure that radio service in any network is 

not degraded by radio communications at any other assigned 

frequency whether in or out of the communications network. 

The transceivers used in each network are tuned to the 

assigned operating frequency. The receiver and transmitter 

sections are designed with 60 to 1000 kHz bandwidth to 

eliminate the need for tuning in those sections. Tuning the 

transceiver only requires the setting of rocket arm switches 

in the digital frequency synthesizer (DFS) section. The 

tuning switch is shown in Figure 48. 

FIGURE 48. DIGITAL FREQUENCY SYNTHESIZER TUNING ELEMENT 
The switch positions for any operating frequency are given 

inside of transceiver enclosure. The wideband design approach simplifies field servicing. When necessary, a defective transceiver can be easily replaced with a standby 

transceiver. The only tuning required is the setting of 

the DFS switches. Because of the wideband design approach 

used in the radio equipment, electrical wave filter networks 

are required to suppress unwanted signals. 

The RF line coupler and antenna are filter networks. 

They discriminate against unwanted signals that can cause 

receiver desensitization. Desensitization is caused by 

harmonic and spurious unwanted transmitter signals falling 

near or within the receiver bandwidth (BWCKT). The couplers 

and antennas provide adequate suppression of unwanted signals 

except in a few cases where additional filtering may be 

required. 

A preselector filter is required immediately ahead of 

the receiver in every repeater installation. When a multiplicity of communication networks share the same wireplant conductors, the base stations associated with each network 

must also include a preselector filter ahead of each base 

station receiver. From a safety and reliability standpoint, 

preselector filters are recommended for use in all haulage 

and hoist transceivers. Except in simple frequency plans 

that have only one assigned frequency. 
Field testing of vehicular transceivers on mine vehicles 

indicates that receivers are also desensitized by radio 

frequency interference (RFI) generated in the electrical 

system. RFI sources such as air compressors on trolley locomotives, DC motors on battery powered service vehicles, and 

generators on diesel powered vehicles produce electromagnetic 

spectrums in the receiver passband. Filtering at the source 

of RFI is mandatory. 

1. Preselector Filter Network Discrimination 

Sufficient isolation must be provided in the transmitter 

to receiver signal path to prevent receiver desensitization 

by high power transmitter signals. 

FIGURE 49. TRANSMITTER TO RECEIVER ISOLATION 

TUNED TO TUNED TO 

,i " dF2 WIREPLANT 

r 

PRESELECTOR 

FILTER 

f 

TRANSMITTER RECEIVER 

. 
The transmitter section of either a repeater or base station 

produces the transmit signal at the assigned frequency (Fl). 

The signal is coupled to the "wireplantt' and reaches the 

receiver input terminal through the RF line coupler and 

preselector filter. The transmitter signal discrimination 

loss requirements can be determined by considering the data 

presented in Table M. 

TABLE M 

SIGNAL PATH 

POWER LEVEL AND 

DISCRIMINATION LOSS 

Transmitter Signal 

Fundemental Harmonics 

Transmitter Output Power 

Coupling Loss 

Preselector Filter Loss 

Level of Signal At 

Receiver Input Termintal 
There are two conditions under which the receiver can be 

desensitized by unwanted signals. First, whenever the unwanted signal reaches the receiver at a level greater than 

-28 dBm, the receiver RF amplifier and mixer will commence 

the automatic reduction of gain (compression). To avoid the 

loss of RF gain, the preselector filter must suppress all 

unwanted signals below -28 dBm. Secondly, any unwanted signal 

falling near or within the receiver passband will also cause 

receiver desensitization (capture effect). The receiver passband and selectivity is determined by a high quality crystal 

filter following the mixer. It is this filter that discriminates against unwanted signals with frequencies just beyond 

its 12 kHz passband. 

As long as the unwanted signal frequencies (and harmonics) 

are assigned beyond 50 kHz from the receiver operating frequency, the preselector filter is required to produce a 

minimum discrimination loss of 52 dB. 

The transient response of the preselector and IF filters 

determines how well the receiver will perform when near 

electrical noise sources. Impulsive electromagnetic noise 

sources such as trolley "shoefT arcing aid the discontinuous 

trolley rectifier current waveform may cause the f i l t e r s t o 

ring. Ring degrades receiver performance. Ring degradation 

may be reduced in the design by appropriate filtering 

techniques. 
The principal technique is the selection of a filter transfer 

function with minimum ring behavior. Transfer function that 

exhibits more linear phase response through the passband 

region exhibit less ring. 

A class of transfer functions including the Bessel and 

Gaussian exhibit minimal ring; however, the stopband discrimination loss is always less than other classes of transfer 

functions of the same order (N). 

Transfer functions that exhibit good passband phase 

characteristics and still achieve acceptable stopband discrimination loss are derived from the Butterworth .and 

Legendre polynomials of mathematical physics. Chebyshev 

transfer functions are optimum in the sense that they produce 

the maximum stopband discrimination loss; however, the phase 

response is always less desirable than either the Butterworth 

or Legendre transfer functions. The Legendre transfer functions are optimum in the sense that they exhibit minimum 

ripple in the passband. They produce considerable more 

stopband discrimination loss than Butterworth (43)(44)(45). 

The Legendre transfer functions are useful in application 

which requires good discrimination loss as well as good phase 

linearity and transient response behavior. Legendre filters 

are recomnended for use in narrowband angle modulated communications systems. 
The discriminations loss of well known transfer functions 

are shown in Figure 50. 

NORMALIZED FREQUENCY 

FIGURE 50. COMPARISON OF THE DISCRIMINATION LOSS OF WELL 

KNOWN TRANSFER FUNCTIONS (5TH ORDER) 
2. Calculating The Discrimination Loss of Bandpass Filter 

Networks 

The operating frequency (fo) and circuit bandwidth 

(BWCKT) are always known in the initial stages of specifying 

the filter discrimination loss requirement. 

The circuit bandwidth defines the passband region 

the filter where the discrimination loss is always less than 

4, 1, ... 3, dB, etc. Other bandwidths are always specified 

in a filter design problem. For example, the 60 dB bandwidth 

(BW60) defines the bandwidth where the loss is always less 

than 60 dB. The lower and upper bandedge frequencies can 

be calculated using the following equations. 

The bandwidth is defined as 

when D represents the dissipation loss value, 

fH the upper bandedge frequency, and 

fL the lower bandedge frequency. 

The bandedge frequencies are given by 

L ' and 

2 2 
The discrimination loss provided by a filter network at the 

bandedge frequencies can be determined from the data presented in Appendix A. 

In the tables, discriminat ion (normalized attenuation) 

loss of the Legendre filter transfer function are given for 

different filter orders (N). The normalized frequency 

(aLp) used in the table can be simply calculated from 

The filter order (N) represents the number of reactive 

elements required in the low pass prototype network. By 

well known frequency transformations, prototype networks are 

transformed into bandpass as well as other frequency response characteristics such as low pass, high pass and band 

elimination. 

3. Discrimination Loss of Couplers and Antenna 

Filter Networks 

The discrimination loss encountered by the transmitting 

frequency signal in the receiving couplers (also antennas) 

will be determined from the tabular data. This is the value 

of coupling loss shown in Table L. 
The coupler (antenna) 3 dB design bandwidth (BW3) is 

12 kHz. The 100 kHz bandedge frequency for a coupler 

(antenna) operating at 400 kHz may be calculated from 

Equation (69) and (70) as 

kHz, and 

fL = 353.1 kHz. 

It should be noted that these frequencies are slightly 

skewed because of geometric symmetry in the loss characteristic. Referring to Appendix A (N--1 data) , at a normalized 

frequency given by 

0 100 kHz = 8.3, LP= 7 7 LTJv 

the discrimiilation (normalized attenuation) loss is found to 

be 18.3 dB for all frequencies outside of the 100 kHz bandwidth. This loss is identified as coupling loss in Table L. 

4. ~iscrimination and Dissipation Loss of The 

Yrese~ector lue LWOX'K 

The required preselector filter order (N) may be determined from the Appendix A data. A 3rd order filter can 

provide 62.8 dB of discrimination loss. Thus a 3rd order 

filter design is required. Preselector filters exhibit 

signal dissipation loss at the center frequency. This loss 

can be determined from Appendix B data. 
In the Appendix B data, the table element Q(QLp) is defined 

by 

where Qu is the unloaded Q of the inductors used in the 

filter (measured at fo). 

In the MF band, Qu's are typically greater than 250 in a 

well designed inductor. Thus with 

the band center dissipation loss is estimated to be less 

than 3 dB. 

5. Designing Filter Networks 

The design data for Legendre filters has been included 

in Appendix C. The element values are given for a normalized 

low pass prototype filter that has a cut-off frequency (R) 

of one radian per second and equal load and source termination 

resistances of one ohm. 

FIGURE 51. LOW PASS PROTOTYPE FILTER 
This particular normalization of filter element values make 

the design of actual filters as simple as pie (a). 

a. Designing Low Pass Filters 

The actual low pass filter element values are given 

and, 

where fc is the cut-off frequency, and C and L are the low 

pass prototype element values. 

Equations (74) and (75) tell us a great deal about a 

filter network. First of all, increasing the cut-off frequency always reduces the size of the actual element values. 

Secondly, the terminating ( source and load) resistances 

influence the size of the actual element values in different 

ways. Increasing the termination resistance increases the 

inductance values while decreasing the capacitance values 

in the actual network. The topology of the low pass network 

is invariant in the design of an actual low pass filter. 

The dissipation loss of the low pass filter network is 

determined with the use of the table in Appendix B - 

Dissipation Loss of the Legendre Transfer Function. 
The Q of each inductor used in the filter network is 

measured with a Q meter at the cut-off frequency of the 

filter. The Q may also be determined from data supplied by 

the inductor manufacturer. 

For example, a QU of 250 is easily realizable in a low 

pass filter with a cut-off frequency of 100 kHz. The zero 

frequency insertion loss in a third order low pass Legendre 

filter is 0.09 dB. 

b. Designing A High Pass Filter From a Low Pass 

Prototype Network 

The first step required is to redraw the low pass prototype filter such that the inductors become capacitors and 

capacitors become inductors with inverted values. The redrawn filter is a high pass prototype filter with a cut-off 

frequency of one radian per second. The actual low pass 

filter element values are calculated from the redrawn filter. 

Use Equations (72) and (73) to calculate the element values 

of this filter. 

c. Designing Bandpass Filters From Low Pass Prototype 

Filters 

Bandpass filters are designed from the low pass prototype filter element values by use of the following frequency 

transformations : 
The mechanics of the frequency transformat ion are simply 

carried out by dividing each inductance and capacitance in the 

low pass prototype filter by the bandwidth (in Hertz) of the 

band-pass filter (instead of the cut-off frequency as was the 

case in the low pass filter denormalization process) and 

resonating each of the filter elements at the center frequency 

of the filter. That is 

C, C and - 1 

2nBW R ' 2 

CKT (2nf0) 

- 

L= LR and C - 1 

nBW~~~ (2~f~)~~ 

where BWCKT is the bandpass filter bandwidth and fo is the 

center frequency. Equations (77) and (78) provide a great 

deal of insight into the design characteristics of a bandpass filter. 

The low pass prototype elements are changed by dividing 

by the circuit bandwidth of the actual filter. These filter 

elements increase in value as the filter bandwidth is decreased. Thus the series inductors and shunt capacitors in 

the bandpass network always increase in value when the 

circuit bandwidth (BWCKT) is reduced. Further, these elements 

are influenced by the filter termination resistance as defined 

in Equation (77) and (78). 
In many practical filter design problems, the "spread" in 

filter element values may be too great. Impedance levels 

within the filter can be changed by alternating operating 

impedance levels (R) within the network as indicated by 

Equations (77) and (78). 

The dissipation loss (insertion loss) at the band center 

(fo) of a bandpass filter is also easily and accurately 

determined with the use of Appendix B. Equation (75) is 

used to determine QLp. 

d. Designing Band-Elimination Filter Networks From Low 

Pass Prototv~e Filter Networks 

Band-elimination filters are designed from low pass 

prototype filters by first constructing a high pass prototype network and then finding the actual element values 

(< and 5) by using Equations (75) and (76). 

e. Determination of the Discrimination Loss of Actual 

Bandpass and Band-Elimination Filters From the 

Discrimination Loss of a Low Pass Prototype Filter 

The discrimination loss of the low pass Legendre prototype filters orders (n=1,2, ... 9) are shown in Appendix A. 

Figures 52 and 53 show the discrimination loss plotted 

for odd order filters. A noteworthy feature is the fact that 

the frequency scale (f) is normalized by the circuit bandwidth (BWCKT). Similarly, the low pass or high pass prototype filter elements are de-normalized by dividing by (BWCKT) . 

to find the actual filter element values. This necessarily 

follows from Equation (74). 
FIGURE 52. LEGENDRE BAND PASS FILTER DISCRIMINATION LOSS 

FOR ORDERS n= 3,5, and 7 
NORMALIZED FREQUENCY ,aLp 

0 I 2 3454 3 2 I. 0 

FIGURE 53. LEGENDRE BAND ELIMINATIOIJ FILTER DISCRIMINATION 

LOSS FOR ORDERS n=3,5,anC 7 
The figures also show the direct relationship between the low 

pass prototype normalized frequency (QLp) and circuit bandwidth (BWCKT). 

The discrimination loss characteristic can be plotted 

on multiple cycle semi log graph paper. The y axis is labled 

in discrimination loss (dB) and the x axis is labled in units 

of operating frequency. 
SYSTEM DESIGN SPECIFICATIONS 

SUMMARY 

The design doctrine for the whole mine radio communications system includes the system level specifications as 

well as the flowdown specifications for the equipment and 

module level printed circuit boards. To insure interface 

compatability throughout the system, standardized interconnecting loads and levels have been strictly adhered to 

in the design practice. 

The theoretical basis for the design specifications 

follows from discussions set forth in Chapter IV. , 

B. INTRODUCTION 

The equipment used in the MF radio cornrnunications system 

consists of: 

. Remote Control Console (RCC) and Remote Control 

Terminal (RCT) units to operate a multiplicity of 

fixed location and mobile transceivers in an underground mine. 

. A base station comprising a standard transceiver and 

RCT unit for creating a cell of radio coverage. 

. A vehicular transceiver comprising a standard transceiver and Remote Audio Head (RAH) unit for comrnunications on mobile platforms. 
. Vest transceiver for communications with roving 

miners. 

. Global repeater to increase the operating range between 

mobile transceivers along the "wireplanttl. 

. Cellular repeater to illuminate a working face. 

. Highly efficient RF line couplers and antennas to 

"illuminateu the "wireplant". 

A cell of radio coverage is created by installing an RCC 

unit ( s) in the network "nerve" center( s) . The base station 

is remotely controlled by a two-wire remote control (RC) 

cable. The RCC unit can remotely control fixed location 

base station and repeater transceivers for distances greater 

than five miles. Additional networks are created by installing 

separate network RCC units, RC cables, and base stations. 

C . GENERAL SYSTEM SPECIFICATIONS 

The general system specifications set forth the principal 

design objectives for the equipment. Equipment designed to 

these specifications will achieve excellent radio coverage in 

the mining complex. The equipment will also exhibit extremely 

high reliability when operating in the hostile mine environment. 

Strict adherence with the equipment interconnection (interface) 

specifications will insure a degree of compatability among 

radio equipment deployed in the Nation's underground mines. 
1. SIGNAL EMISSIONS: 

Emission 

Frequency Range 

Tuning 

Peak Deviation 

Frequency Separation 

National Rescue Team 

Frequency 

2. MODULATION: 

Processing (voice) 

Frequency Range 

3. SQUELCH: 

Type 

SIGNALLING TONE 

FREQUENCY 

OPERATING RANGE: 

6. ENVIRONMENTAL: 

Operating Temperature 

Range 

Shock (Drop) 

Narrow band FM 

10F3 

60 kHz to 1000 kHz 

5 kHz increments 

2.5 kHz 

50 kHz (mid for repeaters 

400 kHz 

Enhanced average voice signal processing 

Two (2) alternate types of squelch 

control : 

Noise Operated Squelch, and 

Tone Operated Squelch 

100 Hz + 20 Hz for subaudible tone 

1000 Hz-+ - 100 Hz for inband signalling 

200 to 400 meters (in coal quasi-free 

conductor area) 

20,000 feet 1.5 meters from wireplant 

conductors 

-20 to 60 degrees c. 

4 feet onto soft pine board 2 inches 

thick. 

Dust Dust Resistant 
Special Condition Withstand sulfide ore body ground 

water drip 

Vibration 0.045 inches P-P amplitude vibration 

10 to 55 Hz 

7. CONSTRUCTION: Sealed Stainless Steel enclosures 

Activated Desiccant per Mil-D-3464D 

Interior protected with vapor corrosive inhibitors 

Use of aluminum is prohibited 

Humiseal coated printed circuit boards 

STANDARIZED INTERCONNECTION LOADS AND LEVELS 

RF Signal 

Load Impedance 50 ohm load plane 

Remote Control Cable 

. Load Impedance 300 ohms win lead cable) 

Audio Interface 

Load Impedance 600 ohms 

Level for rated 

output 

Squelch Flag Sq Flag (1) 

Unsquelched Less than 0.7 V DC 

Squelched More thzn 7 V DC 

Trans Kev (1) Key Transmitter 

Command (PTT) 

Less than 0.7 V DC 

F1-+ F2 Trans (1 Tuning Command 

Less than 0.7 V DC 

RCC Unit DC Comd 

DC Command More than 7 V DC into 300 ohms 

Tone More than 4 V rm into 300 ohms 

(1) Underlined Command Symbol indicates that signal must go 

low (sink 100 MA of current). 
PERMISSIBILITY 

10. CABLING E CONNECTORS 

Remote Control 

(RC) Cable 

RF Signal 

(RS) Cable 

Remote Control Head 

(RCH) Cable 

12 V DC Power Cable 

11. Vehicular Transceiver 

Hazard Prevention 

Vehicular Transceiver 

Power Supply 

Vest per UL 913 and MSHA CFR, 

Title 30, Part 23 

2 Conductors 

3 Conductors (l)~ype Sg with 

Connector 

7 Conductors (1) Type SO with 

Connector 

2 Conductors (1) Type SO with 

Connector 

Every metal transceiver enclosure 

must be grounded to vehicle frame 

ground. 

Installation of a transceiver on 

vehicles with floating primary 

battery sources and DC motors 

requires mandatory use of isolated 

DC to DC converter to supply 

power to the transceiver. 

(1) One conductor to be attached to frame ground. 
BASE STATION AND VEHICULAR TRANSCEIVER SPECIFICATIONS 

The electrical specifications for the fixed location 

base station and mobile vehicular transceiver are identical. 

They both use the same standard transceiver enclosure. This 

greatly simplifies maintenance training and repair activities 

because the maintenance man only needs to become familar with 

one transceiver design. 

Remote Audio Head (RAH) permits a standard transceiver to 

be installed on all vehicles used in the mining process. The 

RAH is mounted on the vehicle in a physical location that is 

convenient for motormen usage. The RAH uses a Remote Control 

Head (RCH) cable to interface with the transceiver. 

A Remote Control Terminal(RCT) unit permits the standard 

transceiver to operate as a base station. The RCT unit is 

mounted on the rib next to the transceiver. The RCT unit 

also uses the RCH cable to interface with the transceiver. 

Thus, both the RAH and RCT are plug compatable with the 

transceiver. The remote control (RC) cable interfacing 

the "nerve" center RCC connects directly to the RCT unit. 

The electrical specifications for the transceiver are 

shown in Table N. The block diagrams of the equipment 

are described in the following sections. 
Standard Transceiver 

The transceiver specifications are given in Table N . 

The block diagram is illustrated in Figure 54 . The control 

board (All) is the mother board for the receiver (All, 

synthesizer (A2), exciter (A31 and RF power amplifier (A41 

printed circuit modules. This board determines the operational characteristics of the transceiver (1) . 

(1) A similar board (A11R) is used to construct a 

repeater transceiver. 
TABLE N 

USE : 

OUTPUT POWER : 

RF OUTPUT LOAD: 

STANDARD 

TRANSCEIVER SPECIFICATIONS 

POWER REQUIREMENTS : 

Operating Voltage Range 

Demand Current 

Receiving Standby 

Receiving Audio 

Transmit 

ELECTRICAL SPECIFICATIONS: 

Receiver 

Synthesizer 

Exciter 

Transmitter 

Audio Power Amplifier 

Universal transceiver for use as 

either a base station or vehicular 

transceiver. 

Watts (adjustable) 

Optimized to drive loop antenna, 

200 ohm transmission line or RF 

line coupler. 

11 to 15 VDC 

35 rnA (max) 

300 rnA (max) 

3.5 Amperes 

A1 Specifications 

A2 Specifications 

A3 Specifications 

A4 Specifications 

A5 Specifications 
CONNECTORS: 

PIN 

RF Signal 

RF Output 

Frame Ground 

F1-2 (Trans) 

12 V DC Power (1) (2) 

(base station application) 

Ground 

Remote Control Head 

SQ Flag 

Fl-F2 (trans) 

Audio Output (All 

Audio Input (A2 ) 

Trans Key 

12 V DC 

Frame Ground 

(1) Enclosure hardware grounded to Pin 2. 

(2) 12 V DC power supplied through Remote Control Head 

connector in base station application. 
FIGURE 54 BASE STATION AND VEHICULAR TRANSCEIVER BLOCK DIA

FI -4 F2 (TRANS.) > 

SQ. FLAG > 

AUDIO OUTPUT (Al ) > 

TRANS. KEY > 

AUDIO INPUT (A2) > 

12 VDC > 

FRAME GND. > 

CONTROL Al I 

r--- -1 

I I NOISE 

I OPERATED 1 1 

I SQUELCH I 

I----- J 

DC POWER 

CONNECTOR 

12VDC > 

FRAME GND. > 

RF CONNECTOR 

FI - F2 (TRANS.) > 

12 VDC > 

RF SIGNAL > 

FRAME GND. > 

1, 

RF IN 

SWITCHED @ 

DC rn 

AUDIO OUT 

(All 

f 

RF OUT 

I 

RF POWER AMPLIFIER A4 

REC

INPUT (A2) 

SET 

FREQ. b 

SYNTH

AUDIO 

SWITCHED 

DC Ir 

EXC
Recovered audio signals (audio out-Al) from the receiver (All are applied to the noise operated squelch network on the Control Board (All). Audio signals (audio inputA2) from the microphone are connected through printed circuit 

wiring on the All board to the input terminal of the signal 

processor network on the synthesizer board (A2). After 

processing, the audio signal modulates the digital synthesizer 

local oscillator (LO) output signal frequency. 

The power connector is used to source DC supply voltage 

to the transceiver. The microphone push to talk (PTT) switch 

generates a standard transmitter key command. The,Trans Key 

command turns on the transmitter by switching on the DC supply 

voltage to the RF power amplifier (A41 and turns off the receiver (All by switching off the receiver DC supply voltage. 

The standard transmit frequency select command F1-F2 

(Trans) causes the All board to generate a digital binary 

frequency code to tune the synthesizer to the frequency F2. 

In the absence of Fl-FZ (Trans) command, the synthesizer is 

always tuned to the frequency F1. 

The transmit frequency select command F1dF2 (Trans) 

also appears at the RF connector and is used to tune either 

the antenna or coupler to the frequency F2. 

The noise operated squelch network generates the standard 

squelch flag (SQ Flag) signal. 
The All board uses relay' switching to direct RF signals 

to the receiver in the receiving mode and to send RF power 

amplifier signals to the RF signal connector. 

The Remote Control Head (RCH), 12 V DC power and RF 

signal connectors are located on the enclosure. 

2. Remote Control Terminal (RCT) unit 

The specifications are shown in Table 0 . Figure 55 

illustrates the block diagram of Remote Control Terminal (RCT) 

unit. The RCT unit is used when the standard transceiver is 

operated as a base station. The RC cable is connected to 

the RCT unit line matching transformer terminals. . The 

transformers are designed to cancel unwanted common mode 

signals and pass legitimate differential mode signals. The 

legitimate signals are: 

Audio baseband (voice) signals, 

DC command signals, and 

Subaudible control signals. 
TABLE 0 

REMOTE CONTROL TERMINAL (RCT) 

SPECIFICATIONS 

USE : Used with standard transceivers 

and repeaters to provide remote 

control capabilities from the 

remote control console unit. 

STANDARD LOADS : 

300 ohm 

600 ohms 

RC Cable 

Transceiver Audio 

AC POWER SOURCE: 

DC OUTPUT: 

Operating Voltage 

Regulation 

Over Shoot Max voltage 16 V DC 

DEMAND CURRENT 

Receiving Standby 40 mA (mid 

4.0 amperes 

Lead Acid, 5 AH capacity 

Transmit 

Standby Battery 

CONNECTORS: 

RC Cable 

Remote Control Head 

Pin NO. 

SQ Flag 7 

F1 +F2 (Trans) 

Audio Output (All 

Audio Input (A2 ) 
Trans Key 

Frame Ground 

ENCLOSURE: 

SIGNALLING: 

Remote Control Socket 

SQ Flag 

0 dB Audio Output (All 

Trans Key 

F1-F2 (Trans) 

Audio Input (All 

0 dBM 

Sealed Enclosure 

DC Comd 

3 V AC (RMS) 

DC Comd (3 V DC rnin)( 

100 Hz signal 

1/2 V AC rms (min) 

1 V AC rms 
RC CABLE 

LINE MATCHING 

TRANSFORMER 

I 

AUDIO 

* 

SUBAUDIBLE 

TONE 

DECODER 

DECODER 

ENCODER 

REMOTE CONTROL 

SOCKET 

< TRANS. KEY 

SQ. FLAG 

FI - F2 (TRANS.) 

1 < AUDIO INPUT (A21 

SET 

0 dBM 

F FRAME GND. 0 

< AUDIO OUTPUT(A1) 

I STAND-BY I I AC TO DC 1-n 

- 

I BATTERY /I CONVERTER 

AMPLIFIER 

VAC 

FIGURE 55 BLOCK DIAGRAM REMOTE CONTROL TERMINAL (RCT) UNIT 
- 

AUDIO 

POWER 

AMPLIFIER 

A5 

FI --, F2 TRANS. > 

SQ. FLAG > 

TRANS. KEY > 

AUDIO OUTPUT ( Al ) > 

AUDIO INPUT (A2) > 

12 VDC> 

GND. > 

REMOTE CONTROL 

SOCKET 

AUDIO CONTROL 

MICROPHONE 

VOLUME 

CONTROL 

C INPUT 

12 VDC 

I MICROPHONE SOCKET 

t+ PTT SWITCH 

t- FI- F2 (TRANS.) 

SWITCH 

i MESSAGE 

LAMP 

FIGURE 56 REMOTE AUDIO HEAD (RAH) BLOCK DIAGRAM 
Any RC cable DC command signal is detected by the DC 

decoder. The decoder generates the Trans Key command, keying 

base station transmissions at the frequency (F1). Any 

transceiver squelch flag command (SQ Flag) causes the DC 

encoder to generate a DC command signal (DC Comd) and apply 

it to the RC cable. This allows the base station to key any 

other base stations (or repeaters) in the network as well as 

enabling the "nerve" centers RCC units to receive audio base 

band messages recovered in the base station receiver. Any 

subaudible tone on the RC cable is decoded generating the 

Fl-FZ (Trans) command. This permits the RCC unit to remotely switch the base station to the transmit frequency (F2). 

The base station can acquire any global repeater in this mode 

operation. Any RCC unit can be used to talk through a stand 

alone global repeater to an out of range mobile transceiver. 

The RCT unit includes the AC to DC converter and standby battery for the base station. 

3. Remote Audio Head (RAH) 

The specifications are shown in Table P . Figure 56 

illustrates the RAH block diagram. 

The Audio Power Amplifier (AS) is controlled by the 

SQ Flag command. The amplifier is turned on when the transceiver is unsquelched by a received radio signal. The message 

lamp also turns on, signalling the motorman of a message. 
Microphone audio input signals are transferred directly 

to the remote control socket. PTT switch signals become 

Trans Key commands. 

The Fl/F2 switch position F2 generates the Fl-FZ (Trans) 

command. 

The RAH is enclosed in a sealed box. It obtains its DC 

supply voltage from the transceiver. 
TABLE P 

USE : 

STANDARD LOADS: 

Transceiver Audio 

DC SUPPLY: 

Operating Voltage 

Demand Current 

Standby 

Full Audio 

CONTROLS : 

Audio Output Level 

Push to Talk 

Fl4F2 (Trans) 

CONNECTORS : 

Microphone 

Microphone 

Ground 

PTT Switch 

REMOTE CONTROL HEAD (RCH) 

SPECIFICATIONS 

Used with standard transceiver to 

allow convenient transceiver 

operation by motorman. 

600 ohms 

Volume Control 

On Microphone 

SPDT Switch 

Pins 

1 

2 

3 
REMOTE CONTROL SOCKET 

SQ Flag 

Fl-F2 (Trans) 

Audio Output (All 

Audio Input (A2 ) 

Trans Kev 

Frame Ground 

SIGNALLING: 

Remote Control Socket 

SQ Flag 

Trans Key 

SQ Flag 

Enclosure 

RAH Unit 

Enables audio . 

Depress PTT 

Message lamp on 

Sealed case 
E. REMOTE CONTROL CONSOLE 

The specifications are shown in Table Q . The block 

diagram of the Remote Control Console (RCC) unit is shown 

in Figure 57 . 

Depressing the PTT switches the standard DC command 

(DC Comd) onto the RC cable. Microphone voice messages are 

simultaneously applied to the cable. 

Depressing the F2 switch generates a 100 Hz subaudible 

tone. The tone is applied to the RF cable to command the 

base station to the transmit frequency (F2). This allows the 

base to acquire the global repeater for F1 transmissions to 

an out of range mobile transceiver. 

Depressing the PAGE switch generates sequential tones 

required to unsquelch pocket pagers (1) . 

(1) These are paging tones used to unsquelch "pocket" pager 

receivers designed by the Pittsburgh Research Center (PRC). 
TABLE Q 

USE : 

STANDARD LOAD : 

RC Cable 

AC POWER: 

Standby Battery 

CONNECTOR: 

Microphone 

RC Cable 

ENCLOSURE : 

SIGNALLING: 

Depressing F2 

Switch 

Depressing PAGE 

Switch 

Depress PTT Switch 

REMOTE CONTROL CONSOLE (RCC) 

SPECIFICATIONS 

Used in the mining complex "nerven 

centers to generate remote control 

signalling. 

3.0 0 ohms 

117 V AC 

12 V lantern battery 

Type 

Type 

Sealed enclosure 

Generates 100 Hz + 20 Hz - 

Generates 1000 Hz + 100 Hz tone - 

and DC Comd 

DC Comd 
RC CABLE 

FIGURE 57 REMOTE CONTROL CONSOLE ( RCC) 

LINE 

MATCHING 

TRANSFORMER 

1 

1 

f 

DC 

DECODER 

ENCODER 

MICROPHONE 

CONNECTOR > 

MIC > 

> 1 

AUDIO 

AMPLIFIER 

12 VDC > 

PTT SWITCH > 

TONE 

GENERATOR 

- 3 - 

F2 PAGE 

(100 HZ) 

CONTROL 

b 
VEST TRANSCEIVER SPECIFICATIONS 

The electrical specifications for the vest transceiver 

are shown in Table R . They are similar to the standard 

transceiver specifications with many notable exceptions. 

First, the RF output power is limited to 4 Watts. This 

prevents the transceiver magnetic moment (?I) from exceeding 

the safe limit of 2.5 ampere turn meter. The design includes 

tone signalling capabilities (100 and 1000 Hz). Secondly, 

and most importantly, the transceiver modules have been designed exclusively for use in hazardous atmosphere per 

Underwriters Laboratory Document UL 913 (and MSHA .requirements). 

The receiver, synthesizer, transmitter, antenna, and 

battery pack plug into a wiring harness that includes the 

speakers and control head. Maintenance requires troubleshooting to the module level. Module servicing is strictly 

prohibited other than by factory certified electrical technicians. 

The block diagram is shown in Figure 58. 
TABLE R 

USE : 

MSHA Approved Model 

RF OUTPUT LOAD: 

VEST 

TRANSCEIVER SPECIFICATIONS 

POWER REQUIREMENTS: 

Operating Voltage 

Demand Currents 

Receiving Standby 

Receiving Audio 

Transmit 

Enclosure 

Garment 

Wire Harness (1) 

Antenna Module : 

Type 

Magnetic Moment 

Transceiver for use by roving miners 

and rescue teams. 

ART-29 Transceiver 

Optimized to drive tuned loop 

antenna. 

ABS plastic 2kx5%x1 inches (WLD) 

with canyon type DS connec,tors . 

Nylon mesh with pockets fo:r modules. 

Vest wiring harness includ.ing control 

head epaulet speakers, tuned loop 

connector,, speaker jack and connected for transceiver modu:Les. 

Tuned loop with sealed tuning unit. 

Switch for F1 F2 (Trans) command. 

2.1 amper turn meter 

(1) Wire harness for approved vest will not accept power from 

standard battery pack. 
Control Head Functions : 

Volume Control 

Squelch Control 

Page Switch 

Signal Switch 

PTT Switch 

Receiver Module: 

Enclosure Symbol 

Frequency Range 

Sensitivity 

Selectivity 

3 dB BW 

70 dB BW 

Two Signal Selectivity 

Spurious Response 

Rejector 

Image 

IF 

Audio Output 

Squelch 

Threshold 

Tight 

Adjust speaker volume 

Set Threshold squelch 

Subaudible tone 

100 Hz tone 

Key transmitter 

Intrinsically safe A1 receiver 

ART-29 P/N 301C193 

60 to 1000 kHz 

1.0 microvolt 12 dB sinad 

10 kHz (minimum) 

22 kHz 

65 dB (minimum) 

Better than 90 dB 

Better than 60 dB 

0.4 Watt into 8 ohms 

3.0 microvolt 

10.0 microvolt 
Synthesizer Module: 

Enclosure Symbol 

Frequency Range 

Tuning Increment 

Peak Deviation 

Transmitter Module: 

Enclosure Symbol 

Output Power 

Power Flatness 

Permissible Battery Pack: 

Enclosure Symbol 

Vest Antenna Module 

Magnetic Moment 

Area 

Switching 

DC Characteristics 

Output Voltage 

Capacity 

Limiting 

Maximum Instantaneous 

Peak Current 

Foldback 

Intrinsically safe A2 synthesizer ART-^^- P/N 301~192 

60 to 1000 kHz 

5 kHz 

+ 2.5 kHz - 

Intrinsically safe A3 transmitter ART-29 P/N 301C194 

4 Watts (adjustable) 

Intrinsically safe APP-2 Nicad 

battery ART-29. Must be recharged in fresh air. 

2.1 ampere turn meter 2 

Fl/F2 switching 

Nikel-Cadium 

11.7 V DC 

500 mAH 

4.0 amperes (max) 

2.5 amperes 
Fail Safe: 

Fuses 

Connector 

Standard Battery Pack: 

Enclosure Symbol 

Type 

Output Voltage 

Capacity 

Fuse 

Redundant current limiting 

circuits. 

None 

Canyon DE-95 

APP-1 Nicad Battery ART-29 

Nicad battery 

11.7 V DC 

500 mAH 

2A 

The vest can only be used inby with a MSHA approved battery 

pack. 

The vest transceiver block diagram is illustrated in 

Figure 58 . 
ANTENNA I AND I-< FI/F2 SWITCH 

I MATCHING I A 

I I 

A3 

)I 

Al 

TRANSMITTER RECEIVER 

KEY 

AUDIO IN (A21 

SQUELCH /J 1 LivoLuME 

MIC 

RIGHT 

JACK 

Fl BATTERY 

ONE 

FIGURE 58 VEST TRANSCEIVER BLOCK DIAGRAM 
The tuned loop antenna module includes a F1/F2 switch. 

Depressing the switch generates the F1+F2 (Trans) command. 

This tunes the synthesizer to the frequency (F2) and keys 

the transmitter module (A3). 

Depressing either the PTT, or SIGNAL switch on the control 

head keys the transmitter to the frequency (Fl). The receiver 

is always tuned to the frequency (F1). Depressing the PAGE 

switch keys the transmitter to the frequency (F2). This is 

used in cellular repeater switching (See Figure 9). 

The receiver (All module incorporates a noise operated 

squelch network. The recovered audio out (All signal is used 

to drive dual epaulet speakers and the earphone jack. The 

receiver (All module plug into the interconnecting harness. 

The transmitter (A31 DC module incorporates the power 

and RF switching relay function. 

1. Permissible Battery Pack 

Figure 59 illustrates the block diagram of the battery 

pack. The battery current limiting circuitry meets the 

Intrinsically Safe Electrical Circuits and Application requirements for use in hazardous locations per Underwriters 

Laboratory Document UL 913. 
< CHARGE 

LOAD 

- 

FIGURE 59 BLOCK DIAGRAM OF PERMISSIBLE BATTERY PACK 

11.7V= - 

CURRENT 

LIMITER 

- - 

A r 

- 

- - 

I 

CURRENT 

LIMITER 4 L 

r 1 

CURRENT 

LIMITER i 

, 

I SENSING * 

CURRENT I 
The battery pack at 11.7 V DC is limited to supplying 

less than 5 amperes instantaneously or continuously at any 

accessable terminal. The pack consists of an 11.7 V DC, 

500 mah rechargeable nickel-cadmium battery with double 

redundant current limiting circuits. The pack is potted and 

sealed in an ABS plastic case. 

The circuit consists of three independent current limiting 

circuits in series but sharing one common sensing resistor. 

When pack is in overload condition, fold-back condition occurs 

essentially disconnecting the battery from the load. The 

circuit is reset by simply removing the short or load then 

reapplying load. 

2. ART-29 Vest Transceiver 

Figure 60(a) illustrates an individual wearing the vest 

transceiver. The vest includes transceiver modules and speaker 

assemblies. 

A wire harness interconnects the transceiver modules 

supported in pockets on the vest garment. On the top of the 

vest at the shoulder blade area, a pair of epaulet speakers 

are enclosed in pockets. The epaulet speakers are oriented 

to direct sound waves along the neck of the individual towards 

the miner's ears. The miner's hardhat acts as an acoustical 

collection chamber for sound waves. The vest is designed 

with Velcro fasteners technique to enable the wire harness 
and all modules to be easily removed for the purpose of 

cleaning the vest. Figure 60(b)shows the tuned loop on the 

back of the vest. 

(a) FRONT VIEW 

(b) REAR VIEW 

FIGURE 60. FRONT AND REAR VIEWS OF VEST TRANSCEIVER 
G. REPEATER TRANSCEIVER SPECIFICATIONS 

The electrical specifications of the global and cellular 

repeater are identical. The specifications are also similar 

to the standard transceiver specifications because they use 

the same radio circuit modules with the exception of the 

AllR control board. 

1. Repeater Block Diagram 

The repeater block diagram is shown in Figure 61. 

The all^ is the mother board for the Al, A2, A3 and A4 

modules. The AllR control board connects the RF power amplifier (Aq) output directly to the RF output connector. The RF 

in signal is connected directly to the receiver (All input 

circuits . 

The repeater incorporates two synthesizer (A21 PC boards 

to enable simplex/half duplex mode of operation. That is, F2 

RF in signals are received and demodulated by the receiver 

(All. Simultaneously, the recovered audio output (All signal 

is applied through the AllR board to the synthesizer (A2, F1). 

This signal (audio input (A2 ) ) frequency modulates the 

synthesizer low signal. The exciter (A3) and RF power amplifier (A41 increase the modulated signal power to 20 Watts. 

To conserve standby power, the AllR includes a noise 

operated squelch network. This network keys the exciter and 

RF transmitter on only when an RF' signal is applied to the 

receiver input terminals. 
100 HZ 

TONE 

DECODER 

REMOTE CONTROL 

CONNECTOR 

FI-F~ (TRANS) 4 

SQ. FLAG >-I 

TRANS KEY 

AUDIO INPUT (A21 

12 v 

GROUND 

DC POWER 

12 VDC 

GROUND 

RF SIGNAL 

CONNECTORS 

FI RF OUT =I 

A1 IR 

CONTROL 

SET 

FREQ. 

SET 

SWITCHED 

I RF POWER AMPLIFIER 

A l 

RECEIVER 

A2 

SYNTHESIZER 

A3 

EXCITERFIGURE 61 REPEATER BLOCK DIAGRAM 
The AllR board also includes a 100 Hz tone decoder. 

Unlike the All board, it is the tone decoder that generates 

the SQ Flag command signal. 

The RCT unit can be directly interconnected with 

repeater by a standard RCH cable. 

The repeater receives its DC power from the standard 

system AC to DC converter which also includes a standby 

battery. 
STANDARD MODULE SPECIFICATIONS 

The modules used in the radio system were provided as 

proprietary products by the Mine Safety Appliances Company 

(MSA). The MSA part numbers are shown in the specification. 

1. Receiver Specification 

PC Board Symbol 

MSA Part Number 

Frequency Range 

Sensitivity 

Spurious Response Rejection 

Image 

IF 

Audio Output 

Transceivers 

Squelch 

Threshold 

Audio Output Power 

Hum and Noise 

Squelched 

Unsquelched 

A1 

D468179 

60 to LOO0 kHz 

1.0 microvolt 12 dB Sinad 

Better than 90 dB 

Better than 60 dB 

No other responses 

0 dBm into 600 ohms for 

2.5 kHz peak deviation 

signal (F,= 1 kHz). 

1.0 microvolt 

0 dBm 

45 dB below rated audio 

output power 
2. Synthesizer Specifications 

PC Board Symbol 

MSA Part Number 

Frequency Range 

Tuning Increment 

Peak Deviation 

3. Exciter 

PC Board Symbol 

MSA Part Number 

Output Power 

Power Flatness 

4. RF Power Amplifier 

PC Board Symbol 

MSA Part Number 

Output Power 

Power Flatness 

Load VSWR 

Operating 

Momentary 

60 to 1000 kHz 

5 kHz 

+ 2.5 kHz for 0 dBm audio 

input (A21 signal 

200 mW (adjustable) 

+ 1/2 dB - 

60 to 1000 kHz 

20 Watts (adjustable) 

1 dB 

60 to 1000 kHz 

3;l 

Open or short ckt. 
Battery Pack Specifications 

Type 

Voltage 

Rating 

Usage 

Transceiver Standby 

Sealed Lead Acid 

5 Ampere-Hour 

8 Hours (R/T=10/90) 
RF LINE COUPLER AND ANTENNA SPECIFICATIONS 

The RF line coupler is used with the base station and 

repeater transceiver. The global repeater uses two RF line 

couplers to efficiently couple MF signals to the "wireplant". 

Figure 38 illustrates the equivalent circuit of the coupler. 

Figure 19 shows that the coupler may be easily clamped 

around electrical conductors in the "wireplant". 

Tuned loop antennas are used with vehicular transceivers 

and cellular repeaters. 
TABLE S 

RF LINE COUPLER 

SPECIFICATIONS 

Dielectric Withstanding 

Type Clamp around 

Part Number 

4" inside diameter 

1" inside diameter 

Transfer Impedance (Zt) 

ACU-10-1 

350 kHz 

520 kHz 

820 kHz 

ACU-10-4 

520 kHz 4.0 ohms 

10.0 ohms 

11.2 ohms 

17.8 ohms 

toroidal design 

Voltage (cable to coupier 50,000 V (minimin) 

frame and inductor winding) 
TYPE : 

ENCLOSURE: 

MAGNETIC MOMENT: 

PHYSICAL SIZE: 

TABLE T 

ANTENNA SPECIFICATIONS 

Twin-Loop Design 

Lexan 

Non-Reflecting Black 

5.0 ~~rn~ (rnin) 

14 inches high 

28 inches long 
VI. FIELD DEMONSTRATION 

The results of the field demonstrations in the four 

mines will be described in the following sections. 

A. MAGMA COPPER COMPANY, SAN MANUEL DIVISION 

The underground mine is located near San Manuel, Arizona. 

Block caving mining method is used on three operating levels. 

Figure 62 is an illustration of grizzly and production level 

drifts. 

FIGURE 62. GRIZZLY AND PRODUCTION LEVEL DRIFTS 
FIGURE 62 GRIZZLY AND PRODUCTION LEVEL DRIFTS 
The upper grizzly level is used for gathering muck and loading 

the Y-transfer raises. The transfer raises are temporary muck 

storage bins and loading chutes for the trains. Trains on the 

lower production level transport muck to dump and hoist area of 

the mine. Hoists are used to lift the muck from the dump surge 

bins to the surface of the mine. Train loading process is 

illustrated in Figure 63. 

FIGURE 63. ILLUSTRATION OF LOADER AND MOTORMAN LOADING TRAIN 
Haulage panel 

- 
In actual practice, the loaderman in the pony set blinks 

incandescent lamps to signal the motorman to move the train 

during the loading process. 

Vest radios were evaluated for use in the loading process. 

The use of radio reduced the time required to load the train. 

It should be noted that vest radios are expected to be of 

great value in unloading clogged transfer raises. 

1. Maama ' s Cornmunicat ion Svstem 

The underground mine uses trolley radios and an audio 

system to communicate in the mine. The physical aocations of 

these communications resources are illustrated in Figure 64. 

COLLAR 

AUDIO I 

LINES\, 1 GRIZZLY DR 1 FT 

I 

1 RAISE 

I / 

I 

AMP - - - -- -- 1 

' "//I / /+,b,i,;/ / / /7 \ p,, ,,,ON AUDIO 

ROOM WIRE PANEL 

FIGURE 64. MAGMA COMMUNICATIONS RESOURCES 
The audio system is similar to a pager tekphone system. Remote audio heads (speaker symbol) are located at strategic 

locations in the drifts. Each head includes a microphone, 

speaker, and push-to-talk switch. A four (4) conductor cable 

connects each head to a central audio amplifier (audio room) 

and the surface control center. The surface control center is 

the nerve center in the Magma communication system. Roving 

supervisors on the 2315 grizzly and 2375 production levels use 

the audio system to coordinate muck haulage with the dispatcher. 

The mucking supervisor on the grizzly level identified which 

transfer raises are being filled. The trolley communication 

system (dashed lines) is used by the dispatchers to direct the 

locomotive motormen to a production panel with llfullu transfer 

raises. The dispatcher controls rail traffic to and from the 

train car dump and hoist areas. Fifteen (15) 300 VDC trains 

are used in the rail haulage system. Battery powered service 

locomotives are also used on the rail system to transport men 

and materials in the mining process. Although these locomotives 

have carrier current transceivers, the transceivers can only 

be used when the locomotive is stopped. The trolley communication system uses a dedicated wire to distribute trolley 

signals in the main haulage drifts. "J Boxesu are used to 

couple the 145 kHz signal to the trolley wire. The base station 

drives the dedicated wire and is remotely controlled from the 

control center. Each shaft cage has a hoist communication 

system that enables the surface hoist operator to communicate 

with the cage man. 
2. The MF Communication System 

MF radio equipment is used to create a party line production/maintenance network. The equipment is also used to 

improve shaft cornmunicat ions. 

In the mine, MF signals propagate (tunnel mode) on the 

existing mine wiring; specifically , the audio and dedicated 

carrier wires. Figures 65 and 66 are mine maps of the 2315 

and 2375 levels respectively. The maps indicate the locations 

of these conductors in the grizzly and production level drifts. 

MF signals are coupled to the audio conductors by an RF 

line coupler in the audio room. The audio room MF base station 

is remotely controlled from the surface control center. The 

audio conductors and base station provide radio coverage on 

both the grizzly and production levels. 

A MF base station and RF line coupler are also used to 

couple MF signals to the dedicated wire. 

Field demonstration of the equipment showed that the 

mucking and production supervisors were able to immediately 

communicate first hand information about the haulage status. 

Maintenance supervisors were immediately advised of haulage 

equipment problems. The radio system decreased the time required to reach keymen from an average of 35 minutes to 

seconds. 


MF equipment on battery powered service vehicles enabled the 

dispatcher to communicate with moving equipment on the rail 

system. 

An MF hoist cornmunications system was also evaluated in 

the field test. 

The present hoist communications system exhibits serious 

maintenance problems. The "bat'! antennas used to illuminate 

the wire rope at the head frame sheave wheel is difficult and 

costly to maintain. An MF loop antenna was used to illuminate 

the wire rope at the collar. A RF line coupler was used to 

efficiently couple signals to the cage transceiver.. 

3. Test ~esul'ts 

A number of tests were performed at Magma to measure the 

signal to noise ratio of the transmitted radio signals at 

the base station location. All tests were performed at 

400 kHz. 

a. Test 1 - Vest Communications To Audio Room Base Station 

From Grizzly and Production Levels 

A base station was installed in the 2375 audio room. A 

1" RF line coupler clamped around the East or West audio "wireplanttr bundles emerging from the audio amplifier bank. A 

Singer MN-25T signal strength meter was connected to a 4" RF 

line coupler clamped around the same wire bundle for measurement purposes. Signal levels were measured from a roving 

miner wearing an ART-29 vest transceiver. A trolley rectifier 

is also located in the audio room. This resulted in noise 
level variations and poor signal to noise tests at times. 

The audio quality tests are purely subjective and pegged 

to a listening scale of 0 to 10 as follows: 

0 = no squelch break 

1 = squelch barely broken - not audible 

3 = speech approx. 80% audible with heavy noise 

5 = speech audible with medium noise 

8 = speech clear and audible with low noise 

10 = speech clear no noise 

The tested locations are keyed to the mine maps for the 2375 

and 2315 levels. 
TABLE U 

VEST TMMSCEIVEEI COFliiUNICATIONS 

TO AUDIO ROOM BASE STATION 

(VIA 2315 and 2375 LEVEL AUDIO CABLES) 

TEST VEST 

NO. LOCATION 

NOISE 

LEVEL 

dB 

SIGNAL S/N 

LEVEL dB 

dB 

AUDIO 

QUALITY NOTES 

1 2375 20 

Crossover 

Couplers on 

West audio 

cables routed 

on 2375 E past 

rectifier 

20 North 36 

Raise 36 

Raise 50" 3 6 

Top Manway 2 1 

2 315 Couplers on 

East audio 

line - 2315 

away from 

rectifier 

NFD T.O. 

Panel 20 2 1 

Panel 18 2 1 

Panel 16 7.0. 20 

Panel 14 

North 

Panel 12 

N Lunchroom 

Panel 18 N 

Panel 4 N 

Panel 4 N 

150 " 

Panel 2 pr 

T.0. 

2 Pare1 6 

Line 
NOISE 

TEST VEST LET'EL 

NO. 

___I 

LOCATION dB 

SIGNAL 

LEVEL S/N 

dB dB 

AUDIO 

QUALITY NOTES 

19 P41 South A 

2315 Manway 35 

Couplers on 

\Jest audio 

line on 2375 

2 0 P41 South A 

2375 3 5 

2 1 P41 S to 

Main Line 36 

P17 S to 

Main Line 35 

P17 B South 33 

P17 North B 33 

16 Footwall 33 

15 N Turnout 35 

PI0 Stub 

Turnout 

Couplers on 

West audio 

line 2375 

P10 Stub 

Lunchroom 35 

10 Crossover 

Main Line 34 

NH2 Nain 

Line 

P12 350' 

Service 

Drift 

Ore Pass 

Turnout 

Ore Pass 
Summary: 

Generally, communications near audio lines in the grizzly 

were good while some signals became weak away from the lines. 

Communication was acceptable to good at 30 of the 33 locations 

tested. This test clearly demonstrates the potential performance and usefulness of the vest radio. 

Magma personnel were very pleased with this radio coverage. 

b. Test 2 - Vehicular and Vest Comunications To Audio 

Room Base Station Via Audio Conductors On Production Level 

The base station (with coupler) and the signal strength 

meter (with 4" coupler) were installed in the audio room as 

in Test 1 using the West cable bundle for the 2375 level. 

A vehicular radio and antenna were mounted on a battery locomotive for signal strength tests around the entire 2375 loop. 

A second person wearing a vest also rode the locomotive during 

the test. Due to the heavy production,-traffic tests had to 

be made quickly while on the move and could not be repeated. 
TABLE V 

VEHICULAR AND VEST COMMUNICATIONS TO 

AUDIO ROOM BASE STATION (VIA MAIN HAULAGEWAY 

AUDIO CONDUCTORS) 

- VEHICULAR VEST 

NO1 SE SIGNAL S/N AUDIO SIG VEST A

LOCATION LEVEL LEVEL dB QUALITY LEVEL S/N 

dB dB 

TEST 

NO. 

17 B South 41 

17 B North 40 

20 Crossover 40 

.30 Crossover 

NH1 40 62 2 2 10 4 7 7 

5 Shaft 

Turnout 11 0 61 2 1 10 50 10 

3C Shaft 4 0 - - 

3D Departure 39 

17 South 

Main Cross 3 9 50 11 8 4 

4 3 

2A South 

2A Mid Panel 39 

3A North 39 50 11 6 39 0 
TABLE V CON' D 

TEST 

NO. LOCATION 

12 3N Ladder 

Drift 

13 5N Turnout 

14 7N Turnout 

15 10X Service 

Stn 

16 10X Off 

Motor 

NOISE 

LEVEL 

dB 

SIGNAL 

LEVEL ,S/N AUDIO SIG VEST AU

dB dB QUALITY LEVEL S/N QU

1 1 l 

o o o 48 9 

17 Service Drift 

Turnout 39 54 15 8 5 4 15 

Summary: 

Vehicular communications to the audio room were good except from areas not ha

lines. Good results were obtained from the middle of loading panel 2A which 

lines. Vest communications were poor whenever the operafor transmitted from 

locomotive. However, the vest could receive all signals. 
c. Test 3 - Vehicular Communication To Base Station 

Relocated To 3 Shaft (Via Dedicated Wire on 2375 Level) 

The base station and signal strength test set were moved 

to 5 shaft and coupled to the dedicated carrier line using a 

1" coupler for the base and a 4" coupler for the signal 

strength test set. The locomotive had the same vehicular 

transceiver with antenna. No rectifier was near the 5 shaft 

area. Measurements were made as in Test 2 from around the 

2375 loop. Again, a vest was used on the locomotive. 
1 TEST 

1 NO. 

TABLE W 

VEST AND VEHICULAR COMPIUNICATIONS TO 5 SHAFT BASE STATION 

1680 VEHICULAR VEST 

NOISE 

LEVEL SIG S/ PJ Audio SIG S/N AUD

LOCATION dB LEVEL dB Q LEVEL dB Q 

3C departure 30 80 50 10 7 5 4 5 10 

3D departure 30 7 6 4 6 10 65 3 5 7 

Between 3D dep 

& 17 South 30 7 3 4 3 8 6 1 31 5 

17 S Crossover 30 70 4 0 8 6 0 30 3 

41B North 30 35 5 2 - - 0 

8A South 2 8 3 7 9 3 - - 0 

Footwall P11 2 8 50 2 2 7 - - 0 

5 North 2 8 52 2 4 8 3 5 '7 3 

2 North 

20 North 2 8 5 8 30 7 5 2 24 5 

30 Crossover 2 8 52 24 8 4 3 15 4 

5 Shaft 

Turnout 
Summary: 

As in Test 2, signal levels and communications were good 

except in areas lacking a carrier line. The vehicular radio 

audio quality was acceptable in 12 of 13 test points. The 

vest radio audio quality was acceptable anywhere in the area 

of the carrier line and did perform better from the locomotive 

than during the audio line tests. 

d. Test 4 - Hoist Communications Test Base Station In Hoist 

Control Center - 

A vehicular antenna was mounted in the hoist control room 

at shaft 3C with the antenna about 3 feet from the wire rope 

and about 8 feet from the wire rope drum. 

MF TRANSCEIVER I 

VEHICULAR ANTENNA 

PLER 

FIGURE 67. ILLUSTRATION OF HOIST COMMUNICATIONS SYSTEM 
This antenna was coupled to the signal strength test set. 

A base station for comrnunications was located in the same area 

with a vehicular antenna mounted just ahead of the large 

antenna 3 feet from the rope. Another transceiver (battery 

powered) was mounted in the cage using a 4" coupler on the 

rope just above the bonnet. 

Test results are as follows: 

TABLE X 

HOIST CO!I,"IUNICATIONS SIGNAL LEVEL 

CAGE TO BASE AT THE DRUM 

NOISE 

LEVEL 

dB 

AUDIO 

SIG S/N QUALITY COXMENTS 

LEVEL dB 

TEST 

NO. 

CASE 

L13CATION 

Collar 

400 ' below collar 

1000' going down 

full speed 

1500' going down 

full speed 

2075' stopped 

2675' going down 

2750' pocket 

going 

Summary : 

Good to excellent signals were obtained with no dead spots. 

A slight noise level was noted when the hoist was running. 
Test 5 - Hoist Communication Test Base Station At 

The Collar 

A vehicular antenna was mounted on the headframe at the 

collar about 3 feet from the cage rope. This antenna was 

used with the Singer FSM to measure noise ratio. A vehicular 

antenna was mounted on the headframe opposite the large antenna. A vehicular transceiver was connected to the antenna. 

The cage radio and coupler remained as in Test 4. 
TEST 

NO 

CAGE 

LOCATION 

Collar 

TABLE Y 

HOIST COMMUNICATION SIGNAL LEVELS 

CAGE TO BASE AT THE COLLAR 

NOISE 

LEVEL SIGNAL 

dB LEVEL 

-2 7 +85 

400' moving down -27 +82 

1000 ' moving 

down -2 7 

2675 moving down -27 

AUDIO 

QUALITY NOTES 

10 Clear & LOLLJ. 

Summary : 

The signal strengths on this test were outstanding at all 

levels, with the cage moving or stopped. 

Comparing the signal levels of the antenna at the hoist 

house and at the coilar, the losses over the "sheaT~e"wheel 

appear to generally range from 50 to 60 dB. 

Using MF equipment in hoist communication decrease maintenance cost. Servicemen need not climb the head frame to 

service the ''sheaveV wheel antenna. 
Conclusion 

The tests at Magma clearly show that the equipment performs very well in a large multiple level mine. The Magma 

people were pleased with the performance and coverage. 
PLATEAU MINING COMPANY 

The Plateau coal mine is located near Price, Utah. 

Annual production exceeds 1 MTPY. The mine presently operates 

a Gai-Tronics pager system as its primary communications network. Telephone cable (single pair) interconnects each pager 

telephone. Pagers are located at key points in the office, 

warehouse, shop, along beltways, and in the face areas. 

A simplified drawing of Plateau Mine is shown in Figure 

68. The Mud-water mining is in retreat status while the South 

faces are in an advancing status. 

The existing "wireplant" includes the telephone pair 

cable and AC power cable. Telephone cable runs in the beltway. 

The beltway is more than one entry away from the Mud-water 

manway and the West/Main entries. 

Separate 7,100 and 13,200 volt three phase AC power cables 

supply power to the Mud-water and South faces, respectively. 

Transformers along the cable supply power to the conveyor belt 

drives in the belt entries. 

Switches are also installed in the AC cable. The AC 

power cable is installed in some, but not all of the manway 

entries. 

The 7,100 and 13,200 volt cables are in the same entry 

at the intersection of the Mud-water and Xest entries. 
FACE 

SOUTH 

FACES 

REACTIVATED 

DRIFT -. - 

WEST ENTRY 

1.5 MILES 

- I 

I 

REMOTELY CONTROLLED I AB

FROM WAREHOUSE AND I 

OFFICE. I 

A REMOTE CONTROL CONSOLE (RCC) 

fl REPEATER 

-- - SINGLE - PA1 R (RC CABLE 

FIGURE 68 SIMPLIFIED DRAWING OF PLATEAU MINE 
FIGURE 69. PHOTOGRAPH OF VEHICULAR TRANSCEIVER INSTALLATION 
FIGURE 70. PHOTOGRAPH OF VEHICULAR ANTENNA INSTALLATION 

The photographs show that the available mounting surface is 

limited. In the installation process, precautions were taken 

to protect all cabling. For example, the antenna cable is 

protected by welding an angle iron to the fender. The angle 

iron protects the antenna cable from damage. 
In the initial system tests, vehicular transceivers could not 

talk back when in the Mud-water and South face areas. Listening 

was also a problem in the South area manways. 

The poor communications was due to excessive transmission 

loss associated with the AC power transformers installed along 

the AC power cable. Transformers were found to introduce from 

8 to 10 dB of signal loss in the SC power cable signal path. 

In an attempt to improve communications quality, repeaters 

were installed in the Mud-water and South face areas. 

2. Installation of Repeaters 

The primary frequency (F1) remained at 400 kHzqand secondary frequency (F2) was added at 520 kHz. This required that 

all antennas be capable of two frequency operation. The use 

of two frequencies allows access to global repeaters when 

transmitting on the frequency (F2). The global repeater boosts 

the received signal and retransmits it on F1. 

The first Fl/F2 repeater was installed in Mud-water entry, 

approximately 3600 feet from the base station. An additional 

5000 feet down the entry is the face. 

The second repeater was installed near the entrance to 

the South area, approximately 7330 feet from the base station. 

From this location to the furthest South face is approximately 

6500 feet. 
3. Test Results 

Signal and noise measurements were taken at the base 

station location on the AC power cables serving the Mud-water 

and main South mining areas. Due to the constant output and 

fixed location of the repeaters, only one measurement was 

needed. These are given in Table 2. 

TABLE Z 

SIGNAL TO NOISE RATIO MEASUREMENTS 

AT BASE STATION FROM REPEATER LOCATIONS 

Mud-Water 

Noise - 12 dB 

Signal - 92 dB 

S/N Ratio - 80 dB 

South 

Noise - 2 dB 

Signal - 78 dB 

S/N Ratio - 80 dB 
Quality And Performance 

System performance was found to be optimal when the 

vehicular antenna was positioned within 6 to 8 feet of the 

power cable and the vehicle was not running. 

Under the above conditions, excellent comunication 

quality was obtained throughout the Mud-water entry between 

vehicular transceiver and base station. The observation point 

was the remote control console (RCC) located in the warehouse. 

Similar results were obtained in a reactivated drift which is 

an entry off the Mud-water entry. Farthest attempted communication path distance in the Mud-water repeater network 

reached approximately 14,000 feet. 

Due to limitations of time and an unexpected power failure 

while testing the South area, extensive results were not 

obtained. 

5. Lessons Learned 

AC power cable does provide radio coverage in the mine. 

However, because of AC line switches, signal distribution 

can be interrupted when needed the most. 

It is recommended that a feasibility study be made to find 

ways to reduce loss acorss transformers and open switches. 
Twin-lead cable should have been installed in the manways 

of this mine instead of using the AC power cables for MF 

signal distribution. There are many advantages seen in the 

use of twin-lead cable. First, radio coverage can be provided 

all along the manways. Secondly, repeaters would not have 

been required lowering both equipment acquisition and maintenance cost. Finally, the complexity of the Fl/F2 signalling 

could have been avoided. 

6. Demonstration Results 

As soon as the MF system was installed in the mine, a 

continuous mining machine was buried by a rock fall.at the 

Mud-water face. Radio was used to instantly alert the underground superintendent of the problem. The superintendent 

praised the use of radio for the instant alert and saving 

many hours in the recovery effort. 

Beltmen were given vest transceivers to use along the 

conveyor belt line. They report that the vest was very 

comfortable to wear. The vest saved a great deal of time 

because beltmen are no longer required to walk to the nearest 

pager telephone. 
YORK CANYON COAL MINE 

The Kaiser Steel Corporation York Canyon Coal Mines are 

located in Colfax County near Raton, New Mexico. Both underground and surface mining are in progress. 

The immediate area surrounding the mine is composed of 

flood plains, valley slopes and broad-ridge crests. Coal is 

produced from the York Canyon seam in a local zone of the Raton 

formation. The formation includes beds of sandstone, siltstone, 

mudstone and coal. Annual production from the underground mines 

exceeds 1MTPY. Kaiser uses continuous mining equipment to mine 

ahead of two (2) longwalls. A simplified sketch of.the York 

Canyon mining complex is shown in Figure 71. 

rn HOUSE 

TO MIDDLE I I

YORK MINE 9 LER I 

I( DEVELOPMENT) J 

J 

I 

gw" ' 

1 

f 1 5700' 

I 

z a 

2" 

I 

I 

-MANWAY 

BELT 

*HAULAGE 

RETURN 

10.0 0 0'------4- AIR 

-- -TELEPHONE 

SUPPLlES 

L 

AC PWR CABLE 

-@ BASESTATION WITH 

RF LINE COUPLER 

FIGURE 71. SIMPLIFIED PLAN VIEW DRAWING OF THE YORK 

CANYON MINE. 
The four (4) entry underground mining complex was developed on a South heading for a distance exceeding 10,000 

feet. The coal seam height varies along the entry; however, 

the average height is seven (7) feet. The entry passageways 

are separated by fifty (50) feet. The fresh air manway is 

used to transport men, supplies and equipment required in the 

mining process. A cross section of the manway is shown in 

Figure 72. 

/ ?ET!;:ONE 

CABLE 

FIGURE 72. CROSS SECTION OF MANWAY (LOOKING INBY) 

A shielded 25 pair telephone cable is installed on the upper 

right hand corner. The belt haulageway is in an adjacent 

entry. The passageway contains a Continental conveyor belt 
haulage system, AC power cable and other electrical conductors 

used in the belt fire detection system. The return air 

passageways were originally used as part of the mine ventilation system. Bore holes to the surface are now used to 

transfer the return air to the surface. 

Longwall panels are developed to the left of the entry. 

The panels are approximately 550 feet wide and 6000 feet long. 

The surface substation converts the 69 kV transmission 

line power to 7.2 kV power for distribution in the mine. 

A Gai-tronics telephone system serves the office/shop 

building (location of PBX), the underground mine, and the 

surface mining shop. The general routing of telephone cable 

is illustrated by the dash-dot line symbols in Figure 73. 

Battery powered scooter, diesel powered "Tera Jet" jeeps, 

and Elkhorn man carriers are used for vehicular transportation 

in the mine. 

1. Installation of MF Equipment 

Medium frequency (MF) vehicular transceivers and antennas 

were permanently installed on battery powered scooters and 

diesel powered jeeps. 

The installation of the RF line coupler is shown in 

Figure 73. 
FIGURE INSTALLATION LINE COUPLER 

The RF line coupler is clamped around the 25 pair telephone 

cable at the portal. The belt fire detection cable also 

threads the center of the coupler. The fire detection cable 

has been installed in the manway for a distance of approximately 3000 feet. Through a crosscut the cable enters the 

beltway and then is routed along the conveyor belt. 

The telephone cable terminates in several junction boxes 

along the manway. From these boxes, telephone pairs enter 

crosscuts and continue to pager telephones at critical 

locations. The cable is finally terminated in a junction box, 

6100 feet from the base station. A single pair continues along the manway for an additional 3000 feet. The cable then 

enters the Nine Left longwall manway. 

The vehicular transceiver mounting on the "Tera Jet" jeep 

is shown in Figure 74. 

FIGURZ 74. PHOTOGRAPH OF THE TERA JET JEEP ANTENNA 

INSTALLATION 
The vehicular transceiver remote control head (RCH) is 

mounted near the steering wheel. The antenna is mounted in a 

vertical plane to the right of the diesel engine compartment. 

2. Measurement Results 

Communications signal levels were measured at the base 

station with the test set-up shown in Figure 26. 

The quality of the communications signals were excellent 

along the manways with the telephone cable. 

The measured induced line current at 520 kHz was previously shown in Figure 27. Figure 75 shows the measured line 

current at 350 kHz. The average attenuation rate is approximately 1 dB/1000 feet as compared to 2.4 dB/1000 feet at 

520 kHz. 

The dashed line represents the induced line current required so that at least 70 percent of the spoken words are 

intelligible. The difference (in dB) between the induced line 

current signal (upper solid line) and the dashed (C/N = 20 dB) 

line at any distance represents the margin in the communications system. The margin exceeds 35 dB at one mile from the 

base station. The intersection of the signal and dashed lines 

(not shown) predicts that the maximum communication range will 

exceed 34,000 feet at 350 kHz. his compares favorably to 

the 18,000 feet expectation at 520 kHz. 
I 2 3 4 5 6 7 8 9 10 11 

MANWAY DISTANCE FROM BASE (THOUSAND FT.
Equation (14) shows that the efficiency of coupling signals 

from loop antennas to cable increases with frequency. If 

the transmitting loop antennas are generating equal magnetic 

moments, the 520 kHz induced current curve must be above the 

35 kHz curve at short range. The 350 kHz curve must eventually 

cross the 520 kHz curve owing to the higher attenuation rate 

of the 520 kHz signals along the telephone cable. Comparison 

of the 350 kHz and 520 kHz induced line current data indicates 

that the crossing occurs at approximately 3000 feet. 

Tests were made to determine the differences in induced 

line current caused by the orientation of the vehicular antenna 

in the manway. The measured data in Figures 27 and 75 applies 

when the vehicular antenna is in a vertical plane (HMD) and 

that the plane is parallel to the telephone cable. When the 

antenna is in a horizontal plane (VMD), the induced current 

level is reduced by 2 dB. Mounting the vehicular antenna in 

a horizontal (as will be required in low coal) will not significantly degrade system performance. 

Some interesting coupling effects were noted when the 

antenna was in a plane orthogonal to the cable. In coal, when 

the antenna (HMD) was located more than 40 feet from the cable 

maximum induced current was measured at the base. When the 

antenna (HMD) was rotated to plane pa~allel to the cable, 

induced current was minimum. This is just the opposite effect 

observed in the manways with cable. 
It is interesting to note that vest signal level arriving 

at the base station location was approximately 8 dB less than 

vehicular signal levels. This corresponds closely with the 

differences in vest and vehicular antenna magnetic moments, 

2.0 and 5.2 ATM*, respectively. 

The vest transceiver radio coverage areas in the mine are 

shown in the following sketches of crosscut intersections 

along the manway. 

FIGURE 76. RADIO COVERAGE AREA AT CROSS CUT 31 ALONG MANWAY 

The talkback (transmitting) range (dot symbol) included 

the manway and the beltway. It also extended along a feeder 

beltway. The listening (receiving) range (shaded area) 

extended into the drift adjacent to the manway. Note that 

range measurements were limited by sealed stoppings in the 

crosscuts. 

FIGURE 77. RADIO COVERAGE AT CROSSCUT 91 ALONG MANWAY 

(9100 FEET FROM BASE STATION) 

The NineLeft longwall entry is at crosscut 91. The 

longwall face is 5600 feet from the crosscut 91. A single 

pair telephone cable extends to the face in the entry. The 

talk back range is limited to the longwall entry. The total 

talk back range from the longwall face to the base is 14,700 

feet. The listening range extends to drifts adjacent to 

the manway. 

The surface telephone cable extends to the shop. The 

talk back range is limited to within 53 feet of the cable. 

The listening range limit is approximately 200 feet from the 

cable. The range includes the shop and office areas. 

3. Mine Rescue Communications 

The ability of rescue team members to communicate with 

MF ~adio was evaluated at the York Canyon Mine. 

The single pair cable that is used by the mine rescue team 

for sound power audio communications was pulled from a take 

up reel and laid on the surface of the earth as shown in the 

following Figure 78. 

&RECEIVE ONLY /TALK BACK 

END OF 

---- J KC,,, GOOD RADIO COVERAGE #CABLE I I- # 1 1 L I I 1 

W 

\, I 1 I r I 

W 100 2w 300 400 500 600 700 8C0 900 1000 

LL I I ------ -- FEET- - - - - - - 7- - 

f = 520 KHZ 

FIGURE 78. PLAN VIEW OF THE TRANSMISSION LINE AIDED RADIO 

COVERAGE ( PAIR OF 1:JSULATED # 16 CONDUCTORS ) 
Range from the cable was maximum when the plane of the vest 

antenna was parallel to the cable. The base station induced 

signal was 100 dB greater than the line noise measured on the 

cable a few feet from the RF line coupler. The test clearly 

indicates that rescue team members with a permissible vest 

can communicate with the fresh air base station via the two 

pair cable. 

Members of award winning mine rescue teams from the York 

Canyon Mine and the Colorado Westmoreland Mine near Paonia, 

Colorado, made a number of interesting observations concerning 

the use of MF radio. First, use of radio will revolutionize 

mine rescue procedures. The present life line communications 

cable is bulky and difficult to use. It is so onerous that 

it is not frequently used in mine rescue competition. The 

cable can be redesigned with a smaller diameter cable. This 

allows cables length to be greatly increased. As is the 

present practice, the team would lay the cable as they advance 

into the mine. When they arrive at a blocked entry (rock fall, 

hazardous environment), the cable can be simply cut and 

abandoned to hasten retreat. By simply splicing the cable, 

the team can advance along a new route. Secondly, the vest 

could be easily equipped with a telemetry capability to 

transmit local mine conditions immediately to the fresh air 

base station. A recorder at the base location could automatically record data. Finally, radio will speed recovery, 

an exceedingly important factor in successful rescues. 
The use of MF radio by mine rescue teams is described 

in a USBM published report by Dobroski and Stolarczyk (29). 

4. Demonstration Results 

With only four vehicular and four vest transceivers, radio 

communications is limited to supervisory personnel. On many 

occasions, the production superintendent used the radio to 

immediately summon emergency repair work on mining equipment. 

He estimates that the MF system reduces down time by more than 

one hour per shift. 

Maintenance crew members use the vest transceivers in 

their work. The maintenance foreman uses the radio' to comrnunicate to the point of equipment breakdown. The foreman 

assists in troubleshooting and obtaining repair parts from the 

warehouse. 

The mine superintendent is planning to install additional 

equipment on all service vehicles. 

Do RANCHERS EXPLORATION AND DEVELOPMENT COXP. 

The Redco Silver (Escalante Silver) Mine is owned and 

operated by Ranchers Exploration and Development Corp., 1775 

Montano Road, N.W., Albuquerque, New Mexico. The mine is 

located in Iron County (42 miles west of Cedar City) Utah. 

The property has been known as the Holt Mine, The Enterprise 

Mine and The Escalante Mine. First claims were located in 
1896 by Heber Holt. Between 1900 and 1930, three incline 

shafts were sunk on the vein (201, 30f, and 130' deep) and 

one vertical shaft was sunk in the footwall to 120'. In 1959, 

the shaft was extended to the water table. First water drawdown test were made in 1960. Shipments of ore totalling 

13,500 tons at 8.7 oz/T silver were made in 1966. The host 

rock are water-lain tuffaceous sediments of mid-tertiary age. 

The beds are composed of volcanic material with the composition 

of latite to rhyolite. The material is fine grained to conglomeratic, rounded to sub-rounded, and occurs in beds ranging 

from a few inches to 4 feet in thickness that dip lo0 - 15O 

southwest. A cross cut of the ore body is shown in Figure 79. 

FIGURE 79. REDCO SILVER ORE BODY 
The vein strikes N25E and dips 70' - 75' west. Northwest 

trending fracture zones intersect the vein in two or more 

areas. The ore reserve portion of the vein averages 20 feet 

in thickness. 

A modified vertical crater retreat (VCR) developed in 

Canada is used in the mining process. A plan view of VCR 

mining at the face is illustrated in Figure 80. 

SECTION A-A 

FIGURE 80. PLAN VIEW AND ENTRY CROSS SECTION OF THE 4970 

LEVEL DRILL SUB-LEVEL NORTH UNDERCUT.. 
High pressure (250 psi) air line (dash line symbols) is 

suspended by chains from the left hand side of the roof in the 

drift. (See A-A' cross section view). Blasting caSle (dasheddot symbols) is suspended from hooks mounted on the wall of 

the drift. The blasting machine is connected to cable on the 

haulage drift (at the TX location). The cable is terminated 

in the blasting cap in the undercut (at the M location). Detonating cord connects the blasting cap to each of the nine 

(9) delay/booster/explosive charges in the drill holes. The 

blasting delay sequence is shown by the number next to the 

hole in the down-hole pattern. 

The B-B' cross section of the down-hole pattern is shown 

in Figure 81. 

UNDER 

= CHARGE 

FIGURE 81. B-B' VIEW OF THE ORE BODY (VCR MINING) 
Escalante Communication System 

The Escalante radio communication system is shown in the 

block diagram below. 

 GENERALI MANAGER -1 LED HAHNE 

-7-- 

DUMP 8, 

MILL \ 

fl 

I------ 

UNDERGROUND 

--- 

CONTROL 

HEADS 

FIGURE 82. SYSTEM BLOCK DIAGRAM 
The radio communications system block diagram overlays 

the organizational chart (shown by dashed block and connecting 

lines). The dashed lines show the existing communication 

paths. The shifter (front line foreman) insure that the mining 

process is carried out in an efficient and orderly manner. 

The shifters report to the mine superintendent (Mr. Leding). 

Four diesel powered haulage vehicles are self dispatched 

in this mine. Up decline vehicles have the right-of-way to the 

dump. Round trip time on each vehicle is approximately 21 

minutes. The per shift muck rate is 457 tons per haulage 

vehicle. Haulage cost increases because down-decline vehicles 

must frequently back-up to a turn-out to yield to the updecline vehicle. 

Vehicular radios were needed to enhance safety and productivity of muck haulage. Radio communications between the 

superintendent, shifter, and haulage vehicle driver were also 

needed to increase haulage efficiency. Since this is a small 

mine the maintenance and supervision networks were combined 

into one network (FT = 400 kHz). 

2. Installation of MF Equipment 

Figure 83 illustrates the haulage drift decline use to 

transport muck out of.the mine. 
DISTANCE IN FEET 

SOUTH SECTION -IFIGURE 

REDCO S

HAULAG

An MF transceiver and antenna were mounted on each twenty ton 

Eimco" haulage trucks. 

FIGURE EIMCO TRUCK SHOWING VEHICULAR ANTENNA 

Because of the diesel truck engine noise, the truck driver uses 

the acoustical transducers shown in Figure 85. 

AEirnco Salt Lake City, Utah speakers with quick disconnect 

speaker cable. 
FIGURE 85. CIRCUII-AURAL EARCUPS 

3. FieldTest 

In the initial installation, signals were measured at the 

base station. The measured signal levels are shown on Figure 

83. A comparison of vehicular and vest signal levels are shown 

on Figure 86. 
MINE NOISE LEVEL 

VEHICUL

TRANSC

I 

I 

MANWAY DISTA

A 

t*s 

- ATTENUATION RATE 

--" 2.4db/1000' 
The measured signal attenuation rate was approximately 

2.4 dB/1000 feet along the telephone cable. The telephone 

cable terminated 1000 feet from the base station. High 

pressure air pipe continued to the drill level. 

The carrier to noise ratio of received base station 

signals exceeded 32 dB for mobile transmissions along the pipe 

(beyond the end of the telephone pair). Test measurements 

revealed that the signal coupling loss between the telephone 

pair and air pipe in the same drift was approximately 30 dB. 

The quality of the received voice signals was excellent. 

Base station messages could be received throughout the mine. 

The acoustical noise level of the diesel engine exhaust 

system in the decline was high. Communications from moving 

diesel powered vehicles required the use of circum-aural earcups and noise cancelling microphones. 

When the base station was exciting the "wireplantl1 the 

maximum signal measured in the blasting cable was 0.34 microamperes. A transmitting vehicular antenna next to the telephone pair could excite less than 1.2 milliampere of line 

current. When the vehicular antenna was illuminated the 

sending-end of the blasting cable, the differential current 

in the terminal-end of the cable was less than 12 microamperes. 
In summary, the worst case radio frequency radiation 

hazard safety factor was better than three (3) times less 

than the CFR safe limit of 50 milliamperes. Under normal 

operating conditions, the radiation hazard safety factor was 

better than 40 times less than the CFR limit. 

Besides the high voice quality achieved in the system, 

the most noticable feature was the low attenuation rate of 

MF signals on the existing "wireplant". Low signal attenuation 

rate (2.4 dB/lOO1) means that the system Is capable of operations beyond 15,000 feet. This can be achieved without 

the use of a repeater. 
VII. RECOMMENDATIONS 

The MF communications system is expected to emerge as 

the principal comrnunications resource in mining. 

The underground mine tests suggest the need to improve 

and add additional equipment to the MF system. The needs 

will be briefly described in the following paragraphs. 

A. BIDIRECTIONAL AMPLIFIER 

Manways without conductors are usually adjacent to 

entries with conductors. Since twin-line cable must be installed in those manways, installation could be simplified 

if bidirectional amplifiers were available to provide an 

efficient interface with gain between the "wireplant" coupler 

and the twin-lead cable. 

B. REDUCE LOSS ACROSS AC POWER TRANSFORMERS AND SWITCHES 

The AC power cable MF signal reliability can be improved 

by developing efficient couplers for use around high loss 

transformers and switches. 

C. BETTER WAYS TO DEPLOY TWIN-LEAD CABLE 

Efficient methods of attaching twin-lead cable to the 

rib or roof should be developed for the system. 

D. TELEPHONE SYSTEM INTERFACE NETWORKS 

Dial telephone capability should be added to the vest 

transceiver. This will enable the -yest to operate as a 

Bell System compatable radio telephone. 
E. PAGING AND EMERGENCY COMMUNICATIONS 

Since MF signals can be received everywhere electrical 

-conductors exist, MF can be used for paging and emergency 

communications. 

A low cost tone activated receiver should be made part 

of the cap lamp battery design. The MF receiver can be used 

in non-emergency situations to "pagefT and give miners vital 

information (even music - to insure that the miner will 

report a defective pager). 

An illustration of the use of a cap lamp receiver is 

shown in Figure 87. 

FIGURE USE CAP LAMP RECEIVER FOR EMERGENCY 
In emergency situations, evacuation routes can be given 

to underground miners. If trapped, the miner can receive MF 

signals and know that help in under way. 

A tone oscillator can be added to the cap lamp to enable 

a trapped miner to signal to rescue teams. Figure 88 

illustrates the use of the trapped miner transceiver. 

FIGURE 88. LOCATION AND RESCUE BY MEDIUM FREQUENCY TECHNIQUES 
In energy situations, evacuation routes can be given to 

underground miners. If trapped, the miner can receive MF 

signals and know that help is under way. 

A tone oscillator can be added to the cap lamp to enable 

a trapped miner to signal to rescue teams. Figure 88 

illustrates the use of the trapped miner transceiver. 

FIGURE 88. LOCATION AND RESCUE BY MEDIUM FREQUENCY TECHNIQUES 
Mine unring/ TW) MeCllum TreqUenCy 

signals - 

Repeater 

T

LOCATION AND RESCUE BY 

MEDIUM FREQUENCY TECHNIQUES 
A bast station at the portal can be used to communicate 

with a trapped miner. In the event that the portal base 

station has been rendered inoperable, for any reason, a base 

station and RF line coupler can be used to couple MF signals 

to bore hole conductors. Thus, bore hole base station can 

be used to communicate with trapped miners. 

F. RESCUE TEAM COMMUNICATIONS 

The vest transceiver will revolutionize mine rescue 

methods and speed recovery of the mine. The use of the vest 

transceiver by rescue team members is illustrated in Figure 

89. Vest transceivers should be used for the communications 

man,to inform the base of conditions encountered in the 

mission. 

FIGURE 89. BASIC MF COMMUNICATIONS BETWEEN RESCUE 

TEAM MEMBERS. 
BASIC MF COMMUNICATIONS 

BETWEEN RESCUE TEAM MEMBERS 
As the rescue team advances from the fresh air base, a 

two conductor life line can be deployed as shown in the 

figure. The life line provides a reliable MF signal path 

between the fresh air base station and the rescue team. If 

a blocked or hazardous area is encountered by the rescue team, 

the life line can be left in place. The team can retreat 

along the line to an acceptable passageway. A branch of the 

life line can be connected to the original line to enable an 

MF signal path along the revised rescue team route. 

Improved communications enable the team to rapidly 

determine entry conditions. By equipping the fresh air base 

with a tape recorder, the rescue record can be automatically 

recorded (logged). 

The vest transceiver can be equipped with a telemetry 

module. Methane, CO, etc., monitor data can be immediately 

sent to the fresh air base. The briefing officer will be 

immediately aware of environmental conditions encountered 

by the rescue team. 
G. HOIST COMMUNICATIONS 

Hoist communications safety and reliability can be 

achieved with the MF radio equipment. 

Hoist signalling microprocessors are required to enable 

transmission of the bell code and emergency signals. 

Because the highly efficient vehicular antenna can be 

used at the collar to illuminate the wire rope, the MF 

system is much safer to maintain. MF equipment should be 

considered for hoist communications. 

H. NATIONAL EMERGENCY FREQUENCY 

The mine maintenance network and national rescue frequencies should be identical. The national rescue frequency 

is 400 kHz. 

I. EMERGENCY COMMUNICATIONS 

A vest transceiver should be assigned to each location 

of stored underground self-rescue breathing apparatus. 

J. TRAINING MINE MANAGERS 

Mine manager training seminar materials are needed to 

insure leadership in adopting the radio resource in mining. 
APPENDIX A 

NORMALIZED DISCRIMINATION 

LOSS (NORMALIZED ATTENUATION) 

OF THE 

LEGENDRE TRANSFER FUNCTION 
~RM~LI ZEL H ITEIY~JHT I (JIV LOSS IN r)~p..~d.F I tit LEGENDRE TRANSFER FU

PASS BAND RIPPLE aLERANCE 3 UB 

NORMALIZED 

FREQUENCY N=1 N=2 N=3 hj=4 Ns5 4=6 Y
N(IRMAL1ZED ATTENUATIOY LOSS IN DB OF THE LEGENDHE TRANSFER FUNCTION 

PASS BAND TOLERANCE 3,000 DB 
APPENDIX B 

DISSIPATION LOSS 

OF THE 

LEGENDRE TRANSFER FUNCTION 
1 AHYLITI~DF DETERIORATION IN DB AT Z~RO FREQUENCY OF THE LFGENDHE FILTER WITH EO

I 3,000 DH PASS BANI) TOI.EHANCE 
AMPLITUDF DETERIORATION IN DR AT ZERO FREQUENCY OF THE LEGENDRE FILTER WITH EQ
APPENDIX C 

3 dB LEGENDRE FILTER ELEMENT 

VALUES 

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