AN EVALUATION OF LEAKY FEEDER 

COMMUNICATION IN UNDERGROUND MINES 

FINAL REPORT 

By: 

Dana T. Updyke 

Wayne C. Muhler 

Howard C. Turnage 

Prepared for: 

United States Department of the Interior 

Bureau of Mines 

Contract No.: JO 199048 

June 1980 
The views and conclusions contained in this docunlent are those of the authors and 

should not be interpreted as necessarily representing the official policies or recommendations of the 

Interior Department or of the U.S. Government. 

Reference to specific brands, equiprnei~ts or trademarks in this report is made to 

facilitate understanding and does not imply endorsement by the Bureau of Mines. 
REPORT DOCUMENTATI ON PAGE 1 

1. Report No. 2. 3. ~ecipient 's Accession No. 

7. Author(s) 

D. T. Updyke, W. C. Muhler, H. C. Turnage 

P 

4. Title and Subtitle 

An Evaluation of Leaky Feeder Communication in Underground 

Mines 

/ 8. Performing Organization Report No. 

I 

5. Report Date 

June 1980 

6. 

1 9. Performlog Organrza tion Name and Address I 10. ProjectITasklWork Unit No. I 

United States Department of the Interior 

Bureau of Mines, Pittsburgh Research Center 

< 

Cochran's Mill Road, P.O. Box 18070 

Pittsburgh, Pennsylvania 1 5236 

Final Report 

Atlantic Research Corporation 

5390 Cherokee Avenue 

Alexandria, Virginia 223 14 

- - 

15. Supplementary Notes 

11. Contract or Grant NO. 

JO 199048 

Bureau of Mines Contract Manager: James C. Cawley 

' 13. Type of Report I 

12. Sponsoring Organization Name and Addrese 

16. Abstract 

The objective of this project was to develop technical data and evaluate performance and utility 

of leaky feeder communications systems currently used in North American underground mines. 

The desired information was obtained principally through on-site surveys. Altogether, six of the 

seven mining companies known to be using leaky feeder communications were visited. This 

repbrt covers the findings of these surveys. In addition, the report provides a brief background 

summary of mine communications, a technical discussion of leaky feeder systems, and conclusions 

and recommendations based on the results of the survey. 1 I 

Mine communications, leaky feeder communications, 

tunnel communications, leaky feeder cable, leaky feeder 

systems, induction cable, radio communications in mines 

I 

17. Originator's Key Words 

Unclassified I Unclassified I 102 1 1 

18. Availability Statement 

I 

19. U. S. Securlty Classlf. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 22. Pr~ce I 
FOREWORD 

This report was prepared by Atlantic Research Corporation, Telecommunications 

Department, Alexandria, Virginia 223 14 under US Bureau of Mines Contract No. 50 199048. The 

contract was initiated by the Pittsburgh Research Center. It was administered under the technical 

direction of US Bureau of Mines, PRC, with Mr. James C. Cawley acting as Technical Project 

Officer. Mr. Francis M. Naughton, Branch of Procurement, Washington, was the contract 

administrator for the US Bureau of Mines. The period of performance on this project was August 

1979 to June 1980. 
ACKNOWLEDGEMENT 

We wish to express our appreciation to those mining companies without whose 

cooperation the project would not have been possible. Our thanks also go to those individual mine 

employees who took precious time from their busy schedule to participate. 

Every effort has been made to protect the anonymity of those companies and 

individuals who took part. 
TABLE OF CONTENTS 

FOREWORD .......................................... 3 

ACKNOWLEDGEMENT .................................... 4 

EXECUTIVE SUMMARY ................................... 10 

1.0 INTRODUCTION AND BACKGROUND ....................... 19 

1.1 Introduction .................................. 19 

1.2 The Need for Communications ......................... 19 

1.3 General Types of Mine Communications Systems ............... 20 

1.3.1 Bell Signalling Systems ......................... 20 

1.3.2 Pager Phone Systems .......................... 20 

1.3.3 Dial Telephone Systems ........................ 20 

1.3.4 Carrier Current Radio Systems ..................... 21 

1.3.5 VHFIUHF Two-way Radio Systems .................. 21 

1.4 General Description of a Leaky Feeder Radio System ............. 22 

1.4.1 Components .............................. 22 

1.4.2 Configurations ............................. 23 

1.4.3 Uses of Leaky Feeder Systems ..................... 24 

2.0 TECHNICAL DISCUSSION OF LEAKY FEEDER SYSTEMS IN MINES ....... 25 

2.1 Propagation in Tunnels and Mines ....................... 25 

2.2 Leaky Feeder Cables .............................. 27 

2.2.1 Background .............................. 27 

2.2.2 Cable Types and Characteristics .................... 28 

2.2.3 Cost Comparisons of Cables ...................... 31 

2.3 Single Repeater Systems ............................ 32 

2.4 Multiple Repeater System ........................... 34 

2.5 Alternative Leaky Feeder Configurations ................... 34 

3.0 SURVEY FINDINGS ................................. 38 

3.1 Description of the Survey ........................... 38 

3.2 Mine Survey Findings ............................. 39 

3.2.1 Survey Data - Mine A ......................... 39 

3.2.2 SurveyData-MineB ......................... 50 

3.2.3 Survey Data - Mine C ......................... 59 

3.2.4 SurveyData-MineD ......................... 67 

3.2.5 Survey Data - Mine E ......................... 75 
TABLE OF CONTENTS (Continued) 

Page 

3.2.6 Survey Data - Mines F and G ..................... 82 

4.0 CONCLUSIONS .................................... 89 

Summary of Leaky Feeder Use and Justification ............... 89 

Procurement Practices ............................. 91 

Installation Practices .............................. 92 

Maintenance .................................. 92 

Training .................................... 93 

Miner Attitudes and Acceptance of Radio Communications .......... 94 

Cost Effectiveness ............................... 95 

Intangible Benefits ............................... 96 

Alternative Forms of Communications ..................... 97 

5.0 RECOMMENDATIONS ................................ 98 

5.1 For Mine Owners and Operators Considering the 

Use of Underground Radio Communications ................. 98 

5.2 For Bureau of Mines Sponsorship of Activities Leading 

Toward the Lowering of Cost or Increasing the Benefits of 

Leaky Feeder Cable in Underground Mining .................. 99 

REFERENCES ......................................... 100 
LIST OF ILLUSTRATIONS 

Figure 

2.1 

2.2 

2.3 

2.4 

3.1 

3.2 

Page 

Commercially Available Cable Antenna Types ................... 30 

Single Repeater System ............................... 33 

Typical Multiple Repeater Systems ......................... 35 

Daisy Chain Systems ................................ 37 

System Layout. Mine A ............................... 40 

Primary Haulage Dispatch Console on the Haulage 

Level at the Loading Drifts ............................. 42 

UHF Repeater at the Haulage Dispatch Center ................... 42 

Railroad Style UHF Antenna Mounted on Haulage Motor ............. 43 

Railroad Style UHF Mobile Radio Control Head in 

Cab of Haulage Motor ................................ 43 

Railroad Style UHF Mobile Radio Mounted under Motor 

Operator's Seat ................................... 44 

Cable Trays Carrying all Cables. Including Radiax Mounted 

in Roof on the Main Haulage Tunnel . Tray also Supports 

Trolley Power System ................................ 44 

Blasting Damage Done to Unprotected Radiax in Loading Drifts .......... 46 

New Method of Protecting Radiax in Blasting Areas. Insalled 

within Fabric Reinforced Hose ........................... 46 

In-house Radio Maintenance Work Area ....................... 48 

VHF Repeater. Wall Mounted (Front View) ..................... 51 

VHF Mobile Radio Mounted under the Dash of a Maintenance Jeep ........ 53 

Railroad Style VHF Antenna Mounted on the Hood of a Maintenance Jeep .... 53 
LIST OF ILLUSTRATIONS (Continued) 

Figure Page 

3.15 Method of Mounting Twin-lean Antenna Cable to Top of 

Entrance. Turn Lead is to Right of Large Power Cables ............... 54 

Ore Haulage Belt and Drive Motors ......................... 56 

VHF Repeater with Convection Cooling Vents Sealed to 

Protect from Dust .................................. 56 

Repeater Cabinet Located Adjacent to the Haulage Belt (Radio was 

Cleaned Less Than 60 Days Earlier) ......................... 57 

System Layout. Mine C ............................... 61 

Primary Dispatch Console Located in the Hoist House ............... 63 

Typical UHF Mobile Radio Package Used on Personnel Haulage 

Motors (Radio. Enclosure. Control Head and Antenna) ............... 63 

Internal View of Custom Radio Enclosure . Power Supply/Battery 

Charger on Door. 12 VDC Battery on Left End. and 

Modified Mobile Radio on Right .......................... 66 

Snapper. Hooking and Unhooking Cars. with UHF Portable Radio in 

Upper Right Pocket ................................. 66 

System Layout. Mine D ............................... 69 

Railroad Style VHF Antenna Mounted on Battery 

Operated Rail Motor ................................ 71 

Railroad Style Mobile Radio Mounted in Electrical 

Compartment of Rail Motor ............................. 71 

System Layout. Mine E ............................... 76 

Photo of Underground UHF Repeater ........................ 78 

Repackaged UHF Mobile Radio for use on Mine Vehicles .............. 78 

Splitter Installed in Radiax Line ........................... 80 
LIST OF ILLUSTRATIONS (Continued) 

Figure Page 

3.3 1 Radiax. Improperly Bent and not Properly Terminated ............... 80 

3.3 2 System Layout. Mines F and G ........................... 83 

3.33 Radio Equipment Inside Manstrip Cab ....................... 84 

3.34 Photo of Rear Cab Area of Supply Motor . Hard Hat Mounted 

in Electrical Box ................................... 84 

3.35 Processing Plant Located in Ravine between the Two Sister Mines ......... 86 

3.36 Main Entry Portal . Hard Hat Antenna Connected to Radiax is on 

Upper Right Rail Train Shown ........................... 86 

Table 

2.1 Propagation Characteristics in a Coal Mine ..................... 26 

2.2 Propagation Chracteristics in an Iron Mine ..................... 26 

4.1 Communications Systems Summary ......................... 90 
EXECUTIVE SUMMARY 

This report is the result of a project conducted by Atlantic Research Corporation 

under contract to the U.S. Department of Interior, Bureau of Mines. The objective of the project 

was to "Develop technical data and evaluate performance and utility of leaky feeder 

communications systems currently used in North American underground mines." 

As a general principal, radio waves do not propagate well through underground 

tunnels and mines at frequencies ordinady used for communications. This fact has tended to 

frustrate the use of two-way radio in mines except over very short distances. However, the range of 

radio communications in tunnels can be greatly extended by the use of leaky feeder cables. As the 

name implies, "leaky feeder" cables are radio frequency transmission lines that permit, by 

deliberate design or otherwise, external leakage fields large enough to allow reception by mobile or 

portable receivers. Reciprocally, such cables are also able to pick up the transmissions of mobile or 

portable transmitters, thus permitting two-way radio communications with other units connected or 

coupled to the cable. 

Serious interest in the use of leaky feeder systems in mines did not occur until the 

late 1960's and that primarily in Europe. Much pioneering work was sponsored by the Institute 

National des Industries Extractive (INIEX) in Belgium and by the National Coal Board (NCB) in the 

United Kingdom. A number of studies have been sponsored by the U.S. Bureau of Mines and an 

experimental installation was made in Bethlehem Steel Corporation's Grace Mine, near Morgantown 

Pennsylvania. To date, however, the use of leaky feeder systems in US mines is still rather limited. 

A leaky feeder radio system, as used in a typical mine or tunnel application, can be 

subdivided for discussion into its major components. The major components of this type of a 

system are: ( 1 ) the mobile radio transceivers (transmit terlreceivers), (2) the base station transceiver, 

(3) the remote control equipment, and (4) the leaky feeder cable antenna system. The first three 

components are used in much the same manner as in surface mobile radio systems. They are as a 

matter of fact, adaptations of equipment normally sold for use on the surface. The unique feature is 

the leaky feeder cable, which replaces the antenna system used with base stations above ground. 
The only leaky feeder used in US mines at the time of this study was slotted coaxial 

cable. It is available in 112-inch and 718-inch diameter sizes and is very similar to coaxial radio 

frequency transmission lines used in radio base stations on the surface. It differs only in that a series 

of closely spaced slots has been cut into the sheath along one side of the cable. Other types of cable 

have been used in Canadian and European mines. Cost of the slotted coaxial cable for lengths 

between 5000 and 25,000 feet were quoted in May 1980 at $1.66 per foot and $3.32 per foot, 

respectively, for 112-inch and 718-inch sizes. 

To carry out the survey, an exacting questionnaire was developed and a two-man 

survey team was assembled to personally visit selected mines known to employ some form of leaky 

feeder radio system. The two team members were selected with backgrounds specifically oriented 

toward the needs of the study. One team member was a communications engineer with experience 

in two-way radio systems. The second member of the team had experience in mining, mine safety 

and human factors relative to mining operations. During these visits mine personnel responsible for 

the maintenance and/or management of the radio system were interviewed. The objective of the 

interviews was to collect the information necessary to characterize experience with this type of 

system (i.e., typical advantages claimed, typical costs, typical complaints, etc.). Altogether six 

mining companies controlling ten leaky feeder equipped mines were interviewed. One of these was 

in the Rocky Mountain region of the US, one in the southwest, one in Canada, and the others were 

in the Appalachian region of the US. These, with one other company that declined to be 

interviewed, represent all the companies in North America known to have leaky feeder systems in 

place and operating. At least two others had used leaky feeder earlier but had since discontinued its 

use One of these had used a passive system (i.e., a leaky feeder cable only - without a base or 

repeater station) to provide portable-to-portable communications from end to end of a longwall 

coal mining operation. It was discontinued when the longwall was shortened to less than 200 feet, 

making direct portable-to-portable contact possible without the cable. The other was a more 

conventional repeater system, but was reportedly discontinued because the miners rebelled against 

its use. 

It is concluded from the survey that the use of leaky feeder communication systems 

in North America has been limited and has been primarily the result of legal requirements. Two-way 

radio communications are required on all underground rail systems in the state of West Virginia, and 

have been required in other areas if more than one vehicle was to use the rail system at any one 

time. Given the requirements for two-way radio communication, the leaky feeder system was 

adopted at several mine sites. Other mines adopted the leaky feeder system solely on the 

recommendation of their communications equipment suppliers or to keep the underground system 

compatible with existing surface radio systems owned by the company. 
Other rationale for installing two-way radio communications systems underground 

include reduced mine maintenance costs reported by a large Canadian mine through better use of 

their mechanics and perception of increased worker safety. The mines have considered the expense 

of the radio systems with a cost of doing business (West Virginia mines) or a definite asset in terms 

of production and labor cost savings. 

Because the use of two-way radio communications is not common underground, the 

variety of potential radio uses have not been entirely explored. Radio systems are primarily used as 

management tools for communication with workers in remote locations, and for traffic control on 

rail systems or haulage ways. The most common use of two-way radio communications 

underground utilizing a leaky feeder cable has been for the direction of traffic on railway systems. 

Use of the leaky feeder system allows continuous communications between rail vehicles and a 

dispatcher. Ths eliminates the need for rail vehicle operators to leave their vehicle to visually check 

each intersection prior to passing it and to coordinate and time vehicle movements so that they do 

not inhibit each other. Use of the leaky feeder communication system has provided effective 

communications on almost all rail systems employing it, and has allowed several to increase their 

haulage system capacity up to ten times through its use. 

A second use of the leaky feeder communication system underground has been for 

supervision of mechanics and production workers. Use of the radio eliminates the need to travel to 

remote locations or to rely on pager phones for communication with workers. Mechanics and other 

production personnel that travel throughout the mine are much easier to locate using the radio, 

saving substantial amounts of "travel and location" time. Although several mines have found the 

leaky feeder communication system desirable from an operations viewpoint, there have been some 

substantial problems with installation and use of the systems. 

It was observed during the survey that a number of problems could be traced to 

procurement practices. Basically, procurement of leaky feeder systems were initiated without a 

complete understanding of the capabilities or pitfalls of such systems, and without adequately 

defining the needs to be satisfied. It was found that: 

In-house technical expertise was generally nonexistent or 

simply not sufficient during the planning and/or procurement 

stages of the system. 
Investigation of available equipments and sources for 

assistance was inadequate before procurement. 

The actual procurement was, in all cases except one, 

executed without the benefit of comprehensive technical 

specifications or even performance specifications by which 

the end product could be evaluated. 

Procurement under these conditions can be the root of subsequent difficulties such 

as disappointment with the system's performance and costly system reengineering to correct 

original design deficiencies. 

The design and installation of the systems reviewed for this project indicate a wide 

variation in concern for maintenance and durability. Few systems have been specifically designed 

for the extremely rugged environment and the rough handling received by the untrained users. 

Although several systems were installed in locations that afforded the radio protection from falling 

objects and physical abuse, accessory components such as microphones and speakers were 

substantially less protected. It is also apparent that several installations were made with no concern 

for ease of maintenance. Radios were installed in locations difficult to reach or in such a manner 

that they require a significant amount of work to remove. 

Repeater station installations could be improved by providing more substantial cases 

with inlproved dust filtering capabilities. Many installations reviewed indicated a need for a cabinet 

which could withstand limited roof falls as well as provide clean cooling air. Cable installation and 

hanging techniques also varied widely by installation. It is apparent that many individuals installing 

the cables did not know how to correctly install the system or had not considered the possibility of 

physical abuse. 

Only one of the mines surveyed had a complete in-house maintenance capability. 

Others depended wholly or partially on contract maintenance by an outside radio shop. Three of 

the mines did routine repairs and replacement of defective components depending on an outside 

shop for troubleshooting and repair of the defective components replaced. One mine not only 

depended wholly upon outside maintenance but exercised no coordination over calls for service. 

Any miner could call for service even for the replacement of a microphone. This mine complained 

of exorbitantly hgh maintenance bills and yet had the poorest maintained system of all those that 

were surveyed. 
It was found that without exception all mines were deficient in the proper training 

of personnel who were to either use the radio system or be affected by its usage. This lack of 

training contributes directly to many problems experienced by those surveyed. Several of these 

problems are: 

Inefficient implementation of the entire system 

Improper usage of the system 

Abuse of the equipment and thus higher maintenance costs 

And occasionally, nearly total rejection of the new system by 

miners and/or mine supervisors. 

Some systems are fairly complex in their operation. Therefore, lack of instruction 

on the simple operational characteristics of the system can cause operators to assume a system 

malfunction when in fact the problem may be operator error. This applies equally to the mechanical 

operation of a piece of radio equipment itself. 

The effectiveness of the communications systems has been severely hampered at 

several locations due to inadequate understanding by company personnel of the requirements for 

the installation and maintenance of the systems. Initial startup problems characterized by repeated 

system failures was common at most sites visited. This severely hampered the effectiveness of the 

systems due to the negative impression it left on the system users. At several locations the system 

was not reliable enough to be used for management functions or traffic control without a backup. 

This led to a very poor acceptance of the system by the workers as well as management. Only after 

several months of system use and improvements in the in-house maintenance capability have these 

systems grown to be tolerated by the workers and management. For the average installation it took 

approximately one year for the system to become fully functional, both from a reliability and 

worker acceptance standpoint. Another major problem with the use of the leaky feeder systems has 

been a lack of understanding by both management and workers of how to use the system and its 

actual capability. 

A consideration of cost effectiveness is a direct response to question 1 in Section 1.1 

of this document. The procurement of leaky feeder was invariably associated with the objective of 

increasing production. Even in those mines where it is intalled merely to meet a legal requirement it 

is most often tied to some direct production function and not to a management or safety purpose. 
At all but one location the system was perceived by management as meeting' this objective. 

Although only one mine could show an increase in production directly attributable to the radio 

system, the other users also felt production was increased. In the one case, the mine considered that 

the radio made it possible to increase production from an annual gross of about $2 million to nearly 

$10 million. This was accomplished by a capital investment of $800,000 and an estimated annual 

maintenance cost of about $25,000. This increase in production is a direct result of the greater 

number of trains that can be operated on the same track because of a continuous communications 

capability. Other mines reported that benefits were realized because of improved haulage, supply 

delivery and repair. 

No accidents were reported on haulage systems employing radio communications. 

These mines did report accident histories prior to radio installation. The reduction in accidents 

directly increased production. At one mine this saving, or more realistically, increase in production 

was substantial. Accidents prior to the radio system installation stopped production for an average 

of 14 days. With the current production rate of 50,000 tons per day the annual production of the 

mine has increased approximately 700,000 tons per year due to accident reductions. 

Although no systems were purchased solely for the purpose of mine safety, nearly 

everyone interviewed at each mine agreed that worker safety was enhanced by the radio. The users 

felt that the radio would allow faster response during mine emergencies, as well as allow redirection 

of effort as conditions change in an emergency. The radio also serves as a backup communications 

system where other systems, such as telephones or pager phones, have failed. Safety aspects of the 

system have been the consideration for the establishment of laws requiring two-way radio 

communication. Personnel interviewed at the mines indicated that the radio reduces the probability 

of intersection collisions of rail and rubber tired vehicles. The radios allow communications between 

vehicles at intersections as well as allow warnings in the event of a runaway vehicle. 

Some radio system users have installed leaky feeder cable to remote locations where 

a single person or small crew works. This allows these individuals to work in a complete contact 

with supervisors or other crews away from their immediate area. A simple call to these people by a 

supervisor confirms whether or not an unusual condition exists. The radio also allows the remote 

person to relay requests for assistance. 

The following recommendations are directed to mine owners and operators 

considering the use of underground radio communications: 
(1 ) Radio systems require planning. Management should acquire information on 

both the capabilities and limitations of radio systems from suppliers and from other mines with 

operating systems. If possible, a responsible representative of management should visit a mine 

already equipped and personally observe operations. Before proceeding with procurement, 

management should have prepared a performance specification defining exactly what the system is 

to include and what it is expected to do. 

(2) Radio systems require management. Without an individual in a lnanagcmelzt 

position pushing for and overseeing the radio system it is doomed to failure. In systems observed 

where the performance was exceptional, there was always an individual who felt that he was 

responsible for the system and who had an interest in its best performance. 

(3) Radio systems require maintenance. In several instances, it was found that 

the maintenance function was left to mine electricians who did not fully understand the radio 

system and thus provided poor maintenance. It is crucial that the maintenance of the system be 

performed by radio technicians with a knowledge of mining and its unique environment. 

(4) Users of radio equipment require training. All underground personnel 8 

including supervisors should be thoroughly trair~efin proper radio use, radio communication 

etiquette, and operational procedures. Without thorough training of the entire underground work 

force the radio will be severely limited. Every individual with access to the system should know how 

to use it, when to use it, and its potential value to him. 

Additional recommendations are made for Bureau of Mines sponsorship of 

activity leading toward lowering cost or increasing the benefits of leaky feeder cables in 

underground mining. These are: 

(1) It is recommended that alternative cable designs be investigated with a vic\v 

toward reducing cable costs. The most expensive single item in leaky feeder systems is the cable. 

Many designs have, in fact, been studied and no investigation should be conducted without 

reference to the literature on this subject. Nonetheless, a would-be user has a very limited choice of 

commercially available and proven designs. The investigation should include comparative tests in a 

mine environment of various designs, including designs and techniques used in other countries. 
(2) It is recommended that some Bureau of Mines sponsored entity be 

established for the provision of training and the exchange of information relating to 

communications and perhaps other mining technology. In a recent report by John Short and 

Associates the creation for coal miners of an "extension service" patterned after the agricultural 

service now provided for farmers was recommended. Among the senices the extension service 

would provide are guidance for training in mine productivity, safety and health and a means for the 

exchange of technology in the mining industry. This concept is endorsed with the proviso that the 

exchange of technology include radio communications technology, and that training include the 

operation and use of radio equipment. 

(3) It is recommended that support be given to the further development and 

improvement of bi-directional line-powered cable amplifiers (or in-line repeaters) for underground 

mines. Advantages to be achieved are the elimination of multiple base station repeaters and their 

interconnecting audio and power lines, the reduction of required base station RF power and the 

reduction of RF power required of mobile and portable transceiver power. Ruggedness, reliability, 

intrinsic safety, and reasonable cost should be prime objectives in the development effort. Another 

consideration should be the use of frequency bands, such as 800 - 1000 MHz, known to have good 

propagation characteristics in tunnels but which are not currently used in underground mines. Full 

advantage should be taken of the existing cable-television technology (6 to 400 MHz) and European 

daisy chain repeater technology (mostly 68 to 88 MHz). 

(4) It is recommended that the development of prototype mobile and portable 

trailsceivers for underground use he undertaken. In some mines surveyed extensive modifications to 

equipment designed for surface use had been made. In all mines the reliability of mobile and 

portable transceivers suffered in the mine environment. Emphasis should be placed on simplicity, 

ruggedness, and intrinsic safety. Units should be single-channel and contain an absolute minimum of 

controls and switches. Used with a system of in-line cable amplifiers the transceivers would require 

RF power outputs considerably less than one watt. The ultimate objective should be that no miner 

is ever out of voice contact. 

(5) It is recommended that the Bureau of Mines sponsor the development of a 

"recommended practices" document for the design, installation and operation of underground 

leaky feeder systern. The mine survey revealed a wide variability in the installation and use of leaky 

feeder systems and uncovered a number of poor practices, many of which had already been found 

and corrected by the mines in question. The document should cover possible uses and design 

configurations, installation practices for cable, installation practices for fixed and mobile radio, 

recommended operating procedures and recommended maintenance procedures. The purpose of the 
document would be to provide guidance to mines which are considering the use of leaky feeder 

communications or which may be seeking to improve systems already installed. 
1 .O INTRODUCTION AND BACKGROUND 

1.1 Introduction 

This report is the result of a project conducted by Atlantic Research Corporation 

under contract to the U.S. Department of Interior, Bureau of Mines. The project commenced in mid 

1979. The objective of the project was to "Develop technical data and evaluate performance and 

utility of leaky feeder communications systems currently used in North American underground 

mines." The primary goals for this project were to collect sufficient data and evaluate it for the 

purpose of answering the following basic questions: 

1. Are leaky feeder communications systems as used to date 

cost effective? Are they attractive to mine operators from the 

standpoint of cost savings, such as would result from a 

reduction of required personnel or equipment, or greater 

labor efficiency? 

2. Are there intangible benefits, such as improved safety or 

better working conditions, which may be worthy of 

consideration even though not readily amenable to a 

cost-benefits analysis? 

3. Are there alternate forms of communications which may be 

as good or better in the environment studied? 

4. Is there anything in the data collected, or in the larger field 

of propagation and leaky feeder technology that suggests 

possible improvements which would lower the cost or 

increase the benefits of leaky feeder cable in underground 

mining? 

1.2 The Need for Communications 

Some form of communications between workmen and/or between work crews is an 

absolute necessity in order to yield a coordinated work effort. As long as workers are within voice 

range of each other, there is little problem. However, when workers are separated by considerable 

open distances or even by as little as a few feet of rock, this vocal communications is rendered 

useless. In a mining environment underground workers are not only separated from surface workers 

but are very often separated from each other. 
1.3 General Types of Mine Communications Systems 

1.3.1 Bell Signalling Systems 

The first apparent need for communications appears at the portal. Those requiring 

the services of the cage must somehow communicate this need to the hoistman. One early solution 

has been that of a signal bell system on which simple codes take on specific meanings. In later years, 

cage and hoist equipment have become more automated and have come to lend themselves to other 

forms of communications systems. 

1.3.2 Pager Phone Systems 

The use of telephones for underground and underground-to-surface communications 

is by far more simple and more consistent than bell signalling systems. Battery-powered paging 

telephones have replaced the magneto telephones of years past, thanks largely to the advent of 

transistorized circuitry and reduced power requirements. 

Pager phone systems have basically two wiring configurations. The first is tile party 

line which consists of a single No. 14 or No. 16 gauge twisted pair wire strung throughout the mine 

and extended to the surface. This wiring may have branches to various parts of the mine and 

instruments may be added anywhere along the line. A second, but less commonplace wiring 

configuration is a multi-line scheme in which several twisted pairs, normally 6 to 8, are strung 

throughout the mine. The pager phones are equipped with a line selector switch to allow the user to 

select the desired line on which to communicate. 

1.3.3 Dial Telephone Systems 

Many mining operations employ central battery powered, rotary dial PBX (Private 

Branch Exchange) telephone systems. The majority of these systems are in use for surface 

communications only as the telephone companies in the United States will not always provide 

underground service in all localities. There are, however, exceptions to this rule when the mine has 

sufficient technical manpower to install PBX equipment and lines below the surface and to maintain 

them. These systems lend themselves to greater versatility than pager phone systems but require a 

large multi-pair cable network to fulfill the needs of the mine. 
Carrier Current Radio Systems 

Carrier current radio systems were evolved to satisfy the need for continuous 

communications to electric powered rail vehicles. In earlier designs, a frequency modulated (FM) 

carrier in the range of 60 to 190 kHz is coupled directly to the trolley wire. Vehicular units in such 

systems are capacitively coupled to the trolley and also draw power from the trolley line. They 

provide satisfactory communications between dispatcher and vehicle but not between vehicles. The 

power rectifiers and large motors across the line are a source of electrical noise and high line 

attenuation, both of which limit system range. More recent innovations use a separate dedicated 

wire, typically AWG 12, mounted about 6 inches from the roof. The dispatcher is coupled directly to 

the dedicated wire. In one design, the dedicated line parallels the trolley line and communication 

with conventional "trolley phones" is made possible through the mutual coupling between trolley 

wire and dedicated line. The advantage achieved is greater range through reductions in attenuation 

losses. Still further advantages are achieved through a "wireless trolley phone" which employs an 

oblong coupling loop about 42 inches long and 10 inches across. This couples directly to the 

dedicated line, conlpletely eliminating the original trolley wire as a communications link. This 

system results in reduced noise and reduced attenuation losses, improving range and making 

vehicle-to-vehicle communications possible. It also makes practical the use of carrier current 

communications on rubber tired trolleys and battery powered vehicles, which were excluded under 

the original trolley wire concept. 

VHF/UHF Two-Way Radio Systems 

Conventional two-way radio has, in the past 5 to 7 years, found its way into the 

mining industry. It was thought that the portability which two-way radio provides to surface 

vehicles and personnel would be equally beneficial to the mining community. However, radio 

propagation through mine tunnels at these frequencies is very poor, even in tunnels providing 

line-of-sight between transmitter and receiver. Bends and corners make the situation even worse. 

Propagation is improved by the use of leaky feeder cables suspended in the tunnels and connected 

to the radio base station. The cables transmit radio signals as would any ordinary cable except that 

the cable is intentionally designed or chosen to "leak" radio frequency fields all along its length. A 

mobile or portable radio on the correct frequency and anywhere within a reasonable distance of the 

cable can receive the signal. Conversely, the leaky feeder cable can pick up radio transmissions from 

mobile units and transmit them back to the radio base station. In effect, the leaky feeder cable acts 

as a very long antenna system which can extend many thousands feet away from the radio base 

station. Leaky feeder cable and systems using the cable are covered in greater detail in Section 2.0. 
1.4 General Description of a Leaky Feeder Radio System 

1.4.1 Components 

A leaky feeder radio system, as used in a typical mine or tunnel application, can be 

subdivided for discussion into its major components. The major components of this type of a 

system are: (I) the mobile radio transceivers (transmitter/receivers), (2) the base station transceiver, 

(3) the leaky feeder cable antenna system, and (4) the remote control equipment. 

1.4.1.1 Mobile Radio Transceivers 

The mobile radio transceivers are of the same basic style one might expect to find in 

a taxi, police vehicle, or other radio equipped surface vehicle. Mobile radios are generally available 

in one of two hardware packaging styles, front mounted and trunk (or rear) mounted. In a front 

mounted radio tranceiver all electronics, including the operator controls and speaker, are assembled 

into one chassis and is usually installed in the operator's compartment. In the case of a trunk 

mounted radio transceiver, the radio electronics are in a chassis which is mounted in a remote 

location from the operator (such as an automobile trunk, under an operator's seat or in a power 

compartment of a locomotive). The operator controls, including speaker, are mounted in what is 

termed a "control head" which is mounted in the close proximity of the operator. The radio and 

the control head are interconnected with a control cable. Mobile radios may be equipped for singleor multi-channel operation depending on the user's needs. Mobile radios normally require 12V DC 

or 48V DC power. 

The mobile radio classification also includes handheld portables. Here, the entire 

assembly, including controls, speaker/microphone, antenna and battery power supply, is contained 

in one small package convenient for carrying on one's person. 

1.4.1.2 Base Station Transceiver 

A fixed (or base station) radio transceiver is designed for stationary operation. 

Electronically it is very similar to a mobile radio except it usually produces a higher RF transmit 

output power and is usually powered by 1 10V AC. The greatest difference is the addition of remote 

control circuitry which allows the base station to be operated from a considerable distance away 

(up to several miles). 
Leaky Feeder Cable 

The only leaky feeder used in US mines at the time of this study was slotted coaxial 

cable. It is available in 112-inch and 718-inch diameter sizes and is very similar to coaxial radio 

frequency transmission lines used in radio base stations on the surface. It differs only in that a series 

of closely spaced slots has been cut into the sheath along one side of the cable. Other types of cable 

have been used in Canadian and European mines. 

1.4.1.4 Remote Control Units 

One or more remote control units can be used to control a base station transceiver. 

These units are used by those generally in control of the radio system such as dispatchers or 

supervisors. The remote control unit is usually powered by 110V AC and is connected to the base 

station radio by a No. 20 gauge single twisted-pair wire. 

1.4.2 Configurations 

111 general, two-way radio systems can be categorized in to two main configurations: 

( I ) "simplex" operation and (2) "relay" (or "repeater") operation. This section will describe the 

0:1sics of both configurations as a foundation for technical reference later. However, throughout this 

doiui~~ei~t the emphasis will be placed on RELAY operations as they are the most prevalent in 

North Ar-nerican underground leaky feeder radio systems. 

As an illustration, a simple radio system with one fixed base station, one remote 

~.oritrol unit several miles away, and two mobile radio units will be hypothesized. In simplex 

t ,I) ratloll all radio transceivers transmit and receive on the same radio frequency, for example, 452 

111 i~. When the dispatcher desires to communicate with a mobile he would transmit via the base 

station which would radiate an RF signal on 452 MHz. Assuming either or both mobile units were 

within receiving range of the base station radio, they would receive the 452 MHz signal. Conversely, 

when the appropriate mobile operator responds to the dispatcher's call he would transmit via the 

mobile radio back to the base station by radiating an RF signal on 452 MHz. It is also possible for 

one mobile unit to communicate with the other PROVIDING they are within radio range of each 

other. If both mobile units were within range of the base station and within range of each other the 

scc.ond mobile unit would be able to receive both sides of the base to mobile cominunication. If, 

however, both were within range of the base station but were not within a radio range of each 

other. the second mobile unit would receive only the side of the communications generated by the 

1~1~ stat~on. 
In practice, the radio range with this sytem is far greater for communications 

between the base station and mobile units than it is between two mobile units. This occurs because 

base station transceivers usually have a higher transmitting power and their antenna systems are 

much more efficient. This is especially true when the mobile units are hand-held portables. 

Relay operation capitalizes on this higher transmit power and antenna efficiency of 

the base station radio equipment in order to extend the useful communications range between 

mobile units. This is done by a method of relaying or repeating the radio signal radiated by a mobile 

unit. Stated simply, the base station radio simultaneously retransmits (at higher power) all signals 

that it receives. Since it is not feasible to receive and transmit on the same frequency, the first 

difference between simplex and repeater operation is that all radios in the system must transmit and 

receive on different radio frequencies. Going back to the example, repeater operation will now be 

assumed. The dispatcher now transmits via the repeater station in the same manner as before on 452 

MHz and the called mobile unit receives this signal. When the called mobile unit responds it will 

transmit back to the repeater station on a frequency of 457 MHz. Now, however, as the dispatcher 

is receiving the mobile's signal, the repeater is also retransmitting (or repeating) the mobile's 

communications on 452 MHz. This retransmitted signal can be received by all other mobiles within 

communications range of the repeater. The overall result of this is that each of two mobiles needs 

only to be within range of the repeater to communicate with each other and not necessarily within 

range of each other. 

1.4.3 Uses of Leaky Feeder Systems 

Leaky feeder radio systems are used for a number of surface communications needs. 

They serve as paging and maintenance communications systems in large buildings where the leaky 

feeder is installed the entire height of the building (i.e., in the elevator shaft). Leaky feeder systems 

are also used to provide communications in highway and train tunnels that are too long for the use 

of standard antennas. 

The underground mine environment and its requirements for communications align 

themselves very closely with the capabilities of a leaky feeder system. Its many uses include haulage 

system control, maintenance personnel and equipment dispatching, production crew control and 

safety enhancement. 
TECHNICAL DISCUSSION OF LEAKY FEEDER SYSTEMS IN MINES 

Propagation in Tunnels and Mines 

As a general principal, radio waves do not propagate well through underground 

tunnels and mines at frequencies ordinarily used for communications. This fact has tended to 

frustrate the use of two-way radio in mines except over very short distances. Theoretical 

analysis typically treat the tunnel as an imperfect waveguide whose walls partially absorb and 

partially reflect incident radio energy. Propagation is therefore a function not only of tunnel size 

and dimensions, but of the electrical properties of the surrounding material. Measurements of radio 

wave attenuation along straight tunnels does show that, as in a waveguide, attenuation expressed in 

decibels (dB) varies linearly with distance. Measurements also show very large losses associated with 

corners, bends and in fact, any deviation from a straight line. Irregularities and wall roughness also 

contribute to observed propagation losses. Typical results of propagation measurements in mine 

tunnels are shown in Tables 2.1 and 2.2. Table 2.1 is based on measurements by ~oddard(~) in a 

large coal mine near Sesser, IL. Tunnels were 14 feet wide and 7 to 8 feet high with pillars running 

60 feet by 74 feet. Polarization was observed to have a significant effect. Table 2.2 is based on data 

reported by Delogne and ~ie~eois(~) for an iron mine with tunnel cross sections of 7 meters by 8 

~neters (23 feet by 26 feet). Polarization was not reported, but insofar as the cross section more 

nearly approximates a square, there should be less sensitivity to polarization. 

The total propagation loss (between isotropic antennas) is determined from both 

tables as follows: 

where 

L = total propagation loss 

Lo = fixed or coupling loss 

A = attenuation per 100 feet 

D = distance between transmitter and receiver (in units of 100 feet) 

LC = loss associated with 90 degree bend (if applicable) 
Table 2.1. Propagation Characteristics in a Coal Mine 

7 foot by 14 foot Tunnel Cross Section 

Frequency Polarization Coupling Loss Attenuation Bend Loss Approx. Range in Feet 

(MHz) (dB) (d~/ 1 00') (dB) Straight Line One Bend 

200 Vertical 65 15.0 - 480 - 

41 5 Vertical 78 6.5 35 908 369 

41 5 Horizontal 40 5.9 35 1644 1051 

1000 Vertical 65 4.3 36 1674 83 7 

1000 Horizontal 57 2.5 38 3480 1960 

Table 2.2. Propagation Characteristics in an Iron Mine 

23 foot by 26 foot Tunnel Cross Section 

Frequency Coupling Loss Attenuation Bend Loss Approx. Range in Feet 

(MHz) (d 6) (dB/ 1 00') (dB) Straight Line One Bend 
The above equation may not be valid for very short distances (i.e., D less than 100 feet). To 

understand the significance of the propagation losses in terms of the possible ranges of 

communications between hand-held portable radios, the following assumptions can be made: 

effective radiated power: 0 dBw (1 watt) 

effective receiver sensitivity: -1 37 dBW (1 microvolt across 50 ohms) 

The maximum propagation loss would be 137 dB. From this, the maximum ranges of 

communication have been determined and are shown in Tables 2.1 and 2.2 for straight line 

communications, and with one 90-degree bend included. 

The ranges shown in the tables apply to rather idealized conditions, yet they are not 

adequate for most mining purposes. In practice, ranges may be much smaller because of multiple 

bends and corners, smaller tunnel dimensions, or greater energy absorption of the surrounding 

material. A particular case in point is the experience of a longwall coal mining operation in Dante, 

Virginia. It was found that UHF portable-to-portable communications along the longwall in 38-inch 

coal was limited to about 250 feet. 

2.2 Leaky Feeder Cables 

2.2.1 Background 

The range of radio communications in tunnels can be greatly extended by the use of 

leaky feeder cables. As the name implies, "leaky feeder" cables are radio frequency transmission 

lincs that permit, by deliberate design or otherwise, external leakage fields large enough to allow 

~c.c.t~~)tion by mobile or portable receivers. Reciprocally, such cables are also able to pick up the 

t rc~nsmissions of mobile or portable transmitters, thus permitting two-way radio communications 

with other units connected or coupled to the cable. 

An early use of leaky feeder cable was made by ~alstead(~) in 1940. He used a 

specially designed cable installed in the George Washington Bridge between New Jersey and New 

York City to communicate with motorists on standard AM broadcast frequencies. A similar system 

was operated in the Lincoln Tunnel from 195 1 to 1 95d6). It was suspended at that time only 

because of concern that the radio signals might detonate blasting caps during the construction of a 

supplementary tunnel. A further development was reported in 1956 by Monk and ~inbi~ler(~), 

who attempted to use standard coaxial cable to feed a series of closely spaced antennas providing 

communications with moving trains in a long tunnel. They discovered that leakage from the coaxial 

cable alone was sufficient for this purpose; the antennas were not necessary. They subsequently 

went on to find that better coupling and greater range could be achieved with a balanced twin-lead 

cable. 
Serious interest in the use of leaky feeder systems in mines did not occur ~lntil the 

late 1960's and that primarily in Europe. Much pioneering work was sponsored by the Institute 

National des Industries Extractive (INIEX) in Belgium and by the National Coal Board (NCB) in the - 

United Kingdom. (8-18) A number of studies have been sponsored by the U.S. Bureau of 

~ines(l 9-22) and an experimental installation was made in Bethlehem Steel Corporation's Grace 

Mine, near Morgantown ~enns~lvania.(~~) To date, however, the use of leaky feeder systems in US 

mines is still rather limited. 

2.2.2 Cable Types and Characteristics 

1. Twin Lead 

Following the work of Monk and Winbigler (op.cit.) a number of twin-lead 

systems were installed for the purposes of providing tunnel communications. A popular feeder for 

this purpose was the now obsolete 200 ohm RG-86/U. The original specification covering RG-86/U 

(Mil C-1714 1, issued 195 5) was deleted in 1969. It remained available from surplus stocks for some 

time afterward, but these stocks are now virtually exhausted. However, some still remains in use. 

Advantages noted were its relative low cost and ease of installation. However, tests by the National 

Coal Board in the very wet Longannet mine in Scotland showed twin lead cable to suffcr 

catastrophically from contamination by moisture and grime, and to be very sensitive to proxiniity 

to walls and other cables. An open braided cable was eventually adapted for the Longannet mint: 

and remains the NCB preference for coal mining use. (1 8) 

2. Open Braided Cables 

Open braided cables are similar in construction to standard flexible coaxial 

cables with the exception that the outer conductor braid is loosely woven to permit a substarltial 

leakage field outside the cable. Although preferred in the United Kingdom by the NCB there is no 

known use of this type of cable in US underground mines. A similar cable is sold by Locrad, Inc. in 

the United States for use at standard AM broadcast band frequencies for highway advisory radio 

systems, Locrad cable is illustrated in Figure 2.1A. 

3. "Radiax" Slotted Coaxial Cable 

Illustrated in Figure 2. IB, Radiax is manufactured and sold by the Andrew 

Corporation. It is similar in construction to the Andrew "Heliax" cable but with a series of holes or 

slots milled into the corrugated solid copper outer conductor. It is available in boll1 112 ant1 718 

inch diameter sizes. To date, it is the only leaky feeder known to be in use in US mines. 
INlEXjDelogne system recommended by INIEX and used in Belgian mines.(4) The principles of 

tlic: \).stem are described in US patent 3,829,767 issued in 1974 to Paul Delogne. Discontinuities are 

ititroduced periodically into the coaxial cable which convert radio frequency energy from a 

nonr'ldiating "bifilar" mode to a "mono-filar" mode in which the fields travel along the exterior of 

tht. cable between the outer conductor and the walls of the tunnels. The discontinuities are created 

by the insertion of specially designed mode converters, or "radiating devices" in the cable at the 

dc~sired intervals. The mode conkperter design is adjusted to provide the exact degree of discontinuity 

rcclu~red. 

7. Alternating Standard and Leaky Feeder Coax 

Yet another technique proposed by Delogne and covered by US patent 

4,159,648 issued in May 1979 is the alternation of sections of standard nonradiating coaxial cable 

with lengths of leaky feeder cable. The length of the leaky feeder sections is determined from: 
LOOSELY WOVEN 

COPPER BRAID 

PVC JACKET 

/ / DRAIN WIRE 

A. LOCRAD NF 2 

COPPER CLAD 

ALUMINUM CENTER 

HELICALLY WOUND 

MYLAR TAPE 

FOAM DIELECTRIC TAPE FOAM 

POLYETHYLENE 

DIELECTRIC 

B. ANDREW RADIAX Rx4-3A C. "TENNAFLEX" INDUCTION CABLE 

\ 

COPPER COAXIAL CABLE SHIELD 

(FORMS RETURN PATH FOR 

RADIATING CONDUCTOR) Ad 

PVC PL 

7 / COPPER RADIATING CONDUCTOR 

LOOSELY SPIRALED AND EMBEDDE 

IN INNER SHEATH 

PVC PLASTIC 

INNER SHEATH 

D. HALSTEAD COMM/SCOPE 

Figure 2.1 . Commercially Available Cable Antenna Types. 
(718 inch diameter). 1980 prices for quantities between 5,000 and 25,000 feet were quoted at 

S I .6O/foot and $3.32/foot respectively. Prices are higher for quantities less than 5,000 feet, and less 

t'or quantities exceeding 25,000 feet. The larger size has the advantage of lower radio frequency 

~tttenuation, allowing the number of baselrepeater stations to be reduced by approximately 

one-half. For example, to equip 10,000 feet of tunnel with the 112 inch diameter cable would 

require at least two baselrepeater stations. A similar installation with the larger size should require 

only one. If the cost of a repeater station is estimated at $5,000, plus another $5,000 to maintain 

that station for 10 years, the two examples may be compared as follows: 

a. Example 1 

10,000 feet of RX4-1 $16,600 

2 repeater stations at $5,000 10,000 

Maintenance for 10 years 10,000 

Total $36,600 
b. Example 2 

10,000 feet of RX5-1 $33,200 

1 repeater station at $5,000 5,000 

Maintenance for 10 years 5,000 

Total $43,200 

These figures do not include installation costs, which are likely to be somewhat higher for Example 

2 because of the greater difficulty in handling the larger size cable. In general, the smaller size cable 

is likely to prove more cost effective in most situations. 

There are other leaky feeder cables available in the United States (Section 2.2.2) 

which have possible applications in underground mines, but none is yet known to have been tested 

in a commercial mine installation. One is Cablewave Systems, Inc. "Tenna/FlexW which is designed 

for applications similar to Andrew Radiax and has been used in train tunnels. Cost is competitive 

with Radiax. Other cables referred to in Section 2.2.2 include Locrad and Halstead. Based on 

simultaneous purchases of 6,000 foot lengths of Locrad NF-2, Halstead, and Andrew RX4-3A in 

late 1978, the cost of Locrad and Halstead were respectively 57 percent and 6 1 percent of the cost 

of the Andrew cable. Further investigation of such alternatives could possibly result in reduced 

cable costs. 

2.3 Single Repeater Systems 

The operation of a leaky feeder single repeater system is illustrated in Figure 2.2. 

The repeater base station transceiver in the center is connected to a length of cable through a power 

splitter. Typically, the cable will consist of about 5,000 feet of 112 inch Radiax. It is assumed in the 

figure that the operator of the mobile Transceiver A is speaking to the operator of the mobile 

Transceiver B. Transceiver A transmits on frequency Fl. This is picked up by the cable and 

transmitted to the repeater receiver. The received audio keys and modulates the repeater 

transmitter, which transmits on F2. The retransmitted signal propagates along the cable (in both 

directions from the repeater) and can be received by any receiver tuned to F2 and in the proximity 

of the cables. In the illustration, it is heard by the operator of mobile Transceiver B. If the operator 

of Transceiver B wishes to reply to Transceiver A, the process is reversed. Transceiver A transmits 

on F1 which is received and repeated on F2 by the repeater, which is received by Transceiver A. 

Not shown is a dispatcher's control console which can be at the repeater site or at some distance 

away from the site with wire line interconnection. The dispatcher, by direct control of the repeater 

transmitter and receiver, can monitor or communicate with all mobile transceivers using the system. 

The system also allows all mobile and portable units capable of receiving F2 and within the area of 

coverage to monitor both sides of all conservations conducted on the system. 
RADIAX CABLE (ANTENNA FOR REPEATER) 

f b ) b b b b b~,,,, 

i DUPLEXER ' f 

TRANSMIT R X 

RADIO 

FREOUENCY TX 

REPEATER 

MOBILE ANTENNA SPEAKER DISTANT 

OPE RATOR'S 

OPERATOR'S VOICE ) D wD - VOICE SPEAKER FROM 

INTO MIC 

TRANSCEIVER A 

D AUDIO SIGNAL 

) TRANSMIT FREO, F1 

t RECEIVE FREO. F2 

TRANSCEIVER B 

Figure 2.2. Single Repeater System. 
Multiple Repeater System 

A single repeater system as illstrated in Figure 2.2 might cover up to 5,000 feet of 

tunnel with 112 inch Radiax, or perhaps up to 10,000 feet with 718 inch Radiax. When more 

coverage is required, practice in North America has been to use multiple repeater systems connected 

for simultaneous operation. A typical system of three repeaters is illustrated in Figure 2.3. The 

repeat function is the same except in the way the repeater audio is handled. Any mobile unit 

attempting to transmit may be received by any one, or more than one of the repeater stations. 

Therefore, the received audio from all repeaters is returned to an audio comparator or "voting" unit 

which selects the best signal (i.e., the best signal-to-noise ratio). The selected audio is then applied 

to the common transmit line to simultaneously key and modulate all repeater transmitters. Any 

properly equipped mobile unit anywhere within range of any of the multiple repeaters can receive 

the transmission and reply to it. Further, by means of the cross patch at the console, the entire 

system can be connected to any other system either on the surface or in another area of the mine. 

2.5 Alternative Leaky Feeder Configurations 

The use of single and multiple repeater systems as described in the preceding 

sections are extensions to underground mines of well known techniques long used in surface radio 

systems. The radio equipment used is identical to that used on the surface and is therefore readily 

available and familiar to installation and maintenance personnel. In US practice, a standard base 

station transmitter is limited to about 5,000 feet of 112 inch diameter leaky feeder cable. An 

extension beyond this requires additional base stations. However, practice in other countries, 

particularly in the United Kingdom, has shown that there are a number of advantages to be achieved 

by other use of small line-powered, in-line cable repeaters. The technique is similar to that used in 

cable television technology. The principal advantages are: 

a. Transmitter powers can be greatly reduced 

b. Much greater lengths of cable can be driven from a single base 

station 

c. Signal levels are more uniform over the entire system. 

Work by the UK National Coal Board (NCB) indicates that a repeater spacing of 500 m ( 1640 feet) 

in the 68-88 MHz band allows transmitter power to be reduced by a factor of 1,000 or more (from 

watts to milliwatts) as compared to the use of multiple base stations. Even the powers of mobile 

units can be reduced by a factor between 10 and 100. The total length of a repeatered cable as in 

cable television, is limited only by the accumulation of noise, which increases by 3 dB each time the 

number of repeaters is doubled. 
1 SPLITTE R 

I 

TO e I CABLE CABLE CABLE I 

SECTION 

SYSTEM 

I 

I 

I b * L 

I 

I T~ J T~ - T~ 

I 

I 3 D - . A D- I 

CONTROL x CROSS ,. - 

CONSOLE PATCH R2 R2 R2 

b .' 

A i b b 1 . COMMON A L 

7 TRANSMIT LINE 

- - 

I *; b 

- COMPARATOR * : b 

4: h 

I 

ABOVE GROUND I UNDERGROUND 

I 

Figure 2.3. Typical Multiple Repeater Systems. 
The simplest system using in-line repeaters is the "daisy chain," illustrated in Figure 

2.4A. The transmitter and receiver are located at the opposite ends of the cable. A particular 

requirement of this system is an audio line (or other means) for returning the received signal to the 

control point. Nonetheless, over 70 coal mines in the UK are reportedly equipped with this type of 

system. 

Another disadvantage of the daisy chain is the difficulty of adding branches and 

spurs to the basic system. This problem can be overcome by the use of a double daisy chain as 

shown in Figure 2.4B. However, this system has its own disadvantage, which is the doubling of 

leaky feeder cable cost. The most desirable solution is the use of a single cable with bidirectional 

repeaters - already a well established technology in cable television systems. With good linear 

amplifier design, a number of frequencies can be transmitted simultaneously in both directions. As 

shown in Figure 2.4C, this is achieved by splitting the frequency band into upper and lower parts. 

One part is used for "up-stream" transmission, and the other for "down-stream," or transmission in 

the opposite direction. At the repeater, the up-stream and down-stream input signals are separated 

by filters, amplified, and transmitted on in their original directions of travel. 

There was not at the time of this study any US underground mine known to be 

using in-line repeaters in a leaky feeder communications system. However, it was learned that such a 

system is under development by Motorola Communications, Inc., and is scheduled for installation in 

an Inland Steel mine at Sesser, Illinois. The initial system will employ 50 to 70 thousand feet of 

Andrew Radiax cable. It will carry five channels as follows: 

1. 2 base-mobile communications channels 

2. 1 data channel 

3. 1 mobile-to-mobile talking channel 

4. 1 alarm channel. 

It is planned that this system will be in operation by late 1980. 
POINT 

TELEPHONE LINE CARRYING AF SIGNALS AND DC CONTROL SIGNALS 

BASE 

TRANSMITTER Y LEAKY FEEDER WITH ONE-WAY REPEATERS BASE 

RECEIVER IT] MOBILE SETiSl 

A. SIMPLE DAISY-CHAIN SYSTEM 

B. DOUBLE DAISY-CHAIN 

LEAKY 

FEEDER 

C. BI DIRECTIONAL AMPLIFIER 

HI-BAND FREOS. 

LO-BAND FREQS.) 

L 

HI-BAND FREOS. 

LO-BAND FREOS. 

Figure 2.4. Daisy Chain Systems. 

I 

* .' 

\' 

1; 

.I 

, i f L 

FILTERS FILTERS 

J b 
The following sections contain the data collected from seven mines. Altogether six 

mining companies controlling ten leaky feeder equipped mines were interviewed. These, with one 

other company that declined to be interviewed, represent all the companies in North America 

known to have leaky feeder systems in place and operating. At least two others had used leaky 

feeders earlier but had since discontinued its use. One of these had used a passive system (i.e., a 

leaky feeder cable only - without a base or repeater) to provide portable-to-portable 

communications from end to end of a longwall coal mining operation. It was discontinued when the 

longwall was shortened to less than 200 feet, making direct portable-to-portable contact possible 

without the cable. The other was a more conventional repeater system, but was reportedly 

discontinued because the miners rebelled against its use. 

The production figures which appear in the following sections were approximated 

from public records for the latter half of 1978 and early 1979. 
Mine Survey Findings 

Survey Data - Mine A 

( 1 ) Description of Mine 

The mine is located in the Rocky Moutain area of the United States. It 

produces approximately 4 million tons of molybdenum disulfide ore per year (with an estimated 

value of $9.8 million), using the block and cave method of mining and electric locomotive ore 

haulage. The mine has 15 miles of railroad, most of which runs underground, connecting the loading 

drifts to the processing plant. The mine uses a 13,600 VAC primary power distribution system. This 

is rectified to produce 600 VDC and 1400 VDC to power the locomotives. DC locomotive motors 

are shielded to reduce RF interference. Mercury vapor stationary mine lighting is utilized. 

(2) Total Communications System 

The mine employs several varieties of communications systems both above 

groilnd and below ground. Two-way radio is employed on the surface for the coordination and 

control of surface operations and the dispatching of maintenance crews while on the surface. A 

microwave system is used to interconnect the mine site with the processing site on the other side of 

the ~nountain. The mine also maintains its own PBX telephone switchboard and rotary dial 

telephone system for both surface and some underground communications. 

Below the surface a multichannel Gai-Tronics phone system is used 

throughout most of the mine. The leaky feeder radio system is employed on the haulage level only. 

Thc hard wired Gai-Tronics pager phone system is used only for emergency communications, and 

occasionally by repairmen to avoid loading the radio system when long conversations are needed. 

(3) Description of the Leaky Feeder Communication System 

The leaky feeder radio system, operating in the VHF (1 50 MHz) range, is 

~ltilized in the management, operation and maintenance of the underground railroad ore haulage 

system. The system layout is shown in Figure 3.1. The system consists of three subsystems. The 

first, a single repeater subsystem, services the haulage loading area. The second, a five repeater 

sitbsystem, services the main tunnel to the portal. The third subsystem services the haulage 

locomotives on the surface from the portal along a 4.0-mile surface rail system to the processing 

mill. All three subsystems are interconnected via audio cable and a receiver voting comparator. 
ANTENNA INTER-REPEATER 

CABLE GAP - 200 FT. 

MAIN 2 TRACK HAULAGE TUNNEL 

REPEATER NO. 4 REPEATER NO. 5 REPEATER NO. 6 

+ TX4 I I 

(LOADING DRIFTS) 

VOTING COMPARATOR 

LOCATED AT PORTAL CONSOLE 

(REPEATER NO. 7 IS A 

Figure 3.1. System Layout, Mine A. 
A dispatch control center (DCC) is located at both ends of the system, one 

near the loading drifts and one at the processing plant (Figure 3.2). The entire system operates on a 

single VHF transmitlreceive frequency pair, such that any mobile or portable unit anywhere within 

the coverage area can conduct two-way communications with any other mobile or portable unit, or 

with either of the two DCC's. 

The radio system is used by all employees engaged in haulage activities, 

including maintenance personnel. The primary purpose of the system is to control the loading atid 

operation of an 8 to 10 train electric haulage system. Repair functions are also coordinated by 

radio. Maintenance and rescue are secondary functions to control of haulage, and are provided only 

on an as-needed basis. Two dispatchers coordinate all operations using the radio system. A typical 

UHF repeater is shown in Figure 3.3. The antenna, control head and mobile radio used on the trains 

are shown respectively in Figures 3.4, 3.5 and 3.6. 

Haulage control communications average 1 call per minute. The system is 

used for other functions only as needed. Peak radio useage corresponds only to haulage system 

failures. This includes train failures, derailings, power failures, etc. 

It should be mentioned that the mine has had at least two haulage train 

runaway incidents. The management feels that the presence of the radios greatly reduces the 

possibility of serious injury in such cases. 

(4) Equipment Description 

All radio equipment was furnished and installed by Motorola. Currently uscd 

inside the mine are: 

6 Micor VHF repeaters (90 watts) 

50 HT 220 portables with extended speakerlmikes (5 watts) 

37 Micor railroad radios (45 watts) 

Most of the 15 to I8 miles of cable is 718-inch Andrew RX5-1 Radiax. The only exception is about 

1200 feet of 112-inch Radiax between haulageway and loading drifts. In the haulage tunnel, the 

Radiax cable is laid in a steel cable tray from which the 1400 VDC trolley (Figure 3.7) is suspended. 

Ends of the Radiax cable are not terminated, but left open-circuited. This appears to create no 

problcm because RF fields are sufficiently high inside the tunnel even at the standing-wave minima. 
Figure 3.3. UHF Repeater at the Haulage Dispatch Center. 
Figure 3.5. Railroad Style UHF Mobile Radio ~o6rol 

Head in Cab of Haulage Motor. 
Figure 3.7. Cable Trays Carrying all Cables, Including Radiax Mounted in Roof 

on the Main Haulage Tunnnel. Tray also Supports Trolley Power System. 
A 5-pair shielded telephone cable is used for audio interconnection of the 

system (repeaters, voting comparator and DCC's). This cable is laid in the same cable tray with the 

Radiax and other cables. 

(5) Procurement Background 

Procurement was initiated by the mine through inquiries made to several 

manufacturers. Only Motorola responded. Contract was a basic "furnish and install" agreement 

which included no detailed technical specifications. The system was installed between March 1975 

and May 1976. Initial performance of the system was well below expectations of mine personnel 

primarily because of noise (hum) in the audio and prolonged outages due to equipment failures 

which were aggravated by the long travel time of the service contractor. Considerable work has since 

been performed by the mine's in-house maintenance staff thereby eliminating most of these start-up 

problems. 

(6) RFI Problems 

In the initial installation an annoying 120-Hz rectifier hum was picked up by 

the audio lines running parallel to the 1400 VDC trolley line. This has subsequently been reduced to 

an acceptable level by the addition of line driver amplifiers. These increased the audio levels with 

respect to the hum pickup, resulting in a higher signal-to-hum ratio. No other interference problems 

were reported. All re-engineering and repair connected with the elimination of the interference was 

performed by the in-house maintenance staff. 

(7) Problems of the Mine Environment 

Radiax damage frequently occurs in the loading area by the blasting of 

excess ore from the top of overloaded rail cars (Figure 3.8). The blasting is necessary to ensure the 

minimum required clearance of 4 inches between the top of the loaded ore car and the trolley 

power system. The blasting causes the Radiax to be peppered with small high speed projectiles 

which either completely destroy a section of cable or penetrate enough to cause the outer 

conductor to collapse against the inner conductor causing either a short circuit or dramatic change 

in impedance characteristics. As cable is replaced within the loading area, it is being placed inside 

fabric reinforced air hose and then reinstalled (Figure 3.9). This operation is performed by inserting 

the Radiax in sections of used hose and reinstalling in the drifts. It is assumed that the lengths of 

both fabric reinforced hose and the Radiax must be kept to a manageable length. This has proven 

effective in reducing damage caused by blasting. 
Figure 3.9. New Method of Protecting Radiax in Blasting Areas, 

Installed within Fabric Reinforced Hose. 
Due to high humidity, dust and mud, all radio duplexers have had to be 

sealed to prevent continued damage to the cavity wiper arm. This was accomplished by covering all 

openings in the duplexer housing with plastic electrical tape. 

Portables have suffered a fair amount of damage due to simple abuse. Three 

have been totally destroyed within a 3-year period. Two of these were dropped into the ore crusher 

and one was retrieved from a sump pond after 6 months. Other radios suffer from cracked cases, 

damaged crystal lattice filters, etc., from either dropping or from misuse as a "hammer." A small 

number have suffered accidental water damage. 

(8) Current Level of Performance 

The system serves the mine communications needs for the haulage system 

very well. There is continuous coverage to the trains and to 5-watt portables (with helical antennas) 

throughout the haulageway, the loading drifts, and cross cuts between loading drifts. 

(9) Maintenance 

During the first year of operation all maintenance was contracted to an 

outside service agency. Subsequent maintenance has been performed by an in-house staff of one 

supervisor and six FCC licensed technicians. This staff also maintains the mine's telephone, pager 

phone, and other (surface) radio systems. It was observed that the quality and professionalism of 

the maintenance is outstanding. The shop is very well equipped with a more than adequate stock of 

spare parts and state-of-the-art test equipment. It is felt that because there are experienced radio 

personnel in the management positions responsible for radio service that the maintenance facility is 

staffed and equipped adequately. A view of the maintenance area is shown in Figure 3.10. 

Preventive maintenance and performance testing is performed every 6 

months or as a part of normal servicing. Repeaters are cleaned every 30 days. 

(10) Costs 

The initial leaky feeder communications system costs the mine 

approximately $800,000. Annual maintenance was estimated by the electrical superintendent to be 

$100,000 for all of the mine's communication systems including parts and labor. It was estimated 

that this amount breaks down into $20,000 for the leaky feeder system, $20,000 for other radio 

systems, and $60,000 for the telephone system. In view of the seven man shop, the $100,000 

estimate appears to be low. It appears more probable that the annual maintenance figure exceeds 

$140,000 with perhaps the same 20-20-60 percent breakdown. 
Figure 3.10. In-house Radio Maintenance Work Area. 
(1 1) Benefits 

This system was installed new with the mine. Because no comparison can be 

made, management can only state that production would be limited to 115 the present level because 

of a two train operating limit. MSHA now approves the 10 train ore haulage system because of the 

continuous communications system. 

Safety has been improved by the radio as it provides immediate 

communication between trains. This allows an operator to warn others of haulageway dangers, 

stopped trains or tunnel hazards. This system also allows rescue workers complete communications 

while on an accident scene, not the limited telephone communications common in most mines. 

(1 2) Attitudes of Miners and Mine Operators 

The leaky feeder system meets the expectations of management. Simply 

stated, these expectations were, and still are, to provide dependable, instant communications within 

the tunnel haulage system. It did not when it was originally installed because of reliability problems, 

limited coverage and poor maintenance. When the in-house maintenance shop was added the system 

was quickly brought up to a reasonable level of performance. Management now likes the system and 

supports it. They understand that without it, large production losses would occur. 

Management also feels most miners like the system because without it most 

would not have their jobs. Most miners feel the radio is part of their job and more than likely abuse 

the equipment only because of their lack of kncwledge of proper operating procedures. The only 

complaint of miners themselves is with failed radios. 

(1 3) Plans for Expansion 

Management expects to expand the system as haulage expands. 

Consideration has been given to the use of radios on the production levels. 

( 1 4) Management Recommendations to New Purchasers 

Management feels their purchase was correct. This was the first private 

sector mine in the United States to install such a system, and this was at a time when no b b experience" data was available. They wish they had specified more precise performance standards 

and had more in-house radio experinence before the acceptance of the newly installed system. 

49 
They feel new purchasers should contact current operators of radio systems 

to avoid the start-up pitfalls. They also recommend site visits to get a first hand feel for operating 

systems. They further recommend installing cable protection in areas where rock blasting occurs. 

3.2.2 Survey Data - Mine B 

(1 ) Description of the Mine 

The mine is located in the south central area of Canada. It produces 

approximately 684 thousand tons of potash annually (at an estimated value of $1 1.6 million). A 

continuous mining method is used employing boring machines and extensible belt ore haulage. 

Mined material is transported to the surface by the mine hoist. Entries range from 12 to 14 feet in 

height and 20 feet in width with the limitation being the availablity of larger boring machines. The 

mine employs only AC power with a primary distribution system of 13,600 VAC with reduction to 

4,160, 575, 220 and 120 VAC. Primary lighting is cap lamp with some stationary fluorescent 

lighting. 

(2) Total Communications Systems 

The mine uses a small amount of tweway radio on the surface for such 

things as security, dispatching and so on. The entire mine is equipped with a rotary dial telephone 

system installed and operated by the local telephone company. Telephone instruments below the 

surface are the only items replaced by mine personnel. The leaky feeder system is utilized 

throughout the mine. 

(3) Description of the Leaky Feeder Communications System 

The leaky feeder radio system, operating in the VHF (150 MHz) range, is 

used for general management, operation and maintenance of the mine. The system is currently 

comprised of five VHF repeaters without a receiver voting comparator. A view of one of the 

repeaters is shown in Figure 3.1 1. This system does not utilize radiating coaxial cable, but instead 

uses RG-86/U (an unshielded 200 ohm impedance twin-lead 'lossy' cable) for the radiating antenna 

lines. The system covers the primary drift areas leading to and from the major development areas of 

the mine. 
Figure 3.1 1. VHF Repeater, Wall Mounted, (Front View). 
The system is used primarily by maintenance staff and mine supervisors to 

dispatch maintenance personnel where they are needed and to aid in the timely dispatch of parts 

and other repair equipment. Nearly all transportation vehicles are equipped with mobile radios 

(Figures 3.12 and 3.13), and at one time, the extensible belt miners were equipped with remote 

control sets which allowed the operators direct access to the radio system. This has been 

discontinued primarily due to the noisy environment, but management expressed the opinion that it 

could be reimplemented at any time deemed necessary. 

The radio system augments a dial telephone system installed within the mine 

which is maintained by the telephone company. The telephone system carries most mine-to-surface 

communications. 

(4) Equipment Description 

All radio equipment was furnished and installed by Motorola. Equipments 

currently in use within the mine include: 

5 MicroVHFrepeaters(100 watts) 

27 Mocom 35 mobiles ( 1 5 watts) 

1 Consolette base station 

9 Tone remote control desk sets 

The antenna system uses 50,000 feet of 200 ohm RG-86/U in 2,000-foot 

sections. For the purposes of proper impedance matching and maximum power transfer, baluns 

(impedance matching transformers) are used. A 1 :4 balun is used to feed a single twin-lead cable 

(2,000 feet) from a standard 50-ohm coax connected to the repeater. A 1 :2 balun (Figure 3.14) is 

used to feed a double twin-lead cable (4,000 feet) from the repeater. Figure 3.1 5 shows the method 

of mounting the cable to the top of the entrance. 

(5) Procurement Background 

Procurement was initiated by the mine in early 1975 through informal 

inquiries to major radio manufacturers. Motorola was the only responding source. The contract was 

a basic "furnish and install" agreement which included no detailed technical specification. The 

system went into operation in April of 1976. The system suffered major problems during initial 

installation which were finally resolved jointly by the manufacturer's field engineers and the local 

outside service center. 
.daay a3ueuaju!eyy e 40 POOH 

aqj uo pajunoyy euuajuv AHA alAjs peoll!eu -E 1-g j 
Figure 3.15. Method of Mounting Twin-lead Antenna Cable to Top of 

Entrance, Twin-lead is to Right of Large Power Cables. 
(6) RFI Problems 

The initial system design called for inter-repeater audio to be transmitted 

over the RF twin-lead antenna lines thereby negating the necessity for installing additional 

dedicated lines from repeater to repeater to carry this audio. During preliminary testing the system 

suffered from significant audio distortion problems which were thought to be caused by this 

piggyback audio/RF design. It was therefore deleted and separate audio cables were run 

interconnecting each repeater. Continued testing proved that a circuit modification was necessary 

within the radio control electronics and that the piggyback design was not at fault after all. The 

piggyback scheme was not reinstated, however, as the separate audio cables had already been 

installed. 

(7) Problems of the Mine Environment 

The system suffers problems because of the fine potash dust emanating from 

the rotary miners and the belt haulage (Figure 3.16). Subsequent to installation, all repeater stations 

have been modified to include covers over the convection cooling vents (Figure 3.17). No cabinet 

fans are used. The accumulation of large amounts of dust reduces the efficiency of the heat sink fins 

used to cool some electronic components like power supply rectifiers, regulators and RF power 

amplifiers thus causing premature failure of equipment due to excessive heat damage. Figure 3.18 

shows two views of a repeater cabinet cleaned less than 60 days earlier. 

Mobile and portable radios suffer normal wear and abuse. The major effect 

of the dust on the mobiles is the rapid deterioration of the volume and squelch control 

potentiometers. 

(8) Current Level of Performance 

The system serves the mine's maintenance communications needs. There is 

saturation coverage in the primary entrances that are equipped with radio. 

(9) Maintenance 

The entire system has been under a maintenance contract from an outside 

repair firm since installation. Simple repeater relocations, cleaning and wiring repairs are performed 

by mine electrical personnel; all other maintenance is done by contract personnel. The maintenance 

contract calls for on-site repair of the repeaters as necessary and preventive maintenance checks to 

be performed on-site every 6 months. Repair of mobiles and other easily transportable equipment is 
Figure 3.17. VHF Repeater with Convection Cooling Vents 

Sealed to Protect from Dust. 
Figure 3.18. Repeater Cabinet Located Adjacent to the Haulage Belt 

(Radio was Cleaned Less Than 60 Days Earlier) 
accomplished by mine maintenance personnel removing the faulty unit and mailing it to the 

contract maintenance firm. This leaves vehicles without radio communications for significant 

periods of time due to long turnaround time. This tends to create the false impression that the 

entire system suffers abnormal failures and therefore is not reliable. This does not seem to be the 

case at all, but seems to have affected some miner's acceptance of the system as a viable 

communication system. 

(10) Costs 

The initial communications system cost was approximately $60,000 for the 

original equipment which included only 15 mobiles. Since then, additional equipment has been 

added as necessary. The current cost of contract maintenance is approximately $600 per month 

plus travel time and mileage if on-site repairs are necessary. No estimate of mine personnel expense 

for minor relocations and minor maintenance was available. 

(1 1 ) Benefits 

Miners and supervisors feel the system increases overall efficiency of the 

mine's operations. It eliminates the necessity to walk or drive to the nearest mine telephone to 

request maintenance personnel or to request parts and materials. This type of communications has 

been especially useful due to the extreme distances between supply depots and working surfaces. It 

is felt that personal safety is enhanced by the continual presence of the radio in most portions of 

the mine development area. 

(1 2) Attitudes of Miners and Mine Operators 

As a whole the underground workers appreciate the radio communications 

system. The major complaint with the system has been reliability of the mobile units. Although the 

failure rate does not seem exce~~sive, it is apparent that the long delay in repair sometimes gives the 

impression of a much higher failure rate than actually exists. The workers appreciate the radios 

ability to eliminate their need to walk to a communications telephone. They also appreciate the 

ability to have a radio with them at all times, which they feel increases their personal safety. The 

miners themselves do not feel that the radios are used as a management tool for overseeing their 

work but have expressed the opinion to management that they often are interrupted while making a 

repair became a foreman calls them for a second failure. Management also indicated that the men 

felt the radio made it more difficult for them to "hide", especially when the repair schedule 

becomes especially busy. Several miners have found that by turning the volume down completely 
they can eliminate these interruptions and feel that this is an acceptable solution to their problem. 

Some individuals also reduce the volume so they could not hear what they consider to be noise on 

the radio. Both of these procedures effectively disable the radio, thus seriously impairing the 

communications capability of the system. Management indicated they have instructed miners to not 

reduce the volume and that this instruction has had limited success. 

Management at the mine definitely feels that the radio system is an asset. 

They feel that the savings are substantial in both production downtime, and the cost to repair an 

individual item. Given the option, management expressed the opinion that they would like to have a 

more elaborate system, and some in-house maintenance capability. Overall the communications 

system is thoroughly accepted at this mine. 

(1 3) Plans for Expansion 

Management plans to expand the system as development of the mine 

continues. The next major expansion is expected in the very near future and will be primarily an 

extension of the existing twin-lead antenna system. Also under consideration by management is a 

suggestion by the contract maintenance firm which calls for all new mobiles purchased to be of the 

Motrac line whch are mounted in a watertight enclosure. It is felt that this would reduce failures of 

mobile radios due to the dusty environment. 

(1 4) Management Recommendations to New Purchasers 

This mine had no particular suggestions in this area. 

Survey Data - Mine C 

(1 ) Description of the Mine 

This relatively new mine is located in the northeastern portion of the United 

States. It produces approximately 370 thousand tons of coal per year (at an estimated value of 

$15.9 million), from eight working surfaces. Mining is by continuous miners and the coal haulage by 

shuttle cars and electric belt. Personnel and supply transportation is by electric rail system. Primary 

power distribution is 7,200 VAC with rectification to 300 VDC for the electric locomotive trolley 

system. Both shielded and unshielded DC motors are employed. All mine lighting is by cap lamp 

and vehicular lighting. The mine is classified as a gassy (methane) mine. 
(2) Total Comrnunica tions Systems 

A surface radio system is in use and tied into the underground leaky feeder 

radio system. Although interconnection of both systems is possible electronically, this feature is not 

used very often. The mine also has its own PBX telephone system with rotary dial capability 

extended underground. This telephone system is the main form of communications to and from the 

surface. A Gai-Tronics dial pager phone system is also in use in the mine. 

(3) Description of the Leaky Feeder Communication System 

The mine has a rather large radio system for use underground and on the 

surface. Although the underground system and the surface system may be interconnected at the 

main remote control console, they are primarily used independently of each other. The 

underground system is used almost exclusively for control of the electric rail personnel and supply 

haulage system. It is occasionally used for direct communications between the hoise operator and 

underground personnel. Peak usage coincides with shift changes and routine supply drops. 

The underground portion of the system presently employs three UHF (450 

MHz) repeaters and approximately 4 miles of Radiax. The system layout is shown in Figure 3.19. 

Repeater No. 1 is permanently located at the base of the slope with Radiax extending into the mine 

and up the slope to the portal. At the slope portal the Radiax is terminated into a ground plane 

antenna which allows access to the underground system with a surface portable or mobile radio. 

This configuration provides convenience as well as backup access to the underground system for the 

normal remote control equipment located in the hoist house. The remaining two repeaters are 

located within the main entries of the mine. The repeater system utilizes a receiver voting 

comparator located in the hoist house. The primary dispatch console (Figure 3.20) is also located in 

the hoise house. 

Although the leaky feeder systems were envisioned as playing a far greater 

role in overall mine communications when associated with a Collins MCM, the system still fills 

an important communications need in the mine. All personnel and supplies are transported 

within the mine by rail and the system serves to aid in the coordination of the rail system. It was 

reported to be extremely useful at major switching points within the rail system. It can, of course, 

be utilized in case of a mine emergency. The majority of mine-to-surface communications is 

provided by the Gai-Tronics dial telephone system. 
OMNI -DIRECTIONAL 

ANTENNA AT DRIFT MOUTH 

L ,,,,,,,- J COMPARATOR & CONTROL 

CONSOLE AT HOIST HOUSE 

Figure 3.19. System Layout, Mine C. 
1 Master control console 

1 Voting comparator 

3 UHF Micor repeaters 

10 Portable radios 

20 Modified Mocom mobiles 

The Radiax is Andrew 112 inch and is suspended from roof bolts and 

conventional cable hooks. All end cable runs are terminated in UHF yagi antennas which serve to 

properly terminate the radiax as well as extend the useable radio coverage off the ends of the cable 

to cover an approximately 200-300 foot gap between the end of one cable section and the start of 

another. 
Figure 3.21. Typical UHF Mobile Radio Package Used on Personnel Haulage 

Motors (Radio, Enclosure, Control Head and Antenna). 
(5) Procurement Background 

The mine's initial procurement efforts were oriented around the purchase of 

a Collins MCM System (Mine Communications and Monitoring System) to which Motorola was to 

supply the radio communications in a joint bid with Collins. However, the Collins MCM did not 

materialize and the mine continued to pursue the concept of a stand-alone radio communications 

system such as that offered by Motorola. The result was an abbreviated radio system. The complete 

leaky feeder radio system was supplied and installed by Motorola in early 1977 and was operational 

by 1978. Initially all underground mobiles were motorcycle type radios augmented by portables 

with converta-com units. Due to the high expense of the motorcycle radios, the mine later turned to 

the Mocom mobile radio modified for use in the mine environment as previously described. 

(6) RFI Problems 

During initial installation, standard pager phone wire was utilized to 

interconnect the repeaters, control console and the receiver voting comparator. This cable was not 

shielded and this resulted in 120 Hz rectifier hum from the trolley power system being coupled into 

the radio system audio. The problem was later corrected by the replacement of the pager phone 

wire with shielded twisted pair audio cable. No other RFI problems were reported. 

(7) Problems of the Mine Environment 

The major difficulty reported seemed to be the hearing and understanding of 

voice communications over the radio in the high noise environment created by the continuous 

miners. It was noted that mine workers refuse to use such items as hardhat headsets or lapel mikes. 

The converta-coms which were installed in the underground environment did 

not hold up well to the corrosive atmosphere. The units have since been removed from underground 

service and replaced with either mobile radios or portables which are exchanged at the end of each 

shift. 

(8) Current Level of Performance 

In the limited application for which the communications system is used, it 

performs very well. 
(9) Maintenance 

The mine performs as many of the routine maintenance functions as 

possible. This in-house maintenance includes swapping of major components with spares kept on 

site, installations and removals of mobile radio equipment, and minor preventive maintenance which 

includes cleaning and battery maintenance at 30-day intervals. The in-house maintenance staff 

includes one electrical supervisor, one FCC licensed radio technician and one telephone technician. 

The in-house staff is also responsible for the maintenance of other electrical systems within the 

mine complex including a Gai-Tronics Dial phone system and PBX telephone switchboard 

equipment. 

All comporlent level maintenance on the radio equipment is performed by an 

outside service agency under a time and material maintenance contract. The mine has no access to 

radio test equipment even though one technician is FCC licensed. It would appear that management 

considers the cost of such test equipment uneconomical in light of the current size of the system 

and its use. 

(10) Costs 

The initial procurement of communications equipment cost the mine 

approximately $78,000 and included only two repeaters underground, two remote control consoles, 

4,000 feet of radiax and ten portables. Since that time additional equipment has been added to the 

system including two additional repeaters, 15,000 feet of radiax, ten more portables, twenty 

modified Mocom and mobiles various miscellaneous hardware. The total system cost to date is 

estimated to be $150,000. These figures include equipment used in both the underground and 

surface systems. 

The annual maintenance, including in-house maintenance cost and the time 

and material maintenance contract, totals approximately $10-$17 thousand. 

(1 1 ) Benefits 

Like Mine A, the leaky feeder system was installed new during the early 

development of the mine. No comparison can be made by managemont as to effects on production 

and no direct tie to safety can be made as there have been no major incidences in which the 

communications system was needed. The single most obvious benefit is that of convenience and 

smooth operation of the electric rail system (Figure 3.23). 
Figure 3.23. Snapper, hoking and Unhooking Cars, with UHF Portable 

Radio in Upper Right Pocket. 
(1 2) Attitudes of Miners and Mine Operators 

The leaky feeder radio system meets the expectations of management. 

Management feels that operational costs are reasonable for the benefits and use derived from the 

system. Management also feels most miners that are associated with the system like the system and 

consider it useful. As with other mines surveyed, operator abuse of the equipment seems to stem 

from their lack of knowledge of proper operating procedures and cost of such equipment. 

(1 3) Plans for Expansion 

Management is reviewing the benefits of expanding the system both above 

ground and below the surface toward the working faces. 

(1 4) Management Recommendations to New Purchasers 

Management seems to feel that the purchase of the radios system even in the 

absence of the original applications was correct. 

They recommend that prospective new purchasers contact operators of 

existing systems in order to avoid procurement pitfalls and start-up problems caused by lack of 

information on the use of radio systems of this type in a mining environment. 

3.2.4 Survey Data - Mine D 

(1) Description of the Mine 

The mine is located in the southwestern area of the United States. It 

produces approximately 980 thousands tons of copper ore annually (at an approximate value of 

$88 million). A stoping mine plan is used employing drill and blasting. Ore haulage is by a 

combination of battery powered electric locomotive, diesel locomotive and hoist skip. The mine 

employs only AC power with a primary distribution system of 4,160 VAC. Locomotive motors are 

shielded to reduce RF interference. All permanent stationary lighting is mercury vapor. 

The mine can be classified as wet and has working temperatures in the 100°F 

range with humidity approaching 100 percent. Rock pressures are extremely high forcing heavy 

timbering. Due to heaving of the floor it is necessary to excavate the drifts occasionally to keep the 

rails operable. 
(2) Total Communications Systems 

This mine uses a Bell type PBX rotary dial telephone system for surface 

communications. This system is also configured for site-wide one-way paging using industrial paging 

speaker equipment. Talk-back in response to a page is accomplished either through the dial 

telephone or the leaky feeder radio system. 

(3) Description of the Leaky Feeder Communications System 

The leaky feeder radio system, operating in the VHF (1 SO MHz) range, is 

used primarily for management, operation and maintenance of the underground ore haulage system. 

Additionally it is used by production supervisory personnel, mine maintenance personnel and safety 

personnel. A system layout is shown in Figure 3.24. 

The system currently uses a single VHF repeater positioned a short distance 

from shaft No. 9 on the 3500-foot level of the mine. In addition to the normal repeater function, 

there is surface control via a remote control console operating with DC control signals. This sytem is 

somewhat unique in that it serves the communications needs of several levels of the mine, i.e., the 

3200-, 3400-, 3500-, and the 3600-foot levels. 

At the present time leaky feeder cable layout coincides with the primary 

haulage track on production levels. 

The surface remote control console is located in the mine Production 

Manager's office, although it is not manned continually as a dispatch point. The system is also used 

for some paging. The paging encoder is configured for single unit paging or group paging. This will 

allow, with the expansion of the total number of pagers, for the paging of individuals or entire work 

crews. This will depend on the makeup of the pager groupings and assignments. 

Mobiles and portables are equipped with two channels, one for normal 

repeater usage and one for unit-to-unit talkaround which bypasses the repeater. When units are 

using the talkaround channel, they are still able to receive transmissions directly from the repeater. 

The mine has undergone substantial modernization and upgrading over the 

past five years. With the sinking of a new shaft, new production areas were established utilizing a 

combination of new equipment (jumbos) and the existing haulage equipment. The primary mine 

communications underground is a dial telephone with a speakerphone system as backup. The radio 

system serves as an enhancement to general communications. It is used in the maintenance of the 

mine and operation of the haulage system. Some paging is employed. 
1 REP 

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'EATER 

35001 

! 

! -.-. -.-.-.- ENCODER 

CONTROL 

CONSOLE 

I 3200 LEVEL 

j ,.-.-.-.-. -.- 

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i I 

3400 LEVEL 1120 FT. 200 FT. 

i 

1600 FT. 3500 LEVEL 

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1200 FT. 125 FT. 175 FT. 575 FT. 3600 LEVEL ! - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . - . -. - . - . - . - 

(pRODUCTION OFFICE' - 
Several operational and component changes were made since the time the 

system was first installed. Initially the radios underground were multiple channel radios with 

features such as external microphones. These accessories were severely abused and found to be a 

major source of radio failure. The availability of multiple channels allowed individuals to change 

channels for individual communications and then make themselves unable to be reached on the 

primary communications channel. These problems are currently being solved by making all radios 

single channel and by removing the external accessories such as microphones from the portables. 

(4) Equipment Description 

All equipment was supplied by Motorola but was installed by mine 

maintenance personnel. The underground equipment complement consists of: 

1 Micor VHF Repeater 

8 Micor railroad radios 

16 Portable radios (mixed HT220's and MX330's) 

1 Multiunit portable charger 

4 Pocket pagers (Director Series) 

1 Multiunit pager charger 

Sinclair Excaliber antennas 

1 Remote control console with paging encoder. 

Views of an antenna and a mobile radio mounted on a rail motor are shown in Figures 3.25 and 

3.26. 

All of the leaky feeder cable is Andrew 112-inch Radiax. The cable is 

suspended from the roof by means of a 114-inch steel messenger cable attached by standard roof 

bolts. As originally installed the leaky feeder cable was situated a minimum of 12 inches away from 

all other power and telephone cables. Ends of the radiax are not terminated but are left open 

circuited and sealed with electrical tape. This does not appear to be a problem because RF coverage 

is sufficiently high in the desired areas of communications even at the standing wave minima. 

(5) Procurement Background 

Initial procurement investigation commenced in late 1975. Installation 

started in early 1977 with the first radios operating on the leaky feeder system in mid 1977. 
Figure 3.26. Railroad Style Mobile Radio Mounted in 

Electrical Compartment of Rail Motor. 
The procurement was initiated by the mine management through inquiries to 

the three major radio equipment manufacturers. Motorola was the only firm to respond. No 

detailed technical specification was developed and leaky feeder cable was not specifically requested. 

The resultant contract was for equipment only and the mine personnel performed all fixed plant 

cable and mobile installations following the recommendations of the vendor. According to mine 

personnel, there were no significant startup problems and the system was reported to be living up to 

expectations. 

(6) RFI Problems 

There were no RFI problems reported nor were any discovered by the survey 

team. 

(7) Problems of the Mine Environment 

Because of the extreme rock pressure, some portions of the various drifts 

must be shored, and occasionally reshored with 10" X 10" or 14" X 14" timber. When this occurs, all 

cabling must be removed from its mountings and reinstalled when shoring is completed. In many 

instances, it was observed that the Radiax and its messenger cable were not reinstalled in the satne 

manner as it was originally. A typical problem is slack or insufficient clearance between the Radiax 

and passing motors. On several occasions the Radiax became entangled with a passing motor and 

cable damage resulted. 

The messenger cable originally installed was 114-inch aircraft control cablc. 

Duc to the corrosiveness of the water within the copper mine this cable has deteriorated and broken 

in several places. Plans are to replace existing messenger with 114-inch stainless steel cable as well as 

use it for new installations. 

Due to the high humidity, water and mud, all portable and mobile radios 

must be cleaned and inspected frequently. Portables have suffered some damage due to operator 

abuse. To date, only one portable has been totally destroyed because it was dropped into an acidic 

pond. Flex antennas which are used on the portable radios seem to have a fairly high fatality ratc. It 

was felt by maintenance personnel that the antenna was simply not flexible enough to withstand 

catching of the antenna in ladder rungs, against shoring, etc. 
(8) Current Level of Performance 

At the present time the single repeater system serves the major portions of 

the haulage system very well. All main drifts are approximately 12' by 12' or smaller and the 

haulage motor operators report continuous saturation coverage. Communications into cross-cuts 

with 5 watt portables is limited to 30-50 feet on the average. Pager performance (selective calling) is 

reported to be very satisfactory for as much as 300 feet from the cable. This is likely attributable to 

the fact that tone decoding is not dependent upon voice intelligibility. 

All motor radios have been detuned and now operate with a power output of 

approximately 10-15 watts. This was done in preparation for the implementation of a new 

electronic blasting system which never materialized. However, since system performance was not 

degraded, low power operation of the motor radios still continues and it is anticipated that as the 

system expands, motor mounted mobiles will be replaced with less expensive, more versatile 

portables. 

(9) Maintenance 

All component level maintenance performed on the leaky feeder radio 

system is accomplished by contract maintenance. This contract calls for all radios, except the 

repeater, to be serviced on the surface. This contract covers only the actual radio, not accessories 

like DC-DC converters, filters, etc. 

I n s t alla t i ons, preventive maintenance routines, and antennalcable 

replacement and repairs of non-RF devices are completed by in-house instrumentation maintenance 

technicians. The instrumentation shop consists of one supervisor and six unlicensed general 

electronic technicians. This staff also maintains general mine instrumentation, a mine owned PBX 

dial telephone system used above and below the surface, the pager phone system and other (surface) 

radio systems. 

Costs 

The initial leaky feeder communications system expenditure was 

approximately $45,000 for materials only. No estimates were available for in-house labor expense 

for installation. The procurement of additional equipment, both operational and equipment 

procured for expansion in the immediate future bring the total equipment expenditure to 

approximately $84,000. Direct maintenance cost for last year totals approximately $2,300 ($580 

for in-house labor; $1,500 for contract maintenance, and $200 for miscellaneous parts not covered 

under contract). 
(1 1 ) Benefits 

Most miners and management feel production efficiency and general 

maintenance effectiveness have been improved by the use of the leaky feeder radio system. Safety 

personnel point to the radio system as an asset to the mines safety program. 

(1 2) Attitudes of Miners and Mine Operators 

When the system was first installed the miners at this mine, like others, felt 

that the radio system was just another management tool to keep an eye on them. The vast majority 

have now come to develop the attitude that the system is useful and aids in reducing their 

workload. Production supervisors appreciate the radio system as it allows them to eliminate 

substantial walking while maintaining direct communications with several of the miners they 

oversee. They feel this increases their productivity as supervisors as well as enhances the safety for 

all of the workmen. The radio system now appears to meet all of the needs of the persons using it 

and the general attitude is that it should be expanded throughout the mine to improve mine 

communications. 

(1 3) Plans for Expansion 

A second repeater and additional portables are on order for expansion of the 

system in the immediate future. It is desired to expand the cable to the stopes and development 

faces. It is also forecast that further pager operation will be implemented. 

The mine is presently experimenting with the use of the radio system for 

controlling the dumping of ore from one level to another in an effort to speed the process and 

improve safety. When ore is dumped from one level to the next (approximately 100 feet vertically) 

the person controlling the dump and the person at the level overseeing the receiving of the ore must 

communicate over telephones located away from the ore chutes. The present operation can be 

hazardous as it does not provide real time communications at the points where ore is loaded and 

received. It is felt that the radio communications would be far superior and should be implemented. 

(1 4) Management Recommendations to new Purchasers 

Management feels their purchase was correct. It is felt, especially by 

production personnel, that additional equipment should have been installed with the initial 

procurement. 
As did many other management personnel, this mine feels that new 

purchasers should contact current operators of radio system in order to educate themselves with the 

benefits as well as the problems associated with this type of communications system. 

Mine management expressed the opinion that top of the line portables are 

not necessary for the vast majority of underground operations. It is felt that the operator control 

should be at a minimum to prevent tampering, overly complicated operation and because less 

sophisticated circuitry maintenance costs should be less. 

3.2.5 Survey Data - Mine E 

( 1 ) Description of Mine 

The mine is located in Appalachian mountain range of the United States. It 

is one of several mines on the same property, all served by a single processing plant. While it is a 

relatively new mine and is in the development stages, the mine produces approximately 54,000 tons 

clean coal per year (at an estimated value of $1.19 million). It employs a room and pillar method 

using three continuous miners. The ore haulage system is electric belt with shuttle cars supplying 

feeder breakers from each of the miners. The personnel haulage is battery powered rail vehicles. 

Primary power distribution is 7,200 VAC with reduction to 575 VAC for equipment at the face and 

1 10 VAC for normal domestic equipment. No Direct Current (DC) is utilized in this mine. 

(2) Total Communications Systems 

Communications on the surface is provided for all of the mines on the 

property and the processing plant by an extensive VHF two-way radio system supporting as many 

as 50 mobiles. Underground communications in all mines on the property are provided by 

Gai-Tronics pager phone systems augmented in two mines with leaky feeder radio. The remaining 

mines use a trolley wire style radio system. 

(3) Description of the Leaky Feeder Communications 

The leaky feeder radio system operates in the UHF (450 MHz) range and is 

utilized entirely for the operation of the personnel haulage system. The system is a single repeater 

system and does not use a receiver voting scheme. A single dispatcher is located in the lamp house 

and normally controls the system through the use of a standard DC remote control unit. He also has 

the capability of interconnecting the radio system and the pager phone system such that dispatch 

functions can be done from a pager phone location. A system layout is shown in Figure 3.27. The 

UHF repeater station is shown in Figure 3.28. 
I! ! 

I I li I CONTROL i . - . - . - . - . CONSOLE 900 FT. i 

(LAMPHOUSE) I . ._._._._._._. i 

.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. - 

ODD 

2800 FT. 

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- 

GAI - TRONICS 

PAGE PHONE 

REPEATER 

Figure 3.27. System Layout, Mine E. 
(4) Equipment Description 

All equipment was furnished and initially installed by Motorola. Currently in 

use within this mine is a single UHF repeater station (70 watts) and three to five mobile radios 

(25-35 watts) mounted on rail vehicles (Figure 3.29). 

The leaky feeder cable is Andrew 112-inch Radiax and there is 

approximately 6,900 feet in place at the present time. The cable is suspended by securing it to the 

roof bolt plates at approximately 40-foot intervals, As in most installations, the cable is fed from 

the center via a two-way splitter as shown in Figure 3.30. Ends of the Radiax cable are not 

terminated, but left open-circuited. As with previous mines visited, no problems were reported nor 

seemed to be caused by this open-circuited cable. 

(5) Procurement Background 

Procurement was initiated by the ]nine through Motorola who was the 

supplier of the extensive surface two-way radio system. The mine company owns and operates the 

several mines on the property in addition to processing facilities. The surface radio system evolved 

over the years to serve this complex. Since Motorola furnished and installed this surface system, 

they were the logical point of contact to fulfill the company's requirements of underground radio 

systems. 

The initial procurement called for sufficient equipment to equip six mines 

with single repeater leaky feeder radio systems. The radio equipment in Mine E was installed in 

1978-79. Some of the mines were "short life" operations and have since closed down. One was 

recently converted to a Femco trolley wire system to provide the required man trip coverage. At the 

time of the survey, only two of the mines were still equipped with a leaky feeder system. 

(6) RFI Problems 

No interference problems were reported nor were any discovered by the 

survey team. 

(7) Problems of the Mine Environment 

The radio equipment seems to suffer a normal amount of abuse. It was 

reported that damage to Radiax bordered on the abnormal side. When this was investigated further 

it was discovered that Radiax is occasionally removed from one of the short life mines to be 
Figure 3.29. Repackaged UHF Mobile Radio for use on Mine Vehicles. 

7 8 
yy y

operationally up to standards. As for the mine actually visited, the inspection team found the 

repeater transmitter output (rated at approximately 70 watts) to be approximately 0.5 watt. Tlie 

Racliax cable, as mentioned previously, was in various states of disrepair. 

(9) Maintenance 

Maintenance of the leaky feeder radio system is presently in a state of 

suspension. Prior to this writing, maintenance had been under a time and material service contract 

to a local repair facility. There are negotiations currently under way with a new contractor in an 

attempt to procure better maintenance for the systems. 

It was reported that approximately one year ago there were 

personnel changes in the area that was both responsible for the procurement of the undergrountl 

radio systems and the administration of the maintenance contracts. Since that time there has been 

little, if any, management of the radio systems or the maintenance contracts that covered thcm. It 
Figure 3.31. Radiax, Improperly Bent and not Properly Terminated 
was reported by the newly added personnel that there are two drastic problems created by this lack 

of proper management; (I) for the last year or so nearly anyone on the property could call out the 

maintenance contractor for even the most insignificant of problems and this eventually drove the 

cost of servicing these systems upwards of $15,000 monthly; and (2) since maintenance was not 

properly overseen the system's overall performance has deteriorated to the point where upper level 

management has decided to do away with all leaky feeder systems. 

(10) Costs 

No accurate prccurement costs were available from those the team had 

access to. 

( 1 1 ) Benefits 

The main justification for the procurement of an underground radio system 

for each of the mines is that continuous communication is required on man trips by the West 

Virginia state mining laws under which this mine operates. 

(1 2) Attitudes of Miners and Mine Operators 

Until the deterioration of the system in the last six months or so, both the 

miners and management felt the system was a great benefit, enhanced the safety of the personnel 

haulage system and was generally an enhancement to the overall mining operation. The current 

attitude of the miners is one of dislike and distrust of the system. Management considers it to be 

uneconomical and totally unsatisfactory. 

It must be pointed out that the personnel now responsible for the operation 

and maintenance of the radio system feel that the leaky feeder systems have been unfairly judged in 

light of the lack of proper management and the inefficiency of the former maintenance contractor. 

They make reference to the former acceptance of the leaky feeder radio systems by the miners 

before the recent deterioration. 

(1 3) Plans for Expansion 

As might well be expected, there are no plans for expansion of the leaky 

feeder systems at the present time. It was expressed that if the systems were to recover their status 

as viable communications systems then it would be desirable to expand these systems closer to the 

working faces and possibly make additional use of the systems by equipping maintenance functions 
and perhaps supervisory personnel. However, since the mine visit, it has been learned that 

management had decided to replace the leaky feeder in mine E with a trolley wire carrier system. 

This will leave only one mine equipped with a leaky feeder system, which being a "short life" mine 

will probably continue to use the system until the mine closes down in the near future. 

(1 4) Management Recommendations to New Purchasers 

Management had no recommendations to new purchasers. 

3.2.6 Survey Data - Mines F and G 

(1) Description of Mine 

These mines are located in Appalachian mountain range of the United States. 

Each mine produces approximately 290,000 tons clean coal per year (at an estimated value of $12.7 

million combined). One mine employs exclusively conventional cut, blast and load methods while 

the sister mine employs both conventional mining in addition to two continuous miners. The coal 

haulage system is electric belt directly to the processing facility which is located approximately 114 

mile away. The personnel and supply haulage system is by battery powered rail vehicles. Primary 

power distribution is 7,200 VAC with reduction to 575 VAC for equipment at the face and 1 10 

VAC for normal domestic equipment. No Direct Current (DC) is utilized in this mine. 

Both mines are equipped with leaky feeder radio systems which are very 

much alike. Only one mine was entered and surveyed. 

(2) Total Communications Systems 

Surface communications is accomplished through a VHF surface two-way 

radio system. Mine communications is done primarily through the use of a pagephone system and is 

augmented by the UHF leaky feeder radio system. 

(3) Description of the Leaky Feeder Communications 

The leaky feeder radio system operates in the UHF (450 MHz) range and is 

utilized entirely for the operation of the personnel haulage system. The system is a two repeater 

system with a receiver voting comparator. A single dispatcher is located in the lamp house and 

normally controls the system through the use of a standard DC remote control unit. He also has the 

capability of interconnecting the radio system and the pager phone system such that dispatch 

functions can be done from a pager phone location. A system layout is shown in Figure 3.32. 

Installation of mobile equipment is shown in Figures 3.33 and 3.34. 
HARDHAT ANTENNA 

/AT DRIFT MOUTH 

/ YAGI ANTENNAS 

3280 FT. 2600 FT. 2250 FT. PLANNED EXPANSION W/DEVELOPMENT 

CONTROL 

CONSOLE 

fl 1 &INTERFACE TO 

GAI - TRONICS 

PAGER PHONE 

L ------------- A REPEATER NO. 1 

Figure 3.32. System Layout, Mines F and G. 
Figure 3.34. Photo of Rear Cab Area of Supply Motor. 

Hard Hat Mounted in Electrical Box. 
The initial equipment purchase was for a single repeater system for one mine 

in late 1976. This initial system was recently expanded in January of 1980 to include the addition 

of a second repeater and a receiver voting comparator. The sister mine was equipped with 

underground radio in September of 1979. 

(6) RFI Problems 

There were no RFI problems reported with the system. It was noted that 

due to the close proximity of the two mines (Figure 3.35) and the operation of both mine leaky 

feeder systems on the same frequency, there is co-channel (same channel or party line like) 

interference. This interference is only apparent to mobiles on the surface as both mines terminate 

the slope Radiax in a surface mounted antenna (Figure 3.36). The annoyance of this interference 

was reduced by adding tone coded continuous squelch to both systems. This effectively prevents a 

mobile from one mine from hearing signals from the other mine. 
Figure 3.36. Main Entry Portal. Hard Hat Antenna Connected to 

Radiax is on Upper Right Rail Train Shown. 
(7) Problems of the Mine Environment 

No significant problems were reported by those interviewed in relation to 

the mine environment directly. It was pointed out that because of the way in which the battery 

connections from the mobile radio are made to the rail vehicle battery casing, power cable feeding 

the radios were frequently damaged and sometimes severed completely. This would appear to be a 

simple matter of installation mechanics and more than likely could be corrected by careful routing 

of all battery power cables. 

(8) Current Level of Performance 

The present level of performance seems to be satisfactory to those in charge 

of the systems. 

(9) Maintenance 

Maintenance on the radio electronics of the leaky feeder systems is 

accomplished through outside contract. This maintenance contract is a basic labor and minor parts 

contract with. service being rendered on demand. Mobiles are routinely covered for service calls five 

days a week, 8 a.m. to 5 p.m., while repeater stations are covered 7 days a week, 24 hours a day. 

Those who are responsible for the radio systems seem satisfied with the 

maintenance service rendered. All installations on underground vehicles and minor repairs or 

changes in the cable system are accomplished by mine electrical personnel. 

(10) Costs 

No accurate procurement costs were available from those the team had 

access to. It is estimated that the procurement cost of each system was approximately $70,000. 

Since mine electrical shop personnel installed the Radiax cable the estimated labor cost was $2,000 

and the cable cost was $5,000 per repeater station. The average monthly cost of the maintenance 

contract is $400.00. 

(1 1) Benefits 

As with Mine E, the main justification for the procurement of an 

underground radio system for both mines is that continuous communication on man-trips is 

required by the West Virginia state mining laws under which this mine operates. This mine does 

however report the enhanced accessibility to repair parts from the surface through the use of the 

radio to plan and coordinate supply drops. 
(1 2) Attitudes of Miners and Mine Operators 

As is common in most of the mines visited, miners themselves feel that the 

radio system renders them too accessible to supervision and management. They do not apparently 

abuse the equipment and of course recognize that it is a state mining law requirement. 

(1 3) Plans for Expansion 

The company plans to expand both systems as the main entry advances with 

the working surfaces. At the present time this primarily involves the addition of leaky feeder cable 

to the inner most repeater in the older mine. A second repeater for the sister mine (originally 

equipped in 1 979) is now in the planning stages. 

(14) Management Recommendations to New Purchasers 

Management felt that the experiences derived from several years of using 

their surface system better equipped them to cope with the procurement and operation of the 

underground systems. They recommend that new purchasers gain as much exposure to radio 

systems and especially mine oriented radio systems as is possible. 
4.0 CONCLUSIONS 

4.1 Summary of Leaky Feeder Use and Justification 

There were a total of six mining companies visited and interviewed. These companies 

controlled, at the time of the interviews, ten mines in which leaky feeder communications were 

employed. Adding one mine that declined to be interviewed, these represent all the mines in North 

America using leaky feeders which could be found through queries of communications equipment 

suppliers and of other leaky feeder equipped mines. A summary of the communications systems 

used in these mines is given in Table 4.1 . 

It is concluded from the survey that the use of leaky feeder communication systems 

in North America has been limited and has been primarily the result of legal requirements. Two-way 

radio communications are required on all underground rail systems in the state of West Virginia, and 

have been required in other areas if more than one vehicle was to use the rail system at any one 

time. Given the requirements for two-way radio communication, the leaky feeder system was 

adopted at several mine sites. Other rnines adopted the leaky feeder system solely on the 

recommendation of their communications equipment suppliers or to keep the underground system 

1 compatible with existing surface radio systems owned by the company. 

Other rationale for installing two-way radio communications systems underground 

include reduced mine maintenance costs reported by a large Canadian mine through better use of 

their mechanics and perception of increased worker safety through the use of two-way radio. The 

mines have considered the expense of the radio systems with a cost of doing business (West Virginia 

mines) or a definite asset in terms of production and labor cost savings. 

Bezause the use of two-way radio communications is not common underground, the 

variety of potential radio uses have not been entirely explored. Radio systems are primarily used as 

management tools for communication with workers in remote locations, and for traffic control on 

rail systems or haulage ways. The most common use of two-way radio communications 

underground utilizing a leaky feeder cable has been for the direction of traffic on railway systems. 

Use of the leaky feeder system allows continuous communications between rail vehicles and with a 

dispatcher. This eliminates the need for rail vehicle operators to leave their vehicle to visually check 

each intersection prior to passing it and to coordinate and time vehicle movements so that they do 

not inhibit each other. Use of the leaky feeder communication system has provided effective 

communications on alnlost all rail systems employing it, and has allowed at least one to increase its 

haulage capacity up to five times. 
Table 4.1. Communications Systems Summary 

Descriptions 

Type of mine: 

Hardrock 

Coal 

Surface Communications: 

Two-way radio 

PBX Telephone (mine owned) 

Underground Communications: 

Pager-phone (no dial) 

Pager-phone (dial) 

Leaky feeder radio system 

Radiax cable 

Twin-lead cable 

Radio paging via Leaky Feeder 

Carrier Current Radio system 

PBX Dial telephone system 

Characteristics of Leaky Feeder Sys: 

Multiple repeaters 

Receiver Voting scheme 

Hardwire Repeater interconnect 

1 50 MHz band 

450 MHz band 

Type of Radio Equipment used: 

Standard radio repeater 

Standard mobile radios 

Railroad mobile radios 

Repackaged mobile radios 

Portable hand-held radios 

Radio pagers 

Maintenance: 

I n-House 

Contract 

Contract with in-house support 

Mines 

A B C D E F G TOTALS 

X X X 

X XXX 

XXX XXX 

XXXX 

X XXXXX 

XXX X X 

X X X X 

X X X X X 

X X X 

X XXX 

XXXXXXX 

X X X X 

X X 

X X 

X X X 

X 

XXX 

X X X 
A second use of the leaky feeder communication system underground has been for 

supervision of mechanics and production workers. Use of the radio eliminates the need to travel to 

remote locations or rely on pager phones for communication with workers. Mechanics and other 

production personnel that travel throughout the mine are much easier to locate using the radio, 

saving substantial amounts of "travel and location" time. Although several mines have found the 

leaky feeder communication system desirable from an operations viewpoint, there have been some 

substantial problems with installation and use of the systems. 

Only one of the mines surveyed used radio between the mine foreman at each 

working area and the individuals responsible for haulage. A better coordination between various 

faces and the haulage system can ease production bottlenecks due to haulage limits as well as 

increase worker safety by coordinating remote operations that affect a wide area of the mine. 

4.2 Procurement Practices 

It was observed during the survey that a number of problems could be traced to 

procurement practices. Basically, procurement of leaky feeder systems were initiated without a 

complete understanding of the capabilities or pitfalls of such systems, and without adequately 

defining the needs to be satisfied. It was found that: 

a In-house technical expertise was generally nonexistent or 

simply not sufficient during the planning and/or procurement 

stages of the system. 

a Investigation of available equipments and sources for 

assistance was inadequate before procurement. 

a The actual procurement was, in all cases except one, 

executed without the benefit of comprehensive technical 

specifications or even performance specifications by which 

the end product could be evaluated. 

Procurement under these conditions can be the root of subsequent difficulties such 

as disappointment with the system's performance and costly system reengineering to correct 

original design deficiencies. 
Installation Practices 

The design and installation of the systems reviewed for this project indicatc a wide. 

variation in concern for maintenance and durability. Few systems have been specifically designcd 

for the extremely rugged environment and the rough handling received by the untrained irscrs. 

Although several systems were installed in locations that afforded the radio protectioll fro111 falli~lg 

objects and physical abuse, accessory components such as microphones and speakers w~~rc. 

substantially less protected. Several locations used hard-hat type antennas designed for SCVLII-L~ 

service. While these antennas were installed to provide antenna system protection, tlie a11 ten lla lcact:, 

were routed over open areas of the equipment, exposing them to severe damage slid abusc. SLIL-li 

inappropriate installations indicate a lack of awareness by the installer of the potential for ~~LIS' 01- 

simply a display of "lack of effort." It is also apparent that several installations were made wit11 no 

concern for ease of maintenance. Radios were installed in locations difficult to reach or in ~11ill a 

manner that they require a significant amount of work to remove. If the radios wcre inst:rllccI ill 

such a way that they could be quickly changed out, spare radios could be installed wllile rCp:r~rs 

were being made. Such a scheme would improve the apparent reliability of the systems by making 

them available for a greater percentage of the working hours. Other problems with tllc r:rdio\ 

concern their basic design. 

Repeater station installations could also be improved by providing niort: SLI bsta~i t ILII 

cases with improved dust filtering capabilities. Many installations reviewed indicated a nccd for 'I 

cabinet which could withstand limited roof falls as well as provide clean cooling irii-. C':11)1c> 

installation and hanging techniques also varied widely by installation. 1 t is apparcn t t li:i t 111 ariq 

individuals installing the cables did not know how to correctly install the systc~n or IiLld 120; 

considered the possibility of physical abuse. The best installation technique wa:, to iidng tllc i;ilil~l 

from the mine roof using plastic wire ties which would give under the load of \niall root' i';rlls 

without causing damage to the cable. This system is rarely used. Cable termination ttxl~~licl~~~s :rl\o 

varied widely but without a noticeable effect on system performance. One area wl~erc in:rppropr~iltc* 

technique did display a substantial degradation of system performance was in cablc ~pl~i~tly 01 

repair. 

4.4 Maintenance 

Only one of the mines surveyed had a complete in-house ~naintenanic capabil~t). 

Others depended wholly or partially on contract maintenance by an outside radio stlop. 'I ~TL>C 01 

the mines did routine repairs and replacement of defective components depending otl all ou t.~tlc 

shop for troubleshooting and repair of the defective components replaced. One I~III~C 1101 011ly 

depended wholly upon outside maintenance but exercised no coordination over calis for \c>rvlc'C. 

Any miner could call for service even for the replacement of a microphone. This rliine c.onipl~~~~lc~~l 

of exorbitantly high maintenance bills and yet the maintenance of its leaky feeder systc111 wa:, 

judged to be the poorest of all those surveyed. 
It is concluded that active participation of properly trained mine personnel in the 

maintenance functions is virtually a necessity. A complete in-house maintenance capability may not 

be cost effective for a small operation. However, there appears to be a great advantage in assigning 

one or more radio trained mine employees responsibility at least for routine maintenance and 

component replacement level repairs. The maintenance contractor can then be limited to the repair 

of defective components and for on-call service when required by the in-house staff. 

Training 

It was found that without exception all mines were deficient in the proper training 

of personnel who were to either use the radio system or be affected by its usage. This lack of 

training contributes directly to many problems experienced by those surveyed. Several of these 

problems are: 

Inefficient implementation of the entire system 

Improper usage of the system 

Abuse of the equipment and thus higher maintenance costs 

And occasionally, nearly total rejection of the new system by 

miners and/or mine supervisors. 

Some systems are fairly complex in their operation. Therefore, lack of instruction 

on the simple operational characteristics of the system can cause operators to assume a system 

malfunction when in fact the problem may be operator error. This applies equally to the mechanical 

operation of a piece of radio equipment itself. 

Upper levels of mine management do not always take into account the fact that 

many of their miners may look upon the system as just another piece of equipment to carry. Also it 

is often viewed as another management trick to spy on their everyday movements and work 

efficiency. Much of this attitude can be attributed to lack of understanding of what the system is 

intended to do, both for the benefit of the miner as well as the mine owners. 
4.6 Miner Attitudes and Acceptance of Radio Communications 

The effectiveness of the communications systems has been severely hampered at 

several locations due to inadequate understanding by company personnel of the requirements for 

the installation and maintenance of the systems. Initial startup problems characterized by repeated 

system failures was common at most sites visited. This severely hampered the effectiveness of the 

systems due to the negative impression it left on the system users. At several locations the system 

was not reliable enough to be used for management functions or traffic control without a backup. 

This led to a very poor acceptance of the system by the workers as well as management. Only after 

several months of system use and improvements in the in-house maintenance capability have these 

systems grown to be tolerated by the workers and management. For the average installation it took 

approximately one year for the system to become fully functional, both from a reliability and 

worker acceptance standpoint. Another major problem with the use of the leaky feeder systems has 

been a lack of understanding by both management and workers of how to use the system and its 

actual capability. 

Very few leaky feeder installations are being used to their full extent by the mines. 

Each firm has a specific preconceived use for the system and has not explored other possible uses. 

In most cases the system user has not been trained in the use of the system, nor does he understand 

its primary function. This lack of training has hampered the startup of several systems as a result of 

individuals resisting its use or failing to use it properly. It is apparent that the usefulness of almost 

any leaky feeder system visited could be substantially improved through an employee and 

management training program in which proper radio use is explained, and samples of potential uses 

for the radio presented. Education should also reduce the abuse the systems receive. 

Because the radio systems reviewed during this project have been unable to cope 

with "normal" underground abuse, miner attitudes towards these systems have been significantly 

influenced. Many radio failures have been and are likely to continue to be compounded by miner's 

attempts to "repair" radios by banging them on a hard surface. This sometimes works (by 

improving conductivity of corroded battery or volume/squelch control contacts) thus encouraging 

this behavior. However, the net result is degradation and eventual damage which then reinforces the 

attitude that the radio system is not appropriate for underground use. Few workers understand the 

sophistication of the system and do not comprehend its cost. In mines where the maintenance and 

training functions have been best, worker acceptance of the system has been best. It is apparent that 

these are related factors. 
Although only one mine could show an increase in production directly attributable to the radio 

system, the other users also felt production was i~~crease;I in the one case, the mine considered that 

the radio made it possible to increase production fronl an annual gross of about $2 million to nearly 

$10 million. This was accomplished by a capital i~lvestrnent of $800,000 and an estimated annual 

maintenance cost of about $25,000. This increase in production is a direct result of the greater 

number of trains that can be operated on the same track because of a continuous communications 

capability. Other mines reported that benefits were realized because of improved haulage, supply 

delivery and repair. 

Improvement in haulage efficiency attributed to the radio system is the result of 

improved load-haul-dump cycle timing, reductions in accidents, and increases in the number of 

haulage vehicles. Use of the radio system has allowed itnyrovement in the load-haul-dump cycles of 

several haulage systems by improved timing, which reduces waiting time for loading or dumping. By 
having the haulage vehicles amve at the production loading area when material is ready to be 

loaded, and not having to wait to be loaded or not having the capacity to "keep up" with 

production, fewer vehicles are required. Not having to slow production to wait for haulage vehicles 

allows more ore to be mined with fewer vehicles. At one mine visited the production foremen were 

in radio contact with the rail haulage vehicles at all times, and could always know when they would 

return to be loaded. This allowed the foremen to adjust the mining cycle to match the capability of 

the haulage system, eliminating nonproductive waiting time. 

No accidents were reported on haulage systems employing radio communications. 

These mines did report accident histories prior to radio installation. The reduction in accidents 

directly increased production. At one mine this saving, or more realistically, increase in production 

was substantial. Accidents prior to the radio system installation stopped production for an average 

of 14 days. With the current production rate of 50,000 tons per day the annual production of the 

mine has increased approximately 700,000 tons per year due to accident reductions. 

Production increases and cost savings have also resulted from use of the radio system 

to order supplies and repairs. The use of the radio system has demonstrated significant savings by 

allowing supply orders to reach delivery vehicles prior to arrival at working areas. Changes or 

additions to the order do not need to be made after the supply vehicle reaches the working area, 

often allowing substantial savings in the required travel distance and time needed for the additional 

items. 

Maintenance costs can also be reduced through the use of the radio. Accurate 

descriptions of the failure and failed parts can be given to mechanics at a remote location while 

looking at the machine needing repair. This eliminates the need to remember the failure or parts 

from a fixed phone to the machine to describe failed parts and systems. The mechanic can help the 

person on the machinery troubleshoot the failure, often eliminating the need for him to travel to 

the broken machine. This improved communication also allows the mechanic to bring the needed 

parts and tools to the scene, without first going there to identify the problem. At one mine the 

savings in maintenance cost and an increase in production due to improved machine availability has 

paid for the radio system many times. 

Intangible Benefits 

This subject deals with question 2 in Section 1.1. Although no systems were 

purchased solely for the purpose of mine safety, nearly everyone interviewed at each mine agreed 

that worker safety was enhanced by the radio. The users felt that the radio would allow faster 

response during mine emergencies, as well as allow redirection of effort as conditions change in an 
emergency. The radio also serves as a backup communications system where other systems, such as 

telephones or pager phones, have failed. Safety aspects of the system have been the consideration 

for the establishment of laws requinng two-way radio communication. Personnel interviewed at the 

mines indicated that the radio reduces the probability of intersection collisions of rail and rubber 

tired vehicles. The radios allow communications between vehicles at intersections as well as allow 

warnings in the event of a runaway vehicle. 

Some radio system users have installed leaky feeder cable to remote locations where 

a single person or small crew works. This allows these individuals to work in a complete contact 

with supervisors or other crews away from their immediate area. A simple call to these people by a 

supervisor confirms whether or not an unusual condition exists. The radio also allows the remote 

person to relay requests for assistance. 

4.9 Alternative Forms of Communications 

Question 3 in Section 1.1 deals with alternatives to leaky feeder communications. 

The capabilities of leaky feeder communications are actually those of mobile radio 

communications, the principal advantage of which is the freedom of movement without loss of 

communications. Leaky feeder is merely a scheme for increasing the effectiveness of mobile radio in 

an environment which would otherwise severely limit range. Other schemes may exist. 

An alternative to leaky feeders is the trolley wire carrier current system. It provides 

continuous communications to moving trains or vehicles through either a trolley wire or a special 

dedicated single conductor line. Conventional trolley wire systems are limited to communications 

between dispatcher and vehicle. Improved wireless systems available from major suppliers may make 

vehicle-to-vehicle communications feasible. However, the relatively large (typically 42-inch) 

coupling loops required for wireless trolley phones may limit the development of convenient 

personal portable units for use with carrier current systems. 

The only true alternative to leaky feeder communications would be another means 

for enhancing radio propagation in underground mine tunnels, facilitating the use of mobile radio. 

No such alternative is currently known to be in commercial use, though the possibility of its 

development is not ruled out. For example, a U.S. Bureau of Mines sponsored system using passive 

reflectors to enhance propagation in a room and pillar mine is currently being evaluated in Black 

River Mine in Kentucky. 
RECOMMENDATIONS 

For Mine Owners and Operators Considering the 

Use of Underground Radio Communications 

(1) Radio systems require planning. Management should acquire information on 

both the capabilities and limitations of radio systems from suppliers and from other mines with 

operating systems. If possible, a responsible representative of management should visit a mine 

already equipped and personally observe operations. Before proceeding with procurement, 

management should have prepared a performance specification defining exactly what the system is 

to include and what it is expected to do. This document can be prepared either by a technically 

qualified in-house staff member or by an outside consultant, but should not be left up to a potential 

supplier. Subsequently , the document can serve as a basis for procurement and installation. 

Incorporated into the installation contract, it will provide a reference against which actual 

performance can be compared. 

(2) Radio sys tems require management. Without an individual in a management 

position pushing for and overseeing the radio system it is doomed to failure. In systems observed 

where the performance was exceptional, there was always an individual who felt that he was 

responsible for the system and who had an interest in its best performance. Without a person of this 

type on the staff or with this responsibility it is unlikely that a highly complex and technical system 

will be able to meet the demands of a harsh and abusive mine environment. Further, all leaky feeder 

communications system users should have an in-house radio technician or an engineer familiar with 

radio systems. While an in-house maintenance and repair capability is desirable, it is often 

economically not feasible. In such a case it should be a requirement that some management level 

personnel in the organization have a radio background or the necessary knowledge to properly 

oversee outside contract personnel. Without this, performance will suffer and maintenance expense 

is likely to run higher than necessary. 

(3) Radio systems require maintenance. In several instances, it was found that 

the maintenance function was left to mine electricians who did not fully understand the radio 

system and thus provided poor maintenance. It is crucial that the maintenance of the system be 

performed by radio technicians with a knowledge of mining and its unique environment. Systerns 

with good in-house capability were without exception the best systems studied by the project team. 

Certain of the mines where a good in-house capability existed were able to make modifications to 

the radios to counter several of the maintenance problems described earlier. Frequency selection 

capabilities were removed, remote microphone capability eliminated, and the radios reduced to 

simply having an on and off switch with volume control. Several mines indicated that the less 

expensive and less complex portable radios provided the greatest reliability and performance. 
(4) Users of radio equipment require training. All underground personnel 

including supervisors should be thoroughly trained in proper radio use, radio communication 

etiquette, and operational procedures. Without thorough training of the entire underground work 

force the radio will be severely limited. Every individual with access to the system should know how 

to use it, when to use it, and its potential value to him. Because many workers in the mining 

industry are skeptical of management goals, the system's benefits to them should be highlighted. 

This would increase the acceptance of the system and improve its reliability by a reduction in 

physical abuse. Many individuals do not understand the radio system and fear that they will look 

strange to their fellow workers if they show ignorance of its use. This feeling should be eliminated 

and the miners made to feel as comfortable using the radio as they would using paging phones or 

any other communication system. The training for all personnel underground should also include a 

review of the system components, what they do, and how much they cost. The need for this 

training was recognized at almost every mine visited yet little was being done to rectify the 

problem. 

5.2 For Bureau of Mines Sponsorship of Activities Leading 

Toward the Lowering of Cost or Increasing the Benefits of 

Leaky Feeder Cables in Underground Mining 

The recommendations that follow are a response to the fourth question listed in the 

beginning of this report. A lowering of cost does appear feasible as does an increase in benefits 

achievable with leaky feeder systems. 

(1) It is recommended that alternative cable designs be investigated with a view 

toward reducing cable costs. The most expensive single item in leaky feeder systems is the cable. 

Many designs have, in fact, been studied and no investigation should be conducted without 

reference to the literature on this subject. Nonetheless, a would-be user has a very limited choice of 

commercially available and proven designs. The investigation should include comparative tests in a 

mine environment of various designs, including designs and techniques used in other countries. 

(2) It is recommended that some Bureau of Mines sponsored entity be 

established for the provision of training and the exchange of in formation relating to 

communications and perhaps other mining technology. In a recent report by John Short and 

~ssociates(*~) the creation for coal miners of an "extension service" patterned after the agricultural 

service now provided for farmers was recommended. Among the services the extension service 

would provide are guidance for training in mine productivity, safety and health and a means for the 

exchange of technology in the mining industry. This concept is endorsed with the proviso that the 

exchange of technology include radio communications technology, and that training include the 

operation and use of radio equipment. 
(3) It is recommended that support be given to the further development and 

improvement of bi-directional line-powered cable anaplifiers (or in-line repeaters) for undergro~rrrd 

mines. Equipment of this kind is being developed and is available from U.S. and foreign suppliers. 

Advantages to be achieved are the elimination of multiple base station repeaters and their 

interconnecting audio and power lines, the reduction of required base station RF power and the 

reduction of RF power required of mobile and portable transceiver units. Ruggedness, reliability, 

intrinsic safety, and reasonable cost should be prime objectives in the development effort. Another 

consideration should be the use of frequency bands, such as 800-1000 MHz, known to have good 

propagation characteristics in tunnels but which are not currently used in underground mines. Full 

advantage should be taken of the existing cable television technology (6 to 400 MHz) and European 

daisy chain repeater technology (mostly 68-88 MHz). 

(4) It is recorninendell that thc development of prototype mobile and portublc 

transceivers for underground use be urzdertuken. In some mines surveyed extensive modifications to 

equipment designed for surface use had been made. In all mines the reliability of mobile and 

portable transceivers suffered in the mine environment. Emphasis should be placed on simplicity, 

ruggedness, and intrinsic safety. Units sllould be single-channel and contain an absolute minimum of 

controls and switches. Used with a system of in-line cable amplifiers the transceivers would require 

RF power outputs considerably less than one watt. The ultimate objective should be that no miner 

is ever out of voice contact. An ideal for a miner's portable might be the equivalent of a very rugged 

pocket pager with talk-back capability. 

(5) It is recommended that the Bureau of Mines sponsor the development of'a 

'>ecomrzzended practices" document for thc design, installation and operation of ~rndergrozrrzd 

leaky feeder systems. The mine survey revealed a wide variability in the installation and use of leaky 

feeder systems and uncovered a number of poor practices, many of whch had already been found 

and corrected by the mines in question. For example, one mine which had employed aircraft 

control cable as a messenger (i.e., supporting cable) for leaky feeder was forced to replace it with 

stainless steel because of the corrosive mine environment. The document should cover possible uses 

and design configurations, installation practices for cable, installation practices for fixed and mobile 

radio equipment, recommended operating procedures and recommended maintenance procedures. 

The purpose of the document would be to provide guidance to mines which are considering the use 

of leaky feeder communications or which may be seeking to improve systems already installed. 
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