UNITED STATES DEPARTMENT OF THE INTERIOR 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Rogers C. B. Morton, Secretary 

BUREAU OF MINES 

John D. Morgan, Jr., Acting Director 
1. Communication. 2, Mines and mineral resources-U.S. 3- 

Mining engineering. I. Bureau of Mines Technology Transfer 

Seminar, Bruceton, Pa., 1973. 11. U.S. Bureau of Mines. III. 

Title. (Series) 

TN23.U71 no. 8635 622.06173 

U.S. Dept. of the Int. Library 

. 
CONTENTS 

Page 

Abstract .................................................................. 1 

Introduction .............................................................. 1 

Acknowledgments ........................................................... 2 

~mergency/~on-~mergency Mine Communicatiorls. by Howard E . Parkinson ....... 3 

Roving Miner Paging. by Richard H . Spencer and Howard E . Parkinson ........ 17 

Two-Way Communications With Face Machine Operators. by Robert A . Bradburn 

and Howard E . Parkinson ................................................. 36 

Two-Way Communications With Roving Miners, by Robert L . Lagace and 

Howard E . Parkinson ................................................... 46 

Interconnecting New Communications to Existing Systems, by Dean Anderson, 

William Stout, and Howard E . Parkinson .................................. 73 
MINE C0MMUNIC:AT IONS 

Proceedings: Bureau of Mines Technology Transfer Seminar, 

Bruceton, Pa,, Marctl 21 -22, 1973 

1 / Staff-Mining ResearchA BST RACT 

The Technology Transfer Seminar on Mine Communications held on 

March 21-22, 1973, at the Pittsburgh Mining and Safety Research Center, 

Bruceton, Pa., presented information about recently developed equipment, 

instruments, and techniques for use in mine communications systems. All 

of the basic ideas presented in the fine seminar are operational in the 

Bureau of Mines Safety Research Mine in Bruceton. 

INT RODUCT 

The mine communications research program at the Bureau of Mines, in its 

present form, was initiated in 1970, and irlcludes research projects encompassing the field of mine communications and monitoring. 

The Bureau of Mines initiated in 1972 a program aimed at solving some 

of the problems associated with transferring technology from the developer 

to the user. The technology transfer program is an intensive, active, and 

vital Bureau effort to shorten the lead time required for newly developed or 

improved technology to make its way from m:ining laboratory to mining practice, 

One mechanism by which the Bureau helps speed transfer of technology to users 

is through the conduct of topics seminars which are attended by mine operators, equipment manufacturers, union representatives, and others interested 

in new mining technology. 

Significant advances in mine comm~ni~cations have been made by the 

Bureau of Mines and its contractors. Sincie the inception of the program, 

new and improved means of communication between men on the surface and 

underground have resulted. Many of these advances are reported in this 

publication, which presents the proceedings of a seminar held at the Bureau's 

Pittsburgh Mining and Safety Research Center on March 21-22, 1973. 

- 11 Additional information may be obtained by writing the Bureau of Mines, 

4800 Forbes Avenue, Pittsburgh, Pa. 15213, Attention: 

Howard E. Parkinson. 

EMERGENCY/NONEMERGENCY MINE COWNICATIONS 

by 

Howard E. Parkinson 1 

ABSTRACT 

The Federal Bureau of Mines has developed new and improved means and 

methods of communicating from the surface: to the underground areas of mines, 

thereby strengthening and extending existing telephone line and trolley 

wire communications in those areas where the needs are greatest. 

New forms of audio and carrier equipment make use of the mine roof, 

overburden, power cable pilot wires, and phone lines as means of interconnecting equipment for paging and two-way voice communications. 

Entries, crosscuts, and special cables are also used to propagate UHF 

radio, UHF repeater and base station concepts strengthen the system and 

extend wireless radio operating range. 

Emergency communication equipment is intrinsically safe, battery 

operated, and connected with more than one signal path between the underground and surface. Attention is given t:o personnel safety, mine monitoring, increased communication effectiveness, trapped miner location, and 

cost-effective alternative schemes, 

New and improved mine communication concepts, extended to satisfy 

emergency requirements, are being readied for testing in the United States 

Steel Robena No. 4 mine near Waynesburg, Pa. 

INT RODU CT ION 

Mining is a team effort which depends upon communication for its 

effectiveness and safety of operation. Members of the team in a mine 

such as that depicted in figure 1 communicate with each other mostly 

face-to-face, but communication equipmen,t is required to provide communication channels between the in-mine and surface members of the team. 

This equipment traditionally consists of mine telephone and trolley wire 

communication systems. However, the sys,tems in their present configurations are becoming increasingly inadequ.ate under modern mining conditions. 

1 

Supervisory electrical research engineer, Industrial Hazards and Comunicat ions, Pittsburgh Mining and Safety Research Center, Bureau of Mines, 

Pittsburgh, Pa, 
The Bureau of Mines is actively conducting studies, research, experiments, and demonstrations to develop new or improved means and methods to 

solve communication problems between the surface and the underground, and 

within the workings of mines. These efforts have identified solutions to 

the problems, solutions that can be implemented by modifications to existing communication systems. Our general approach to identifying solutions 

involves six types of effort. 

1. Apply Off-The Shelf Equipment. - We have concerned ourselves with 

a direct approach. We have procured communications equipment that 

will solve- immediate mine communications problems. his- equipment has been installed in the Bruceton Safety Research Mine so 

that it may be demonstrated to the mining industry. 

2. Establish Future Requirements and Equipment. We have begun conducting studies into future requirements of underground comnications and the availability of modern communication equipment that 

will satisfy these requirements. 
3. Measure Signals and Noise Prop~erties. - We have begun a series 

of experiments to measure in-mine electromagnetic noise, to measure the electromagnetic properties of the coal and overburden, 

and to measure electromagnetic wave propagation in entries, 

crosscuts, the roof, and through the overburden. 

4. Demonstrate Major Systems in Operating Mines, - We have planned 

for at least three major demonstrations, in operating mines, of 

whole-mine communication systems designed to provide both 

operational and emergency communications, These will be cooperative efforts of the mining operators, the Bureau of Mines, and 

the miners. 

5. Establish Groundwork for Equipment Standards. - We have set out 

to study the technical requirements for mine communications 

equipment. The results of this study will lead to the development of industry standards that will assure the mining industry 

that communication equipment suppliers will provide equipment 

that will satisfy operational requirements, be tough enough to 

withstand the harsh day-to-day environment, and provide instant 

communications during an emergency. 

6, Develop Special Products. - We have begun a product-development 

program directed toward special products designed to satisfy 

particular requirements unique, to mine communications. These 

products will be extensively evaluated in operating mines prior 

to finalizing designs that can! be used by the suppliers to the 

mining industry. 

NEEDS AND ALTERNAT WE SOLUTIONS 

The results of the ~ureau's work h~ave been many and varied. Here 

we describe briefly six mine communicat,ion needs and the methods that we 

have found promising for meeting them. 

Reduce Traffic Overload Need. - Mines have been expanding, and some 

now have 20 or more operating sections, all of which work with the same 

production team on the surface. This frequently leads to heavy communications traffic demands and traffic overload (fig, 2), whereby important 

messages are delayed or even fail to get through. 
the shift maintenance foreman on the surface, and vice versa. This extra 

circuit can be added to each section to provide a private line for use 

by the section foreman. A battery-operated permissible 61-kHz trolley 

wire phone is presently in use on a telephone line in the Safety Research 

Mine to provide additional circuits. Special telephone-grade carrier is 

now being investigated, and it is anticipated that telephone-grade 

carrier will be less expensive than the trolley line carrier. 

When interconnected with an ultra-high-frequency (UGF) radio centrally located on the section, this carrier telephone placed on the 

telephone line can provide a private line between the shift foreman on 

the surface and a roving section foreman equipped with a small two-way 

handy talkie radio as depicted in figure 3. 
FIGURE 4. - Need: Reliable call alert to key personnel. 
one-turn loop of wire wrapped around a pillar. The alert signal can cover 

a typical mine section. The section foreman or maintenance man has a 

special electromagnetic pocket receiver that receives the call alert. 

The call alert pocket receiver is energized only when the section foreman or maintenance man is wanted on the phone. To answer the call alert 

he walks to the phone. 

There is also an emergency feature available for this system. In 

emergencies the call alert signal can be keyed fromthe sections and will 

penetrate the mine overburden, thus reaching the surface. Similarly 

the call alert receiver will receive audio frequency emergency signals 

transmitted through the earth from a surface transmitter as much as 

1, 000 feet above the mine working area. 
, ppgp

cations can be established between the face machine operators on a section as shown in figure 7. 

FIGURE 7. - Trailing cab1 e communications systems. 
Since the dc shuttle cars are a.l.ready connected to the trolley wire, 

a permissible battery-operated mine phone of the trolley wire type can 

be installed on the shuttle car, thus providing comunications with all 

other trolley phones. 

Communication to a diesel rail haulage locomotive has also been 

achieved with a battery-operated permissible trolley wire phone, loopcoupled to an open-wire phone line installed in a haulage way. A diesel 

phone system looped back to the surface through a borehole has been installed in the Safety Research Mine. This system is connected to a twofrequency coupler which couples the message to the overland power line 

back to the foreman's office. 

Roving Miner Communications Need. - Presently, communications equipment is mounted in working places or on vehicles. The roving miner can 

be reached only as he comes within the zone of the vehicle or the working 

place communications (fig. 8). To get an urgent message to a roving miner, 

it is frequently necessary to dispatch another miner to serve as a messenger. 

FIGURE 8, - Need: Communications with key roving 

miners, 
Solution A: Paging the Roving Miner,, - Trolley wire communications 

networks make excellent underground broadcasting systems. The Bureau of 

Mines has located a small pocket pager receiver and had it modified to 

operate on 88 and 100 kHz, the two standard trolley wire communication 

frequencies. This system has a selectivity that allows each pager to 

have its own private receive channel. An audio tone alert signals that 

a short message will follow. The operating range is in excess of 600 

feet from the trolley wire. A special arrangement of this system, shown 

in figure 9, has been procured by the Bureau. A transmitter and repeater 

are so connected that a message originating at any surface dial phone is 

transmitted into the mine over the pilot wire in the power mains, or over 

the phone line, then connected by a repeaiter onto two roof bolts. The 

roving section foreman can receive a page message anywhere in the section, 

and he can return to the section phone to answer the page. 

FIGURE 9. - Roof bolt paging system. 
Solution B: Two-Way Communications With the Roving Miner. Intrinsically safe, vehicle-mounted and personnel radio equipment can provide 

radio-type communications throughout the main working areas of the Safety 

Research Mine. Ultra-high frequencies around 420 MHz can provide mobile 

radio coverage to roving miners equipped with low-power handy talkie radios 

in the working section without the aid of tranmission line cables. Private communications are established on the working section between the 

section foreman and the maintenance man using a special UHF section channel, as previously depicted in figure 3, The communications range can 

be further extended by mounting another handy talkie radio to the roof 

at a point centrally located in the section, and using it in a repeater 

mode. To call the surface, the section foreman can use a second UHF 

channel of the roof-mounted radio which interconnects with the telephone 

line at a carrier frequency dedicated to mine-to-surface communication. 

w/ Over land Rod* Llnkxp1 Trunsmhr 

FIGURE 10, - Guided wireless radio system, 
The UHF signals can also be transmit:ted from an in-mine base or 

repeater station to an antenna on the sec:tion via a special Radiax cable 

transmission line as shown in figure 10, thereby providing two-way 

communication between the surface and a roving miner carrying a portzble 

UHF radio. The base or repeater stations can also provide communications 

between the surface and miners in the harilageway because of the continuous 

radiation from the Radiax cable along the haulageway. In addition, roving 

miner-to-roving miner communications on the section and in the haulageway 

can be provided by a two-frequency repeater station connected to the Radiax 

cable. Such a system can include a paging capability that can be used to 

reach key personnel carrying less expensive UHF pocket pagers when roving 

within range of the Radiax transmission line or section antenna. A loop 

back over an overland radio link also can be provided by UHF transmitterreceiver stations on the surface as show11 in figure 10. 

Adequate Emergency Communications N(+. - Communications are vital 

to rescue and recovery operations. Some mine operators have selected 

permissible phone systems that are powered from batteries to provide a 

two-way communications system in the event that the main electric power 

source is shut off. However, more is neleded to assure an operational 

system. A phone system requires an intalct phone line. Experience has 

demonstrated that phone lines are often broken during an emergency (fig. 

11). 

FIGURE 11. - Need: Emergency communications. 
traffic on each of these systems is heavy, and the resultant interconnect 

system traffic is the sum of the individual system traffic. Thus, in 

general, the traffic is too great for good communications in a continuous 

interconnect system. However, through a selective interconnect placed 

deep inside the mine, the two systems can be selectively monitored from the 

surface. A call originating on the mine telephone can be heard on the 

surface over a trolley phone connected to the trolley wire. If the 

phone line is down outby the interconnect point, phones inby the phone 

line break can be reached over the combination of the trolley wire and 

phone line. 

There are many other methods for deriving a loop back to monitor 

communications and to reach the line break, One such alternative method 
FIGURE 13. - Public-to-mine telephone interconnect system. 

ROVING MINER PAGING 

by 

1 2 

Richard H, Spencer and Howard E. Parkinson 

ABST RACT 

Mine paging telephones increase the effectiveness of the mine personnel. The page message reaches the personnel within hearing distance 

of the phone, Personnel paging extends the page to the individual roving 

miner wherever he may be. 

One system installed at the Bureau of Mines Safety Research Mine 

is a "dial-in" system. An in-mine page can originate from any mine 

public phone. The system, exclusive of the Bell System equipment, 

includes an encoder, a 88-kHz transmitter, a pilot wire signal coupler, 

a 88-kHz repeater, a roof bolt signal coupler, and pocket receivers, 

There are two configurations of the system, One configuration is 

a whole mine configuration, and the other is a working section configuration. 

There are two forms of the working section configuration, One form puts 

the selective page onto the mine phone line and converts the message to 

88-kHz at the section, thereby extending the page area to the face. 

The second form is a call alert system. This system keys a call 

alert transmitter on the section, The system has a capacity to handle 

24 sections. It is a cost-effective system with an added feature of providing an emergency beacon locator at the time of a mine emergency. 

INT RODUCT ION 

Current Paging Systems 

Mine telephones are the backbone of most present mine communications 

systems, There are two main telephone instruments: the magneto telephone and the mine pager telephone. A large mine may have 40 or more 

of these phones. Selective calling is at:tempted on both types of phones, 

1 

Arthur Do Little, Inc., Cambridge, Mass, 

2 

Supervisory electrical research engineer, Industrial Hazards and 

Communications, Pittsburgh Mining and Safety Research Center, 

Bureau of Mines, Pittsburgh, Pa. 
Personnel paging extends the page message to the individual. A 

small pocket pager is carried by the individual. This pager receives a 

message only when the particular individual is being paged. The selective 

call feature of the page removes the confusion that is common in the mine 

page telephone system. Many personal paging systems are in use in a 

variety of communication applications. These systems are very effective 

in hospitals, industrial plants, and other large buildings. In their 

original form they are not satisfactory for mine use; however, relatively 

straightforward adaptations based on extensions of existing mine communication systems have proved to be fruitful. These adaptations are based on 

existing trolley wire and mine telephone systems, as described below. 

Demonstration of paging capabilities was made by using carrier frequency equipment operating at the 88-kHz trolley wire phone frequency. 

Signals from the 88-kHz transmitter were connected to the leads of the main 
FIGURE 1. - Current flow produced by driving 

roof bolts. 
FIGURE 2. - Block diagram of roof bolt experiment, 

Generator 

 

I 
FIGURE 3. - Roof bolt attachment. 
- --- - 

FIGURE 4. - 88-kHz repeater. 

I Main Shaft 

Pocket 1 paw 

Pilot Check W~re 

Termmation \[ Roof 

'i '

88 kHz 

27 

Pocket 

Pager 

Wire 

- 

FIGURE 6. - Whole mine paging system. 

- Bolts - 88 kHz Roof 

88 kHz Section B 

Repeater , Bolts 

Repeater 

c Section A 
FIGURE 7. - Reach encoder installation. 


FIGURE 10. - Miner wearing pocket pager. 
The 88-kHz system described above for whole-mine paging has many 

similarities with the trolley wire carrier communication systems used 

to dispatch dc haulage vehicles. As such, paging signals placed on the 

trolley wire can also be extended into t'he section via the cables of dc 

face machines connected to the trolley wire power system. Hence, in the 

vicinity of a trolley wire or trailing cables, a miner with a pocket pager 

will be able to pick up the page signals via the magnetic fields in the 

vicinity of these cables. Such an application is illustrated in figure 11. 
gpgg y

it is very effective in the working section. Once again additional 

equipment was added to the existing mine communications system. This 

time the equipment was added to the mine telephone line. A simple 

transmitter was added in the mine foreman's office, and a receiver and 

call alert transmitter were added in the mine section. The loop antenna 

of the call alert transmitter was wrapped around a pillar. 

In order to receive a call alert, the individual carries a pocket 

alert receiver. The receiver has a blinking light to indicate a call. 

A nonaudible tone is sent over the telephone wires from the surface 

and is received by a selective filter, which in turn energizes the 

call alert transmitter on the section being paged. Instead of coming 

over the mine pager telephone system, the paging is personalized to 

those section individuals carrying the call alert receivers. When 

the pocket receiver indicates a call alert, the individual walks to the 
mine pager phone on the section and replies to the page call. This 

system was developed from work performed in the Bureau of Mines program 

on electromagnetic detection of trapped miners. 

There is an additional benefit to this system. The signal being 

transmitted on the section is a low-frequency signal that also penetrates 

the overburden. It has been possible to receive such signals on the surface some 1,000 feet above the mine section, Miners on the section can 

use this transmitter for emergency signaling to the surface. Conversely, 

the miners can also use the call alert receiver to receive similar operational or emergency transmissions from a surface transmitter. 

Figure 12 illustrates a call alert transmitter antenna and its 

associated magnetic field. The current flowing in the loop produces a 

magnetic field which links this loop with a small pickup loop in a 

call alert receiver carried by a person, Th.e operational range of this 

system is essentially the distance at which the received signals have 

become small enough for the background noise to interfere with their 

reception. 

Expected Coverage 

Once again, an experiment was done in t,he Bruceton experimental mine 

to determine the efficacy of this system in providing paging coverage 

throughout a working section. A loop antenna was placed around a 

coal pillar and driven with a transmitter operating at a frequency of 

3,030 Hz, and a calibrated receiver tuned to this frequency was carried 

through the mine to determine the signal strength received at various 

parts of the mine, The results of these measurements are shown in 

figure 13, which illustrates the extent of t:he call alert coverage. 

Call Alert Coverage al Bruceton 

15 db SIN Criterion 

Ij It For Bruceton Now - lLow Notre) - 136 db re IAIMIfi 

AFor Medlum Nose - (Lincoln & Allen M~nel 

- 126 db re IAIMIflz 

DFor Hlgh Nolse - (Robena Near Car Pull) 

- 106 db re /A/MIfi 

FIGURE 13. - Call alert coverage. 
FIGURE 14. - Call alert transmitter. 
FIGURE 15. - Call alert receiver worn by miner. 

the keying receiver connects operating power to the call alert transmitter 

connected to the pillar-mounted loop. In the present system this call 

alert transmitter drives a 3,030-Hz signal current into the loop antenna 

of the system, thereby producing a 3,030.-Hz signal that penetrates to all 

regions of the section. A pocket-sized call alert receiver incorporating 

a small pickup loop is carried by a person roving through the section. 

This receiver responds to the presence of the 3,030-Hz signal by flashing 

a light on the receiver or by generating an audio alert signal. The 

person paged is thus notified to call thle mine office. 

A word of caution: Call alert systems use carrier signals over the 

telephone wires, A preliminary examination of several of the mine pager 

telephones indicates that these phones are not fully compatible with the 

normal range of telephone grade carriers. We are now investigating this 

problem and anticipate that a simple add-on device (applique) can be made 

for installation on existing mine pager phones to make them compatible 

with carrier applications. At this time, it is possible that some carrier 

frequency systems will require excessive amounts of power if utilized 

on present mine telephone installations. 

CONCLUDING REMARKS 

The emphasis of our paging efforts has been placed on the extension 

of existing mine communications to improve their utility under operational 

and emergency conditions. Primarily we have been concerned with extending the page message from the equipment that receives the page to the 

person who is being paged. Paging can also be added to wireless radio 

communication system; however, very few mines currently use wireless 

radio, The objective in paging is to alert a person that he is wanted 

on the telephone. The person replying to the page will generally not 

reply over the same channel by which he was paged. The paging system 

and the call alert system discussed here meet different needs. The general 

features of these two systems are summarized in table 1. 

TABLE 1. - Roving miner paging 

-- - 

Coverage 

Voice Page 

Selectivity 

Roof bolt system 

Emergency use 

Call alert system 

Equipment 

available 

Part or whole mine 

Yes 

To individual 

Not practical 

Current 

By section 

No 

To section 

Yes 

60 days 
Electrical engineer 

2 

Supervisory electrical research engineer 

Both authors are with Industrial Hazards and Conununications, Pittsburgh 

Mining and Safety Research Center, Bureau of Mines, Pittsburgh, Pa. 
INTRODUCTION 

Existing mine communication systems stop at the last open crosscut 

of the section. Present mine communication systems are aimed at satisfying the need that the mine section foreman be able to communicate with 

the mine shift foreman. However, in some mines there are additional 

communication needs within the mine section, needs which are not adequately 

met as follows: 

Between the continuous miner operator and the shuttle buggy 

operators . 

Between the shuttle buggy operators and t'he "gathering" 

locomotive operator. 

Between the general maintenance foreman and the section 

maintenance man repairing a machine. 

FIGURE 1. - Tro i ling cable cornrnunicotions system. 
FIGURE 2. - Loudspeaking phone on roof bolter. 
By satisfying these needs, both the safety and efficiency of mining operations can be improved. The existing power trailing cables to the face 

machines provide the means to achieve these communications capabilities 

in a reliable and economic manner. Figure 1 provides an overview of the 

communications systems to be discussed below. 

The operational and safety advantages of the aforementioned communication capabilities are several and diverse. The shuttle buggy operator 

will be able to alert the continuous mining machine operator of an impending roof fall. The shuttle buggy operators will be better able to 

coordinate their activities as they go in to dump on the belt or into the 

cars. The maintenance mechanic will be able to communicate with the surface while working at a face machine. When maintenance on a face machine 

is required, the maintenance mechanic can be called directly from the 

trobled machine. This paper describes some of the trailing cable techniques that we have developed to fulfill the above communication needs. 

Adaptations of existing mine communication hardware have been used to 

the fullest extent possible, subject to the following requirements: 

1. Hardware must be permissible. 

2, Hardware must be battery-operated, 

3. System must provide intermachine c:ommunications. 

4, System must selectively interconnect to a surface system. 

APPLICATION OF EXISTING TECHNIQUES 

Loudspeaking Teleph.o!nes 

Loudspeaking telephones can be used on mine face machinery. Figure 2 

shows an experimental installation on a roof bolter. This phone is battery operated, and the newer versions are .not only designed for rugged 

mine usage, but also are intrinsically safe. An overall diagram of a 

loudspeaking phone trailing cable communi.cations system for face machines 

is presented in figure 3. The system depicted in figure 3 allows a shuttle 

buggy operator (face machine No. 1) to communicate with the continuous 

miner operator (face machine No. 2) on standard loudspeaking (pager) 

mine telephone apparatus. The fact that continuous miners are powered 

from ac and shuttle buggies from dc does not jeopardize or hinder this 

form of communication, 

To facilitate the use of these phones on face machinery, it is 

necessary that telephone wires be provided in the trailing cables. Figures 

4 shows a cross-sectional view of a trailing cable that the Bureau procured with a shielded telephone pair of No. 22 wire. 
r Twisted Pair Shielded 

Ground Check -. / 

FIGURE 4. - Trailing power cable with a shielded 

telephone pair. 
To allow the face machjne operators tlo occasionally communicate with 

the "gathering" locomotive operator, it is necessary that a loudspeaking 

telephone-to-trolley wire telephone selective interconnect coupler be 

placed in the mine section as indicated in figure 3. We have modified 

a standard, Femco loudspeaking phone-to-trolley phone coupler to provide 

this selective coupling. The coupling is selective in order not to burden the trolley system with routine face machine communication traffic 

and vice versa, Either the shuttle buggy operator or the "gathering" 

locomotive operator can initiate the interconnect by simply applying an 

audio tone to the mouthpiece of his phone using a pocket-sized tone 

generator. 

The advantages and disadvantages of this trailing cable communication 

system are summarized as follows: 

Advantages Disadvantages 

1. Permissible. 

2. Rugged, 

3. Battery powered. 

4, Reliable. 

5. Simple. 

1, Extra wires in trailing cable. 

2, Isolation required between interconnected phones, 

3. Special coupler required for providing paging voltage. 

4. Eixtra terminals at plug. 

5. E:xtra slip rings in cable reel. 

Carrier Tv~e Tele~honles 

We have also examined a second approalch to meeting face machine 

communication needs. Carriertype telephor~es normally used on the trolley 

wire system have been placed on face machinery as shown in figure 7. One 

difficulty with this approach is that permissible trolley wire phones are 

not yet commercially available, although one of the manufacturers of trolley 

wire phones isnow considering submitting its equipment for approval. Therefore for this experimental installation, we modified a trolley wire phone 

and obtained a permit to operate it in a gaseous mine. These section trolley 

wire telephones are also battery operated, which permits them to be used when 

machine power is shut off, such as during maintenance operations. 

FIGURE 7. - Carrier phone on face machine. 
system are summarized as follows: 

Advantages Disadvantages 

. No extra wires or contacts. 1. Presently nonpermissible. 

. Couple onto phase wire. 2. Isolation required between 

machines. 

3. Battery power option. 

4. Rugged. 

5. Reliable. 
Surface 1nterconn.ect 

Both of the above face machine communication systems can also be 

connected to the surface via the mine trolley wire or phone line. If 

the dispatcher, mine foreman, or any other surface personnel wish to 

contact the section, the section can be selectively coupled into the 

trolley wire system or the phone line system. Each section can be 

assigned a special selective audio tone for coupling purposes. This 

permits the sections to be isolated one from another and to be paged 

selectively. Therefore, the selective page for any particular section 

will not be heard on any other section. 

CONCLUS IONS 

Two-way communication between face machine operators and between 

face machine operators and surface personnel on a selected call basis 

is possible with existing communication hardware or modification of 

existing hardware, These cormnunications can help mining personnel 

improve safety and efficiency of mine operations. 

Gathering Trolley Line 

Locomotive (~requency A) 

FIGURE 9. - Face-machine to face-machine carrier phones show ing interconnect ion 

to gathering locomotive. 

Carrier Phone t (Frequency A) 

Shuttle Mining 

Car Machine 

\ Carrier 

Phone Carrier (Frequency B) 

Phone C> C> 

Frequency 

A 

(Frequency B) 

Conductor 

- - 

Power 

Load ' 

Signal center Freq- Carried by I3 

Trailing Cable 

Selective 

Coupler 

and 

Retransmitters 
1 

Arthur D. Little, Inc., Cambridge, Mass. 

2 

Supervisory electrical research engineer, Industrial Hazards and 

Communications, Pittsburgh Mining and Safety Research Center, 

Bureau of Mines, Pittsburgh, Pa. 
INTRODUCTION 

Need for Two-Way Communications With Roving Miners 

Historically, communication equipment: for underground mine use has 

been based on "wired" systems, namely, the loudspeaking mine telephone 

system and the trolley wire carrier phone system. The mine telephone 

system includes both magnetophones and loudspeaking telephones, while 

the trolley wire carrier phone system utilizes carrier current transmitters and receivers. In both cases all the transmitting and receiving 

equipment is "hard wired" to the telephone line or to the trolley wire, 

respectively. As such, this equipment is not portable. Therefore, it 

is inadequate for paging or communicating with key induviduals, such as 

foremen and maintenance men, when they are not in the immediate vicinity 

of the communication equipment. 

The roving miner paging systems recently developed by the Bureau of 

Mines and discussed in a companion seminar paper meet the need to deliver 

one-way paging messages and call alerts to key individuals on the move in 

the mine. These are messages or alerts that the paged individual must 

either act upon, or acknowledge via another communications channel in the 

mine. However, situations also arise in which an instantaneous and 

continuing response from key roving miners is either essential or extremely 

desirable from an operational or safety point of view. The ability to reach 

and talk with an individual where he happens to be, and not only at a limited 

number of fixed stations, is particularly beneficial when1. Downt5me can be reduced by permitting individuals working on 

machinery to communicate with surface supervisors without 

leaving the machinery; or 

2. The message is urgent and the individual is on the move 

underground. 

Two-way wireless and guided wireless radio systems recently investigated 

by the Bureau can provide this personalized instantaneous communication 

to individuals over important parts of the mine, 

Two-way Wireless Radio in Mines 

The thrust of our two-way wireless radio communication work has 

been to extend two-way communications to key miners roving within 

the section and in the haulageway. The principal objective has been 

to find ways in which commercially available, portable radio equipment 

can be adapted for practical use in operational coal mines. 
section applications, so it has been named UHF wireless section radio. 

The second makes use of a special coaxial cable for guiding and 

radiating UHF radio waves along mine entries, so it has been named 

- UHF guided wireless radio. 

UHF WIRELESS SECTION RADIO SYSTEM 

Two-way wireless section radio systems can provide communications 

between key individuals who may be working at different locations within 

a section, and between these individuals and the surface. These systems 

can also be applied to haulageway communications. Figure 1 gives an overall 

view of such a system for a section application. It is described in detail 

under "System Description,'' after discussion of the system's principles of 

operation and expected communications coverage. 
entry can be considered as imperfect mirrors and the radio waves as light 

beams. As the light beam, or radio wave, travels down the mine entry, 

bouncing off the walls, roof and floor, part of its energy is reflected 

at each bounce and therefore retained in the entry, while part of its 

energy is transmitted into the coal or rock by refraction and therefore lost. 

High Coal Entry (7 feet x 14 feet) 

Low Coal Entry (3.5 feet x 14 feet) 

RIMS Wall Roughness - 4 inches 

RMS Wall Tilt - 1.2 degrees 

Dielectric Constant - 10 

Signal 

Attenuation 

Loss in dB 

per 100 Feet 

1 

\, 

1 Experiment High Coal 

\ ---- High Coal Theory - - - - Low Coal 

1 

I \ 

- 

0 200 400 600 8001000 1 500 2000 2500 3000 

4 

420 Frequency in Megahertz 

FIGURE 3. - UHF wireless radio signal attenuation loss in coal 

mine entries. 

The other major frequency dependent losses are antenna coupling 

loss and corner loss. When they are added to the attenuation loss, the 

appearance of an optimum operating frequency band becomes more pronounced. 

In high coal, the optimum band is 400 to 1000 MHz, Within this band, the 

best frequency for a particular application will depend on the desired 

communication distance and whether the signal must travel around a corner 

to reach the receiver, For example, operating frequencies near 400 MHz are 

favored for transmission paths about 500 feet long that include one corner. 

Such paths are typical for section applications. Frequencies near 1,000 MHz 

are favored for long straight-line transmission paths along haulage ways. 

The Bureau has tested portable mobile radio equipment up to the 

present frequency limit of equipment availability, the 450-MHz band, the 

band which also offers the most favorable performance for section applications in high coal. Allocation of a new band of frequencies around 960 MHz 

for land mobile industrial applications is presently under consideration 

by the Federal Communications Commission. However, portable and fixed 

station 960-MHz equipment for haulageway applications will still not be 

commercially available for several years. Therefore our present investigations and range predictions were concentrated on the 450-MHz band. 
0 

m 

50 100 ft. 

Scale 

I- ha1 

0 Satisfactory Coverage 

Marginal Coverage 

No Coverage 

FIGURE 4. - Predicted UHF wireless radio coverage. 
UHF H& TaLb 1420 Mud 

FIGURE 5. - UHF two-way wireless section 

radio coverage in the Safety 

Research Mine. 
Miner to-Miner D~rect. and Surface 

Interconnect Via Flxed Statlon 

-. 

z - .. - , -. 

. .- 

I 

Section ... :-, ... : :, , 

. 

'. ..... 

. .:,>-: ' 

- 

. ... 

FIGURE 6. - Two-way wireless section radio system block diagram. 

Standard Mine 

Carrier Phone 

(61 kHz) 

Audio Frequency 

Interconnect for 

RadioICarrier Systems 
As stated in the coverage discussion, the roving miner-to-miner 

communication range can be doubled, thereby extending roving miner 

coverage to the whole section by using a roof-mounted repeater at the 

central location. To operate in the repeater mode, miners would switch 

to channel 1. In this repeater mode of operation, the portable units 

transmit on channel 1 but still receive on channel 2. This allows a 

centrally located repeater station to pick up the channel 1 transmissions 

of the miners and rebroadcast them on channel 2 for subsequent reception 

by the other handy talkies, thereby doubling the miner-to-miner range of 

the system. 

Another benefit is obtained when in the repeater mode, namely, roving 

miner-to-miner communications traffic will not clutter the section-tosurface interconnect channel, but messages from the surface will still be 

receivable by the roving miners. 

Figure 7 shows a Motorola HT220 intrinsically safe handy talkie unit 

attached to a miner's belt. Operation cam be via a push-to-talk switch 

and speaker-microphone that are integral parts of the handy talkie unit. 

Alternatively, the switch and speaker-mic:rophone can be in the form of a 

handheld accessory, as shown in figure 7. This accessory can be conveniently clipped to a pocket or lapel. Operation is also possible by means 

of a bone conductance microphone and ear speakers attached to the miner's 

hardhat as shown in figure 8. The bone c:onductance microphone is 

situated in the middle of the hardhat webbing so that it can pick up the 

skull vibrations created when a person speaks. The ear speakers are put 

close enough to the ears to hear the received audio while still leaving 

the ears open to the normal sounds in the mine. This hardhat unit can 

be operated by a belt-mounted pushbutton as shown in figure 8, or by 

means of a voice-operated switch which keys the transmitter on whenever 

the person speaks, This allows complete1.y hands-free operation. 

Figure 9 depicts a handy talkie unit inst:alled in a roof-mounted radioto-carrier surface interconnect unit fabricated by Collins Radio Co. 

This station is typically mounted horizorltally at a 45O angle in an 

intersection centrally located in the secttion. The cabling on the 

left goes to a standard mine carrier phone attached to the mine telephone 

line. 
FIGURE 7, - Miner using intrinsically safe handy talkie unit, 
FIGURE 8. - Handy talkie operation using hardhat with ear speakers and 

bone conductance microphone. 
FIGURE 9, - Roof-mounted radio-to-carrier surface interconnect unit and handy 

talkie unit. 
FIGURE 10. - Guided wireless radio system. 
I/ 

7hrough the Shield 

Signal 

strength 

Fields 

of IL 

I t 

Distance from Cable 

FIGURE 11. - Guided wireless radio with 

coaxial cable-principle of 

operat ion. 
As shown in Figure 11, the fields coupled to the external space will 

continue to decrease in strength with increasing distance from the cable. 

In addition, the internal and external fields will be attenuated, primarily 

because of the cable's resistance, as they travel along the cable to and from 

the fixed and portable communication stations. The amount of coupling loss 

and longitudinal attenuation loss experienced depends on the material and 

construction of the cable and on the operating frequency. 

The UHF guided wireless system treated in this discussion is one based 

on the use of special semiflexible RX4-1 IRadiax coaxial cable of 

%-inch diameter and 50-ohm characteristic impedance. The cable has a 

solid copper shield in which holes have been machined to increase the 

amount of coupling to the external space, as opposed to the braidedtype shield used in conventional flexible cables for lower frequency 

applications. A cutaway view of the Itaditax cable is shown in figure 12. 

Its cost is more than ten times that of c~onventional braided cable used 

for cable television home installations. According to the cable manufacturer, Andrew Corp., a lateral coup1in:g loss of 855 10 dB is experienced 

when the external signal strength is measured at a distance 

of 20 feet from RX-1 Radiax cable. This loss includes the shield 

coupling loss and the radial spreading loss for this distance and applies 

for both incoming and outgoing signals. The longitudinal attenuation 

loss is 2.1 dB1100 feet. 

FIGURE 12. - Radiax coaxial cable, cutaway view. 

In spite of the holes, the coupling loss imposed by the shield is 

high and requires the use of repeaters (to amplify and retransmit 

incoming signals) to allow communication via this cable between roving 

miners carrying portable handy talkie radios. The spacing of these 

repeaters along the cable (base stations if only a surface-to-mine 

channel is desired) will be governed primarily by the lateral range 

desired from the cable, the longitudinal attenuation rate of the cable, 

and the transmitter power of the portablle units. Since the transmitter 

power available for portable units is generally lower than that available 

for fixed repeater or base stations, th~e portable units set the coverage 

limits for two-way communications. 

Expected Coverage 

The two-way coverage obtainable with a guided wireless radio system 

has been estimated for a haulageway ins'tallation consisting of the 

Andrew RX-1 Radiax coaxial cable, 2 watt base stations and repeaters, 

and the same Motorola HT220 2 watt handy talkies used for the wireless 

section radio system. As in the case of wireless section radio, 

communication range will be limited by intrinsic receiver noise as 

opposed to external electrical noise. The coverage estimates are based 

on lateral coupling loss and longitudinal attenuation data supplied by 

the cable manufacturer, preliminary experimental data obtained for the 

Radiax installation in the Bureau's Safety Research Mine, and some of 

the theoretical and experimental results discussed under wireless section 

radio. Of particular interest are the ranges expected along haulageways 

and down entries crossing haulageways. 

When an entry crossing the haulageway is close to a repeater station, 

two-way lateral coverage should be possible to handy talkie radios located 

300 to 500 feet down the cross entry. Figure 14 illustrates the expected 

signal behavior and coverage down such a cross entry. Once the UHF signal 

field becomes well established in the cross entry, its propagation down 

the entry and around subsequent corners will be governed by the same 

principles and attenuation rates discussed under wireless section radio. 

Frequency - 42'0 MHz 

FIGURE 14. - Guided wireless radio system, propagation down 

crosscuts off hau loge ways, 
FIGURE 15, - UHF guided wireless radio system using Radiax cable. 

Control and Audio Lines 

i 

T R T R t 

Repeater or Base 

Station with Surface Sect ion 

Interconnect Branch-off 

Second Repeater 

or Base Station 

I Antenna 

Radiax Cable Termination 

11111111111 

Haulageway 

Roving Handy-Talkie 
System Descriptnon 

Figure 15 is a block diagram of a basic UHF guided wireless radio 

system using Radiax cable. It represents the kind of equipment needed 

for a UHF haulageway application. The system also has a branch-off and 

associated antenna termination to allow communication with roving miners 

on a section. Communications from the surface to a roving miner are 

established by means of audio and contirol lines that go from the control 

console on the surface to repeaters (or base stations) at fixed locations 

in the haulageway. The transmitters of these fixed stations send UHF 

radio signals down the Radiax cable to roving miners equipped with 

portable handy talkies. These handy talkies pick up a portion of the 

signal energy coupled into the haulageway by the holes in the shield of 

the cable. Conversely, radio transmissions from the roving miners are 

picked up via the holes in the cable and carried inside the cable to a 

repeater or base station, where the audio output is sent via the audio 

and control lines to the control consoZe on the surface. 

600 ft. 

FIGURE 16. - UHF 420-MHz guided wireless radio system installed in the Safety 

Research Mine. 
in Figure 15. This encoder provides a more limited call alert or paging 

mode of operation with less expensive pocket pagers instead of handy 

talkies. 

Figure 17 shows the system control console which would normally be 

located on the surface. Figure 18 is a photograph of the two-frequency 

12-watt repeater station, while figure 19 shows the 40-watt base station 

and special power supply unit. The 2-watt handy talkies are the same 

one discussed under wireless section radio and are shown in figure 7. 
were largely located in the 1 ft half of the mine, particularly in the 6 vertical crosscut with the 45 corner on the map in figure 16, but pockets 

of weak performance were also present in other parts of the mine, Means 

of improving this performance by adding antenna terminations at selected 

locations are currently under investigation. 
FIGURE 18. - Two-frequency 12-watt repeater station. 
FIGURE 19. - Single-frequency 40-watt base station and 

special power supply unit. 
FIGURE 20. - Surface transmitter-receiver-antenna station for overland radio loopbock. 
By placing the surface stations at strategic locations, the mine phone 

line, trolley wire, and environment monitoring channels as well as wireless 

and guided wireless channels can be looped back together. In this manner 

every transmission that goes into the mine via a primary route can be sent 

out again via the overland loopback, If a break should occur in any one of 

the communication channels and a miner inby the break cannot be reached by 

the primary route, the loopback route can be used to reach him. Surface 

power lines and telephone lines are also suitable for looping back in-mine 

communication channels, 

CONCLUDING REMARKS 

The general features of the methods discussed in this paper for 

establishing two-way wireless and guided wireless radio communications 

between underground roving miners at UHF are summarized in table 1. 

Table 1. - UHF Radio In Mines for Roving Miner-to-Miner Communications 

Direct wireless 

Method 

Wireless 

via repeat ere 

Guided wireless 

via repeater and 

Radiax cable. 

Units of coverage 

Half section, or 0,3 mile 

of haulage way,, 

Equipment 

(per unit of coverage) 

Whole section, or 0.6 mile 

of haulage way. 

Whole section, or 0.8 mile 

of haulage way. 

Handy talkies 

Handy talkies, plus 

central low-power 

repeater. 

Handy talkies, plus 

central high-power 

standard repeater, 

I plus Radiax cable 

along haulageway or 

distributed in sec- 1 tion. 

Furthermore, roving miner communicati.ons can be established with 

the surface, and between separate coverage units along haulageways or 

different sections, by adding interconnect equipment appropriate to each 

method. The wireless-via-repeater method can use a radio-to-carrier interconnect to the existing mine phone line at each repeater location, together 

with a standard carrier phone at the surfa.ce end of the mine phone line. The 

guided wireless method can use interconnect equipment similar to that for the 

wireless method, or install a set of audio and control lines connecting all the 

INTERCONNECTING NEW COMMUNICATIONS 

TO EXISTING SYSTEMS 

by 

Dean ~nderson, William stout, and Howard E. Parkinson 2 

ABSTRACT 

The Bureau of Mines has developed a number of interfaces devised to 

extend mine communications. 

A selective interface loops back the mine telephone over the mine 

haulage carrier phone and vice versa. Tl~e interface is connected and 

disconnected upon remote command from wiithin the mine or from the surface. 

A unique coupler interfaces the mine telephone to the public phone. 

A preassigned number is dialed upon command from the in-mine pager telephone, and the two-way communications are established with the selected 

public phone. In addition any public phone can be used by an individual 

who has a special pocket-carried tone geinerator to establish an into-themine telephone connection to the mine pager telephone system. The individual in the mine is paged, and two-way communications can be established 

with any in-mine pager telephone. 

Mine pager communications are selectively coupled into portable twoway radio on the section, thus extending mine telephone paging to the 

working face. The coupler also mounts one of the portable two-way radios 

to serve as the centrally located fixed end of the radio link. 

A novel call alert system selectively interfaces with the mine telephone line. The call alert is activated upon command when a page is intended for a key individual on a particular section. Each section is 

commanded separately. 

11 Collins Radio Co., Cedar Rapids, Iowa. - 

- 21 Supervisory electrical research engineer, Industrial Hazards and 

Communications, Pittsburgh Mining and Safety Research Center, Bureau 

of Mines, Pittsburgh, Pa. 
INTRODUCTION 

U. S. coal mining industry experience has demonstrated that the 

communication requirements of a mine are best met by a combination of 

different communications systems. The industry has wisely selected the 

best solution for each major communication link. The most important and 

least expensive communication system is the hard-wired mine pager type 

telephone used throughout the mine in fixed locations. The other major 

communications system is the trolley wire phone used between the locomotives and the fixed dispatcher stations. 

As coal mines have grown and mining technology has improved, needs 

have arisen for new and improved communication capabilities which cannot 

adequately be provided by the traditional mine telephones or trolley wire 

carrier phones. These include the following communication needs: 

1. Ability to communicate when the phone line or the trolley 

wire breaks. 

2. Ability to communicate with personnel not in the vicinity 

of a telephone. 

3. Ability to communicate over private channels. 

4.. Ability to deliver important messages during periods of 

heavy communications traffic. 

5. Ability to communicate with surface public phones. 

Several new techniques for mine communications have been under investigation 

and trial by the Bureau of Mines to meet these needs: 

1, Underground phones with manual trunking or automatic exchanges. 

induction radio for section communications. 

3. Medium-frequency induction radio for whole-mine communications. 

4. Very-high-frequency radio for whole-mine communications. 

5. Ultra-high-frequency radio for wireless section communications. 

The following techniques are capable of satisfying the foregoing needs for 

improved mine communications: 

1. Underground phones with manual trunking or automatic switching can 

provide privacy and an interconnection to the public telephone 

system on the surface. Also, a larger number of simultaneous 

communications can take place. 
2. Low-frequency induction radio offers a means of paging and 

communicating directly through tlae mine structure within a 

working section, and through the mine overburden in times of 

emergency. 

3. Medium-frequency induction radio can be used with power cables, 

trolley wires, and roof bolts to provide haulageway and section 

paging throughout the mine to ke:y mining personnel carrying pocket 

pagers. 

4. Very-high-frequency radio can be used with leaky, radiating 

coaxial cable or coaxial cable with integral passive antennas, as 

a technique for guiding radio waves throughout the mine haulageways and entries. This technique can be used to provide whole 

mine communications via radio handy talkies carried by key mining 

personnel. 

5. Ultra-high-frequency (UHF) radio can provide wireless communication between key roving miners carrying radio handy talkies 

within a working section, without the aid of additional metallic 

guiding structures. 

HYBRID SYSTEMS 

An objective of the Bureau's development work has been to exploit the 

added capabilities of these new communication techniques by incorporating 

them into existing mine communication systems. The approach adopted is a 

hybrid one, whereby two or more ccnmnunication systems are interconnected 

to take advantage of the benefits of each system. Several hybrid arrangements have been investigated: 

1. Selective path between trolley wire and telephone pair. 

2. Personal selective paging via telephone and low-to-medium 

frequency induction radio. 

3. Personal two-way communications to the section via the mine phone 

line and ultra-high-frequency raldio. 

4, Multichannel carrier telephones interconnected to existing mine 

phone system. 

5. Interconnection of the mine phone to selected public phones. 

Interconnection of equipment is required in order to realize these 

hybrid communication systems. The concepts of interconnection are well 

known. However, it has been necessary to devise new equipment so that 
I Phone Line - 

T 

Selective 

Coupler 

.'*... . ..,.; .--.:;2..;.,/..-:. ., ,.. ;, , ,;..,.-\ ,.:.>,;:-: :* L;,.,:,;.- -. .;,:,:., ::';-+ ,.:+ -,.. -;-;:.;>.f:.:*:,;.-:;'. - .:::~:2;-. -. . . . ..:-. ... " '...-' . - ,,. , . . . '- . .. ., .,- . . .. ,: , ;; :. ..... ::I ,,.. .. ,.-. . ..:., .'..:.:-.., .:';.,,::.;,...:::. -. . .:; :.=;. . . . .. > L-.<J:.:::!:;:;>s+- . -.,,,,. . . ,. .. , -. . 

FIGURE 1. - Trolley to mine phone hybrid, 
Relay 

Contact I Phone Line 

FIGURE 2. - Functional diagram of tone-actuated latch. 

I 

The tone-actuated latch is the heart of the interconnect and is 

activated from any trolley phone or mine phone in the system by key personnel equipped with pocket-sized audio tone generators. Once power is 

applied to the coupler, the trolley phone system and the mine telephone 

system are tied together through the coupler. Two-way simplex conversation is then possible between a mine phone and a trolley phone. To disconnect the systems, the audio tone is sent again. This activates the 

tone-actuated latch and unlatches the power from the selective coupler. 

Signal Relay .- 

Tone Decoder Driver Turn On 

Suspected breaks in communications lines may be tested for as follows: 

Phone Line to 

Trolley Line 

Coupler 

A selective turn-on signal is sent into the mine over the trolley wire. 

An attempt at communication is made with the signal going in on the trolley 

wire and coming back out on the phone line to the surface. If the signal 

is heard on the surface, then one can assume that there is no break in the 

lines, If the signal is not heard, the assumption is that a break exists 

in one of the lines. In the latter event the signal would return only as 

far as the break in the line, so that if the individual being paged was inby the break on the phone line, he could now be reached via the trolley 

wire system and the inby section of the phone line. Thus, all fixed locations on the phone line system inby the break would be reached. The same 

reasoning would apply if the phone line were intact and the trolley line 

Trolley Wire 
17 Pocket pa*. 

Pilot Check W~re 

88 kHz 0. 

Roof 

- Bolts - 88 kHz Section B 

FIGURE 3, - Whole mine paging system interconnects. 

5y Roof 

Bolts 

Repeater 

Sect~on A 
Two such regions are shown. The first is a call alert keying transmitter. 

A functional diagram of this transmitter is shown in figure 5. A push-topage push button connects power to a 19-kHz oscillator, the output of which 

is amplified in a driver stage and then fed via a transformer and isolating 

capacitor to the phone line. (Operation of the oscillator is verified by 

causing a 2-kHz audio tone to be generated when the oscillator is functioning.) In this way the keying signal is sent into the mine. At an area 

near the load point of the section, the signal is fed to a call alert keying receiver. A functional diagram of the receiver is shown in figure 6. 

When this receiver detects the keying signal, a relay connects power to a 

call alert transmitter. As may be recalled, this transmitter feeds an 

audio frequency signal to a loop antenna wrapped around a pillar in the 

section. Signals from this loop are picked up by pocket call alert 

receivers, and the person carrying the call alert receiver is notified by 

means of a blinking light or tone that he is being paged. Prototype equipment for this call alert system was designed and fabricated by Westinghouse Georesearch Laboratory. 

Push Button 

To Phone Line r'" 

2 kHz Audio 

Monitor 

FIGURE 5. - Call alert keying transmitter. 

FIGURE 6. - Cal l alert keying receiver. 

19 kHz 

Phone Line Envelope 

Tuned Detector 4b- Relay +Power to 

Call Alert 

Transrn itter 

Threshold 

Device * 
Mine Off ice 

Main 

Shaft 

Push to Page Page V Phone 

Phone Line 

Keying 

Transmitter 

(19 KHz) 

t 

\\I11 

B 

Alert Receiver 

I 

Receiver 

Section 

Load 

Point 

Haulage Way 

FIGURE 4. - Call alert paging system interconnects. 
Tx Audio In 

61 kHz 

Carrier 

Standard 

Carrier 

Phone 41 

Handy Talkies 

13 Mine Phone Line audio) 

6, kHz IC - ' 

Carrier 

FIGURE 7. - UHF-to-carr ier- hone interface. 

Two-Way Wireless Section Radio Syst:em. - Two-way communication is 

possible today in the mine using UHF harF talkies. These units can be 

interfaced to a carrier phone which is c:oupled to the surface either via 

the trolley wire or multiplexed onto the nonnal mine telephone line. The 

frequency of the carrier phone will be different from the mine's nonnal 

trolley phone frequency to prevent interference with nonnal trolley phone 

communications. Communication between the surface and a roving miner on 

the section will then be possible via a surface carrier phone coupled to 

either the mine phone line or the trolley wire, which is in turn coupled 

to a matching carrier phone and a special interface unit on the section, 

The interface unit couples the section carrier phone to a stationary UHF 

radio handy talkie that can communicate to a portable UHF radio handy 

talkie carried by a key miner. A prototype system designed for use by the 

Bureau of Mines uses two MSA 1601P carrier phones, one Collins Radio Coo, 

UHF to carrier phone interface unit, and two Motorola ~T220 UHF handy 

talkies as shown in figure 7, A block diagram of the system is shown in 

figure 8. A photo of the interface unit with a HT220 transceiver mounted 

in it is shown in figure 9. 
Existing Mine Phone System 

Sometimes a mine phone system becomes tied up, for example when a 

maintenance man is working out a complicated repair problem with his 

foreman on the surface. Carrier telephone systems can overcome this 

tie-up by establishing private channels over the present mine phone line. 

To interconnect this equipment, it is necessary that the mine phone line 

equipment be :ornpatible with the carrier equipment. New mine communications carrier equipment called Mine Telephone Grade Carrier will be 

developed by the Bureau of Mines. This equipment will be readily connectable to the mine phone line to provide a private channel. 

Carrier over the mine phone line can provide not only a private 

channel, but also additional channels. This multichannel concept is 
FIGURE 9. - UHF-to-carrier interface with 

UHF portable transceiver. 
often called trunking, whereby the phone line can be used by selecting at 

each carrier phone, one of the carrier channels that is not busy. The 

mine telephone line is thereby not dedicated to single conversations nor 

to any one particular purpose such as communication with the dispatcher or 

with the section foreman. To accommodate the necessary communications 

traffic, a group of extra carrier channels can be supplied on each section 

phone and each of the main surface phones. A total of five channels could 

easily be achieved in this way. 

Need: Ability To Communicate With Surface Public Telephones 

Solution: Interconnection of Mine Paging Telephone to Selected 

Public Telephones 

An interconnect device is now available that permits mine paging 

telephones to be interconnected with the public phone system on a selective basis. The intent of this system, illustrated in figure 10, is 

to provide greater off-hours or emergency communication capability. The 

system enables a person at a mine pager phone to gain access to the public 

phone system and call one or more preselected phone numbers. Likewise it 

permits access to the mine pager phone system from any public phone that 

can dial a selected telephone number at the mine, subject only to the condition that the caller have the required audio tone generator to initiate 

the interconnect between the public phone and the mine pager phone system. 

Similarly, a person calling from inside the mine must also have an audio 

tone generator to initiate the outgoing interconnect to the public phone 

system. 

I 

Selective I 40% 1 nterconnect 

I 1 Auto Answerb 

Mine Office 

----- - ----- I I 

- Public Phone 

I 

PBX 

7 d-1 Generator 

i 

1 Mine 

. 

ludspeaking Phone 

Phone Line 

I Loudspeaking Phone I 

I I 

8 

L ----,--,,, Sect io n J 

FIGURE 10. - Publ ic-to-mine-phone interconnect. 
If a person in the mine is equipped with the small hand held tone 

generator and wants to reach a prearranged public telephone number from 

his mine phone, he sends the tone via the mine phone to a telephone interconnect unit on the surface. At this surface interconnect, the tone is 

detected and activates a relay which in turn dials the preset telephone 

number. System operation is illustrated by the flow diagram of figure 11. 

Once the public telephone is answered and the conversation is concluded, 

the telephone must be disconnected from t:he mine phone line. 

FIGURE 11. - Operational flow diagram public telephone-to-mine pager phone interconnect 

system, 

This is also accomplished by the sending of the audio tone, or by an automatic time-out circuit. When a person calls the selected mine public 

telephone number from the outside, the in.terconnect unit answers the phone, 

and upon reception of the audio tone from the outside party, connects the 

incoming call directly to the mine pager phone line, thereby enabling the 

calling person to page and talk to the de.sired person in the mine. 
FIGURE 12. - Public telephone-to-mine pager phone interconnect unit and handheld audio 

tone generator. 

SUMMARY 

Today's mine phone and trolley or carrier phone system can be greatly 

expanded with the use of currently available communication equipment and 

the appropriate interfaces developed by the Bureau of Mines. Not only can 

operational communications be improved for greater productivity, but also 

emergency communications can be provided to increase mine safety. Table 1 

shows a selection of new communications and interface equipment that is 

either currently available to the mining industry or will be in the near 

future. 
Table 1. New Mine Communications and Interfacing Capabilities 

Function System with Manufacturer Availab

Hybrid Interface 

1, Selective Couple Trolley Trolley Phone Interface to Mine Interface Coupler - Femco, Ye

Phone to Mine Phone Phone Through Use of Pocket Tone Decoder - Signetics , DictaTone Generator phone Pocket Tone GeneratorCode-a -Phone, ~ictaphone 

2. Selective Surface Page Surface Dial Telephone Inter- Telephone Interface to Encoder- Ye

To Working Section via face to Reach Encoder through Telephone Company, Encoder, PocDial Telephone ket Pager - Reach, TransmitterF emco 

3. Selective Surface Page Surface Dial Telephone Inter- Telephone Interface to Encoder- Ye

to Haulageway via Dial face to Reach Encoder to Femco Telephone Company, Encoder, PocTelephone Transmitter Tied to Trolley ket Pager - Reach, TransmitterLine to Reach Pocket Pager Femco 

4. Selective Surface Page Combine both 2 and 3 above Combine both 2 and 3 above 

to Total Mine via 

Dial Telephone 

Ye

5. Selective Call Alert to Future Equipment that can be Transmitter, Receiver, Pocket Near 

Working Section with used on Mine Phone Line or Alerter - Westinghouse GeoreEmergency through-the- with Modified Mine Phones search Laboratory 

Earth Capability 

6. Two Way Communications Surface Carrier Phone Tied Into Carrier or Trolley Phone - Ye

to Roving Miner on Work- Mine Phone Line to Working Sec- MSA, Coupler - Collins 

ing Section tion Carrier Phone Tied Via Radio Co., UHF Transceiver - Coupler to Stationary UHF Trans- Motorola 

ceiver to Portable UHF Transceiver 

Fut

- 

z 

7. Private Mine Phone Future Equipment that Can Be Used m Communication Channels on Mine Phone Line 

C using Mine Telephone 7 

3 Grade Carrier 

z 

8. Mine Phone Coupled Surface Outside Public Interface Unit - Prototypes - Ye

D 

G, to Select Public Telephones Interfaced With Arthur Do Little, Inc., ProducI Telephones Mine Phones Through Use of tion Unit - Mine Suppliers, u 

D Pocket-Tone-Generator Pocket Tone Generator-Codea -Phone, Dictaphone