UNITED STATES DEPARTMENT OF THE INTERIOR 
Information Circular 8743 

Underground Mine Communications 

(In Four Parts) 

2. Paging Systems 

Compiled by Staff-Mining Research 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

BUREAU OF MINES 
This publication has been cataloged as follows: 

Pittsburgh Mining and Safety Research Center 

Underground mine communications (in four parts ) : 2. Paging systems / compiled by staff-Mining Research, Pittsburgh Mining and Safety Research Center. [Washington] : 

United States Department of the Interior, Bureau of Mines, 

1977. 

37 p. I ill. ; 26 cm. (Information circular - Bureau of Mines ; 

874 3) 

1, Mine communication systems, I, United States, Bureau of 

Mines, 11. Title, 111, Series: United States, Bureau of Mines, 

Information circular - Bureau of Mines ; 8743. 

TN23 .U71 no. 8743 622.061 73 

U.S. Dept, of the Int, Library 
CONTENTS 

Page 

Abstract ................................................................. Introduction ............................................................. MCM-101 call-alert paging. by Harry Dobroski. Jr ......................... Pager-phone guidelines and test equipment. by Robert L . Chufo 

and Roger G . Long ...................................................... Visual paging system. by Harry Dobroski. Jr.. and John E . Trombly ........ Call-alert paging for pager-phone systems. by Harry Dobroski. Jr., 

Stuart J . Lipoff. and John E . Trombly .................................. Radio paging. by Harry Dobroski. Jr ....................................... Appendix.--Communication reports . ........................................ 
UNDERGROUND MINE COMMUNICATIONS 

(In Four Parts) 

2, Paging Systems 

Compiled by Staff-Mining Research 

ABSTRACT 

This Bureau of Mines report summarizes the research, development, and 

evaluation demonstrations conducted by the Bureau of Mines under the Health 

and Safety Act of 1969 to improve the means of notifying miners underground, 

who are away from their own phone, that they are being called. 

INTRODUCTION 

It has been observed that it typically takes 30 minutes for a person on 

the surface to reach a person underground by phone. The research reported has 

been directed toward reducing this time so that it will be no longer than is 

usual for a person responding to a normal surface-to-surface phone call. 

The primary operational requirement of a communication system is that 

an individual must be able to initiate and receive communications as necessary 

regardless of where that person is within the mine. The fully integrated mine 

communication and monitoring (MCM) system discussed in the first paper satisfies this requirement. The MCM-101 call alert is a pocket paging receiver 

that can be used to alert a called party to go to the nearest phone and return 

the call. In addition to call alert, another subsystem and interface to a 

wireless radio make it possible for the person to hold a two-way conversation 

with the calling party, or to initiate a call when a person is remote from a 

fixed-location phone. 

Although much of the research has been devoted to new paging concepts, 

some research has been devoted to improving performance of existing paging 

systems. The second paper, Pager-Phone Guidelines and Test Equipment, reports 

on research that provides guidance information on the installation, operation, 

and maintenance of pager-phone systems. This work will familiarize operators, 

miners, and inspectors with practices and procedures that will allow optimum 

performance of pager phones. 

The primary operational requirement cannot be satisfied by adding on to 

existing mine pager-phone systems, but intermediate paging equipment has been 

developed that can be added on to existing systems. The Visual Paging System 

adds on to the pager-phone lines. By posting a coded signal at display boxes 
throughout the mine, personnel are notified that they should call the dispatcher or the switchboard operator. An alternative or addition to the visual 

pager is an electromagnetic pocket receiver that can be activated from the 

same office equipment used to post a visual page, as discussed in Call-Alert 

Paging for Pager-Phone Systems. 

The radio pager discussed in the final paper is a pocket page receiver 

capable of receiving a voice page. The advantage of voice paging is the 

ability to direct a person to return a call to a specific individual, or to 

deliver other simple one-way messages or instructions. 

Throughout this report, reference to specific companies or trade names 

is made for information only and does not imply endorsement by the Bureau of 

Mines. 
MCM-101 CALL-ALERT PAGING 

by 

Harry Dobroski, Jr .' 

ABSTRACT 

Under a Bureau of Mines contract, an advanced communications and monitoring system, the MCM-101, has been developed for mine use by Collins Radio. 

When it is equipped with radio transmitters and receivers, the MCM-101 becomes 

a call-alert system that enables persons remote from telephones to be contacted. Paging can be either selective or general, but both types are controlled by the system center. The selective pager is a small pocket- or beltcarried unit which, when activated by any telephone in the MCM-101 system, 

sounds a buzzer and lights a lamp. First-generation units have been tested at 

the Robena mine. The experiences gained in these tests are being applied to 

second-generation units now under development. 

INTRODUCTION 

In any paging system, two things are of prime importance. First, the 

system must have great range, because personnel underground, especially management, may be anywhere in the mine. Second, the system must be capable of 

being selective; that is, only the person being paged should actually receive 

the signal. Otherwise, there would be a tendency to turn off or ignore the 

pager altogether because the large number of calls generated would be a nuisance. In the MCM-101 system, both general and selective paging are possible; 

that is, all mine personnel can be paged simultaneously, or a single individual can be paged. 

DISCUSSION OF SYSTEM 

Dual Paging Capability 

A system center, usually located on the surface, controls and monitors 

all of the devices associated with the entire MCM-101 system. The center consists of a minicomputer, interface circuitry, a teletypewriter, and monitor 

readout devices. Figure 1 presents a diagram of the MCM-101 paging system. 2 

The most important underground device in the MCM-101 system is the telephone. Besides offering more private, single-channel communication, the 

l~lectrical engineer, Pittsburgh Mining and Safety Research Center, Bureau of 

Mines, Pittsburgh, Pa. 

2~ollins Radio Group. Call Alert Receiver Manual --Model 59D-1. June 1975, 

4 pp.; available from H. Dobroski, Bureau of Mines, Pittsburgh, Pa. 

Collins Radio Group. Call Alert Pager Modification--Model 59D-1. June 1975, 

11 pp.; available from H. Dobroski, Bureau of Mines, Pittsburgh, Pa. 
11 

monitor 

Pumps, fans,etc. 

FIGURE 1. - Diagram of MCM-101 telephone system equipped with call-alert paging, 

telephone can be equipped with a variety of devices, such as monitors and control units. In addition, each phone can be equipped with a special internal 

radio transmitter that also can be controlled by the system center. Each 

phone used in the system has a jack on the bottom to accommodate an antenna. 

The antenna consists of a single loop of wire around the coal pillar nearest 

the telephone. The antenna and the associated internal radio transmitter form 

the basis of the general paging system. 

Operational Features 

Assume I am near a phone, either in the mine or on the surface, and you 

are in the mine. As shown in figure 2, I can contact you from any of the 

telephones in the MCM-101 system. Obviously, if I know you are near a 
FIGURE 3. - MCM-101 pager unit. 
In addition to selective paging, the system also offers general paging. 

In this mode, dialing 7-000 results in all pagers in the mine coming on 

simultaneously--an important feature under emergency conditions. Although 

this system is sometimes called "whole-mine paging," there is, of course, a 

limit to how much actual coverage is possible. If the loop antennas are put 

around coal pillars about 70 feet on a side, the range is about 800 feet from 

each antenna. Coverage of several thousand feet is possible, but in this case 

the signals are being complemented by mine wiring, and this is not considered 

typical. 

PROGRESS TO DATE 

Experience with the pagers to date has been limited. Systems have been 

installed at the Robena mine of United States Steel Corp. and the Safety 

Research Mine of the Bureau of Mines. Tests on these systems showed that the 

pagers should be modified to reduce their size and improve their stability. 

However, since these particular units were first-generation prototypes, such 

modifications are not unusual. 
PAGER-PHONE GUIDELINES AND TEST EQUIPMENT 

Robert L. chufol and Koger G. on^^ 

Pager phones continue as a widely used communication system in coal mines. 

Certain limitations, such as the lack of selective calling and the party-line 

type of operation, are offset by the ease of operation and maintenance, low 

cost, and proven reliability in the mine environment. 

The Bureau has developed technical memoranda to teach operating personnel, 

maintenance workers, and inspectors how to install and maintain pager-type 

telephones. These technical memoranda include installztion, lightning protection, cable selection, cable splices, and testing. Line drawings illustrate 

the basic principles of telephone operation, cable splices, protective cir - cuits, and recommended installation and maintenance. The memoranda will be 

published as a Bureau handbook. 

To assist in testing the pager phones, commercial-telephone-testing equipment was modified to suit the unique requirements of these telephones as normally used in coal mines. Additional test equipment was designed to provide a 

tone-test signal and circuit switching to disconnect the test signal generator 

during paging. 

INTRODUCTION 

In large mines, complex communication equipment is used and maintained by 

appropriately trained personnel. Where traffic loads warrant it, the more 

complex telephone systems allowing zone and/or selective calling are used. 

However, in the vast number of smaller mines, the party-line pager phone does 

the job, and the general maintenance crew is able to service the phone system. 

Figure 1 shows the pager-phone models now in use in underground coal mines. 

To help mine personnel install and maintain a pager-phone system, technical memoranda have been developed, and test equipment has been identified for 

use within the mine for go no-go testing. Additionally, to assist manufacturers in developing consistent, quality equipment suitable for the environment, and to assist operating personnel in judging the capabilities of a wide 

choice of pager phones, guidelines were developed for evaluating the acceptability of pager phones. 

lElectrica1 engineer, Pittsburgh Mining and Safety Research Center, Bureau of 

Mines, Pittsburgh, Pa. 

2~lectronics systems section, Arthur D. Little, Inc . , Cambridge, Mass. 
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STATUS OF HARDWARE AND ITS INSTALLATION AND MAINTENANCE 

Controlling and Monitoring Communication Equipment 

Adequate communication within a mine and between the surface and the 

underground work stations is a vital part of the proper operation of an underground facility. Communication is not only an important safety factor, but 

also aids in day-to-day operations and the task of moving coal to the surface. 

In certain classes of coal mines, current regulations require that telephone 

communication be provided between each working section and the surface. The 

comunication equipment installed inby the last open crosscut must be approved 

by the Mining Enforcement and Safety Administration (MESA) as either intrinsically safe or permissible. The MESA inspector must verify that all installed 

equipment functions and meets the safety requirements. By training and current practice, the mine inspector's duties in the area of communication equipment are limited to verifying that acceptable equipment is installed at the 

minimum required locations, and that the equipment is ~perational.~ 

Lack of Training 

A major problem in service and maintenance in all but a few of the larger 

mines seems to be the lack of trained personnel on site, as well as a lack of 

uniformity in installation standards. Reportedly, only minimum effort is made 

to ascertain whether the equipment is reliable and suitable for a particular 

application as long as it is safe to operate. Certain mines experience high 

rates of communication-equipment downtime, while others with the same or similar equipment have minor problems. The only correlation seems to be in the 

on-site maintenance practices, which include installation. 

Operating personnel are becoming more aware of the necessity for reliable 

communication. Many of the systems were installed at the insistence of the 

operating personnel to provide greater reliability, more flexibility in direct 

comunication to isolated work crews, and the capability to interface with a 

public-service network. In some mines, however, operating personnel have no 

interest in communication facilities other than using them to assist in controlling vehicle traffic. 

Federal, State, and company mine-safety inspectors have training and 

experience in matters of structural safety and safe mine-operating procedures; 

in addition, equipment has been developed that enables these personnel to compare these parameters with a common reference. However, the tools and experience required for periodic inspection of communication installations are not 

universally available. To improve this situation, descriptive guidelines have 

3~ong, R. G., and J. J. Ginty. Investigation of Communication Standards as 

Related to Coal Mines. BuMines Open File Rept. 5-75, 1973, 56 pp.; available for reference at Bureau of Mines libraries in Pittsburgh, Pa., Denver, 

Colo., Twin Cities, Minn., Spokane, Wash., and Morgantown, W. Va., and the 

Central Library, U.S. Department of the Interior, Washington, D.C.; and 

from National Technical Information Service, Springfield, Va., PB 240 552. 
been developed that define procedures and instruct personnel in their 

application. 

Im~rovement Possibilities 

The suitability of the telephone performance is, to a large degree, a 

qualitative judgment at present. To change this situation, the following 

steps should be taken: 

Recognize that good communication contributes to safety and to the economic production of coal. Within a busy mine, the ability to control 

vehicle traffic improves productivity and promotes safety, as does the 

ability to call fixed stations easily. 

Examine and define acceptable levels of communication performance. Work 

that has been done by groups such as the telephone companies on analysis 

of parameters that limit the transfer of intelligence in alien environments can provide a basis for this examination. 

Provide the inspector and maintenance personnel with simple measurement 

aids to enable them to evaluate a communication system by comparing it 

with prescribed performance levels. 

The minimum necessary measurements are-- 

Personal judgment of fidelity or clarity of reproduction.--This can be 

referenced to standard recordings taken in typical installations to provide a 

basis of comparison of marginal, acceptable, and nonacceptable conditions. 

Examination of these standard recordings could be part of the training of the 

inspectors and maintenance personnel. 

Measurement of battery status. This can be done with suitable meters 

that measure voltage under load and display the status of remaining capacity. 

Measurement of the signal-to-noise ratio of the audible transmission.-- 

This can be done with a sound meter, again using training and judgment to 

determine the relative effect of the background noise. 

It is evident that mine communication is becoming a more important factor 

in mine safety as well as in day-to-day operations. In fact, because cornrnunication equipment has become so widely used in day-to-day operations, operating 

personnel have become dependent upon communication, and this becomes a part of 

mine-safety considerations. 

GUIDELINES AND TEST EQUIPMENT 

Instructional Guidelines 

Guidelines were developed to provide instruction in some of the fundamental aspects of installation, maintenance, and inspection of underground 
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Methods of testing and 

inspecting the pager phones 

are described, including how 

to test and judge the operational readiness of a pager 

phone. For a more specific 

judgment of pager -phone per - 

formance, detailed instruc - 

tions are given on the use 

of basic test equipment. 

A modified subscriber 

loop test set (fig. 7) was 

manufactured for the Bureau 

by Northeast Electronics of 

Concord, N.H., to measure 

h\\\\\\l\'~\\~'~\'i\\\l~~~Y certain basic phone operations. The set will test 

direct-current voltages to 

FIGURE 3; - Excerpt from guidelines showing recorn- verify battery level and 

mended practice for pigtail splice. paging signal, audio -signal 

levels to measure the audio 
\ Page 

Battery A Switch 

'-~1~1~1~ Page 

Battery B Switch 

FIGURE 5; - Excerpt from guidelines showing system in talking (A) and listening (B) modes. 

output of the transmitter, the audio level on the line, signal losses or 

attenuation, and line leakage to ground. 

An audio test tone can be applied to the line by a specially designed 

tone generator developed for the Bureau by Arthur D. Little, Inc. (fig. 8) 

to provide a standard audio-signal reference for telephone and system diagnoses. A standard tone signal is useful in system diagnoses and in evaluating 

system losses. To avoid interference of normal operation of the pager phone 

during testing, this tone generator produces tone bursts for 10 seconds every 

30 seconds. An additional circuit was added to shut off the tone during paging so that the tone would not be broadcast by the paging speakers. The tone 

source and switching circuit are included in a self-contained, batteryoperated test set. 
'-i~1~1~1.;5 \ Page 

Battery A Switch 

1 

6 1 Page 

+ 

f ier 

4 

Page 

Speak 

Page 

Relay 

4~1~111~;5 Page Switch 

Battery B 

FIGURE 6. - Excerpt from guidelines showing system in paging mode. 

Acceptability Guidelines 

Continuing in this program of developing instructional information on 

pager-phone systems for the use of operating personnel, a set of guildelines 

was developed to establish a common reference for manufacturers, inspectors, 

equipment-certification personnel, and mine operating personnel to judge the 

acceptability of a pager phone for underground coal mines. The guidelines 

cover recommended design, construction, and performance. With this common 

reference, manufacturers can design and fabricate pager phones to meet a known 

standard, and the users can judge acceptability by the same reference. The 

guidelines include recommendations on electrical parameters, construction 

practices, compatibility with other equipment, intrinsic safety, and 

permissibility. 

Electrical parameters included are the paging function, audio transmis - sion and reception, loudspeaker volume, the ability of the telephone to 

function with typical electrical-noise levels, and the relative impact of 

power drain on battery selection, life, and replacement. 

Construction practices applicable to the underground coal mine environment include recommendations for materials selection, packaging methods, serviceability requirements, and selection criteria for components suitable for 

reliable operation underground. 

The telephone must function in the presence of other signals in such a 

manner that it will not interfere with the transmission of these signals on 

the telephone lines. Recommendations are made to guard against interference 

or degradation of the telephone signal or of the other signals on the telephone line. 
FIGURE 7. - M
Practices and procedures are prescribed to insure that a telephone can 

operate safely within an underground coal mine or in a gassy area. These procedures are described in applicable regulations, and they are discussed in the 

guidelines with alternative procedures for conforming to the regulations. 

PROGRESS TO DATE 

These guidelines are currently being reviewed by key industry personnel 

in addition to review by the Bureau of Mines and MESA. They should be available from the National Technical Information Service (NTIS) during the second 

quarter of 1977. 
VISUAL PAGING SYSTEM 

Harry Dobroski, Jr . ,' and John E . 

ABSTRACT 

Pager phones are the primary method of communication in many mines. When 

an audio page message is transmitted, the person called may be out of audible 

range, or the paged message may not be understood because of ambient noise. A 

system has been developed under a Bureau of Mines contract that presents a 

visual indication that a call is being held for a specific person working in 

the mine. This signal can be left on view for a prolonged period without 

additional power drain. Power drain occurs only during the actual time of 

signaling, and this power is supplied by internal battezies. The visual paging system operates over the two-wire system of the pager phone. 

Experimental units have been tested at the Bureau of Mines Safety 

Research Mine in Bruceton, Pa., and smaller, more advanced units have been 

built and are scheduled for testing. 

INTRODUCTION 

Experience with pager phones has clearly indicated the need for additional methods of summoning mine personnel to a telephone. Loudspeaking pager 

phones are ineffective in a working area where the ambient noise level is high, 

and when personnel are simply out of reach of a telephone. For this reason, a 

visual paging system, with a stored message capability, has been developed to 

alert mine personnel to contact the dispatcher. 

DISCUSSION OF SYSTEM 

To alert personnel to a call, the visual pager uses an easily recognized 

pattern of signals (fig. 1) that can be read from as far away as 100 feet or 

more by the light from a miner's cap lamp. The pattern can be of any type, 

but the work to date has focused on a matrix of letters and numerals presented 

so that selected symbols appear in a predetermined position on the grid. The 

code called is identified by its position within the matrix as well as by the 

imprinted symbol on the displayed disk. 

The visual display unit (fig. 2) is about the size of a pager phone, is 

controlled by the dispatcher, and can be operated over the existing pagerphone line. The system can be put into service by simple two-wire connections 

on the pager-phone line. The self-contained visual display unit is powered by 

l~lectrical engineer, Pittsburgh Mining and Safety Research Center, Bureau of 

Mines, Pittsburgh, Pa. 

"~lectronic systems section, Arthur D. Little, Inc., Cambridge, Mass. 
a 12volt lantern battery of the type normally used in a pager phone. Power 

consumption is low and the service life of the battery exceeds that of one 

installed in a typical pager phone. 

In operation, a coded signal is generated at the dispatcher's location by 

depressing a series of pushbuttons or keys on the console (fig. 3). To place 

a page, the dispatcher first presses the "Post" button. This action puts a 

direct-current voltage on the line, which activates the visual display circuit 

and energizes the page circuit at each pager phone. He/she next depresses the 

key (or keys) to identify the person(s) being called. The console sends a 

coded signal to all visual pagers to display the appropriate symbol. The displayed symbol remains in view until the dispatcher presses a ''Clear" button. 

The signal transmitted to the visual pager by the console is a two-tone 

pair of the type used in touch-tone telephones. Just prior to sending the 

signal tones, the direct-current voltage is put on the pager-phone lines. 

This voltage activates all pager phones for a few seconds and also activates 

the visual-pager circuitry. When the tones that select the visual-display 

symbols are transmitted, the pager phones broadcast the tone signal. This 

signal alerts personnel within hearing distance that a call is being made. A 

quick look at a nearby visual pager shows the viewer who is being contacted. 

When a signal has been displayed for about 10 minutes, a lamp on the 
FIGURE 3. - Dispatcheras console. 

dispatcher's panel flashes to remind him/her that the call has not been 

answcred and that he/she should try to contact the desired person by other 

means. 

The display unit (fig. 4) activated by the console consists of disks on 

which the code numbers and letters are imprinted, and the electronics required 

to rc~ceivc and decode the number or letter for display. These disks can be 

grouped into four quadrants, which are divided by reflective axes. The side 

of the disk normally in view is blank; the other side is brought into view 

only on command and is imprinted with a number or letter of a reflective material. When a page is posted, the disk rotates so that the side with the symbol is displayed. When the page is cleared, the disk rotates to its normal 

position with the blank side in view. 

The reflective material (fig. 5) is well suited for use in a mine. Since 

light is reflected in the direction of its source, the display can be read 

over a broad viewing angle by the beam from a cap lamp without additional 

illumination. The letters or numbers may be individually assigned to 
The present display unit prototype is totally self-contained, and has 

integral decoder and driver electronics, in addition to a power supply and 

dry-cell battery. This assembly evolved from a previous engineering model, 

housed in two interconnected assemblies (fig. 2). Additional space was needed 

in the original unit to accommodate rechargeable batteries, power supplies, 

and fixtures provided for display illumination. Experience with the display 

during mine tests (fig. 6) has proven that the best visibility is obtained by 

employing the miner's own cap lamp as the light source to illuminate the 

reflective display symbols, without added illumination. The prototype weighs 

less, is much more compact, and is as simple to install as a pager phone 

(fig. 7). 
FIGURE 6; - Visual pager being tested in mine. 
paging to the visual pager system. 
FIGURE 8. - Visual pager viewed from a distance. 
FIGURE 10. - Sing le-unit zone-pager 

display. 
CALL -ALERT PAGING FOR PAGER -PHONE SYSTEMS 

by 

Harry Dobroski, Jr . ,' Stuart J. Lipof f ," and John E . ~rombl~~ 

AB S TRACT 

The pager-phone system can be upgraded or expanded by adding a visual 

paging system. To further expand the capability of this system, a radio link 

for selective paging to key personnel is under development by the Bureau of 

Mines. In one version, an ultralow-frequency radio transmitter and antenna 

are added to each visual pager unit. Key personnel carry a small radio 

receiver that will provide both visible and audible indication of a page signal. When the dispatcher enters a page signal into the visual paging system, 

the transmitter broadcasts a signal to the called party in addition to the 

visual display. This system is currently under development and is scheduled 

to be demonstrated during 1977. A further refinement of this system will 

allow operation of the radio call alert as part of the basic pager-phone system without the visual pager. 

INTRODUCTION 

Individual radio receivers with selective-code-calling features are 

available in a variety of applications. As noted in earlier papers, certain 

of these systems have been adopted for use in underground coal mines. The 

call-alert paging associated with the computer-controlled MCM-101 telephone 

system is designed to provide selective calling of key personnel in remote 

locations. By adding small radio transmitters to recently developed visual 

pagers, remote selective radio calling can also be implemented reliably over 

two-wire mine pager-phone systems. A 3-kHz, differential-phase, shift-keyed 

signal is used with a parity bit to minimize false alarms. The codes used are 

the same signals used to operate the visual-pager system. 

DISCUSSION OF SYSTEM 

Arthur D. Little, Inc., is developing a self -contained, call-alert radio 

paging system. This system is designed as a low-cost modular addition to the 

visual pager equipment in underground coal mines that have a two-wire audio 

paging telephone system. Another system that will operate independently of 

the visual pager system is also under consideration. A diagram of the visual 

pager system is shown in figure 1. The call-alert system can be added to the 

visual pager (fig. 2), or it can be installed as a completely separate system. 

l~lectrical engineer, Pittsburgh Mining and Safety Research Center, Bureau of 

Mines, Pittsburgh, Pa. 

"~lectronic systems section, Arthur D. Little, Inc., Cambridge, Mass. 

can be limited by gallery acoustics,noise levels, available amplifier power, 

and speaker distortion. Although visual paging systems are well suited to 

high-noise environments, they can be limited by poor visibility and must be 

within a miner's line of sight. To improve underground communication systems 

with a minimum of added cost and equipment, an ultralow-frequency (ULF) radio 

paging system has been designed. 

'all-Alert System 

The call-alert system is compatible with present two-wire underground 

pager-phone systems and the new visual pager system. It can alert any one or 

all of the radio-receiver-equipped personnel in a particular mine area. Each 

receiver is capable of decoding two signals: One signal is unique to each 

receiver; the other pages all receivers simultaneously. 

To trigger the ULF 3-kHz radio transmitter at the dispatcher's console, 

the call-alert system is designed to use the same audio tone pairs for signaling over the pager-phone line as used by the visual paging system. The transmitter antenna consists of a single loop of wire wrapped around the nearest 

pillar. The system is designed for use where mine personnel may be working 

outside the range of both the audio and visual paging systems. Any personnel 

who must work in such areas can carry a small, lightweight, battery-operated 
the same mine. For independent installations, the same dispatchers console 

used for the visual pager is required on the surface. Underground, the 

battery-operated call-alert transmitters can be connected to the two-wire 

pager-phone line at convenient locations, and the associated antennas 

installed around nearby coal pillars. 

In operation, the dispatcher keys a particular page button, which sends a 

two-tone audio pair along the pager-phone's two-wire circuit. The two audio 

tones cause any visual pagers on the line to display an alphanumeric character 

and cause the call-alert radio transmitter to send a coded signal five times. 

The receiver responds to its unique code (or the general signal) with both an 

audio alarm (buzzer) and visual signal (light). Each time a receiver is 

turned on, both the audible and visible alarms go on, as a check of both 

battery condition and alarm operation. The on-off test switch can be recycled 

at any time to test the alarms. A reset button is prwided to turn off the 

alarms . 

The pocket-sized receiver is powered by rechargeable batteries that can 

operate the receiver continuously for up to 16 hours (two shifts) before 

requiring an 8-hour recharging cycle. The radio transmitters are powered by 

self-contained batteries. 
By supplementing audio and visual paging systems with a radio-transmitted 

call alert, personnel response to pages should be greatly improved, and mine 

safety should be enhanced by the ability of aboveground dispatchers to provide 

rapid and early warning of safety hazards or broadcast evacuation alerts to 

all underground personnel. 

PROGRESS TO DATE 

The visual pager is currently undergoing field trials. The electronic 

components of the call-alert system are undergoing laboratory tests, and field 

trials are expected to begin in mid-1977. The complete call-alert design 

package should be available early in 1978. 
RADIO PAGING 

by 

Harry Dobroski, Jr.' 

ABSTRACT 

It is necessary to page key operations personnel in underground coal 

mines reliably and selectively. A system of commercially available hardware 

developed by the Bureau allows a dispatcher to voice-page selected individuals, 

deliver short messages, or inform them where to go to receive detailed 

instructions . 

INTRODUCTION 

A modern coal mine is a vast underground complex of working sections, 

haulageways, and repair shops, which extends for several square miles underground. Key personnel may not work in fixed locations; for instance, a section foreman may be assigned to a single section, but that section could 

embrace a vast area, or maintenance personnel or electricians could be anywhere in the mine at any time. Because such personnel are important to the 

smooth operation and high productivity of a mine, considerable production 

losses could occur if they cannot be located when they are needed. 

The communication system in most mines consists of pager phones, carrier 

phones, or both. Although these systems are reliable, they do not provide for 

communicating with roving personnel. In fact, they are simply station-tostation devices. If a person being paged is not within hearing range of the 

speakers on these phones, he/she will not get the message. Thus, considerable 

time may be lost in trying to locate an individual just out of range of a 

phone, or maybe thousands of feet from a phone. Clearly, a system is needed 

that can page selected individuals wherever they may be in an underground 

complex. 

DISCUSSION OF SYSTEM 

System Characteristics 

In a mine that uses rail haulage, there is usually a carrier phone in 

each locomotive or jeep. These carrier phones allow the vehicle operators to 

communicate with each other and with a dispatcher who controls the flow of 

traffic. The trolley line itself is the communication link between all the 

vehicles and the dispatcher. 

1Electrical engineer, Pittsburgh Mining and Safety Research Center, Bureau of 

Mines, Pittsburgh, Pa. 

Does not turn 

on 2 

Trolley line . - ' - - 

Selective paging 

signals to pager 1 

Carrier 

phone 

Beep plus \ 

\ voice - Manual Pocket pager message push button / 1 turns on 

encoded / 

Dispatcher's office 

FIGURE 2. - Block diagram of general radio-paging system. 

tone bursts whose frequency depends on which pushbutton was activated. These 

tone bursts are transmitted from the carrier phone in exactly the same way 

that a voice signal would be sent out. As explained before, all the mine wiring acts as an antenna, allowing these tones to be broadcast throughout the 

mine. 

The pocket receivers that have been developed to respond to these tones 

are really small FM radio receiver^.^ They are activated by the tones, and 

remain on for about 15 seconds. 

Once the tones have been sent, the dispatcher then talks into his carrier 

phone in the usual manner. Only the pocket pager activated by the tones will 

receive the message. Hence, the dispatcher can radio-page any individual, no 

matter where that individual is in the mine. In an emergency, a special tone 

activates all pagers at once. Of course, the radio pager is a receiver only 

and cannot be used to talk back to the dispatcher. Therefore, the system 

should be used only for paging, not for giving instructions. 

O~eration of Svstem 

The current system (fig. 2) is designed so that only the dispatcher can 

initiate a page, because he/she is the only one who has a carrier phone 

equipped with an encoder. However, other encoders could be used with other 

carrier phones, if necessary. Figure 3 shows a system in which the encoder 

is remotely accessed by a dial telephone line. Thus, any dial telephone 

'spencer, R. H., and H. E. Parkinson. Roving Miner Pager. Proceedings of 

Bureau of Mines Technology Transfer Seminar on Mine Communications, Bruceton, Pa., Mar. 21-22, 1973, BuMines IC 8635, 1974, pp. 17-35. 
Controlledby associated with themine 

telephones switchboard (PBX) could be 

v , used to initiate a page 

voice message. 

FIGURE 3. - Block diagram of system with remotely 

I/'//' ////I 

accessed encoder, Existing pager 

=+g- .. 

/'//I- ate the system, a user goes 

receivers are equipped with 

a small internal timer that 

Automatic 

encoder 

turns the device off after a preselected time, usually 15 seconds. Any voice 

without ever being near the 

encoder. Such a system 

offers an advantage should 

many people have to page 

-- - 

Telephones in mine ,' into the mine from several 

to a telephone and dials the 

message lasting longer than this is cut off unless an override button on the 

PBX 

surface buildings Surf ace 

Underground 

pager is depressed to hold the call. 

surface locations. To oper - 

A continuous "On" mode is not desirable because it wastes battery power. 

That is why the pagers are equipped with the automatic timing device. In this 

mode, batteries last for months. However, there are times when the continuous 

"On" mode is useful; for example, when continuous monitoring of the radio paging system is important to certain maintenance personnel. 

_I telephone dial pulses into 

Trolley line 

---- tones and transmits them via 

y, /t/ 

the carrier phone. The 

tones turn on the desired 

pager, at which time the 

user can speak into the 

Pagers mouthpiece to deliver the 

Carrier phone 

The radio paging system can be operated on a special channel, or on the 

regular channel used by the locomotives. The only difference is that if 

everything is included on the same regular channel, all the carrier phones 

will hear the paging traffic, but the pagers will hear only what is sent to 

them directly. 

number assigned to the pager 

he/she wishes to call. Then, 

the encoder converts the 

In spite of the large amount of mine wiring that aids paging-signal propagation, it may still be impossible to transmit a paging signal to certain 

areas in the mine. When this occurs, the mine overburden can often be used as 

a large antenna to aid the signal in reaching these areas (fig. 4). However, 

this scheme is somewhat complicated compared with the other paging schemes, 

although it provides good local coverage. 
From manual or automatic 

encoder system 

PROGRESS TO DATE 

Trolley line 1 A radio paging system 

Pocket pagers 

- ---- -- - - 

(Gives haulageway coverage) that incorporates the auto- 

(Gives remote coverage) o/ matic encoder system (fig. 3) 

I Pocket pager and the roof-bolt system 

I (fig. 4) is in operation in 

I the Bureau of Mines Safety 

connected to the carrier 

phone by No. 12 wire. With 

Roofbolts Carrier 

phone 

repeater 

L 

FIGURE 4. - Block diagram of system using roof-bolt- this system, paging can be 

type antenna; effected from as far away as 

500 feet from a roof bolt. 

All hardware is commercially available from the National Mine Service Co. 

Research Mine near Bruceton, 

Pa. The automatic encoder 

and carrier phone are 

Several pagers (fig. 5) were loaned to the Robena mine of United States 

Steel Corp. for informal evaluation. Although no encoder was pruvided, the 

mine made excellent use of the pagers. By taping the "On" button down, the 

I located on the surface; all 

else is underground. The 

in-mine roof bolts are separated by about 300 feet and 

mine superintendent used the pager to monitor all carrier-phone traffic from 

dispatcher to locomotives and jeeps, and excellent pager coverage resulted in 

all areas of the mine of reasonable distance. It appears that if a mine contained only a single wire (say, the trolley line with no branches), pages 

could be received several hundred feet from this line. Other lines, such as 

phone lines, control lines, and the like, either parallel to or across the 

trolley line, would simply improve the coverage that much more. 

Regular haulageway communications (88 kHz) 

/r- Pocket pager - 1-7- 

Locomotives 4 Jeeps 

Supervisory and maintenance 

personnel monitoring all 

haulageway communications 

FIGURE 5, - Robena experiment. 
APPENDIX. - -COMMUNICATION REPORTS 

The following is a list of reports available in the area of communications. These reports may be obtained from the National Technical Information 

Service (NTIS), U.S. Department of Commerce, Springfield, Va. 22161. Microfiche copies are $2.25 each, and paper copies are available at the prices 

indicated. 

Company name NTIS No. NTIS price Title 

Wes tinghouse Coal Mine Rescue and Survival 

PB 208 266 $5.50 V. 1--Survival Subsystem 

PB 208 267 9.00 V. 2--Communications/Location 

Subsystem 

PB 208 268 9.00 V. 3 --Rescue Subsys tem 

J. H. Crary PB 213 204 9.00 Determination of the Electromagnetic Environment 

A. D.Little PB218688 4.00 A Field Program and Instrumentation 

System for EM Noise Measurements 

A. D. Little PB 218 658 4.50 Assessment of EM Noise Measurements 

Taken by Bureau of Mines 

Contractors 

Westinghouse PB 226 600/AS 5.50 EM Location System Prototype and 

Georesearch Communication Station Modification 

West Virginia PB 225 862/AS 6.00 Analysis of Communication Sys tems 

University 

National Bureau PB 226 773/AS 4.00 Survey Report of the USBM EM Noise 

of Standards Measurement Program 

National Bureau PB 226 781/AS 3.50 Applicability of Speech Bandwidth 

of Standards Compression Techniques in Mine EM 

Communications 

Colorado School PB 231 154/AS 7.75 Thru-the-Earth Electromagnetics 

of Mines Workshop 

Mine Safety Develop, Assemble, and Install a 

Appliances Permissible Surveillance and Communication System in the Bureau of 

Mines Mining and Safety Research 

Center Coal Mine, at Bruceton, Pa. 

PB 231 574 4.00 V. 1--SystemDescription 

PB 231 575 4.50 V. 2--Circuit and Installation 
Company name NTIS No. NTIS price Title 

Westinghouse PB 232 880/AS $4.50 Electromagnetic Location ExperiGeoresearch ments in a Deep Hardrock Mine 

Continental Oil PB 232 887/AS 5.50 Seismic Miner Detection and LocaCompany tion System; Phase I--Final Report 

A. D. Little Survey of EM and Seismic Noise 

Related to Mine Rescue 

Comunications 

PB 235 069/A~ 6.00 V. 1--Emergency and Operational 

Mine Comunications 

PB 235 070/AS 10.50 V. 2--Seismic Detection and Location of Isolated Miners 

Westinghouse PB 235 604 21.50 Trapped Miner Location and Comuni- 

(set> cation System Development Program 

PB 235 605/A~ 7.50 V. 1--Development and Testing of an 

EM Location System 

PB 235 606/AS 4.50 V. 2--Detection and Location of 

Entrapped Miners by Seismic 

Means (by Dr. S. J. Duda) 

PB 235 607/AS 5.00 V. 3--Monitoring, Locating, and 

Communication System for 

Normal Mine Operation and 

Post -Disas ter Rescue 

Operations 

PB 235 608/AS 4.50 V. 4--PerformanceTestandEvaluation of a Full Wave Location 

Transmitter 

Collins Radio PB 237 218/AS 4.00 System Study of Coal Mine 

Communications 

Colorado School PB 237 852/AS 5.50 Research on the Transmission of EM 

of Mines Signals Between Mine Workings and 

the Surface 

A. D. Little PB 240 552/AS 4.50 Investigation of Communication Standards as Related to Coal Mines 

Collins Radio PB 240 481/AS 3.50 Waveform Generator for EM Location 

of Trapped Miners 

National Bureau COM 741 1688/AS 4.00 Surface Magnetic Field Noise Meaof Standards surements of Geneva Mine 

National Bureau COM 741 1687/AS 6.00 Electromagnetic Noise in Grace Mine 

of Standards 
Company name NTIS No. NTIS price Title 

National Bureau COM 741 1717/AS $6.75 Electromagnetic Noise in McElroy 

of Standards Mine 

National Bureau COM 741 1718/AS 5.50 Electromagnetic Noise in Itmann 

of Standards Mine 

National Bureau COM 741 1450/AS 4.50 Time and Amplitude Statistics for 

of Standards Electromagnetic Noise in Mines 

National Bureau COM 751 0258 6.00 Electromagnetic Noise in Lucky 

of Standards Friday Mine 

Continental Oil PB 243 068/AS 5.00 Seismic Mine Monitor System-- 

Company Phase IV report 

Continental Oil PB 241 504/AS 4.00 SeismicMineMonitor System-- 

Company Phase I1 report 

A. D. Little Technical Services for Mine Communications Research 

PB 249 829/AS 5.00 TaskD--ApplicabilityofAvailable 

Frequency Multiplexed Carrier 

Equipment 

PB 249 830/AS 5.00 TaskB--ApplicabilityofState-ofthe-Art Repeaters for Wireless 

Mine Communications 

PB 249 831/AS 5.00 TaskA--ApplicabilityofState-ofthe-Art Voice Bandwidth Compression Techniques for Wireless Mine 

Communications 

Collins Radio PB 244 896/AS 20.00 Research and Development Contract 

(set> for Coal Mine Communication 

Systems 

PB 244 897/AS 4.50 V. 1--Summary and Results of System 

Study 

PB 244 898/A~ 5.50 V. 2--Mine Visits 

PB 244 899/A~ 7.50 V. 3--Theoretical Data Base 

PB 244 900/AS 4.50 V. 4--Environmental Measurements 

Continental Oil PB 251 705/AS 4.00 Seismic Mine Monitor System 

Company 
The following publications are available without charge from the Publications Department, U.S. Bureau of Mines, 4800 Forbes Avenue, Pittsburgh, 

Pa. 15213: 

Lamonica, J. A., R. L. Mundell, and T. L. Muldoon. Noise in Underground Coal 

Mines. BuMines RI 7550, 1971, 11 pp. 

Lee, F. R. Permissible Mine Equipment Approved by the Bureau of Mines During 

1967-68. A Supplement to Bulletin 543 and Information Circulars 8220, 8299, 

and 8372. BuMines IC 8463, 1970, 25 pp. 

Lepper, C. M., and J. H. Scott. An Improved Electrical Resistivity Field System for Shallow Earth Measurements. BuMines RI 7942, 1974, 20 pp. 

Parkinson, H. E. Mine Pager to Public Telephone Interconnect System. BuMines 

RI 7976, 1974, 14 pp. 

U.S. Bureau of Mines (Staff--Mining Research). Mine Communications. Proceedings: Bureau of Mines Technology Transfer Seminar, Bruceton, Pa., 

Mar. 21-22, 1973. BuMines IC 8635, 1974, 86 pp. 

In addition, Preprint No. 76-F-133, entitled "A Review of Research on 

Underground Mining Communications," by John N. Murphy and Howard E. Parkinson 

is available from the Society of Mining Engineers of AIME, 540 Arapeen Drive, 

Salt Lake City, Utah 84108. 

a8U.S. GOVERNMENT PRINTING OFFICE: 1977-703-001 I71