U.S. BUREAU OF MINES NEW DEVELOPMENTS 

IN MINE COMMTJNICATIONS 

Howard E. ]?arkinson 

Industrial Hazards and Conawnicat ions 

Pittsburgh Mining and Safety Research Center 

Bureau of Mines 

U.S. Department of the Interior 

Pittsburgh, Pa. 

ABSTRACT 

A brief description is given of various Bureau of Mines research 

activities that have begun since July 1974 and are not being reported on by others at the Third West Virginia University (WW) 

Conference on Coal Mine Electrotechnology. 

An essential feature of the various projects is that they are 

pragmatic. The projects are applied research and are carried out 

both by the Bureau in-house research group and by other research 

groups through contract research. 

Pro j ects have been directed toward wired-type communications with 

a special effort to modify the wired systems so as to be more effectively used. The projects are in three groups: Pager phone systems, 

trolley line phone systems, and guided-wire wireless communications. 

Also, a brief sketch is given of research that is essential for further 

developments in mine communications. 

From the early results of these various projects, the Bureau 

has good reason to project that there will be improved performance 

of existing communication systems and that communications will be 

extended to other individuals working in areas that are excluded 

from present mine communication systems . INTRODUCTION 

Certainly the winds of change that will bring about lasting 

communication improvements in many mines have been set in motion. 

Two years ago, at our Second WVU Conference on Coal Mine Electrotechnology, our conference chairman took a poll of the attendees 

and over 82 percent expressed themselves as feeling that, for both 

the near and long term, it would be necessary to have improvements 

in mine communications. The communication session this morning 

provides the opportunity for highlighting two approaches that will 

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improve phone systems: (1) Providing private line voice communications 

to any phone in the mine and (2) a direct connection of the under 

ground phones with the above ground phones. About 60 percent of our 

second conference conferees felt that both these features were desirable . 

A second area highlighted at this morning session is the 

two-way radio. Although only about 20 percent of the' previous conferees expressed the feeling that this was desirable, there is a 

need for radio as the usage of trolleyless and also trackless 

haulage increases. The Bureau has new developments since the 

second conference, in both phone systems and wireless radio. 

These will be presented by others at this conference. 

The new developments that I shall be talking about are to 

improve existing telephones and trolley phone systems and to provide 

a new type of communications in face areas. I shall also discuss the 

developments required for future improvements in mine communications, 

supervisory control, and automation. 

MINE PAGING TELEPHONES 

Paging telephones are the most widely used mine communications 

system. A particular limitation of this system is the inability 

to alert a person,who is somewhat removed from the location of the 

phone that he has been paged. Paging or call alert has been singled 

out for improvement. The Bureau has selected means for improvement 

that permit a call alert while keeping the telephone system intact 

and without undesirable interference with the phone operation. 

A visual page display has been developed. The prototype of 

the visual system allows for 16 call displays. The display is 

controlled by the dispatcher who controls two basic functions: 

Post or clear, and identification. He first makes a selection 

of post or clear by depressing the post or clear button. The 

depressing of one of these buttons will actuate a switch that supplies 12-volt dc to the phone line and illuminates the switch 

button to indicate that 12 volts is applied to the phone line. 

Simultaneously with the applying of the dc voltage, there is a 

short-duration, multiple-frequency tone code that distinguishes 

a post operation from a clear. A post or clear selection must 

be followed by an identification selection from one of the 16 

symbols, which are associated with particular individuals. Depressing an identification button causes transmission of a multiple 

frequency tone. This tone burst is also transmitted simultaneously with the dc voltage. If a post function was initiated, 

the depressed symbol button will light, indicating that posting 

has been accomplished. If a clear was initiated, the lighted 

symbol button is extinguished, indicating the clear is completed. 

The post or clear light is extinguished when the dc is removed 

from the phone line. This is accomplished after an identification 

button has been depressed or by the runout of an 11-second timer 
that begins running when either the post or clear function button 

is depressed. The symbol button illumination is a reminder to 

the dispatcher of the pages posted and their status. A flashing 

symbol key indicates that the page h.as been posted for more than 

10 minutes. 

The display units, which will be located throughout the mine, 

consist of a 16-disc display module, a protective NEMA-type 12 

enclosure, and a lamp assembly. The overall size is 14 inches 

by 12 inches wide by 6 inches deep, with top and bottom flanges 

for wall mounting. In the prototype, there is a second box housing 

a rechargeable battery, a charger with 115-volt ac line connector, 

a tone receiver and decoder, a solid state relay, and display 

driver electronics. The unit can be powered from 12-volt lantern 

batteries, and battery life is comparable to the pager phone 

battery life . The 16 discs are in a 4 x 4 matrix. Each disc is free to 

rotate on a horizontal axis through the center and in the same 

plane as the disc. The disc is 2-114 inches in diameter; one 

side is phosphorescent green, and the other has a retroreflective 

red symbol. Mounted on one edge of the disc is a permanent magnet 

that is alined with an electromagnet mounted behind the disc. 

The pole piece of the electromagnet is magnetized by a pulse in 

the coil. The remnant magnetism in the pole piece rotates the 

permanent magnet which is affixed to the disc, thus causing either 

the blank side or the symbol side to be seen. The disc is magnetically held in the desired position by the permanent magnet. Thus, 

no power is required to hold the disc for viewing. The background 

is caused to glow either by a blinking strobe or by the rays from 

an approaching cap lamp. The entire background of the display 

glows a faint green, thus enabling the approaching viewer to detect 

the presence of the display. The display is periodically flashed 

by the blinking strobe. The phosphorescent surface will first 

glow brightly, and in about 112 hour, 80 percent of the brightness 

will be dissipated. In the absence of any light, the display 

can be read, depending upon the viewer's eye-dark adaptation, 

up to 112 hour after a light flash. Also, because of the red-green 

contrast, the symbols can be read in bright light. 

There is also a call alert pocket page version that utilizes a 

loop in place of the visual display box and emanates an electromagnetic signal that is received in a small pocket receiver carried 

by the miner. Each system provides a means of selectively calling 

attention to an incoming call. All call alert replies are directed 

to the dispatcher, who forwards a message. 

TROLLEYWIRE PHONE 

There are two backbone mine communications systems, the paging 

phones and the trolleywire phone. The trolleywire phone is a 

carrier current communications system for the dispatch and control 

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of track haulage vehicles. The problems encountered are more severe 

than those of the paging phone. The equipment must operate from 

the adverse environment of a mine haulage locomotive and over a 

transmission line intended for dc power distribution. Despite 

frequent instances of performance deficiencies such as dead spots, 

garbled transmissions, and damaged equipment, especially microphones, the carrier communications are used because there is not 

presently available a satisfactory alternative. Hopefully, from 

the radio developments being discussed at this conference, there 

will come a viable alternative to the trolleywire phone. Because 

the carrier phone is in extensive use in the mining operations, 

the Bureau has initiated a program to eliminate present performance 

deficiencies and to improve the overall capability of a trolleyline 

communications system. 

Dr. James R. Wait and his associates at the Institute for 

Telecommunication Sciences, Office of Telecommunications, have 

analyzed the utilization of the trolley wire and its rail-ground 

return as a radiofrequency transmission system. The results of 

the analysis, which took into consideration the rock conductivity, 

the mine geometry, the position and size of the trolleywire, and 

frequency variation from 50 KHz to 800 KHz, show that the trolleywirerail system represents a low-loss transmission line and should 

provide communications over very long ranges, like 100 miles, for 

typical equipment now in use. 

Richard Spencer, Arthur D. Little, Inc., has been actively 

pursuing a trolley phone improvement program. Dick has completed 

his study and has identified particular deficiencies, has singled 

out the restraints that inhibit the obtaining of a 100-mile range, 

and ,has proposed some means of overcoming these deficiencies and 

restraints. 

For this talk, I have singled out just two problems--(l) dead 

spots and (2) the restricted space aboard locomotives and jeeps. 

Dead spots, places where signal level is beneath the threshold 

of the receiver, result from the shunting and mismatch conditions 

caused by various noncommunication devices connected to the trolleywire. 

A large number of devices have been identified as low-impedance 

loads at the frequency of the phones, 88 KHz or 100 KHz. Of these 

devices, two are most important, the rectifiers feeding the dc to 

the trolleywire and the lights on the vehicle. These problems 

can be solved by isolating the low impedance loads from the carrier 

frequencies. Fortunately, this can be accomplished by inserting 

a tuned circuit between the low impedance device and the trolleywire. 

For the lights, which have small dc currents and low rf impedance, 

the solution is practical. The inserted tuned circuit comprises 

a coil and a capacitor in a parallel arrangement; this allows the 

dc current to flow uninhibited and blocks the carrier from being 

shunted by the low-impedance device. 
Westinghouse Research Laboratory, Pittsburgh, Pa., has developed, under Bureau contract, an active impedance multiplier that 

can be used for elevating the carrier frequency impedance of a 

locomotive. It is relatively small and can be used at the input 

of a locomotive. This causes the trolleywire to look more like 

a 200-ohm carrier transmission line. However, impedance multipliers 

are rather costly and are not yet commercially available. 

The more severe problem is the rectifier. The approach of 

the solution is the same as that for isolating the locomotive 

headlight, but the wire in the coil must be of the same size as 

the feeder conductor. The large wire is difficult to arrange in 

a coil that will have a high reactance to the carrier frequency, 

and thus a rather inefficient large-value capacitor is required 

to form a parallel resonant circuit. Experiments with the lowquality resonant circuit have resulted in doubling of the carrier 

voltage. This is not much of an improvement. However, a Bureaudeveloped hoist phone has a super sensitive receiver, i.e. about 

1,000 times more sensitive than the present trolleywire phone, and 

works very effectively from a small pickup loop. By separating 

the transmitter and receiver portion of the phone, it is possible 

to directly connect the transmitter to the trolleywire and inductively couple the receiver to the signal field near the loop. 

Because of the high sensitivity of the new equipment, it might 

be possible to develop a new trolleylj-ne phone that would work 

better where there are low-impedance devices on the trolley. 

This has been tried, and field measurements showed as much as 

an 8-db improvement in signal-to-noise ratio for a loop-received 

signal. It might be necessary to have input both from a loop 

and from direct contact. This would require selecting the better 

signal. 

Sometimes, everything begins to fall in place. The other 

big problem with carrier phones is the restricted space for mounting 

microphone, speaker, trolleyphone, and voltage-adjusting devices 

upon, in and on the locomotive. New electronic chip-type cop 

ponents, some of which are used in the Bureau-developed hoist 

phone, allow the designer to do away with the bulky passive tune 

circuits. If we exercise a little ingenuity, a trolleywire phone 

could probably be miniaturized to the point where it would fit 

into the extra space in the housings of some of the heavy duty 

speakers. The Bureau is seeking a cost-sharing agreement with 

an equipment builder to develop an improved unit. The improved 

phone sensitivity might allow for a good reduction in the transmitter 

power; if this happened, the unit could operate from a small, 

sealed 12-volt battery with a generatolr somewhat like a present 

car generator. Then, at long last, we would have removed from 

the trolley, except for the signal con.nection, all of the communications equipment that has been bedeviled by the 300- or 600-volt 

dc on the trolley. 
FACE AREA COMMUNICATIONS 

The Bureau, in the Inherently Safe Mining System program, 

has developed a face communications system for both a shuttle car 

haulage and an extensible belt face haulage. These systems combine 

radio, carrier, and telephone to permit communications between 

the roving face boss-and his crew and between the roving face boss 

and the top-side office, There is some fallout from these programs 

that looks practical for longwall sections and bridge conveyor 

sections, 

Wireless, or radio as it is better known, is seldom totally 

wireless in mine communications. Radio wave propagation is very poor 

in the pit, The British have developed the leaky feeder cable with 

inserted repeaters in their attempt to get minewide wireless communications. But it isn't wire LESS--it has a helper wire called a 

leaky feeder. The Bureau has been prodding the development of radio, 

not minewide, but at places in the mine where the miner's freedom to 

move about makes it essential that he have wireless communications. 

There are three aspects to the wireless development. One is 

the work of the Motorola Co. which is now providing a portable 

repeater and a new line of handi-talkies that are half the size 

of the HT220 series used by the Bureau in the earlier experiments. 

This equipment has the MESA approval for intrinsically safe devices. 

A second aspect is the applications--the longwall section 

and the beltway section are such that radio wave movement must 

be through openings that are restrtcted by machinery. These 

restrictions greatly reduce the already limited radio propagation 

in the mine openings. The restriction is so bad that it is 

impossible to establish communication without the aid of helping 

leaky cables. In these particular applications, one termination 

of the leaky feeder is an antenna that enhances the propagation 

into free space and the other is a repeater. The handi-talkies 

cannot communicate with each other without the repeater. They 

transmit on one frequency and receive on another frequency that 

is transmitted by the repeater. The repeater has been modified 

and can also double as a base station if required. To enhance 

the acceptance of the units by the miners, there is a battery 

charger on the section so the miners do not have to take the units 

in and out of the mine. 

The third aspect of the problem is the microphone/speakerto-miner interface. The Bureau has contracted with EPSCO Labs 

for a thorough study of the problem of communicating with a 

working miner who often does not have his hands free and is in 

an area where acoustic noise is very restrictive to hearing a 

speaker on portable radios. Thomas Giordano of EPSCO has well 

defined the problem and has made some excellent recommendations 

which the Bureau is implementing in a prototype system. The 

system uses a noise canceling airpath microphone that picks up 

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the speech signals at the miner's lips. The hearing device is 

an earphone-earcup combination. This arrangement also provides the 

added benefit of protecting the hearing of the wearer of the device. 

These devices are coupled to the helmet, and a small cord with 

plug connector allows for the separating of the microphone-speaker 

helmet set from the transreceiver, which is carried either on the 

belt or in a chest pack. A small switch, which may be clipped 

onto the coveralls, is used to key the transmitter. Of course, 

some miners do not need the special modifications for high-acousticnoise areas, and they can utilize the microphone-speaker 

provided with the handi-talkie . 

A fully wireless section radio system, coupled to a dial telephone; has been developed by the Bureau in conjunction with Collins 

Radio as an add-on feature to the coaxial cable telephone system, 

thus permitting the interface of wireless radio with the mine telephone. This will be more fully discussed by Harry Dobroski in his 

talk later this morning. 

These developments of radio are attractive, and the Bureau has 

made arrangements with mine operators to thoroughly evaluate the 

systems and to measure their effect iveness . 

An incidental benefit that most likely will develop from these 

face radio systems will be control (and monitoring systems. Already 

there is talk of using the radio to remotely monitor the continuousmining-machine me thane reading outb y at the section telephone. 

There is an active interest in remotely controlling a longwall 

shearer, and there is also talk about automatic control of the 

mobile bridge conveyors from the continuous-mining machines. 

Next, we want to look at some of the work the Bureau is 

doing that is essential for further developments in mine corn 

munications, monitoring, and remote and automatic controls. 

RESEARCH FOR FURTHER DEVELOPMENTS 

The communications program is im ongoing program. The 

studies, the developments of hardware, the developments of systems , and the demonstrations of hardware ;and systems will enable us 

to better provide for the future needs of the mining industry. 

An extensive study was made of "The Applicability of State of 

the Art Voice Bandwidth Compression Techniques for Wireless Mine 

Communications." This study was undertaken with the hope that I I now" might be the time to develop is real time bandwidth corn 

pression scheme that would enable equipment builders to come 

up with a portable radio unit that would consume 1/100 of the 

power of those developed by the Sourth Africans for mine rescue 

teams. The conclusion is that "now'" is not the time; the best 

that can be done with bandwidth compression will not greatly 

reduce the physical size of the unit or significantly reduce 
the battery drain. However, from other advice in the report, 

we have moved ahead with refuge chamber communicat ions wherein 

we are having developed a non-real-time, non-voice-type sys tem 

that can be used for character transmission from the mine to 

the surface. 

Another study, titled "Applicability of State of the Art 

Repeaters for Wireless Mine ~ommunications ,I1 was initiated with 

the expectations that the mining industry might soon have a means 

of communicating with trackless and trolleyless vehicles without 

the expense of installing and maintaining a special leaky feeder 

cable. There is no available utopian Fl/Fl repeater that can 

simplify the solution to our problem of high propagation loss 

that would require repeaters about every 2,500 feet. But all 

is not bleak, for it does appear that we can develop a Fl/F2-~3 

repeater system that will function in conjunction with the 

telephone system. With the combined systems it will be possible 

to communicate with vehicles about 1,350 feet from the phone 

line. This will require that telephones be established every 

2,500 feet along the phone line and that they be interfaced 

to the radio. 

Another study , titled "Applicability of Available Multiplex 

Carrier Equipment for Mine Telephone Systems," also turns out to 

have a discouraging conclusion for coal mines. However, we are 

also actively engaged in metal-nonmetal communications where we 

are not faced with the problem of permissibility and the problem 

of interfacing between carrier and pager phones. Very few metalnonmetal mines use pager type telephones. The Bureau is cooperating 

with the Sunshine Mining Co. and we hope to derive about five 

additional phone channels over a single existing telephone pair. 

Generally, this concept is not economical for coal mines using 

the mine pager phone system. 

There is a report titled "Propagation of Radio Waves in Coal 

Mines" that will interest designers who would like to know more 

about radio propagation in haulageways and shafts. There is an 

interesting finding for most of you who might want to communicate 

between the front and the rear of a 600-ioot-long train in a haulageway. The finding is that if you have 5 or 6 feet of clearance between 

the train and one sidewall and you use the 450-MHz frequency, you 

can do it without any helping cable. Also, for those of you who 

never asked but always wished you knew huw a hoist phone really 

worked, there is a good theoretical analysis of deep shaft communication. 

Another study is entitled "~ata Flow Requirements for 

Remote Supervisory Control of Continuous Mining ~achines." The 

purpose of this investigation was to get a feel for the magnitude 

of data that must be transmitted if indeed a supervisor was to 

monitor and control a mining section from a point outby the working 
face. In order to restrict communication channels to bandwidths 

that are practical for mining, it was decided that some machines 

would have their own small computers and that only video and voice 

signals would be transmitted in analog form. All other information 

would be transmitted as a synchronous bit stream over digital 

channels. The conclusion is that for short distances like 2,000 

feet there would be no difficulty in transmitting 60,000 bits 

of information per second, and that if necessary it could be done 

over a single twisted pair. This is encouraging because the Bureau 

is looking into the possibility of developing a remote supervisor's 

station from which the mine section foreman might be able to monitor 

and control an entire mining section. 

There are other Bureau studies, hardware projects, systems 

developments, and demonstrations tha.t I have not mentioned. These 

are covered in a summary way by John ~urphy's paper entitled 

"Overview of U.S. Bureau of Mines Research in Electrotechnology. !I 

This paper will be published in the proceedings of the Third WW 

Conference on Coal Mine Electrotechnology. 

CONCLUSIONS 

The Bureau has started a number of development projects, 

some of which have already reached the mining industry and have 

begun to provide improvements in mine communications. Others 

will be reaching the mining industry in the next two years. 

The Bureau and others in the mining industry are accepting the 

challenge to improve mine communications as needed to conmnicate 

with both voice and data.