COLLINS 

report 

Cottins Radio Company 

Volumc? 7 Summary and Results of System Study 

Research and Development Contract 

for Coal Mine Communication System 
523-0765829-00 7 2 1 M 

15 November 1974 

report 

Volume 1 Summary and Results of System Study 

Research and Development Contract 

for Coal Mine Communication System 

Prepared for Department of lnterior 

Bureau of Mines 

Washington, 0. C. 

USBM Contract No. H0232056 

Printed in the United States of America 

DisclaimerNotice: "The views and conclusions contained in this document are those of the authors and should not be interpreted as 

necessarily representing the official policies of the Interior Department's Bureau of Mines of the US Government." 

Collins Radio Company 1 Cedar Rapids, Iowa 
Volume 1 

Table of Contbnts 

Page 

Section 1 Introductioln ............................................... 

Section 2 Summary ................................................... 

2.1 Communication System Specification ...................... 2.2 Communication Systems Evaluation ........................ 2.3 In-Mine Data Gathering ........................................ 2.3.1 Telephone Systems ........................................... 2.3.2 Trolley Phone Systems ...................................... 2.3.3 Longwall Comrnunications ..................... .. ........... 2.3.4 Communications Center Requirements ................. 2.4 Theoretical Data Base ......................................... 2.5 Experimental Programs ....................................... 2.5.1 UHF ................................................................ 2.5.2 VLF .............. I ................................................. 

Section 3 Communications Systems Evaluation .............. 

3.1 'UHF Systems ..................................................... 3.2 LF Systems ....................................................... 3.3 Wired Systems .................................................... 3.4 Mixed Systems .................................................... 

Section 4 Communiczttion System Specification ............... 

4.1 Operational Requirements ..................................... 4.2 Technical Specification ........................................ 4.2.1 Environmental ................................................. 4.2.2 Reliability and Repairability (Usability) ................ 4.2.3 Minimal Fixed- Mount Intrarnine Communications ... 4.2.4 , Fully Integrated Fixed-Mount Intrarnine 

Communications ............................................... 4.2.5 Supplementary Communications ........................... 

Section 5 Nonvoice Clommunications ............................ 
Volume 2 

Table of Contents 

Section 1 Analysis of Mine Communications ................... 

Section 2 A Matrix of Mine Characteristics ................... 

Section 3 Reports On Individual Mines .......................... 

3.1 Robena No . 4 Coal Mine On-Site 

Survey (May 1-2.. 1973) ......................................... 3.1.1 Mine Contactedl ................................................. 3.1.2 Initial Mine Contact ........................................... 3.1.3 Personnel Interviewed ........................................ 3.1.4 General Mine Information ................................... 3.1.5 Current Mine Communications ............................. 3.1.6 Communications Requirements-- Userst 

Viewpoint ......................................................... 3.1.7 Communications Requirement s-B ased 

On Survey Analysis ............................................ 3.2 Greenwich Colliery Mines. On-Site 

Survey of May 3 and 4. 1973 ................................... 3.2.1 Mine Contacted ................................................. 3.2.2 Initial Mine Contact ........................................... 3.2.3 Personnel Inteinviewed ........................................ 3.2.4 General Mine Information ................................... 3.2.5 Current Mine Communications ............................. 3.2.6 Communicationls Requirements-- Usert s 

Viewpoint ......................................................... 3.2.7 Communicationl Requirement s-Based 

on Survey Analysis ............................................ 3.3 Somerset Coal Mines. On-Site Survey 

of June 19 and 201. 1973 ......................................... 3.3.1 Mine Contacted1 ................................................. 3.3.2 Initial Mine Contact ........................................... 3.3.3 Personnel Interviewed ........................................ 3.3.4 General Mine Information ................................... 3.3.5 Current Mine C.ommunications ............................. 3.3.6 Communications Requirements-Usert s 

Viewpoint ........ ....... .......................................... 3.3.7 Communication Requirements-Based 

on Survey Analysis ............................................ 3.4 Keystone No . 1 Coal Mine On-Site 

Survey (July 16 - 317. 19 7 3) ...................................... 3.4.1 Mine Contacted ................................................. 3.4.2 Initial Company Contact ...................................... 3.4.3 Personnel Interviewed ........................................ 

Page 

1-1 

2-1 

3-1 

iii 
Volume 2 

Table of Contents (Cont) 

Page 

3.4.4 General Mine Information .................................... 3.4.5 Communication Requirement s-User1 s 

Viewpoint ................... ... .... .... .... ... .................... 3.5 Harris Mine No . 1. On-Site Survey 

of July 18 and 19. 1973 .......................................... 3.5.1 Mine Contacted .................................................. 3.5.2 Initial Mine Contact ................................... ......... 3.5.3 Personnel Interviewed ........................................ 3.5.4 General Mine Information .................................... 3.5.5 Present Communications ..................................... 3.5.6 Communications Requirements-- User1 s 

View ......................... ... .................................... 3.5.7 Communications Requirements.. Based 

on Survey Analysis ............................................. 3.6 Baldwin Underground No . 1 Mine. On-Site 

Survey of November 14. 1973 .................................. 3.6.1 Mine Contacted .................................................. 3.6.2 Initial Mine Contact ............................................ 3.6.3 Personnel Interviewed ........................................ 3.6.4 General Mine Information .................................... 3.6.5 Current Mine Communications ............................. 3.6.6 Communications Requirements-- User1 s 

Views .............................................................. 3.6.7 Communications Requirements.. Based 

on Analysis ....................................................... 3.6.8 Communications Related Human Factors ................ 3.7 Lovilia No . 4 Coal Mine. On-Site 

Survey of December 6. 1973 ................................... 3.7.1 Mine Contacted .................................................. 3.7.2 Initial Mine Contact .................... .... ......... ........... 3.7.3 Personnel Interviewed ........................................ 3.7.4 General Mine Information .................................... 3.7.5 Current Mine Communications .......................... ... 3.8 Orient No . 3 Coal Mine. On-Site 

Survey of January 10. 1974 ..................................... 3.8.1 Mine Contacted .................................................. 3.8.2 Initial Mine Contact ............................................ 3.8.3 Personnel Interviewed ........................................ 3.8.4 General Mine Information .................................... 3.8.5 Communications System Analysis ......................... 
Volume 2 

Table of Contents (Cont) 

Page 

Section 4 Related Ch;iracteristic s of Mines and 

Communica.tions Needs and Requirements .......... 

4.1 Communications Quality of Existing 

Telephone Systems ................................................ 4.1.1 Telephone Systems .............................................. 4.1.2 Harris Differences .............................................. 4.2 Requirements to Meet Present and Future 

Telephone Communications Needs ............................ 4.2.1 Channel Capacity Requirements ............................. 4.2.2 Secure Accident-Reporting Channel ........................ 4.2.3 No Battery Replacement Requirement ..................... 4.2.4 The Basic Te1e;phone Unit ..................................... 4.2.5 Add-On Features Requirements ............................. 4.3 A Composite of Existing Trolley Systems .................. 4.3.1 Present Values of Trolley Phone Systems ............... 4.3.2 Trolley-Phone :Requirements ................................ 4.4 Longwall Communications ....................................... 4.5 Communications (Center Requirements ...................... 4.6 Alarm Systems .., ........................................... ....... 

Volume 2 

List of Illustrations 

Figure Page 

3-1 Map of Robena 4 Mine ......................................... 3-5 

3-2 Total Time Phone is Used .................................... 3-7 

3-3 Total Number of Calls Each Hour .......................... 3-8 

3-4 Percent of Time Phone is Used ............................. 3-9 

3-5 Telephone Call Categories ................................... 3-10 

3-6 Total Time Trolley Phones Used 

(Dayl) ............................................................. 3-11 

3-7 Total Time Trolley Phones Used 

(Day2) ............................................................. 3-12 
Volume 2 

List of Illustrations (Cont) 

Figure Page 

3-8 Percent of Time Trolley Phone Used (Day 1) ........... 3-9 Percent of Time Trolley Phone Used (Day 2) ........... 3-10 Number of Calls Placed on Trolley Phones (Day 1) ... 3-11 Number of Calls Placed on Trolley Phones (Day 2) ... 3 -12 Table of Organization ....................... .... .............. 3-13 Map of Greenwich Mines ................................ ...... 3-14 Telephone Call Categories (South Mine) .................. 3 -15 Telephone Call Categories (North Mine) ................. 3-16 Percent of Time Phone Used - South Mine .............. 3-17 Percent of Time Phone Used - North Mine .............. 3-18 Total Time Phone Used ........................................ 3 -19 Number of Calls Placed ....................................... 3-20 Number of Calls Completed .................................. 3-21 Percent of Calls Completed .................................. 3-22 Phone Call Duration Distribution - South Mine ......... 3-23 Number of Calls Placed for Phones and Trolley ....... 3-24 Somerset Mine (B Seam) ...................................... 3-25 Somerset Mine (C Seam) ...................................... 3-26 Extension 223 Call Categories ............................... 3-27 Total Time Extension 223 is Used .......................... 3-28 Number of Calls Placed on Extension 223 ................ 3-29 Percent of Time Extension 223 Is Used ................... 3-30 Trolley and Pager Call Categories ......................... 3-3 1 Total Time Trolley and Pager System Used ............ 3-32 Number of Calls Placed on Trolley and 

Pager System ..................................................... 3-33 percent of Time Trolley and Pager System Used ..... 3734 Keystone Mine No . 1 ........................ .... ............... 3 -3 5 Keystone Electrical Map ...................................... 3-36 Total Time Phone Is Used .................................... 3-37 Number of Calls Placed ....................................... 3-38 Percent of Time Phone Used ................................ 3 -39 Telephone Call Categories ................................... 3-40 Total Time Trolley Phone Used (250 Volt) .............. 3 -4 1 Number of Calls Placed on Trolley 

Phone (250 Volt) ................................................. 3-42 Total Time Trolley Phone Used (550 Volt) .............. 3-43 Number of Calls Placed On Trolley 

Phone (550 Volt) .................................................. 3-44 Percent of Time Trolley Phone Used 

(250 Volt) .......................................................... 
Volume 2 

List of Illustrations (C ont) 

Figure 

Percent of Time Trolley Phone Used 

(550 Volt) ........................................................... Trolley Phone Call Categories (250 Volt) ................. Trolley Phone Call Categories (550 Volt) ................. Harris Mine No . 1 ............................................... Telephone Call Categories .................................... Total Time Pholne Used ........................................ Number of Calls Placed ........................................ Percent of Time Phone Used ................................. Trolley Phone Categories ..................................... Total Time Trolley Phone Used ............................. Number Calls Placed on Trolley Phones .................. Percent of Time Trolley Phone Used ...................... Peabody Mine Phone Stations ................................. Orient No . 3 Mine-Map ......................................... Trolley Phone Usage for Track Haulage 

Mines - Yearly Tonnage ....................................... Trolley Phone Usage for Track Haulage 

Mines - No Trolley Phones in Service ..................... 

Page 
Volume 3 

Table of Contents 

Page 

Section 1 Theoretical Approach to VLF Throughthe-E arth Propagation .................................... 

Section 2 Signal-to-Noise Analysis for Loop-to-Loop 

Mine Comimunic ations ......................... ....... .... 

2.1 Abstract .............................................................. 2 . 2 Introduction .......................................................... 2.3 Loop-to-Loop Power Transfer Within a 

Homogeneous Medium ............................................ 2.4 Loop-to-Loop Power Transfer on or Within 

a Lossy Half -Spz . ce ................................................ 2.4.1 System Signa1.t o-Noise Analysis ........................... 2.5 Computer Signal-to-Noise Analysis for 

Loop -to-Loop Mine Communications .................. .. ..... 2.5.1 Relation of Loop Design to System 

Performance ...................................................... 2.5.2 System Noise Representation ................................ 2.5.3 Signal and Noise Processing ................................. 2.5.4 Results of Signal-to-Noise Ratio Analysis ............... 2.6 Predictions for Theoretical S/NO ............................. 

Section 3 The Horizontal Electric Dipole ........................ 

3.1 The Field Equations for a Submerged 

Horizontal Electric Dipole ...................................... 3.2 The Submerged Vertical Magnetic Dipole ................ ... 3.3 The Submerged HED and VMD ................................. 3.4 The Field Components of a Submerged 

Infinite Line Sou'rce ............................................... 3 . 4.1 Results of the Submerged Infinite 

Line Source Analysis ........................................... 

Section 4 Signal-to-Noise Analysis for Down-Link 

Line Source Mine Communications ................... 

4.1 The Subsurface H-Fields for a Line 

Current Source .... ................................................. 4.1.1 Signal-to-Noisc2 Ratios ......................................... 4.2 Computational Results ............................................ 4.3 Theoretical Predictions for S/N~ ............................. 
Volume 3 

Table of Contents (Cont) 

Page 

Section 5 LF Communication ......................................... 5-1 

5.1 On Intramine Wireless LF Communications ................ 5-1 

5.1.1 Comparison of Experiment With Theory .................. 5-2 

5.1.2 System Design of Basic Intramine Paths .................. 5-9 

5.1.3 Conclusions and Recommendations ......................... 5-16 

Section 6 The Application of Recent NBS Noise 

DatatoMineCommunications .......................... 6-1 

6.1 Method of Analysis ................................................. 6-1 

6.2 Robena Mine ......................................................... 6-1 

6.3 McElroyMine ....................................................... 6-8 

6.4 Itman Mine ........................................................... 6-19 

6.5 Geneva Mine ......................................................... 6-26 

6.6 Summary .............................................................. 6-30 

6.7 Results of Propagation Program Analysis .................. 6-32 

Section 7 Analysis of Mine Communications 

Propagation Programs .................................... 7-1 

7.1 User's Guide for the Mine Communication's 

Propagation Programs ............................................ 7.2 Program Number One ............................................. 7.3 Program Number Two ............................................ 7.4 Program Number Three .......................................... 7.5 Theoretical Predictions for In-Mine 

Propagation .......................................................... 7.5.1 LF Propagation (Theoretical - Fixed 

Station - NG 14) .................................................. 7.5.2 LF Propagation (Theoretical . Portable . 

NG 14) ............................................................... 7.5.3 LF Propagation (Theoretical . NG 14) ..................... 7.6 Summary .............................................................. 
Volume 3 

List of Illustrations 

Figure Page 

Transmitting VMD ............................................... Transmitting Loop at Surface . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equivalent Background Noise Fields ........ ........ ....... Receive Signal-to-Noise Ratios as a Function of 

Lateral Displacement and Frequency (100 m) . . . . .. . . .. . Receive Signal-to-Noise Ratios as a Function of 

Lateral Displacement and Frequency (300 m) ........... Receive Signal.-to-Noise Ratios as a Function of 

Lateral Displacement and Frequency (500 m) . . . . . . . . . . . Receive Signal--to-Noise Ratios as a Function of 

Lateral Displacement and Frequency (100 m) . . . . . . . . .. . Receive Signal--to-Noise Ratios as a Function of 

Lateral Displacement and Frequency (300 m) .. . . .. . . . . . Receive Signal--to-Noise Ratios as a Function of 

Lateral Displacement and Frequency (500 m) ....... . ... Submerged Horizontal Electric Dipole.. . . . . . . . . . . . . . . . . . . . Submerged Infinite Line Source .............................. Submerged Infinite Line Source... ........................... Submerged Linle Source ........................................ Line Current Source ............................................ Receive Signal--to -Noise Ratios as a Function of 

Lateral Disp1ac;ement and Frequency (300 m) ........... Receive Signal--to-Noise Ratios as a Function of 

Lateral Disp1ac:ement and Frequency (500 m) VMD. ... Receive Signal--to-Noise Ratios as a Function of 

Lateral Displac!ement and Frequency (500 m) HMD. ... Receive Signal --to-Noise Ratios as a Function of 

Lateral D isplactement and Frequency (3 00 m) HMD.. . . Receive Signal--to-Noise Ratios as a Function 

of Lateral Displacement and Frequency 

(300 m) Loop . .,, . . . . . . . . .. . . .. . . .. . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . Receive Signal--to-Noise Ratios as a Function 

of Lateral Displacement and Frequency 

(500 m) Loop . .,,... .. . . ... . .. . . .. .. .. . . . . . . . .. . .. . . .. . . . ... .. . . .. . Comparison of Theoretical and Measured 

Transmission Losses Between Line 

Sources - ~$14 = "/2.. ... ...... .. .. .. . . .. . . ... . .. .. .. . . ...... . Comparison of Theoretical and Measured 

Transmission Losses Between Line 

Sources - EP/+ = o ............................................. Comparison of 'Theoretical and Measured 

Transmission 1,osses Between Line 

Sources - H4, {$ = 0 ..... . . . . . .. . . . .. . . . . . . . . . .. . . .. . . .. . . .. . . . . . 
Volume 3 

List of Illustrations (Cont) 

Figur Page 

Comparison of Theoretical and Measured 

Transmission Losses Between Line 

Sources . Hp 4 = 90 ............................................. Comparison of Theoretical and Measured 

Transmission Losses Between Line 

Sources . Hz 4 = 90 ............................................. Portable VMD to Line Source ................................. Portable VMD to VMD .......................................... Line Source to Line Source (Broadside) ................... VMD to VMD ....................................................... Line Source to ~~D/Displacement . 100 Meters ....... Line Source to v~D/Displacement . 200 Meters ....... Robena Bensema Noise Spectrum Data/ 

Trolley and Face Area Noise Levels ....................... Robena Bensema Noise Spectrum Data/ 

Noise Components Crosscuts 7 and 9 ....................... Robena Kandu APD-Data Spectrum (RMS) ................. Robena HN(H) Extremes (RMS) Subsurface ............... Robena HN(V) Extremes ........................................ McElroy Spectrum Data/~ertical Noise Fields. 

Face Area. and Location No . 2 ............................... McElroy Spectrum Datahertical Noise Fields. 

Headpiece. Crosscut. and Shaft ............................... McElroy Spectrum D~~~/APD (RMS) ........................ McElroy Spectrum Data/~dditional 

Vertical Field Data .............................................. McElroy Spectrum Data/various 

Locations and Components ...................................... McElroy Spectrum Data/~dditional High Vertical 

Noise Fields. Crosscuts and Face Areas .................. McElroy Surface Spectrum Data ............................. McElroy Spectrum Data ........................................ McElroy Spectrup data/^^ Extremes ..................... McElroy Surface Spectrum Data/~ummary ............... Itman Spectrum Data/~oise Levels - 

Portal Buses and Cabin Creek ................................ Itman Spectrum Data Farley ~anel/~oise - 

16 Ft From Miner ................................................ Itman Spectrum Data Farley ~anel/~oise - 

16 Ft From Miner - Continued ............................... Itman Spectrum Data/30 Ft From Miner .................. Itman Spectrum Data/~pD ..................................... Itman Spectrum Data/~xtremes .............................. Geneva Spectrum data/^^(^) East-West .................. 
Volume 3 

List of Illustrations (Cont) 

Figure Page 

Geneva Spectrum D~~~/HN(H) North-South.. . . . . . . . . . . . . . . Geneva Spectrum ~ata/HN(v) ................. ........... .. .. . Geneva Spectrurn/~ata Extremes. .. . . . . . . . . . . .. . . . . . . . . . . . . . All ~ines/~xtremes ............................................. Vector Relat iorlships of Electric and Magnetic 

Field Componeints for Printouts on Pages 6-34 

Through 6-83 .............. .... ..... .. . . ........... . .. . .... ... .. .. . Loop-to-Loop Lateral Transmission for 

Varying Displacements . . .. . . . . . . . . . . . . . . .. . . .. . . . . . . .. . . . . . . . . . Line Source to Loop Lateral Transmission 

for Varying Displacements .................................... Loop-to-Loop S/N Ratio for Various 

Displacements - Noise Grade 14. ... . . .. . . .. . . .. . .. . . ... . . .. . Loop-to-Loop S/N Ratio for Various 

Displacements - Noise Grade 2 .. ... . . ... ... . . . . . . .. . . . . . . .. . Loop-to-Loop Lateral Transmission for 

Varying Displacements . . .. . . . . . . .. . . .. . .. .. . .. . . .. . . .. . . . . . . .. . Line Source-to-.Loop S/N Ratio for Various 

Displacements Down-Link ..................................... Line Source -to-- Loop S/N Ratio for Various 

Displacements Down-Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Line Source-to--Loop S/NO Ratio for Various 

Displacements Down-Link ..................................... Down-Link Loop-to-Loop S/N Ratio for 

Various Displacements . . .. .. .. . . .. . . .. . . .. . . .. . . . . . . . . . . . .. . .. . Down-Link Loop-to-Loop S/N Ratio for 

Various Displacements - Continued ......................... Down-Link Loop-to-Loop S/N Ratio for 

Various Displacements - Continued.. .. . . .. . . . . . . . . . . . . . . .. . Down-Link Loop-to-Loop S/N Ratio for 

Various Disp1ac;ements - Continued ......................... Up-Link Loop-to-Loop S/N Ratio for 

Various Disp1ac;ement s . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Up-Link Loop-to-Loop S/N Ratio for 

Various Displacements - Continued ......................... Up-Link Loop-to-Loop S/N Ratio for 

Various Disp1ac:ements - Continued. ... . . . . . . . . . . . . . . . . . . . . . Up-Link Loop-to-Loop S/N Ratio for 

Various Disp1ac;ements - Continued ......................... LF Propagation (Theoretical - Fixed Station - 

NG 14) ...........,,..................................... ............. . LF Propagation (Theoretical - Portable - 

NG 14) ...........,,........... .. ............ ........ ................ LF Propagation (Theoretical - NG 14) ..................... 

Volume 4 

List of Illustrations 

Figure Page 

2-1 Coal Mine Test Site ............................................. 2-2 Tunnel Cross Section .....................o.................O.e. 

2-3 Corner No . 1 Layout .......................................O.... 

2-4 Corner No . 2 Layout ............................................ 2-5 Observed 200-MHz Transmission Loss for a 

Straight Coal Mine Tunnel ..................................... 2-6 Observed 415-MHz Transmission Loss for a 

Straight Coal Mine Tunnel ..................................... 2-7 Observed 1000-MHz Transmission Loss for a 

Straight Coal Mine Tunnel ...............................o..O.O 

2-8 200-MHz Corner Attenuation for Coal Mine Tunnel .... 2-9 415-MHz Corner Attenuation for Coal Mine Tunnel .... 2-10 1000-MHz Corner Attenuation for Coal Mine 

Tunnel ......................................o.o.o...o.o............ 

2-11 Observed Transmission Loss for Roof-Bolt 

Antennas in Coal Mine .........................o...oo..O...O.. 

2-12 Observed Transmission Loss for Roof-Bolt 

Antennas in Coal Mine ...................O..............Oee... 

2-13 Observed Transmission Loss for Roof-Bolt 

Antennas in Coal Mine ........................O.............oo 

2-14 Observed Field Strength for Roof-Bolt-to-Loop 

Antennas in Coal Mine ....................o......o............ 

2-15 Observed Field Strength for Roof-Bolt-to-Loop 

Antennas in Coal Mine .........................Oo.........o... 

2-16 Observed Field Strength for Roof-Bolt-to-Loop 

Antennas in Coal Mines ......................................O 

3-1 8-Inch Loop to 20-Meter Loop ........................~......O 

3-2 Line Source to Loop ............................................. 3-3 Line Source to Loop .............................o..ee........... 

3-4 Received Signal Vs Frequency (8-Inch Loop to 

20-Meter Loop) ................................................... 3-5 Received Signal Vs Frequency (8-Inch Loop to 

Roof Bolt) .......................................................... 3-6 Received Signal Vs Frequency (Roof-Bolt to 

8-Inch Loop) ....................................................... 3-7 Received Signal Vs Frequency (20-Meter Loop to 

8-Inch Loop) ...................o...O..........o.....e...........e.e 

3-8 S/N, Vs Separation (Roof-Bolt to 8-Inch Loop) .......... 3-9 S/N~ Vs Separation (20-Meter Loop to 8-Inch Loop 

and Roof Bolt to 8-Inch Loop) ......................e..o.....O 

3-10 S/N~ Vs Separation (8-Inch Loop 

to Roof Bolt) ...................................................... 3-11 S/No Vs Separation (8-Inch Loop to 20-Meter Loop) . 
Volume 4 

List of Illustrations (Cont) 

Figure Page 

-12 S/No Vs Separa~tion (8-Inch Loop to 20-Meter 

LOOP) ............, ..e...****..*******.**~.*****e*******ee****.e.*.* 

-13 S/N, Vs Separa~tion (Roof-Bolt to Loop 

Transmission) ................... ee.eeeee..eeeee.ee....eee..e..m 

3-14 S/N, Vs Separation (20-Meter Loop to 8-Inch 

LOOP) me.. ............... **..e**...**..e*e*..*..****e***..*.*.**...* 

3-1 5 Lateral Magnetic Field Intensity for Varying 

Displacement ................... .eme..m~ee..emm..e...e.me..e~.~m 

4-1 UHF Propagatiori (I-Watt Transceiver 

Transmitting to 1-Watt Transceiver - 1,800 ft) ........ 4-2 UHF Propagation (1-Watt Transceiver 

Transmitting to 1-Watt Transceiver - 3,300 ft) ........ 4-3 UHF Propagatiorl (20-Watt Transceiver 

Transmitting to :l-Watt Transceiver - 2,000 ft) ........ 4-4 UHF Propagation (20-Watt Transceiver 

Transmitting to :L-Watt Transceiver - 3,800 ft) ........ 4-5 UHF Propagation (1-Watt Transceiver 

Transmitting to 1-Watt Transceiver With 

Corner Reflectors - 1,800 ft) ................... e.m.mmmm.ee.m 

4-6 UHF Propagation (1-Watt Transceiver Transmitting 

to 1-Watt Transceiver, With Corner Reflectors - 

3,300 ft) ................... eeem.e..m..ee..e..e..eeee.ee.ee...e..m... 

4-7 UHF Propagation. (20-Watt Transceiver Transmitting 

to 1-Watt Transceiver With Reflectors - 2,000 ft) .... 4-8 UHF Propagation. (20-Watt Transceiver Transmitting 

to 1-Watt Transceiver With Corner Reflectors - 

3,800 ft) ...... ....... m.e~...e.mm.....m..mm...e.e.me..e.eeme~.e~ 

4-9 UHF Propagation (20-Watt Transceiver Transmitting 

to 1-Watt Transceiver With Corner Reflectors - 

2,000 ft) .................. ..**.**.*~.*..*.~*~~.**********..**..****. 

4-10 UHF Propagation (1-Watt Transceiver Transmitting 

to 1-Watt Transceiver With Corner Reflectors - 

3,300 ft) .........O.......................OO ............... . ....... A-1 UHF Test Setup.,, ................................................ A-2 VLF Test Setup.,, ........... ee..e.mm.e~..e..~e....ee..eee.....m.~ 

A-3 Antenna Complernent for Coal Mine Tests .............. A-4 4 15-MHz Corner Reflector Assembly .................... A-5 Corner Attenuation Curves for 

Cover age Predic tions. .. . . .. .. .. . . . .. . .. . . ... . . . . . . . . .. . . .. . . .. 

xvii 
Volume 4 

List of Tables 

Table Page 

UHF Test Parameters ......................................... VLF Test Parameters ........................e......... .... Observed Attenuation Rates for a Straight Coal 

Mine Tunnel ................... ...........................e... 

Observed Attenuation At Tunnel Edges Re1 ative 

TO Center .........................................................e 

Observed Corner Reflector Gain ........................... UHF Noise Sensitivity Threshold ........................... Roof-Bolt Antenna Measurements . Robena No . 1 ...... Roof-Bolt Antenna Measurements. Robena No, 1 ...... Roof-Bolt Transmitter. 8-Inch Receiver Loop ......... Large Loop Transmitters. 8-Inch Receive Loop ...... 8-Inch Transmit Loop ........................................ Roof-Bolt and Large-Loop Transmission ............... 8-Inch Transmit Loop Normalized to 10-W. 1-Hz 

Bandwidth ......................................................... Large Loop Transmission ....................e.............. 

Roof-Bolt Transmission ...................................... Small-Loop Transmission .................................... 

xviii 
Section 1 

Introduction 

This report is a compilation of all information obtained in accordance with the requirements 

of contracts SO122076 and H0232056. A series of eight coal mines were visited to determine 

their communications usage and requirements. Presently available equipment was surveyed 

and evaluated to determine its applicability to the needs of the mines. The equipment studied 

includes that made by the following companies : 

Anaconda Telecommunications Division 

Andrew Antenna 

Bendix Communications Division 

Collins Radio Group of Rockwell International 

Executone Communication and Sound Systems 

Mine Safety Appliances Company 

Motorola Communications and Electronics, Inc 

National Mine Service Company 

Plessey Communications Systems Corp 

Pye Electronics Limited 

Reach Electronics 

Set Com Corporation 

Sonex Incorporated 

Mine visits and in-depth interviews were made alt the following sites: 

Robena No. 4, Pennsylvania 

Greenwich Colliery Mines, Pennsylvania 

Somerset Coal Mine, Colorado 

Keystone No. 1, West Virginia 

Harris Mine No. 1, West Virginia 

Baldwin Underground No. 1 Mine, Illinois 

Lovilia No. 4 Coal Mine, Iowa 

Orient No. 3 Coal Mine, Illinois 
The study considered the possibility of using wireless communication underground. A data 

base defining equipment capabilities was needed so both analytical and experimental programs 

were formulated. The analytical program combined presently available information into an 

overall profile which predicted the underground communication capabilities using transmissions between 1,000 and 200,000 Hz. The tests in the experimental program checked 

these predictions and evaluated the use of the 150- to 1,000-MHz portion of the spectrum. 

The requirements, as determined from the surveys, and the capabilities, as determined from 

analysis and experiments were summarized. These groups of data were then combined into 

a set of requirements for an integrated underground communications system. The requirements are contained herein as specifications for a fully integrated communications system. 

An additional subset of specifications describes the requirements for a minimal system for 

use in small mines or those with little remaining operating life. 

At the conclusion of contract SO122076 a final report was written detailing the findings and 

recommendations to that point. Comparison of those recommendations and the ones contained 

herein reveals several differences. These are the result of additional information gained 

during the present contract. This information includes additional mine surveys and the low 

frequency propagation studies. Predictions of low frequency propagation were updated and 

were checked experimentally. 

The four volumes comprising this report address separate major items. 

Volume 1 summarizes the entire report and includes both a dissertation on the strengths and 

weaknesses of various available communication techniques and a set of requirements for 

several grades of comprehensive mine communication systems; 

Volume 2 details the eight mine visits, along with the conclusions reached following each 

visit and the final conclusions reached when the requirements of all mines visited were 

considered. 

Volume 3 contains all information used in predicting the performance of low frequency transmissions in through-the-earth systems, along with the predictions themselves for typical 

situations. 

Volume 4 describes the propagation measurements made in selected mines during both 

contracts, along with the findings resulting from these measurements. 
Section 2 -- 

Summary 

2.1 COMMUNICATION SYSTEM SPECIFICATION 

In an ideal system an individual must be able to initiate and receive calls as necessary, 

regardless of his location within the mine. To accomplish this a group of semiautonomous 

subsystems are required. A basic fixed intramirle phone system is used, along with vehicular, 

hoist, and (if necessary) longwall communication systems, and is integrated into a single 

functional system. System operation should be a,s familiar to the user as possible, with a 

goal of operating like the public phone system. 

Studies of operating mines showed that the fixed intramine communications equipment requires a 6-to-20 channel capacity. The number of channels required in such a minimum system is related to size of mine, number of workin:g sections, and desire to include vehicles and 

longwall sections as part of the overall system rather than as isolated elements. If an entire 

mine, including the surface complex, is integrated into a single system, more channels are 

required. The mine requires 6 to 10 of the operz~ting voice channels, while the extent of the 

surface communications and data transmission dletermines the total number of channels 

necessary. 

Operators of underground vehicles must be in coinstant communication with one another. Both 

production efficiency and safety are served by this constant contact. Production efficiency is 

further improved by selectively connecting vehicles with the fixed intramine system, permitting the mine management to be contacted while in transit. 

Longwall sections present a unique situation and special effort is required to obtain acceptable communications. Personnel are dispersed over a large area, yet all need to be in 

constant contact. A radio system provided with voice operated transmit (VOX) is required 

for greatest operating efficiency and safety, yet VOX presents its own problems. The extreme 

noise levels at the face require an exceptional grade of noise canceling microphone or VOX 

will not work and, in fact, noise cancellation is required for any usable system. In the 

absence of a radio system, a series of stations mounted to the longwall machinery is usable 

but cannot be considered to be a good system. Both operating efficiency and personnel safety 

requires that the longwall installation selectively interconnect with the fixed intramine system. 

During normal section operation, interconnection is not desirable unless a call is specifically 

directed to the section. When the section is down, any men performing maintenance must be 

able to monitor and call on the main system as they move about the longwall. 

A mine presents a uniquely harsh environment in many areas. Equipment will receive harsh 

treatment when in operation. Rock dust and/or coal dust will pack in and around all exposed 

surfaces and crevices. High humidity and dripping water will erode surfaces. The moisture 

may be corrosive. The equipment must be designed to operate under all these conditions. 

2.2 COMMUNICATION SYSTEMS EVALUATION 

Both wired and wireless communications have belen evaluated during this program. Each has 

certain strong points; however, the best integrated system appears to be a mixture containing 

various elements of both types. 
Wireless communication systems do not tie the user down to a specific location. There is no 

one "bestff frequency to use, instead different segments of the radio spectrum have different 

strong points. In the uhf (300 to 3000 MHz) region equipment and antennas are small and 

lightweight. Power consumption of portable gear is low, with a resultant low battery weight 

for a given operating life. Straight line signal attenuation is low; however, to operate around 

corners, either high power or additional antenna structures are required. Operating range 

may also be extended with the added system complexity of repeaters. 

By shifting to the vlf/lf region (3 to 300 kHz) problems involving signal loss in adjacent entry 

operation are eliminated. Transmission is directly through the earth and via existing wiring 

in the mine. With sufficient power and antenna structure, direct operation is possible between 

in-mine and surface stations. Necessary power level and antenna size are both significant 

factors at the low frequencies. Antennas for portable equipment are heavy and inefficient. 

The prime use for this frequency region within a mine appears to be in one-way paging 

operation where a fixed transmitting antenna can be a sizable wire structure. 

Wired communication systems can be simpler than any other type. Some form of wired system 

is installed in every one of the mines studied during this program. Most of these installations 

consisted of a single party line system. Unfortunately, not one of the wired systems truly met 

the mine's needs. 

A single line telephone system is inexpensive and simple, but provides neither adequate line 

capacity nor privacy. Multiple single -channel systems are limited in connectability and can 

become expensive since redundant equipment and cabling are required. A PBX system provides no paging capability and is complex to wire and maintain, but supplies the required 

privacy and channel capacity. A single-cable multiplex system meets all needs as long as 

the individual called is near a station. In addition to the preceding strengths and weaknesses, 

no wired system provides vehicular communication except in the incidental case wherein the 

vehicle is near a fixed station just as a paging call is made. 

A mixed system, with both wired and wireless elements integrated into an operating unit, provides the best whole-mine communications.' A multiplexed, wired system should be used to 

selectively interconnect the bulk of the mine. Wireless subsystems then extend communication to personnel moving about when they are away from fixed phone locations. Vehicles communicate on their own wired or wireless subsystem, which can be interconnected selectively 

with the wired system. With a properly designed mixed system no key man is ever out of 

touch. 

2.3 IN-MINE DATA GATHERING 

A working understanding of present coal mine communications equipment and its usage is an 

essential prerequisite to the determination of future communications systems needs. A field 

survey program was planned and implemented in order to gain this background. Eight mines 

were selected as locations for on-site interviews of those personnel responsible for installation and maintenance of communications equipment and for in-mine inspection of communications equipment and signal distribution networks. The mines selected were chosen to provide 

the greatest possible cross-sectional sampling of mine size, age, mining methods, and 

haulage means. 

The performance characteristics of various communications systems were determined through 

listening to conversations (noting noise levels) and by talk testing from randomly selected 

stations throughout each mine. Management, maintenance personnel, and working miners were 

asked to make general comments on the communications systems and to note any specific 

difficulties experienced in their use. Observations were made of mining operations and usage 
of communications in addition to the interviews with mine management personnel (from 

superintendents to section foremen) to determine whether correlations existed between 

communications, productions, and safety. 

The individual interviews and resulting reports were analyzed to identify communication 

system requirements for each mine. These requirements were examined additionally to 

determine those items common to all mines. 

2.3.1 Telephone Systems 

A comparison of the performance quality of the telephone systems in the eight mines studied 

shows that the mines with poorer system perforrnance are usually the larger, older mines. 

This characteristic appears to result from the o!lder equipment and lines found in the larger 

mines. Typically there are many more miles of line (increasing probability of noise pickup), 

many line splices, and many telephone units on each circuit. As a strong trend we found that 

the greater the number of telephones the poorer the performance quality. 

New equipment providing more channels and private line operation should be compatible with 

the best of presently installed systems so that th.e two can operate together until the older 

equipment reaches the end of its economic life. A substantial cost savings is thus realized 

by a sharing of the older but adequate telephone lines by both the old and new equipment. 

Tape recordings were made of phone system activity in some of the mines visited. Statistical 

analysis of these recordings and a knowledge of telephone industry channel capacity requirements indicate that a minimum of six channels are required to handle mine communications. 

Twelve to twenty channels are needed in the larger, more active mines to handle expected 

communications increases. Most channels may lbe party line but mine management personnel 

said they wanted at least one private line channel1 in any new system. 

Rechargeable batteries should be used to power .the phone system. These should be capable 

of being recharged from power on the telephone :lines so a system goal of at least one year 

mean-time-between-servicing can be met. 

2.3.2 Trolley Phone Systems 

An evaluation of present day trolley phone systems shows that they work very well indeed - considering the physical, electronic, and acoustic abuse under which they must exist. The 

most severe problems with these systems seem to be physical, such as microphone cord 

breakage and switch failures. 

Their most severe performance constraint is irnlposed by the impedance characteristics of 

the trolley wire transmission system. The impedance varies widely within a mine and from 

mine to mine. Operating into a poorly matched 1;ransmission system results in high distortion and low signal strengths (which results in poor signal-to-noise ratios) at randomly 

distributed points in the mine. 

The eisting systems are made usable only by using high-power transmitters and with 

receivers operating over a wide dynamic range. The high ambient acoustic noise levels that 

must be overcome also present design problems with the trolley phone system. Trolley 

phone usage seems to correlate very closely with yearly output for track haulage mines and is 

at the saturation point in many high output mines. 

Physical ruggedness of future designs for vehicular mounted equipment should equal or exceed 

that of the more rugged present designs. Loudspeakers must be separable from trolley phone 
units and swivel mounted to accommodate the operator. Audio power output must be adequate 

to override the high ambient acoustic noise levels without distorting. Careful system design 

and impedance control is required as a means of overcoming the null patterns that plague 

present transmission systems. Trolley power distribution lines must be isolated from 

rectifiers and loads by high current line traps to minimize loading on the signal paths. 

Finally, an adequate inventory of portable test equipment sould be available for installing 

and maintaining the system. 

2.3.3 Longwall Communications 

The longwall communications system must aid in reducing maintenance downtime and aid in 

increasing productivity. The goal in a longwall system is the provision of hands-free operation between all maintenance and operating personnel on the section. Present systems consist of wired intercoms using loudspeakers and handsets in a push-to-talk configuration. 

These systems permit communication within the section but are difficult to hear since the 

loudspeakers are fixed while workers move around as necessary. 

2.3.4 Communications Center Requirements 

There are two fundamental requirements for a communications center. First, the center must 

be flexible and expandable to accommodate growth with the mine. Second, the communications 

center should be located outside with multiple signal paths to the inside. This location provides an environment more conducive to maximal output from both the center and its operator, 

which in the long run offsets the cost of an outside location. The communications center must 

be economically expandable from a simple monitoring operation by a lamp man or hoist operator to a complex data center having a full time operator as mine size increases. Besides 

serving as an information center, the communications center must be flexible enough to interconnect the various networks and to serve as a broadcast center for full coverage announcements to all mine personnel. 

Interface requirements for alarm and monitor systems are simply that they be compatible 

with voice grade communication distribution systems. Economics dictate that alarm and 

monitor sensors utilize communications networks for the transfer of data to the monitoring 

centers. 

2.4 THEORETICAL DATA BASE 

The effective design of efficient communications systems for mining environments demands 

a thorough knowledge of wave propagation characteristics through the earth. A series of 

theoretical studies have been prepared to obtain a reliable basis from which accurate propagation predictions can be drawn. These studies predict the absolute signal levels to be expected 

versus antenna configuration, power level, and displacement. 

Another series of studies have been made by the National Bureau of Standards. These studies 

resulted in a tabulation of the noise level versus frequency to be expected for various underground conditions. Integration of the National Bureau of Standards measurements with the 

predicted signal levels results in a series of predictions as to the signal-to-noise ratios that 

can be achieved with an underground communications system. 

Signal-to-noise predictions have been made for several antenna configurations as a function 

of antenna size, depth, and lateral displacement. From an analysis of the signal-to-noise 

ratios as a function of frequency, predictions were drawn concerning optimum usable frequency versus maximum transmission displacement for the various antenna configurations. 

A number of conclusions can be drawn from the predictions. 
Low frequency waves can be transmitted through overburdens ranging in thickness from 150 

to 1,500 feet. The two most common methods of coupling energy through-the-earth are the 

loop or magnetic dipole and the line source, sometimes referred to as an earth probe (surface) 

or roof bolt (subsurface) antenna. Vertical magnetic dipole (VMD) antennas exhibit maximum 

coupling when their orientation is coplanar, while horizontal magnetic dipoles (HMD) exhibit 

nulls and maxima as the antennas are rotated. T'hese nulls render the horizontal magnetic 

dipole an unattractive coupling device for mine communication. 

Examinations of curves drawn from the general predictions permits a series of specific 

predictions to be made assuming a minimum of 37 dB S/NO (noise in a 1-Hz bandwidth) ratio 

is required for adequate information transfer. 

a. Loop (VMD) to loop (VMD) provides the highest S/NO ratio. 

b. For a 20-meter (66-ft) radius transmit loop a maximum of approximately 225 meters 

(738 ft) separation can be achieved with an optimum frequency of 10 to 20 kHz. At lesser 

separations, the 100- to 200-kHz range provides higher signal-to-noise ratios. 

c. For a 0.2-meter (8-inch) diameter transmit loop, a maximum of approximately 80 meters 

(263 ft) separation can be achieved at an optimum frequency of 70 to 100 kHz. 

d. For a 100-meter (328-ft) line source transm:itter, a maximum of 200 meters (656 ft) can 

be achieved at a frequency of 10 kHz. At separations below 500 ft, however, the 100-kHz 

frequency range provides the highest S/NO ratio. 

e. For up-link and down-link propagation using a 13.6-meter (44.6-ft) radius loop, maximum transmission was 175 meters (574 ft) ait a frequency of 10 kHz, and for the 100- 

meter line source antenna, maximum depth was 225 meters (738 ft) at a frequency of 10 

kHz. 

Predictions for transmission from a loop to a line source can not be made because reliable 

E-field noise data is not available for this mode of propagation. 

It has been noted in recent in-mine tests that there appears to be a gap between the propagation predictions and the experimental results as frequencies increase beyond 50 kHz. Additional experiments need to be conducted to obtain reliable predictions for these higher 

frequencies, and to define the differences between pure through-the-earth propagation and 

that which is aided by the wiring running within the mine. 

2.5 EXPERIMENTAL PROGRAMS 

A series of radio measurements were conducted j.n a working coal mine to determine uhf and 

vlf propagation characteristics. Measurements included the effects of frequency, polarization, 

antenna type, and distance. The uhf tests included propagation along straight tunnels and 

around corners, and a comparison of results using passive reflectors at tunnel corners. The 

vlf tests evaluated the performance of roof-bolt and loop antennas. A number of results were 

obtained that have practical significance in the definition, design, and implementation of radio 

communications systems in mines. 

2.5.1 UHF 

At uhf, a strong dependence of signal attenuation on frequency and polarization was noted. 

Along a straight tunnel, attenuation rates varied from 15-25 d~/100 ft at 200 MHz to 2.5-4 

d~/100 ft at 1 GHz. Minimum attenuation is expected at frequencies above 1 GHz. Horizontal polarization was found to yield significantly improved results compared to vertical or 

cross polarization. The attenuation of horizontally polarized signals averaged 40 dB less 

than vertically polarized signals at 415 MHz and 30 dB less at 1 GHz. Considerable attenuation was observed in radio signals propagated around tunnel corners. Signal attenuation was 
approximately 45 dB at a point 20 feet past the corner at 415 and 1000 MHz. The rate of 

attenuation past 20 feet averaged 30 dB/100 ft as opposed to the 3 to 6 dB/100 ft rate observed 

in the main tunnel at 415 and 1000 MHz. Complete signal depolarization was noted along the 

cross-tunnel as opposed to the strong horizontal polarization observed in the main tunnel. 

The use of a comer reflector raised the signal level from 20 to 30 dB at a point 65 feet past 

the corner. At 1 GHz, the reflector appeared to lower the attenuation rate along the crosstunnel, resulting in even greater effective gains further away from the comer. 

2.5.2 VLF 

At vlf, minimum attenuation between two roof-bolt antennas occurred in the end-to-end configuration, but other combinations yielded only 10 to 15 dB more attenuation. Attenuation was 

relatively flat over the frequency range 1 to 50 kHz and exhibited an attenuation rate of 

approximately 5 dB/100 ft for all frequencies and orientations. The communications radius 

of a 25-watt, roof-bolt voice radio system is predicted to be 1,200 and 1,400 feet. 

Minimum attenuation for a roof -bolt-to-loop antenna sys tem occurred along the axis of the 

roof-bolt antenna with the loop magnetic axis oriented vertically. The field strength produced by the roof-bolt antenna was relatively independent of frequency over the range 1 to 

50 kHz. The attenuation rate averaged 4 dB/100 feet over all frequencies and orientations 

with individual measurements deviating only slightly from the average. 
Section 3 

Communications Systems Evaluation 

Three basic types of communication systems have been examined during this program. Two 

of these are pure radio systems, operating in the 300- to 3000-MHz (uhf) and 30- to 300-kHz 

(If) portions of the rf spectrum. The third system type includes all forms of wired communications. This includes both the baseband-type telephone systems of which the pagers are a 

prime example, and the various carrier systems such as the trolley phones. While the following paragraphs discuss each type of system iLS an entity, it must be remembered that the 

best overall system in a given situation may well be some composite form. 

3.1 UHF SYSTEMS 

The primary strong points of a uhf system are tlhe small size and light weight of the system 

components, plus low signal attenuation along a given entry. These advantages are in addition to the basic advantage of any rf system in that the user can be in constant communication 

as he moves about. Uhf is today's most desirable portion of the spectrum to use in 

implementing a 2-way system. 

The physical size of uhf antennas is such that horizontal, vertical, or circular polarization 

may be chosen for a system. Tests in an operating mine have shown that horizontal polarization propagates much better than vertical. A str~dy undertaken to explain the results of those 

tests predicted that the polarization should be in the direction of the greater linear dimension 

of the tunnel for least attenuation. Measurements have not been made to determine the 

degree of signal loss along passages in the presence of vehicular traffic; however, there are 

indications that this may exceed 10 dB. Circular polarization may be helpful in this case. 

Since antennas are so small in this region, there is a good possibility that high gain units may 

be installed at all base stations. The effective power and range are thereby increased. 

The tests that have been run show that uhf signals suffer very high attenuation when the signal 

path includes one or more corners. In negotiating these comers, the rf becomes depolarized, 

losing the advantage of horizontal polarization present in the signal as transmitted. Simple 

reflectors may be used to reradiate signals arolund corners, extending the coverage area 

greatly. These reflectors are small and light, but still cannot be considered to be desirable 

items. They occupy space that can be at a premium, especially if vehicles must negotiate the 

corner where they are installed. Unless they are rugged and mounted in a very secure manner they will be dislodged or damaged shortly after installation. In addition, if they are not 

properly aligned they will not accomplish their purpose, and they are one more item that must 

be installed when developing a section, then removed when retreating. 

For the user of transportable equipment, operalion in the uhf region is a great advantage. 

The small size and light weight of this end of the link, especially the antenna portion, is 

advantageous. Good communication can be provided within a small area such as a working 

section. Vertical polarization is easier to implement in personal portable equipment (with 

the use of a simple monopole antenna), however the use of horizontal signals presents no 

great difficulty. One form of horizontal omnidi:rectional antenna which can be readily carried 

consists of a crossed pair of dipoles, or turnstile, molded into the surface of the miners 

protective cap. 
There are alternatives to the use of direct radiation from base stations which may be used in 

the uhf region. A form of "leakyff coaxial cable may be run along entries. Booster stations, 

similar to the base stations listed above, are required to periodically regenerate the signal 

on the cable for transmission and reception. There are two primary problems with this type 

of system. Signal loss along the cable at uhf is similar to that of a directly radiated signal, 

so approximately the same number of boosters are required in a cable system as base 

stations in a radiating system and the cost of the cable must be added in. Additionally, the 

radiation range of the cable is much shorter than that of transmitted rf from a base, so there 

is greater difficulty in coupling signals into adjacent entries. In the cable's favor, operation 

is not disrupted by the passage of the vehicles or machinery. 

3.2 LF SYSTEMS 

The primary advantage in using If in a wireless system lies in the ability of the radiation to 

propagate through the mine and overburden in all directions. Communications between user 

and base may therefore be maintained as the user moves throughout various entries and 

crosscuts. Besides providing intramine communications, an If system can supply a direct 

link from within a mine to the surface, should this become necessary. 

The antenna becomes a major consideration when designing an If system. A good low-frequency 

antenna is both large and heavy. In addition, the generation of sufficient power may result in a 

transmitter/antenna system which is not intrinsically safe. Two types of base antennas have 

been considered. The first consists of a single-turn loop of wire wrapped around a coal 

pillar, the second is a length of wire connected between two or more roof bolts. The singleturn loop may be attached to J-hooks and thereby kept out of the way by running it alongside 

other wiring in the mine. In most cases each loop will be a different length and will have 

varying amounts of other metal and wiring coupled to it. These factors affect the input impedance of such a loop, resulting in a need to individually match each antenna to its transmitter. In the absence of individual matching, optimum radiation of the base station power 

can not occur. 

The roof bolt antenna may be installed in a manner similar to that used with a loop, by attaching the wire to J-hooks. Overburden characteristics and the length of the roof bolts in use 

cause the input impedance of this type of antenna to vary even more than that of a loop. As 

a result, to obtain maximum radiated power, it becomes even more important to have a good 

adjustable matching system built into the base station. The matching system must be easily 

adjusted for best operation by untrained personnel. 

Only one form of antenna appears to be practical for use at the personal portable end of an If 

system. This is the loop, wound to form a vertical magnetic dipole. There are two possible 

locations for such a loop. One of approximately 8-inch diameter may be wound around and 

molded into the protective cap. To maintain intrinsic safety, it might be necessary that at 

least the power amplifier or the antenna matching network also be part of the cap. A second 

possible loop configuration could be built into a new form of the belt used to carry the lamp 

battery, self-rescuer, etc. This would be a more complex assembly, with its need for a 

connection and the requirement that the length be adjustable, but the larger diameter is a more 

efficient radiator. There is a similar antenna presently in use in South African mines. This 

loop is formed into a bandolier. The loop is of a reasonable size but is an unwieldy item that 

interferes with movement on a section. 

The antenna used on a vehicle is under far fewer restrictions than that carried by a man. 

Either a monopole or a fairly large loop may be installed without difficulty. As always at 

low frequencies, antenna tuning for maximum power transfer is very important. 
The major difficulties in the if region involve propagation characteristics and bandwidth. 

Signal attenuation versus distance is very high, md rises with increasing frequency. Some 

electromagnetic interference (EMI) is present, generated by machinery within the mine. Some 

tests have been made indicating that a way may exist to get around at least part of this 

drawback. By using the high If band, or perhaps by going into the low mf (300- to 3000-kHz) 

region, the trolley, track, etc, conductors within the mine may be made to serve as a virtually 

continuous antenna. Since such conductors are located at or near nearly all points of activity 

they may serve to provide a wired/wireless system. The testing that has been done has not 

indicated the reception distance that may be expected as the receiver is moved into adjacent 

entries. Neither has there been any work done to optimize the power transfer into the intramine conductors, or to determine the reverse characteristics in which the portable station 

transmits and signals are picked up off the mine wiring. 

The Q of both the fixed and portable loop antennas is very high. As a result, the transmit 

matching networks may be expected to handle 0nl.y one, or at the most two, operating channels. 

At the lower frequencies even the bandwidth of a single voice channel is difficult to attain. 

This difficulty is not normally present when using roof bolt antennas, as their resistive 

component is relatively high. 

3.3 WIRED SYSTEMS 

A wired communication system can be simpler tlnan any other type. It can also be easier for 

the user to operate properly. The simplest wired system is enough like the public telephone 

system that minimal training in its use is required. Finally, a single-channel wired system, 

operating with baseband audio, forms the least expensive system that can be installed. 

One problem with the single-channel system using baseband audio is that it does not meet the 

needs of any mine that has been studied. In every case either supplementary systems have 

been installed or mine personnel "make doM with the equipment installed, rarely realizing 

the adjustments made to cope with an inadequate system. 

A number of methods of adding channels are available.'One involves multiple independent 

systems. Each system includes its own wiring, power, functions, and station locations. 

Users of one system cannot talk to users of another. As a result, either each group of users 

is isolated or one or more persons must act as an information transfer point, repeating 

messages which must be "interconnected" betwelen systems. In many mines a switchboard 

operator interconnects systems as needed. To obtain any form of privacy, separate privateline circuits must be installed, and the privacy only exists between the points where the privateline terminals are located. With more than two stations connected to a given circuit, the attendant loss of privacy is partially compensated by the conference capability gained. 

A complete private branch exchange (PBX), either manually or automatically operated, may be 

installed as another way to increase channel capracity within the mine. This provides voice 

privacy, as every circuit is independent; however, a separate pair of wires must be installed 

between the control switching point and each stat-ion. General paging becomes much more 

difficult, although the ringer on the phone serves to alert those in the vicinity of a terminal 

when it is being called and individual phones may be designed to page instead of ringing. To 

page a person whose location is unknown, a completely separate additional system must be 

installed, and to direct vehicles yet another systlem is required (assuming the vehicles are 

trolley powered). If the vehicles are self-powerled they remain out of communication at all 

times. 

Yet another form of wired system provides mu1t:ichannel capability with minimal wiring by 

multiplexing signals on a single pair of wires. Shch a system requires minimal intramine 
wiring, can provide any number of required channels (all of which are private) yet can also 

give an "all call" paging signal throughout the mine when an individual's location is unknown. 

It shares a disadvantage of any wired system in that the called party must be near enough to 

a system terminal to hear or see a "ringing" indication or to hear a page. As with any of the 

wired systems, signals may be coupled to a separate trolley phone system so vehicle occupants 

may call or be called. Again, as with any wired system, self-powered vehicles are out of 

communication except as they happen to pass a terminal. 

3.4 MIXED SYSTEMS 

A mixed system, containing both wired and wireless elements, solves most of the problems 

of either type alone. The wired portion of the system provides the multichannel capability 

needed. All channels may be either private or conferenced, as determined by the switching 

center. Assuming a multiplexing type system, this capability requires only minimal intramine wiring. The wireless portion of the system may then be configured to provide one or 

more channels of party-line communications, for use when personnel are away from fixed 

terminals. One of the wireless channels can serve purely as a calling channel, directing 

that the person called go to the nearest terminal. By eliminating the need for transmission 

by the portable unit problems of transmitted power, antenna configuration, and intrinsic 

safety of the unit are eliminated or drastically reduced. Vehicles may still interface with 

the system via a trolley wire or wireless transmitter-receivers on a common channel. The 

use of a party line channel for vehicular traffic is highly desirable to keep all vehicle 

operators informed concerning the location of others, thereby reducing the possibility of 

accidents. 
Section 4 

Communication System Specification 

4.1 OPERATIONAL REQUIREMENTS 

The primary operational requirement may be stated as: An individual must be able to initiate 

and receive communications as necessary regardless of his location within the mine. In 

practice, this basic requirement will normally be modified. The size and age of a mine ,and 

the operating conditions will affect the degree to which a system installation is fully integrated 

to provide maximal communications capability. .Economic considerations as assessed by the 

mine management may result in the selection of a system providing anything from minimal 

capability upward to full communications integration. 

The operation of a system should be as familiar :IS possible to the user. As a goal, this 

operation should match that of the public telephone system. A handset should be used except 

under special circumstances and there should be no push-to-talk switch on this handset. Calls 

should be initiated by means of a pushbutton dial. The less special training required, the 

more likely the user is to react properly under stress. 

A fully integrated ommunications system should provide interconnection capability so that 

selected phones can place and receive calls on the public system. Each station should be 

individually addressable without regard to the total number of available communication channels. This separation of addresses or phone numbers from channels or circuits permits 10 

to 14 private line phones to be installed for each available channel with little chance of a 

user finding all channels busy. A central switching system ensures that any given phone is 

connected to the next available channel. The cap;~bility increases in importance as system 

size increases. 

In addition to the normal private line operation w:ith each phone addressable, there should be a 

reversion mode for abnormal conditions in which all stations operate on a common party line 

channel until the system can be restored to normal. The party line channel would also be used 

whenever an originating party chose to dial an "all call" address rather than an individual 

address. 

As features are deleted, the phone system requirles more and more of the user, until only the 

essential capabilities are left. In this minimal system very few operating channels are available. One channel is a party line "all callM or paging channel on which initial contact is made. 

The parties involved then manually select a nonbusy working channel to conduct their business. 

All channels are party line. The ability to select private line operation on a channel is the 

first feature that should be added in increasing system capabilities. 

Vehicles operating on rails within a mine should have a communications unit mounted in every 

powered vehicle (required in some states). This installation is desirable for various reasons. 

Among them: operational safety is increased when there is an intervehicular communication 

system. Operators can report to each other or to a central dispatcher, thereby reducing the 

chances of a collision. Carried to the ultimate, tlie central dispatcher can control the movement of all vehicles at all times. Additionally, with communications in every vehicle an 

individual may be contacted any time he is needed as he moves about in the mines. If a given 

vehicle is needed at a specific location, its opera1;or can be notified. Essentially the same 
reasons exist for placing communication gear on rubber-tired vehicles as exist for those 

operating on a system of tracks, the exception lying in a lessened need for vehicular position 

control. 

The vehicular system should selectively interconnect with, and use one or more channels of, 

the main communications system. The interconnection should not require the use of a 

dispatcher for patching or relaying, but should be included in the design of a fully integrated 

system. One channel must be common, monitored by all vehicle operators at all times. There 

should be selective access to this channel by any phone in the system. If additional operating 

channels in the vehicles are desired, they can be used either for initiation or reception of 

calls. The continuous monitoring of the common channel is required during operation on any 

additional channels. The system may have direct addressing of each individual vehicle, or 

the common channel may be used as a calling channel, followed by a call-back or the selection of a mutually agreed-upon channel. In a minimal system only the single common channel 

needs to be implemented. Access between the vehicular equipment and the balance of the 

mine phones is then controlled by the dispatcher or by a separate paging control on the 

vehicular phones. In the latter, less desirable case the units in the vehicles would then hear 

all paging calls on the main phone system. 

Ofttimes there is a need to call a man who is away from his own phone and cannot tell that he 

is being called. In many cases he is not near any phone. As a minimum, spe form of oneway paging capability should be included in the overall mine phone system. The paging 

receiver light and/or tone can be used to tell a called party to go to the nearest phone and 

return the call. 

An intermediate grade of paging system will both page and deliver a voice message to a 

selected individual. 'when implemented, one-way page must be used only for paging purposes 

and not be used to deliver one-way messages or instructions. The advantage of voice paging 

lies in the ability to direct call-back to a specific number rather than to a party line channel. 

Until this call-back is received, there is no assurance the page has been received. To assume 

otherwise is unsafe. Since proper usage of one-way voice paging cannot be enforced, its use 

has been forbidden in many parts of Europe. 

A highly desirable wireless paging system includes full two-way communication. This grade 

of equipment should include selective calling of the portable unit and should permit the 

portable to access the balance of the system and selectively address any other station. 
4.2 TECHNICAL SPECIFICATION 

4.2.1 Environmental 

No complete study has been made to identify the environmental limits experienced in coal 

mines. 

Equipment is mounted on top and throughout the mines. 

Mining is done at various depths and mines are located in areas with widely differing 

climates. 

An overall study should be performed so a complete and definitive environmental specification 

can be written. 

In the absence of data from such a study, the following recommendations are made. They are 

the result of observations, on-site interviews, and engineering estimates. 

4.2.1.1 Temperature 

4.2.1.1.1 Operating 

Inside buildings: 0 "C (+32 OF) to 50 "C (+I22 OF) 

Ambient air at top or near air entries: -30 "C (-822 OF) to +40 "C (+I04 OF) 

Location unrestricted: -30 "C (-22 OF) to +55 "C (+I31 OF) 

4.2.1.1.2 Nonoperating and Storage 

Any location: -40 "C (-40 OF) to +85 "C (+I85 OF) 

4.2.1.2 Humidity and Moisture 

Top-mounted: To 95 percent relative humidity 

In-mine: To 100 percent relative humidity with condensation 

Additional requirement: In-mine equipment to be dripproof and splashproof 

4.2.1.3 Shock 

Measurements have not been made to determine ;the precise shock environment to be 

expected on vehicles and machines. 

Accelerometers and recorders should be fitted to a number of vehicles in each of a number 

of mines. 

Analysis of the data obtained will determine the actual operating environment seen by equipment mounted to or carried in the various vehiche types. 

The effects of differing track conditions within the mines will also be seen. 

Lacking precise data, an estimate must be made. Collins maintains an extensive environmental facility that has been in operation for over 25 years. Over this period tests have been 

performed and data gathered on a wide variety of equipment, this equipment designed to be 

used under virtually all possible operating conditions. Personnel experienced in the shock 

and vibration areas within the environmental facility were consulted for their recomrnendations before selecting the following requirements. 
4.2.1.3.1 Operating 

Fixed equipment: Unlikely to receive shocks while in operation. 

Mobile mounted: 

Vehicles on rails: 600 g with 2 ms duration at l-second intervals 

Rubber-tired vehicles: 20 g with 25 ms duration. 

4.2.1.3.2 Nonoperating and Transit 

Transit and handling shock is best simulated by drops of up to 36 inches onto a hardwood 

surface. 

4.2.1.4 Vibration 

4.2.1.4.1 Operating 

Fixed equipment: Not significant 

Mobile Mounted: 

Vehicles on rails: 0.010 inch double amplitude, 5 to 100 Hz 

Rubber-tired vehicles: 0.020 inch double amplitude, 5 to 70 Hz. 

4.2.1.4.2 Nonoperating and Transit 

Smooth vibration: 0.030 inch double amplitude, 10 to 55 Hz. 

4.2.1.5 Dust 

Equipment shall remain operational under highly dusty conditions. 

A rock or coal dust buildup shall not damage or degrade performance of cases, handsets, 

loudspeakers, controls, or connectors. 

The abrasive effects of the dust must be considered in all designs. 

4.2.1.6 Corrosive Materials 

All equipment shall be designed to withstand the effects of the corrosive materials 

encountered in a mine. 

Mine acids, chiefly sulfuric, may be expected to drip or condense on any surface. 

Components exposed to these acids must be protected. 

4.2.1.7 Abuse 

All equipment shall be designed to withstand abusive treatment while continuing to operate 

normally. 

Particular attention must be paid to any cords and attachments as to abrasion resistance 

and pull strength. 

~icrophone/handset cases shall be impact resistant. 

Equipment cases shall be as nearly unbreakable as possible. 

Projections and controls shall be protected against being struck or abused in any 

conceivable way. 
4.2.2 Reliability and Repairability (Usability) 

4.2.2.1 Reliability 

The minimum acceptable mean-time-between-failure (MTBF) shall not be less than six 

months. 

Routine service shall not be required at less than 6-month intervals with a 1-year interval 

as a goal. 

Greater MTBF is desirable, but not at the expense of repairability. 

4.2.2 .2 Repairability 

The mean-time-to-repair (MTTR) shall not exceed 30 minutes. 

A shorter MTTR is desirable, with a goal of 10 minutes. 

Equipment shall require minimal test equipment for troubleshooting and repair. 

The preferred repairability technique involves the following: 

a. Ready equipment access 

b. Modular construction 

c. Self-test or minimal test 

d. Small, lightweight spares arranged for ready transport 

Repairable modules should be returned to a central facility, not field repaired. 
4.2.3 Minimal Fixed-Mount Intramine Communications 

4.2.3.1 System Performance 

A minimal system provides for the basic communication requirements within a mine. 

The system is basically a party line but should provide a limited private line capability. 

It supplies minimum required intrarnine communications only, providing no added interoffice 

or public phone connections required by the mine office complex. 

The objective is to keep system hardware as simple as possible, so operator skills must make 

up for any lack of equipment sophistication. 

4.2.3.1.1 Channel Capacity 

The base equipment shall have a 6-channel capability. 

The equipment shall be capable of expansion to accommodate additional channels. 

Expansion to 12 channels shall be provided, with expansion to 20 channels desirable. 

All channels shall be usable either as voice or data paths. 

4.2.3.1.2 Calling Channel 

One of the operating channels shall be at baseband. 

This channel is to be used as a calling and emergency channel. 

The use of baseband permits single-channel party line operation in the event of failure of 

channel selection capability. 

4.2.3.1.3 System Operation 

Initial contact should be made on the calling channel. 

This channel shall function as a paging channel to contact the desired party. 

After contact is made, it is the operators' responsibility to select a nonbusy working channel 

to conduct their business. 

At the termination of a contact it is desirable that the phones automatically revert to the 

calling channel. 

4.2.3.1.4 Paging 

A page call shall be heard at all phones. 

Phones in an "on hook" condition shall broadcast the page over a loudspeaker. 

At phones which are "off hook" the page shall be heard in the earpiece, added in to any call 

in progress. 

4.2.3.1.5 Page Control 

A pushbutton or momentary switch shall be used to place the system in a page mode. 

This control shall be placed on the body of the phone and shall be recessed or otherwise 

protected to prevent damage or inadvertent operation. 
4.2.3.1.6 Private Line Communications 

At least two of the working channels should be equipped to provide private line operation. 

When this is implemented only the parties involved in the contact shall be able to hear 

one another. 

4.2.3.1.7 Channel Busy 

It is desirable that a means of indicating busy channels be provided. 

The indicator will prevent disturbance of contact,^ in progress while searching for an 

available working channel. 

4.2.3.1.8 Data Communications 

Data exchanges shall be possible over any channels not required for voice communications. 

These channels shall accommodate any combination of voice-bandwidth control and monitoring 

devices. Data channels shall be dedicated to data exchanges, inaccessible from standard 

phones. 

4.2.3.2 Multichannel Implementation 

Single sideband suppressed carrier signaling is recommended when multiplexing channels on 

a single cable. 

Use of single sideband, along with a hybrid balancing network, permits full duplex operation 

within a single frequency segment. 

Suppressed carrier transmission extends battery life since less power is consumed than is 

required for full carrier operation. 

4.2.3.3 Equipment Power 

Equipment shall operate from self-contained power. 

The preferred technique involves a rechargeable power pack maintained by the phone interconnecting cable. 

A nonrechargeable power pack is acceptable if attention is required at six-month or greater 

intervals. 

When a rechargeable power pack is used, a nickel-cadmium battery is nonpreferred because 

of its apparent loss of capacity when kept fully charged. 

4.2.3.4 Interconnecting Cable 

All units shall connect with a single cable, run ars necessary throughout the mine. 

The cable should be rugged, insulated, and inexpensive such as nonmetallic sheathed cable 

(type NM) as defined in the National Electrical Clode. 

An acceptable cable is a shielded line such as coaxial cable or shielded pair, however 

shielded line systems require careful design and installation to avoid noise pickup via 

ground currents . Parallel-wire cable should be twisted when installed to reduce noise pickup. 

Cable hangers must release during a roof fall so they do not cause cable breakage. 
4.2.3.5 Cable Connections 

Units should connect to the cable via bridging taps, so that attachment or removal of a given 

instrument leaves the line undisturbed. 

Series connection in which the cable loops through each phone is undesirable but acceptable 

if failure of any one phone does not degrade the performance of the remainder of the system. 

4.2.3.6 Redundant Communication Paths 

Fixed systems should be designed so the interconnecting cable can be connected back on 

itself, providing an alternate path to maintain communications in case of damage. 

Neither a broken nor a shorted cable should affect operation of a redundant system. 
4.2.4 Fully Integrated Fixed-Mount Intramine Communications 

4.2.4.1 System Performance 1 

 his grade of system provides for all communication needs within a mine. 

(~ll connections are private line, but more than two parties may be involved. 

Full integration permits expansion to interconnect the entire mine, as well as any office 

complexes associated with the mine, into a single functional system. 

(operator skills need be little higher than those required to operate a dial telephone. 

1 4.2.4.1.1 Channel Capacity 

1 A fully integrated installation shall have at least a 10-channel capacity. 

It shall be expandable to at least 40 channels, with a minimum capability of 100 channels 

desirable. 

1 Any usable channel shall be capable of serving as either a voice or data link. 

1 4.2.4.1.2 Station Capacity 

The system shall accommodate a minimum of 100 stations. 

It shall be expandable to at least 400 stations, with expansion to 1,000 desirable. 

1 4.2.4.1.3 Interconnectability 

/ It shall be possible for any given station to call any other given station directly. 

The system shall be designed so interconnection :may be forbidden between selected stations 

or groups. 

4.2.4.1.4 Emergency Communication 

1 Under emergency conditions all stations should revert to a common channel. 

The common channel should be at baseband; however, the use of a common system channel 

is acceptable. 

1 4.2.4.1.5 System Operation 

/ The system should function as nearly like a public telephone system as possible. 

Selection of a called party should be by means of a pushbutton dial or suitable alternate, 

sealed against dust damage. 

Standard ffdial, ff !ringing, ff and !!busyM tones should be used to appraise the operator of the 

status of a call. 

It should be possible not only to select any other fixed station, but to call mobile stations such 

as those on vehicles or carried on one's person. 

1 4.2.4.1.6 Ringing 

The called station should provide both an audible and visible indication that it is being called. 

Either type of indicator shall be as attention-getting as possible. 

4-9 
4.2.4.1.7 Channel Assignments 

Channel assignment for a given connection shall be made automatically by the equipment. 

This method permits the greatest number of stations to operate in a given size system 

without interference. 

4.2.4.1.8 Communication Security 

It shall not be possible for parties other than those involved in a given connection to monitor 

that connection. 

4.2.4.1.9 Conference Calls 

It shall be possible to set up multiparty connections. 

It should be possible for any party to set up multiparty operation without central operator or 

dispatcher assistance. 

4.2.4.1.10 Public Phone Interface 

It shall be possible to place or receive calls on the public telephone system at any station 

without central operator assistance. 

There should be a provision to selectively delete either or both of these capabilities at any 

given station. 

4.2.4.1.11 Wireless Paging 

Direct paging to transportable devices should be possible either as a standard or an expansion 

feature. 

Such page may operate in either of two ways: 

a. One-way page only. To call a given pager a number is dialed. The pager responds with 

an audible and/or visible signal. Answer back is via the nearest phone instrument. 

b. Page with answer-back. Following a page as in a, above, the recipient is able to hold a 

two-way conversation with the calling party. A single remote channel must be provided 

for this feature, operated in a party line manner. To eliminate eavesdropping, the page 

receivers should not be able to access the channel until a paging signal is decoded. 

4.2.4.1.12 Antinoise Provisions 

Either standard or optionally the underground phones shall provide for effective communication 

in a high-noise environment. 

Microphone elements with a noise-canceling feature should be available. 

High level earpieces should be available, preferably with a user-accessible level adjustment. 

4.2.4.1.13 Data Communication 

Data exchanges shall be possible over any system communications channel. 

These channels shall accommodate any combination of voice-bandwidth control and monitoring 

devices. 
It should be possible to dedicate specific channels to data exchange, rendering them inaccessible to phone instruments. 

4.2.4.2 Multichannel Implementation 

Single-sideband suppressed carrier signaling is recommended when multiplexing channels 

on a single cable. 

Use of single sideband, along with a hybrid balanc:ing network, permits full duplex operation 

within a single frequency segment. 

Suppressed carrier transmission extends battery life since less power is consumed than is 

required for full carrier operation. 

4.2.4.3 Equipment Power 

Equipment shall operate from self-contained power. 

The preferred technique involves a rechargeable power pack maintained by the phone 

interconnecting cable. 

A nonrechargeable power pack is acceptable if att,ention is required at six-month or 

greater intervals. 

When a rechargeable power pack is used, a nickel-cadmium battery is nonpreferred because 

of its apparent loss of capacity when kept fully charged. 

4.2.4.4 Interconnecting Cable 

All units shall connect with a single cable, run as necessary throughout the mine. 

The cable should be rugged, insulated and inexpensive such as nonmetallic sheathed cable 

(type NM) as defined in the National Electrical Code. 

An acceptable cable is a shielded line such as coaucial cable or shielded pair, however 

shielded line systems require careful design and installation to avoid noise pickup via 

ground currents. 

Parallel-wire cable should be twisted when installed to reduce noise pickup. 

Cable hangers must releaseduring a roof fall so they do not cause cable breakage. 

4.2.4.5 Cable Connections 

Units should connect to the cable via bridging taps, such that attachment or removal of a 

given instrument leaves the line undisturbed. 

Series connection in which the cable loops through each phone is undesirable but acceptable 

if failure of any one phone does not degrade the performance of the remainder of the system. 

4.2.4.6 Redundant Communication Paths 

Fixed systems should be designed so the interconnecting cable can be connected back on 

itself, providing an alternate path to maintain communications in case of damage. 

Neither a broken nor a shorted cable should affect operation of a redundant system. 
4.2.5 Sumlementarv Communications 

Each supplementary communication installation shall be an independent communication 

system capable of interconnection with the fixed-mount system. " 

4.2.5.1 Longwall Sections 

All members of a longwall crew must be in continual party line communication with one 

another. 

4.2.5.1.1 Wired Systems 

The system shall consist of a base and a series of satellite stations. 

The base unit should be mounted at the control position for the headpiece. 

4.2.5.1.1.1 System Power 

The system shall be powered from the base station. 

Prime power shall be supplied by the longwall system power line. 

Backup battery power should be provided to permit at least 6-hour operation in the event of 

prime power loss. 

4.2.5.1.1.2 Wiring 

Interstation wiring should utilize armored, jacketed cable. 

Cable mounting should be resiliant so rock falls will not cause cable breakage. 

4.2.5.1.1.3 Equipment Description 

All switching capability shall be located in the base station. 

Expansion capability shall include provision for interconnection with the primary intrarnine 

communication system. 

Satellite stations should consist of a microphone and a loudspeaker. 

Handsets should not be used. 

Loudspeaker levels shall be such that one or more stations can be monitored from all 

working positions at all times. 

Microphones shall be of the noise canceling type. 

Particular attention shall be paid to audio intelligibility to combat the high noise levels on 

the longwall. 

4.2.5.1.1.4 Intramine System to Longwall System Interface 

4.2.5.1.1.4.1 Minimal System Interface 

There shall be a dedicated channel assigned to each longwall section. 

The entire longwall system shall monitor the dedicated channel, while the base station 

additionally monitors the paging channel. 
The intramine system may be designed to permit either of two forms of access to the 

dedicated longwall channel. Either method maintains private line operation between the 

longwall party line and the balance of the mine. 

a. All phones have access, but can only call; bidirectional communication is enabled at the 

base station. 

b. Access is always bidirectional, but only selected phones (such as dispatcher, maintenance, mine foreman) can select the channel. 

It shall be possible to switch the entire longwall system to full interconnection with the 

paging channel. 

Either wired or wireless interconnection between the systems may be implemented. 

4.2.5.1.1.4.2 Fully Integrated System Interface 

Wireless interconnection with the intramine system is preferred, but a wired connection 

may be used. 

The base unit of the longwall system shall serve as an extension of the intrarnine system. 

It shall be possible to interconnect the audio of the two systems. 

When interconnected, it shall be possible to answer an incoming call from the intramine 

system at any longwall system satellite position. 

The satellites need not be capable of initiating calls. 

4.2.5.1.2 Wireless Systems 

Wireless longwall systems are preferred over wired systems for the safety value of section 

worker access regardless of position around the section. 

A wireless system has no interconnecting cable subject to breakage. 

4.2.5.1.2.1 System Configuration 

There shall be a base unit mounted on the head piece. 

A portable unit shall be carried by every workman on the section. 

The system shall operate in a "party line" mode ;at all times. 

The base station should serve as a repeater with the portable units operating full duplex, 

however, half duplex or simplex is acceptable. 

4.2.5.1.2.2 System Power 

The base station shall be powered by the longwall. system prime power line. 

Portable units should be powered off cap lamp or self-contained batteries. 

If the base station operates in a repeater mode it should have battery backup to provide at 

least six hours of operation in the event of prime power loss. 

4.2.5.1.2.3 Portable Unit Objectives 

All or part of the unit should attach to or be molcled into the miners cap. 

The balance of the unit should mount to the equipiment belt. 
Any interconnecting cable should be molded with or clipped to the cap lamp cable. 

There should be no manually activated transmit control; however, if a manual control is 

required, it should be attached to the equipment belt, attachable on either side. 

An omnidirectional, nonpolarized antenna should be used. 

Items mounted to the miner's cap should be as light as possible. 

4.2.5.1.2.4 Intramine System to Longwall System Interface 

4.2.5.1.2.4.1 Minimal System Interface 

There shall be a dedicated channel assigned to each longwall section. 

The entire longwall system shall monitor the dedicated channel while the base station 

additionally monitors the paging channel. 

The intramine system may be designed to permit either of two forms of access to the 

dedicated longwall channel. Either method maintains private line operation between the 

longwall party line and the balance of the mine. 

a. All phones have access, but can only call; bidirectional communication is enabled at the 

base station. 

b. Access is always bidirectional, but only selected phones (such as dispatcher, maintenance, 

mine foreman) can select the channel. 

It shall be possible to switch the entire longwall system to full interconnection with the 

paging channel. 

4.2.5.1.2.4.2 Fully Integrated System Interface 

The base unit of the longwall system shall serve as an extension of the intramine system. 

It shall be possible to interconnect the audio of the two systems. 

When interconnected, any incoming call shall be automatically answered by the longwall 

system so workers anywhere on the longwall may speak. 

Disconnect of the call shall be controlled by the calling party. 

The portable units need not be capable of initiating calls. 

4.2.5.2 Trolley Phones 

4.2.5.2.1 Power Sources 

Trolley phones shall be powered from the vehicle power system. 

Backup battery power shall be provided and should permit at least 6 hours of operation in the 

event of trolley power loss. 

4.2.5.2.2 System Design 

A trolley system must be designed to eliminate the standing waves which can result in signal 

dropouts. 

Traps must be used to isolate power feed points. 
~um~ed impedances must be available to alter effective line lengths, eliminating resonant 

'sections. 

l~he trolley system should be designed around a modulation method in which limiters are 

used in the receiver for the best performance in the presence of the extreme noise levels 

Ion the trolley wires. 

4.2.5.2.3 System Configuration 

 here shall be a station mounted on each piece of powered equipment. 

For safety purposes there should be a dispatcher at a fixed location monitoring all communication on the trolley system and keeping track of the location of each vehicle. 

4.2.5.2.4 System Operation 

( There shall be at least one simplex (one-way transmission) channel in each station. 

1 There should be an expansion capability to at least two channels. I 

Regardless of the total number of channels implemented, the base channel shall be monitored 

at all times for safety purposes. 

1 Full duplex (simultaneous transmission and reception) operation is desirable. 

1 Operation shall be via microphone and loudspeaker. 

Handsets should not be used. 

Noise canceling microphones should be used on tlne vehicles. 

Because of the high noise levels involved, particular attention should be paid to audio 

intelligibility. 

1 Loudspeakers should be adjustable so they may ble positioned for best operator intelligibility. 1 

1 4.2.5.2.5 Intrarnine System to Trolley System Intierface I 

/ In simplest form interface may be through the dispatcher. 

The dispatcher shall have the capability of patching the trolley and intrarnine systems 

together. 

1 4.2.5.2.5.1 Minimal System Interface I 

1 There should be a dedicated channel assigned to the trolley system. I 

1 4.2.5.2.5.1.1 Single Trolley Channel I 

The entire trolley system should monitor the dedicated channel, while the dispatcher 

additionally monitors the paging channel. 

Privacy is maintained by allowing the dedicated channel of the fixed system to monitor only 

transmissions during which a special control has been operated. 

The dispatcher shall have the capability of shifting the monitor connection to the paging 

channel of the fixed system. 
4.2.5.2.5.1.2 Multiple Trolley Channels 

The primary trolley channel should monitor the fixed system paging channel in the absence of 

a dispatcher. 

Transmission from the trolley system to the fixed system should only occur when a separate 

control is operated. 

The fixed system dedicated channel should be connected to a secondary trolley channel. 

The dispatcher should monitor both the paging and working channels at all times. 

4.2.5.2.5.2 Fully Integrated System Interface 

Incoming calls shall ring at the dispatch point and on the secondary trolley channel unless 

patched into the primary channel. 

Signaling shall be provided so trolley phones shall have full access to the fixed system. 

If more than two trolley channels are implemented, each shall have its own phone number. 

4.2.5.3 Nontrolley Vehicles 

Nontrack, nontrolley vehicles do not require a party line channel to maintain traffic safety as 

do track vehicles, since one vehicle can move aside for another. Independent motion does not 

eliminate the need for this channel to provide communication at blind corners and similar 

situations. 

4.2.5.3.1 Power Source 

Phones shall be powered from the vehicle power system. 

4.2.5.3.2 System Configuration 

There shall be a station mounted on each piece of powered equipment. 

For safety purposes there should be a dispatcher at a fixed location monitoring all communication on the vehicular system and keeping track of the location of each vehicle. 

4.2.5.3.3 System Implementation 

Fixed repeaters shall be located throughout the mine so vehicles are not out of communication while traveling normal paths. These repeaters may be independent or may be included 

as stations in the fixed intrarnine system. 

4.2.5.3.4 System Operation 

Each vehicular station shall provide at least one simplex channel. 

There should be an expansion capability to at least two channels. 

Regardless of the number of channels implemented, the base channel shall be monitored at 

all times for safety purposes. 

Operation shall be via microphone and loudspeaker. 

Noise cancelling microphones shall be available as an option. 
4.2.5.3.5 Intramine System to Trolley System 1nI;erface 

There shall be a dedicated channel assigned to the vehicular system. 

This dedicated channel shall be used to interconnect the repeaters used to control the 

vehicles. 

4.2.5.3.5.1 Minimal System Interface 

Only selected phones (such as dispatcher, maintenance, mine foreman) shall be able to select 

the vehicular channel. 

The dispatcher shall be able to patch other channels to the vehicular channel. 

Interface in a multichannel system shall be by m.eans of additional dedicated channels 

identical to the base channel. 

4.2.5.3.5.2 Fully Integrated System Interface 

Whenever the vehicular channel is dialed, a "ringff signal shall sound in all vehicles. 

The calling party shall hear no transmission on .the vehicular system unless a separate 

control is actuated by the answering vehicle. 

All vehicles will monitor the call and any may join the call by actuating the control. 

By actuating the control any vehicle shall be able to initiate calls on the intramine system. 

Additional channels shall operate in the same manner as the base channel. 

4.2.5.4 Hoist Communications 

Hoist communication installations may be implemented as either a wired or a wireless 

system. 

The wireless system is preferred as it is immune to interruptions resulting from cable 

damage. 

Frequency diversity is not needed on wireless systems. 

4.2.5.4.1 Minimal Systems 

A fully independent single-channel system shall be operated between the shaft top, bottom, and 

the interior of the cage. 

Operation shall be via a microphone and loudspeaker. 

Handsets should not be used in the cage. 

It shall be possible for the hoist operator to patch this system into the intramine communication system or; 

As an alternate to hoist operator patch capability, a station on the intramine system may be 

installed in the cage. 

4.2.5.4.2 Fully Integrated Systems 

The cage shall contain an extension of the main intramine communications system. 

Handsets should not be used in the cage. 
All transmissions from this extension shall be monitored at the top and bottom, whether or 

not a number has been dialed. 

A loudspeaker shall monitor transmissions from the hoist operator if no call is in progress. 

Transmissions from the hoist operator shall be able to override any call in progress. 

4.2.5.4.3 Portable Communications 

A portable system shall be available so anyone performing inspection or maintenance within 

the hoist shaft will be in constant communication with the hoist operator. v 

A hand-held radio transceiver is suitable for this function. 
Section 5 

Nonvoice Communications 

Channels over and above those required to conduct the telephone business within the mine may 

be used to provide a number of nonvoice capabilities. There is a constant need to monitor 

conditions throughout the mine. Monitors may check items such as air flow, carbon monoxide, 

oxygen, and methane. Items monitored may be on either a proportional or a go/no-go basis. 

Each channel diverted to monitor service can handle a number of items gathered throughout 

the mine on a time-shared, sampling basis. As an example, status of fans, pumps, and circuit 

breakers may be read remotely and their operation controlled in many cases. Data that must 

be monitored continuously can still be multiplexed on one channel as long as a 2400 bit-persecond data rate is not exceeded. 

If a large amount of information must be transmiltted, a dedicated channel is required, An 

example is provided in slow-scan closed circuit TV. A complete picture can be transmitted 

every eight seconds using 128-line resolution, or one frame per minute with conventional 

525-line resolution, 

If low-speed data is being sent, the encoding devices may be scattered throughout the mine. 

So long as each encoder operates on its own frequency, all may share a single data channel. 
- -- 

BIBLIOGRAPHIC DATA 1. Report No. 

SHEET 1 523-0765829-0012M I 3. Recipient's Accession No. 

1 I I 

4. Title and Subtitle 

Research and Development Contract for 

Coal Mine Communication System 

Volume 1 Summary and Results of System Study 

9. Performing Organization Name and Address 110. Project/Task/Work Unit No. I 

I 

5. Report Date 

November 1974 

6. 

7- William C. Laubengayer, K. Michael Ware, Robert D. 

Telecommunications Division 

Collins Radio Group 

8. Performing Organization Rept. 

Roc kw ell International 

Cedar Rapids, IA 52406 

Gehring, Larry R. Wilson, Ramsey P. Decker, Deain T. Anderson No. 523-0765829-0012M i 

11. Contract/Grant No. 

12. Sponsoring Organization Name and Address 113. Type of Report & Period 1 

Bureau of Mines 

U.S. Department of the Interior 

washington, D.C. 20240 

Covered I Rnal 

b 

15. Supplementary Notes 

16. Abstracts 

This report contains a recommended specificatior~ for an integrated coal mine 

communication system. The communications requirements within coal mines were determined following a series of mine visits during which existing communications were 

evaluated. Theoretical and eqerimental progralrls were performed to determine the relative 

rf propagation characteristics of LF and UHF emissions within mines. Details of all 

programs supporting the specification are included as part of the report. 

17. Key Words and Document Analysis. 17a. Descriptors 

Telecommunication 

Telephone Systems 

Radio Communication 

Earth Current Communication 

Intercom Systems 

Multichannel Telephone Systems 

Electromagnetic 'Wave Transmission 

Electromagnetic Radiation 

Coal Mines 

Mine Haulage 

17b. Identifiers/Open-Ended Terms Underground Mining 

1 17c. COSATI Field/Group 9903 I 

18. Availability Statement 

Release Unlimited 

FORM NTIE35 (REV* (0-73) ENDORSED BY ANSI AND UNESCO. THIS FORM MAY BE REPRODUCED USCOMM-DC 82a~-P74 

19. Security Class (This 

Report) 

UNCLASSIFIED 

20. Security Class (This 

Page 

UNCLASSIFIED 

21. .No. of Pages 

47 

22. Price