WIRELESS COMM-UNICATIONS 

FOR T RAG-KLE S S 

HAULAGE VEHICL.ES 

PREPARED FOR 

UN 1 TED STATES DEPARTMENT OF THE I NTR l OR 

BUREAU OF MI NES 

TERRY S. CORY, P.E. 

ENG I NEER 1 NG CONSULTANT 

CEDAR RAPIDS, IOWA 

- FINAL REPORT - 

REPOFT PREPARATION: CONTRACT 30395072 

ORI GI NAL WORK: CONTRACT KO 3770 1 3 

17 JULY 1979 
The views and- conclusions contained In this 

document are those of the author and should 

not be i nterpreted as necessarl l i y represent i ng 

the official pol lcies or recommendations of the 

l nterior Department's Bureau of Mines or of 

the U.S. Government 
REPORT DOCUMENTATION PAGE. 

1. Report No. 2. 3. Reciprenr's Accessron No. 

' 4. Trtie and Subt~rie 

Wi re l ess Communications for Trackless 

H3ulsge Vehicles I 

'. Aurhor(s) 

Terry S. Cory 

I 

9. Performing Or~an~zation Name and Address 

vision 

Terry S, Cory, P.E, I 2857 West, bunt Vernon Rd. S.E. 

Cedar Rapids, Iowa 52403 

I r2. Sponsorrng Organlzatlon Name and Address 

, Off ice of the Assistant Dl rector - Mining 

Bureau of Mines 

Department of the Interior 1 Washington, D.C. 20241 

5. Supplementary Notes 

5. Reporr Dare I7 July, 1979 

6. 

8. Perfornl~ng Or~anrzatron Report No. 

10. Pro~tct/Tark/W'ork Unrt Xo. 

11. Confrarc or Grant No. 

J0395072 r 

13. Type of Repon 

Final Report 

I 

14. 

. 

1 

I Prior related work - Wi re 1 ess Commun i cat i ons for Tracl: l ess hau I aq? 

Veh i,c l es, USBW Contract H03770 13 

6. Abstract 

I 

Th i s report descri bes a conp 1 ete system des l gn methodo l ogy for 

1 rned i urn frequency ( MF 1 w l real ess rad io systems for use i n coa l 

mines. The emphasis is on AC mines where no trol ley wire exists 

and, for which, conventlona 1 trol lev phone cornmunica~ions can 

not be used, 

The report constitutes an MF system des i gn handbook and I nc l udes 

a compendi urn of al l pravious MF technolagy elements as we1 l as 

a reference i ndex with abstracts of a l 1 perti nent I lterature. 

A particular strawman system design analysis is included for the 

He l vet i a Coa l Co. Lucerne $8 rrii ne i n the Upper Free~ort Seam. 

, 7. Orr~~nator'r Key Words 

I h.4F wireless radio propacation; carrler I 

i current coup l i ng to mi ne cond uctars; 

i face-area noise; system radio elementsPortab l as, Veh i cu l ars, Base Stat l on, 

1 Remte Base Reoeater, etc. 

1 

18. Availability Statement 

I 

I 'hcunty Classif. of the Repon 

L,! a?; sified A 

20. U.S. Suurtty Classif. of Thls Page 

Unclassified 

21. No. of Pagn 

153' 

22. Price 
FOREWARD 

This reportwas ~repared by Terry S, Cory, P.E. for the U,B. Bureau 

of Mines under Contract J0395072, The contract was Initiated under 

the Coal Mine Health and Safety Program, It was administered under 

the technical direction of PMSRC, Bruceton Research Center, with 

Mr. Robert Chufo acting as the Technical Project Officer. Mr. Mike 

Nowicki was the Contracting Officer for the U.S. Bureau of b~ines. 

This report builds on work completed during calendar 1977 under the 

original Wireless Communications for Trackless Haulage Vehlcles 

contract, Phase 1, ( H0377013 wlth Rockwell/Collins and bears 

the same ti tie, Thl s report is intended to replace the Phase I 

draft report, same title, original ly submitted by Rockwel l/Col l ins 

i n August, 1977. The current work was performed begi nn i ng f!ay 1 1 , 1979 and completed with the submittal of this report on July 17, 1379. 

Any reference to specific brands, equipments, or trade names eiiher 

speci f i ca l I y written or i mp l ied does not i mp l y endorsement by the 

U,S, Bureau of Mines, 

Work performed under this contract has not resulted in any patentable 

items of equipment, designs, or techniques, 
Table of Contents ( cont. ) 

Page 

Compend i urn of Foundat l on Technology--- 

El ements 

MF Propagation-------------------- 

Summary Characterlstlcs------------ 

Quas i -Conductor-Free Transmi ss ion &--- 

Constltuitlve Parameter Analysis 

Conductor Proximity Transmission----- 

E I ectromaanet i c No i se/ I nterferance---- 

Antenna Consideratlons----------- 

Conductor Coup l i ng---------------- 

Prototype Equlpments----------- 

Application of Other Technologies--- MduIation---------------------- 

Intrinsic Safety Considerattons---- 

System Capabil ity Demonstration Plan-- 

Objectives of Demnstration/Testlng--- 

Proposed System Canf i gurat i on---- 

Demnstration/Testing Technical---- 

Approach 

Demnstration/Test Schedule----- 

Task & Schedu le Descrl ptions-- 

Estimated Level of Effort----- 

Reference l ndex of MF Techno l ogy-- 

Resources 

basured Propagation Data- - 

Conductor-Free Propagation Analysis- 

'Coup l ed Conductor Pro~agat i on Ana l ys i s 

Measured Noise 3ata And AnatysisPrototype System E l ement Deve l opments 
List of I l l ustratlons 

Fi gure Page 

I Latera I Range vsRange A1 on9 Cond uctors 2------ 19 

890 kHz 1 n Upper Free~ort Seam with 21 0 

dB SWR on Conductors and One Radio 

Located 3 Fkters f rorn Conductors 

2 OverviewofCornmunicationLinkPo~sibillt~es--- 21 

for Medl urn Frequency System 

3 Topological Diagram of Helvetla Coal Co.----- 26 

Lucerne #8 Mine Show l ng Estlrnated Work Areas 

and Active AC Cable Runs for Late 1977 - 

Annotated wl th Estimate of Desl red 

Commun i cations Coverage Area 

4 Veh i cut ar-To-Base Aiea Coverage Contours for--- z7 

He I vet 1 a Coa I Co. Lucerne #8 Mi ne Show i ng 

Location of Line Ampl ifier or Remte Base 

Repeaters 

5 Veh i cu 1 ar-To-Veh i cu l ar Area Coverage Contours-- 2S 

for Helvetla Coal Go. Lucerne #8 Mine for Close 

Coup I i ng and 0 ne-Entry-Away Coup I i ng at 

T ransmi tter 

6 I l 1 ustrations of Portab I e MF Rad lo Packa~e---- 35 

Des i gns 

7 l 1 t ustrat ion of the 1 mo 1 ementation of a------ 36 

Typical Vehicular Radio System 

8 Illustration of the Implementation of a Typlcal 37 

Base Statlon 

9 l l l ustrat l on of the I mp 1 ementat ion of a Remte 40 

Base Station 

10 Illustration of-the lmplementatlon of a Line--- 41 

Amplifier Repeater 

I1 lllustrationof the lrnplementatlonof a Llne- 43 

Coup 1 er Repeater 

12 lllustration of the Implementationof a Remote 44 

Repeater 

13 lllustrationof the Implementation of Active--- 45 

and Pass! ve Ll ne Extenders 

14 Functional Block Diagram of Base station----- 47 

15 Functional Block Diagram for Portable or-- 49 

Vehicular Radios ( Vehicular Shown 

16 Functional Block Diagram of Remte Base---- 51 

Showi ng Baseband Audio and MF 1 nput Options 

from Bifilar Phone Line 
List of I I l ustrations ( cont, 1 

Fi gure Pa ge 

17 Functiona l Block Diagram of Remote---------- 52 

Repeater 

18 Functional Block Diagram of Line Amplifier--- 54 

19 Functional Block Diagram of LI ne Coupler---- 56 

20 Functional Block Diagram of Passive and------ 57 

Act i ve Li ne Extenders 

21 Overvisw of Communication Link Posslbillties-- 61 

for bdi urn Frequency System 

22 System Link Possibllitles Local Area-To- --- 64 

Centra l Dl spatcher 

23 System Li nk Possi b i l i tles Local Area/Central-- 65 

Dl spatcher-bb i l e Un I ts 

24 System Link Posslbilltles Local-Area-Only or-- 66 

Between Local Areas 

25 Lateral Range VS Ranae Along Conductors for- 70 

Vehicu lar-Veh icu l ar Operation i n Upper 

Freeport Seam @ 890 kHz with + 10 dB SWR and 

One Radio Located 3 Meters fr& Conductors 

26 Topological Diagram of Hel vetia Coal Co.-- 26 

Lucerne #8 Ml ne Showing Esiimated ~iork Areas 

and Acti ve AC Cable Runs for Late 1977 - 

Annotated wi th Esti mate of Des i red Camnunlcation 

Coverage Area 

27 Veh i cu l ar-To-Base Area Coverage Contours for-- 74 

He l vet i a Coa l Co. Lucerne #8 Ml ne Showi ng 

Locat i on of Li ne Amp l i f i er or Remote 3ase 

Repeaters 

28 Veh i cu I ar-TOVeh i cu l ar Area Coverage Contours- 75 

for tielvetla Coal Go. Lucerne #8 Mlne for 

Ciose Coupling and One-Entry-Away Coupling 

at Transmitter 

29 Summary Wax? mum Communication Ran~e Data for-- 86 

Seven Coa l Seams under bd ian-Mi ne-Noi se 

and Set-Noise Limits 

30 Excess Si gna l brgi n Character1 stics vs Ranae 88 

for an AC Mine In the Upper Freeport Seam at 

890 kHz Us i ng FM Vo i ce Rda i os w l th 5-Watts 

Output and a 6 dB Noise Figure Receiver 
List of Illustrations ( cont, 1 

Fi gure Pa ge 

31 Composite Plot of Signal Attenuation Rates----- 89 

in dB/IOOFeet for Ten Mines in Six Different 

Coal Seams 

32 Attenuation Character 1 st 1 cs of Phone Ll nes--- 92 

33 bkasured Quasi-Conductor-Free Pltagnetic Field--- 94,95 

Strength vs Range and Frequency Curves 

Typi fyi ng Seven Coal Seams 

34 Cop l anar Loop Or i entzt i on Geometry for----- 97 

Opt i mum Transmi ss ion us I nc Ouas i -TEM Coa l Seam 

kde 

35 The Geometry of a Comunicat Ions LI nk Emp loyl ng 105 

a Pass i ve Li ne Extender 

36 mao one tic Fiel d Strength Coverage M~D of Lucerne 106 

#8-~i ne with the Transmitter Placed Adjacent to 

the Power Cable at ?he Junction of the North 

and South Mains Belt Entrles - 910 kHz 

37 Summary of Ori gi nal NBS Veasured Edoise Data in- 107 

Coal Mines Extrapolated Above 200 kHz Expressed 

as flel d Strength ( Or1 gl nal 1 and as Conducted 

Noise Power Assuming 2 Meter Spacing from 

Conductor to Fl e i d Strength 

38 CorrecTed Noi se Curves for Coa I Mi nes aased on 109 

NBS Measured Fie l dstrength Data Corrected Us i ng 

l nstantaneous Commn bde >.lo i se Data From 

Harewood and Sesser tlli nes - Fiei d Strength 

Ap~ropriate for 2-Meter Soaci ng from Phone Line 

39 Average Dl f ferenti a l Wde l nstantaneous Noi se- 1 10 

Levels on Phone Line in Harewood Mine - 

Characteristic of DC Mi ne with 100$ Tracked 

Haul age - Phone Li ne was 16-3 Rorex ( Gnd 

Floating 1 and Not Twisted Pair 

40 Average Differential Mode Instantaneous Noise-- 111 

Levels on Phone Line In Sesser Mlne - 

Characteristic of AC Mlne with 100% Belt Haulage 

- Phone Line in Same Entry as AC Powercable 

41 a Norma l i zed Spectrum of a Carrler Angle-Modul atsd 1 13 

by a Narrow Band Gaussian Random Process 

41b Peak Amplitude of Gaussian Phase bbdulation---- 113 

Spectrum vs Mean Square Phase Deviation 

42 Familiar Phase IbdulatIonTriangle forTwo J 15 

Signals 
List of ll lustratlons ( cont. 

Fi gure Page 

43a Veasured Resl stance of the Phase I Veh lcul ar---0 I 19 

Test Antennaand Com~ar l son w 1 th the \*i ne Wi re l ess 

and EM S i cna 1' l i ng 7-Turn Antennas Show I ng the 

Low-Frequency Log-Linear Variation of Resistance 

with thesquare Root of Frequency . 

43b Measured Reactance of the Phase I Vehlcular--- I19 

Test Antenna and of the Mine Wireless Prototype 

Antenna Show i ng the Low-Frequency Log-Li near 

Var l at i on of Reactance w i th Frequency 

44 N I A vs Frequencyior 6- l nch By 3-Foot Veh i cu I ar-- 122 

Antennao f 12 Turns in a I$-Inch Electrostetlc 

Shield wlth 1700/44 Litz Wire 

45 Quas i -Stati c Graph i ca l Fie l d Mapp i ng of Entry--- 123 

Crossections and Coupl ing Estimates Made From 

These Mappings 

46 Veh i cu l ar Antenna Prototype-------- 131 , 

47 Winding and Wiring Configuration for the Vehlcularl32 

Antenna Prototy~e Showing the Connection 

Arrangement of Turns to !!If ni mi ze. Di stri buted 

Capac i tance 

48 Tun i ng Curve for Prototyoe Veh i cu l ar Antenna---- 133 

Tuned to Nomi na l I y 920 kHz Show i ng Frequency 

Shi it Due to t&asurement Dver Dielectric and 

Steel Mounting Surfaces 

49 FM Voice bdulation Spectrum, M = I, Deviation-- 139 

= - + 3 kHz 

50 Minimum Frequency Se~aration for Achieving Full-- 140 

Recei ver Sens i t l v i ty for Repeaters 

51 Possible AC Intrinsic Safety Crlteria Using---- 143 

Bandwidth of Antenna as a Measure Showing 

Minimum Bandwidth as a Functlon of Input 

Power 
List ~f Tables 

Table Page 

I Der i ved Coa l Seam and Rock Conduct i vi t i es From-------- 96 

Curve Fi tt i ng to Measured Data Us i ng the ADL 

3-Layer Ana l ys l s ?lade l 

2 Summaryof Short Formulas forScatterGain----------- 99 

Calculatlon vs Coal Seam 

3 Summary of Short Formulas for Conductor Attenuation--- I0 I 

vs Coa l Seam ( Based on S i ngl e Conductor Geometry I--- 

4 Cornpar~isons of kasured and Computed Scatter Gains---- 192 

In Three Mines 

5 Performance Di aanos i r for Veh i cu l ar Frototype------- 123 

Antenna as Obta i ned Dur i ng Pre l i mi nary Test l ng 

@ 476 kHz 

6 NIA, Toral Series Resi stance 9, and Antenna Current-- 12k 

for 5 Watts ln~ut vs Number of Turns for Portable 

Antenna 3esisti vely Padded to 12 kHz Bandwidth 

7 Msasured Current Coup 1 i ng Cowf f icient vs Transverse-- (77 

Spaci ng of a Base Station Loop Antenna from a 

Monof i 1 ar Li ne Section Over a Conduct1 ng l nterface 

( ,Ground I 

8 ComputedandFAeasuredSensltivitiesofRACALand- 134 

Col l ins Prototype Portable Radios 

9 SumryCon~arisonsof FMvsSSBbdulatlonSased- 137 

on Intel I igibi l ity 
1.0 l NTRODUCT l ON 

This report presents the first complete treatment of medium frequency 

wireless radio cornmunicatlon system design methodology oublished as 

a resul t of U.S. Bureau of Ml nes funded research and deve loprmnt. 

The report contents consist of a compendium of a1 l medium frequency 

foundation technology elements tcrdate in a form directly usable 

for system design; a detailed description of medium frequency system 

architecture and of the equipment elements comprising the system; and 

of a particular system design example In an AC mlne with trackless 

haulage leading toward a prototype systsm demstration plan. 

The work reported here i n i nc l udes techno l ogi ca l deve l opments from 

several sources within the USBM PMSRC research comnunity being 

brought together for the first time as a composite methodology. Some 

of the analysis techniques reported herein .are newly developed by 

the author or are being appl ied to medl urn frequency ( MF systems 

by the author for the first ti me. 

The starti ng effort to deve lop an MF system design conce~t was ~erformed 

for the aureau by Rockwe l l /Co l I i ns under contract #H03770 1 3 ent i t l ed, 

Wireless Communications for Trackless Haulage Vehicles, Phase I. This 

contract "vehicle" for mti vat i ng MF system des i gn th i nki na was 

predicated on the mast obvious and needed requirement for wlreiess 

comrnun i cat i ons i n underground coa I mi-nes; name I y, to provi de ve h i cu l ar 

comnunications in AC mines equivalent ( or superior 1 to trolley 

phone communications in DC mines. Previous medium frequency electromagnetic 

mine measurements has shown th9 feasibi l ity of serving this need 

through carrier current coup l i ng i nto exi st1 ng mi ne wi ri ns. 

Using the original RockweII/CoI Iins results and their review by PMSRC 

as a starting point, this report extends these results and provides 

the bas i s for camp lete system desi gn. Th i s report has been prepared 5\f 

Terry S. Cory, P.E. under separate contract J0395072. The work has been 

accompl ised over a 90 day period from Apri l through July, 1979. 

1.1 STATEMENT OF THE PR0BLEF.I 

This report serves a dual purpose; namely to focus all ~revious wireless 

MF R 8 D in underground coa l mines toward a general mi ne-wide system 

design concept, and then to apply the concept to a particular ~ractical 

communications problem - providing communication in AC mines for which 

there is no direct track and trolley connection to vehicles, Once 

establ ished, an MF comnunication system offers increased versati l ify 

over the use of trol l ey phones because it is not constrai ned to locations 

where there i s track and tro l ley, but i nc l udes an operat i ona I area for 

vehicular communications potential ly covering all locations where 

vehicles may be found. Also, the system is usable with man-carried 

portable radios which may talk to the vehicles or, by thevselves, 

directly back to the base station, 
As a "para 1 l e 1 " to conventi ona l trol l ey phone communications, the 

wireless system also depends upon carrier current flowlng in rnlne 

w i r i ng conductors for long range comrnun i cati ons In mi nes. Previous 

R & D has established medium frequencies in the 300-1000 ki(z rance 

as being optimum for wireless coupling into these conductors with 

the normal trolley phone frequency band of nominally 88-108 kHz as 

being too low for efficient coupl ing. An added feature of the use 

of medium frequencies is that they have also been found to be optlmum 

for wireless transmission directly through the coal seam in absence 

of conductors. While MF is optimum for wireless coup1 ing, the 

coup l i ng losses p l us i ncreased attenuation of carrier current i n 

long runs ( with respect to trol ley phone frequencies, due to the 

higher frequencies involved wil l mst often require the use of 

repeaters. This is in contrast to trol ley phone operation, where 

repeaters are not used. 

A general purpose MF system may have wide appiicabil ity to many types 

of underground mi nes, i nc l ud l np i rnproved DC coa l mi ne mi ne commun i cations 

and metal/non-metal mine communications. The trackless haulage 

application, for which the trolley phone parallel is drawn , serves 

hau l ageway comnun i cat i ons on l y. Add i t I ona I requ i rerents i n underground 

coal mi nes which ray be served vi a an MF w i reless system i ncl ude: 

Section Comnunications 

voice commun i cat ion coverage poss l D i l i ti es 

forward of the sect ion power center i nto 

the area where coal is being mined 

voice communications conirol by a face boss 

of all shift crew and maintainance or 

i nspect i on personne l over an ent l re pane l 

to serve automat i c remote man i tor i ng of a l rf low, 

methane, and carbon mnoxide levels in an ares 

being mined 

Paging 

the locatlon of particular personnel in the min2 

rather than just a vehicle 

Emergency 

wireless comnunicatlons within the seam may no? 

be hampered by rock-fa l l s or broken phone I i nes, 

etc. 

inspector discovering potentially hazardous 

conditions can quickly inform all ~ersonnel 

affected 

Hoi st/shaft Comnunicatlon 

poss I b l e s i mp l i f i ed commun l cations surface-tounderground 1 n portal area vla carrler currani 

induced in holst/cage conductors 
In common with trolley phone operation, the use of MF wireless radic 

communications uses existing mine wiring conductors; thereby el iminatina 

the need to "string" addi tional wires. 

1.2 HISTORY OF MF WIRELESS RADIO R & 0 

The possibility of extended throuoh-the-seam wireless communications 

( with respect to that through homoaeneous earth 1 was first observed 

in August 1974 by PMSRC personnel testing a pair of South African 

ECAM radios in the Ireland mine, 

As part of a USBM sponsored mi ne w l re l ess prototype hardware deve l o~ment 

program in early 1975 ( H034067 1, magnetic field strength measurements 

were performed by the author toward selecting the best operating 

frequency for the radios. l.lF was determi ned to be optimum i n areas 

without conductors i n the Pi ttsburgh seam. Under USBM contract ( H0346045 1, 

Arthur D, Little, Inc. ( ADL identified theoretically the auasi-TEM 

para l l e l p late wavegui de mode as bei no predomi nant i n conductor-f ree 

areas. Concurrently with this, the author noted substantial coupling 

of carrier current into existing mine wiring conductors, and the first 

coup l ins models were developed. 

I n 1976- 1977 under FbnSRC sponsorshi D ( H0366028 1, the author performed 

magnetic field strength measurements in 6 mines in 3 seams in high coal 

i n both quas i -conductor-f ree and cond uctor-oroxi mi ty weas. The resu I ts 

were analyzed by ADL, progucing estimates of the constltultive 

parameters In the coal seam environm~nt ( H0346045 1. Concurrently, the 

author developed the scatter gain theory, uslng ADLrs 3-layer field 

strength model as a basis, for coup! ing into conductors fron a remete 

transmitter.This theory was used to show, for the first time, thtt 

near-opt i mum frequenc i es for d i rect through-the-seam transmi ss i on and 

for remte coup l i n i nto conductors were compatl b l e. 

In 1977-1978 under PMSRC sponsorship ( H0377053 1, the author performed 

magnetic field strength measurements in 5 mines in 4 seams in low coal 

i n both quas i -conductor-free and conductor-proxl mi ty areas, These resu l ts ' 

were again analyzed by ADL C H0346045 1 in the same fashion, Care was 

taken to obtain experimntal measures of scatter gain and, using tbe 

ADL der i ved const i tui t i ve parameters, the remote coup l i ng scatter ga i n 

theory was va l i dated vi a close compari son of theoret i ca I and emp i rl ca I 

resu Its, 

I n 1978, under PMSRC sponsorsh i p ( PO382223 1, the author deve l ~ped 

prototype vehicular antenna hardware for eva l uation ( track1 ess haul age 

vehicles 1 and conducted "close" conductor coupling studies including 

graphical field mappings of magnetic field fn typical entry crossectlons. 

Th i s work, i n conjunction with the remote coup l i ng scatter ga I n techn 1 que 

has provi ded the bas i s for the pred ict l ve coup l i ng mode l presented i n 

this report. 

In 1978 and 1979, as part of a program to masure noise on twisted pair 

phone lines ( PO382497 1, the author extrapolated common mode noise 

data into field strength near conductors and combined the results with 

previous NBS derived noise data. This has provided the basis for selection 

of noi se \eve l s near conductors i n AC ml nes and has provi ded the f 1 rs? 

estimate of the im~ulsi ve nature of no1 se near conductors In DC mines. 
I t has a I so provi ded the basi s for est i mat i ng b i f i lar mode contro 1 

l i nk performance at MF over phone l i nes l ncl udi ng the f i rst est i rratss 

of phone line attenuation in the MF region. 

Pri nc i pa l contr i butors to red i urn f reouency techno l ogy at Pb5RC have 

been H. Dobroski and R. Chufo. Principal contributors to rnsdlum 

frequency technology at ADL have been Robert Lagace and Fred Ernsl ie. 

The above is a rather short summary of selected VF 4 8 9 actlvlties 

which have lead directly to system design. A more complete 

understanding of all the medium frequency work and its chronology, 

incl udi ng the fine ADL work i n the area of dedicated wi re and mu1 ticonductor mde analysis can be-obtained from Section 7 of this report. 

1.3 REPORT CONTENTS 

Two particular sections, Section 3 and Section 5 , have been preparsd 

on a stand-alone basis. These are, respect1 veiy, MF System Desi pn Primer, 

and Compend i urn of Foundation Tecnno logy E I ements. 

Section 2 comprises the Executive Summary of the work. 

Sect ion 4, MF System El ement Speci f i cations, draws heavi l y on Sect Ions 

3 8 5 and summarizes pertinent equipment parameters in a sinsie location 

i n the report. 

Section 6, System Capability Demns-kration Plan, is written in ?hz form 

of a proposal based on the imp lemntation of a "te~t-bed~~=systern in ?5e 

He1 vetia Coal Co, Lucerne #8 mine - the mine for which the strawran 

calculations given in this report were made. 

Section 7, Reference Index of MF Technology Resources, Includes a rather 

complete bibliography of the topic together with brief abstracts of the 

work performed. 
2.0 EXECUT I VE SUMMARY 

The potential performance characteristics of medium frequency ( MF 

w i re less communications systems i n underground coa l mi nes are we l l 

understood. The state of deve loped hardware to imp lement MF systems 

i n U.S. coal mi nes is embryonic ., but growl ng. 

This technology was initiated throu~h testing of a 15-20 watt SSB 

portable radio developed in South Africa by ECAM. The possibilities 

for wireless comnunications in underground mines stimulated the 

development of the first U.S. prototype radios by PPSSRC during 

1975-1976 via Rockwell/Cellins. These radios, consistine of portables 

and a bass station, were tested along with the ECAM radios in 

conjunction with the magnetic field strength measurement prosram. 

The Co l l i ns portab l e, packaged nearly i dent1 ca l 1 y to the ECAP rad 1 G, 

was a 20-watt norrowband FM unit. Unfortunately, both of the above 

radios embodies cumbersome designs and rigid antennas which were 

unappea l i ng and coul d not be conven i ent 1 y "worn" w i thou* ham~er i na 

the normal work duties of a miner. EbtS of these radios ( ECAM 2 

335 kHz and the Co I l i ns @ 520 kHz exh i b i ted s i mi l at maxi mum range 

performance i n conductor-f tee areas, gi vl ng up to 1600 feet of range 

in the Pittsburgh seam and up to 400 feet of range in the Herrln f6 

seam. During this early 1975-1976 period, these radlos were viewed 

primarily as curiosities by the industry with little active interesi 

in the technology being expressed. 

The f i rst i ndustry-stimul ated "look" at MF occurred duri ng the 1076- 

1977 tineframe when Consolidation Coal ( via Lee Engineering and 

Ferry Telemetry of Hiawatha, Iowa developed a low power ( 7-watt 

"second generat ion'' SSB portab l e for test i ns based on CONSOL requi remnts 

in the environmental safety area. Somewhat concurrently with this, a 

new smal ler South African radio ( I-watts > of improved packaging 

desi gn was devl oped by RACAL and i s now ava i lab l e i n l i mi ted auant i t l es 

in the U.S. market. Unfortunately, both of the above radios have been 

found to be unsati sfactory for extended system use in coa l mi nes 

because : 

The power level is too low ( in the case of the 

RACAL radio) 

+ SSB radio Inherently suffers severely from impulse 

noise near conductors ( i n particular, the automatic 

squelch on the RACAL radio and Its long AGC recovsry 

time constant renders it nearly unusable in impulse 

no i se 

Dur i ng the 1975- 1 976 USBM eva I uat 1 on of the " f i rst generat i on" proto+ype 

rad ios, cornparati ve tests near conductors were neglected I n favor of 

tests to support character1 zat ion of performance I n qui et areas; the 

case of most scientific interest, but least operational significance. 

Currently, the narrowband FM radio is clearly viewed by the author as 

beingth e type mst desired for use in large-scale MF systems in both 

AC and DC mines. During this same time perlod, and into 1978, PPlSRC 

was i nstrumen-lal i n the development of improved "second generstion" FM 
radio hardware for a different reason; namely, the devalopment of a 

multiplex wireless MF methane mnitoring system for continuous miners. 

A new i nd ustry-st i mu l ated i nterest i n w i re l ess commun i cations I n coa 1 

mi nes has evo l ved natura l l y because of the track1 ess haul age commun i cation 

problem in AC mines. Trol ley phone manufacturers are now working towards 

wireless-coupled vehicular radios to solve this problerr, Additional ly, 

interest is growing in the potential of wireless communications in 

sections, 

I t i s now safe to say that MF w i re l ess rad io development w i l l occur 

via natura l industry sti mulation over the next several years for coal 

mines, even without additional R & D sponsored by USBV. The idea was 

spawned by the early :feasibility1' technology transfer efforts by 

PMSRC, 

The only problem with this natural growth is that it is likely to occur 

to meet speci f i c i sol ated requi rements without ever recogn i zi ng ths 

full large-scale communication systen potential that is possible by 

f i tt i ng the rad io des i gns i nto an overa l l arch i tecture. Recogn i z i ng 

th i s, PMSFiC has provi ded for the control l ed devel opment of a "+h i rd 

generation" of radios ( H0395120 1 which wit I, hopeful ly, be compaiible 

with a concept for large-scale system Implementation. 

PMSRC has recogn i zed the need for th I s "system des i gn l eadersh l pl' s i nce 

1976 when the ( H0366056 1 Wireless Communications for Trackless Haulage 

Vehicles contract was initiated, Circumstances, beyond the control of 

USBM and the R 8 D commun i ty have prevented 3 ear l i er treatment of 

systems and the dissemination of MF system design guidance to the 

i nd ustry, 

Hopeful ly, it is not too late to guide the course of developments 

in this exciting technology area to its ful l potential. 

2,l MF SYSTEM POTENTIAL 

2, I POTENTIAL FEATURES 

As will be shown in this report, the use of a sultably designed MF 

w i re l ess rad I o commun i cat ion system provi des the capab i I i ty for mi newide communications,not l i mited by very close proximity to conductors, 

between Portable, Vehicular, and Base Station radios in underground 

coal mines, 

Amajor feature of an MF system is that It Is not inherently constrained 

by special wiringand, in fact, requires no s~eclai wiring save, perhaps, 

for a separate phone line cpntrol link to Remote Base repeaters. 

Because there is nol'cable plant" directly Interfacing the system and 

powering any of the system elements, the intrinsic safety of the systsm 

resides soley in the intrinsic safety of the individual radlo anifs. To 

drive home this point, the reader is reminded of the KM-IOI system 

in which the intrinsic safety of any element of the systen Is tisd ineo 

the intrinsic safety of the entire system. The system, thus, provides 

an interface between the haulageway "Iong-haul" links and +he c9nduc+,r- 
free local l inks in the area being mined that is no more compl icafed 

than the design of the individual element radios. 

2.1.2 SYSTEM PERFORMANCE OVERVIEW 

While the maximum communication ranae new the optimum frequency ir, 

conductor-f tee areas emp l oy i ng d i rect through-the-seam transmi ss ion vat i es 

considerably with seam characteristlcs, the maximum range in close 

proxi mi ty to conductors vari es on l y s l i ght l y for d i fferent seams. Thus, 

for remte coup l i ng into conductors, on1 y the chpl l no latera l rmge 

is significantly affected by the seam. 

Detailed dependancies of corrtrnunicatlon range on frequency and on seam 

characteristlcs are i l lustrated in Section 5.1 of this report, 

As a typical case, the comrnunicafion ranges expected via close coupling 

i n the Upper Freeport seam are i l l ustrati ve of performance ach i svzb l e 

in many mines. 

For a cont i nuous conductor stri n~ w i thou? stand I ng waves or ?aps/brancnes 

and for iiadio Terminal Elements with the above cited close coupiei spaciass 

for bof h transrni tter and recei ver ( antenna centers to CO~~UC?O~ ensexb 1 E 

center 1, the maxi mum cowuilica~!or, ranges a long fhe conc'uc?or stri n~ are: 

(I) In an AC mine 

kdio type Range AI ong Conducfors 

v-v 

3-B 

40 19ri ( 2.50 RT l as ) 

3426m ( 2.13 miles j 

6096rn ( 3.79 mi 16s 1 

(2) In s LC minc w/belt haulage - 

%die fyp6 

P-P 

v- v 

i3-a 

iian~e hl on~ ;orid ucfors 

2727m ( 1.69 mi fes 1 

21Xm ( I ,33 mI les 1 

4b05m ( 2.99 mi les ) 

(3) I r, a CC &i ne w i ?h f racked haul as6 & 60 ?rol i eyphone 

i nterferazca 

Radio typ aange Al on5 Conductors 

P-? 

v- v 

B-B 

1013m ( 0,63 miles ) 

422m ( 0.26 fii les ) 

3091111 ( I .a8 ~iies ; 

the mine type differencas oeisg ihe noise levels experienced; Thess 

' operationally si~nifican; types to be shown in Sec~ion 5.2. 
Close exaci-nation of a greai deal of wgnetic field strsngtt, data has 

resulted in ihe foilowins expectations for rnonofi lar mo~e s~anains wave 

levels and ta? losses: 

For sfand.i.ng wevas 

* 3 dB in ;ozg hzu;~geways wi?h tap spacin~ of a? hast iGCO feet 0 

I 

+ 4 d3 In subma! ns wiih approxinate 400 foot fa? spacings, 

single Tap 

- + 6 dB in submaizs with a?proximaTe 400 foot tap spactnss, 

doub l e tap 

+ 6 a5 in conductor-dense areas in seckions near cefi-?sr of sec?io~~

0 

- + iOd6 in conductor-dense trac~ec, beiiea secyions wi% service 

tracks 

Note: 2 10 db was also measure^ in Lucerne 88 

For taps/ j unctions 

-3 dB/s i fig l e tap 

-5 da/doub l e tap 

For a large scaie overview, the to: lowing average conditioris my be assumec; 

I each NS or EN rains spIi? -3 dB 

I each subrain spl If -3 dB 

iA) For hau lap arsas 

each 

4 each sins;€ t6ps 

giving an aS5ragaTa ap?roxlrnaie loss to consider of -22 to -24 

d3 with rsspct To a i 1at unta?pe~ I i ne 

(3) For sect ion arsas 

2 each single Taps -6 dB piusil0 c3 VSWR 

giving an assrafata app~oxinate !oss of -22 d3 
Nofe that the assumption for boih hauiacjeway and section areas produce asoo? 

the sars loss estiw~e of -22 a6 ir; si~nai marsin due To i-e cc;r.bination of 

stand i ng wave and junction effects under averase con^ i ?ions. Under this 

assumpt ion, The c i ose l y coup i ed maxi rncrr, comnun icai ion range es? i mstss 

a l ong conductor slr i ngs w i fhout repee:ers becomes : 

ibd io Type 

v-a 

P-P 

v-v 

B-Er 

P-3 

Range Along Conduciors 

3138ri ( 1.95 miles 

2859m ( 1.78 miles 1 

2268rn ( 1.41 miles 1 

493717 ( 3,GG miles 1 

3729m ( 2.32 ml Ies 1 

(2) In a GC mine w/belt haulage 

P-? 

v-v 

B-3 

P-0 

v-B 

1566~ ( 0.97 mi les ) 

576m ( 0.61 rni les 1 

3644m ( 2.26 miles 1 

2437rn ( 1.51 miles ) 

l846rn ( 1.15 mi les 

While these ranges are achievable when the transmit and receive radios 

are in the same entry as the conductors, an important feature of the 

MF system is the areas coverage in ierms of lateral ( or transverse 1 

range away f romconductors. For veh icu l ar operat Ion, provi d i np con? i nous 

coverage from a 5-watt radio with an assumed + I0 dB SWR on the 

conductor(s), the lateral ranges vs range along along canductors 

are i l l ustrated for Vehicular-*-Base Statlon and Vehicular-to-Vehicular 

operation both for a long continuous conductor without branches and 

for an average condition of 4 branches In Fi sure . These are ranges 

without repeaters. I n the Pittsburgh seam ( the best seam for conductorfree transrni ss ion ) the l atera 1 range w i l l be about 20-255 greatsr 

except that the d i rect through-the-earth range itse l f w i I l be 1230-1 600 

feet. I n the Herr1 n #6 seam ( the worst seam for cond uctor-free 

transrni ssion 1 the lateral ranges wl l l be about 20-258 less. 

With repeaters in an AC mine for transmf ssion back to a Base Statlon 

from a radio located one-entry remved from the nearest conductor, 

repeater spacings will be i - 3/4 mile ( Line Ampllflers 1 in areas 

with multiple branches and nearly a mile along major haulageways where 

theone-entry-away coverage i s des i red. For transml ss ion area coverage 

constra i ned to the ma Jar haul ageway entry crossect i ons, the a l l owab l e 

repeater spaci ng w i l I approach 2 mi I es. Using %mote Base Repeaters, 

where extended mobile unit-to-mblle unit performnce is not reauired vla 

repeaters, therepeater spac i ngs above my be near l y doub i ed . 

S UbfMARY OF PREFERRED SY STEP CONCEPT 

The communication l Ink possibl l ities on an overs1 l cine-wide bssls 

ernp l oy i ng a l l the System El ements are i l l usfrated I n Fl gure 2; . Tns 

reader is referred to Sectlon 3 for precise definition and features 

of the particular System El ements. 

The design is based on the use of nominaily 5-watt radios empioyi~g 

narrowband FM transmission for a l l hdio Terfiinal Elements and for a i i 

Repeater E lements, I n actua l equ I prrent das I gn, the maxi mum common usap 

- of transmit and recei ve "modules" be'tween a l l acii ve system elements is 

assumed, 

The design uses some Continuous Tone Coded Squelch ( CTCS decoding anc 

encoding to provide operator sirnplecify on the part of fhs ?ortables and 

Vehiculars, and to he1p"decoupls" tne transmission mdes. Use of addi~ional 

CTCS control is discussed as providinc ernbellshments beyond the basic 

design; but are not included as part of the basic design because of the 

recognized size of co~rnerciai ly avaiiable encoder and decoder cori?onents 

and because their use may not prove operational ly fsasible ( except of 

supervi sory rad i os, i f two "tiers" of radios are pract i ca i 1 unt i i 

experience has been gained wifh an ac?uai operatins systen. 

The frequency plan is a two-frequency plan providing for both simplex and 

half-duplex types of operation. The frequency ?tan is the same for all 

Radio Terminal Elernents, with a variation in The Ease Station. The 

frequencies, aesi gnated f: and , are expected Co occur in the 500-ii30 

kHz range with a minimum 6: 105 faperafion and with f beins :he hi~hsr 

frequency of She two. I 

The frequency plan options for the Porfsbles and VehicuIars are envisionea 

as beins selec?abie via a fhres-posifion swiich on the encfosure as 

fol lows: - - 

I' Loca 1 I1 

- 

i rmsfii ? f no CTCS I 

Aecs i ve f, ao CTCS 

" Sa s el' Trcnsmi t f, CTCS 

iisca i va fl no CTCS 

I1Rercote" Transz; -; f2 CTCS 

Rece i ve f no CTCS I 

A single tone encoderis used wlth both Transmi: frequencies ( and a si nsis 

tone i s used throughout the sysTern 1. Use of the s i ng i e recei ve frequency, 

of course, poses the ambi jiuity of which "modet1 Is being received. This 

is acceptable in this type of service where tne operator generally kncws 

to whom he is talking and whether it is l'Locaill or I15ase"; otherwise, i~ 

wi l l mst often be remota, 
TO SURFACE 

I LOCAL AREA --aI WJD PORTAL 

- - - - -- - ----- 4 \ 

m*-/-\ 

\ 

RD 

'. - LFCLid

CTCS - --- 

BS EIASE: STAT I o

\ RI3 REb1OTE BASE 

REMO'I E FII N I I JG AREA p/V F'ORTABL ES O

p-... .- c-- ----- - \ LA L l EJE Af4F'L I F 

LC Ll NE COUPLE

RE14OTE REPE

I ACT l VE L I I IE 

I 

I FOR IdlEDIUf1 FI?CQUEIJCY SYSTEf4 I ! 
The dispaTcher has additional visibiiify wifh regerd to the ~y?s of 

comun i cat ions bei ns serviced and can 6 ; f ferenf 1 af e between 8enofe 3asa -. and "Locai" or "mobile unif" i inks. me frequency pian for tibe base Sfation 

is: 

Rece i va f no CCCS 

;dote: cn base station a~tsnna or on a cou?fed 

- mnof i l cr conductor 

"Remote Base" Transmit f2 no CTCS, or baseband suaio 

Recei ve f2 no CTCS, or baseband aud io 

Note: on ?hone l ine oniy, bifi lar mods 

"Remte/ivbb i l e Transmi t f2 CTCS 

ljn i t" Rece i ve .l no CTCS 

Note: on cou; l ed rriinof i l ar conductor 

I f provisions are made in the 3ase Ststion design for sinulcasiing and, if 

Line Coupler elements are linked to the phone I ine ( bifi iar rk)de ); Then, 

in the simulcast node, CTCS should be transmifted on f, on the ?hone i ine L 

( assuming f is used rzther than bassband audio 1, 2 

The frequency plan for the Remote Base is: 

Recs i ve f no CTCS, or baseband au~io on 

wireline I ink 

CTCS on MF I i n k i 

f no CTCS, or baseband audio on 

wireiine link 

Transmi T 

f no CTCS on MF link I 

The frequency plans ior The iine A~pl lfisr, Line Co~pler, ana 2een;o~e 

Repeater are iaentica, and are: 

Rece l ve f2 CTCS 

Transr;,i t- f, no CCCS 

As an overlay orr this basic freqiiency jlan, additional CXS tones couid 

be added to provi de: 

* Paging/Call hkrt froin the Bass Station 

Each or certain Portables and Venicuiars would hsve a "home" 

eddress tone decoder such that i f this Tone was received, it 

would audibly or visually sisnal the operator of tha radio 

of a call 
e Private Line ( bioc~in~ iron saiectac ra&os 

Selected supervisory radios wouid have a tone encoder anu each 

non-supervisory radio would have a tone decoder such ?hat if 

the tone were sem, it wodid block the receiver of each radlo 

navi ns the decoder 

The system provides for four quasi-decoupled types or modes of 

commun i cat i ons, These are : 

Base Station-to-local area( Portable/Vehicular comnu;7icatlons 

via the Remore Base repeater. 

The l ink is provided usi ng the bi f I iar phone l ine trensrriission 

node wh i ch i so l aies i t f ron Pypes us i ng monof i l ar mode coup I i ng 

and iransmission. This link is isolated from long aisfance locai 

area-to-l oca l area iransmi ss ion vi a frequency separat I on for 

transmissions originating from a Line COG; ier Repeater snd by 

CTCS for transmissions originating from the 3ase Sfation 

Lon~ distance Bass Sfation or PortabIe/Vehicular-to-mbi16 unit 

commun i cai i ons vi a a L i ne Amp l i i ier repeaier 

. The link is provided ~~In~themonofilarriodefransnissiono~ ?he 

AC power cable and/or phone line which isolates ii from types 

using the bifilar mods for trans~ission, This link is isola*eti 

from 1 inks employing a Line Coupler and the monofi lar mods aecause 

of frequency separation ( two repeaters wifh like frequency plans 

cannot be chained 

Enended range loca 1-area-on I y fype of comuni caiions via a 

Li ne Coup i er repeater, coup i ed fo a mnof i l ar conductor 

Same rationals applies as for the above mobils unit monofilar 

l ink. 

e Extended range I oca i area-TO- i oca 1 area connun i cations v i a a 

Line Coupler 3e;eoiar, cou?led to the bifilar phone iine node 

Same rationate a2plies for isolation as for tne sbove Base 

Station-to-locai area link, 

hddifionaliy, local area si~plex connunications are sorewhat IsoisteC fro% 

cormunica~ions from the local area 70 the 3ase Stafion via he Semo~e 

Base throush the use of CTCS, 

Of course, CTCS does not provi de nuch i sol ation under dense Traffic 

conditions; and,due To the co~mnorecaive frequency, here will be 

interferance between "Local" and "2emote" transmissions and between 

"Iocai-area-only" transmissions. 
2.3 FURTHER R 8 D RECOMb.ENDAT I ONS 

For futhering the combined USBM 2 & D cmimunity interest plus industry 

interest in MF system potential, the followinq item would be profitable 

to pursue: 

Using Col lins prototype FM radios, conduct maximum 

range testing in several coal mines, including a link 

to the surface - thus demnstrating, with hard data, 

the maxi mum range capab i l i ty 

Using a Collins prototype FF4 radio working into a 

vehicular prototype antenna, demnstrate the ability 

to couple into complex mine wiring oeometries 

Us i ng a pa i r of Co I l i ns prototype FP4 rad i os, derronstrate 

the communication ranpe through a roof-fall ( containins 

one or mre broken or unbroken conductors 1; thus 

i l l ustrat i ng the potent i a l of MF for rescue comnun i cai i ons 

Using a pair of Col I ins pratotype FM radios, conduct. 

comun i cat i on range exper i emnts near conductors I n e 

DC mine, thus providing hard data on the performncs 

in a highly Impulsive noise environment; the ranpe should 

be correlated with measurement of the signal carrier 

current 1 eve I 

2.4 STRAWMA14 SYSTEF.1 DESIGN FOR LUCERNE #8 

Caluculations of comunication area coverage for Vehicular-to-Venicuiar 

( V-V ) and Veh icul ar-to-Base Station o~eration i ncl ud i ng the loceiion 

of repeaters has been made for the Helvetia Coal Go. Lucerne #8 mine 

in the Upper Freeport seam.This nine is familiar to PMSRC 

and is one for which the Sureau nas an onooi no communicaf ions sysfem 

test-bed program under cooperative aareemn-; with the mine. The author 

visited this mine durino August, 1977, and performed a an electromagneiic 

fieid mapping at rredium frequency in this nine at that time. 14 summtry 

mi ne map was prepared i i l ustrat i n~ fhc status of mi n i ng operat 1 ons, 

top0 logi ca i l y, together w i th assumed arsa coverase reg ions for a 

trackless haulage MF syste~ as of laie 1977. Also shown are areas to 

be mined in the near future. This summary nine map i s gi ven as Fi~urs 3 . The assumed des i rabl e comunica?lon coverage area is _ai ven by -1 crosshatch i ng on the f i gure. I ne i atera i haul ageway coverage area 

assumed was governed by com~n i cat ions i n a l l fresh a I r entr t es, w i f h 

the result 

I45 feet lateral range in Sou?n Mains 

80 feet laTeral range in North Mains 

80 feet laferal range in sections. 

- - - - 

The required area in sections included the size of ?he room-and-pillar 

areas edending about 400 feet on elther side of a center line. The 

acceptable lateral ransa coverage in haulageways has been taken to be 
89 feet in ai i haulaseways, nominal 

65 feet minimum 

;dote: the 65 feet minlmlin ref:lxects the rang6 

requi red I entry removed fron the 

conductor entry as the pi 1 lars at9 

norni na l l y on 65-foot cenFers. 

Also shown on the map are rectangular areas showing rooms to be nined 

( as of that date 1 and dashed linas representing expecied future 

extensions of the AC power cable and beltways. 

The exact operational status of Lucerne $8 as of the tlme of this wrielng 

and that expected at a future tine when demons?ration hardware wil I be 

avai lable for testing are not known. The 'fol lowing analysis, therefore, 

assumes ail dashed AC power cable and beliway exfensions to be aciive. 

The analysis of V-6 and V-V Transmission in fhis mine are illustr~tec 

respectively in Fisures 4 and 5 . The lateral range predicted at 

sei ected locations adjacent tc the coverage contours anti esqecia I I y 

near the ends of particular power cabls/beltway runs. 

The V-3 coverage l l l ustrates the p l acenent of Li ne An? l l f l er or Remote 

Base repeaters io gi ve mi ne-w i de coverage. 

Specific conclusions afforded by this analysis include: 

(1 The maximum throush-tne-seam ( quasi-conductor-free ) 

range expecyea is iG5 neters ( 354 feet 1. 

- (2) if ~0th Radic Terzinai riemen?s of a pair are closely 

couplea TO CO~OUC~CTS, a??roximafe mine-wIde coverage 

i s expec9ed V-3, anti Ven i cu i ars w i i i be ab I e To commm i caie 

with other Venicaiars ( V-V over either the North Mai ns 

or the South bhai ns ereas without repeaters. 

( 3) V-V coverage w l i hout repeaTers w i th one rad lo locaied 

.one miry remvea from conauctors is 1 i mi Ted to about 

2500 feet or less. 

(4) V-V coverage without repeaters with both radios removed 

one entry from conduc~ors is limited TO abou? lOOG feet 

or less. 

(5) With a Base Siation assune~ to be located in the porial 

area, and TO ria i nta i n nomi na 1 one-entry-away coverage 

with vehicles, a Line Azplifier or a 3ernote Ease Rspezter 

is required 2500 feet away in the North Pains and 3750 

feet away in the South Ekins. 

(6) with therepeater spacing of (51, a iaieral range in excess 

of 80 feet is assured over ai i hau lageway Vai ns, in excess 

of 60 feet at tne ena of a l l Guit Seciions ( Subtxa i ns 1 

panels, and in excess of 50 feet at the extreme ends of 

roomand-pi l iar area assuming the AC cable runs this far 

( this should assure at least 60-65 feet of lateral ranp 

at al l secTion power center locations 1. 
! 

I 

1 . , 

'1 ; Q3 * i nC, 

t I - 

I 

\ I 

.\ - .I 

I 

\ 

. , '1 . . 

/--;- - - - -- I 

. , #. 

I /' 

- 

I 

c% \ y \ ,<$- \ (.\ 


3.0 MF SYSTEM DESIGN PRIt4ER 

The purpose of this section i s t o provide the MF system design 

methodology in sufficient detail so that systems can be configured 

once particular e lerents of radio equipment are avai lable, The 

methodology is placed in the context of coa I mines; however, except 

for detai Is of system performance analysis involving radio propagation 

effects, the methodology is appl icable to any type cf mine. 

Because particular radio elements for MF systems are not yet aval lable, 

the f uncti ona l characteri sti cs of MF systems are descri bed generlca l ly 

rather than specifically. This does not dilute the methodology but, 

rather, places the important features and l I mi tati ons of MF systems In 

perspective. A great deal is now known about the expected performance 

of MF systems in coal mines. This section should, indeed, prove 

inva l uab le to potenti a l deve lopers and manufacturers of MF equi pmen~ 

in the assessment of the relative im~ortance of particular features 

and des i gn parameters. 

3.1 SYSTEM OPERAT I ONAL REGU l REMENTS 

3.1.1 REQUiREMENTS FOR COMMUNICATIONS 

A1 I underground coal mines require large scale communications to faci l itafe 

efficient mining operations. To date, these communications consist 

mostly of analog voice plus fire control monitoring of belt haulageways. 

At a mi n i mum, a l l underground coa l mi nes emp l oy baseband pager phones for 

sect i on-to-p l ace commun i cat i on s ; the commun i cat i ons be i n g genera l l y 

centra 1 i zed at the "di spatcher's" center ( usual ly located underground 

near the entry portal). Ebst DC mines currently errploy trolley phones for 

"enroute" haulage and service vehicle traffic control and logistics. Thc 

trol ley phone is a low frequency radio ( general ly operatl ng i n the 

88- 108 kHz frequency range by di rect coup l i ng of carrier current i nto 

the DC trolley wire/DC bus via the vehicular powering an. Newer AC nines, 

while not experiencing the direct haulage traffic of older DC mines 

without be1 t haulage, have no means of mbi le communications with 

personnel carriers( man-tri ps 1, service vehicles, and mobi le supervisory 

personnel underground, Often, the dilute pager phone system provldes 

for phones near section power centers, section belt headpieces, and at 

major main/submain junction points only. 

Additionally, newer AC mines often employ extended working section panel 

topologies of up to 3500 feet ( room and pillar mining in length hen 

the headings are ful ly driven. Section mining operations in these long 

pane l s often i nc l udes the coord i nat i on of--activi ti es of ma i nta i nance/ 

support crews and inspectors by the face boss in addition to the face 

work crew. In high-production room-and-pi l lar mining and/or long wall 

mining using modern mini ng rnachi nes, even the face crews are separated 

by distances well beyong the normal voice or convenient walking range 

of the boss. There is, thus, a need for improved section comrnunicaticns 

i n these modern mi nes. 
Use of med i urn frequency permi ts w i re l ess commun i cat i ons to be 

i mp l errtented i n mi nes. The d i rect rad i o-to-rad io range obta 1 nab1 a i s 

greater than that in any other frequency range ( except, perhaps, for 

UHF a long a l arge smooth entry in hi gh coal without any bends/corners 1 

and does not vary significantly whether along headings or crosscuts 

ord i agona l l y through coa l b I ocks/pi I l ars. Th is frequency range usage 

also enables the most efficient wireless coupling into existing mine 

wiring, 

The particular requirements for communications vary from mins-to-mine, 

but generally include the following whether the mines are AC or DC: 

Ha u l ageway Coverage 

a long ( w i th i n one or more entries of 1 the major veh i cu 1 ar 

traffic routes through the mine back to a central communications 

center and/or back to major producing or maintaining areas of 

the mine, 

In AC mi nes, vehicular coverage is requi red a long the hau l ageway 

an i nto branches where vehicles are parked wh i ie men perforn 

mai nta i nance; and i s a l so requi red- a long the belt haul age entry 

both back to the comnun ications ( dispatcher 1 center and fc 

the sections, 

General ly, vehickesr or men carrying portable radios can be 

expected to be within 1-2 entries of mead tngs containing mTne 

wiring, 

Section Area Coverage 

over all section panel headings C including return air ),?[us 

recently mined-out roomand~i l tar areas, plus current face 

areas. Often, there wi I l be no conductors forward of the present 

section power center location, Usually, the face is within about 

800 feet of the power center and the room-and-pillar areas in 

which men may be expected to be found are within about 1300 feet 

of the power center, Toward the subma in from the power center, 

there will be at least an AC power cable, a phone Ilne, beltway 

support and control/alarm cabling; and sometimes metal water and/or 

rock dust l i nes. Section head i ngs se I dam exceed a f i ve-entry 

pattern, so that all locations are usually within 1-2 entries 

of mine wiring conductors. 

Loca l commun i cat i ons over the sect ion area are genera i l y requ i rsd 

p l us d i stant commun i cations from the sect l on a long hau l ageways 

and/or directly back to the dispatcher or to the surface. 

Ma i nta i nance Area Coverage 

for si ngle-portal ( or l arge mines with several wildel y separaied 

porbals 1, the mainiainance areas are located undercorund near 

the porta I. These a teas i nc l ude an e l ectrica I shop, a mechn i ca l 

shop, and one or more rooms for personnel and vehicles. In punch 

mines or drift mines, there may be no maintainance ( or l imited 
ma i nta i nance 1 underg rcund ; w i th these f unct i on s be i ng 

located on the surface near each drift portal. It is imporiant 

to provide communications from the dispatcher location ( at 

least to these maintainanace areas and, if possible, from 

the major workings di rect ly to these maintainance areas. 

Remte l nspecti on Area Coverage 

Nearly every ol der and/or l arger underground coal mine has 

f i xed areas, removed from acti ve worki ng areas and henca fro^ 

existing mine wiring, requiring periodic inspection and/or 

maintainace and from which cornmunications to the dispatcher 

or to the surface would be highly desirable. These include: 

- Previous l y mi ned-out areas, genera l l y bei ng "b l ed-out" i nto 

return air 

- Fresh ai r escapeways not a long major traffic routes 

- l sol ated fresh a i r vent i l at i on boreho l es or exhaust return 

air vent holes 

- Areas toward the end of previously driven main or submaln 

head i ngs to eventua l l y be extended in future mi n i ng operations. 

Conmunication links are highly desl.table between these isolated 

areas or specific locations and the dispatcher or to the surface. 

These situations requ i r i ng commun i cat Ions are i l l ustraied i n Fi gures 

3.1.2 AVAILABLE MF COMMUNICATION LINKS 

From the requirements out1 ined in Section 3.1.1, there are three major 

i dent i f i ab I e types of w i re less commun i cations needed i n underground 

coal mines. These types consist of: 

Loca 1 area commun i cat i ons on i y 

Between crews or functional operations within crews In a given 

operating area such as a working section panel ( or perhaps mare 

than one working section panel, if adjacent 1, a long wall section, 

or a maintainance area typically near a portal. Typical functional 

operations in a conventional room-and-pillar section include 

roof bolting, rock dusting, timberins, masonry constructing of 

air flow barriers, miner and shuttle car operating, and tipple 

operating controlling the loading of coal from a section beliway 

either onto a submain belt or onto coal cars ( including the 

snapper 1. 

An extension of thIs type of corrmunicat~ons includes transmissfan 

between distantly separeted local areas. 
Comnunications between a local area and a central undergr~und 

dispatcher or an operations center on the surface 

In addition to working areas described above are remote 

inspection areas. In case of a major logistics/repair problem 

or of a heal th/safety problem, a di rect l i nk to the central ized 

location is required. 

Comnun ications f rom local areas or from the centra l d i spatcher 

to mobile units enroute or worktng along major arterial 

haulageways i n the mi ne. 

Included here as mobile units are haulage trains, supply trains, 

servi ce/ma i ntai nace veh icl es and crews, i nspectors, and at-l arge 

supervi sory personnel . The local area comunications are accomplished either dirsctly using 

through-the-coal-seam radio transmission or else via carrier current coupling 

into the existing metallic conductors which are usually rather densly 

d i stri buted over these worki ng areas. Most often, the cornmunicaiions can 

be accomplished via transmission between portable radios and/or between 

vehicular radios only with aiding electronics such as repeaters or line 

extenders not bei ng requi red. Occasional l y, such as in I.arger-tnan-usua I 

room-and-pi l lar mining areas or between nearby mined areas requlrins 

inspection and current face areas, the use ofrepeatersor line extenders 

to a i d commun i cat i onsarea coverage w i l I be requi red. 

The medium affecting longer distance transmission required for communicaiing 

from local areas to a central dispatcher or from either or these to mobile 

units is via purposeful coup1 ing into existing mine wiring. Considering 

the dilutely distributed conductor ensembles normally encountered in AC 

mines, the transmission medium is via either the monofilar mde along 

the AC power cable or along the phone line ( co-directional currents 

excited in each of the conductors) or bi f i lar mode transmission along 

the phone line. Other modes are possible between these conductors, but 

these are the predomi nant ones in AC mines. In DC mines, the complex 

conductor ensemb l es i nc l ude the track, the DC tro I l ey w i re, the DC feeder 

bus, and the ground return bus. Often, the excitation of extraneous rnultlconductor modes will cause null areas in field strength radiation along 

these ensembles and junction effects will cause unequal current split 

( s i anal "suck-out" i f the current goes the wrong dl rection ) at these 

junctions. Primary consideration for the remainder of this sectlon will 

be given to the simple AC power cable/phone line geometries of AC mines as 

these are the most previalent In trackless haulage applications. 

To assure the longest distance transmission underground, the local areato-dispatcher communications is accornplised by coupling to the bifilar 

phone line mde, This may be accomplished in several ways, as will be 

discussed later in this section. Once coupled to the phone 1 ine In the 

normal bifilar mode ( bidirectional currents in each conductor 1, ths 

signal currents can travel long distances wlthout being strongly 

influenced by the proximity of other nearby conductors. If the existing 

pager phone line line is used, the signals will be influenced by the 

loads and junctions; however, these are more predictable than the mnof i lar 
mde effects by far.By the same token, only a l ittle radiation wi l l 

occur from a phone line carrying this mde so that only minimal 

wireless coupling can occur to nearby radios noi directly terminating 

the line. Direct radiation from the bifilar mode may be usable 

within the entry(heading1 containing the phone line with the operation 

being analogous to low-frequency leaky feeder operation. This radiation 

occurs only due to line unbalance; it is possible to enhance this 

radiation at certain preferred locations with mode converters or with 

balanced loop antenna radiators. 

For the local areakentral dis~atcher-to-mobile unit transmission, 

portable and/or vehicu tar radios must be able to couple into the m1 ne 

wiring ideally up to 1-2 entries away. This type of cornmunicatlon 

depends on the mnofolar mde(s) transmission. In AC mines, the effect 

of branching and/or standing waves on AC power cable/phone line conductor 

ensembles is predictable. In larpe mines, the principal mnofIlar 

conductor which is the AC power cab1 e may be partitioned into mre ihan 

one power grid. This either localizes the extent of this type of 

comunications or else requires a brid~ing between these grids TO be 

accompl ished. 

The o perat i ona l commun i cati ons requ i rements i n underground mi nes and 

the available corrmunication links to satisfy these requirements at 

med i urn frequency def i ne the nature of the system el ewnts and generic' 

groupings of elemnts comprising the configuration architecture and 

operat i ng methodology of MF systems. 

3.2 SYSTEM ELEEllENT OPERATI NG DESCR l PT l ON 

3.2.1 SYSTEM ELEMENT DESCRITION 

This section defines the system elements, key generic groupings of elements, 

and i denti f i es the el ement/el ement group i nos with particu Iar comnun i cat! on 

requirements and with available link characteristics. The system elements 

consist of 

Radio Terminal Elemnts 

Repeater El ements 

Li ne Extender El emnts 

The basic Radio Terminal Elements consist of personal man-carded 

portable radios ( hereafter ca l l ed "Portables1' 1, veh lcul ar mounted red ios 

( hereafter cal led "Vehiculars" 1, and base station radios ( hereaf~er 

cat led "Base Stations" 1. Both Portables and Vehiculars have the[ r own 

special antennas whose designs form an integral part of the element design. 

The Portab l es are presumed to be powered from the1 r own I ntegra l 1 ntri nsi ca l iy 

safe battery suppl ies. The Vehicul ars are presumed to be powered fmrn he 

vehicle battery or, optionalty, from a separate intrinsically safe 

battery supply. Al l Radio Terminal Elements pvide for simplex and hat fduplex operation. 
Considerable effort has been expended toward indentifying practical 

portable radio packages in recent years and two candidate packages have 

emerged. Both of ihese have evolved from the cumbersome South African 

( ECAt4 ) and Co l l i ns FM prototype packages rh i ch were very s i mi l ar and 

generally unsatisfactory for use in coal mines. These three package 

types are i l l ustrated pi ctora l l y i n Fl gure 6 . Veh i cul ar rad lo packages 

are presumed to be very simi lar to the irol ley phone packages currently 

available in the marketplace, with the exception of the antenna. Previous 

prototype veh i cul ar GF radios have not been bu i l t. The typ i ca I veh i cu l ar 

rad i o package concept and antenna are i l l ustrated 1 n Fi gure 7 . Prototype 

vehicular antennas have been built. 

The Base Station package is presumed to be table mountable and of size 

and conf i~uration very simi lar to VHF or UHF land mobi le unlts currently 

available. Terminations for the base station package are varied;but, at 

a minimum wi l l I ikely include the fol lowing: 

8 A large single-turn base siation antenna tuned to a single 

frequency 

A mu l ti -turn l wp des i gned for permanent c lose-proxi mi ty mount i ng 

to conductors as a current transformer for exci ti ns monof I lar 

carrier current in these conductors; this loop being tunable to 

mre than one frequency. Or, alternatively, a ferromagnetic 

( Magnetic dipole generical ly siml lar to the hoist radio 

. couplers whichmay be permissible for use ( by MSHA in certain 

instal lation situations; also tunableb more than one.frequency. 

One or mre ba l anced phone l i ne termi nations 

Note: additionally, a combined current transformer and antenna 

termination will probably be required in most Installations, 

employing a power splitter to divide the two, Also, a base 

Station should provide for both separate and combined 

transmit and recei ve terminations on the package. 

The Base Station is presumed to be powered from a 1 10 VAC l ine; or, 

alternatively, directly from a battery power supply. The Base Station 

and its termination options is illustrated in Figure 9 . The basic Repeater Elements are of the conversIon/remodulatlon type ( to 

be differentiated from Active Line Extenders 1, each consIstlng of a 

recei ver and transmitter operati ng at dl f ferent frequencies p i is control 

ci rcui try. These el emsnts constitute severa l generic group1 ngs accordi ng 

to the type of comnunicatim link being usedand the particular 

communication requirements being served. The individual element grou~ings 

fo, be discussed in the paragraphs to follow consist of: 

Remote Ease Station 

Line Amplifier 

* Line Coupler 

Remote Repeater 

EPARATE LOU

VEH l CULAR RAD I0 

Fl GURE 7 

l LLUSTRATION OF THE l MPLEMENTATI

TYPICAL VEHICULAR RADIO SYST

# 
FIGURE 8 

l LLUSTRAT l Old OF THE I blPLEMEP4TAT I OtI OF A 

TYPICAL BASE STAT IOI4 
All Repeater Elements zprovide for the half-duplex mode of operation 

( as opposed to full-duplex 1 which, in certain of the above configurations, 

complicates the terminationrinterfaces but which provides for the mre 

cost ef fecti ve des i gn through requ i ring on l y about ha l f the hardware. 

The Remote Base provides phone l ine termi nation of one l ink end wl th 

control emanating directly from the centrally located Base Station. This 

type of repeater services the local area-to-central dispatcher type of 

communications, Generical ly, it simply pr~vldes the means of l nterfaci ng 

the bifilar mde phone line and wireless transrn~ssion/monofIlar carrier 

current med i a with amp l i f i cation. I n some app l i cat i ons, the Remote 3ase 

function could be served passively using made converters at 2 given 

desired locale to convert the phone l ine bifi lar mode to the mnofi lar mode. 

I n its mst sophisticated form, the Remote Base converts a bdio Term1 na l 

Element MF frequency to a lower frequency for transmission over the phone 

l ine ( and visa versa 1 ; and, also, providesthe transmitter and audio 

slope control to enable simulcast transmission from the central Base Station. 

A Remote Base i s envi s ioned for use as fo l lows: 

To be located at or near a section panel belt head piece coupling 

into the belt drive AC power cable segment; or, at the AC power 

cable junction switch or beltway fire zlarm cable junction joining 

mre than one working section panel so as to define a single large 

and cont i guous operat i ng area 

To be located so as to couple into anAC power grid presumed fo be 

isotated from the grid in the imnediate vicinity of the central 

Base Station location; thus, provi di ng the bridge between i sol ated 

power grids with the connection being at the Base Station 

@ To serve as the Base Station for -one of two or mre separafe 

mining operations served from the same central dispatch or operations 

center 

I n its si'mp lest acti ve form, the repeater cou ldtransl ate MF to baseband 

audio thus interfacing with ( but also competing with 1 an existing pager 

phone system, 

I n instances where " leaky Feeder" operat Ion of the phone l i ne at a hi gher 

translation frequency ( presumed to be compatible with For-table and Vehicular 

MF frequencies 1 is not desired, the use of a separate above-base-band 

translation frequency could provide essentia l l y pri vate l i ne communications 

to the surface. 

In its simplest passive form, simple passive circuits are clipped onfo the 

existing phone line to affect mode conversion in a given locale; or else, 

a balanced antenna is connected to the phone line at the desired locatlon. 

Termi nations to the acti ve Remote Base package I ncl ude the phone l i ne 2nd 

a current transformer jointly bridged to both the transmitter and 8eceiver 

( or current transformer plus an antenna 1 for coup l ins into the local 

area mine wiring. The active Remote Base is presumed to be powered from 

the belt drive power source with floating battery backup. 
Possi b l e i rnp lementat i on of the Remote Base i s l l 1 ustrated in Fi sure 9 . The Line Arn~ 1 i f i er provi des a "boost" in the mnof i lar carrier current 

servi ng the loca l area/centra l d i watcher-to-mob i le un it type of 

commun i cations. Both l i n k ends are current transformer coup led 1 nto 

the mnof i lar conductor via separate transformers for the recei ve and 

transmit inputs; a lternate transformer coupi i no into the Sl f i lar phone I i ne 

to amplify long transmissions between local areas is also possible. 

The Line Amplifier is used in long monofi lar runs which would normally 

experience high mode attenuation; or else, fol lowing junction pcinis 

experiencing unusually high splitting loss. In long bifliar runs, the Line 

Amp1 ifier provides frequency compatibi l ity with Line Couplers at the link ends. 

I f there i s a reason to enhance the w i re I ess coup l i ng range to the 

rnonofi lar conductor in the immediate vicinity of the Line Amplifier, 

loop antennas may be bridged with the current transformers. If used, 

these antennas shoul d be oriented so as to minimize d i rect coup l i ng 

back into the monofilar conductor and between each other. 

The Li ne Amp l i f i er i s presumed to be located near a l oca l permanent 

power source; th i s source to be used with f loati ng battery backup, 

Implementation of the Line Amp1 ifier is i l lustrated in Figure '3 . The Line Cou~ler provides an aid in wireless radio coupling at a 

part i cu l ar location to the monof i l ar mode, reduci ng the coup I i ng 

loss from remte l y l ocated Portab le or Veh icu I ar rad i 0s. Thi s w i 1 l 

result in achieving the ful l quasi-conductor-free communication range 

away from the conductor rather than the shorter range to accomodzte 

the field cou~ling loss mechanism. Alternatively, the Line Coupler couples 

to the phone line bifilar mode to enable transmission between distant local area 

The termination for one link end is a current transformer whicn provides 

maximum coup I ing to the conductor. The termi nation for the other l ink 

end is a larger base station type antenna. Of course, to make this a 

half-duplex bidirectional repeater, both the transmitter and receiver 

must be bridged across each l i n k end termi nation. The ti ne Coup l er 

operates essentially identically to a Line Amplifier in which the 

local communication range has been extended through the use of antennas. 

Optional ly, the antenna link end of the tine Coupler can be renoted 

through a long length of coaxial cable to, say, the center of an 

operati ng area somewhat removed from the nearest conductor grid. Thi s 

opt ion forms a variation of the Acti ve Line Extender to be d 1 scussed 

later in this section. 

Aga i n, the Li ne Coup l er i s presumed to be powered f rom a l oca l permanent 

power source with floating battery backup. 

Operationally, the Line Coupler is expected to be used In developing 

mine areas of large extent beyond the nearest AC power center or section 

phone; or in certain arsas along haulageways in which operations ( such 

as a logistical staging area 1 are removed from the nearest conductor; 

or to provi de commun i cat i ons f torn be1 hays i n w i de nu l t i p l e-entry ma i ns 

or subrnains ( say, 12-14 entries wide 1 requiring periodic maintalnance 

and/or inspection where the beltway is several entries removed from the 

AC power cable. 
TO SECT I OtJ PHONE 

POWER CABLE ENTRY 

SECTION HEADP 

?){ONE LlDJE 

SUUMA I I4 PAUL AGE WAY ---- 

FIGURE 9 

I LLCJSTRAT I ON OF THE I MPLEF4EIlTAT lot4 OF A 

REMOTE BASE STAT 1014 
-1 m 

AC POWER CABLE TUNED CURREt TUIdED CURRE I4T 

SUPPORT l NG MF TRANS FORMER TRANSFORMER 

MONOF l LAR MODE 

LINE AMPLIFIER 

C 

FIGURE 10 

l LLUSTRAT l ON OF THE: I MPLEMENTAT I ON OF A 

L l NE AMPL l F l ER REPEATER 
Implementation of the Line Coupler is i l l ustrated in Figure ! I . The Remote Repeater provides extension of local area quasi-conductorfree range between Fortables and Vehiculars serving the local area 

coverage only type of communications, The Remote Repeater does not 

necessari ly tie directly into any existing mine wiring grid. A particular 

application where it does tie into a grid through field coupling is 

associated with section communications where the power center and/cr 

belt is moved often and it is desired to have a semi-permanent repezter 

which does not depend on particular conductor locations. Norma l l y, 

a Remote Base wi l 1 enab l e sect ion-wi de "area coverage" of a panel 

including the face if the face is within a few hundred feet of the 

conductors. I n large sca le roomand-p i I lari ng, where the face may be 

located 700-800 feet from a conductor or where functional crews may be 

working over an extended area of about this same size, the use of both 

a Remote Base and. a Femote Repeater may be requi red to provi'de sectlonwide coverage. 

The Remote Repeater link end terminations are both antennas witn the 

transmitter being connected to one antenna and with the receiver being 

connected to the other. The two antennas can be co-located and oriented 

orthogonal to one another to obtain increased isolation. This will 

permit receive operation down to the full set-noise-limited receiver 

noise floor using a large base station type antenna on the receiver. 

Alternatively, in areas not so quiet or witn exceptionally clean radio 

design, a commn single antenna could be employed. 

The Remote Repeater is presumed to be powered from a replacable 

i ntri nsica l ly safe battery supply. 

lmolementation of the Remote Repeater is [ I 1 ustrated in Fi sure 12 . The basic Line Extender Elements are used to extend the existing mine 

w i r i ng or to br i dge between i sol ated mi ne w i r I ng gri ds on a semi -permanent 

basis where the cost/complexi ty of a sultabl e ~e~eater Element is not 

justifiable, In particular, Line Extender Elements can be considered as 

meeting repeater type requirements in cases where so much Isolation 

exi sis between l i nk ends that a "s i ng I *frequency repeater" can be used. 

Line Extender Elements are comprised of 

Pass i ve Li ne Extenders 

Act i ve Li ne Extenders, 

Acti ve Li ne Extenders may be thought of as bei ng si mi lar to one-way 

CATV/CCTV l i ne amp l i f i ers where two separate 1 i nes are requi red to 

provide bidirectional service. Active or Passive Line Extenders provide 

"link" or "loop" coupling by virtue of being like a length of coax with 

an antenna on each end.The lmplementatIon of Line Extender elements Is 

i l lustrated in Figure 13 . 
TRANSFORMER 

LINE COUPLER 

I LLUSTRAT I ON O

L I tJE 

COAX l AL TRANSM l SS l ON L I14E 

(A) 

PASSIVE LINE EXTENDER SHOWlJ FROM SECTION POWER CENTER FORWARD TOWARD FAC

TUNED MF AWL l Fl ERS COAX I AL TRANSM I SS I ON L l NES 

ACT I VE L l NE EXTENDER SH0WI.I BRl DGl NG TWO SEPARATED AC POWER GRl DS 

FIGURE 13 

l LLUSTRAT l OIJ OF THE I t4PLEMEIITAT 1014 OF 

ACT l VE Al JD PASS l VE L I I4E EXTENDERS 
A Passive Line Extender is envisioned to consist of a current 

transformer on one end ( coup l i ns i nto the monof i l at conductor 1 and 

a large base station antenna on the other end; the ends being joined via 

a piece of coax. Alternatively, the current transformer could be 

replaced with a balun transformer directly coupling into the blfi lar 

mode of a phone line, In some mines with short isolated working sections, 

a Passive Line Extender may be al l that is required to provide the 

local area-to-central dispatcher type communications in lieu of the 

use of a Remote Base and possibly a Remote Repeater, 

Acti ve Line Extenders are formed from Passive Line Extenders by placlns 

a directional tuned amplifier in the coax Ilne, Two such lines are 

required to provide bidirectional service. The amplifier(s) Is presuned 

to obtain power from the coax, tne conductor end of which Is tled into 

a permanent power source. A l ternat i ve l y, i ntr i ns i ca I l y safe rep l acab l e 

( rechargable battery power supplies could be used, 

3.2.2 SYSTEM ELEMENT FUNCTIONS 

This section provides functional block diagrams of the elements within 

each system element grouping and a generic discussion of their operailon, 

Key des i gn consi derations are poi nted out tosether with an out l i ne of 

design alternatives, 

To facilitate understanding of system elemeni operation, the use of 

separate transmit and receive mdules is made and a separate T/ii swifch 

is shown. This form in no way is .meant to impose design limitations. For 

example, transmit excitation and receive tuni ng/mixi ng could very we1 1 

share a commn frequency seneration scheme and control scheme, etc. For 

simplicity, power sources are deleted from the diagrams, Certain preferred 

aspects of overall system design will be postulated in this section ir, 

areas where prior experience or obvious advantages show these aspecrs to 

be the logical choice. A compiete treatment of preferred system design 

functions, features, and parameters wi l l be given in the next two subsections. 

A functional block diagram for the Base Station is given in Figure 12 . . 

Operating system assumptions made i n t h i s diagram include: 

Mu l ti p l e frequency operation of the transmitter 

Single or multiple frequency operaiion of the receiver 

Provisions for more than one Remote Base link for local area-tocentral dispatcher communicatlons; each l ink with a separate 

receive audio circuit 

Single frequency ( simpiex 1 operation locally to the aase Station; 

a single-tuned-frequency base station antenna 

* Requi rement for remote tuning ( switching 1 of the current transformer 

for central dispatcher-to-mobile unit communications via the 

monofilar made on existing mine wiring 
MOEJOF I LAR M

PTT OR TX SWITCH 

B l F l LAR PHONE L l t4E TAPS 

t4OT

VLF FREQUEI4CY 

0 

FIGURE I4 

FUNCT I ONAL BLOCK D l AGRAM OF BASE STAT I Of1 
It w i l l be important to separate Remte Base and Centra l d i soatcher-tomob i le unit comun ication l inks. Separate loudspeaker outputs for these two -- 

links are preferred; however, In a simpllfled system implementation, 

a single speaker with a visual indicator as to which type ( mode 1 of 

communications is active would suffice for low traffic density applications. 

From the Base Station point of view, the simplest Remote Base Interconnection 

is a direct termination of the phone line to the switch matrix wlt5 th9 

signal and control link belng baseband. From the Remote 3ase point of view, 

the simplest implementation would involve passive reception and blfi lar 

mode conversion of the d i rect MF transmit frequency; say, the same frequency 

as is normally received by the Base Sfation.This second situation would 

requi re that the T/R I nterface/Transl ator be anothee-Rx ibdul e and wlih 

amode selector switch on the control panel to route the Tx kbdule output 

to the phone line. Alternatively, the T/R Interface/Translator could 

be a si mp le frequency converter with a means provided to key the Remte Sase 

transmi tter; the convers i on frequency be i ng above baseband. Th i s frequency 

would probably be chosen either to be "just above baseband" in tne 10's 

of kHz range to minimize transmission loss; or el se, at some other MF 

frequency compati ble with the Fortables/Vehiculars so that leaky wave 

operation along the phone line runs could be obtained. 

For maximum coupling efficiency, the tuning for the current trensformer 

should occur at the transformer rather than within the Base Station 

enclosure. This will require a tune line between this enclosure and tne 

tuner , ,. 

A single block diagram for the Portable and Vehicular radio operation is 

given in Figure 15 ; the vehicular antenna connection beins shown. The 

major differences between Portable and Vehicular radio implementations 

include: 

The vehicular antenna is separate ( not attached directly to the 

Vehicular radio enclosure 1 thus requiring a 50-ohm interface to 

permit interconnection via a short length of coaxial cable. The 

Portable antenna is attached directly to the Portable radio 

enc l usure; thus, the i rnpedance transfer l eve l i s essent i a l l y the 

transrni t PA output impedance level ( or the antenna 1 nput rest stance 

level when series tuned 1, 

The Vehicular radio employs an external loudspeaker for displaying 

the receive audio; whereas, the Portable recel ver audIo Is most 

likely incorporated into a speaker mike or else in a smal l audio 

transducer integral to the Portable radio package 

Packages for Portab l e and Veh i cu l ar rad i os have previous l y been i 1 l ustrated 

in Fi gures 6 and 7 respecti vel ye The most important aspects of desi gn 

for the Portable are expected to be in the packaging and in providing 

ease of operation. 

Operating system assumptions made in the functional block diagram of 

Figure 15 include: 
uc 

-0 

ILL 
Multiple frequency operation of the transmitter 

Single frequency operatlon of the receiver 

iiequi rement for tuning of the antenna to accomodate the rnul i-l p le 

transmit frequencies ( remote tuning in the case of the vehicular 

antenna 1. 

A functional block diagram for an acti ve Remote Base repeater I s gei ven 

in Figure 16 . Operating system assumptions made i n t h i s diagram Include: 

Single or multiple frequency operatlon of the MF:tsansmitter 

8 Sinole or multiple frequency operation of the MF Receiver 

the Remote Base operating on a half-duplex basis; 

The requirement for audio spectral amp l itude cornpensat Ion for 

possible use in a simulcast mode with the Base Station and/or 

other Remote Base stations 

A wireline ( phone line ) interface on ihe Tx/Px audio link sides 

of the MF transmitter and receiver ( Tx t'lbdule & Rx Module 1. 

The Remote Base link possibilities have been discussed earlier in This 

subsection. Within the funct lona l framework of the diagram, the T/R 

l nterface could operate at baseband or at some hi gher low frequency; a l so, 

the MF transmit and receive frequencies could be the same or different. 

Thi s type of repeater conf i gurat ion ( as opposed to the conf i gura~ion 

with Rx and Tx audio being joined through a carrier-operated relay ( COR 1 

or aVOX circuit is required to enable simulcast operation. 

If the bifilar wireline transmission were to occur at MF so that "leaky 

feeder" operation along haulageways would be possible ( providing a 

separate "para1 lel" link to rrobile units operating very close to the 

l i ne 1 or so that MF cou l d be carr i ed a longer d i stance than wou l d be 

possible with the monofi lar mode, the Remote Base configuration becomes 

si mi l ar to that of the Li ne Coupler repeater configuration of Fi gure . i n t h i s case, the base station antenna and the monofilar current transformer 

are bridged with a balun to provide the wirel ine interface. 

The functional block diagram illustrating the Remote Repeater is ~iven as 

Figure 17 . This type of repeater is i l lustrated first for ease of 

visual i zation; namely, separate single ( and decoupled antenna ierminhtions 

for the MF transmitter and recei ver. The operati ng system assumptions 

made i n t h i s diagram include: 

Single frequency operation of the transmitter 

*Single frequency operation of the receiver, 

the TX and Tx frequencies are different ( separated 1 with the repeater 

operating on a hat f-duplex basis; 


The transmitheceive isolation is supplied via filtering of the 

transmit exciter output, modu l ati ns spectrum fa l I-of f between 

transmit and recei ve frequencies, and vi a antenna i sol atlcn, 

Transmit keying is activated using a carrier-operated re lay ( COR 

or a voice-operated relay ( VOX ) circuit, 

The use of separate transmi t and recei ve antennas is assumed; each 

si ngle-tuned to the respecti ve transmit and recei ve frequencies. 

These antennas are orthogona I l y oriented to obta i n i ncreased 

transmi t/recei ve isolation, 

The Remte Repeater may be expected to operate in low-noise envlronnents 

requiring maximum receive system sensitivity ( set-noise-limited 1 to 

achieve maxi mum system margin, The recei ve antenna is chosen to be of 

the large tuned base station type, having 2 large capture area, to 

i ncrease the recei vet sensi ti vi ty, The orthogona l antenna ori entatl on 

provides increased transmit/recei ve isolation consistent with the 

increased receive system sensitivity required, 

The f unct i ona i b lock diagram i l 1 ustrat i ng the Li ne Amp I1 f i er repeater i s 

given in Figure 18 . The operating system assumptions made in this diagram 

include: 

Sin~le frequency operation of the transmitter 

Single frequency operation of the recei ver, 

the TX and RX frequencies are di fferent with the repeater operating on a 

half-duplex basis; 

The transmit/receive isolation is supplied via fl ltering of the 

transmit exciter output and vi a mdul at i on spectrum fa l l -of f between 

transmit and receive frequencies 

Transmit keying is acti vated using COR or VOX ci rcuitry 

+ The use of separate sing le-tuned current transformers: is -.assumed 

for transmit and recei ve channel s ( shown 1 for mnof i l ar mode 

coup l i ng or separate transformers for bi f i lar mode phone 1 i ne 

coup1 ing. Alternatively, for monofi lar mode coup1 ing, a double-tuned 

s i ng l e current transformer could be used with switched tun i ng 

controlled being activated from the transmitter keying function. 

Both incoming and outgoing 1 ink interfaces are served via carrier 

current flowing in a selected monofi tar mode conductor. 

The possibility of bridged antennak) at the Line Amplifier locatlcn 1s 

not shown as this would essentially constitute a Line Coupler repeater, 

which is discussed sepraiely to follow. 

The Li ne Amp l i f i er probab l y operates in the no? sl est env? ronment and, thus, 

exper i ences the 1 east transmi t/recei ve s i gna l margin. There i s ns c l ear 

cut choice, performance wise, between the use of separate or a sing l e 

current transformer(s> except for the single-tuned vs double-tuned ccmclexify. 
T U

CURRENT TRAIJS FORMER CU

TX AUDIO It 

KEY Y 1 FI LTER 1 

TUN

S I N

TRA

, 

FIGURE 18 

FUI4CTIONAL BLOCK DIAGRAM OF LINE AMPL l Fl ER 
The functional block diagram illustrating the Line Coupler repeater is 

given in Figure 19 . The operating system assumptions made In this 

diagram include: 

S i ng l e frequency operation of the transmi tter 

Single frequency operation of the receiver, 

the TX and Rx frequencies are di fferent with the repeater operail ng on 

a half-duplex basis; a 

The transrnit/receive isolation is supplied via filtering cf the 

transmit exciter output and modulating spectrum fall-off between 

transrni t and recei ve frequencies 

Transmitter key i ng i s act i vated us i ng COR or VOX ci rcu i try 

The communication circuit links are enabled via carrier current 

coupling ( via a current transformer 1 in-to a mnofilar mode 

conductor and via a large double-tuned base station antenna. 

Alternatively, for long distance local area-to-local area 

transmission, the coupled link end may interface with the phone 

line bifi tar mode through a transformer. The transmitter and 

receiver are bridged across both l ink inputs 

A more sensitive one-way repeater could be bui l t with a single-tuned 

. antenna on one l ink end ( most l ikely the wireless receive mode 1 and 

a current tranformer on the other link end ( most likely the mnofilar 

or bi f i I ar transmi t mode 1. The transmit l i nk end rnargi ns are expected 

to be roughly symmetrical ( i.e., for example, Portable-to-3ase Station 

vs Base Staiio-to-Portable 1 so that bidirectional re~eaters only are 

required. The exception to this ( and the reason for mentioning the 

one-way link possibility 1 is the possibility of implementing satellite 

recei vers which, in a more compl icated Base Station configuration, would 

permit mre careful monitoring and location of traffic in a busy large 

mi ne.The use of sate 1 1 i te recei vers is not herein considered a part of 

the base l i ne system des i gn . structure. 

The f unct iona l b l ock d i agrarn i l l ustrat i ng the Pass i ve and Acti ve Li ne 

Extenders i s gi ven in Figure 20 . The operating system assumptions made 

in this diagram include: 

Acti ve or pass i ve extenders use a current tranformer at one I l nk 

end and a base station antenna at the other end ( except for 

bridging between AC power grids where two current transformers 

would be used 1 

a An Active Line Extender Is comprised of two one-way extenders for 

maximum extension capability; each using a directional tuned 

amplifier 

Separate d i rect i ona I amp l i ii er freauenc i es are emp l oyed to be. 

compatible with the local area-to-mobile unit or local area-to 

central dispatcher type of comnunications being served 
MONOF I LAR FODE CONDUCTOR 

B d 

DOUBLE TUNED DOUDLE TUNED BASE S

CURRENT TRANS FORMER L 

tf f POWER fF TUNER = 

TUNER -? SPLITTER 

A I 

FIGURE IS) 

FUNCTIONAL BLOCK DIAGRAM OF LINE COUPLER 

v \ 

RX TX 

MODULE t 

MODULE 

COR/VO EX PA - I) 

KEY LINES EXC l TER 

NOTE: TUNERS NORMALLY I FILTER I 

ON f UNLESS KEYED s 
COAXIAL .TRAtJSMISS 1014 Ll t4E 

IONOF I LAR MODE CONDUCTOR 

PASSIVE LINE EXTEFJDER 

s B 

TUNED CURRENT 

TRANS FORMER TU

S

I 

.lf---3- 

FIGURE 20 

MONOFILAR MODE CONDUCTOR 

5 a 

TUNED CURRENT TUflED CURREt4 

TRANS FORMERS 1 TRAM FORMERS 

2 - Dl TUNED RECTIOIJAL . f, d 

COAXIAL LINE AWL1 Fl ER COAX l AL L I I4E 

i 

FUNCTIONAL BLOCK DIAGRAM OF PASSIVE AND 

ACT I VE L l NE EXTENDERS 

( 2 

COAXIAL LINE 

, 

COAXIAL LINE 

NOTE: TUNER NOT SHOWN WITH SINGLE 

FREQUENCY TRANS FORMERS & (B) 

ANTENNAS ACT l VE L l NE EMEf JDER 

TUNED 

D I RECT I ONAL 

AtlrPL I F I ER 

- 
In serving local area-to-central dispatcher type of comunicatlons in 

a large mi ne, the Li ne Extenders s i mp l y extend the monof i l ar mode 

range; with operation into a separate Remote Base being assumed. 

3.3 PREFERRED SYSTEM CONCEPT 8 DESIGN BASELINE 

The gener i c con f i gurat i ona l groundwork for MF system des i gn i n underground 

coal mines, emphasizing AC trackless haulagerrines, has been given in 

the previous two subsections, This subsection presents the preferred 

system concept, implementable in part or in whole, which achieves a 

practical compromise between system simplicity and system operational 

flexibi l ity. 

Care has been taken to provide for the three major types of communicatf on 

on a mi n i mum i nterfaci ng bas i s by provi d i ng "quasi -decoup l ed modes" of 

operation.:in so far as possible. Additionally, the design provides for 

decoup l ed transmi ss ion between d.bstant l y separated loca I arees as an 

extension of the local-area-only type of communications; thus, a totzl 

of four distinct quasi-decoupled modes are provided for In the desisn. 

Proliferation of the design beyond that given In this subsection Is 

expected to occur through the selection of di f ferent sets of operari ns 

frequenci es. 

The sifting of some link alternatives put forth in this subsectio~ dspend 

on a more comp l ete understand i ng of the part i cu l ar tarnsmi ss i on character i st i cs 

and prototype equipment design considerations than will be given. Tnese 

details wi.1 l be-given in later sections of this report. 

The design is based on the use of nominally 5-watt radios employing 

narrowband FM transmission for all Radio Terminal Elements and for all 

Repeater Elements, I n actual equipment design, the maximum common usage 

of transmi t and rece i ve "mdu l es" between a l l act i ve system el ements i s 

assumed, 

The des i gn uses some Conti nuous Tone Coded Squelch ( CTCS aecod l ng and 

encoding to provide operator simplecity on the part of the Portables and 

Vehiculars, and to help"decouple" the transmission rrodes. Use of additlonal 

CTCS control is discussed as providing embelishments beyond the basic 

desi gn; but are not i ncl uded as part of the basic design because of the 

recognized size of commercially available encoder and decoder components 

and because their use may not prove operational ly feasible ( except of 

supervisory radios, i f two "tiers" of radios are practica l 1 unti l 

experience has been gained with an actual operating system. 

3.3.1 SYSTEM FREQUENCY PLAN 

The frequency pi an is a two-frequency plan providi ng for both simp1 ex and 

half-duplex types of operation. The frequency plan is the same for a\ I 

Radio Terminal Elements, with a variation in the Base Station, The 

frequencies, desi gnated f and f are expected to occur in the 500-1 030 

kHz range with a minimum bf 10% $&ration and with fl being the higher 

frequency of the two. 

The frequency plan options for the Portables and Vehiculars are envisioned 

as being selectable via a three-position swltch on the enclosure as 

fol lows: 
"Loca I" 

"Base" 

"Remote" 

Transrni t f no CTCS 

Rece i ve fl no CTCS 

Transmi t f, CTCS 

Rece i ve f, no CTCS 

Transrni t f2 CTCS 

Rece i ve fl no CTCS 

A single tone encoderis used with both transmit frequencies ( and a slngle 

tone i s used throughout the system 1. Use of the si ngle receive frequency, 

of course, poses the arnb i gui ty of which "mode" is bei ng recei ved. Thi s 

is acceptable in this type of service where the operator generally knows 

to whom he is talking and whether it is "Local" or "Base"; otherwise, it 

wi l l mst often be remote, 

The dispatcher has additional visibility with regard to the type of 

communications being serviced and can differentiate between Remote Sase 

and "Loca I" or "mob i l e un i t" l i nks. The frequency p l an for the Base STat i on 

is: 

"Local" Transmit , f no CTCS 

' Rece i ve f , no CTCS 

Note: on base station antenna or on a coupled 

monofilar conductor 

"Remote Base" Transmi t f2 no CTCS, or baseband audio 

Recei ve f2 no CTCS, or baseband audio 

Note: on phone line only, bifllar mode 

llRemote/Mob i l e Transmi t f, CTCS 

Unit" L 

Rece i ve 1 no CTCS 

Note: on coupled monofl lar conductor 

If provisions are made in the Base Station design for simulcasting and, If 

Line Couplet elements ate linked to the phone llne ( bifllar rmde 1; then, 

in the simulcast mode, CTCS should be transmitted on f on the phone l i ne 

( assuming f is used rather than baseband audio 1, 2 

2 

The frequency p l an for the Remote Base is : 

Rece i ve f2 no CTCS, or baseband audio on 

wlrel ine l ink 

f, CTCS on MF link 

Transmi t f2 no CTCS, or baseband audio on 

wire1 ine l ink 

f, no CTCS on MF link 
The frequency plans for the Line Amplifier, Line Coupler, and Remote 

Repeater are i dent i cat, and are: 

Rece i ve 2 CTCS 

Transmi t f no CTCS 

As an overlay on this basic frequency plan, additional CTCS tones could 

be added to provide: 

Paging/Call Alert from the Base Station 

Each or certa i n Portab l es and Veh i cu l ars . wou l d nave a "home" 

address tone decoder such that if this tone was received, it 

woul d aud i b l y or vi sua I l y s i gnal the operator of the rad i o 

of a call 

Private Line ( blocking 1 from selected radios 

Selected supervisory radios woul d have a tone encoder and each 

non-supervisory radio would have a tone decoder such that if 

the tone were sent, it would block the receiver of each radio 

havi ng the decoder 

3.3.2 SYSTEM DES l GN L l NK FEATURES 

Using the'system elements previously defined and discussed, and the 

frequency p l an of the previous subsection, a versati l e system des i cn 

can be performed. An overview of the system des i gn possi b i i l t i es i s 

given in Figure 21 which illustrates the majority of the link options. 

The system provides for four quasi-decoupled types or modes of 

communications. These are: 

Base Station-to-local area( Portable/Vehicular 1 communicaiions 

via the Remote Base repeater. 

The link is provided using the bifilar phone line transmission 

mode which isolates it from types using monofilar mode coupling 

and transmission. This link is isolated from long distance local 

area-to-local area transmission via frequency separation for 

transmissions originating from a Line Coupler Repeater and by 

CTCS for transmissions ori gi nat i ng from the Base Station 

Long distance Base Station or Poflable/Vehicular-to-mobile unit 

commun i cations vi a a L i ne Amp l i f i er repeater 

The l ink is provided using the monofi lar mode transmission on the 

AC power cable and/or phone line which Isolates it from types 

using the bifilar mode for transmission. This link is Isolated 

from l inks employing a Line Coupler and the monof i lar node because 

of frequency separation ( two repeaters with l i ke frequency plans 

cannot be chained 1 
TO SURFACE 

FIGURE 21 

OVEfIVIEW OF CO~lf~lUNICATIOI\J LII4K POSSIBILITIES 

FOR IJ~ED I UFj1 FREQUE IdCY SY STEf.1 

' LC LINE COUPLE

\ HR REMOTE REPE

ALE ACT l VE L I tJE 
Extended range local-area-only type of comnunications via a 

Line Coupler repeater, coupled to a mnofi lar conductor 

Same rationale applies as for the above mobile unit monofllar 

l ink. 

Extended range l oca l arsa-to- l oca l area commun i cat i ons v i a a 

Line Coupler Repeater, coupled to the bifi lar phone I ir'ie mode 

Sam rationale applies for isolation as for the above Base 

Station-to-local area link, 

Additionally, local area simplex communications are somewhat isolated from 

comunications from the local area to the Base Station via the Remote 

Base through the use of CTCS, 

Of course, CTCS does not provide much isolation under dense traffic 

conditions; and,due to the common receive frequency, there will be 

i nterferance between "Loca I" and ''Remote" transmi ssions and between 

"local-area-only" transmissionse 

The major l oca l area-to-centra l d i spatcher cornmun i cat 1 on l i nk poss i b i I i ti es 

are illustrated in Figure 22 , The primary link is via the blfiiar 

phone line transmission through the Remote Base. Other secondary monofllar 

mode possibi l ities are shown, 

The major local area/centraI dispatcher-to-mobile unit communications link 

possibi l ities are i l l ustrated in Figure 23 .A1 l possibi l ltles involve 

the use of at least a section of nonofilar transmission along whicn the 

mbi le units are presumed to be, Besides the primary a1 I-monof i lar-mode 

options, hybrid links including Remote-Base-excited mnofi lar mode and 

isolated power grid crossconnections using Active Line Extenders are 

shown, 

The major local-area-only ( or between local areas 1 communications link 

poss,i b i l i ti es are i l l ustrated i n Fi gure 24 . These l inks are arranged 

in order of shortest range to longest range in decending order on the 

diagram page. The shorter range I inks employ direct wireless transmlsslon 

or pass i ve coup l i ng i nto wi ri ng. The longest range l inks emp loy purposeful 

coupling into the bifilar transmission mode on the phone Ilne. 

The configuration of particular systems will depend upon the 

Size of the mine 

Type of mine 

a Size of the areas requiring comnunicat~ons and their locations 

with respect to conductors 

Mine topology; pl us arrangement and number of existing mine wirlng 

conductors 
a Mi ni ng format; how often the wi ri ng changes, and how the 

f unctiona l worki ng crews are deployed. 

The means of configuring the systems is the topic of the next subsection 

of this report, 
PR I ?4ARY 

'i - CTCS 

BASE BAND AUDIO OR f2 NO CTCS RB 

BS 

AC CABLE 9R PHCiIE LI!.IE 

W?.IOF I LAR i4CDE 

YI ' CTCS 

SECONDARY 

/ - I \ /'*\ f2 f( I-\ 5 

IAC CABLE OR FHOidE 

NO CTCS LA ?.lO;.IOF I LAR 

\ 

f, CTCS L 

r 

- 1 ISOLATED I I 

AC POWER GRIDS" Y 

Fl GURE 22 

SYSTEM L 1 FlI< POSS I B I L I T I ES 

LDCAL AREA-TO-CENTRAL DISPATCHER BS 

p /V 

RB 

ALE 

LA 

LC 

LEGEFJD 

BASE STAT1 ON 

PORTABLES OR VEH I CULARS 

REMITE BASE 

ACT1 VE L l NE EXTENDER 

LINE AMPLIFIER 

L l NE COUPLE9 
PR l MARY 

- CLOSE 

/ - /-kt ' \,AC CABLE OR PHO, I L I EJE P.K)NOF I LAR MDE 

f NO CT 

' E 

NO CTCS 

MOBILE UNlT 

RE I4OTE f- f. 

Trf I CTCS 

lU2 

CTCS 

ONE LlNE 

LAR MODE 

L 

i' /Cc -\ /-\AC CABLE OR FHOIJE LlYE t4ONOFI LAR MOEE 

C 

A!fTEI'U'N A 

I 

NO CTCS V3E I LE Ui4 1 T 

SECONDARY 

$ -- PHONE L l NE B l F l LAR VODE 

. BASE 

,40R f2 

BAND AUD 

NO CTCS 

u 

MOBILE UNlT 

CTCS 

I ISOLATED - I 

Y 

AC POWER GRl DS -- - 

FIGURE 23 

SYSTEM LlifiC POSSlalLlTlES 

LOCAL AREA/CEinRAL D I SPATCHER-MOa I LE UN I TS 

BS 

P/V 

RB 

ALE 

LA . 

PLE 

LEGEND 

BASE STATION 

PORTABLES OR VEH l CULARS 

REMI)TE BASE 

ACT l VE L l NE EXTENDER 

LINE AMPLIFIER 

PASS l VE L I ?JE EXTENDER 
Dl RECT THROUGH-THE-SEA!-? TRANS?4 I SS I CN 

1 f 

f2 CTCS 

p/vW 

-0 CTCS 

Dl RECT THROUGH-THE-SEAM TRANSb?I SS I ON 

P/V 

P/V 

PLE 

LC 

LA 

1"JO CTCS 

LEGEND 

PORTABLES OR VEHICULAR5 

PASS 1 VE L I P.JE EXTEIJDEP, 

LINE COUPLER 

LINE AFSPLIFIEil 

/- -, AC CABLE OR PHONE L 1 Y+P 3~; WNOF I LAR MODE 

' - 

F<N: CTCS \PLE&~~ ANT EbJhlA 

RADIO COUPLING TO MII4E!JIRll\(G WlTH LlNE EnENS ION 1 20 CTCS 

,", AC CABLE OR PHONE LlUE- MONOFI LAP, I'IODE 

IP/Y~~ NO CTCS 

RADIO COUPLING TO MINE WIRING 

,' -, AC CABLE OR PHONE L 1 W' , MONOF I LAR MODE 

RADIO COUPLING TO MIIJE WIRING WlTH ADDED LINE COtiPLlNG 

' PHnNF I INF RiFll AR MnnF 

/ f LOOP ANTENIIA 

f ~d CTCS 

3ADIO COUPLING TO MINE WIRING WlTH ADDED LlNE COLPLING 

WD I0 COUPL l NG TO M 1 NE W l Rl NG W ITH ADDED LI F4E COUPL l NG AND AMPL I FI CAT I Ot4 . 

FIGURE 2A 

SYSTEM LIiJK POSSIBILITIES . 

LOCAL-AREA-OM LY OR BETWEEN LOCAL AREAS 
3.4 SYSTEM PERFORFJANCE ANALYS l S TECH14 I QUE 

Deta i l s of the technology "tool stf requi red to predict and ana l yzs system 

performance are given in Section 5.0. This sectlon discusses the 

techn i que for system performance ana l ys i s us i ng these tool s, provl d i cg 

the basis for a particular "strawman" analysis to be oi ven in the next 

subsection. 

The first step in system analysis is to define the critical equlprnsnA 

parameters. Based on the system definition of previous subsections 

and technical specifications to be given in the next section, the 

equ i pment parameters are : 

Frequency, choose 890 kHz as typlca 1 

Transrni t power 5 watts 

Portable transmit NIA 1.5 

Vehicular +ransmit i4IA 0.82 

Portable NA 1.25, R = 3.5 ahms 

Vehicular NA 1.67, R = 22 ohms2 

Portab l e antenna area 0.208 m2 , El = 6 

Vehicular antenna area 0.139 rn 2, N = 12 

Base Station antenna area 14.4 rn , N = I 

Receiver noise figure 6 dB 

Modulation type, FM voice, + 3 kHz deviation ( n = 1 1 

Portab l e rece i ve system sensi t 1 vi ty -33.7 dB above I uamdmeter 

12 dB SINAD 

Veh 1 cu l ar rece i ve system sens i t i vi ty -27.0 dB above I uam~/meter 

12 dB SlNAD 

BaseStat i on recei ve system sens i t I vi ty -49.3 d5 above I uan~/me+er 

12 dB SINAD 

Thermal Noise floor -120.3dSabove I uanp/meter 

Repeaterfrequency spacing 10; or 75 kHz, whichever is greater 

condition: no degradation In receiver sensitivity 

The next st ep i s to define the envi ronmenta l parameters 

Seam; determi ne scatter ga i n, conductor ettenuat i on, and quas i - 

conductor-f ree attenuat i on 

Type of mine; choose AC/trackless haulage, this determlnes that 

"face area" noise along conductors is approprlate 

Conductor ensemble surge impedance; choose Z = 50 ohms 

Average "c l osetf separation of antenna centerg f rorn the conductor 

center 

Portab l es 2 meters 

Veh i cu l ars 3 meters 

Base Station transmit coup1 lng level; choose -28 dB 1 imii 

Base Station rece i ve antenna-to-conductor spac i ng 0.3 meters 

Conductor carrier current SWR design crl terla; choose + 15 d9 

Attenuation increase per conductor tap; choose 3 dB/slngle tas 

5 dE/~ouSle iap 

The remainer of this section will address the choicg of the Upper Free~or' 

seam, with: 
M = 0.02 1 3 dB/meter 1 MHz 

= 0.01896 dB/meter @ 890 kHz 

Face noise = -27.5 dB above I uamp/meter 2 890 kiiz 

t-Jote: face noise and set noise for vehicular opera?ion 

are near-equa 1 8 890 kHz 

The next operat ion is to esti rate system margi n for severa 1 types of 

operat ion vs l atera 1 (transverse) range of the transmi tter f ram the 

conductor assuming zero attenuation along the conductor ensemble. Also 

included is the system margin estimates for quasl-conductor-free 

operat i onvs range.The conductor proxi mi ty data must be prepared us i na 

separate1 y the "remote" (scatter aa 1 n) and "close" ( current cou~ l i ng 

coef f i c i ent ) theor i es, p l ott i ng curves prepared from these theor l es, 

and joi ni ng these curves i n the transition recion of lateral -ranse. 

An examp I e of theconductor-proxi mi ty computat ions for Veh i cu l ar-Veh i c~ l ar 

( V-V 1 operation is as follows: 

Remote COUD l i nawhere, RT is the range from the transmit antenna center to th- conductor 

ensemb l e center I n meters 

GS is the scatter gain ratio In dB 

Hi is the incident magnetic field strength in dB above I uamD 

per meter from an NIA = 0.82 transmitting source 

E is the face noise level in dB above I uamD per meter 

S 

Close Coup1 inqRt R C~ c~ IL E s II I s 

MARG 1 i.1 

15 -79.3 0.49 -27.0 52.9 1.5 +36,0 

7.5 -67.2 0.49 -27.0 213.8 I .5 +48.1 

rib edge 4.83 -59.6 0.49 -27.0513.1 1.5 +55.7 

3.9 0.57 -42.7 -55.9 0.49 -27.0 785.6 1.5 +59,4 

2.9 0.30 -37.1 -50,3 0.49 -27.0 1496.9 1.5 +65.9 

2,O 0,22 -34.4 -47.6 3.49 -27.0 2042.1 I .5 +67,7 
where, 5 is the range from the transmit antenna center to 

to the conductor center, meters 

CR i s the rece i ve current coup l 1 ng coeff i ci ent obta i ned 

from graphical fleld mapping, n = 64, derived from 

Fi sure 

Note: CR is used only to calibrate CT as the field 

mapping coefficient is deemed more accuraie 

than the simple formula and the relationshio 

between transmit and receive coefficlenfs 

i s re I at i ve l y constant 

CT i s the transmit current coup l i ng coeff i ci ent computed 

as 

CT( field formula) 

- 

C~ - 

x CR ( field mapaing 

CR( field formula) 

2 

- then sca led as I /? for ranoes beyond the ri b edaa 

( taken to be located at 4.83 meters lateral rsn~e) 

'L is the transmit antenna current, arcps 

Es is the set-noise sensiiivlty level in dB above I usno/me+er 

I I is the conductor carrier current in amDs 

I is the conductor noise current' In dB above I usm? 

s 

The quasi-conductor-free margin is computed using the Upper Freepori seam 

measured results ( Margaret #11 shown in Figure 33 adjusted for actual 

NIA and fhe corresponding face-noise or set-noise field strength Isvels. 

The system margins for zerc dE l Ine attenuation ( along the mnofi lar 

conductor and quasl -conductor-free margi ns, each for severa I Rad io 

'* 1- Termi na l El ernent types, are given i n Section 5.1 in Fl sure 30 . I~Jte 

in this figure that the "remote1' and "close" coup ing reglons are identified i along with the transition region in which the I/R fzll-off was assunsd. 

The actual field strength fall-off for short lateral ranges beyond ths 

rib edge, once the "remtel' and llclose'l curves are joined, is l ess fnan fhe 2 I/R lay ggsumed. The actual fall-off law in this region is very close fa 

the I/R law measured in the RoseValley mine. 

To enable the conductor proximity results to be easi ly used for system 

analysis, the curves of the above referenced figure are used to prepare 

curves of l ateral range away f rorn conductors vs range a long the mnof 1 l ar 

conductor string. Continuing the examp ie of Vehicular operation in t5e 

Upper Freeport seam, curves are shown in Fi sure 25 for V-V operaticn 

with 0 dB corresponding to no taps, 5 watts, + 10 dB SWR, and 3-meter fixed 

range of one radio termi na l from the conductoFs at 390 kHz. These same 

curves can be used for V-B operation by taking the +I6 d@ curve to 

correspond to 0 dB. Using the curves, a contour of lateral ranoe vs tznoe 

along conductors can be plotted, If there are tapdbranches involv~ci, the 

curves are used as follows: 

for single wlde-spaced taps ( for example) the attsnuafion 

is estimated to be 3 d3/tap. If there are 4 taps beiwnqn 

the transmitter and recei vet for V5 operation, we wcu ld use 

the -12 dB curve; for V-B operation, we would use a +"B 

curve. 
I r I. I 1 I 

Lr I a I I ' . .I . . I I: I. I S'. I I I I, I I' !#I' 'I.' .I I ' 2: I I. 1 1 

I., :. I I 
3.5 STRAWMAN SYSTEM DES l GN EXAMPLE 

The preceeding calculatlons and analysis technique will be used in 

this subsection to estimate the Vehlcular-Vehicular( V-V 1 and 

Vehicular-Base Station ( V-0 1 operation in a particular mine; ihs 

Helvetia Coal Co, Lucerne #8 mine, This nine is fami liar to P!*/ISRC 

and is one for which the Bureau has an ongoing communications systsm 

test-bed program under cooperat i ve agreement with the mi ne, The author 

visited this mine during August, 1977, and performed a an electromegnntic 

field mapping at medium frequency in this mlne at that time. A summary 

mine map was prepared illustrating the status of mining operations, 

topological ly, together with assumed area coverage regions for a 

trackless haul age MF system as of late 1977. Also shown. are arsas to 

be mined in the near future. This summary mine map is given as Figurs 26. 

The assumed des i rab I e comnun i cation coverage area i s gi ven by 

crosshatch i ng on the f i gure, The l aiera l haul ageway coverags area 

assumed was governed by communications in all fresh air entries, with 

the result 

145 feet lateral ran* I n South Ma i ns 

80 feet lateral range in North bins 

80 feet lateral range in sections. 

The reaui red area in sections included the size of the room-and-pl t tar 

areas extending about 400 feet on either side of a center line, Ths 

acceptable lateral range coverage in haulageways has been taken t5 be. 

80 feet in al l haulageways, nominal 

65 feet minimum 

tdote: the 65 feet minimum ref!-acts the range 

requi red I entry removed f ron the 

conductor entry as the D i l l ars ar9 

nominal ly on 65-foot centers. 

Al so shown on the map are rectangu l ar areas show i ng rooms to be mi ned 

( as of that date 1 and dashed lines representing expected' future 

extensions of the AC power cable and beltways. 

The exact operational status of Lucerne 08 as of the time of this writlnc 

and that expected at a future time when demnstratlon hardware wi l I be 

available for testing are not known. The following analysis, therefore, 

assumes all dashed AC power cable and beltway extensions to be acfive. 

The analysis of V-8 and V-V transmission in this mine are 1 l tustr~ted 

respectively in Figures 27 and23 . The lateral range predicted at 

selected locations adjacent to the coverage contours and especially 

near the ends of particular power cable/beitway runs. 

The V-B coverage I l lustrates the olacement of Line Ampl ifier or Remot5 

Base repeaters to gi ve mi ne-w i de coverage. 

Specific conclusions afforded by this analysis include: 
(I) The maximum through-the-seam ( quasi-conductor-free ) 

range expected i s 108 meters ( 354 feet 1. 

(2) If both Radio Terminal Elements of a pair are closely 

coup l ed to conductors, approxlrnate mi ne-w i de coverage 

is expected V-0, and Vehiculars will be able to comrnunlcate 

with other Vehiculars ( V-V ) over either the North Mains 

or the South ?Pa i ns areas without repeaters. 

( 3) V-V coverage w l t hout rebeaters w i th one rad I o located 

one entry remved from conduc+ors I s l i mi ted to about 

2500 feet or less. 

(4) V-V coverage without re~eaters with both radios remcvsd 

one entry f rorn conductors i s l i mi ted to about 1000 f 9et 

or i ess, 

(5) With a Base Station assumed to be located in the poriel 

area, and to maintain nominal one-entry-away coverage 

with vehicles, a Line Amplifier or a Remote Bzse Repeetgr 

i s requi red 2500 feet away in the North Piai ns and 3750 

feet away in the South Mains, 

(6) With therepeater spacing of (51, a lateral range in excess 

of 80 feet i s assured over a l l hau I ageway Ma i ns, 1 n excess 

of 60 feet at the end of all Butt Sections ( Submains 

panels, and in excess of 50 feet at the extreme ends of 

roowand-pi l lar area assumi ng the AC cable runs this far 

( this should assure at least 60-65 feei of latere l range 

at a1 l section power center locations 1. 

td 

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i t---- J , 0, 

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1-, , , *.I 

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Functional detai l s of the System Elements requi red for a mi ne-w i de 

trackless haul age med i um f reauency w i re I ess comun i cat l on system, 

general ly meeti ng the requi rements for a general purpose system 

app l icab l e to many types of underground mines, have been gl ven in 

Section 3.0. The purpose of this section is to summarize certain 

key functional and performance speciflcations for System Elements 

which are apparent as a natural consequence of the technology. 

4.1 PORTABLE RAD I0 

Funct iona lProvi s ion for channe l i zed operat ion; chanai ng channe Is requi ring 

sirno le adjustments interna I to the radio not accessable via the 

external controls) 

Per channel : 

Reception on a single frequency, f, , the lower frequency of an 

fl/f2 pair 

Transmit on either f ( simplex 1 or f ( half duplex 1, as 

se I ectab I e on the trbnt pane I 2 

Frequency p l an- brovi des for 3 re l ectab I e front pane l operati ng 

modes 

" Loca I " transrni t f, no CTCS 

rece i ve f no CTCS 

"Base" transmi t f, CTCS 

rece i ve f no CTCS 

"Remote" transmi t f2 CTCS 

rece I ve f, no CTCS 

single tone encoder for use with both transmit 

f requenci es 

provision for addition of CTCS tones for 

"Ca l l A left" home address tone decoder 

"Prl vate Line" blocking tone decoder on a l l radics; 

blocking tone encoder on selected 

supervisory radios 

Provi slon for externa l ly adjustable squelch 

Provision for flexible, tuned, bandol let antenna with dl rect conneciion 

to transmitter power amplifier; also for f /f swltchlng. For swiichina: 12 
norm I 1 y on f f Tx "rode" sel ecti on on front pane l enab l es 1' 2 switch "line" to antenna, actual switching controlled by Tx 

key 

Antenna "retun i ng" for other cnanne l s contro l l ed by i nterna l ad j usiments 

Normal operation via audio transducer on Portable case and PTT key on 

Portable case; provision for speaker mike operation with noise cancel1 ins 

mi crophone; front panel key i ng control and si detone for tone si gna l l i ng 

Frequency Range 300 - 1000 kHz 

minimum of 4 channels per radio 

Modulation Type FM voice ( m = I ) or tone signal ling 

Intrinsical ly safe design 

Power S upp l y 

Envi ronmenta l 

Transrni tterPower Leve I 

biodul at ion 

Exc i ter 

Frequency Stabi l ity 

Signal l ing Tone 

VSWR Protect i on 

Rece i verNoise Figure 

Receive System Sensitivity 

( i nc l ud i ng antenna ) 

Image and IF Rejection 

rechargable nickel-cadmium battery with 

minimum 8-hour battery life; or externel 

cap lamp battery 

-20 deg C to +60 deg C 

sealed waterproof high-impact ~lastk case 

5 watts 

narrowband FP! voice ( m = I) 

- + 3 kHz deviation 

phase-locked-loop type 

for voi ce mdu I ate6 waveform: 

12 dB/octave to I l -off above 13 %Hz 

10 dB bandwidth 8 kHz nomi na l 

0.0082% or better 

single tone In 700-100 Hz range 

transmitter shall be operable into any 

load without damage 

6 dB maximum 

-33.7 dB or better above I uamp/mefsr 

Beiter than 60 dB re l at i ve to 3.2 uvo l t 
AGC 

Tone S i gna 1 1 i ng 

accomodate I rnpu l se noi se envi rcnment w i tn 

maximum 3 dB gain reduction 

18 dB peaks above background nol se 

of 333- 1 000 usecond d uraf i on ewry 

2-6 rnl l l l seconds 

300 Hz nornlnal IF fl lter activating 

visual indicator and sidetcne 

AntennaFlexible, multi-turn loop antenna attached directly to radio 

Nomi na l Area 

Nominal NA 2 1.25 rn turns 

NI A from 5-watt Tx 1.5 nominal 

Provides fixed resistive paddlna to 12 kHz mlnimum 3 dB bandwidth, 

f i xed res i stance adequate to provi de current l i mi ti ng for i ntrl nsi c 

safety from a 4.5 VDC battery, per UL-9 13 

4.2 VEH l CULAR RAD I0 . . Same specifications as for Portable radio with the following changes/ 

except ions : 

Provi s ion for ri gi d externa l antenna, connect ion vi a untuned length of 

50-ohm coaxial cable plus a switching key line 

Normal operation via Pll noise concel ing external microphone and a 

separaie external l y mountab 1 e loudspeaker 

Power Supply 13.6 VDC from vehicle battery or 

270 VDC trol ley sourve; 12 volt 

internal standby battery with 

automat i c sw i tchover prov I s I on 

Rece i verRece i ve System Sens i ti vi ty -27.0 dB or better above I uamp/meter 

( i nc l ud i ng antenna 1 

AntennaRigid multi-turn loop antenna with self-contained matching and f,/fZ 

switching; antenna winding protected by an electrostatic shield 

Nomi na l Area 

Nominal NA 2 1.67 rn turns 

NI A from 5-watt Tx 0.82 

Frovi des ii xedresi sti ve adding inherent in wi ndin9 to 12 kkz rbi ni mur 
3 dB bandwidth, the high impedance deslgn providing inherent Intrinsic 

safety protection from a nominal 12 VDC source 

4.3 BASESTATION 

Functiona IProvision for channel ired operation; changing channel s requi rl ng simp I e 

adjustments internal to the radio( not accessable via the external conirolsl 

Provision for multiple-link operation; direct transceive operation from 

Base Station location, provision for control or mare than one additional 

Remte Base Repeater; separate loudspeakers for each link 

Per channel : 

Reception on either f I # f2' or baseband audio 

Transmi t one i ther f , +2' or baseband audio 

Frequency plan- provides for 3 selectable front panel o~etaiinc modes 

'I Loca I " transmit f no CTCS 

rece i ve f no CTCS 

"Remote Base" transrnf t f2 no CTCS, or baseband audic 

mrecieve f no CTCS, or baseband aud ic 2 

"Remte/Mab I l e transmi t f2 CTCS 

Un i t" rece i ve f, no CTCS 

s i ngi e tone encoder for use w f ih both transnl t 

frequencies 

provision for additional CTCS tones for 

"Ca l l A l ert" home-tone encoders for each Poriab l e/ 

Vehicular radio on which Cal I-Alert 

I s i mp l emented 

"Private Line" blocking tone encoder; possible 

blocking tone decoder 

Provi s ion for externa I l y ad j ustab l e sque l ch 

Norm l operati on vi a tab l e mi crophone w i th I ntegra l or foot-actuated PTT 

sw i tch; separate loudspeakers for d i rect transce T ve and each Remote Ease 

l ink 

Provision for direct termination of mine phone I ine taps for Remfe base 

link control 
Provi s ion for either mnof i l ar mode ( conductor coup l ed ) or dl rect 

radiation on transcei ve 1 ink; or sf mu1 taneous excitation of botn 

conductor coup led and di rect radiation transmi sslon 

Genera lSame as for Portable/Vehicular except for 

Power Supp l y 

Envi ronmenta l 

Transmi tter1 15 VAC loca l source with 12 VDC battery - 

backup 

-20 deg C to 60 deg C 

tab l e-muntab l e case 

Same as for Portable/Vehicular 

Rece i verSame as for Portab l e/Veh i cu 1 ar except for 

Receive System Sensitivity -49.3 dB or better above I uamp/neter 

(including antenna) when base station antenna is used 

AntennasMu l ti -turncurrent transformer for mnof l l ar node couo 1 i no with se l fconta i ned match i ng and sw i tch i ng 

N,A, I parameters si mi lar to Portable 

Single-turn tuned antenna, tuned to f only, 

Nomi na l Area 

4,4 REPEATER RAD l OS 

For al 1 f /f repeaters, the f reuuency separation per channel sha l 1 be 12 a mi ni mum of 10% or 75 HZ, whichever i s greater 

4,4,1 REWTE BASE 

Funct iona iOption providing for either baseband audio or f on control link to Sass 

Station via bifi tar phone line mde 2 

Per channel : 

Frequency p 1 anrece i ve f na CTCS, or basebard audio 2 

on wlreline link 

f! CTCS on "F l ink 
transmi t f no CTCS, or baseband audio 2 

on wireline llnk 

Power Supp l y 

fl no CTCS on b1F I ink 

1 17 VAC w i th rechargab l e battery backup far 

24-hour operation at 15% reoeat, 85% 

standby, wlth an external indlcatlon of 

battery cond i t 1 on 

For test and mai nta i nance, provi s 1 on for l oca l operat i on from I nterna l 

handset with noise cancel ling microphone 

- Genera lSame as for ?ortable/Vehicular except for power supoly ( per above and 

Sea I ed waterproof and rust res i stant wa l l ornountab l e case 

Transmi tterSame as for Portab le/Vehicul ar exceot for: 

Exciter fi ltering Provide additional filtering of phaselocked-loop exciter output sc as to 

achieve a mi ni mum of 24 dB/ocTave ro l I-off 

above 10 kHz 

Note: comosite voice modulation spectrum and 

exciter fi ltering shout d ~rovide a rcl !-off 

above 10 kHz of 36 dS/octave 

Rece i verSame as for, Portab l e/Veh i cu l ar 

AntennaSi ng le-frequency-tuned current transformer ( f on I y > with id,A, I parameters 

s i mi l ar to Portab l e antenna I 

4.4.2 LINE AMPLl FIER, LINE COUPLER, & REMOTE REPEATERS 

Specifications are the same as for Remote Base except for 

Funct i ona lConnectivity to antennadcurrent transformers differ for each type; the 

reader is referred to Section 3.2.2 for these differences. 

Fer channel: 

Frequency p I anrece i ve 

transml t 

f2 CTCS 

f, no CTCS 
Consisting of: 

Termi nated ded i cated w i re coup I er 

Magnetic current probe ( sl mi l ar to Stoddard current probe ) 

the cha&cteristics of these devices are a maiter of detal led design, if 

used, and remain to be determined - 

Fixed multi-turn loops 

these antennas/transformers will have eram meters similar tc thcse of ih? 

portable antenna; these representing "field-expedient" couplinc devices. 

4.6 PASSIVE LINE EXTENDERS 

Specifications to be determined 
5.0 COMPEND l UM OF FOUNDAT l ON TECHNOLOGY ELEFiENTS 

This section presents sumaries of data, theories, measurerents,and 

analyses comprising the foundation resources for the characterization 

of MF systems. Fami l iari ty with the contents of this section wi l l 

provide the reader with an overview of the state of MF technology. 

This overview can serve as a baseline for extension of the technology. 

To enable MF system performance computations in coal mines, data and/or 

theories are required in the following topical areas: . 

Quasi-conductor-free transmission - magnetic field 

strength vs range in coal seams vs frequency 

Magnetic field coupling to mine wlring conductors - 

current coupling coefficient between transmit/receive 

antennas and conductors vs transverse range and f resuency 

for the seams of interest 

Monofilar mode conductor tttenuation - the attenuatio~ of 

a "matched" transrni ssion system vs frequency for each, 

seam of i nterest 

Monof i iar mode standing wave rati o and j uncti on losses - 

estimates made from conductor-proxirni ty field strengin 

- measurements and from magnetic field strength mapplngs . 

Bi f i l ar mde phone l i ne attenuation characteristics 

including junction losses - assumed to be seam invariant 

E l ectromagnet i c noi se - quasi -conductor-f ree and monof i I zr 

mode noise estimates related to the type of mine, minins 

operations, and to operationa l ly si ~n i f i cant I ocat i ons 

in mines; also, Oifilar mode noise on phone lines 

Type of modulation used and noise bandwl dth 

L i s t o f typica 1 practica 1 equipment parameters 

- NIA and NA of antennas vs power leve I ; effect cf 

antenna or1 entat i on 

- O~erating power level 

- Operating frequency 

Receive system sensitivity 

Data will be provided in each of these topical areas in the subsections 

to fol low. 
5. 1 MF PROPAGATION 

The measurement of quasi -cond uctor-f tee na~net i c fie I d strength vs 

range and frequency and analytical f i ttlng of the measured data to 

a model has been performed in I1 mines comprising 7 seams and roughly(r3fQl-151 

4 d i f ferent geographi c areas. The ana l yses of the measured data has 

provided values for the major consti tui tlve parameters of rock 

( overburden/underburden and coal seam conductivities. The quadconductor-free transmission characteristics can, thus, be determined 

either from measured curves or from model computations for the coal 

seams which have been addressed. 

The quasi-conductor-free transmisslon has been characterized as a 

quasi-TEM mode between lossy para1 lei plates ( the overburden and 

underburden rock 1 with a lossy dielectric ( the coal seam ).(ref- Z4.Z3-31) 

The ana l yt i ca I resu l ts provide the basis for computi ng conductor 

coup l ing via a technique cal led scatter gain which considers the 

comp l ete end-to-end path ( transmitter to recei ver 1 effects, (ref. 9, 15) 

excluding monofi lar mode attenuation, from a remote transmitter ( far 

enough away so that the TEf.1 mode characteristics are establ i shed 1. 

The scatter gain is the ratio of the recei ved magnetic fie Id strength 

in proximity to a conductor located near the receiver to the field 

strength in absence of the conductor, The range assumes the receiver 

lies directly on the shortest path from the transmitter to the 

conductor ( perpendicular to an assumed long straight conductor 

ensemble 1, The receiver can, then, be translated along the conductor 

ensemble taking account of monof i tar mode attenuation. The scatter gain 

ratio is an easily measurable quantity and the validity of its use 

has been carefully established in three mines, 

The monofi lar mode conductor attenuation is estimated from the quasistatic I i mi t of the propag ati on constant of the lowest order TK mde 

on a lossy coaxial transmission line which has been conformally 

mapped into a conductor over an infinite plane interface. Use of this 

ana l yt i ca l techn i que again depends on know l edge of the rock conducii vl ty 

as derived from the theoretical propagation model, (ref *2-') 

Close coup I i ng to conductors vs transverse range from the conductors 

( assumed to.be within the entry contalnlng the conductors ) depends 

on the detailed geometry of the entry crossection and on the conductor 

configuration occurring in the entry, including vehicles ( If any 1. 

The current coup1 ing coeffici-ent Is different, of course, for the 

transmit and receive cases. An important factor is that the maxl mum 

practical transmit,mnofi lar mode coupling achievable Is bounded. 

Coup l i ng measurements have been performed for a s i mu I ated I n-mi ne 

situation on the surface, and coupf ing coefficients have been computed 

for comp l ex entry crossect i ona l geometries us i ng graph i ca l f l e l d 

mapping. Bridging the close and remote coupling cases correctly 

requires estimates of the geometric fa1 l-off law for moderately short 

distances away from the conductor(s). An analysis based on comparing 

measured and computed resu l ts has been performed and compos i te c I ose/ 

remote coupling curves have 'been developed. 
A prime motivator for early propagational R 8 D in the MF frequency 

range has been the selection of optimum or near-optlmum operati ng 

frequencies. There is an optimum frequency range both for quasicond uctor- f ree and cond uctor-p roxi mi ty operat i on from a remote 

transmitter. A fortuitous aspect of MF transmission is that the 

near-optimum operating frequencies are nearly the same for the fwo 

types of transmission. The frequency dependence characteristics have 

been estimated by performing system calculations and determining t+e 

maxi mum commun i cat i on range for each frequency; the opt i mum f requensy 

being that which gives maximum comonnication range. 

The bifilar mde attenuation characterlstlcs of a phone I lne in a' 

large AC mine have been measured and analyzsd and these results(re. 

sugsest that statistically in long runs with many taps/junctions, 

the junction losses approach 3 dB/tap; also, moderate runs give 

about 6 dB/tap. On a per-tap basis, the losses can be significantly 

.. 

areater. 

MF propagation i nforrnat ion and characteri st ics gi ven i n th i s subsecf i on 

wi I l proceed from the mst general and/or most significant to the 

mst deta l led. 

5.1.1 SUMMARY CHARACTE2ISTICS 

The maxi mum commun i cation range characteri st I cs vs frequency for the 

several seams provi de the broadest overview of potential MF system 

local area performance coverage without the use of repeaters or of 

b i f i l ar mode transmi ssions. Much greater range, even without repeaters, - cab be achieved, of course, with close coupling to conductors. ~hese 

maximum communication range curves were d.eveloped considering a 

transmit NIA of 2.5 and receive system sensitivities commensurate wifh 

the Collins prototype FM radios in medianwine-noise and set-noisel imited operation; a set-noise 1 irnited sensitl vity of -35.5 dB above 

I uarnpheter beins assumed. These curves should be used to compare 

seams and ranges genericai ly. The original NIA of 2.5 was that expected 

from a 20-watt Portable into a separate( not Integral 1 antenna metchea 

to 50 ohms. We have since determined that a Portable radio NIA of 1.5 

developed from an approximate 5-watt transmiiter using a more efficient 

antenna is more representati ve. Al so, we have si nce determined that 

median-mine-noise, while an easily definable statistic, has limited 

operational significance. Curves of maximum comnunlcation range are 

shown in Figure 29 representing all seams in which testing was conducted. 

The u i mate cornmun i cation range I s more near l y apparent by cons i der 1 ng 

curves of excess signal margin vs either range between radios employing 

direct through-the-seam transmission in absence of conductors; or else, 

vs transverse range from an assumed monof i 1 ar conductor ensemb l e (bri dg i ng 

between the close and remote coupling theories 1. Curves have been 

prepared for the Upper Freeport seam for several combinations of Radio 

Termi na l :.E I ements w i thout repeaters at a representat i ve f rsquency of 

890 kHz. 
L.Y - C rz WWD- Ud WWC ri 'CLLLY *lz 
Tne excess signal margins from these curves are convertable to range 

estimates emp loying a known factor of dB/meter of attenuation along 

a mnofilar conductor ensemble or else known dB/100 feet factor for 

direct through-the-seam transmission. Assumptions embodied in the 

curves include: 

Power l eve1 al I RTE's 5 watts 

Portab l e transmit NIA = 1.5, 1 = 1.2 amps 

Vehicular t t " "0.82, 1 = 0.49 amps 

Base Station 

Receiver range 

Noise type 

tightly coupled, 

1.2 amos in current transformer 

-28 dB transmit current coup l i ng 

coefficient ( max coupl ing l imii ) 

Portable avg. 2 meters from conductors 

Vehicular avg. 3 meters fro^ conductors 

f ace-no i se- I i mi ted or set-no l se- I i mi tsd 

typical for AC mines 

Portable face-noise-limited 

Veh icul ar set-noi se-l i mi ted ( face 

and set noise levels nearly . - equa I 1 

Receive sensitivity Por-Fable -33.7 dB above I uamp/metsr 

( 6 dB noise figure Vehicular -27.0 " It It It !I 

recei ver assumed Base Stat i on-49.3 " t~ tt 11 It 

The excess signal margin vs range curves are given in Figure 30 . For 

conductor attenuation, the factor is 0.01896 dB/meter @ 890 kHz. For 

quasi-conductor-free attenuation, the factor is 17.7 dB/100 feet. Tne 

excess s i gna l margi ns are, of course, h i gher for d i rect through-the-seam 

transmission because there is no coupling loss into and out of conductors. 

Once current is coupled into conductors ( the mnofilar mode is excited 1, 

then the attenuation along the conductors is much lower. A sumnary of 

quasi-conductor-free attenuation rates vs frequency for 6 seams and I Q 

mines is given in Figure 31 . A f i na i summary of expected maxi mum mnof i i ar mode commun i cat i on ranges 

fo I iows, as computed for the Upper Freeport seam. 

For a cont i nuous conductor stri ng without stand i ng waves or taps/branches 

and for Radio Terminal Elemnts with the above cited close coupled spacings 

for both transmitter and recei ver ( antenna centers to conductor ensemb t 2 

center 1, the maximum communication ranges along the conductor string are: 

(1) In an AC mine 

Radio type Range Along Conductors 

P-P 

v-v 

3-6 

4019m ( 2.50 miles 1 

3428m ( 2.13 miles 1 

6096m ( 3.79 mi les 1 


(2) In a DCmine w/belt haulage 

2ad i o type Range Along Conductors 

P-P 2727m ( 1.69 mi les 1 

2136m ( 1.33 miles 1 

4805m ( 2.99 mi les 1 

(3) In a DC mine with tracked haulage & no trol leyphone 

interferance 

Rad i o type Range Along Conductors 

F-P 

v-v 

8-B 

1013m ( 0.63 miles 1 

422m ( 0.26 mi l es 

309lm ( 1 .88 miles 1 

the ri ne type d i f ferences be i ng the no i se 1 eve l s exoer i enced ; these 

operationally significant types to be shown in Section 5.2. 

Close exa~t~nation ofa great deal of magnetic field strengih data has 

resulted in the following expectations for monofi far mde standing wave 

levels and tap losses: 

For stand i.ng waves 

+ 3 dB in long 'haulageways with tap spaclng of at least In63 feet 0 

- + 4 dB in submains with approximate 400 foot tap spacin~s, 

single tap 

0 

+ 6 dB in submains with approximate 400 foot tap spacings, 

doub l e tap 

+ 6 dB in conductor-dense areas in sections near center of sections 0 

- + IOdB in conductor-dense tracked, belted sections wifh service 

tracks 

Note: 2 I0 db was ai so measured l n Lucerne $8 

For taps/ j unct i ons 

-3 dB/s i ng l e tap 

-5 dB/doub l e tap 

For a large scale overview, the fol lowing average conditions may be assumed: 

I each NS or EW mains sp l it -3 dB 

I each submain spi it -3 dB 
(A) For haulage areas 

2 each doubt e taps 

or 

4 each single taps 

gi vi ng an aggragate approxl mate loss to consider of -22 to -26 

dB with respect to a flat untapped llne 

- 

(81 For section areas 

2 each single taps -6 dB p l us + I0 dE VSWR 

giving an aggragate approximate loss of -22 dB 

Note thai the assumption for both haulageway and section areas produce about 

the same loss estimate of -22 dB in signal margin due to the combination of 

standing wave and junction effects under average conditions. Under this 

assumpt i on, the c l ore l y coup l ed maxi mum cornmun i cat ion range est i maies 

a i ong cond uctor str i ngs w i tho ut repeaters becomes : 

(1) in an AC mine 

Radio type 

v-B 

P-P 

v- v 

ti-B 

P-B 

Range Along Conductors 

3138m ( 1.95 mlles 

2859m ( l,78 mi ies 1 

2268m ( 1.41 miles 1 

4937m ( 3.06 mi les 1 

3729m ( 2.32 mi les 

(2) In a DC mine w/belt haulage 

F-P I566m ( 0-97 mi les 1 

976m ( 0-61 mlles 1 

3644m ( 2.26 ml les 1 

2437rn ( I ,5 1 mi I es 1 

1846m ( 1.15 miles 1 

Bifilar mde conductor attenuation for flat twisted pair phone lines, 

without taps/branches,vs frequency is sumnarized for different wire guages 

i n Fi gure 32 . Phone 1 i ne attenuation measurements at MF frequenct es 

including taps, to-date, are limited in extent, but indicate the effscts 

of statistical averaging over long runs at high MF frequencies ( near 

1000 kHz 1 for a large number of taps, In average terms, for numbers of 

taps greater than 1-2 and less than about 10, the available data Indicaies 

6 dB/tap ( based on current spl It 1. For larger numbers of taps, The 

average attenuation per tap is expected to approach 3 dB/tap. 
- !' . ' 

1, I,,, 1 111 .a. Y- ; 

FIGURE 32 - 1-I=- EL-; ATTENUAT I O:J CHARACTER l ST l CS OF PHONE L l NES 

1----,---- - - 1- I=-=!=-=- SOURCE: I TT "REFEREICE BATA FOii E4 
5.1.2 QUASI-CONDUCTOR-FREE TRANSI4ISSlON 6 CONSTlTUlTlVE PARAMETER AtIALYSIS 

Representative fami 1 ies of curves of magnetlc field strength vs range 

and frequency for each of the seven seams are given in Figure 33 for an 

assumed transmit NIA = 2.5. These curves may be used directly to obiain 

range attenuation estimates. 

The quasi-TEM mode 3-layer mdel analysis put forth by Arthur D. Little, inc. 

consists of: (ref'. 24,281 - 

NIA (aZ +@ 2 I 3/4 -wr 

I-! = - e amperes/meter 

Where, r is the range in meters 

W, fl are respect l ve l y the rea l and l mag i nary parts 

of the propagat i on constant gi ven by 

h is the seam hei ght i n meters Sr i s the overburden/underburden ski n 

depth in meters 

dc, 4, are respect i ve l y the coa l seam 

and rock conductivliies 

€ is the dielectric constant of the coal 

C taken to be always equal to 6 

This mdel has been demonstrated to reproduce the measured data accurately 

beyond a range of approximately I/< in the 200-900 kHz range to within 

about 6 dB or less. 

Careful curve fitting has produced the following rock and coal seam 

conductivities as shown in Table I . Using the above formulaiion with 

representative conductivities from the table for the seam of interest, 

range attenuation estimates may be made in lieu of using the measured daia. 
I' - ---- ,- ! I:: I .:.I i I . 

TABLE I 

DERIVED COAL SEAM AND ROCK CONDUCTIVITIES FROM CURVE FIlTING 

TO MEASURED DATA US l NG THE ADL SLAYER ANhLYS 1 S FnODEL 

CONDUCT l V l TY CONDUCTIVITY 

COAL MINE - SEAM COAL, FJHC>/M ROCK, PWO/M 

IRELAND (IST PITTSBURGH 2.0 x 10:: 

VISIT) 1.4 x 

IRELAND (2ND PITTSBURGH 1.0 x 10 

VISIT) 

l NLAND STEEL l.~ 

#I (SESSER) HERRIN #6 

CONSOL #95 0.3 x low4 

( ROB. RUN)PITTSBURGti 

FEDERAL #I P ITTSBURGH 0.26~ 1 o-~ 

( EDDY 

VP #i -5 

POCAHONTAS 3 x loo5 

# 3 3 x log5 

6 x log3 PEABODY #I 0 HERRIN #6 4 x 10 

MARGARET #I I UPPER -4 1.6 x 

FREEPORT 1.2 x l OO5 

ADR l AN UPPER 3.4 x 10 

FREEPORT 

NANTY GLO LOWER -5 6.2 x 

KITTANING 6.6 x loW5 

EHREN FELD LOWER 6.3 x 10 

FREEPORT 

STINSON 13 ELKHORN #3 3.0 x 10'~ 

3.0 1 3-SOUTH, ENTRY A 

0.0077 3-SOUTH, ENTRY 0 

0.017 2-NORTH,#I PLOW 

0.3 IMklN SOUTH,lST WEST 

2ND NORTH 

0,3 I-SOUTH 5i EAST/ 

I-SOUTH JUNCTION 

0.013 TX,RX IF.1 SAME ENTRY 

0.006 TX,RX ONE ENTRY APART 

0.0019 
The quasi-TEM mode of transmission is exdted using the HMO ( horizontal 

magnetic dipole )ocientation of the transmit and receive loop antennas 

which is that with the loop planes oriented vertically, The maximum 

coupling between transmit and recelve antennas is obtained when the 

loop antennas are further oriented so that they are coplanar, This 

geometry is illustrated in Figure 34 . The least coupled set of antsnna 

orientations are with both antennas VMD ( vertical magnetlc dipole 

with the loop planes horizontal, One would expect that if both antennas 

were oriented HMO but wl th the loop pl anes perpendicular, there wou Id 

be no coupling. This is not the case, however, ard this type of orientation 

produces coupling typically I I dB below the optimum coplaner case. All - 

further di scussions of quasi -conductor-f ree transmi ss ion w i l l assume ?he 

optimum coplanar antenna orientations. 

OVERBURDEN 

COAL SEAM 

//////////////////////////////////////////////////[/// u/ 

MDERBURDEN 

Fl GURE 34 

COPLANAR LOOP OR I ErJTAT lot4 GEOMETRY FOR OPT I MUM 

TRANSI-1 I SS I ON US l NG OUAS I -TEK C9AL SEAbA MODE 

TABLE 2 

SUMMARY OF SHORT FORMULAS FOR SCATTER GA l N CALCULAT l ON VS COAL SEAM 

- SEAM FORMULA 

POCAHONTAS #3 

LOWER FREEPORT 

UPf ER FREEPORT 

LOWER K l TTANN I NG 
(I Choose ranges, and %, of the transmit and recelve 

antennas vely from the conductor(s); the shortest 

possible perpendicular distances 

(2) Obtain the magnetic fie1 d strength at the conductor 

location assuming the conductor to be absent, uslng F$ 

as the range ( quasi-conductor-free field strength curves; 

or else, ADL1s model 1, properly scaled to account for the 

actual transmi t N I A 

(3) Multi ply the field strength of (2) by the scatter gal n 

ratio ( or add dB as co~puted for the seam of interest 

from the table 

(4) Reduce the field strength of (3) by the attenuation 

corresponding to the translation distance, I f any, of 

the receive antenna location along the conductor from 

the shortest path location 

The mnofi tar mde conductor attenuation is given approximately by the 

fo l low i ng norma I i zed attenuation constant expres i ton : 

Where, a is the distance from the conductor ce~ter 

to an assumed flat InfInite conducting 

interface ( distance to the rock ?redominates 

a. 1s the conductor radius 

I 

Taking k = 2Ti/p and multiplying by 8.686 to change nepers to dB, the 

attenuation constants are readily expressible In dB/meter at any particular 

frequency of i nterest. 

Short formulas for the particul ar seam attenuation constants are given I n 

Table 3 using a/ai = 9 and Zo = 50 ohms. 

Except for very short ranges const 1 tuti ng c 1 ose coup I i ng, the optimum 

orientation of the remate transmitting antenna for conductor coupling is 

with the loop plane perpendicular to the conductor. 

To i l I ustrate the va l ues typ i ca l l y taken on by the scatter ga i n ratio and 

to show correspondance to measured data, parflcular comparisons of 

measured and computed scatter ga I n are gi ven i n Tab l e 4 . 
TABLE 3 

SUMMARY OF SHORT FORVULAS FOR COi4DiiCTOFi ATTENUATION VS 

COAL SEAM ( BASED ON SINGLE CONaLCTOR GEOMETRY 

- SEAM 

P l TSBURGH 

POCAHONTAS #3 

HERRIN #6 

LOWER FREEPORT . UPPER FREEPORT 

FORMULA 

LOWER Kl TANN i NG 4 = 0.22171 ~3/Vr'@ I MhZ 

NOTE : ASSUME- H l S PROPORT I ONAL TO FREQUENCY 
AC WHER " 

CABLE " 

II 

ONLY 

WONE LlNe 

6 BELT ,, SUPPORT 

, TABLE ' 

COWARISONS OF MEASURED WD COWUTED SCAVER 

GAINS IN THREE Mll4ES 

. a -. . . . . . 

COT~PARISON OF MEASUWD 6 COMPUTED SCATTER GAINS 

MARGAeT 111 MINE - UPPER FREEPORT SEAM 

FULL FOW SHORT FOFIN 

0.25 -26.0 -15.6 10.4 NOTE: AC POHE?. CABLE WST HAVE ' 

0.25 -41.5 -20.7 20.8 BEEN OPEN CIRCUITED NEAR : THE MEASUREIENT AEA ' 

3.7 -57.5 -42.8 14.7 

NO=: CALClJUTION ASSUMPTIONS 

Zo 5Q OHMS, FULL FORMULA 

25 OHMS, SHORT FOFWULA 

-. - 

COMPARISON OF MEASURED h UNRITED SCArlTR GAINS 

EHFENFELD 138 MlNE - LOWER FREEPORT SEAM 

FULL FOW SHORT FOFM 

MASUED CAt:LA;ED CALCULATED 

%'MI GS (DB) FREQ(KHZ) ~~(DEI) GS(DB) 

NOTE : CALCULATION ASSLMPT IONS 

. .- - .. --.-- . ._______ 

CWARI SON OF MEASURED 6 COMPUTED SCAVER GAINS 

NANTY ti0 131 MlNE - LOWER KlTTAlWlffi SEAM 

FULL FOIW 

MEASURED CALCULAED 

--- ?(MI RR(M) Gs(D8) GS(DB) 

SHORT FOR4 

CALCULATED 

t, (Dt3) 

NOTE: CALCULATION ASSUMPTIONS 
A d i f ferent ana l ysis i s requi red for 'rclose coup l 1 ng" when the iransni t 

and/or receive antennas are within the entry containing the conductor(s) 

or el se genera l l y w ithi n one entry of the conductor entry. For very close 

coupling within the conductor entry, the coupling coefficient is a 

function of the transverse crossect iona I deta i l s approxi mat l ng the 

quas i-stat i c field di stri but ion over the crossection cons i deri ng the 

antenna ( transmit case) or the mnofi lar conductor ( receive case to be 

the "DCr' source. For si mple geometry where the distance from an assumed 

single conductor to the antenna center Is smaller than the entry 

crossectional dimensions, the field fall-off is approximately l/r and the - 

correspond i ng transmi t and rece 1 ve current coup l i ng coefficients are 

given by; 

Where, R is the loop antenna series resistance, ohms 

r is the range In meters 

A Is the antenna area in meters 2 

N is the number of turns 

Where, Zo i s the monof I l ar l i ne surge impedance 

( "matched monof i I ar l i ne assumed ) 

A mre detailed treatment of close conductor coupling will be given in 

Section 5.4. As a practical matter, the maximum coupling value for 

transmitt i ng, C , i s bounded and is of the order of -28 dB; this va I ue 

havi ng been conTi rmsd both ana l ytica l l y and empi-rica 1 l y. 

Beyond the very close range, where the range i s comparab I e to or greater 

than the entry crossecti ona l d i menslons and much greater than the 

separation between the monofilar conductor(s) and the ,nearest "return 

currentrr conducting surface, the field geometrically falls off at a 

much faster rate. Ass m totically, the field in this intermediate range YP 

can fall off at a l/r rate because this is the rate at which the field 

of a l ine source imaged in a conducting interface fa1 Is off along the 

interface. Based on measurements performed In t38 Rose Val ley mine, 

f he geometric fa l l-of f law was found to be i/r , Cunsi deri ng the 

sumnary data for the Upper Freeport seam previously shown in Figure , which bridged between the remote coupling and the close coupling, the 

composite curve fa l l s off 14 dB between 7.5 and 15 meters ( I5 meters 

transverse range being the pIv?tfb tran ition range for this seam 1. 

Computing the fa1 I-off for I /r -0CF 

e , taking~cto be 17.7 dB/130 feet, 

the fall-off is 13.86 dB. The bridging between regions for the curves of 

Fi gyre 30 assumed l/r geometric fa l l-off to the edge of the entry and 

I/r geometric fall-off beyond for the close coupling before the composife 

curve(s1 was drawn, 
Measurements have been performed in conductor-dense section area 

panels and in conductor-dense haulageways as excited from a central 

transmitter at one end of the area in oder to investigate the "area 

coverage" provi ded from mu l ti p l e-exci ted conductor ensemb l as. Th i s 

has been accomplished by measuring the field strength at many points; 

sufficient, in detail, to define mappings or contours of field 

strength, Such a set of measurements was performed in the Upper Freeport 

seam in the Helvetia Coal Co. Lucerne 88 mine, A field map for this 

mi ne i s i l l ustrated i n Fi gure 36 . A f i na l cons i derat I on i n the conductor-proxi mi ty transmi ss i on area i s 

the expected performance of a Passive Li ne Extender. Assume that this 

extender i s coup i ed i nto a mnof i l ar conductor us i ng a current 

transformer with the parameters of a Portable antenna and with a base 

station antenna at the input end, as shown In Figure 35 , Assume that 

the maxi mum coup l i ng of -28dB 1 s ach i eved with the current transformsr. 

Consi der the examp l e to be appropriate for the Upper Freeport seam so 

that the greatest range at which a Portable can normally field-couple 

into the conductor is 54 meters, For this case, the excess signal 

margi n above that required, M, is gi ven by: 

Where, H. is the incident magnetic field 

I 

A is the base station antenea area ( one turn 

assumed 1, taken = 14,4 m 

R Is the base station loop antenna series 

loop resistance taken = 66 ohms 

Rp i s the portab I e antenna series resistance 

taken = 3.5 ohms 

The maximum range ( between base station and portable antennas to permit 

a usab ie si gna 1 to be coupled i nto the monof i l ar conductor i s 68 meters, 

assumi ng no transmi ssi on l i ne loss. 

5,2 ELECTROMAGNETIC NOISELINTERFERENCE 

Noise representing operationally significant situations has only recently 

been obtained in the MF region for both wnafllar mode and b[fiiar wde (ref.45 

phone l i ne transmission, Prior to this, the only avai lable resource for 

MF noise was an extrapolation of lower frequency ( below 200 kHz )(ref -43-47) 

monofilarmdenoisedataobtainedbyNBS .Theseextrapolationsare 

i l l ustrated i n Fi gure 37 . Consequent l y, previous system performance 

estimates were made using median-mine-noise from this curve, conveniently 

defined as 

'krn = 175.8 - 32.5 loolO f (hz) dB above one microamp/meter 

in a I2 kHz bandwtdth, (ref .A31 

or set noise. Median-mine-noise was known to be pessimis*lc for use in 



mines because even in DC mines in quasi-conductor-free areas, field 

strength measurements were set-noise-limited; the measuring equipment 

sensiti vi ty bei ng of the order of -40 dB above one rnicroarnp/meter. 

Thus, previous system calculations were also made using the set-noise1 imi t for cornpari son purposes. 

The recently obtained monofilar node data is appropriate for use in 

the entry containing the conductors, with the set-noise-limit deemed 

as being appropriate for uze at remote coupling locations ( where the 

scatter gain technique applies 1. The new noise data has further been 

partitioned according to DC and AC mines; and, further, in DC mines 

for tracked and trackless haulage and also account1 ng for average 

trol leyphone interferance levels. Although representing a limited 

sampling of several areas in only two mines, the new monofi tar mode 

data is in good agreement with the large body of NBS obtained data 

below 200 kHz; thus,adding confidence to the new data. 

The new mnofi lar mode data is shown in Figure 38 . Note,in partfcular, 

that a single curve is appropriate for use in AC mines and, thus, for 

trackless haulage communications situat'ions. Fortuitously, there i s arl 

abrupt rol I-of f in the noise frequency slope for AC mines at frequencies 

above 200 kHz. 

The bifilar mode noise levels have also been bartitioned according to 

operationally significant situations in AC mines with a single set of 

curves being appropriate for DC mines. The noise data in DC rninss, in 

particular, has si gni f icant i mpuisi ve content so that the broadband 

noise" bandwidth rule" cannot be applied. Rather, the data is ~resen+ed 

in terms of 30, 3, 0.3 kHz 6 dB bandwidths and the 30 kHz 6 dB bandwidth 

is appropriate for use with narrowband FM medi um frequency radio systems. 

The DC mine bifllar mode noise data is given in Figure 39 . The 

corresponding AC mine data is gi ven i n Figure A9 . A system embodying the use of repeaters and/or Remote Base stations will 

resu 1 t i n i nterfer-a~e f ri nges i n genera l l y we1 i -def i ned areas of the 

mi ne due to the s i mu I taneous .transmi ss ion from two or mare sources. 

These fringes will occur when the potentially interfering signals are 

nearly of the same ampi itude. The fol lowing interferance cases are 

possible: 

Reception of "simulcast" type of signal where the sane 

"message" is being broadcast simultaneously from two or 

more transmitters. This may consist of the simultaneous 

broadcast f ram a Base Station and/or one or more Remotn 

Base stations; or else, the reception of direct and "rsoeated" 

signals or the reception of two or mare repeated signals. 

In this type of transmission, using FM, the mean square 

phase deviation between sources must be less than a certain 

value in order to receive a given "grade" or quality of 

transmi ss ion. 

Fl GURE 39 

AVE9AGE 3 1 FFERENT I AL bpODE l NSTANTANEOUS 

NO1 SE LEVELS ON PHCINE Ll NE IN HA9Eb!OOD 

MINE - CHAWCTERISilC OF DC MINE WITH 

100s TRACKED HAULAGE - PHDNE LINE WAS 

16-3 ROMEX ( 5;4C FL9ATlNG AND NOT 

TWISTED PAIR I . . .;:, 1 I I I T. I , 7' ' 1 \ 1 ' i " 18'' t.'y',i'/ I i ' ' 11 i \'!]]I;! 11' //I. 

I I I .I ,I 11 1 ' I 1 i, ii.1 i I I I 1 I I !# /I: , I 1 1 '11 I 1 I I c il ,I !,, 1 I * , 

1 nnn 
SECTION :JOISE 

; ljl I I , , I I , 1,. I , I ,i 

HAULAGEWAY WELL (?WAY 

AND BELT 09 1 VES 

I I 

3 YZZ 6 DB BA;;DW 13TH . 

' 

- - - - - I 

SECTION WLTH I009 
Reception of two di f ferent signal s from two sources 

transmitting at the same time because they presu~bly 

cannot hear each other, 

In this type of transml ssion, using FM, one si gnal must 

be greater in amp1 i tude by a predetermi ned va l ue to 

ensure a gi ven grade of service; the amp l i tude l l mi ti ng 

the maximum phase deviation which can occur, this phasa 

deviation be1 ng the same as that for the si mu1 cast type 

of transmission. 

Generally, because of the way in which systems will be laid out, 

regions of potenti a l i nterferance can be "designed" i n to l i e i n 

mine areas of minimal operational significance. Also, for the 

second type of i nterferance, the FM capture effect wi l l mi nimi r6 

the i nterferance zone s i'zes, 

For simulcast transmission via path segments employ1 ng the monof l lar 

mode, the phase "s l i p" which can cause "beat notes" in the i nterferance 

region wi l l probably be affected by phase path differences due more 

to i mhomgenei t ies i n the coal seam rather than by transmitter frequency 

off-set or audio phasing control. The only sure way to determine the 

degree of the problem is by experiment. 

Because the wavelengths are much iqnger at MF than for VHF(1n the land 

mob i l e servi ce 1, the transmi tter frequency stab i l i ty cou l d be relaxed 

somewhat from the suggested 0.00015%; however, this degree of stability 

i s easy to meet. 

Let us define the mean square phase error which can be toleraied wnlle 

still meeting the 12 dB SlNAD ( 13.5 dB Hamshur S/N 1 type of sarvlcc 

requ i rement, 

Abramson has considered the case of a carrier phase mdu l ated by a (ref. 1 

Guassian random process under both baseband and narrow band conditlons. 

He gives a formula for computing the spectral density of such a 

mdulation process which is a function of the center f equency-tobandwidth ratio and the mean square phase deviation, d . For the 

case of I b i t/Hz of bandwidth ( i n dig i ta i terms, the gandw i dth equa l l i ng 

the signal ling rate 1, the above ratio is essentially unity and there 

is a curve for this case which is sh2wn here in Figure 4la. The spectrum 

shows a carrier of amplitude exp( -P 1 in the center of a continuous 

spectrum of peak amp l i tude X 

A curve of this peak amp1 itude vs P' is shown as Figure4lb . For smal l 

devi at ions, th i s spectrum has essenPi a l l y the same shape as the or i gi na l 

modulation process ( amplitude modulation 1. For larger deviations, the 

spectrum becomes much wider than that of the origl nal process and takgs 

on a Gaussian shape via the central limit theorem. Let us consider the 

the spectrum of the FM radio signal in the presence of interferance to 

be the convol ution of this spectrum with the above spectrum. We now need 

to know the effect of thi s convol utlon on the peak amp l i tude of the 

continuous "noise/interferencett o that we can ratio the 

signal spectrum of peak 1 to this spectrum to 

get a si gna i -tominterference ratio. I f th8 noise spectrum i s much 

wider tha the signal spectrum, then the peak amplitude of the 

convolved spectrum is, for unity signal amplitude, 

Where, B2 is the signal bandwtdth 

SIO is the original peak before convolvln~ 

As this bandwidth is equal to that of the interference process and 

is equal to unity from the normal ization of Figure 413, the convolved 

peak is equal to the original peak and ~igures4la&Cb apply dlractly 

tor rat i o i ng. I f the resu l tant noi se/ 1 nterf erence spectrum 1 s eaua! 

in bandwidth to the signal spectrum, then the peak amplitude of ihe 

convolved spectrum is ( again assuming unity amplitude for ihe peak 

of the signal spectrum 

Where, Sn, i s the spectrum of the i nterference 

normalized to both unity peak and bandwidth 

4 

It i s reasonab l e to expect that the val ue of th 1 s 1 ntegra l wi l l be about 

1/2 so, under that assumption, 3 dB must be added to the desired signal 

to noise ratio before using Figures 41aA dlbto obtain a value of PL 

X. 

The remain i ng prob l em i s then to bound p2 i n tens of the requi red 

values of the des i red si gna l strength an# an assumed i nterferl ng 

signal strength in a radio sense. Assume the interference is of ths 

second type with the des i red si pna l amp l i tude be1 ng 6 and the amp l i iude 

of the i nterferi ng signal being A. This is shown i n the "undulaii n~" 

phasor triaole of angle mdulation, Figure 42 . If the anale be+ween 

9 and the resultant of A 6 0 is taken to be Px, then a retio of B/A 

can be interpreted as a signal-to-interference ratio. The value of P 

so determined wl l l also be the value which must be beaten in terms oT 

phase error(due to frequency offset and phase path difference) in order 

to permi t commun i cat ions through a s i mu1 cast f 1 nge region. 

I f the requi red S/N is taken to be 13.5 dB for 12 dB S INAD, then we 

must look up 13.5 + 3 = 16.5 dB on Figure 41b, or 

This gives an rms phase deviation, P , of 15.7 degrees which, interpreted 

a si gna I-to-i nterference ratio, i 1 1.4 dB. For the second type of 

'4 nterference, th i s def i nes the capture ratio to ensure 12 dB S I NAD. As 

a practical matter, a reed i b le sl gna 1 can be obtained for a ratio more 

near ly 6 dB. W i der band FM woul d result in even a sma l l er capture ratio 
Figure .: 42 

Familiar Phase Modulation Triangle For Two Signals 
as is our norm l experience with FY radio broadcast reception. 

Consider the 15.7 degree rms phase deviation in tens of the requirements 

it w i 1 l i mpose for s i mu l cast operati on. Let us f i rst eva l uate the "s l i p" 

in carrier frequency to produce this rms phase error. The slip is 

1.04333 wavel engths. Assume a mnof i lar mode */k = 3 so that a wavel ength 

at I MHz is approximately 300 feet. If a desired comunication range 

of 3 mi l es is assumed, then the number of wavel engths is about 53 so 

that the "slip" per wavelenoth Is 0.00082. Considering that the desired 

maximum frequency off-set would be at least an order of magnitude less, 

the requ i red frequency accuracy i s 0.00825. Th i s assumes comp l e$e 

homqeneity in the mnofi lar mode constituitive characteristics. 

In terms of audio phase to cause the same effect, the phase equals 

2~r(Af = deviation 1 , radlans 

where fm is the mdulati ni ng frequency. For a mean mdulail ng frequency 

of I kHz, the audio modulating frequency must be control led to within 

14.6 Hz maximum. 

5.3 ANTENNA CONS l DERAT l ONS 

Designs fpr MF wireless radio system antennas include: . 6 Portable antennas 

Veh i cu l ar antennas 

Base Station antennas 

Current transformers 

Unti l recently, on l y Iwo types of antenna.- designs were avai lab 1 e 

corresponding to the older prototype system radio equipmnts. Both 

the South African ECAM and Co l l ins Portab l es used a grouping of wi res 

( without particular regard for spacing or orientation inside a 

rigid tubular oval shaped enclosure. The antennas had nominally 7 

. turns. The Collins antenna had 7 ohms of segies resistance before 

matching ( @ 520 kHz 1, approximately 0.2 rn of area, and a Q of 44. 

The ECAM antenna was tuned to 335 kHz. Both these antennas were 

matched to 50 ohms at a single frequency. With 20 watts of input 

power, the Portab l e antennas cou 19 achieve a magnetic current moment 

( NlA of about 2.5 amperemmeter .turns. 

The other antenna type was a large single-turn rectangular Base Station 

antenna, approximately 2 meters by 7.2 meters which could develop a 

transmit NIA of 14 with a 20-watt radio and which would enable Increased 

receive system sensitivity in quiet areas of a mine. 
The major di ff icul ty with these early Portable antennzs was that 

the para l lel resonant frequency was low enough that performance near 

the high end of the MF region ( of the order of 1000 kHz 1 began to 

degrade significantly. This is illustrated graphically In the impedance 

data shown in Figure 43 . The use of spaced optimal ly arranged turns 

( so as to minimize and distribute the winding capacitance 1 was 

expected to reduce the impedance level and improve the available tuned 

bandwidth characteristics over a range of MF frequencies. Add i t lona l l y, 

the possibility of an integral connection between a Portable radio 

package and the antenna is expected to lnprove perfornance through 

the el imination of a transformer and/or matching circuitry, with an 

attempt being made to series-tune the antenna and derive it essentially 

directly from the PA output impedance level. 

A design algorithm was developed for use with multi-turn loop antennss 

to enable opti mi zation of antenna parameters. Thi s a l gori thm, g i ven 

to fol low, was first used to design a suitable mechanical ly rugged 

antenna for vehicular use. 

The antenna inductance, L , is given by 

where, L is the low frequency lnduciance given by 0 

= 0.02339 n2 [(s, + s2) log 2s l s2 

Lo 10 nD 

- 5, log 10 ( S, + g ) - s2 loglO ( S2 + g ) J 

mi crohenr i es 

s2 are the side lengths In inches 

g Is the diagonal in inches 

n is the number of turns 

D Is the wire separation In inches 

fr is the self resonant frequency given by 

C Is the dlstrlbuted capacitance of one turn 

and Is 
cor h- ' (- U~ 1 (36 x lo9) d 

1 is the length of one turn in meters 

d fs the wl re diameter in l nches 

D Is the effective wire separation In inches I 

Dl is greater than D by about 17% 

The antenna resistance, R , is gi ven by 

where, for copper, 

R i s the low-frequency resl stance gi ven by 0 

-4t 3 n 4 i n inches 

The NIA product for matched condi tions info 50 ohms is given by 

NIA = NA I 

0 

where, IO is the input current into 50 ohms 

(exp. 0.632 amps for 20 watts 1 

The antenna resfstance Ts that for sol id or stranded copper wire. The use 

of Litz wire has been considered durlng this program to reduce the wire 

resistance component of the total antenna series resistance including losses 

external to the winding. 

Lltz wire consists of a number of separately Tnsulated strands woven 

or bunched together so that each strand tends to take a1 l possible 

pos 1 t ions I n the crossect i on of the ent l re conductor. The purpose of 

Litz wire Is to reduce skin-effect losses by distrlbutlng the flow of 

rad i o frequency current more un T forml y over the w i re crossect i on. 
l OCOO 

FKO2ENCY - Ci2 
The resistance of Litz wire is frequency dependent with the resistance 

being a function of the overall wire diamter, d, the strand diameter, d 

and the w i re-w i re spac i ng, D. A low f requencl es, the use of Li tz w i re 

s' 

results in a significant reduction in the low-frequency ac resistance, R . At higher frequencies, typical l y I - 3 MHz, the advantage disappears ando 

Li tz w i re can actua l l y have a greater resl stance than sol 1 d wi re. This 

latter effect is primarily a function of the strand diameter, d , and 

operation at hi gher frequencies requ i ras a sm l l er strand dl ameaer and, 

hence, mre strands for a fixed desl red wl re diameter. 

Terman gives an expression for the ratio of R to Rdc for Litz wlre. 

Fo antenna design, we are mst interested in th8 ratio R / R 

so that the R LITZ can be used wlth the loop antenna desTgn aig0r??%!' 

The author hag never seen curves of this ratio plotted in the l 1 terature, 

so these curves as applicable to antenna design were developed as part 

of this program and should serve as a standard reference for the future. 

The appropriate formulations for Ro / Rdc and R /R wlll be 

der i ved and then rsti oed to obta 1 n \he above 1neasur8~g\~ tz iFre 

advantage for antenna desl gn. 

For a sol id wire, 

Kbm 

L where k for rnulti layered coi Is &( - ) 

D 

with Kb/D = 5 typically and with rn 3 

layers typically, so that A = i(15) = 56.25 

G is a proximity factor for multi layer 

coils varying nearly linearly wlfh x 

( x = 0.1087 d fi for copper) for larger 

va l ues of x so that G is approxl mate l y 

equal to 0.0439 d f. 

H is the ratio by which Rdc of an isolated 

wire Ts multiplied to give Rac and = 

approximate l y 0.0962 d fi for copper. 

therefore, d 

Roso~~~ ' Rdc = 0.092 d fi + 2.469 d 6 ( 

For Litz wire, d 

2 

'~LITZ ' 'dc 

= 

=l+n G(-1 [2 + A (-1 

cl D 

4 -4 d4 

where, G = approx-. x 164 = 0.878 x 10 s 

f2 
A summary of the performance achieved In the vehicular antenna design 

is given in Figure 44 illustrating NIA vs frequency and In Table 5 

i l l ustrat i ng the partition i ng of l osses I n the prototype hardware 

at a part i cu l ar frequency. 

Use of the desi gn algorithm has revealed several important aspects 

of MF multi-turn loop antenna design, which include: 

There are two optimum approaches for the design of these 

antennas which depend upon power level and whether or not 

the antennas are matched to a coaxial line irnoedance 

before connecting to the radio. 

One approach enta i I s a "hi gh i mpedance", many turns desl gn. 

The other approach enta i I s a " I ow impedance", few iurns des i an. 

The opt i mum hi gh i mpedance des i gn is a l so opt i mum for 

intrinsic safety and is also "inherently" intrinsically 

safe ( for only a 5-watt radio, either design approach can 

easily be made intrinsically safe]. 

The "high impedance" approach is to operate the antenna at as high an 

impedance level as possible for as high a raw antenna Q as possible; then 

use fixed series resistance t.0 de-Q the antenna' to the propoer bandwidth 

( which a l so aitomatica 1 l y provides DC current-1-i mi ti no resistance. This 

means us i ng as many spaced turns as possi b l e before the N I A beg i ns to 

drop ( and also before the i nductance enters the constant-energy portion 

of the i ntri nsic safety curve for the chosen DC supply voltage 1. This 

type des i.gn has been used for prototype vehicul ar antennas. Use of Litz 

w i re shou I d be made to provide as near constant a bandwidth as poss1 b l e 

by maxi mizi ng the ratio of fixed added resi stance to wi re resistance. 

The "low impedance" approach is to use only a few turns and keep the 

impedance level as low as possible. The number of turns is dictatsd 

by the number requ i red to enter the near-constant N I A regi an of operat i on. 

and also to provi de maxi mum drive current from a di rectly coup l ed PA. 

The des i gn character i st i cs ach l evab l e with a Portab l e antenna are i l l ustrated 

in Table 6 . The most critical aspect of Portable antenna design is the choice of 

operating bandwidth so that the potential detuning of an operationally 

requi red flexible antenna can be accomodated. For a narrowband FM radio 

with a modulation index = I and with 2 3 Hz deviation, the 10 dB 

bandwidth is expected to be about 8 kHz so that an antenna bandwidth of 

12-15 kHz should be adequate. This means that the rnaxlmum allowable 

antenna Q will be less than 100 and probably of the order of 67. 
3 KHz BANDWIDTH 

SOLID WIRE 

UNPADDED 

00 1000 

FREQUEI'JCY - KHZ 
PERFORPANCE D I AGXGS 1 S FOR VEE i CULA2 ?FIGTOTYPE 

ANTENNA AS GBTAlNED 

DURING PELIMINARY TESTING @ 476 KHZ 

ANTENNA TUNED AND TRANSFQRMED 

W l TH TUN1 NG CKRT IN ENCLOSURE 

ANTENNA TUNED AND TRANS FORMED 

W lTH TUN l NG CKRT NOT ENCLOSED 

ANTENNA TUNED BUT NOT TRANSFORME3 

W iTH TUNING CKRT NOT ENCLOSED 

ANTENNA NOT TUNED( RAW AATENNA) 

TUN l NG CAPAC ITORS ( ' 100 VOLT 

St LVERED MICA) 

TRANS FORME2 

ENCLOSURE 

3.63 OHMS OF LOSS 

. 4.23 03MS OF LOSS 

2.42 OHVi OF LOSS 
3 0NNama3a 

u-m~(VOV\mU3 

Y 0.0.-0- ---- 

- ooc 
General ly speaking, the conductor "close coup1 ing" coefficients can 

be expected to vary between 

over the typical transverse crossection of an entry containing 

conductors; depend i ng on the conductor conf i gurat i on and the separat i on 

distance between the radio antenna center and the conductor(s) center, 

Considering the most likely operating positions of Portables and 

Vehiculars in the entry crossection, the Portable coupling coef+icienis 

are expected to be 

and for Vehicul ars 

-40 dB to -50 dB 

,027 dB to -37 dB. 

The presence of a vehicle in the entry crossection Is expected to enhance 

the vehicular coupling approximately 3 dB from that at the same location 

using the same antenna ( but with the vehicle absent 1 if the antenna 

is mounted on the side of the vehicle closest to the conductor(s) ( assumed 

near a rib 1, If the antenna is mounted on the other side of the vehicle, 

no coupling enhancement is expected. 

The maximum transmit coupling Is bounded and is expected to be about 

-28 dB ( -30 dB is obtained using the simple CT formula previously 

presented for NA = 1.4, Zo = 50 ohms, r = 0.3 meter. That this Is true 

can be vi sua l ized from the fol lowi ng argument: 

The surge impedance of the transmission I ine formed by the 

AC power cab le i n close proxi mi ty to the roof and ri b has 

to be in the vicinity of 50 ohms. Because the " l I nel'/cab l e 

goes in two directions, and assuming match, the series 

impedance level of this line Is about 100 ohms, The total 

series path resistance of a typlcal transmit loop antenna 

of near-optimum desi gn is about 4 ohms, 

Now, coupling from a transmit loop to the AC cable is 

equi va l ent to using a transformer whose secondary Is 

constrained to always be I turn. As the transmlf loop tuned 

impedance is always less than the surge impedance(x21, the ideal 

coup l I ng for maxi mutn power transfer wou Id be from a 

transformer with a fractional turn on the primary. This 

cannot be in the physical world and, thus, the "avai lab l a" 
transformer is always "reversed" from that which we would 

like. Thus, for very close coupling, one could argue that 

the best transformer has just 1 turn on the primary. I f 

we had an ideal transformer and the coupling were perfectly 

tight, then a resistance level of 100 ohms would be 

"reflected" into the primary instead of the typical ly 4 

ohms when loosely coupled. Thus, for a fixed power i nput 

properly matched, the available current drops by a factar 

of 25 in going from the loosely coupled to the tightly 

coupled case, which is - 28 dB. 

Th i s transmi t coup I i ng bound was measured experi mnta I l y vl a transmi tt i ng 

from a Base Station antenna to a section of monofilar line placed over 

ground ( the experiment was conducted on the surface 1. The results of 

this testing are shcwn in Table 7 . Note that the coupling is quasiindependent of the transverse spacing of the antenna from the line. 

This i s due to "overki I 1'' i n antenna size as the antenna l i nks essenti a f l y 

a1 I the magnetic flux surrounding the I ine conductor at a! I ranges. 

This same effect can be expected in a mine and, thus, a large Ease Station 

antenna located antwhere in the conductor entry and oriented for maxirnurr 

coupling can be expected to couple as well as a very close spaced 

( to the conductor) current transformer. 

Perhaps the most accurate coup l i ng level s for more comp lex geometri es 

can best be determined using the graphical fleld mapping technique C quasistatic l imit for the mnofi lar mode transverse fields ). Coupl lng estimates 

have been made and the results as shown f n Figure 45 for fQ /X of A L the antenna equal to 55,000 which is appropriate for the vehicular antenna. 

The coupling coefficient, CR , is given by: 

Where, n = the number of flux 11-nes per 360 

degrees of rotation around the 

conductor ( 64 for the charts shown 1 

R Is the loop antenna series resistance 

( 18 ohms used 1 

AR i s the curvi 1 i near square dimens ion 

in meters 

For use in two-frequency systems, a l i Portab-Pe & Vehicular and selected 

Base Station antennas and current transformers will have to be tuned or 

tunable to both frequencies. This can be accomplished passively ( no tuning 

control required 1 or actively via a switch line from the radlo. The 

acti.uel y ,tuned-antenna i s envi sioned as havi ng two separate match I ng 

circuits which are switched into place on command. The control Is 

envisioned functionally as follows. Normally ( without a control signal 1, 

the antenna i s tuned to the recei ve frequency. I f the rad lo control s 

are set to transmit the second frequency, a key I i ne Is energi zed so that 

when the radio is keyed, the antenna tuning circuitry Is switched. 
CONDUCTOR 

END 

TABLE 7 

MEASURED CURRENT COUPL 1 NG COEFF l C I ENT VS 

TRANSVERSE SPACING OF A BASE STATION LOOP 

ANTENNA FROM A MONOFILAR LINE SECTI0F.I OVER 

A CONDUCTING l NTERFACE ( GROUND 1 

COUPLING COEFFICIENT 

TEW INAT I ON LOOP/CONDUCTOR SEPARAT I ON - FEET 

l MPEDANCE -- 3 6 12 24 - 48 

25 ohm -27.6 

100 -21.9 -29.0 -28.4 -26.2 -27.2 . . 

infinite. -30.9 

B 50 -30.4 -31.1 -28.7 -26.6 -27.4 

infinite -31.9 

5.5 PROTOTYPE EQU l PMENTS 

The purpose of this subsection is not to present an exhaustive descrlptlon 

of equipment avai lable to-date; but, is to briefly review the operati ng 

parameters of these equipment, to discuss receive system sensitivity, 

and to present additional detail on the prototype vehicular antenna 

des i gn . To date, only four prototype radios have been built and evaluated on a 

1 i mi tad bas i s i n coal mi nes. Trad l tiona l tro l leyphone manufacturers 

such as Femco and Comptro l are adapting the1 r equi pment for use in 

trackless haulage applications. The MF prototype radios to-date Include: 

South African ( ECAM 1 

e Collins ( built for USBM 1 

Lee Engineerin9 ( Ferry ~elernetr~ 1 

South African ( RACAL 

The ECAM and Co I l i ns radio packages for Portab I es were very si mi l ar; bel ng 

roughly 10f' x 10" x 4" with self-contained batteries, top-mounted controls, 

voice and tone signalling, and a nominal 20 watts of power. These radios, 

furthermore, shared a nearly i-dentica l antenna desl gn wnsi st1 ng of about 

7 conductors hoysed i nside an ova I-shaped ri gi d tube rough I y 1-1 nch i n 

diameter, 0.2 m area, and separately tuned to 50 ohms at single 

frequencies ( 520 kHz for Co l l i ns, 335 kHz for ECAM 1 for connect ion to 

the radios via a short length of coaxial cable. The major differences 

consist of mdulation type and operating frequency. 

The Collins radio used narrowband FM. The ECAM radlo used SSB. The ECAM 

radio used a small handset whereas the Collins radio used a speaker mike. 

The ECAM radio was housed in a canvas carrying case wlth a shoulder strap 

whereas, the Col lins radio was intended to be belt-mountable. Coll ins 

provided a table-mountable Base Station version of their radlo with 

internal tuning for the large antenna. The Col tins radio employed a 2 dB 

noise f i gure recei ver. Comparati ve testi ng of these two radio types i n 

quiet mine areas produced nearly identical communication ranges. 

The Lee Engineering radio is a smal l unlt of approximate dimensions 

24" x 7" x 7" powerable from an external 4.5 volt battery, expected to 

be the cap lamp battery. This SSB radio was factory tunable to a variety 

of single frequencies over the MF range with a power output of 6-7 watts. 

The radio is i ntended for belt mount1 ng and uses top-mounted contra l s. 

This radio radio has been manufactured for Lee Engl neeri ng/CONSOL by 

Ferry Telemetry of Hiawatha, lowa.in Portable versions only. The antenna 

i s f i exi b l e, s i ng I e-f requency matched, and connects to the rad 1 o package 

via a short length of coaxial cable. Limited testing by BuMInes of this 

radio in a DC mine resulted 1n.llmited ranae which, presumably, was due 

to the inherent impulse noise susceptabi llty of SSB radios. The ECAM 

radio was never careful ly tested in a heavlly impulse nolse environment. 
The most recent prototype radio available is the South African RCAL 

unit operating at a I-watt level using SSB modulation and with orovisions 

for tone signal ling. This single-frequency radio is factory tunable 

via a programmable divider to a variety of frequencies in the YF range. 

The tad io operated from a se I f-conta i ned battery and i s i ntended to be 

carried on a persons chest. The radio package itself is approximately 

3" x24" x 14" . The antenna is a flat canvas/wi re strap of the bandoll er 

type and the radio attaches directly to the antenna via a special quick 

disconnect arrangement. The radio has been found to be susceptable to 

impulsenoiseduetotheautomaticnon-adjustableAGCtypesquelch. A 

100 usecond impulse of sufficient amp1 ltude will shut the radio down 

for approximately two seconds. The RACAL radio Is also packaged in a 

table-mountable Base Station version. 

A prototype vehi cul ar antenna has been bui l t and bench eva l uated; the 

antenna employing a single-frequency Integral matching circuit to 50 

ohms. The design employs a rigid rugged electrostatic shield with a 

single circumferential slot to enable radiation. When balanced-fed 

with the shield at ground potential, the shield has no effect on The 

basic winding electrical characteristlcs. The antenna, depicted in 

Fi gures 46&47 is attached to a frame which provides for magnetic mount1 ng 

to a flat metallic ( ferrous 1 surface on the vehicle. The rigid loop 

radiator is positionable for vertical, 45-degree, and horizontal loap 

plane orientations to accomodate low vehicle head clearance when 

necessary. The antenna w i nd i ng charaderi st 1 cs are dep Lcted i n Fl gure . The radiator consists of 12 circumferenti a l I y spaced turns of Lltz w i re 

in a rectangular 6-Inch by 36-inch shape. The tuning characteristlcs of 

the prototype antenna(s1 as bui I t are gi ven i n Fi gure 48 . The recei ve system sensitivity is large1 y deteni ned by the antenna 

size. A simple formula for computing the sensitivity Is given by: 

Where, Af i s the no1 se bandwidth , Hz 

Q is the antenna q~ality~factor 

A is the antenna area, m 

N is the receiver noise figure 

The Proport i ona I i ty constant has been adjusted to def i ne the nl n 1 mum 

incident magnetic field strength to achieve 12 dB SlNAD for narrowband 

FM modulation ( 13.5 dB signal-to-noise ratio per Hamshur 1. 

A Potentla1 ly more accurate sensitivity expression is that after the 

method of Shimbo, and is given by: 
-- -- .- . --. - VM I CULAR ANTEN~~A PROTOTYPE 

SHOWN WITH LOOP IN THE 45 DEGREE 

OR l ENTAT I ON 

-- . - - - 

VEH I CULAR A; ITE! I! IA PROTOTYPE 

SHOWN WITH LOOP IN THE HORIZO!.ITAL 

OR I EPTATI 01 

FI GURE 46 

VEH l CULAR A?ITEt,JFJA PROTOTYPE 
F l GURE 47 

W I NDI IJG AIID kII RI f4C COI IF I GIJRAT I Or4 TOR TtIE VCH I CULAR Al.ITTfJt\lA PfiOTOTYPE StIOW I1.G 

THE COi\llJECT lOl.1 ARRAI%JGEI!Er\JT OF TURI4S 1-0 1-11 14 Il~ll ZE [)I SIR I BIITED CAPAC lThl4CE 

---. - -..--- 

~r.-'7 

C I RCUlb!FERENT I AL GAP 

6 I IJCHES 

.___I 

- -a 

1 

---UICIIL-. 

ELECTROSTAT I C S1-l l t Lfl 

-- ---.----C*\--U~.U~U~U~U~ UhUhUhUh__N~~~-~~.~~~~~~.cII

- . 

I BALANCED TEED LINE . 

Where, f= 41FNA x lorn7 

F is the receiver noise figure r 

k is BoltzmanTs constant 

To i s the ambient temperature 

R is the antenna series resistance L 

A is the antenna area, rn 

2 

N is the number of turns 

Hn is the external noise field strength 

Comparisons of sensitivities for the Collins FM prototype radio as 

calculated by the simple formula( Hamshurl, by the method of Shlmbo, 

and as measured; and, as ca lcul ated by the simp ie formula for the RACAL 

radio are given in Table 8 . 5.6 APPL I CAT I ON OF OTHER TECHNOLOG l ES 

The system design put forth in Section 3 is capable of providing a 

compati ble interface with either an existi ng pager phone system; or 

else, with a new select channel FDM type multiplex phone system ( should 

one be developed 1. Add i t iona I I y, i f MF I s used for long d i stance 

local area-to- loca l area transmi ssion, a means to provide either dl rect 

radiation from the bifilar mode phone I lne, carrying the MF signal, at 

discrete locations or else to convert the bi f l lar mode to the manof i l ar 

mode transrni ss ion Es needed. 

Baseband aud lo s i gna l I i ng and control l i nks from Base Stat 1 on to Remoie 

Base repeater el ements' could provi de the i nterf ace to ex1 st i ng pager phong 

systems. Similarly, an above-base-band translation frequency on the 

same links could be made compatlble wlth an FDM channel freauency on 

a select-~cbannel phone system. Alternatlvely, although not included 

as a link signalling option in Section 3, TOM signal ling could be 

employed on the same I i nks; however, the MF system e lement des i gns wou l d 

become mre comp I ex. 

MF energy can be extracted from a b 1 f l lar mde phone I 1 ne at ,d l screte 

locations or in desired localized areas by two means; placing balanced loop 

antennas in shunt across the line or by purposely unbalancing the line 

and favoring the excitation of common ( monofl lar ! mode currents. The 

excitation of a single antenna can, at best, extract only a portfon of 

the available energy from the line. Also, the antenna then radlates direcily 

over a I irni ted area and/or excl tes mnof 1 lar current in the phone l 1 ne 

w l th substant i a I "convers Ion l ossff . &re ef f 1 ci ent energy extract ion can 

be accomplished by either using a sequence of spaced antennas or else, a 

sequence of spaced " unba lancers" .on the I l ne act1 ng as a I ea ky feeder 

and converti ng the energy from bi f I l ar to monof i l ar. 

For mst efficient mode conversion, the distributed loading must slow the 

transmission si gnal wave down so that the phase veloclty matches the 

phase velocity of the mnofi lar mode. An aid in visualizing this concept 

is afforded by considering spaced antennas as an array. The phase of the 

antenna currents must match the phase of an assumed mnofi lar mode 

travel i ng wave at the discrete locatfons of the element antennas. Also, as 

with leaky feeder structures from the blfllar exciting wave pain: of 

view, the periodically loaded modal eigen~lues must be between -I 

( backward wave l and +I ( forward wave 1 placing the "rode" I n the "v1 sl b lev 

region. 
TABLE 8 

CO?PUTED AND MEASURED S ENS [ T I V I T I ES 0 F RACAL Ai4D 

COLL l NS PROTOTYPE PORTABLE RAD l OS 

(1 ) Col i ins fm radio for 12 dB 

SINAD 8 2 dB noise figure 

@ 520 KHz, 12 KEz BW 

(2) RACAL SSB radio 

0.2 uv for 15 dB S/N 

Se~sitl viiy, d3 ebove I ua/m 

(a1 Hamshur -34.0 

(b) Shirrrbo -37.6 

(c) measured -35.5 

For 10 dB S/N -34.9 
Spaced antennas can accomplish this slow wave loading with shunt 

capacitance, meaning that the antennas must be tuned with their 

input impedance being capacitive. Alternatively, the use of unbalanced 

devices on the line must effectively use series inductance to slow 

the wave down. The efficient extraction on energy from the bi f i l ar 

line does involve some impedance matching for antennas and/or minimlzlng 

the reflection of Incident energy when using line "unbalancers". This 

may require both shunt C and series L so as to be able to vary ihe 

characteristic impedance of the line. It should be possible to build 

"clip-on" devices to be periodically spaced on the phone line for 

mode con ve rs i on, 

This section deals with the qua1 itative comparison of narrowband FM vs 

single side band ( SSB 1 modulation and, given FM as the choice for 

mine wi re less radio systems, the factors governing the frequency 

separation requ i red for operati on of the Repeater E l ements. 

The early South African ( ECAM as well as the more recent RACAL and 

Lee Engineering radios have employed SSB modulation. The Collins 

prototype radios employed narrowband FM ( m = I, + 3 kHz deviation 1. 

Unfortunately, a l l early comparisons of ECAM and l l l ns radios were 

performed in quiet areas of mines; the two being very nearly equal In 

performance i n t h i s type of envlronment. Only recently ( within the 

past year have SSB radios been tested In potentially noisy areas 

of mines. The results of recent tests have suggested that the SSB 

radios are inherently susceptable to mine nolse; particularly Impulsive 

noi sea 

The hypothesis for the impulse noise susceptability of SSB radios resides 

in the i nherent l i neari ty over a l arge si gna l and noise dynamic ran* 

requi rements i mposed on SSB rad i os for use in mi nes. The I l neari *,of 

course, is inherent to SSB modulation. To provide good dynamic range 

for steady state signals, SSB radios employ a fast-attack/slow-release 

AGC. The hypothesis contends that the occurance of nolse Impulses Is 

such that the fast AGC attack "shuts the radio down" and another impulse 

occurs before the AGC can release so that the radio stays "shut downv. 

The alternative of "opening up" the AGC circuitry would cause excessive 

distortion when the Impulses are of much higher amplitude than the slgnal. 

A detailed statistical analysls of impulse noise characteristics In DC 

mines has not been performed, but the data taken in the Harewood mine 

suggests that 

The average impulse arnpl itude is about 18 dB above the averaoe 

"broadband noise level . 

The average noise impulse basewidth varies between 333 and 1300 

mi croseconds 

The average occurrance rate of I mpuf ses Is between 2-6 mi l l l seconds 
This hypothesis is based on operation lnclose proximity to mlne wiring 

conductors and, in particular, in DC rnlnes, In quiet areas of mines, 

which probably comprise all areas remved at least 1-2 entries from 

conductors, the c lass ic advantage of SSB in provi d i ng better i nte l l i gi b i t i ty 

than FM for signals near threshold holds. The choice of mdufation type 

is then dependent on the expected Iocatlons wIthin mines where the redlos 

will be operated. In DC mines, the choice Is clear; M will be necessary 

to effect operation near conductors at a l I, For trackless haul age 

operation in AC mines, the choice based on the above arguments may not 

be so clear; not only in that impulses of hlgh amplitude will be less 

likely to occur, but also in that the expected signal-to-noise dynamic 

ranges are smaller and rather well ordered. Perhaps the posslbie eventual 

usage of MF radios in meta l/non-metal mines provides the "push" for FM 

where, again, the noise environment near conductors Is expected to be 

impulsive. 

Other argurnents can be made for the use of FM over SSB. The author's 

contention for the seiection of FM over SSB Is built on three fectors: 

The potential advantage of SSB over FM in threshold sensItivlty 

( intelligibility 1 is af marginal significance in the first 

place and represents about a maximum of 7 dB irnprovemenf 

assuming that narrower bandwidth antennas can be used for 

receiving SSB signals ( a questionable assumption at best 

if flexible Portable antennas are envisioned ). 

Although the SSB system is perhaps mre conservative of 

transmitter RF power than is FM, the number of low [eve l class 

A stages required equalize this potential advantage In -arms 

of battery drain. The FM system is expected overall to operate 

longer from a glven battery than is an SSB system 

Use of narrowband FM is compatible with FSK data transmission 

( equipment design wise via circuit commonality 1 so that 

comnon radio desi gn techniques apply for both FSK and FM 

voice systems 

The comparison of intel iigibil ity of FM vs SSB is summarized in Table g . The maximum potential advantage of SSB, which occurs for a low arltculatlon 

index of 0.2, presumes a 3 dB narrower bandwidth antenna, On this basis, 

SSB is potentially better than FM in quiet areas by 7 dB on an average 

power basis with SSB and FM being about equal on a peak power bask. 

The frequency separation requi red at MF for repeater operation to 

essentially provide the full receiver sensitivity 1s governed prlrnarIly 

by modulation spectrum fall-off as opposed to broadband noise. This is 

because the spectral width of FM voice signals is a greater percentage of 

the operating frequency at MF than It is, for example, in the VHF land 

mobile bands ( where broadband noise predominates 1. The broadband noise 

of a well designed phase-locked-loop exciter in a 12 Wz band is expected 

to be 80-85 dB down 20 kHz away and 110-lt5 dB down a Wz away from ihe 

center frequency. 
TABLE 3 

SUMMARY COMPARISONS OF FM VS SSB MODULATION 

BASED ON INTELLIGIBILITY 

NON- I WULS I VE NO l SE 

ARTICULATION AVERACZ POWER BAS l S 

l NDEX COMF'AR I SON 

SSB BY 4,O DB 

0,3 SSB BY 0.5 DB 

I F IT WERE POSS 1 BLE TO DES l GN TO A STABLE 3 WZ BANDW I DTH, 

THE MAXIMUM SSB ADVANTAGE ( ARTICULATION INDEX = 0,2 1 

WOULD BE 7 DB 

SSB, OPT1 MALLY CL I PPED, HAS ABOUT A 7 DB PEAK-TO-AVERAGE 

POWER RAT 10; THUS ASSUMING THE MAXI MUM ADVANTAGE, SSB & FM 

I N BROADBAND NO l SE ARE ABOUT EQUAL ON A PEAK POWER BAS l S 
The spectral roll-off of a narrowband FM signal of m=l is Illustrated 

in Figure 49 which shows a 12 dB/octave rol I-off. To achieve ful l 

receiver sensitivity, the recelved signal should be about 160 dB below 

the output of a 5-watt transml tter. A graph show i ng the composi te fa l I-of f 

of a 4-pole filter plus normal spectral roll-off is given in Figure 55 . The composite rol I-of f is expected to be 36 dB/octave so that a l eve1 

of -1 60 dB is achieved about 65 kHz away. Thi s represents rough l y a 105 

frequency separation. Note that at 65 kHz, the spectra l port ton of the 

rol I-of f of about -7 1 dB i s rough l y 20 dB higher than the expected 

boradband noi se l eve I of -92 dB. The mi n i mum frequency separat ion i s, 

thus, expected to be 10%. . 

5.8 INTRINSIC SAFETY CONSIDERATIONS 

This section assumes that the MSHA requirements for obtaining Intrinsically 

safe ci rcui t desi gn have been updated from Schedule 2G to those of 

UL-9 1 3. 

The design of antennas and transmitter RF circuitry for MF systems can 

easi l y be made i ntr i ns ica I 1 y safe for a nomi na I 5-watt power I eve1 for battery 

voltages between 4.5(cap lamp) and 24 volts. The antenna circuits operate 

in the constant power ( voltage-current curve rather than'the canstan" 

energy region of the curves. The antenna desi gn parameters are such that 

the use of blocking capacitors to Isolate the antenna circuit are not 

requi red. Hi gh impedance antenna des I gns ( such as are requl red for 

optimum vehicular antenna operation can be shown to be inherently 

intrinsical ly safe. Low impedance Portable antenna designs can be made 

intrinsically safe with the addition of small current limiting resistors 

which will not degrade the RF efficiency of the antenna. 

This section presents an "appeal1' to provide a conslstant and systemiic 

means for the intrinsic safety evaluation of MF antennas. Additionally, 

the subject of "AC intri nsic safety1' is important for ensuri ng ihai 

all transient current levels are accounted for. 

1 ntrl ns ic safety requi rements are geared toward prevent1 ng potent1 a 1 I y 

dangerous dc sources from producing arcs which might explode a methaneair mixfure under fault condltlons in coal mines. The curves for minimum 

vo I tage-current comb i nations, mi n i mum i gn it ion current in 1 nductl ve 

circuits, and minimum ignition voltage in capacitive clrcuits apply . strictly to dc excitation of circuiSs. The ac excitation of antenna 

circuits at radio frequencies are not explicitly covered by the curves. 

The proceedure for inductive circuit protection now being applied 

involves isolating the antenna circuit from potential dc sources 

through the use of blocking capacitors. The requirements for these 

blocking capacitors come from UL-913 whereby two capacitors are placed 

in series and then tested for voltage breakdown with an ac vo I ?age *keve 1 

equal to twice the working ( potential fault 1 voltage + 1000 volts rms. 

It is reasonable to expect that arcs from ac sources at radio frequencies 

under fault conditions could explode a methane-air mlxture In a circuit 

not intrinsiciy safe at dc. It Is also reasonable to assert that dc 

clrcuit performance represents the worst case; thus, a clrcuit which IsT 

"dc intrlnslcally safe" wI 1 l also be "ac intrinsical ly safe". 

FIGURE 50 

MI Ed l MUM FREQUENCY SEPARAT l ON FOR ACH l EV l NG 

FULL RECEIVER SENSlTl VlTY FOR REPEATERS 

ATTENl 

CS, 24 

RECE I L 

4ITTER 

'ER TH 

PEAK 

RESHOLD 

PO!qE R 
If is probably to the designer's advantage to take any steps toward 

mki ng an antenna "dc intrinsical ly safe", over and above any blocking 

isoi ation, i f thl s can be accomp l lshed without serf ous perforrance loss. 

This could be termed the "inherent safety factor" of the antenna. 

Toward eval uating ac intrinsic safety, it ,may be worthwhl le to define 

operating power levels for which the antenna would be Tntrlnsicly safe 

If the dc and ac sparameters were the same and the dc curves could be 

appl ied. 

It is possible to at least partlallyp-otect a loop antenna without loss 

of performance so as to achieve some Inherent safety. ThIs Is posslble 

because the NIA of a loop antenna of restricted dimensions is relatively 

constant over a range of numbers of turns and because there are ac losses 

in the antenna other than those encountered 'in the wire resistance. 

Specifical ly: 

(1) impedance level; the antenna low-frequency wire resistance 

should be as hlgh as is practical without reduclng NIA in 

order to minimize the peak current which could flow In the 

circuit. This is accomplished by using as many turns as 

possi bie. 

(2) added ser i es loss; the antenna rnatchi ng ci rcu i try 1 asses w i l I 

produce an equivalent series antenna loss resistance In addltion 

to the wire resistance. A lumped current-1 irniting resisto'r of 

value comparable to th6 above loss resistance can be added 

wlthout reducing the NfA significantly, The lumped resistance 

will reial'n its value at dc whereas the wire resistance wil I not. 

It is hewer, in designing to a ilxed allowable wire r6slstance, 

to use Litz wire and then add a lumped current-l imltlng 

resistor than to use solid wire or stranded wire having the 

same res i stance as the LI tz p l us the l umped res l stor. 

Assuming the dc curves app ly, the current in the loop as a function of 

input power is given by 

where, P is the input powei 

1 is the inductance 

(BW) is the 3 dB bandwidth 
so that for a fixed maximum energy level, the at lowable bandwidth is a 

function only of the input power. If for a fixed input power and bandwldth 

the current is to be minim! zed, then the current is inversely proportiona l 

to inductance, so the inductance should be as large as possible whlle st111 

maintaining the bandwidth, 

The minimum ignition current curve Is given for 24 volts and essentially 

plots a constant energy level, which determines the bandwldth power 

relationship for that voltage level. For other voltage levels ( as defined 

on the vol tage-current curve ) , the .constant energy I eve l varies. I f the 

antenna parameters are fixed, as in any particular design, then the 

power cannot be independent of energy level and must fol low the voltagecurrent curve. 

The inductance of the vehicular antenna @ I MHz wl l I be shown in the next 

section to be approximately 190 uh . To l llustrate possible power-bandwidth 

l i mi ts for "ac intrinsic safetyv", ca lculations were made assuming 

( 1) a constant energy of 0.5 mi l l i joule 

(2) energy-power as defined from voltage-current curve 

and antenna parameters 

(3) inherent intrinsic safety provided by 5 and 10 ohm 

current-l i mi t i ng res i stors 

The resulis of these calculations are given in Figure 51. This f lgure shows 

the voltage-current derived condition to be the most stringen? In restricting 

the minimum bandwid+h for higher power levels for a 50 ohm matched antenna. 

Using this condi-kion as the basis, a IO-ohm current limiting resistor ( for 

examp le provi des I nheren-t protection up to a power level of about I I waits, 
- do,: ' ' *- ,, -4- ( = POWEIER/4 ENERGY 

I I 

1-4-1 1.1 1-;.;-1-, 

I, PO55 IDLE AC I NTRl NS 1 C SAFETY CRl TERl A 

~+y~~,--- 242 . ! 'A USIF4G BANDWIDTH OF ANTENNA AS A MEASURE -.+Al 

I SHOW l NG MI !.I I P4UM BANDW I DTII AS A FUIJCT I Ot4 

OF INPUT POWER 

,,:,, *, ,,, ,, . b 

5 I r) 15 2 0 

I I II'IJT POWER - WATTS 

'7 
6.0 SYSTEM CAPAB I L 1 TY DEF40NSTRAT I ON PLAN 

This section containsth e elements of an MF system demonstratlon elan 

based on thepredicted results and configuration alternatives for the 

Lucerne #8 mine from Section 3.5. 

6.1 OBJECT l VES OF DEMONSTRAT I ON/TEST 1 NG 

The purpose of the dewnstration/testing is to: 

Demonstrate the comnunicating capability of a mlne-wide 

MF system desi gn; get mi ne personnel reactions 

Test particular generic radio links and combinattons of 

Radio Terminal Element types independent of the particular 

overa l 1 system con f i gurat i on 

Conf i rm and/or improve upon the MF system performance 

pred i ct i ve mde I capab l l l ty 

Identify any particular factors or features associated 

w l th anMF system and/or the partl cut ar designs of prototype 

Radlo Terminal Elements which will either constrain or 

enhance mi n i ng operati ons 

The overal l demonstration plan should include a period of operational 

usage bymi ne personne! so as to provide subject1 ve i nfbrmation such as 

reliability, mintainabTlIty, user acceptance or rejec+ion, logistics, 

and traffic density/channel ( which may influence the spacing, locatior,, 

and type of Repeater Elements chosen 1. 

To servethese.ends, the demnstratlon/testing plan provides for deflnite 

phases which include: 

Phase I lnstallatlon 8 Scientific Data Gathering 

performed by USBM and/or cornrnun i cation system 

Contractor personne l 

Phase I I Capability Demonstration & Mine Personnel Tralnlng 

i nvo l vl ng technology transfer between USBM/Contractor 

and m[ ne personnel 

Phase I I I Operat iona 1 Eva l uation & Support 

performed by mi ne personne 1 us i ng the system w 1 th 

USBM/Contractor f urn l shed logi st l ca l suppot-? 

At an appropriate time In either Phase I1 or Phase I I I, the plan should 

provi de for demonstrati ng the capab i I Ity to operations personnel of othsr 

mi nes/mi ni ng companies and to commun i cat] on system manufacturl ng 

representat I ves. 
6.2 PROPOSEDSYSTEMCONFIGURATION 

The systemc onfiguration for demnstratlon/testing is pro~osed to 

embrace the use of Portable, Vehlcul ar, and Base Station Rad lo Terrrl na I 

E I ements and of Li ne Amp l i f i er and Remote Base Repeater El ements, Use 

of a Li ne Coup I er Repeater E I ement may be i nc 1 uded i n a sect ion, 

although its use is not further addressed in the technical details of 

the plan in this section, 

Prior to obtaining field strength measurements In the Upper Freeport 

seam, the Lucerne #8 mine was considered by the author to be too smal l 

in extent to adequately demnstrate system capability, Thls was based 

on assuming that the seam characteristics would be similar to those 

experi enced i n the Pittsburgh seam, 

Now, t he Lucerne #8 mi ne appears to be I dea l for system demonstrct ion/ 

testing at MF, This is because: 

The North and South Ma i n areas can be adequately 

partitioned with I iele interference from one ares to 

another expected 

Each North and South ?!ai ns ares can be adequately served 

using a si ngle haulageway repeater ( extended quasiconductor-f ree range i n rooms w i thout cond uctors may 

be i mproved by us f ng an add i tlona l repeater there ) 

basurernents supporting the use of either a Line Amplifier 

or a Remte Base type repeater, Including l nterference 

fringing, can conveniently be made in the general location 

of the portal, 

The particular repeater locations, of Section 3.5, have been chosen 

based on the assumption of using Llne Amplifiers, These locations can 

be adjusted somewhat using Remote Base Repeaters; however, the sslected 

locations are approxi matel y correct for both types. 

The plan calls for testing both types of repeaters in these locatlons 

and, during Phase I ( or perhaps early in Phase il 1 selecting the best 

performing type for continuation into Phases LI and Ill. 

The complement of system equi pments expected to be required for the 

demnstration/testing includes: 

2 ea Base Stations ( one unit underground near the portal 

and one on the surface ) 

2 ea Remote Base Repeaters 

2 ea Line Amplifier 3epeatet-s 

I ea Line Coupler Repeater 
The Vehicular and Portable radio complements consider outfitting two 

sections ( onein each of the North and South Mains 1 plus maintainance 

and supervi sorypersonne l . These comp l ements are i nc l us i ve of: 

18 ea Vehiculars2 ea electrical maintainance jeeps 

2 ea mechanical maintainance jeeps 

4 ea mantrips 

2 ea shop vehicles 

2 ea miscellaneous supply vehicles 

4 ea section ( 2 ea extra for testi ng i n each of 2 

section vehicles 

18 ea Portables8 ea( 4 ea/sectlon) 

2 ea mechanical malntainance foremen 

2 ea electrical maintainance foremen 

2 ea supervi sory or 1 nspectors 

2 ea spares 

2ea shop/porta I area personne l 

6.3 DEMONSTRATION/TESTING TECHNICAL APPROACH 

Phase IThe first step in tesfing is to Install the Base Station plus one or two 

Vehicular radios and to determine the ranges V-V, V-P, P-P, V-8, P-8 

i n operat iona l ly si gn i f i cant areas of the ml ne w i thout rebeaters and 

for both close coup l i ng and remote coup l i ng I-entry away. Th i s tesii ng 

will include determining the effect of line characterlstics; namely, 

taps/branches and SWR ( identifying any "dead" zones 1. 

The second step is to install the haulageway repeaters ( one type at a 

time and to determine V-6, P-B coverage for an assumed single user 

in all operationally significant areas of the mine. Next, the multiple 

user and interferance related characteristics will be determined. These 

i ncl ude: 

The i nterferance f ti ngi ng produced,due to sirnul cast 

transmissions, in the portal area; defining the effect 

'on Base Station reception, i f any 

The threshold "capture" levels for simultaneous mulflple 

users des i r i ng repeater access 

The distortion caused by muitlple "unhearing" Vehlculars 

or Portables accessing the repeaterk) at approximately 

the same amp l i tudef- leve l 

Deducing the ground rules for operation when a Vehicular 

or a Portable radio is close to a repeater 
From these studies, the locations chosen for the repeaters will be 

evaluated and the locations will be modified as required.Bepending 

on the detai led operations in sections, the Line Coupler Repeater may 

be installed, evaluating the range extensions away from conductcrs 

achievable for Portable or Vehicular operation in a quasi-conductorfree envi ronmnt. 

The above scientific studies will be used In conjunction with the 

system performance predictive model, modifying the model ( if reauirqd 1 

toward obtai ni ng compati b I e theoretics l and experiments l results. 

The operational s i gn i f i cance of part i cu l ar commun i cation l i nks w i l l . 

be determined from mine supervisory personnel during Phase I and wi l l 

impact the detai l s of the testing. 

Phase I IThe f i rst step i s to conduct or1 entat i on sess ions for potent i a l user 

personnel on the capability of and the mainatainance of the radio 

system. Specific emphasis will be placed on acquainting dispatcher 

or communication center personnel on the capabilities. 

Some of the Vehicular and Portab le radios w i l l be d 1 ssemi nated 

se l ect i ve l y to mi ne superv i sory and ma i nta i nance personne l for e 

"pre l i mi nary eva l uat i on1' of capab i l i ty and user acceptance, The 

resu l ti of this eva l uation wi l l govern the detai led plans for 

i ncorporat i ng add i ti ona l rad i os i nto :at. system l arge enough for 

a demonstrat i on. 

The next step will involve a brief fami liarization and training 

program ( i f requ i red 1 and then the demonstrati on of the system 

capability to all mine personnel. Some mine personnel will only be 

convinced of the uti l ity of the system once they are actively using 

it; others will require only a comprehensive demonstration of 

capability, 

Phase ll is expected to result in some mdiflcationsof the overall 

conf i guration to accomdate particul ar requi rements. These modi f i cat ions 

wi l l be accomp l i shed prior to a longer term eva l uation program which 

i s the objecti ve of Phase I I I, 

Phase I 11- 

Phase I I I embodies a relatively long term evaluation of the fully 

operat iona l system 1 nc l ud i ng l ogi st I ca l support to be f urn i shed by 

USBM/Contractor. 

The f i rst step i n Phase I I I i s the "hand-of f" of the system to the 

mine for normal maintainance and support. Durlng the first part of fhk, 

USBM/Contractor personnel will periodlcally evaluate the condition ant 

operability of the System Elements, systematically recording the 

reliability/maintainability experiences. This step w1 I I establish the 

true cost basis of such a system to the mine. 
The second step in Phase Ill involves a combined mine/USaM analysis 

of the system benefits, system features, and identification of 

additional features which, if avai table, would enhance the value 

of the system, 

Throughout Phase Ill, control of spare/repair parts inventory will 

be the respons i b i l i ty of USBM/Contractor to ensure proper service 

and the establ i shmnt of records. 

Also during Phase I I I wltl be an organized "public relations" effcrt 

toward technology transfer to the industry based on the "test-bed" 

system under eva I uat i on. 

6,4 DEFaNSTRAT I ONITEST TASK SCHEDULE 

6.4-1 TASK 8 SCHEDULE DESCRIPT1ONS 

Considering the MF System Elements to be on-hand at the start of this 

activity, a program involving approximately 23 months is envisioned. 

Phase I is estimated to require 3 mnths for completion; allowing, 

(I) I-month for initial installation of ?he Base Station 

and selected Vehicular radios 

. - - (2) I-month for gathering scientific data and for the 

installation of rebeaters 

(3) I-month for data evaluation and for Phase I I planning, 

these steps to be roughly sequential. 

Phase I I is estimated to require 8 months for com~letion; at lowing, 

( I I omnth for user or i entat ion 

(2) I -month for prel lmi nary system eva l uation by supervl sory 

personnel and for p l ann i ng the overa l mi ne dernons?r?t i on 

activity 

(3) 2-months for i nsta l lation of the remaining Vehicular 

rad i os 

(4) I-mnth for personnel training and famlllarlzatlon with 

the system operation 

(5) 2-months of capabil ity demonstration via trial operation 

of the ent i re demonstrat Ion system 

(6) 2-months for assessment of results and mine system 

reconfiguration, if necessary 
Steps (I) d (2) performed concurrently, 2-mnths dapsed time 

Steps (3) 8 (4) performed concurrently, 2-months eia~sed Time 

Steps (4) 8 (5) performed concurrently, 2-mnths elapsed tin2 

Step (6) performed sequentially following Steps (4) b (5) 

Phase Ill is estimated to require 12 months, minimum, for campletion; 

a1 lowing, 

(I) 2-months for "hand-off" of responsibillty for normal 

maintainance and support; USBM/Contracfor furnishing 

very close support 

(2) USBM/Contractor vi s its every 30-60 days to exam1 no 

equi pment, and to rev1 ew the system operat iona l 

exper i ence for the rema i n i ng 10 months 

(3) USBM/Contractor provid i ng "on-ca l I" support 2nd h i 55- 

level repai r and mai ntai nance of the system 

(4) USBM/Contractor meetings periodically with mine personnsl 

for overal l reviews; also providing during pre-planned 

demonstration act i vi ti es to the mi n i ng l ndustry 

6.4.2 EST1 MATED LEVEL OF EFFORT 

Phase I is estimated to require the equi.valent of 2 men full time for 

3 months; or approximately 126 man days of effort. 

Phase I I Is estimated to require the equivalent of I man ful l time for 

8 mnths; or approximately 168 man days of effort. 

Phase I I1 is estimated to require the equivalent of man full iime for 

10 mnths and I man for 2 months; or approximately 147 man days of effort. 
7.0 REFE3EXE I F.133 83' MF TEZI-1>J(? LOGY RESOURCES 

This section is intended as a resource guide to available literature 

on MF technology pertaining to underground coal mines. Many of the 

documents listed in thfs section are not in the open literature, 

including NTIS. Access to these documents may be obtained through 

consul tation with U.S. Bureau of Mines PMSRC technical personnel at 

the Bruceton Research Center or via contact with the author(s), 

General release of information may be subject to governmental 

app rova I. 

The documents are herein divided according to subject matter; the 

major topical areas being subsections of .this section. 

7.1 MEASURED PROPAGATION DATA 

The fo l low i ng two reports were prepared under USBM Contract H0346067, 

Phase I, Rockwet l/Coilins Subcontract C-651171 by Spectra Associates, 

Inc. entitled "Mine Wireless Propagation Test Program". 

( I Cory, T.S., "Summary Data Report-I , Rose Va I I ey Mi ne MeasurementsT', 

7 January, 1975 

This cornproses the first documented set of MF field strength 

measurements ever made. This report is contained as Appendix 111 

to the Mine Wireless Phase I Final Report. Rose Val ley Is an 

AC mine. 

Measuremnts were performed in the I-Left, Main East working 

section of this mine in the Pittsburgh seam. Data includes quasiconductor-free field strength, field strength near conductors 

( 4160 VAC cable and phone line > and conductor current distrlbutlons. 

Test transmit antennas included the coal pillar VMD. Field poiarlzatlon 

of the receive antenna was varied, South African ( ECAM and 

Motorola UHF portables were range tested, 

- HMD pol ari zation was observed for the f I rst ti me to provi de the 

strongest coup l i ng, but close proxl mi ty to conductors prec l uded 

positive identification of it as the exciter of the primary 

conductor-free coal seam propagation mde. 

(2) Cory, T.S., "Sumnary Data Report-2, l re land Mine ~basuremnts", 

12 March, 1975 

This comprised the first documented results in a conductor-free 

area in a coal mine. HMD polarization was confirmed as providing 

the strongest coup l ing i n the coa 1 seam. re1 and i s a DC mi ne. 

Measurements were performed in the 8-North Escapeway area of the 

mine. Magnetic field strength vs range and frequency was obtained; 

also, the maximum range limit of the ECAM radios was determined, 

The August 1974 observations of BuMlnes personnel i n t h i s same 

mine were confirmed with range; with a range of 1200 feet in the 

Pittsburgh seam being verified. 
The f i rst maxi mum communication range vs frequency curve used 

as the basis for the Collins FM Mine Wireless radio development 

was derived, 

The fo l low i ng s i x reports were prepared under USBM Contract H0366028, 

Rockwell/Collins Subcontract C-651333 by Spectra Associates, Inc. 

ent i tl ed "Propagation of EM S i gna l s i n Underground Mi nes". 

(3) Cory, T.S., "Summary Data Report-I, Ireland Mine Test Data at 

Med i urn Frequenq ," I October 1 976. 

Measurements were performed in the 8-North Submain,close to the 

8-North Escapeway of Reference (21, one entry removed from the 

AC power cable. The presence of the cable was observed not to 

cause a decrease in field strength ( null regions 1. Both 

principal HMD polarizations of magnetic field were taken. 1033 

kHz was observed to produce the greatest field strength excitation. 

The first measuremnt of a field strength "she1 f" due to conductor 

scattering was made and observed. Quasi-conductor-free ranges In 

excess of 1000 feet were again observed. . 

Data was gathered compri s i ng the f i rst "area coverage" fie l d 

strength contour mapping in the 8-North 3-Right working section. 

This data showed for the first time that complete area coverage 

of a working section panel could be obtained from a single 

transmi Wer l ocat i on near the sect i on belt headp i ece. 

(4) Cory, T.S., "Sumnary Data Report-2, Sesser Mi ne Tests at Medl urn 

Frequency .and UHF, " November 1976 .J 

Measurements were performed in the Esat Maios and in the East 5-Left, 

6-Left, and 9-Ri ght worki ng sections. Cornparati ve test1 ns of the 

Co l l i ns FM Mi ne W i re1 ess prototype and the ECAM SSB rad 10s were 

made in a quasi-conductor-free area. The measurements included 

quas i -conductor-f ree magnet l c f i e l d strength tests and extens i ve 

magnetic field strength mappings. The maximum range of the UHF 

portab l e radios was a i so observed. Sesser I s an AC mI nee 

These measurements,in the Herrin #6 seam, were the first to be made 

out of the Pittsburgh seam. The results exhibited a greatly 

decreased quasi-conductor-free maximum range of about 400-500 feet. 

Cornparab l e ranges were observed with the FM and SSB radios; the 

Collins FM radio having a slight edge over the ECAM SSB radlo. 

The first confirmation of carrier current conducted in mine wiring 

producing in excess of one mile of comnunication range was obtained. 

The Herr i n #6 seam exh i b i ted the h i ghest f i e l d strength attenuat I on 

properties with range of any coa I seam measured to date. 
(5) Cory, T.S., "Summary Data Report-3, Consolidation Coal Mine No. 

95 ( Robinson Run Portal 1," December 1976. 

bkasurements were made in the blain North 2-West area of this nine; 

consist i ng of both quasi -conductor-free and conductor-proxi mi ty 

data. This mine was the third to be used for teslng in the Pittsburgh 

seam. Robinson Run is a DC rnlne. 

The results i n thi s mi ne conf i rmed the results from the Rose 

Valley and Ireland mines. Testing was limited, for the first time, 

tothe principal HMD polarization except near conductors. 

(6) Cory, T.S., "Summary Data Report-4, Eastern Associated Coal Federal 

No. I Mine ( Eddy Portal 1 ," December 1976. 

Testing was conducted in two areas of this DC mine in the PTttsburgh 

seam; the 8-Main-North and 3-Main-Left working sections 10 and 22. 

Both quas i -cond uctor-f ree and conductor-proxi mi ty magnet i c f i el d 

strength data were gathered. 

The resu Its in this mine again confirmed previous measured results 

in the Pittsburgh seam. The resul ti ng data curves were so we1 I 

ordered that they have been used by the author as being typical of 

the Pittsburgh seam for system calculations. 

(7) Cory, T.S., "Sumnary Data Report-5, isloand Creek Coal Co. Virginia 

Pocahontas No. I Mine," February 1977. 

Testing was conducted in two areas of this ~d mine in the Pocahontas 

#3 seam; the 2-North #I Plow and 3-South areas. Th i s was the f l rst 

mine in low-medium coal In which measurements were made. 60th quaslconductor-free and conductor-proxi mi ty magnetic field strength data 

were sathered, Also, the Cot l i ns FMp-ototype radlos were range 

tested both in a room-and-pillar area and through a solld block of 

coa I. 

The concept of scatter gain was first applied to measured results to 

predict the f lel d strength I n proxi ml ty to conductors. 

This is the first mine in which the in-seam field strength was 

observed to be significantly topology dependent.The apparent maximum 

communication range between portables was 140-150 meters through 

the coa l b i ock compared w i th up to 280 meters i n the room-and-p l l t ar 

area , 

Quas i -conductor-f ree ranges were i ntermed l ate to those typ I f y l ng 

the Pittsburgh and Herri n 86 seams. 

(8) Cory, T.S., "Summary Data 2eport-6, Peabody Coal Co. Mlne No. 10," 

March 1977, 
Testing was conducted in two areas of this DC mine In the 

Herrin #6 seam; the I-South 1st West and 5i-East/l-South 8 I-Sou+h 

Main junction areas. Both quasi-conductor-free and conductorproxi mi ty magnetic fie 1 d strength data were gathered. 

The results conf i rmed the previous Sesser results in the Herri n #6 

seam, 

Further evi dence of the topologica l dependence of fie i d strength 

data was obtained for frequencies above-1000 kHz. 

A part i cu 1 ar tro l l eyphone branch s i gna I t'suck-out't prob l em was 

ana l yzed and reported, 

(9) Cory, T.S., "Propagation of EM Signals in Underground Mines," 

Spectra Associ ates, I nc. on Subcontract C-65 1 333 for Rockwe l I/ 

Collins under BuMines Contract H0366028, September 1977. 

This final report sumnarizes the results of references (3) - (8). 

Computation of maxi mum communication range i n quasi-conductor-free 

areas were made us i ng Co I l i ns FM prototype equi pment parameters 

and set-no i se/rned i an-mi ne-no i see 

The details of the measuring equipment arrangement and callbration 

are described i ncl udi ng the development and packaging of the test 

transmi tt i ng equ i pment. 

The Fo 1 l ow i ng f i ve reports were prepared under USBM Contract H0377053, 

-Rockwe1 l /Col I ins Subcontract C-65 1672 by Terry S. Cory, P.E. entl tled 

"E l ectromaonet i c Propagat i on i n Low Coa l Mi nes at kd i urn Frequenc i 8s." 

(10) Cory, T.S.,"Sumary Data Report-I, Helvetia Coal Co. Margaret #I I 

Mine", January 1978. 

Testing was conducted in two areas of this AC mine In ihe Upper 

Freeport ("E") sesm; quasiwnductor-free magnetic field strength 

measurements were performed in the I-Butt sectlon and conductorproxi mi ty measurements were performed i n the 2-Butt section. 

The quasi-conductor-free field strength attenuation rate I n t h i s 

mine was exceeded only by that experienced in the Herrin #6 seam. 

This mine is in the same seam as Lucerne #8 which employs roughly 

comparable mining techniques. The data from this mine has been 

used to estimate MF system performance In Lucerne #8. 

( I I 1 Cory, T.S., "Summary Data Report-2, Upshur Coa l s Corporation 

Adrian Mi ne," February 1978. 

Testing was conducted in the area parallel to Road 83C between 

I st Right and 2nd Right in this DC mine in the Upper Freeport ("En) 

seam. This mi ne Is i n h I gh coal near where the Upper Freeport seam 

outcrops. 

Magnetic field strength data was obtained for The quasi-conductorfree case only at 90 d 220 kHz due to equipment malfuncifan. 
( 12) Cory, T.S., "Summary Data Fceport-2, Bethlehem Steel Coal Mlne 

131 Nanty Glo," March 1978. 

Testing was conducted in two widely separated areas In this 

large old DC mine in the Lower Ki ttanni ng ("6") seam; the Main N 

and 5-Cross areas. Both quas i -conductor- f ree and cond uctor-proxi mi ty 

data were gathered. 

Conductor-proximi ty data was gathered for the first time in a form 

to enab l e the d i rect determi nation of scatter gai n from the measured 

data. 

Data was gathered for the f i rst ti me i n a partlcu l arly low head 

clearance area where yb largely f i I led the entry crossectIon in 

which measurements of magnetic field strength were being made. 

The maxi mum communication range for this seam was i ntermed I ate to 

the lJpper/Lower Freeport and Pi ttsburgh/E l khorn X3 seams. 

(13) Cory, T.S., "Summary Data Report-4, Bethlehem Steel Coal Mine 3aD 

Ehrenfeld," brch 1978. 

Testi ng was conducted i n the I-Ri ght Ma1 n B area of this DC mi ne 

i n the Lower Freeport ("D" ) seam. Both quas i -conductor-f ree and 

conductor-proxi mi ty magnet i c f l e l d strength data were gathered. . . 

Aga i n, conductor-proxi mi ty data was gathered i n a form compri sing 

the d i rect measurement of scatter ga i n. 

Maxi mum comnuni cation ranges for the Upper and Lower Freeport seams 

were observed to be comparab le. 

(14) Cory, T.S., "Summary Data iteport-5, National Mlne Corp. Stinson 13 

Mine," May 1978. 

Testing was conducted in the C-Section area of this AC punch mine 

i n the El khorn #3 seam. Both quas i -conductor-f ree and conductorpmxi mi ty magnet i c fie l d strength data were gathered. 

Conductor-proxi mi ty data was gathered with primary emphasi s on the 

partitioning of field strength polarization. VMD polarization was 

determined to be predominant at low frequencies; HFD polarization 

was determi ned to be predomi nant at higher frequenci es. 

Quas i -cond uctor-free maxi mum correnun Icat ion range was observed to be 

second only to the Pittsburgh seam. . 

(15) Cory, T.S., "Electromagnetic Propagation In Low Coal Mlnes at Medium 

Frequencies," Terry S. Cory, P.E. on Subcontract C65 1672 for 

Rockwe l l /Co l I i ns under But41 nes Contract H0377053, June 1972. 

This final report summarizes the results of References (10) - (14). 

Computation of maximum communication range in quasl-conductor-free 

areas was made us i ng the Col l I ns FM prototype equipment parameters 

& set-noise/median-mine-noise. 
The composite maxi mum range resu Its of Reference (9) and the low 

coal measurements is gi ven. 

(16) Cory, T.S., "Magnetic Field Strength Mapping of the Helvetla Coal 

Co. Lucerne 18 Mi ne at bdi um Frequency," Terry S. Cory, P.E. 

under BuMines Purchase Order P0372716, September 1977. 

The results of MF magnetic field strsngth rapping are presented 

for thi s mi ne i n the Upper Freeport ("El') seam. 

This measured data provides a basis for area coverage and conductor 

carrier current standing wave ratio estimation for this mine. 

(17) Cory, T.S., "In-Situ Peasurement of Coal Seam Conductivity us1 ng' 

a Para1 lel Wire Transmission Line Method," Special Technical 2epor-t 

on Terry S. Cory, P.E. Subcontract C-65 1672 for bckwel l /Cot l ins 

under BuMi nes Contract H0377053. 

This report presents a unique technique for determining the coal 

seam conductivity via measurement of the propagat ion phase constant 

on a spaced open two-wire transmission line and curve fitting with 

computed data. Deri vation of the theoretical model is given; 

conductivities are determined using the technique for two mines. 

(18) Cory, T.S., "Wireless Radio Transmission at Medium Frequency in 

Underground Coal Mines - Sumnary of Measurements and Expected 

System Propagat i ona l Effects ," 1 978 USBM Gu l ded Wave El ectromagnet I c 

Workshop under BuMi nes Purchase Order PO38 1076, March 1978. 

Th i s paper summar i zes MF propagat 1 on f i el d strength measured resu l ts 

to data and the maximum range computations which can be made from 

them ( i nc l ud i ng those us 1 ng scatter gai n 1. The paper draws from 

References (9) and (15). 

(19) Balanis, G.A., et. al., "Electrical Properties of Eastern Bltuminous 

Coal as a Function of Frequency. Polarization, and Direction of the 

Electromagnetic Wave, and Temperature of the Sample," West Viroinia 

Un i vets i ty , 1 978 USBM Gu i ded Wave El ectromagnet 1 cs Workshop, 

March 1978 

This paper reports on a series of systematic laboratory measurements 

on coal samples toward determining the constituitlve prcpeeies 

( dielectric constant and conductivity). 

The dielectric constant is essentially independent of wave polarization, 

direction of travel, and decreases slightly with increase in temperature. 

The conductivity is less by a factor of 3-6 for a vertically polarized 

wave than for a horizonta l I y po lari zed wave and decreases sl i ghtl y 

w i th i ncrease i n temperature. 

The conduct i vi ty l ncreases and the d i el ectri c constant decreases w I th 

i ncrease i n frequency . 
(20) Chang, D.C. d Kuester, E.F., "In-Situ Determination of Bulk 

Electrical Properties of Coal ," Final 2eport, USBM Contract 

P0172080, April 1977. 

This fine survey work reviews the techniques of conductivity 

determi nat ion appropri ate for various frequency ranges of 

interest. The techniques are described in detail together 

with the necessary inforrnatioddata to implement them, 

(21 1 Lytl e, R.J., "Measurement of Earth bbdi urn Electrical Characteri st1 cs 

Techniques, Results, and App I i cations," Lawrence Li vermore 

Laboratory, IEEE Trans. Geosclence Electronics, July 1974. 

This survey paper is similar in structure and content to 

Reference (20) but is more genera l ly oriented toward earth 

materials, 

(22) Parkhomenko, E.I., "Electrical Properties of Rocks," lnstitufe of 

Physics of the Earth, Acadamy of Science of the USSR, Translated 

and Edited by G.V. Keller, Pienum Press, New York 1967. 

This book is a foundation resource for the electrical properties 

of earth and rocks; also incl uding some data on coal. 

7.2 CONDUCTOR-FREE PROPAGAT l ON ANALYS I S 

(23) Cory, T.S., "Research Report - MIne Wireless Comnunicaf Ion Models . 

at Medium Frequency," Spectra Associates under Subcontract 

C-651 171 for Rockwel l Col I ins, 7 March 1975,. 

This report was prepared for Packwe1 l/Col llns fol lowing completion 

of the measurements of References (I) and (2) and was probably 

not furni shed to the Bureau. Thi s report i s avai fable from the 

author. 

The report works toward validation of the Ireland mine measured 

data by: 

(a Emp I oy i ng the method of images and mod i f i ed geornetr 1 ca l 

optics to predict the coal seam mde excitation levels. 

(b) Exploring the close-in transition of the optimum field 

polarization from VF83 to HMD 

(c) Fitting the far range field strength data to an exponential 

decaying model 

This report developed an analytical model for the first predictlon 

of conductor scattering effects. This analysis included a rr~odel 

for the monofilar mode propagation constant on a quasi-static basis. 

(24) Lagace,R.L., et. al. , "Propagation of Radio Waves in Coal Mines," 

Arthur D. Little, lnc., Contract Report, Task F, Task Order #I, 

USBM Contract H0346045, October 1975 
This report presents the first theoretical quasi-EM mde 

analysis for the MF coal seam waveguide mode propagation 

and the model is validated via comparison of measured results 

and theoretical analyses, 

The theory, subsequently refined, has provided the basis for 

not only validating measured results in all ensuing measurement 

programs, but a l so for deri vi ng consti tui ti ve properties for 

the coal seam and for the rock overburden/underburden. This 

is a 3- 1 ayer mdel assumi ng equa l overburden/underburden 

const i tui t i ve parameters. 

The theory and analysis technique are particularly useful for 

engineering R & D purposes as they can be implemented on an 

HP-67/97 ca l cu 1 ator, 

(25) Decker, RoPo, "Notes on Comparison of Measured Mines Magnetic 

Fi el d Strength Data by Mu I ti -1 ayer Theory," Spectra Associ ates, 

Unpubl ished monograph, 13 Decmber 1976, 

This paper is available only from the author, It employs the 

senera l mu1 ti -layer theory of Walt to coal seam waveguide 

propagation us i ng a f i ve- l ayer mdel permi tt l ng d i f ferl ng 

constituitive parameters for the overburden and the underburden, 

The paper contains comparisons of both the 5-layer and ADL 

3-layer mdels with the measured data. 

This analysis is particularly useful in making propagation 

predictions at the lower LF/MF frequencies of nominal ly 200 kHz 

and below. 

(26) Wait, J.R. & Spies, K.P., "On Calcuiatlon of the Modal Parameters 

of an 1 dea 1 i zed Earth-Crust Waveguide," ONR Report #I , March 197 1 . This report provides the foundation theory on which Decker's 

analysis ( Reference 25 was based. 

(27) Wait, J.R., "Note on the Theory of Transmission of ElectromgnetIc 

Waves in a Coal Seam," Radio Science, Vol. 11, N0.4 pp.263-265, 

April 1976. 

This paper constitutes Waits identification of MF coal seam 

waveguide propagation to his earl ier work, putting the theory 

i n the open l i terature. 

(28) Lagace, R.L. A Ernslie, A.G., "Theory of the Propagation of Low 

and Vedi urn Frequency Radio Waves in a Coal Seam," Radio Science, 

Vol. 11, No.4, pp. 253-262, April 1976. 

This paper constitutes a refinement of the Reference (24) material 

and presents the f i rst exposure of the 3-layer quasi-TEM mode theory 

in the open literature. 
(29) Lagace, R.L., et. a I., "bdel l ing and Data Analysis of I n-Mi ne 

Electromagnetic Wave Propagation," Arthur D. Little, Inc., 

Interim:. Report, Task Order #4, USBM Contract H0346045, May 1978. 

This report presents va l idation of the measured data of 

References (2) - (8) with a companion analysis based on the 

3-layer mdel. From the analysis, constituitlve parameters of 

the coal seam and of the rock are derived for each mine/seam 

eva I uated vi a measurements. a 

(30) Lagace, R.L. & Emslie, A.G., "Analysis of MF Propagation Data 

from Margaret #I I , Nanty Glo, Ehrenfeld, and Adrian Coal Mines," 

Art hur D. Little, I nc., Worki ng Memrandurn, Task Order #4, 

USBM Contract H0346045, May 1978. 

This report provides the companion analysis, simi lar to that of 

Reference (291, for the low coal mi nes for which measured data 

is given in References (10) - (14). 

(31) Emslie, A.G. 8 Lagace, R.L., "Medium Frequency Radio Propagation 

and Coupl ing in Coal Mines," Arthur D. Little, Inc., 1978 U56W 

Guided Wave El eciromagnetic Workshop, March 1978. 

This paper reviews some of the Reference (29) results and presents 

a ref i nement to the theory, us i ng Bann i sterl s quasi -stat i c l mage 

.technique, to improve on the mdal excitation level and the 

close-in predicted field strengths. Good agreement with measured 

data is obtained between nominally 100 and 1000 kHz. 

7.3 COUPLED CONDUCTOR PROPAGAT I ON ANALYS I S 

(32) Ibid. Ref, (231 Section 4.0 "bde12s for-Flelds In an-:Area Wlth 

bnd uctors? 

A simp l e theory i s presented based on coup l i ng from a matched, 

terminated single line source to multi-turn transmit and receive 

loop antennas is presented; including definition of the monofilar 

mde propagat ion constant. The range decay of fie id strength .58 perpendicularly away from the line source is modified to be l/r 

based on measurements taken i n the Rose Val ley mi nee 

(33) Ibid.Ref. (91, Section 4.2 " Analysis and Development of System 

Appl ication of Data" 

The theory of scatter gain is put forth for the prediction of 

conductor-proxi mi ty f i el d strengths from a remote transml tter. 

Ca 1 cu 1 at i ons of conductor-proxi mi ty maxi mum commun l cat I on range 

are given for the Pittsburgh, Herrin 86, and Pocahontas #3 seams 

vs range of the transmitter away from the conductor ensemble us1 ng 

Collins FM prototype radio parameters and set-noise/rnedian-rnine-nolse. 

At the time of the writing, correlation of scatter gain from 

theoretical and measured data was available only in two Isolated 

cases. Formul as for scatter gai n were developed for each of the 

three seams. 
(34) Ibid. Ref. (151, Section 2.2.1 "Computation Criteria 8 Techniquest'; 

Section 3.3 "Scatter Ga i n Cornpar i sons" 

Scatter gain formulas are presented for the Lower and Upper Freeport, 

and Lower Ki ttann i ng seams. 

Extensive comparisons of computed scatter gain and scatter gain 

determi ned d i rect l y from measurements are gi ven; va I i datl ng the 

use of the theory. 

(35) Ems l i e, A.G., et.a I. , "Theory of the Dedicated Wi re as a Means of 

Aiding Propagation on a Trolley Wire," Arthur D. Little, Inc., 

Working Memrandurn 1-8, USBM Contract H0346045, September 1976. 

A theoretical analysis is given which puts forth the value of a 

dedicated wire placed paral lei to and In close proximity to a 

trol ley wi re conductor to "stabi l i ze" the transrni ssion of carrier 

current past branch/ j unct i on po i nts md a long mu l ti -conductor 

ensembles to minimize junction signal rtsuck-out" problems and 

wh i ch prec l udes severe I osses due to unwanted mde conversion. 

(36) Ems1 ie, A.G., et. al ., "Use of Auxi I 1 iary Dedicated Wires as a 

hans of Aiding Carrier Current Propagation on a Trobley Wire/ 

Rail Transmission Line," Arthur D. Little, Inc., 1978 USBM 

Gui ded Wave El ectromagnet i c Workshop, March 1978. 

Extending Refernce (351, an application of the dedicated wlre 

theory to the coup l i ng between a dedicated wire and the DC 

trol ley wire/rai l transmission line is given. Results show the 

advaniages of a loosely coupled dedicated wire toward precluding 

nu1 l zones in trol ley wire carrier current operation. 

(37) Lagace, R.L. 8 Emslie, A.G., "Coupling of the Coal Seam Msde to a 

Cable in a Tunnel at Medium Radio Frequencies," Arthur D. Little, 

I nc., 1978 USBM Gui ded Wave Electromagnetic Workshop, March 1978. 

A theory is put forth, based on the use of multiple ''Bannister 

images", to predict the coupl i ng into exi sti ng mi ne wi ring cab l i ng 

as an extension of the 3-Layer mdel, Sufficient data Is not 

available to MI idate the use of the theory. 

(38) Wait, J.R., "Quasi-Static Limit for the Propagatlon bde Along a 

Thin Wire in a Circular Tunnel," IEEE Trans. PGAP, Vol. AP-25, No.3 

pp.441-443, May 1977. 

Th i s note develops essent i a l I y the same quas i-static l i mi t for 

estimating the monofilar mode propagation constant along an Idealized 

coaxial lossy line as has been used by Cory for monofilar mode loss 

conrputati ons, This technique requ i res ref 1 nement, however, to 

handle the complete MF frequency range In coal mines. This refinement 

for the phase constant only has been put forth by Cory in Reference (17). 
(39) Wait, J.R. 6 Hi l I, D.A., "Guided Electromagnetic Waves Along an 

Axial Conductor in a Circular Tunnel," IEEE Trans. PGAP, Vo. AP-22, 

pp. 627-630, July 1974, 

This paper gi ves the foundation theory for monof i iar made 

propagation along a symmetrically spaced axial conductor In 

a lossy coaxial transmission line, 

(40) Reid, D.G.,"Wireless Communications for Trackless Haulage Vehicles," 

Section 7 "Antennas" by T.S. Cory under Subcontract C-65 1 196 to 

Rockwe1.l /Co l l l ns, Phase I Report on USBM Contract H03770 13, 

August 1977, 

Section 7.4 "Coup I ed-Repeater Antennas" gi ves results of the 

coup! ing coefficient between a large base station loop antenna 

and a conductor over a lossy interface, 

The coup l i ng i s quas i-i ndependent of range ( for short ranges up to 

48 feet at least because of the concentration of magnetic flux 

near the interface such that the flux threads the loop for 

essent i a l l y a I l spaci ngs for which measurements were made. 

(4 I) Cory, T.S., "MF System Ca lcul ations for Lucerne #8 and Sesser Mi nes," 

unpub l i shed mnograph prepared far Rockwel I/% l ! ins on Subcontract 

C-65 1 196 under USBM Contract H03770 13, J u l y 1977. 

Th i s monograph presents the f i rst system performance pred t ct ions 

merging the close coupling theory with sca-l-fer gain computations 

f torn a remote transmi tter. 

(42) Cory, T.S., "Antenna Design and Coupling Studies at Medium Frequency 

for I mproved Coal Mine Comnunications," Terry S. Cory, P.E. under 

BuMi nes Purchase Order P0382223, December 1978. 

Th i s report presents coup l i ng coef f i c i ents for antennas to an assumed 

AC power cable,including the effects of vehicular muntbng, derived 

from quas'i-statlc graphical field mapping. 

The following five reports were prepared under USBM Contract H0133005 by 

the Electromagnetic Di vi sion, l nsti tute for Basic Standards, Not lonal 

Bureau of Standards. 

(43) Bensema, W.D., et. al., "Electromagnetic Noise In Robena No.4 Coal 

Mine," NBS Tech Note 654, Apri l 1974. 

(44) Adam, J.W., et. al., "Electromagnetlc Noise in Grace MIne," NBSlR 

74-388, June 1974. 

(45) Kandu, M., et. at., "Electromagnetic Noise In kEiroy Mine," 

NBSlR 74-389, June 1974. 

(46) Bensem, W.D., et. ale, "Electrornagnettc Nolse in ltmann Mine," 

NBS l R 74-390, June 1974. 
(47) Scott, W.W., et. at., XElectrornagnetfc Noise in Lucky Friday Mine," 

NBSlR 74-391, October 1974. 

These reports, on a per-mine basis, describe extensive measurements 

of el ectromagnet f c no i se i n underground mi nes. These measurements 

were performed at 200 kHz and below. Until recently, extrapolation of 

these data into the MF region provided the only estimates of MF 

noise. Care must be taken in using some of the data as it was 

set-no i se- I i mi ted. 

This fine work, unfortunately, did not consider partitioning of 

noise according to type of mining operations ( for example, AC, DC, 

be1 t or tracked haul age, close to or away from conductors, presence 

of tro l ley phone i nterferance, etc. 1. 

(48) Decker, Rep., "Research and Development Contract for Coal Mine 

Communication System - Vol. 3 Theoretical Data Ease," Collins 

Radio Co. Final Report, USBM Contract H0232056, November 1974. 

This report surnmrizes the NBS noise measurements and put forth 

an empirical formula for the computation of median-mine-noise 

( a va l ue wh i ch, si nce, has been determi ned to have l i mi ted 

operational significance 1. 

(49) Cory, T.S., "Evaluation of Electromagnetic Noise in Coal MI nes at 

VLF and MF Frequencies Based on Noise Measurements on Mine 

Telephone Lines," Working Memorandum #8, Terry S. Cory, P.E. 

under BuMi nes Purchase Order P0382497, March 1 979. 

Th i s report descri bes d i f ferent i a l mode and common mode noi se 

measurements made on te l ephone l i nes i n underground mi nes. The 

common mde data has been interpreted at MF frequencies in terms 

of a radiated noise field strength close to existing mine 

wiring. Use of this data in conjunction with extrapolations of 

the NBS data has been made to establish operationally significant 

noi se curves from which MF system performance can be estimated. 

7.5 PROTOTYPE SYSTEM ELEMENT DEVELOPbIENTS 

(50) Anderson, D.T., et. at., "Phase-l Mine Wireless Final Report," 

Rockwell/Collins under USBM Contract H0346067, 1975. 

This report describes the desl gn parameters chosen for the ensuing 

Phase I1 development of MF wireless radio prototype equipments; 

to consist of portables ( plus antennas ) and base stations ( plus 

antennas 1. 

(51) Wilson, L.R., et. al., "Phase-ll Mine Wireless Flnal Report," 

Rockwe l l /Co l l i ns under USBM Contract H0346067, 1977. 

This report provides the complete deveiopmental description of the 

two-frequency FM prototype equipments developed and furnished fo 

the Bureau for eva 1 uation. 
(52) Ibid. Ref. (42) 

This report describes the design and build of two prototype 

vehicular MF antennas for use In coal mi nes. l ncl uded is the 

theoretical description of a multi-turn antenna design algorithm 

from which the developed antenna design performance was optimized. 

(53) Cory, T.S., "bthane Telemetry System for Conti nuous Mi ners," 

Fi na l Report of Contract J0 166094 with Rockwe 1 I /Co l l i ns prepared 

on USBM Contract J0 199026, Apri l 1979, 

This report describes a wireless MF radlo remote monitoring 

system for the simultaneous and continuous unattended monitoring 

of up to 8 methane sensors installed on a continuous miner. 

Complete descriptions of the digital modulation, control ( rnicroprocessor 1, and RF transmi tter/recei ver des i gns are gi ven. 

(54) Ibid. Ref. (40) 

This report provides a f i cst order functional description of a 

possible MF system configuration for use in trackless haulage 

appl ications. 

(55) Austin, B.A., "Underground Radlo Communication Techniques and 

Systems in South African.Mlnes," Eiectronics Division, Chamber 

of Mines of South Africa, Research Organfzatlon, 1978 USBM Guided 

Wave Electromagnetic Workshop, March 1978. 

Th i s report descr i bes the deve 1 opment of radio components and the 

implementation of communication techniques ( based on the MCAL 

SSB radio equipment parameters 1 tn use In South African mines. 

(56) Lagace,R.L., e?. al., "Transmit Antennas for Portable VLF to I4F 

Wireless Mine Communications," Arthur D. Little, Inc., Final 

Report Task C, Task Order #I, USBK Contract H0346045, May 1977. 

With regard to MF antennas, this report provides a cursory 

overview of the thinking which has taken place prior to 1977 

regard i ng w i re l ess rad i o antennas. 

(57) Lagace, R.L. 8 Emslie, A.G., "Antenna Technology for PCdium Frequency 

Portable Radio Communications In Coal Mines," Arthur D. LiWle, Inc., 

1978 USBM Guided Wave Electromagnetic Workshop, March 1978. 

This paper discusses considerations related to the design and 

selection of MF portable radlo antennas for use In coal mines; 

including the recommendation of R & D on ferrite-loaded antennas. 

Deta i 1 ad des i gn ana 1 yses and/or resu l ts are not gl ven. 
(58) Chufo, R.L., et. aI.,"F"Rdium-FrequencyMne Wireless Radio", 

Bureau of Mines Information Circular/l977 IC 8745, pp.63 - 72 

This report describes the Rockwel l/CoI l ins narrowband FW 

prototype radios and the general potential for MF w i re1 ess 

systems based on the results experienced during the f i rst 

major field strength measurement Drogram ( Reference 9 ). 

The paper describes the communications requirements whlch 

lead PMSRC to ini t i tate. R 8 D efforts in this technology 

a rea .