Collins Radio Company 

COLLINS 

report 

Volume 4 Environmental Measurements 

Research and Development Contract 

for Coal Mine Communication System 
Washington, D. C. 

USBM Contract No. H0232056 

Printed in the United States of Arner~ca 

I)isrlaimer Notice: "The views and conclusions contained in this document are those of the authors and should not be interprr~ed 

as necessarily representing the official policies of the Interior Department'5 Bureau of Mines nr the 1)s 

Government." 

Collins Radio Company / Cedar Rapids, lows 
Table of Contents 

Page 

Section 2 Experimental UHF and VLF Tests 

at the Inland Steel Mine .............................. 

2.1 UHF Tests ....................................................... 2.2 VLF Tests ....................................................... 2.3 Test Site .......................................................... 2.4 Propagation Characteristics ............................... 2.4.1 UHF Propagation ............................................ 2.4.2 Experimental VL F Propagation ......................... 2.4.3 Summary and Conclusion .................................. 2.5 Acknowledgment ................................................ 2.6 References ....................................................... 

Section 3 Experimental VLF to LF Tests at 

Robena No . 1 Mine .................................... 

3.1 VLF and LF Tests ............................................. 3.2 Comparison of VLF Predictions ........................... 3.3 VLF Summary .................................................. 3.4 Tables ............................................................. 

Section 4 UHF Predictions ....................................... 

Appendix A Test Equipment and Experimental 

Setups 

Appendix B Tables 
List of Illustrations 

Figure Page 

2-1 Coal Mine Test Site ............................................. 2-2 Tunnel Cross Section ........................................... 2-3 Corner No . 1 Layout ............................................ 2-4 Corner No . 2 Layout ............................................ 2-5 Observed 200-MHz Transmission Loss for a 

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

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

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

Tunnel ............................................................. 2-11 Observed Transmission Loss for Roof-Bolt 

Antennas in Coal Mine ........................................ 2-12 Observed Transmission Loss for Roof-Bolt 

Antennas in Coal Mine ........................................ 2-13 observe^ Transmission Loss for Roof-Bolt 

Antennas in Coal Mine ........................................ 2-14 Observed Field Strength for Roof-Bolt-to-Loop 

Antennas in Coal Mine ........................................ 2-1 5 Observed Field Strength for Roof-Bolt-to-Loop 

Antennas in Coal Mine ........................................ 2-16 Observed Field Strength for Roof-Bolt-to-Loop 

Antennas in Coal Mines ....................................... 3-1 8-Inc h Loop to 2 0-Meter Loop ................................ 3-2 Line Source to Loop ............................................. 3-3 Line Source to Loop ............................................. 3-4 Received Signal Vs Frequency (8-Inch Loop to 

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

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

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

8-Inch Loop) ....................................................... 3-8 S/No Vs Separation (Roof-Bolt to 8-Inch Loop) .......... 3-9 S/N~ Vs Separation (20-Meter Loop to 8-Inch Loop 

and Roof Bolt to 8-Inc h Loop) ................................ 3-10 S/N~ Vs Separation (8-Inch Loop 

to Roof Bolt) ...................................................... 3-11 S/No Vs Separation (8-Inch Loop to 20-Meter Loop) . 
List of Illustrations (Cont) 

Figure Page 

3-12 S/No Vs Separation (8-Inch Loop to 20-Meter 

LOOP) .......*..............................**..*...*............. 

3-13 S/No Vs Separation (Roof-Bolt to Loop 

Transmission) ., ............ ,.. .........o.........o..oe.....~oe. 

3-14 S/No Vs Separation (20-Meter Loop to 8-Inch 

LOOP) .........*.*...*... .......*................*............e.o... 

3-1 5 Lateral Magnetic Field Intensity for Varying 

Displacement .................... ......o......................o. 

4-1 UHF Propagation (I-Watt Transceiver 

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

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

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

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

Transmitting to 1-Watt Transceiver With 

Corner Reflectors - 1,800 ft) ................... ..* 

4-6 UHF Propagation (1-Watt Transceiver Transmitting 

to 1-Watt Transceiver, With Corner Reflectors - 3,300 ft) ................... ........~..........~....~~.~............e 

4-7 UHF Propagation (20-Watt Transceiver Transmitting 

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

to 1-Watt Transceiver With Corner Reflectors - 

3,800 ft) ................... ..o...............~........~............. 

4-9 UHF Propagation (20-Watt Transceiver Transmitting 

to 1-Watt Transceiver With Corner Reflectors - 

2,000 ft) .................... ........ .*.O.OQ..............* ..... 0. 

4-1 0 UHF Propagation (I- Watt Transceiver Transmitting 

to 1-Watt Transceiver With Corner Reflectors - 3,300 ft) ................... ..............OO....................... 

A-1 UHF Test Setup...... ........ ...............~...................e 

A-2 VLF Test Setup .............. .......~...~...O..................~o 

A-3 Antenna Complement for Coal Mine Tests ............ .. A-4 41 5-MHz Corner Reflector Assembly .......... .......... A-5 Corner Attenuation Curves for 

Coverage Predictions. .... .... .. ... . . ............... .... ..... .. 

iii 
List of Tables 

Table Page 

2-1 UHF Test Parameters ......................................... 2-2 VLF Test Parameters ......................................... 2-3 Observed Attenuation Rates for a Straight Coal 

Mine Tunnel ................... ............~.~...~.~.~.~.o.. . 2-4 Observed Attenuation At Tunnel Edges Relative 

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

Bandwidth ......................................................... Large Loop Transmission ................................... Roof-Bolt Transmission ...................................... Small-Loop Transmission .................................... 
Section .I 

Introduction 

This report summarizes the results of several field tests conducted by Collins for the 

Bureau of Mines under contract SO122076 and contract H0232056. The field projects represent a part of Collins continuing effort on a broad study of coal mine communications. 

These experiments analyze the propagation characteristics of radio signals in a working coal 

mine environment. The intent of the program is to provide basic propagation loss characteristics by which we may evaluate various approaches to an integrated mine communications 

system. The goal of such a system is to satisfy both operational and emergency communications needs in the mine. 

Field testing was conducted during the last week of November 1972, at a coal mine operated 

by Inland Steel Company, near Sesser, Ill, and in the Robena No. 1 Mine, Waynesburg, Pa, on 

12 March 1974. The tests included uhf propagation losses and noise (200 MHz to 1 GHz) in 

the Sesser, I11 mine location and vlf propagation loss and noise (1 to 200 kHz) in both of the 

above locations. The basic experimental parameters were frequency, polarization, antenna 

type/orientation, and distance. 

The following reports treat the various aspects of the test programs in detail. Since different 

antenna configurations were used in the two mines, each report contains its own experimental 

predictions drawn from its corresponding test activities. 

A test equipment list and block diagrams of typical experimental setups for the tests of 

section 2 are contained in appendix A. 
Section 2 -- - 

Experimental UHF and VLF Tests at the 

Inland Steel Mine 

The coal mine test program has substantially followed the test plans and procedures as 

presented to Bureau of Mines personnel at a program review held in Cedar Rapids on 

20 October 1972. The original scope of vlf testing was reduced slightly to accommodate uhf 

corner reflector tests. Propagation loss and noise measurements were conducted in two 

regions of the radio spectrum, 200 MHz to 1 GHz (uhf) and 1 to 50 kHz (vlf). 

Paragraphs 2.1 and 2.2 explain these tests in further detail. 

2.1 UHF TESTS 

Primary emphasis of the test program was on uhf propagation characteristics in mine 

tunnels. The basic measurements include transmission loss along tunnels and around corners 

and received noise level. The variable parameters include frequency, polarization, distance, 

and the orientation of corner reflectors, when used. Table 2-1 shows the various test types 

and associated parameters. 

Table 2-1. UHF Test Parameters. 

Propagation characteristics were determined by measuring signal and noise levels at 

selected points in the mine. A 20-watt uhf transmitter and h/4 ground-plane antenna were 

used as a fixed source of signals. The receiver consisted of a battery-powered field intensity meter and standard dipole antenna of the type normally used for field strength measurements. The receiving apparatus was transported to the measurement points by a batterypowered mine scooter. Before any measurements were made, the scooter was driven into a 

crosscut to prevent interference with signals in the main tunnel. Specific test equipment 

types and experimental setups are described in appendix A. 

FREQUENCY 

200 MHz 

415 MHz 

1000 MHz 

- 

f 

SPOT NOISE 

3 

At each signal point 

At each signal point 

At each signal point 

SIGNAL LEVEL 

DISTANCE 

(ft) 

0 to 800 

0 to 2000 

0 to 2750 

POLARIZATION 

Vert, cross 

Vert, cross, 

horiz 

Vert, cross, 

horiz 

CORNER 

REFLECTOR 

None 

Yes , 

Yes 
At each receive point, a series of measurements was made to determine local signal strength 

variation over a range of several wavelengths. Horizontal and vertical polarization measurements were conducted to determine the extent of signal depolarization. Measurements were 

continued along straight tunnels and around corners at appropriate intervals determined by 

the rate of signal attenuation. Measurements were continued outward from the transmitter 

until no further signal could be detected, Spot noise measurements were made at each point 

by tuning the receiver slightly above or below the transmitter signal and observing the 

incident noise level. 

Throughout the field measurements, 1-watt uhf walkie talkies (460 MHz) were used for 

c oordination between the fixed transmitter and mobile receiver locations. Owing to the 

20-watt transmitter power and propagation differences, the measurement range often 

exceeded the walkie talkie range. In these cases, a relay point was established to maintain 

coordination for polarization changes, etc. Qualitative performance of the walkie talkies was 

recorded along with signal/noise measurements for later comparison. 

2.2 VLF TESTS 

Phase two of the field measurements concentrated on the vlf propagation characteristics of 

intramine paths. Basic measurements include transmission loss or field strength and noise 

levels. The variable parameters include frequency, distance, receive antenna type, and 

antenna orientation. Table 2-2 shows the various test types and associated parameters. 

Table 2-2. VLF Test Parameters. 

Propagation characteristics were determined by measuring signal and noise levels at 

selected points in the mine. An audio oscillator and power amplifier provided a nominal 

10-watt transmit signal into a roof-bolt (line source) antenna. The receiver consisted of a 

battery operated preamplifier and tunable voltmeter. Two different receive antennas were 

evaluated; the first was a roof-bolt antenna of similar configuration to the transmit antenna, 

the second was a calibrated loop (magnetic dipole) antenna of the type normally used for 

field strength measurements. Vlf receive equipment was also transported via batterypowered mine scooter. Specific test equipment types and setups are described in appendix A. 

FREQUENCY 

1 kHz 

3 kHz 

10 kHz 

20 kHz 

50 kHz 

*Each loop measurement includes readings for three orthogonal axes; each roof bolt 

measurement includes readings for two orthogonal axes. 

'I 

SPOT NOISE 

At each signal point 

At each signal point 

At each signal point 

At each signal point 

At each signal point 

SIGNAL LEVEL 

DISTANCE 

(f t) 

0 to 675 

0 to 675 

0 to 675 

0 to 675 

0 to 675 

*ANTENNA 

Loop, roof bolts 

Loop, roof bolts 

Loop, roof bolts 

Loop, roof bolts 

Loop, roof bolts 
At each receive point, signal strength readings were made for two orthogonal positions of the 

roof-bolt antenna and three orthogonal positions for the loop. The entire measurement 

sequence was then repeated for a second orientation of the transmit antenna. Measurements 

were conducted at three points spaced at intervals determined by the rate of signal attenuation. Spot noise measurements were made at each receive location and operating frequency. 

Uhf walkie talkies were used throughout the vlf tests for coordination. 

2.3 TEST SITE 

The Inland Steel Coal Mine is located in the Illinois No. 6 seam, approximately 10 miles north 

of Sesser, Illinois. The mine has a vertical shaft entry with 7 50 feet of overburden. It is a 

9,000-ton-per-day continuous mine operation with belt haulage to a second vertical shaft 

where an elevator removes the coal to the surface. Transportation of men, equipment, and 

supplies to the various sections is done using dc battery operated rover carts. The mine is 

presently 8,000 feet north-south by 13,000 feet east-west with an ultimate size 3 miles 

north-south by 7.5 miles east-west. All tunnels and haulage ways are 14 feet wide by 7 to 8 

feet high with pillars running 60 feet by 74 feet. Roof bolts are 6 to 9 feet in length and are 

placed on 4-foot centers. 

A layout of the test area within the mine is shown in figure 2-1. The general measurement 

area extends along the no. 1 mains west for a 4,450-foot segment extending from the 2 left 

entry to the 8 right entry as indicated in the figure. The fixed transmitter location is shown 

between the 4 and 5 right entries at a point where 115-Vac power was available. Measurements taken along the 4,450-foot east-west dimension were in the same entry used for 

haulage of men and supplies. This tunnel also contained a 7200-Vac, 3-phase prime power 

cable suspended from the roof. A typical cross section of the mine in the measurement area 

is shown in figure 2-2, 

Measurements of corner attenuation were made along tunnels or crosscuts at right angles to 

the main tunnel. Because of the importance of these measurements, expanded scale layouts 

of the corner geometry are shown in figures 2-3 and 2-4. All measurement points, including 

the points at right angles to the main tunnel were located in the inlet airways. This precaution was necessary to permit the use of nonapproved test equipment. As a result, measurements were not made near working faces of the mine. However, the test locations and 

geometries as shown in figures 2-2, 2-3, and 2-4 are representative of working areas within 

the mine so that the measured signal levels are generally valid. 

2.4 PROPAGATION CHARACTERISTICS 

The coal mine tests as described in paragraphs 2.2 and 2.3 have yielded a number of significant results at both uhf and vlf. These results are presented below in the form of graphs and 

tables showing transmission loss, field strength, or noise density as a function of the test 

parameters given in tables 2-1 and 2-2. The data are arranged for convenience in the engineering of communications systems as well as to demonstrate the radio propagation characteristics in mines. 




DEPTH IN FEET 

(NOT TO SCALE) 

597 

LIMESTONE 

6 06 

COAL 

6 08 

SOFT SHALE 

619 

LIMESTONE 

- 624 

SANDSTONE 

- - -- - - - - - - - - -- - - - 

SANDY SHALE WITH SANDSTONE BANDS 

- 650 

SANDY SHALE 

FIRE CLAY 

737 

LIMESTONE 

Figure 2-2. Tunnel Cross Section. 
TO TRANSMITTER- - - 

BELT ENTRY- - - - - - ---- 

0 = M E A S U R E M E N T P O I N T 

SCALE, 1 INCH = 100 FT 

Figure 2-3. Corner No. 1 Layout. 

,-&-----I. BELT ENTRY 

O= M E A S U R E M E N T P O I N T 

SCALE, 1 INCH = 100 FT 

Figure 2-4. Corner No. 2 Layout. 
2.4.1 UHF Propagation 

2.4.1.1 Straight Tunnels 

The observed signal attenuation along a straight tunnel is shown in figures 2-5, 2-6, and 2-7 

for 200, 415, and 1000 MHz respectively. Attenuation is plotted as the power transfer ratio 

between isotropic antennas (basic transmission loss) for the indicated polarizations. Transmission loss may be combined directly with transmitter power, antenna gains, and rf cable 

losses to determine the received signal for any candidate uhf system. In terms of transmission loss, a pair of 1-watt uhf walkie-talkies has a range of 143 to 146 dB. 

It should be noted that the uhf attenuation curves are the result of an "eyeball fit" to the 

observed data. As with any uhf field measurements, individual points show some deviation 

from the curve owing to small-scale differences at each measurement location. In most 

cases, scatter from the established line is less than 3 to 4 dB. In a few cases, deviation in 

excess of 5 dB is observed. The transmission loss measurement accuracy is estimated to be 

k2.5 dB. 

Significant propagation characteristics apparent from figures 2-5, 2- 6, and 2-7 are as 

follows : 

a. Attenuation (in dB) increases nearly linearly with increasing distance. 

be Horizontal polarization produces significantly lower transmission loss at a given distance than does vertical polarization. Cross polarization produces a loss intermediate 

between horizontal and vertical. 

c. Transmission loss decreases significantly at a given distance as the frequency is 

increased. 

Linear attenuation (in dB) versus distance is a characteristic of waveguide propagation; the 

tunnel geometry (figure 2-2) also suggests a guided mode of propagation. From the slope of 

attenuation curves, attenuation rates have been determined as shown in table 2-3. The values 

for 200 MHz are considered to be very approximate because they are based on a small number of data points. For comparison, Farmer and ~hepherdl* report a value of 12 dB/100 ft 

at 160 MHz for straight passageways underground and in buildings. crary2 reports calculations for a circular waveguide tunnel approximation of 5.2 to 8.0 d~/meter (158 to 254 dB/ 

100 ft) at 160 MHz, 0.6 to 1.5 dB/meter (18.3 to 45.5 dB/100 ft) at 500 MHz and 0.1 to 0.2 

dB/meter (3.05 to 6.1 d~/100 ft) at 1 GHz. 

Table 2-3. Observed Attenuation Rates for a Straight Coal Mine Tunnel. 

- -- 

*See references at end of this section in paragraph 2.6. 

2-9 

FREQUENCY 

200 MHz 

415 MHz 

1000 MHz 

*Vertical transmit, horizontal receive. 

POLARIZATION 

VERTICAL 

= 2 5dB/100 ft 

6d~/100 ft 

4dB/100 ft 

*CROSS 

15dB/100 ft 

6dB/100 ft 

3dB/100 ft 

HORIZONTAL 

--- 

6d~/100 ft 

2;5dB/100 ft 
1000 1500 2000 

DISTANCE, FEET 

\ 

1 

, ',. 

\ \ 

8 

I 

1 

\, \\ 

\ 

1 

\ 

\ 

_j 

Figure 2-5. Observed 200-MHz Transmission Loss for 

a Straight Coal Mine Tunnel. 

\ 

\ 

8 

I 

\ 

+ 

200-M HZ 

POLARIZATION 

TX RX 

Av v 8 v H 

A 
Figure 2-6. Observed 415-MHz Transmission Loss for 

a Straight Coal Mine Tunnel. 
DISTANCE, FEET 

Figure 2-7. Observed 1000-MHz Transmission Loss for 

a Straight Coal Mine Tunnel. 
The considerable difference between vertical and horizontal polarization is an interesting 

result. At 400 MHz, the observed signal attenuation for horizontal polarization is typic ally 

40 dB less than that for vertical. The cross-polarized (vertical transmit, horizontal receive) 

attenuation is 22 dB less than vertical. At 200 MHz, no horizontal measurements were made, 

however the cross-polarized attenuation is on the order of 25 dB less than vertical, while at 

1 GHz horizontal attenuation averages 30 dB less than vertical, and cross-polarized attenuation averages 17 dB less than vertical. A further result, seen at both 200 and 415 MHz is that 

this polarization behavior is observed within 130 feet of the transmitter. 

As the frequency is increased, propagation along the guide should become less affected by the 

presence of dissipative walls because of the method of launching signals from an antenna 

completely internal to the tunnel. However, as the frequency is increased without limit, 

signal attenuation will become practically infinite when a line-of- sight path along the tunnel 

does not exist. Evidence of reduced wall effects is seen in comparing attenuation values for 

the three frequencies. As frequency is increased, the transmission loss decreases, the 

attenuation rate decreases, and the difference between horizontal and vertical polarization 

also decreases. Particularly evident at 1 GHz at the 130-ft distance is the fact that the 

observed vertical signal strength is only 10 dB below horizontal, while the cross-polarized 

value is 20 dB below horizontal. Thus, the observations are approaching the more typical 

case for short distances at uhf where horizontal and vertical attenuations are approximately 

equal and the cross-polarized value is considerably weaker. It is apparent from the 

observed data that the optimum frequency for the measured tunnel lies above 1 GHz. 

In an attempt to determine what effect, if any, the 7200-Vac power cable had upon observed 

transmission loss, measurements were made across the tunnel at each distance increment. 

Referring to figure 2-2, measurement points were located in the center of the tunnel, 

directly under the cable, and away from the cable within three feet of the opposite wall. 

Table 2-4 shows the average signal attenuation relative to that observed at the tunnel center 

position. These results indicate that the lowest transmission loss occurs at the tunnel 

center with modest increases in attenuation near the tunnel walls. At 415 MHz there appears 

to be no appreciable field distortion caused by the power cable, while at 1 GHz signal attenuation is slightly larger under the cable. 

Table 2-4. Observed Attenuation At Tunnel Edges Relative To Center. 

2.4.1.2 Corners 

FREQUENCY 

200 MHz 

415 MHz 

1000 MHz 

With the straight tunnel measurements as a reference, data were also obtained around corners for the two situations shown in figures 2-3 and 2-4. Observed corner attenuation is 

shown in figures 2-8, 2-9, and 2-10 for 200, 415, and 1000 MHz, respectively. Corner attenuation is plotted in dB relative to the horizontally polarized signal level observed in the center 

of the main tunnel. The same statements regarding curve fitting and measurement accuracy 

that pertain to the straight tunnel data also pertain to corner data. 

HORIZONTAL 

UNDER 

CABLE 

--- 

5 dB 

2 dB 

VERTICAL 

UNDER 

CABLE 

--- 

3.5 dB 

2.0 dB 

POLARIZATION 

AWAY FROM 

CABLE 

--- 

6.5 dB 

0.5 dB 

POLARIZATION 

AWAY FROM 

CABLE 

--- 

4.0 dB 

0.5 dB 
DISTANCE, FEET 

200-M HZ I 

I 

I I 

POLARIZATION 

TX RX 

A v v 

V H 

v 

I** * .FROM NORMAL 

OR1 ENTATION 

b 

Figure 2-8. 200-MHz Corner Attenuation for Coal Mine Tunnel. 

Significant propagation characteristics apparent from figures 2-8, 2-9, and 2-10 are as 

follows : 

a. Signal attenuation immediately around a corner is consider able at all three- frequencies. 

b. There appears to be complete depolarization of signals around the corner. 

Because of the high attenuation of a single corner, propagation around multiple corners is 

expected to be even more severely attenuated. Consequently, the signal existing at any point 

can be reasonably assumed to have followed the path including the least number of corners. 

The transmission loss at any point along a cross-tunnel can then be estimated by adding the 

attenuation from the appropriate curve in figure 2-8, 2-9, or 2-10 to the transmission loss 

corresponding to the distance along the main tunnel from the transmitter to the corner of the 

cross-tunnel. The corner attenuation curves are relative to the horizontal field at the center 

of the main tunnel. Therefore, if transmit polarization is horizontal, the horizontal curve 

from figure 2-5, 2-6, or 2-7 is used; if transmit polarization is vertical, the cross-polarization curve is used, (Note that receive polarization is unimportant because of depolarization 

around the corner .) 

For example, if the receive point lies 750 ft along the main tunnel and 60 ft along a crosstunnel, the transmission loss at 415 MHz is 147 dB when horizontal transmit polarization 

is used and 166 dB when vertical transmit polarization is used. 

As a check of the measured data, the walkie talkies were used to determine communications 

range along the main tunnel and several cross-tunnels. At three points where the communication signal became marginal, the transmission losses were determined to be 148, 150, and 

136 dB using the appropriate 415-MHz curves. These losses compare favorably with the 

143 to 146 dB range of the 1-watt walkie talkies. 
0 20 4 0 6 0 8 0 100 120 140 

DISTANCE, FEET 

Y 

&\ 

A - - - 

1 

Figure 2-9. 415-MHz Corner Attenuation for Coal Mine Tunnel. 

415-MHz 

POLARIZATION 

TX RX 

A v v !: H 

H * v 0 H H 

OH H * 

* 90° FROM NORMAL 

ORIENTATION 

I 

2.4.1.3 Corner Reflector 

Because of the severe attenuation experienced around corners, measurements were made to 

determine the amount of improvement gained through the use of corner reflectors to divert 

additional energy along the cross-tunnels. At 415 MHz, the reflector consisted of two corner 

reflector antennas connected back-to-back electric ally and physic ally. Design parameters and 

a picture of the antenna assembly (configured for vertical polarization) are provided in 

appendix A. At 1 GHz, a square aluminum plate of 6~' area was used. 

Observed corner reflector gain is shown in table 2-5 for 415 and 1000 MHz. No tests were 

performed at 200 MHz. Reflector gain is defined as the difference between signal levels 

observed before and after the reflector is set in position. The reference point for signal 

measurement is 65 feet along the cross-tunnel from the corner of the main tunnel. In each 

of the cases tested, significant reflector gain was noted. 
-- 

4 0 6 0 8 0 100 12 0 140 

DISTANCE, FEET 

Figure 2-10. 1000-MHz Corner Attenuation for Coal Mine Tunnel. 

Table 2-5. Observed Corner Reflector Gain. 

FREQUENCY 

415 MHz 

1 GHz 

*Flat plate reflects either polarization. 

TRANSMITTER 

H 

H 

V 

V 

H 

V 

V 

POLARIZATION 

REFLECTOR 

H 

H 

V 

V 

* 

* 

* 

RECEIVER 

H 

V 

H 

V 

H 

H 

V 

GAIN 

31 dB 

17 dB 

18 dB 

19 dB 

25 dB 

20 dB 

23 dB 
Two trends appear in the measurements of corner reflector that require additional data points 

for confirmation. 

The first trend is away from the depolarized fieldobservedwithout the corner reflector toward 

a dominant horizontal field, as observed in the main tunnel. This effect can be seen in table 

2-5 in comparing the 31-dB gain value to the 17-dB value. Unfortunately, no corresponding 

data was taken at 1 GHz for comparison to the 25-dB value. With a vertical transmitter, 

however, the field appears to remain depolarized (18 vs 19 dB, 20 vs 23 dB). 

The second trend, observed at 1 GHz, indicates a much lower attenuation rate along the 

cross-tunnel when a corner reflector is used. The observed attenuation rate more closely 

matches the 2- to 3-dB/100-ft rate observed in the main tunnel rather than the 30-d~/100-ft 

rate shown in figure 2-10. No data is available at 415 MHz for comparison. 

2.4,1,4 UHF Noise 

Spot noise measurements were made at each receiving point for horizontal and vertical 

polarization. In each case the external noise level was sufficiently below internal receiver 

noise to be undetectable. This type of noise survey is very superficial; however, the most 

probable source of uhf noise in the mine is from machine and power line generated rfi. 

Measurements made in the vicinity of heavy, battery-operated equipment and the 7200-Vac 

power line produced no observable noise. Threshold noise sensitivity for the uhf field meter 

is listed in table 2-6. 

Table 2-6. UHF Noise Sensitivity Threshold. 

2,4.2 Experimental VLF Propagation 

FREQUENCY 

200 MHz 

415 MHz 

1000 MHz 

b 

2.4.2.1 Roof Bolts 

. 

NOISE THRESHOLD SENSITIVITY 

-166 dBm/Hz 

-166 dBm/Hz 

-157 dBm/Hz 

Observed signal attenuation for intramine roof-bolt-to-roof-bolt antennas is shown in figures 

2-11 and 2-12 plotted against frequency and in figure 2-13 plotted against distance. Attenuation is plotted as the power transfer ratio between the roof-bolt antenna terminals. Transmission loss may be added directly to transmitter power to determine the received signal 

level (available power into matched load). The vlf attenuation curves are straight line segments connecting related data points. Transmission loss measurement accuracy is estimated 

to be h2 dB. 

Because of emphasis on the uhf measurements, only three field points were measured at vlf. 

During vlf testing, the antennas were established in cross-tunnels just north of the main 

tunnel (figure 2-1) so that no line-of-sight path existed between receiver and transmitter. 

Walkie-talkie communication between the field points was possible ; however, signals were 

typic ally weak. 
I 

(A) ORIENTATION 

TX N-S RX E-W 

130 

1 KHZ IO-KHZ 

FREQUENCY 

100 KHZ 

b I 

(B) ORIENTATION I TX E-W RX E-W 300, 

4801 

A --- CI 

4 

675 1 

I 

Figure 2-11. Observed Transmission Loss for Roof-Bolt Antennas in Coal Mine. 
10 KHz 

FREQUENCY 

2 

I 

(A) ORIENTATION I TX N-S RX N-S 

3001 

I 4' 3001 

(B) OR1 ENTATION 

TX E-W RX N-S 

/- 

-A 

Figure 2-12. Observed Transmission Loss for Roof-Bolt Antennas in Coal Mine. 

0 

- 

I 6751 I 

4801 
. = 10 KHZ 

= 3 KHz 

A 1 KHz 

0 100 200 300 4 00 500 600 700 800 

DISTANCE, FEET 

Figure 2-13. Observed Transmission Loss for Roof-Bolt Antennas in Coal Mine. 
Tests were conducted for two orientations of the receive and transmit antennas for a total of 

four configurations. An antenna was established by clamping a pair of test leads to two roofbolt heads separated by 52 feet. Each roof bolt was cleared of accumulated rock dust and 

rust to ensure good electrical connection. The north-south antenna orientation resulted in the 

antenna leads running perpendicular to the main east-west tunnel. The east-west orientation 

resulted in antenna leads running parallel to the main tunnel. A roof-bolt spacing of 52 feet 

was used throughout the tests. The impedance of the antennas was 100 to 120 ohms, resistive, over the 1- to 50-kHz measurement range. 

Significant propagation characteristics apparent from figures 2-11, 2-12, and 2-13 are as 

follows : 

a. Minimum transmission loss occurs for the east/west-to-east/west antenna combination 

indicating maximum coupling off the ends of the antennas. 

b. Transmission loss is relatively flat versus frequency. 

c. The attenuation rate is approximately 5 d~/100 ft averaged over all frequencies and 

antenna orientations. 

The available measurements do not fully characterize the propagation behavior. In particular, 

measurements over a greater range of distance, frequency and roof-bolt spacing are desirable. 

However, the range of a roof-bolt voice radio system can be estimated from measured data. 

Assuming a 25-watt transmitter, 10-dB noise figure receiver, 10-dB external noise, and a 

required voice S/No of 47 dB-Hz, the system has a range of 158 dB. Further assuming that 

the curves of figure 2-13 extrapolate at 5 d~/100 ft, 158-dB transmission loss then occurs at 

a distance of 1,200 to 1,400 feet, depending on antenna orientation. 

2.4.2.2 Roof-Bolt Noise 

Spot noise measurements were made at each receiving point for both orientations of the 

receiver roof-bolt antenna. In each case, the external noise level was below or on the order 

of the receiver internal noise in the 5- to 50-kHz region. Receiver noise threshold sensitivity was approximately -150 d~m/Hz. This result suggests excess noise was 24 dB or less 

over the 5- to 50-kHz region. 

The spot type of noise survey is superficial, at best, particularly since the measurement 

area was not close to a working face. However, measurements were taken in the vicinity of 

the 7200-Vac power cable. Below 5 kHz, the harmonic levels were sufficient to be a potential 

source of interference to a voice bandwidth communication system; however, specific levels 

were not recorded. 

2.4.2.3 Loops 

Observed field strength for intramine roof-bolt-to-loop antennas is shown in figures 2-14 and 

2-15 plotted against frequency and in figure 2-16 plotted against distance. Field strength is 

shown as the magnetic field intensity in d~/pA/m. This quantity is chosen rather than transmission loss because system performance analysis with loop antenna parameters as a variable is more convenient when the incident field strength is known. Also, direct comparison 

with noise data that is given in units of d~/p~/rn/-is possible without first correcting for 

the differences between the loop used for signal measurements and the loop used for noise 

measurement. The field strength curves are straight line segments connecting related data 

points. Field strength measurement accuracy is estimated at *2 dB. 
10 KHz 

FREQUENCY 

0 1111 

(c) ORIENTATION 

C 

Figure 2-14. Observed Field Strength for Roof-Bolt-to-Loop Antennas in Coal Mine. 

f 
10 KHZ 

FREQUENCY 

I I I 1. 

(B) ORIENTATION 

TX N-S RX HMD N-S 

I 

3001 

480,r 

6751 

100 KHZ 

Figure 2-15. Observed Field Strength for Roof-Bolt-to-Loop Antennas in Coal Mine. 

A 

, 
200 300 400 500 

DISTANCE, FEET 

., 

Figure 2-16. Observed Field Strength for Roof-Bolt-to-Loop Antennas in Coal Mines. 

2-24 

(A) 1 KHz 

ORIENTATION 

--• TX E-W RX VMD 

0 TX N-S RX VMD 

I I I 
During vlf testing, antennas were established in cross-tunnels just north of the main tunnel 

(figure 2-I), so that no line-of-sight path existed between receiver and transmitter. Walkietalkie communication between the field points was possible; however, signals were typic ally 

weak. 

Tests were conducted for three orientations of the receiver loop and two orientations of the 

transmit roof-bolt antenna for a total of six configurations. The north-south and east-west 

orientations of the roof-bolt antenna are described in the above paragraph on roof bolts 

(paragraph 2.4.2.1). 

The three orientations of the receive loop are given with respect to the magnetic dipole axis, 

that is, vertic a1 (VMD); horizontal east-west (HMD E-W); horizontal north-south (HMD N-S). 

The relative configurations of the antennas can be seen with the aid of figure 2-1. 

Significant propagation characteristics apparent from figures 2-14, 2-15, and 2-16 are as 

follows : 

a. Maximum field strength occurs for the E-W roof bolt-to-VMD configuration. 

b. Field strength is relatively flat versus frequency. 

c. The attenuation rate is approximately 4 dB/100 ft averaged over all frequencies and 

antenna orientations. 

The available measurements do not fully characterize the propagation behavior. In particular, measurements over a greater range of distance, frequency, and roof-bolt spacing are 

desirable. However, the range of a roof-bolt-to-loop-voice bandwidth radio system can be 

estimated from measured data. Assuming a 25-watt transmitter, 10-dB noise figure receiver, 

10-dB externally caused antenna noise, loop antenna similar to those used for field measurements, and a required voice S/No of 47 dB-Hz, the required field strength is -14 dB/pA/m 

at 50 kHz and +20 dB/pA/m at 1 kHz. Further assuming that the curves of figure 2-16 

extrapolate at 4 dB/100 ft, the minimum useful field strengths are reached at approximately 

1,500 feet at 50 kHz and 800 feet at I kHz when the loop is oriented as a VMD. 

2.4.2.4 Loop Noise 

Spot noise measurements were made at each receiving point for three receive loop orientations, In each case the external noise level was below internal receiver noise, across the 

7- to 50-kHz region. Receiver noise sensitivity was approximately -1 50 dBm/Hz, equivalent 

to an incident field strength of -43 dB/p~/m&% at 50 kHz, and increasing at 6 dB/octave 

below 50 kHz. Sensitivity from 20 to 50 kHz was adequate only for the detection of noise 

levels near the maximum to be expected according to results obtained at WVU.~ 

The spot type of noise survey is superficial, at best, particularly since the measurement area 

was not close to a working face. However, measurements were taken in the vicinity of the 

7200-Vac power cable. Below 7 kHz, power line harmonics were detected. Below 2 kHz, 

harmonic levels were sufficient to be a potential source of interference to a voice bandwidth 

communication system; however, specific levels were not recorded. 

2.4.3 Summary and Conclusion 

A series of radio measurements were conducted in a working coal mine to determine uhf and 

vlf propagation characteristics. Measurements included the effects of frequency, polarization, antenna type, and distance. The uhf tests included propagation along straight tunnels 

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

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

were obtained that have pr ac tic a1 significance in the definition, design, and implementation 

of radio communications systems in mines. 

2-25 
2.4.3.1 UHF 

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

Along a straight tunnel, attenuation rates varied from 15 to 25 dB/100 ft at 200 MHz to 

2.5 to 4 d~/100 ft at 1 GHz. Minimum attenuation is expected at frequencies above 1 GHz. 

Horizontal polarization was found to yield significantly improved results compared to 

vertic a1 or cross polarization. The attenuation of horizontally polarized signals averaged 

40 dB less than vertically polarized signals at 415 MHz and 30 dB less at 1 GHz. Considerable attenuation was observed in radio signals propagated around tunnel corners. Signal 

attenuation was approximately 45 dB at a point 20 feet past the corner at 415 and 1000 MHz. 

The rate of attenuation past 20 feet averaged 30 d~/100 ft as opposed to the 3 to 6 d~/100 ft 

rate observed in the main tunnel at 415 and 1000 MHz. Complete signal depolarization was 

noted along the cross-tunnel as opposed to the strong horizontal polarization observed in the 

main tunnel. The use of a corner reflector raised the signal level from 20 to 30 dB at a 

point 65 feet past the corner. At 1 GHz, the reflector appeared to lower the attenuation rate 

along the cross-tunnel, resulting in even greater effective gains further away from the 

corner. 

2.4.3.2 VLF 

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

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

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

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

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

roof-bolt antenna with the loop magnetic axis oriented vertically. The field strength produced by the roof-bolt antenna was relatively independent of frequency over the range 1 to 50 

kHz. The attenuation rate averaged 4 d~/100 ft over all frequencies and orientations with 

individual measurements deviating only slightly from the average. The communications 

radius of a 25-watt roof-bolt-to-loop voice radio system is predicted to be 1,500 feet at 50 

kHz and 800 feet at 1 kHz when the loop's magnetic axis is vertical. 

2.5 ACKNOWLEDGMENT 

The cooper ation and assistance of management and engineering personnel at the Inland Steel 

Co. coal mine is gratefully acknowledged. Their interest, patience, and commitment of 

personnel and resources have made the field test program a success. Particular acknowledgment is due to Mr. Doug Dwosh and Mr. Mark Morgan for extra efforts to help get the job 

done. 

2.6 REFERENCES 

1. Farmer, R. A., and No H. Shepherd, "Guided Radiation...The Key to Tunnel Talking," 

IEEE Trans on Vehicular Communications, pp 93-102, March 1965. 

2. Crary, J. H., "Determination of the Electromagnetic Environment in Coal Mines," Final 

Technical Report, ITS, Boulder, Colorado, 1 March 1972. 

3. Mine Communication and Monitoring Second Quarterly and Intermediate Annual Technic a1 

Progress Report (5 Sep to 4 Dec 1972) Department of Electrical Engineering - WVU, 

Morgantown, WVA. 
Section 3 

Experimental VLF to I,F Tests at Robena No. 1 Mine 

A later series of in-mine propagation studies were conducted under contract H0232056 in the 

Robena No. 1 mine on 12 March 1974, and the results are included in the text which follows. 

Large loop to small loop, small loop to large loop, line source to small loop, and small loop 

to line source arrangements are evaluated at separations of 50 ft, 100 ft, 200 ft, and 400 ft. 

In order for comparison of the experimental data with that obtained theoretically, all values 

are normalized to 10 watts input power and a 1-Hz bandwidth. 

3.1 VLF and LF Tests 

For the test setups for each particular configuration, refer to figures 3-1 through 3-3 of this 

section. Figures 3-4 through 3-11 graphically depict the results of the experimental data. 

lowSEPARATION 

TRANSM ISSlON LOOP 

DlAM ETER 8 INCHES/20.32 CM 

WEIGHT 2 LBS/.907 KG 

NOISE GRADE 14 (THEOHETICAL) 

Figure 3-1. 8-Inch Loop to 20-Meter Loop. 
DEPTH 

1 ow <-2 SEPARATION 

TRANSM ISSlON LOOP 

RADIUS 20 METERS/65.7 FT 

WEIGHT 6 KG/13.23 LB 

WIRE SlZE NO 10 

NOISE GRADE 14 (THEORETICAL) 

Figure 3-2. 20-Meter Loop to &Inch Loop. 

SEPARATION 

TRANSMITTING LINE 

LENGTH 100 M/328 FT 

WEIGHT 10.3 LB /4.67 KG 

NOISE GRADE 14 (THEORETICAL) 

WlRE SlZE NO 10 

Figure 3-3. Line Source to Loop. 
FREQUENCY (HZ) 

1 OOK 

Figure 3-4. Received Signal Vs Frequency (8-Inch Loop to 20-Meter Loop). 
1 OK 1 OOK 

FREQUENCY (HZ) 

Figure 3-5. Received Signal Vs Frequency (8-Inch Loop to Roof Bolt). 
1 OK 1 OOK 

FREQUENCY (HZ) 

Figure 3-6. Received Signal Vs Frequency (Roof Bolt to 8-Inch Loop). 
10 2 0 5 0 100 200 

FREQUENCY (KHZ) 

RECEIVED SIGNAL VS FREQUENCY 

- (20 M LOOP TO 8 INCH LOOP) 

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

r 

400 FT 

- 




Experimental predictions obtained from the figures are as follows: 

a. The optimal frequency for a 4-inch radius transmit loop is in the 100-kHz range. 

b. The optimal frequency for a 20-meter transmit loop is the 100- to 200-kHz range. 

c. The optimal frequency for roof-bolt transmission is in the 100- to 200-kHz range. 

d. Loop-to-loop transmission is considerably better than line source to loop at the smaller 

separations; however, at separations of 400 feet, line source transmissions and 20-meter 

loop transmission appear equivalent. Predictions as to maximum attainable separation 

are not made, since readings beyond 400 ft are not available. 

e. Also since readings beyond a 400-ft separation could not be made, optimal frequency 

ranges will probably decrease at the larger separations. 

In the preceding measurements, a VMD to VMDarrangement is employed for all loop-to-loop 

operations; that is, the planes of the transmitting and receiving loops are parallel to the horizontal. The curves illustrating coupling between line source and loop also indicate characteristics with the loop operated as a VMD. During the measurements, however, an anomaly 

was observed while transmitting with the line source. At the higher frequencies and at separations beyond 50 feet, greater signal levels were received with the receiving loop held 

parallel to the vertical. Up to a 400-foot separation, the greatest signal strength occurred 

with the loop parallel to the transmit antenna. At 400 feet, a strong signal was also received 

when the loop was perpendicular to the transmit antenna. These unexpected signals apparently are due to the higher frequencies being coupled into the 7200-volt line and then reradiated. 

However, more study in this area is required before firm conclusions can be made. 

3.2 COMPARISON OF V LF PREDICTIONS 

By use of the NBS noise data and the experimental readings, comparison of observed and predicted propagation can be made. The following graphs, figures 3-12 through 3-14, compare 

theoretical and experimental S/N, ratios for a 20-meter loop transmitting to an 8-inch loop, 

an &inch loop to a 20-meter loop, and a 200-foot line source transmitting to a loop. Many 

discrepancies exist. These can be explained in part by the following: 

a. Theory assumed a homogeneous medium of a = 0.01 ~ho/m. Actual conductivity will 

vary with the layers of different material. 

b. Effect of steel in roof (roof bolts) is not included in theory. 

c. Effect of other conducting material, such as trolley lines, was left untouched. In actual 

communication, these conducting materials may be usable to improve the received signal as demonstrated in the experimental data. 

d. Experimented readings employ actual mine noise that may be higher or lower than 

noise grade 14, which was used for theoretical calculations. 

One of the major differences observed between the predictions and measurements was received signal strength. In theory the received signal could be expected to be highest at the 

lower frequencies and to steadily decline with increasing frequency. In many cases, however, 

the experimental received signal increased with increasing frequency. It appears that, in the 

true mine environment, as the frequency is increased, more scattering of the transmitted 

electromagnetic waves back into the tunnel by the tunnel walls or roof bolts occurs, thus 

resulting in a higher received signal. However, more study and experimentation will have to 

be done in order to obtain a reliable explanation for this inconsistency. 

- 

Ill. 

w 

Overall comparison between experimental and calculated data yields the following conclusions: 

a. Measured data indicated an optimum frequency range comparable to that obtained in 

theory at these separations. 

b. In small loop transmission measured S/No ratio was larger than that calculated. 

c. Large loop and roof-bolt transmission provided higher S/N~ ratio in theory than that 

obtained experimentally. 

d. Actual roof-bolt antennas exhibit a much larger impedance than that predicted. This impedance was also observed to be capacitive instead of inductive as expected. The indication is that such impedances will vary drastically from mine to mine and be dependent 

on the composition of the roof strata. Antenna impedance obtained at Robena are shown 

in tables 3-1 and 3-2. 

Table 3-1. Roof-Bolt Antenna Measurements, Robena No. 1. 

F X Z 0 

Antenna = 100 Feet, 100 Feet Between Bolts 

R 

-9.293 

-10.216 

-11.726 

-7.729 

26.176 

L 

291.83 

262 .I56 

228.775 

201.83345 

163.799 

-47 .I24 

-46.496 

-46.496 

-27 .I43 

72.257 

20 kHz 

50 kHz 

100 kHz 

200 kHz 

500 kHz 

Antenna = 200 Feet, 200 Feet Between Bolts 

288 Q 

258 Q 

224 Q 

200 Q 

147 Q 

-11.2866 

-12.1 

-14.11 

-20.338 

25.618 

-375 

-148 

-74 

-21.6 

+23 

30 kHz 

50 kHz 

100 kHz 

200 kHz 

500 kHz 

-84.82 

-85.755 

-87.955 

-103.044 

109.327 

Antenna = 400-Foot Wire, 385 Feet Between Bolts 

433.38 

409.089 

360.882 

296.483 

252.856 

425 Q 

400 Q 

350 9 

278 Q 

228 Q 

-450 

-273 

-140 

-82 

34.8 

20 kHz 

50 kHz 

100 kHz 

200 kHz 

500 kHz 

b 

-34.934 

-22.619 

4.398 

- 

- 

340 Q 

312 Q 

292 Q 

- 

- 

341.79 

312.819 

292.033 - 

- 

-278 

-72 

7 

- 

- 

-5.866 

-4.146 

0.8629 - 

- 
Table 3-1. Roof-Bolt Antenna Measurements, Robena No. 1 (Cont). 

Table 3-2. Roof-Bolt Antenna Measurements, Robena No. 1 

(Just Outside Dispatcher's Shed). 

I 

F 

FREQ (Hz) 

R L (pH) 

R (Q) L pH) 

200- Foot Roof-Bolt Antenna, Willow Tree Main 

Robena No. 1, 10-Foot Roof Bolts 

Antenna = 200-Foot Wire, 180 Feet Between Bolts 

X 

20 kHz 

50 kHz 

100 kHz 

200 kHz 

500 kHz 

X 

-7.678 

-9.187 

-8.721 

-5.386 

37.729 

Z 

Z 

20 k 

50 k 

100 k 

200 k 

500 k 

8 

530 Q 

500 Q 

420 Q 

420 Q 

390 Q 

v 

0 

-398 

-174 

-73 

-19.4 

+59.6 

371 

338 

299 

258.5 

242 

Antenna ~200-Foot Wire, 150 Feet Between Bolts 

- 

-193 /AH 

-113 pH 

-43 pH 

0 

- 

-60.63 

-71.0 

54.04 

0 

-50.014 

-54.664 

-45.867 

-24.374 

187.238 

20 k 

50 k 

100 k 

200 k 

500 k 

. 

503.662 

475.332 

423.46 

390 

374.356 

342.392' 

302.498 

259.646 

306.0 

-59.062 

-71.628 

-64.088 

-28.9026 

174.044 

-6.914 

-8.59 

7.332 

0" 

415 

372 

322 

282 

235 

419.18 

378.833 

328.32 

283.477 

292.43 

-47 0 

-228 

-102 

-23 

55.4 

-8.01 

-10.899 

-11.257 

-5.85 

36.524 
Table 3-2. Roof-Bolt Antenna Measurements, Robena No.1 

(Just Outside Dispatcher's Shed) (Cont) . 

3.3 VLF SUMMARY 

FREQ (Hz) 

Preliminary analysis of vlf propagation within coal mines indicates adequate operation within 

a limited range. Figure 3-15 shows that intramine propagation characteristics are such that 

signal strengths, from an 8-inch diameter loop, vary several dB to in excess of 100 dB below 

those expected from s u r f a c e t r a n s m i s s i o n at the same displacements. Assuming 10 watts of 

input power and a 20-meter radius transmitting loop or roof-bolt transmitter, communication 

should be possible in excess of 150 meters (492 ft). Larger transmit distances seem possible 

by using techniques to couple into conductive devices such as a trolley wire. Based upon present knowledge, a vertical magnetic dipole (VMD) antenna arrangement provides the best 

signal-to-noise ratio for maximum displacement for a portable unit. Large loop-to-loop 

transmissions at lesser displacements provide the best s/N,; however, at larger displacements, line source to loop and large loop to loop are relatively equivalent. 

The impedance presented by the roof bolt at the Robena Mine was capacitive and much higher 

than expected. Instead of the predicted inductive load of 50 to 100 ohms, a capacitive load of 

400 to 500 ohms was measured. Due to the large ohmic resistance, absence of radiation resistance, and the short length of the roof bolt, efficient signal coupling is rather poor. 

Because of the shortage of time and financing, ultimate solutions may not have been found. 

Much more study and experimental tests are needed in this area to obtain firm conclusions 

as to propagated fields of all the antenna arrangements, especially the roof bolt. 

R 63 

Antenna = 50-Foot Wire - 40 Feet Between Bolts 

3.4 TABLES 

@H) X 

10 k 

20 k 

50 k 

100 k 

200 k 

500 k 

The tables in appendix B show actual measured frequency, voltage, current, noise, and signalplus-noise readings obtained in the Robena Mine for the various antenna arrangements. 

(S + n)/n was calculated in dB and normalized to 10 watts input power, l-Hz bandwidth, and 

corrected for length and weight. These values were used in obtaining the experimental graphs 

evaluated earlier. 

Z 6 

165 

158 

142 

134 

115 

91 

-18.22 

-21.112 

-22 .O 

-24.13 

-8.168 

41.155 

-290 

-168 

-7 0 

-38.4 

-6.5 

13.1 

166.003 

159.4 

143.69 

136.155 

115.289 

99.873 

-6.30 

-7.61 

-8.807 

-10.208 

-4.063 

24.335 

h 

Section 4 

UHF Predictions 

With the foregoing experiments as a reference, many uhf propagation predictions can be 

made. Testing arrangements consist of a transceiver centrally located in a typical mine 

cross section transmitting to a portable unit. For frequencies of 415 MHz and 1 GHz, a 

1-watt portable transceiver transmitting to a 1-watt portable transceiver is shown along with 

a 20-watt fixed station transceiver transmitting to a 1-watt portable unit. These arrangements are also shown with the addition of corner reflectors that reflect the propagated waves 

90 degrees to the original mode of travel, thus allowing for greater overall coverage. 

Figures 4-1 through 4-10 are examples of coal mine entries and crosscuts with propagation 

predictions for different uhf system arrangements shown. Variance of the predicted values 

due to obstructions, such as stoppings, will also be discussed. 

Major uhf characteristics are as follows: 

a. Optimal frequency is in the 1-GHz range. 

b. Corner attenuation is quite pronounced for both 415 MHz and 1 GHz. Propagation around 

more than one corner is quite remote. 

c. Maximum straight line tunnel propagation distance for a system with 144-dB range at 

415 MHz is 1,800 ft, while that for 1 GHz is 3,300 ft. 

d. Use of corner reflectors greatly enhance propagation coverage. 

e. Horizontal polarization provides approximately 25 dB higher received signal than does 

vertical or approximately 18 dB higher than does cross polarization. 

f. Depolarization is noted after propagation around corners. 

It should be noted that all predictions are based on testing that was done in an actual mine 

environment with no visual contact between transmitter and- receiver. 

The presence of stoppings for direction of airflow, passages blocked by machinery, or blockage caused by a roof fall seriously limit the communication range of a uhf system. Obstructions highly attenuate all uhf signal transfer, thus making the same systems rather impractical for some mine applications. Additional testing needs to be completed to obtain a 

quantitative value for the effect these stoppings have on uhf systems. 
Figure 4-1. UHF Propagation (1-Watt Transceiver Transmitting to 

1-Watt Transceiver - 1,800 ft). 

Transmit frequency - 415 MHz 

Polarization - Horizontal 

Base station - 1-watt transceiver 

Portable station - 1-watt transceiver 

System range - 144 dB 

Antenna - Omnidirectional, horizontal polarized, turnstyle 

(Darkened area indicates loss of transmission) 
Figure 4 -2. UHF Propagation (1 -Watt Transceiver Transmitting to 

1-Watt Transceiver - 3,300 ft). 

Transmit frequency - 1GHz 

Polarization - IIorizontal 

Base station - 1-watt transceiver 

Portable station - 1 -watt transceiver 

System range - 144 dB 

Antenna - Omnidrectional , horizontal polarization, turns tyle 

(Darkened area indicates loss of transmission) 
FTI 

Figure 4-3. UHF Propagation (20-Watt Transceiver Transmitting to 

I-Watt Transceiver - 2,000 ft). 

Transmit frequency - 415 MHz 

Polarization - Horizontal 

Base station - 20-watt transceiver 

Portable station - 1 -watt transceiver 

System range - 157 dB 

A.ntenna - Omnidirectional, horizontal polarized, turnstyle 

(Darkened area indicates loss of transmission) 
Figure 4-4. UHF Propagation (20-Watt Transceiver Transmitting to 

1 -Watt Transceiver - 3,800 ft). 

Transmit frequency - 1 GHz 

Polarization - Horizontal 

Base station - 20-watt transceiver 

Portable station - l-watt transceiver 

System range - 157 dB 

Antenna - Omnidirectional, horizontal polarized, turnstyle 

(Darkened area indicates loss of transmission) 
CCC 

000 

000 

X - INDICATES REFLECTOR IN CHC)SSClJT INTERSECTION 

415 MHZ 

Figure 4-5. UHF Propagation (1 -Watt Transceiver Transmitting 

to 1-Watt Transceiver With Corner Reflectors - 1,800 ft). 

Transmit frequency - 415 MHz 

Polarization - Horizontal 

Base station - 1-watt transceiver 

Portable station - 1-watt transceiver 

System range - 144 dB 

Antenna - Omnidirectional, horizontal polarization, turnstyle 

Reflector gain over isotropic - 24 dB 

(Darkened area indicates loss of transmission) 
Hgure 4-6. UHF Propagation (1 -Watt Transceiver Transmitting 

to 1-Watt Transceiver, With Corner Reflectors - 3,300 ft). 

Transmit frequency - 1 GHz 

Polarization - Horizontal 

Base station - 1-watt transceiver 

Portable station - 1-watt transceiver 

System range - 144 dB 

A.ntenna - Omnidirectional, horizontal polarization, turnstyle 

Reflector gain over isotropic - 24 dB 

(Darkened area indicates loss of transmission) 
X - INDICATES REFLECTOR 

IN CROSSCUT INTERSECTION 

Figure 4-7. UHF Propagation (20-Watt Transceiver Transmitting to l-Watt 

Transceiver With Reflectors - 2,000 ft). 

Transmit frequency - 415 MHz 

Polarization - Horizontal 

Base station - 20-watt transceiver 

Portable station - l-watt transceiver 

System range - 157 dB 

Antenna - Omnidirectional, horizontal polarization, turnstyle 

Reflector gain over isotropic - 24 dB 

(Darkened area indicates loss of transmission) 
X- INDICATES REFLECTOR IN 

CROSSCUT INTERSECTION 

Figure 4-8. UHF Propagation (20-Watt Transceiver Transmitting to 1-Watt 

Tranceiver With Corner Reflectors - 3,800 ft). 

Transmit frequency - 1 GHz 

Polarization - Horizontal 

Base station - 20-watt transceiver 

Portable station - 1-watt transceiver 

System range - 157 dB 

Antenna - Omnidirectional, horizontal polarization, turnstyle. 

Reflector gain over isotropic - 24 dB 

(Darkened area indicates loss of transmission') 
X - INDICATES REFLECTOR IN 

CROSSCUT l NTERSECTION 

Figure 4-9. UHF Propagation (20-Watt Transceiver Transmitting to 1 -Watt 

Transceiver With Corner Reflectors - 2,000 ft). 

Transmit frequency - 415 MHz 

Polarization - Horizontal 

Base station - 20-watt transceiver 

Portable station - l-watt transceiver 

System range - 157 dB 

Antenna - Omnidirectional, horizontal polarization, turnstyle 

Reflector gain of istropic - 24 dB 

(Darkened area indicates loss of transmission) 
Figure 4-1 0. UHF Propagation (l-Watt Transceiver Transmitting to l-Watt 

Transceiver With Corner Reflectors - 3,300 ft). 

Transmit frequency - 1 GHz 

Polarization - Horizontal 

Base station - l-watt transceiver 

Portable station - l-watt transceiver 

System range - 144 dB 

Antenna - Omnidirectional, horizontal polarization, turnstyle 

Reflector gain above isotropic - 24 dB 

(Darkened area indicates loss of transmission) 
Test Equipment and Experimental Setups 
This appendix lists the specific test equipments and configurations used during the coal mine 

field measurement program. Each item of standard test equipment carried a valid calibration sticker from Collins test equipment labs. Specific items built for this program, such 

as the vlf preamplifier and rf coaxial test leads were calibrated in Collins engineering lab 

prior to field use. 

Table A.-1 indicates the various items of equipment used to accomplish each test. Figures 

A.-1 and A,-2 show the associated equipment configurations for uhf and vlf, respectively. 

Figure A.-3 shows the antenna complement, left to right: 200-, 415-, and 1000-MHz 

ground-plane antennas; 415-MHz corner reflectors; 200- and 415/1000-MHZ dipoles; 1/3/10- 

and 20/50-k~z loops. Figure A-4 shows a close-up view of the 415-MHz corner reflector 

assembly. 

Specifications for the vlf preamplifier are as follows: 

Bandwidth (3 dB): 1 to 60 kHz 

Gain: 20 dB, nominal at 5 kHz 

Input: 51!2 or 10 k Q, balanced or unbalanced 

60-Hz rejection: Greater than 30 dB 

Power: +12 and -12 Vdc, 5 mA. 

Design of the 415-MHz corner reflectors follows that given by Jasik.* 

Antenna parameters are as follows: 

Center frequency: 415 MHz 

Corner angle: 90 degrees 

Reflector size: h=0.6 X(17 in) 

1=0.7 X(20 in) 

Dipole to corner spacing: s=0.35h (9 7/8 in) 

Predicted gain: 12 dBi 

The complete corner reflector assembly consists of two identical corner reflectors connected 

baclc -to-back physically and electrically. In this manner, the available power from one 

antenna will be reradiated by the other antenna in a direction at 90 degrees to the original 

signal. The effective reradiated power is 2x12 = 24 dB above that reradiated by a matched 

isotropic antenna, equivalent to a plane reflector of 1.3 h ** projected area. The maximum 

projected area of the corner reflector assembly is 0.6X** hence the corner reflector approach 

results in a physical structure of approximately half the area of a plane reflecting surface. 

Figure A-5 is an extended curve of the corner attenuation for uhf transmission at frequencies 

of 415 MHz and 1 GHz. Since measured values only extended to 120 feet, attenuation at 

greater distances was predicted. It was assumed that after rounding a corner, the attenuation 

of the electromagnetic wave would once again approach that of straight tunnel attenuation; 

that is 2.8 d~/100 ft for 1 GHz and 6 d~/100 ft for 415 MHz. This graph was used in the 

preparation of the uhf predictions. More study of corner attenuation is necessary before 

actual curves can be drawn. 

*~asik, Henry, "Antenna Engineering Handbook, f1 McGraw-Hill, New York, 

1961, Chapter 11. 

**Jasik, Henry, "Antenna Engineering," McGraw-Hill, New York, 

1961, Chapter 13. 
T Dl POLE 

AMPLE 

LINE REGULATOR FREQUENCY COUNTER 

SORENSEN 500-S HP 5245/5254 

0 

115 VAC 

Figure A-1. UHF Test Setup. 

LINE REGULATOR OSC l LLOSCOPE 

SORENSEN 500-S TEK 422 

115 VAC 

FIELD METER 

EMC-25 

. AUDIO 

OSCILLATOR 

HP 200 CD 

) 

DYNACO 

AMPLIFIER 

AUDIO 

MK-3 I P REAM F - TUNABLE 

VOLTMETER v HP 302A I 

4 . 

Figure A-2. VLF Test Setup. 

VOLTAGE 

CURRENT 

PHASE ANGLE 
Antenna nt for 

Coal Mil 

Figure A-3. Antenna Complement for Coal Mine Tests. 
Figure A-4. 415-MHz Corner Reflector Assembly. 

Table A-1. Test Equipment List. 

ITEM 

Power Oscillator 

AIL-124 

RF Power Meter 

BIRD 43 

Frequency Counter 

HP 5254~/5254~ 

Field Meter 

EMC-25 

Audio Oscillator 

HP-200 CD 

Audio Amplifier 

DYNACO r\/IK-3 

Oscilloscope 

TEKTRONIX 422 

Tunable Voltmeter 

HP 302A 

VLF Preamplifier 

COLLINS 

A-C Line Stabilizer 

SORENSEN 500-S 

Dipole Antennas 

EMPIRE DM105-T2 

DM105-T3 

Coaxial Log Spiral 

STODDART 93490-1 

A /4 Groundplane 

COLLINS 

Loop Antennas 

EMPIRE LG-105 (20/50 kHz) 

FAIRCHILD ALP-10 (1/3/10 kHz) 

UHF SIGNAL 

ATTENUATION 

AND NOISE 

X 

X 

X 

X 

X 

X 

X 

X 

VLF SIGNAL 

ATTENUATION 

AND NOISE 

X 

X 

X 

X 

X 

X 

X 

-- 
Appendix B 

Tables 
This appendix contains the actual measurements relating to frequency, voltage, current, noise, 

and signal-plus-noise readings obtained in the Robena Mine for the various antenna arrangements noted in Section 3. 

Table B-1. Roof-Bolt Transmitter, 8-Inch Receiver Loop. 

(s+N)/N (s+N)/N 

(dB) 

P 

(watts) 

S-tN 

(PV ) 

FREQ 

(kHz ) 

50-Foo t Separation 

5 

7 

10 

20 

50 

70 

100 

200 

V 

(volts) 

25 

25 

25 

25 

25 

25 

25 

25 

A 

(amperes) 

100-Foot Separation 

NOISE 

(PV) 

5 

7 

10 

20 

50 

70 

100 

200 

19 

25 

25 

2 1 

110 

150 

180 

.1 330 

25 

25 

25 

25 

25 

25 

25 

25 

1.01 

1,04 

1,08 

1,18 

123 

1.29 

1.30 

1.46 

1.4615 

2.5 

3.57 

4.2 

50 .O 

150.0 

180.0 

13 .O 

10.0 

7 .O 

5 .O 

2.2 

1 .O 

1 .O 

Meter 

noise 

200-Foot Separation 

3.296 

7.96 

11,057 

12.465 

33.98 

43.52 

45.105 

.1 

5 

7 

10 

20 

50 

70 

100 

200 

3.8 

3.6 

4.8 

4.5 

1.6 

0.9 

0.8 

Meter 

noise 

25 

25 

25 

25 

25 

25 

25 

25 

6.2 

8.5 

5.5 

7.3 

i1 .O 

12.3 

5.8 

1.2 

15 .O 

11.5 

7 .O 

5.2 

1.8 

1 .O 

1.2 

0.7 

1.63 

2.361 

1.146 

1.622 

6,875 

13.66 

7.25 

-- 

-- 

7.4 

5.5 -- 

1.1 

1.3 

6 .O 

4.252 

7.462 

1.182 

4.202 

16.745 

22.713 

17.207 

1.057 

1.058 

1.1 

1.083 

8.57 

1.01 

1.04 

1.08 

1.18 

1.23 

1.29 

1.30 

1.46 

0.481 

0.487 

0.828 

0.695 

18.66 

1.23 

1.23 

1.23 

1.23 

1.23 

1.6 

1.3 

2.5 
Table B-1. Roof-Bolt Transmitter, 8-Inch Receive Loop (Cont). 

FREQ 

(kHz ) 

V 

(volts) 

A 

(amperes) 

400-Foot Separation 

NOISE (s+N)/N 

(0) 

(s+N)/N 

(dB) 

S+N 

(Vv) 

-- 

-- 

-- 

-- 

1 

1.0625 

-- 

17 

-- 

-- 

-- 

-- 

0 

0.5266 

-- 

24.61 

5 

7 

10 

20 

50 

70 

100 

200 

d 

P 

(watts) 

1.23 

1.6 

1.3 

2.5 

Table B-2. Large Loop Transmitters, 8-Inch Receive Loop. 

25 

25 

25 

25 

25 

25 

25 

25 

-- 

-- 

-- 

-- 

1.3 

0.8 

0.9 

0.5 

FREQ (s+N)/N 

(kHz) 

-- 

-- 

-- 

-- 

1.3 

0.85 

-- 

8.5 

V 

(volts) 

A 

(amperes) 

50-Foot Separation 

(s+N)/N 

(d B) 

P 

(watts) 

NOISE 

(PV) 

S+N 

(mV) 

55.89 

56.00 

65.38 

70.63 

82.40 

90.10 

90.10 

5 

7 

10 

20 

50 

70 

100 

200 

10 .O 

8.25 

9.35 

11.04 

10.5 

9.25 

7.5 

11.5 

100-Foot Separation 

623.08 

630.77 

1857.14 

3400 

13181.82 

32000 

32000 

20 

25 

17 

23 

25 

25 

25 

25 

13 

13 

7 

5 

2.2 

1 

1 

Meter 

noise 

0.5 

0.33 

0.55 

0.48 

0.42 

0.37 

0.3 

0.46 

8.1 

8.2 

13 

17 

29 

32 

32 

30.5 

10 .O 

10.0 

9.69 

11.04 

10.5 

9.25 

7.5 

11.5 

. 

39.53 

40.237 

42.22 

46.114 

59.72 

65.2 12 

65.23 

(PV) 

360 

370 

62 0 

93 0 

1550 

1640 

1460 

1100 

5 

7 

10 

20 

50 

7 0 

100 

200 

94.74 

102.78 

129.17 

202.17 

968.75 

1822.2 

1825.0 

0.5 

0.38 

0.57 

0.48 

0.42 

0.37 

0.3 

0.46 

20 

25 

17 

23 

25 

25 

25 

25 

3.8 

3.6 

4.8 

4.6 

1.6 

0.9 

0.8 

Meter 

noise 
Table B-2. Large Loop Transmitters, 8-Inch Receive Loop (Cont) . 

P 

(watts) 

(s+N)/N 

(dB) 

(s+N)/N 

ZOO-Foot Separation 

S+N 

(mV ) 

NOISE 

(0) 

FREQ 

(kHz ) 

10.0 

10 .O 

9.69 

11.04 

10.5 

9.25 

7.5 

11.5 

10.458 

12.59 

20.71 

25.5 

34.89 

38.588 

33.979 

V 

(volts) 

3.33 

4.26 

10.857 

18.846 

55.56 

85 .O 

50 .O 

400-Foot Separation 

A 

(amperes) 

(I-I~) 

50 

49 

76 

98 

100 

85 

60 

13 

15 .O 

11.5 

7 .O 

5.2 

1.8 

1 .O 

1.2 

Meter 

noise 

5 

7 

10 

20 

50 

7 0 

100 

200 

-- 

-- 

-- 

-- 

1.3 

0.8 

0.9 

0.5 

5 

7 

10 

20 

50 

7 0 

100 

200 

20 

25 

17 

23 

25 

25 

25 

25 

(PV) 

-- 

-- 

-- 

-- 

1.4 

2.4 

2.5 

2.2 

0.5 

0.38 

0.57 

0.48 

0.42 

0.37 

0.3 

0.46 

-- 

-- 

-- 

-- 

6.36 

9.54 

8.874 

12.87 

-- 

-- 

-- 

-- 

1.076 

3 .O 

2.78 

4.4 

20 

25 

17 

23 

25 

25 

25 

25 

10.0 

10 .o 

9.69 

11.04 

10.5 

9.25 

7.5 

11.5 

0.5 

0.38 

0.57 

0.48 

0.42 

0.37 

0.3 

0.46 
Table B-3. 8-Inch Transmit Loop. 

I 

LARGE LOOP ROOF 

NOISE 

(0) 

50- Foot Separation 

NOISE 

(pV) 

FREQ 

(k~z) 

A 

(amperes) 

S+N 

(mv) 

V 

(volts) 

S+N 

(mv> 

P 

(watts) 

58.0 

40.0 

22 .O - 

4.5 

4.0 

1 .O - 

5 

7 

10 

20 

50 

70 

100 

200 

(s

0.52 

0.6 

0.3 

- 

0.3 

0.3 

0.25 

- 

5.5 

15 .O 

25 .O 

- 

25 .O 

10 .O 

25 .O - 

100-Foot 

(s+N)/N 

Separation 

2 ..6 

8.6 

6.1 

- 

14.0 

9.0 

14.0 - 

2.86 

9 .O 

7.5 

- 

7.5 

3 .O 

6.25 

- 

(s+N)/N 

(dB) 

44.83 

215.0 

2 7 7..3 

- 

3111.1 

2250.0 

14000.0 

- 

6 0.0 

35 .O 

25.0 

- 

2.2 

4.0 

1 .O - 

5 

7 

10 

20 

50 

70 

100 

200 

5 

15 

- 

- 

25 

9 

- 

- 

0.52 

0.49 

- 

- 

0.3 

0.3 

- 

- 

33.03 

46.649 

48.86 - 

49.858 

67.04 

82.92 - 

0.100 

0.310 

0.32 

- 

2.05 

2.2 

4.5 

- 

2.6 

7.35 

- 

- 

7.5 

2.7 

- 

- 

230 

250 

230 

- 

16 

12 

80 

- 

2.66 

8.857 

12.8 

- 

93 1.3 

550.0 

4500.0 - 

3.5 

0.7 9 

0.5 9 

- 

1.33 

1 .O 

2.1 

- 

4.436 

18.946 

22.14 

- 

59.34 

54.807 

73.054 - 

- 

290 

210 

- 

16 

12 

7 

- 

- 

0.350 

0.240 

- 

0.35 

0.43 

0.82 

- 

2

1
Table B-4. Roof-Bolt and Large- Loop Transmission. 

(Compensation for 200-Hz to 1-Hz Bandwidth and Normalized to 10 Wat.ts Input Power). 

Table B-5. 8-Inch Transmit Loop Normalized to 10-W, 1-Hz Bandwidth. 

FREQUENCY (5OFT) 

NORMALIZED 

(s+N)/N (dB) 

Root-Bolt Source 

ROOF BOLT 

NORMALIZED (S + N)/N (dB) 

LARGE LOOP 

(200 FT) 

NORMALIZED 

(S+N)/N (dB) 

(100 FT) 

NORMALIZED 

(S+N)/N (dB) 

FREQ (kHz) 

(400 FT) 

NORMALIZED 

(S+N)/N (dB) 

- 

- 

- 

- 

32.1 

3 1.48 

- 

45.32 

I 

(S + N)/N (dB) 

- 

- 

32.58 

32.59 

- 

32.56 

32.56 

50.00 

5 

7 

10 

20 

50 

70 

100 

200 

Large- Loop Source 

50-Foot Separation 

35.396 

40.06 

43.167 

44.565 

66.08 

74.48 

76.96 

5 

7 

10 

20 

50 

70 

100 

36.35 

39.56 

33.28 

36.302 

48.845 

53.09 

49.07 

5 

7 

10 

20 

50 

70 

100 

200 

33.44 

35.81 

43.85 

48.07 

57.68 

61.93 

58.23 

56.03 

70.12 

73.12 - 

92.86 

90.25 

107.97 

- 

- 

- 

- 

29.14 

32.88 

33.12 

35.81 

78.87 

79.833 

88.68 

93.2 

105.19 

113.44 

114.35 

46.65 

33.46 

32.44 - 

62.65 

44.94 

53.43 

62.51 

63.46 

65.36 

68.68 

82.51 

88.55 

89.48 
Table B-5. 8-Inch Transmit Loop Normalized to 10-W, 1-Hz Bandwidth (Cont). 

i 

ROOF BOLT 

NORMALIZED (S + N)/N (dB) 

LARGE LOOP 

FREQ (kHz) (S + N)/N (dB) 

100-Foot Separation 

- 

25.98 

24.16 - 

51.06 

54.09 

64.37 

5 

7 

10 

20 

50 

70 

100 

33.30 

43.29 

45.14 

- 

83.60 

83.50 

96.06 

To Large Loop - 100-Foot Separation 

FREQ 

5 

7 

10 

20 

50 

70 

100 

S + N (mV) 

0.1 

0.3 1 

- 

- 

2.05 

2.2 

- 

S + N (NORMALIZED TO 

10 W) (mV) 

0.2 

0.36 

- 

- 

2.37 

4.23 

- 

To Line Source - 100-Foot Separation 

S + N (NORMALIZED TO 

10 W) (1nV) 

- 

0.41 

0.277 

- 

0.4 0 

0.83 

1.081 

FREQ 

5 

7 

10 

20 

50 

70 

100 

S + N (0) 

- 

0.350 

- 

- 

0.35 

0.43 

- 
Table B-6. Large Loop Transmission. 

FREQ S + N (mV) S + N (NORMALIZED TO 10 W) (mV) 

50-Foot Separation 

8.1 

9.03 

13.44 

16.18 

28.30 

33.27 

36.95 

28.44 

5 

7 

10 

20 

50 

70 

100 

200 

8.1 

8.2 

13 .O 

17 .O 

29.0 

32 .O 

32 .O 

30.5 

100-Foot Separation 

360.0 

401 .O 

629.84 

885 .ll 

1512.65 

1705.0 

1686.0 

1025.76 

5 

7 

10 

20 

50 

70 

100 

200 

360 

401 

620 

930 

1550 

1640 

1460 

1100 

200-Foot Separation 

5 

7 

10 

20 

50 

70 

100 

200 

50 

53 

76 

98 

100 

85 

60 

113 

50 .O 

53 .o 

77.21 

93.27 

98 .O 

88.39 

69.28 

12.37 

400-Foot Separation 

5 

7 

10 

20 

50 

70 

100 

200 

- 

- 

- 

- 

1.4 

2.4 

2.5 

2.2 

- 

- 

- 

- 

1.37 

2.50 

2.89 

2.05 
2 00-Foot Separation 

5 

7 

10 

20 

50 

7 0 

100 

200 

- 

- 

7.4 

5.5 

- 

1.1 

1.3 

6.0 

- 

- 

21.10 

15.68 

- 

2.75 

3.61 

85.68 

400-Foot Separation 

3.71 

2.13 

6.53 

i 

50 

7 0 

2 00 

1.3 

0.85 

8.5 
Table B-8. Small-Loop Transmission. 

FREQ S + N (mV) S + N (NORMALIZED TO 10 W) (mV) 

To Large Loop - 50-Foot Separation 

4.84 

9.07 

7.04 

- 

16.17 

16.43 

17.71 

5 

7 

10 

20 

50 

70 

100 

2.6 

8.6 

6.1 

- 

14 .O 

9 .O 

14 .O 

To Line Source - 50-Foot Separation 

6.54 

0.83 

0.68 

- 

1.54 

1.83 

2.66 

5 

7 

10 

20 

50 

70 

100 

3.5 

0.79 

0.59 

- 

1.33 

1 .O 

2.1