Waveform Generator-Package 

and Receiver 

(Mancarried and Helicopter Receiver Portion) 

Prepared for 

UNITED STATES DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

Collins Commercial Telecommunications Division 

Circuit Switching Systems Operation 

Cedar Rapids, Iowa 52406 

Rockwell International 

FINAL REPORT 

Contract No. H0242010 November 1976 
DISCLAIMER NOTICE 

The views and conclusions contained in this document are those of the authors and 

should not be interpreted as necessarily representing the official policies or recommendations of the Interior Department's Bureau of Mines or of the US Government. 
I Waveforn~ Generatcr Package and Receivers L~el eased Ilaveelber 1976 1 ----_I_-- ___ 

Charles Anema --I---I-------~----l----.CI -- 9. #,,I t(~r#,lt,f, Ot~,4t,l~~,L!1:t0 !.&or nrd /.<~I:~~~ 

Coll ins Corcrnercial Tcl ecommunications Division 

Rockwell International 

Cedar Rapids, Iowa 52406 

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Final I 

The Mancarried and Helicopter Rece-hers were developed under the contract I / for trapped miner location. This program was a five phase program i.ri th I 

15 rnancarried and 5 he1 icopter production recei vers del ivered under Ptiase I 

IV and equipment docurncntation required under Phase V. 

17, Ot(~[iuat~,r'# hcy botds 

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FOREWORD 

This report was prepared by Coll ins Radio Group, Rockwell International , 

Cedar Rapids, Iowa under USBM Contract Number H0242010. The contract was 

initiated under the Coal Mine Health and Safety Research Program. It was 

administered under the technical direction of PM&SRC with Dr. H. K. Sacks 

acting as the Technical Project Officer. Mr. Frank Pavl ich was the contract 

administrator for the Bureau of Mines. 

This is a summary of the work completed as part of this contract during the 

period April, 1974 to March, 1976. 

This report was submitted by the author on November 30, 1976. 

This report covers the mancarried and helicopter receivers part of the contract. 

Addi tional reports for the transmitter and down1 ink receiver complete the - 

final report package. 
TABLE OF CONTENTS 

Foreword 

Page 

Report Documentation Page 1 

1.0 Introduction 5 

2.0 PHase I Define Problem and Identify Solution. 7 

2.1 Receiver Description 

2.2 Receiver Specifications 

2.3 Mancarried Receiver Design 

2.4 Helicopter Receiver Design 

2.5 Mechanical 

2.6 Fi 1 ter Response 15 

2.7 Receiver Noise Figure ana Antenna Determination 20 

2.8 Re-examination of Uplink Signal to Noise Ratio 2 1 

2.9 Battery Selection and Charger 2 4 

3.0 Phase I1 Design Equipment 

3.2 Electrical Design 

3.3 Mechanical Design 

4.0 Phase 111 Construct Working Model 

5.0 Phase IV Build Production Units 

6.0 Intrinsic Safety 

7.0 Conclusions and Recommendations 
LIST OF FIGURES 

FIGURE NO. PAGE NO. 

Receiver Gain Dist,ribution 

Mancarried Recei ver 

Mu1 ti pl e Channel ULF He1 i copter Recei ver. 

Mancarried Receiver Photograph 

He1 icopter Receiver Photograph 

Crystal Fi 1 ter Response 

Gausian Filter Response 

Propagation Curve 100 FT loop. 

Propagation Curve 400 FT loop. 

Battery Data 

Mancarried Receiver Schematic 

Synthesizer ULF Schematic 

Helicopter Receiver Schematic 

Helicopter Pre-Amplifier 

Vol ume Control Attenuation 

XTAL Fi 1 ter Attenuation Curve 

Recei ver Mancarri ed 

Receiver Assembly Mancarried 

Chassis Assembly Helicopter 
INTRODUCTION 

This final report covers the Man Carried and Helicopter Receiver Portion of 

USBM Contract H0242010. This contract consists of three separate tasks that 

include the packaging of waveform generators, design and building mancarried 

and helicopter receivers, and the design and packaging of a voice downlink 

receiver with a waveform generator. The final report for the packaging of waveform generators has been completed. The downlink receiver task is now in 

process and a report will be written at the completion of this task. The 

three reports taken together will complete the final reporting requirements 

for contract H0242010. 

The design and building of mancarried and helicopter receivers portion of this 

contract consisted of the design and builu of 15 mancarried and 5 helicopter 

receivers. These receivers are used for trapped miner location during a 

mine disaster. The helicopter receiver is a six channel ULF receiver used to detect 

a ULF transmitter that would be carried by a miner and turned on during a mine 

disaster. Immediately after a disaster a helicopter is flown over the area 

and with the aid of the helicopter receiver coarse location, and the active 

channels are determined. Final precise location is made with the sinele channel 

mancarried receiver. , 

15 mancarried receivers including antenna and headset were built and delivered to 

the Bureau. 5 he1 icopter receivers including headsets and a 50 foot tetherinq 

cable to support the suspended he1 icopter antenna were del ivered to the 

Bureau. This production experience has r e s u l t e d in a firm producible electrical 

and mechnaical design that can now be manufactured in quantity. 

The information in the following sections discusses the details of the 

mancarried and helicopter receivers. From Phase I - Define problem and identify 
possible solutions through Phase IV build and deliver production units. A 

phase V documentation is provided under another package that includes schematics, 

parts 1 ist, fabrication drawings, production test requirements, and instruction 

manual s. 
2.0 PHASE I DEFINE PROBLEM AND IDENTIFY SOLUTION 

This section will discuss the receiver requirements and present the 

receiver electrical and mechanical design to fulfill these requirements. 

Other design information such as uplink signal to noise ratio, filter 

response, antenna design and battery comparisons are included. 

2.1 RECEIVER DESCRIPTION 

The mancarried and helicopter receivers are used to detect and locate 

the position of a pulsed transmitting antenna below the surface. These 

receivers operate from 1050 to 3030 hertz and use a loop antenna approximately 15 inches in diameter to detect a null in the vertical magnetic 

field of a transmitting loop below the surface. The transmitting antennas 

are a portable 90 foot loop or a fixed 400 foot loop. Location depths to 

1600 feet have been detected. The position directly over the transmitting 

antenna is indicated by a null in the vertical magnetic field. This null 

is indicated by a panel meter and a headset on the receivers. The he1 icopter receiver is essentially six mancarried receivers in one package with 

two operator positions that enable switching to any of the six channels. The 

helicopter receiver also uses a loop antenna that is suspended 50 feet below 

the he1 icopter to provide isolation from helicopter electrical noise. 

2.2 RECEIVER SPECIFICATIONS 

The following receiver specifications are the final design values. Changes 

from the original specification are as follows: Bandwidth changes were made 

to provide a reasonable cost filter, BNC output connectors were eliminated 

because of limited panel space, mancarried rechargeable batteries were replaced 

by primary cells to provide better service, the helicopter receiver was 

changed to have two operator positions to provide better operation. 

2.2.1 MANCARRIED RECEIVER 

Receiver Bandwidth 

3 DB points NMT 30 HZ 

60 DB pointw NMT 125 HZ 

- 7- 
Sensitivity 

.05 microvolts for 6DB S+N/N ratio. 

Environmental Requirements 

-40c0 to +50c0 

Waterproof case, connectors and switches. 

Operator Controls 

On-off, battery test,frequency select, and gain control. Antenna hand he1 d 

and manually oriented to select field component being measured. 

Frequencies 

Designed for Channel 18,1050 to Channel 51) 3030 HZ. Channel frequency (HZ) 

= Channel No. X 60 - 30. Channel 2 to 16 and channel 52 to channel 99 available 

with reduced performance, due to 1000 to 3000 HZ bandpass filter of first 

stages. Channel 17 and 1 are unuseable. 

Signal Strength Range 

.05 Microvol ts to 100 microvol ts 

- 

Shelf Life 

Five Years 

Power 

Four 3.0 volt lithium batteries LR 660 

Continuous Operation Requirement 

Unit shall operate continuously for 120 hours, with fresh batteries. 

Measurements 

A visual field strength meter is provided. A XTAL headset is provided. 

Antenna 

Potted 500 turn loop approximately 15 inch diameter. 
Intrinsic Safetv 

Approved by Mesa Permit number 331. 

2.2.2 HELICOPTER RECEIVER 

Sensitivity 

.05 microvolts for 6DB S+N/N ratio. .5 microvolts without pre-amp1 ifier. 

Receiver Bandwidth 

3DB points NMT 30HZ 60DB points NMT 125HZ 

Envi ronmental Requi rements 

-40c0 to 50c0 

O~erator Control s 

On-off-battery test, frequency select, gain control and receiver select. 

Receiver select allows two operators to select any of the six receiver outputs. 

- Frequencies 

Designed for channel 18, 1050 HZ to channel 51, 3030Hz. Channel Frequency (HZ)= 

Channel No. X 60-30. Channel 2 to 16 and channel 52 to 90 available with 

reduced performance, due to 1 to 3 KHz bandpass filter of first stages. Channel 

17 and 1 are unuseable. 

Sianal Strenath Ranae 

.05 mi crovol ts to 100 mi crovol ts . 

Power 

12 VDC rechargeable lead acid battery. Can operate from external 12 VDC auto 

battery. 

O~erational Use 

With 6 month maintenance recharge. Unit will operate a minimum of 8 hours. 
With 8 hour recharge unit will operate for 16 hours. 

Antenna 

Potted 500 turn loop approximately 15 inch diameter. Includes 20DB preamp1 ifier 

and voltage follower powered from receiver. Antenna is suspended by 50 foot 

cable. 

Measurements 

Six visual field strength meters and two switchable headset outputs are provided. 

2.3 - Mancarried Recei ver Electrical Design 

The required minimum detection of .1 UA/Meter field results in an antenna 

voltage of 

2 VOS = 871 X AfHn 

A = .I13 Meter 2 

For the above antenna, H field and frequency, 

VOS = ,044 Mi crovol ts 

.05 microvolts requires a gain of approximately 160 DB to obtain an acceptable 

level to drive the headset and panel meter. 

The required gain of 160DB would not be stable if the gain is all at one frequency, therefore the gain distribution and up conversion of figure 1 was 

chosen. This frequency scheme provides isolation for input and output frequencies except for channel 17 (990 HZ). At this frequency the isolation 

provided by the XfAL filter is not sufficjent to eliminate oscillation, so 

that channel 17 is unuseable. 

A complete block diagram of the receiver including the synthesizer is shown 

in figure 2. 

The received signal is amplified 80 DB and filtered before mixing with a 

variable injection frequency from the SMO to provide sum and difference frequencies. 

The sum frequency (upper sideband) 50130 Hertz is passed by the selective 

50130 HZ XTAL filter. A1 1 other frequencies are rejected by the filter. After 

passing through the filter a second mixer with a fixed SMO injection frequency 

of 49152 Hertz results in sum and difference frequencies of 99 282 Hz and 978 Hz. 

The difference frequency is amplified 80 DB while the sum frequency is 

completely attenuated by a low pass filter. The resulting 978 HZ signal drives 

the panel meter and the headset. All incoming signals 1050 to 3030 Hz are 

converted to 978 HZ by this conversion scheme. 

2.4 - HELICOPTER RECEIVER DESIGN 

The helicopter receiver design is identical to the mancarried receiver except 

that the first 20DB of gain is removed from the receiver and put in the antenna 

package. Figure 3 shows a block diagram of the mu1 tiple channel helicopter 

receiver. 

2.5 MECHANICAL 

Preliminary layouts of the manpack receiver and helicopter receiver were completed 

during Phase I. The manpack receiver is comprised of a hydroformed aluminum 

can with spotwelded be1 tloop and fusion welded nut blanks. The cover is an 

investment cast alumlnurn with a recessed gasket surface and projecting edge to 

offer protection for the connectors and controls. A vacuum-formed polycarbonate 

cover is slipped over the top of the receiver for protection against dirt 

during long perlods of storage. A picture of the mancarried receiver is shown 


in figure 4. Additional detail can be obtained from the documentation package. 

The helicopter receiver consists of two sand cast aluminum sides which serve 

as handles and protection for the front panel and the connectors and power 

cord on the near panel. Heavy gauge aluminum sheet will be used for the 

remainder of the chassis to provide a low cost, light weight, yet rugged unit. 

A picture of the helicopter receiver is shown in figure 5. Additional 

detail can be obtained from the documentation package. 

2.6 - FILTER RESPONSE 

The filter pulse response for a practical three pole butterworth filter, similar 

to the filter considered for this design, and a minimum ringing Gaussian filter 

was theoretically investigated. 

Figure 6 shows the theoretical dynamic response of a three pole butterworth 

bandpass fi1 ter with figure 7 showing the dynamic response of a Gaussian bandpass filter to a 100 ms pulse. The pulse is a simulation of the input signal 

to the receiver from the waveform generator. The graphs simulate the response 

of the receiver to the pulses with nominal 10 Hz bandwidth. 

From these graphs, it can be seen that although the Gaussian filter does exhibit 

minimum ringing, no apparent over shoot or objectionable ringing will occur for 

the three pole butterworth bandpass fi 1 ter. 




2.7 Receiver Noise Figure and Antenna Determination 

Phase I theoretical investigations were completed relating to antenna 

design and receiver noise figure. The resulting calculations determine 

the minimum loop radius, for a given loop weight, that if this radius is 

increased beyond the minimum size, nothing will be added to the reception 

of the signal or its received signal-to-noise ratio. 

This minimum radius for the receiving antenna is: 

Where 

F = Total receiver noise factor 

'In = Minimum noise field in ua/m for bandwidth tf 

W = Loop weight in Kgm 

f = Receiver frequency in Hz 

of = Receiver noise bandwidth in Hz 

7' = Amount received ambient noise is greater than internal receiver noise. 

Using this equation with? = 10, f = 1 KHz, W = 3.46 Kgm, F = 31.62/15 db, 

nf = 10 Hz, and tin = 0.05 ua/m the minimum radius for an untuned receiver 

is 9.48 inches which is close to the radius of the present loop antenna. 

* For derivation see R. P. Decker, "Signal to Noise Analysis for Loopto-Loop Mine Conunications", Final Report Contract H0232056 Page 5-10. 
From these calculations it currently appears that both the mancarried 

and helicopter receivers can be broadbanded eliminating any tuning 

capacitors. 

2.8 Re-examination of Uplink Signal-To-Noise - - Ratio 

The following Figures 8 and 9, are propagation calculations for expected S/No (for a 1 Hz bandwidth) using the newest NBS noise data 

ava i 1 abl e 21 December 1 973. 

Calculations were made for both Mean Surface Noise and Minimum Surface 

Noise Grades using both a 100 foot transmitting loop and a 400 foot transmitting loop. Overburden depths varied between 50 meters and 300 meters 

for conductivities of 0.01 mhos/meter. 

Although these calculations have no direct effect on the actual design, 

they can be used to determine what effects various transmitter loop 

sizes and powers have on the surface fields. 


2.9 Bdttery Selection and Charger Results 

2.9.1 Helicopter Receiver 

Two 6 volts 4.5 A.H. batteries are required for the helicopter receiver. 

The choice for these batteries are the Gates lead acid cell type. The 

other battery considered was the Globe gel cel. This battery was discarded in favor of the Gates because of the amount of hydrogen and oxygen 

vented. The gel cell has a low pressure seal that vents easily during 

charging, whereas the Gates has a high pressure seal that has a minimum 

amount of venting. This venting of hydrogen and oxygen is deemed undesirable because of corrosion and possible explosion in a sealed, watertight enclosure. 

The 4.5 A.W. battery will meet the 8 hour operation requirements between 

charges. The requirement for 6 hour operatiion after a one hour preparation time can also be met, but it is recommended that a 6 month maintenance 

program be establ ished so that a one hour fast charge preparation time 

is not required. The reasons for establishing a six month maintenance 

program are that lead acid battery manufacturers do not recommend storage 

in a discharged state, deleting the fast charge will simplify the charger, 

and operation readiness will be enhanced. The low self discharge rate of 

6 - 8% per month with a 6 month maintenance charge will provide the required 6 hours of operation without a one hour preparation time. 

The charger for the he1 icopter receiver will be self-contained and will 

consist of an integrated circuit U723 regulator in a constant voltage 

charging configuration. 
2.9.2 Manpack Receiver 

Two 6 volt 1 A.H. batteries are required for the manpack receiver to provide the required 20 hours of operation. A Gates cell of this size is 

not available so that a choice had to be made between a Globe gel cell, 

Ni-Cad or lithium primary cell. A detailed comparison of all of 

these battery types is shown in Figure 10. The gel cell has venting problems and the Ni-Cad has poor self-discharge and a cell reversal memory 

problem. The 1 ithium primary cell is 1 ightweight, has long shelf 1 ife 

and appears to be ideal for this application but is not rechargeable. 

The l i t h i u m c e l l would not require a 6 month maintenance program, but would 

require a shelf life replacement time of 3 - 5 years. The 4 AH would 

provide approximately 80 hours of operation. No preparation time or 

charger is required. 
BATTERY COPIPARI SOG 

(MANPACK RECEIVER) 

XODEL - KIND COMPANY 

Lead-Acid Globe 

VOLTS CELL CAPACITY WEIGHT SIZE STORAGE 

NO* -SELF DISCH

1.5 A-H 1 .15 ib 7.02"L 2% - 3%/

1 ,33I1W 

re: (-) Excessive venting of hydrogen and oxygen dae to fast . 

charging and overcharging,at -40°C 

capacity down to 40%. 

" 

Lead-Ac id Gates 

tcr.~en:s: (-) Too large and heavy 

950/195 Lithium ACR Electronics 12V 6 4 A-H 

Conmenth: (-) !lust carry extra set (+) light weight and small 

don't know charge of no battery charger 

cell. 3 years service life 

XFCR1. OST N I -CAD General - 12V 10 1,2A-H 

Electric 

2.01.lb.t 4.05"L 6% -8%/m

2 , 7O1lh! 

2.03"H 

Individually 

1 ,35"Dia1neter 

2.03"Height 

Con~ents: (-) poor self discharge (+) can be fast charged 

memory pro bl em 

cell reverse probl em 

Figure 10 
3.0 PHASE I1 DESIGN EQUIPMENT 

3.1 INTRODUCTION 

The following information and data were the recommended phase I1 design 

for the receivers of the "Waveform Generator Package and Receiver", 

contract No. H0242010. 

During this phase, the out1 ined solutions from Phase I were used as 

a guide and the receiver circuits were designed, breadboard, and 

tested. The final mechanical configuration and design was completed. 

Electrical design, schematics, significant test resul ts, mechanical 

design, drawings and selected specifications were presented for Bureau 

comnents, changes and approval. This section reflects the final design 

with a1 1 changes incorporated. 

3.2 ELECTRICAL DESIGN 

3.2.1 - Man Carried Receiver 

With reference to Figure 11, the schematic of the man carried receiver, 

a description of the receiver operation will be discussed. 

The received signal picked up by the antenna ranges from .1 UA/M to 

100 MA/M or .05 UV to 50 MV. To raise the minimum vol tage to a 1 V 

level without losses to drive a headset requires 146 dB of gain. 

The first 40 dB of gain is obtained by two FET stages. The low noise 

characteristic of FETS are used for the first stages to obtain the required 

S+N/N ratio. The last FET stage is buffered by an emitter follower 

before the next 40 dB of op amp gain. This operational amp1 ifier 

is configured as a high pass active filter to further reject noise outside 

of the desired receiver bandwidth. High frequency noise is attenuated 

by the inherent high frequency roll off of the op amp and the feedback . capacitor at the emitter foll ower. 

The received signal is then mixed with the variable injection from the 

synthesizer to produce sum and difference frequencies. A 1,050 Hz 

received signal mixes with 51,100 Hz to produce 52,230 Hz and 50,130 Hz. 

The 52,230 Hz is rejected by the crystal filter while the 50,130 Hz signal 

is passed through the filter with 1 i ttle attcnuation. After buffering 

and matching by an emitter follower, the 50,130 Hz signal is mixed with 

a fixed injection frequency of 49,152 Hz, producing a 978 Hz and a 

99,282 tlz signal. The 978 Hz signal is passed through the final two 

op amp stages with a gain of approximately 80 dB. The op amp frequency 

response is rolled off above 1 kHz so that the 99,282 Hz image is 

rejected. This final 978 Hz signal drives the headset and meter circuit. 

This offset frequency scheme provides isolation between the input signal 

and output signal to mininlizc the possibil i ty of oscillations caused 

by coup1 ing between the antenna and output circuits. 

The large (120 dB) of signal range .1 UA/M to 100 MA/M is accomnodated 

by 3 FET attenuators controlling 3 gain stages. These FETs are used 

as voltage controlled variable resistors all being driven by a single 

volume control . 

The receiver is powered by four 3.0 volt lithium primary cells. These 

cells are configured to provide +6 volts and -6 volts. Battery life is 

estimated to be 80 hours. The batteries are made intrinsically safe 

by the addition of a small internal resistor by the battery manufacturer. 
3.2.2 Frequency Syn thes i zer 

Figure /a is a schematic of the digital ULF synthesizer which derives 

a total of 34 discrete RF output frequencies by using a single phaselocked RF frequency determining loop. The accuracy and stability of 

the derived RF output signal is identical to that of the self-contained 

frequency standard. Additionally, a single second injection frequency 

is supplied. 

The synthesizer is composed of two major sections: frequency standard 

section consisting of a 245.76 kHz reference oscil lator, reference 

osci 1 lator divider, and second injection reference divider; and a phase1 ocked RF frequency determining 1 oop consisting of variable divider, 

discriminator VCO, buffer ampl ifier, and output ampl ifiers. 

The reference osci 1 lator, reference osci 1 lator divider, and second injection 

reference divider supply fixed frequency signals . The reference osci 11 ator 

is a crystal controlled anti-resonant oscillator circuit consisting 

of one gate section in a 4049AE C-MOS Hex buffer and a 245.76 kHz 

crystal with associated capacitors and resistors. This crystal oscillator 

drives both the reference divider and the second injection divider. The 

reference divider employs a C-MOS 4020AE 14 stage binary divider using 

12 stages to divide the 245.76 kHz to the desired 60 Hz reference frequency for injection into the phase-locked loop. The second injection 

divider takes the 245.76 kHz output of the crystal reference osci 1 lator 

and by use of a C-MOS 4027AE dual J-K flip-flop and part of a 4013AE 

dual D flip-flop, divides the crystal frequency by five to obtain the 

49.152 kHz which is ampl ified and buffered in two additional gates of 

the 4049AE and suppl ied external ly for the second injection signal . 

The phase-locked RF frequency determining loop consists of a 853 to 886 

divider, a C-MOS phase-locked loop and various amplifiers. The RF 

frequency originates from the VCO contained in the C-MOS 4046AE 

circuit. This VCO is set to cover the proper frequency range 51.18 

to 53.16 by the addition of a capacitor on pins 6 and 7 and by the 

appl ication of the proper control voltage into pin 9. The output of 

the VCO is buffered and supplied two places: the output amp1 ifier 

which drives the first mixer of the radio, and the variable divider 

which is controlled to divide by 853 to 886 and drive thc phase comparator 

in the 4046AE pack. The phase comparator in the 4046AE pack compares 

the variable divider signal with the reference divider signal of 

60 Hz and suppl ies a DC control voltage thru the low-pass filter, 

CR1, CR2, R1, R2, R3, C4 and C5 to the VCO control. The VCO frequency 

is divided by the variable divider until it is 60 Hz. Setting the variable divider at 853, channel 18, for instance will force the VCO to 

go to 51.18 kHz where the loop will become bala.nced. Likewise setting 

the divider to 886, channel 51, will force the VCO to go to 53.16 kHz. 

The variable divider consists of three sections; a programniable section 

consisting of two presettable decade dividers, a fixed divide-by-eight 

and state recognition-reset circuitry. The complete divider uses a 

total of five and one half integrated circuits. The divider has a 

division ratio capability of 800 through 899 but produces the required 

ratios of 853 through 886 in response to channel number (1 8 to 51) in 

BCD encoded form. Division ratios are accornpl ished by setting the counter 

to the channel number in BCD and allowing it to count down through its 

sequence. Note here that the 100's counter is fixed t 8 so for channel 
18 it is set to 818. It is allowed to count down through zero and on to 

the recognition state of 967. It then takes one more count to trip the 

strobe flip-flop (1/2 of 4013AE) and one more count to strobe in the dial 

setti ng which a1 so supplies a pulse to the comparator input of the 4046AE 

pack. The sequence then continues again. The counts add up as follows: 

with the controls set on 18, 818 is set into the counter. It counts 

down through zero to 967, 818 + 33, and requires two more counts to 

completely reset, 818 + 33 + 2 = 853 the division ratio required for 

channel 18. If channel 51 is desired, 851 is set in and counting down 

through zero to 967 plus two more for resetting gives a total of 886, 

851 + 33 + 2 = 886, which is the division ratio desired for channel 

51. The 967 count is recognized by gates 4001AE and 4012 as 

0 0 0 0 - 0 11-1 - bTi 1 1. The other bits are redundant. 

3.2.3 He1 icopter Receiver 

The helicopter receiver schematic seen in Figure 13 is the same basic 

receiver as the man carried receiver. The first FET stage from the basic 

receiver is installed witha voltage follower at the antenna. A 

voltage emitter follwer is required to provide buffering and a low 

impedance source to minimize pickup. A schematic of the antenna, 

and pre-amp is also seen in Figure 14. 

Tne helicopter receiver is powered by a gates sealed lead acid rechargeable 12 V battery with a center tap to provide +6 volts and -6 volts. 

A self contained charger is supplied. The charger is an off the shelf 

low cost limited temperature range power supply that is readily packaged 

into the receiver case. The capability to operate from an external 


12 V auto battery is provided. Access is through two spring loaded 

binding posts. The two headset outputs can be switched to listen to any one 

of the 6 channels. 

3.2.4 Antenna Design 

The equqtions used for the antenna design will be derived in detail 

to show the various rela ti onshi ps between receiver design , antenna 

parameters, and ambient noise. 

Noise contributed by the receiver is first examined and then this noise 

is used in the overall system noise evaluation resulting in an 

optimum antenna design. 

3.2.5 Rece i ver Noi se 

Before the antenna design can be completed, the noise contribution 

due to the receiver must be used with the noise received by the antenna. 

This calculation is as follows: 

Assume a noisy receiver with a gain of A. The noise factor F is given 

by: 

Noisy Rec 

i n -- {,i,-APk out 

Si/Ni F= - Ideal 

So/No Actual 

where Si/Ni is the S/N at the input and So/No is the S/N at the output. 

Both S/N ratios are expressed as a power ratio. 
The signal out equals the signal in multiplied by the gain A: 

So = SiA 

Substi tuting for So: 

Si/Ni = 1/Ni = No F = - - -- 

SiA/No A/No ANi 

Rear ran y i ng : 

No = FANi 

Set the! rioi:,c output ilo cqual to a noisc cquivalcnt Nccl at the input 

No = A Ncq 

No = FANi = A Neq 

F Ni = Neq 

Neq = F Ni 

Noi seless Rec 

Gain = A tI' No 

Jl~c total rloisc power- of the rcceivcr is exprcr,sed in terlrls of ttlc 

no isc r'lctor and the input nois(, powrr Ni . 

Now assurric a generator source ir~~pcdilncc of I( on tl~c inout of the 

receiver. The rloisc generated by this resistor R is given by: 

where K = Boltzrnann's constant 

= 1.38 X joules/deg. 

T = temperature, OK 

= 273 + OC 

R = resistance in ohms 

~f =- noisct 1)andwidttl in hertz 
Since the noise input Ni is NR, the noise in the generator R, equation 

2 can be written as: 

Neq = FNR 

Neq = (F) (~KTRA~) 

R Noiseless Rec 

r -. Neq = F(~KTRA~) 

Consequently, the noise generator is now in terms of the receiver noise 

factor F, the generator resistance R, and the bandwidth nf. The 

receiver can now be considered noiseless with a gain of A. 

This equation is used in the following analysis of the loop antenna. 

3.2.6 System Analysis and Antenna Design 

Assume a loop antenna with a received signal V sig, a received ambient 

noise voltage VAN, and the total receiver noise VRN as follows: 

.r 

r3 

* R (antenna DC resistance) 

Receiver Noise viN = (F) (~KTRA~) 

Received Signal vGig = (8n2f~~~10-7~S)2 

Received Amb. Noise V& = (8n2f~~~10-7~N)2 

1-m-4 L antenna 

i4OTE: Vsig and VAN derived as Vo2 in R.P. Decker's paper: Signal 

to Noise Analysis for Loop-To-Loop Mine Corn., page 3. 

f = frequency, Hz 

N = number of turns 

A = loop area, m 2 

HS = magnetic intensity of signal, amps/m 

HN = magnetic intensity of noise, amps/m. 
Now for sys tens analysis, let the external ambient noise contribution 

override thc receiver noise by a factor of r~. In other words, let 

11 be the amount that vZAN is greater than v&. 

viN = nv$f4 

or: 

(~TI~~NAX~O~I) = ~(f) (4~7~fR) (3) 

Also, from page 6 and 8 of R. P. Decker's report, the equation for the 

loop wirc loss is: 

RL = 271NaRw 

where a = radius of loop in nicters 

and $ = 271aN J in ohnis/m - -i-- (>-I 

where W = weight in Kgni 

P = wi re densi ty in Kgm/rn 3 

o = wire conductivity mho/m 

Substituting for K, in RL: 

Substituting for R in equation (3) and solving for the minirnal acceptable 

antenna radius a: 
Sul~~.t iutir~g for: 

The minimal acceptable radius now becomes : 

The loop antenna radius is now in terms of the frequency f, tile 

ambient noise field intensity HN, the noise factor F, the bandwidth 

~f, the copper weight W, and the factor n. 

The factor Q will be related to the input signal and noise for easier 

evaluation. 

Assune a worst case S/N ratio of 6 dB or 4 for the threshold of detectabil i ty of the receiver: 

substituting for vZRN = -- V~U . 

n 

The factor Q can now be calculated. 
The minimum ambient noise at 1 kHz from Westinghouse Final Report, 

July 1973, page 16, for winter is: 

Also, the minimum detectable signal level is specified as: 

Hsig = 0.1 pa/m . 

Solving for rl in equation (5); 

Hsig = 2 l+ri)1/2 = 0.10 

H AN rI m 

The antenna radius can now be calculated using equation (4) : 

where 

n = 0.287 (from (6) based on S/N = 6 dB) 

f = 1000 Hz (lowest frequency) 

HN = 0.0236 (from Westinghouse ~eport) 

F = 50 or 17 dB (measured in lab) 

~f = 15 Hz (filter bandwidth) 

W = 1.73 Kgm or 3.81 lbs. (same weight as used in Westinghouse units) 

a = 0.187 m or 7.37 in. 

This is essentially the size loop that is presently being used in the 

breadboard model. If the noise factor can be improved during the phase 

111 build, then the size of the loop could be reduced according to 

equation 4. Furthermore, if the weight of the loop is reduced with all 

other parameters remaining the same, then the size of the loop increases. 
For example: 

Let W = 1.0 Kgm 

(Other parameters unchanged) 

a = .246 M or 9.69 inches 

Once the final antenna weight and radius has been calculated, the 

antenna's number of turns and wire size can be determined by 

where a is the loop radius in meters, W is loop weight in Kgrn, 

and Ac is loop wire area in circular-mils. 

Therefore, using the antenna weight of 1.73 Kgm and antenna radius 

of 0.187 meters, the final number of turns can be calculated from 

equation 7 selecting number 22 wire. This calculation results in the 

fol lowing antenna parameters: 

N = 508.7 turns 

Radius = 0.187 meters or 7.37 inches 

Wire Size = Number 22 

Weight = 1.73 Kgm/3.81 lbs. 

3.2.7 Significant Test Results 

A complete breadboard of the receiver was constructed and tested. 

The synthesizer and front end stages of the receiver were temperature 

tested from -40°C to +50°C with satisfactory results. Frequency shift 

was t1.6 tlz at 50°C and -8 Hz at -40°C. Numerous battery charqe and 

discharge cycles were conducted to determine that the 8 hour allotted 

charging time could be accommodated by the charger. 
A graph showing the attenuation range of the volume control is shown 

in Figure 15. 

S+N/N ratio of the receiver was measured to be 10 dB for an input 

signal of .05 uV with a resulting voise figure of 17 dB. 

A graph showing the XTAL filter characteristics with temperature variations 

is shown in figure 16. 


3.3 MECHANICAL DESIGN 

3.3.1 Manpack Receiver 

The manpack receiver consists of a deep drawn aluminum can with an 

investment cast aluminum cover (see Figure 17). The cover is complete 

with a recessed groove for a molded gasket and projecting edges to protect 

the front panel controls (see Figure 18). A1 1 switches and connectors 

are a sealed variety in order to meet the water submersion requirements 

of the receiver. 

The three-sided inner chassis is attached to the front panel and mounts 

two printed circuit boards on the sides of the chassis with a spring 

steel battery holder on the bottom. Access to the four C-sized lithium 

batteries is readily gained by removing two screws in the front panel 

and lifting the entire assembly from the case. Battery replacement 

exposes no more of the receiver's circuitry than the back sides of the 

two printed circuit boards. For further maintenance, the removal of 

the printed circuit boards is required. 

A belt loop is spotwelded to the case, enabling the receiver to be worn 

on either a miner's or a conventional be1 t. Human Facotrs' recomnendations were incorporated in the panel layout, resulting in a package which 

can conveniently be operated when worn on either side of center by both 

left and right handed operators, without interference from the handheld 

antenna or headset cab1 e . 



Antenna, Man-Carri ed 

The hand-held antenna consists of five hundred turns of nunber twenty-two 

magnet wire, wound on a fifteen inch diameter form. Following winding, 

aluminum foil used as a faraday shield is spirally wrapped around the coil 

of wire for electrostatic shielding. The foil is grounded to the center 

braid of the antenna coax. This assembly is then completely potted with 

a tough, resi 1 ient urethane for protection. 

Helicopter Receiver 

The helicopter receiver, because of a low anticipated build quantity, will 

utilize a spot-welded aluminum chassis. Tooling costs will be kept to a 

minimum since all chassis parts can be punched in the flat on numerically 

controlled machines prior to forming and welding. The side panels, symetrically designed to be used for both left and right, extend to the rear to 

serve as legs as well as to protect the AC power cord which is stored on 

the rear panel. 

The front panel is removeable to provide access to the radio. Handles are 

mounted on the front panel for carrying, for easy removal of the receiver 

from the wraparound, and for protection of the knobs, switches, and 

connectors. These controls, under the advisement of Human Factors Engineering, 

have been systematically arranged according to functional importance and 

subdivided into the six individual receivers. Connectors have been positioned 

in such a way as to least obscure or hamper the operator with the connecting 

cab1 es. 

The inner chassis with card cage is attached to and removed with the front 

panel (see Figure 19). Six identical printed circuit boards, each containing 

a complete recei ver and frequency synthesizer, insert 
in card guides and engage edge-on connectors in the bottom of the 

card cage. This faci 1 i tates t r o u b l e shooting and receiver maintenance. 

The battery pack and the power supplylbattery charger are mounted in the 

wraparound due to weight and hea tsi nking considerations. 

3.4.1 Antenna, He1 icopter 

The antenna for the helicopter receiver will use the same winding and 

faraday shield as the hand-held antenna for the manpack receiver. However, 

this antenna will be mounted on an aluminum plate containing eye bolts 

so that the antenna may be lowered from the helicopter on a tethering cable. 

A1 so, the plate provides room for mounting the preamp1 ifier and antenna 

filter. 
4.0 PHASE I11 CONSTRUCT WORKING MODEL 

During this phase one mancarried receiver and helicopter receiver indludinq 

antennas and headsets were constructed. There units were constructed as 

planned during phase I1 with slight chanqes. Durinq this period BNC connectors 

were dropped from the helicopter receivers because of panel space. 

The separate input bandpass filter was also dropped because it was not making 

any apparement improvement. The connector for the antenna and headset was 

changed because of an intermittent re1 iabi 1 i ty problem noticed particularly 

on the helicopter antenna during bureau tests. The helicopter receiver was 

modified to have two operator positions because bureau tests indicated one 

operator monitoring six channels proved to be a difficult task. 

During this phase a calibrated loop generating a .I UA field was set up to 

check out the total system. The 90 foot portable loop was driven by a ULF 

transmitter with a 3.9 meg ohm resistor inserted in series. The power 

stages of the transmitter had to be removed for this test and direct connections 

to the MOS circuitry were made because the receiver picks up the ULF transmitter 

operating without an antenna at distances of 15 feet. With the noise levels 

expected near an industrial complex the field had to be increased to -37 UA/ 

meter before the receiver could detect the signal above the noise level. 

Minor problems encountering during the build of the first units, required 

additional decoupling from the lithium batteries that have a higher internal 

resistance to make them intrinsicaly safe. A capacitor used in the synthesizer 

phase locked loop will have to be selected for some units. Some C-MOS 

failures due to static charges were observed during the building of the 

working model receivers. Other than these parts and minor mechanical problems 

the design is reproducible. 
During this phase printed circuit board layouts of both receivers were made, 

mechanical parts were fabricated and the two receivers were assembled, tested 

and del ivered to the Bureau for evaluation. 

During the Bureau field evaluation it was determined that the use of a XTAL 

head set gave a better null than the inductive type headset. A1 1 headsets 

are now of the XTAL type to provide a better null and totally eliminate 

inductive feedback from the headset to the antenna. 

An interaction problem between channels on the helicopter was observed in the 

field. This problem was eliminated by running separate grounds and adding 

additional filtering in the preamplifier and other qain stages. Also it 

was determined during field use that a sound isolatinq ear muff would be 

beneficial for use with the helicopter receiver. To provide this isolation the 

XTAL headset for the he1 icopter receivers are now inserted into an MSA. 

MARK I1 sound barrier ear protector. This provides the isolatian required 

for the noisy helicopter environment. 

5.0 PHASE IV BUILD PRODUCTION UNITS 

Durin~ this phase all drawings and documentation were updated to reflect all 

changes as a result of the phase IV construction and evaluation. Fifteen 

mancarried and 5 helicopter receivers were assembled, tested and delivered 

to the Bureau. These units were assembled and tested with a minimum amount 

of difficulty. Again selection of the capacitor for the SMO was required on 

some units and some MOS failures occurred due to static charges. Additionally 

some MOS devices failed after delivery to the Bureau. The only other qua1 ity 

problems during the build of these units was one fractured headset and a 

loose piece of plastic fn one of the-panel meters. These parts were returned 

by the Bureau for replacement. 
INTRINSIC SAFETY 

The 515H-1 mancarried receiver is designed to be intrinsically safe. It 

was approved by MESA permit 331, October 9, 1975. 

The 515H-2 helicopter receiver is not intended for underground use and 

is not intrinsically safe. The battery charger transformer, large 

fi 1 ter capacitor, and battery prevent the he1 icopter receiver from beinq 

intrinsically safe. 

CONCLUSIONS AND RECOMMENDATIONS 

This five phase program has resulted in the development and documentation 

of a mancarried and helicopter receiver that is now ready for production 

in quantity, after the completion of some additional field testing by 

the Bureau. 

Because of the significant number of MOS failures due to static, it is 

recomnended that future units be constructed using high reliability 

ceramic MOS devices, and complete static discharge protection be exercised 

throughout the assembly and test phases of production.