DOT/FRA/ORD-22/35 Final Report | September 2022

Onboard Broken Rail Detection

Research and Development
i 
ii

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ADDRESS.

1. REPORT DATE (DD-MM-YYYY

September 2022

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

October 2019–April 2022

4. TITLE AND SUBTITLE

Onboard Broken Rail Research and Development

5a. CONTRACT NUMBER

DTFR5311D00008L

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

David Khasenye: 0000-0003-3622-7664

Mohamad Khater: 0000-0002-1288-9906

Xu Li: 0000-0003-2777-2214

Alan Polivka: 0000-0002-6424-5846

Scott Gage: 0000-0002-8424-0479

Chase Askins: 0000-0003-2028-9473

Mathew Holcomb: 0000-0001-7799-2202

5d. PROJECT NUMBER

5e. TASK NUMBER

693JJ619F000048

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Transportation Technology Center, Inc.

55500 DOT Road

PO BOX 11130

Pueblo, CO 81001-0130

8. PERFORMING ORGANIZATION REPORT 

NUMBER 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Railroad Policy and Development

Office of Research, Development, and Technology

Washington, DC 20590

10. SPONSOR/MONITOR'S ACRONYM(S)

11. SPONSOR/MONITOR'S REPORT 

NUMBER(S) 

DOT/FRA/ORD-22/35

12. DISTRIBUTION/AVAILABILITY STATEMENT 

This document is available to the public through the FRA website.

13. SUPPLEMENTARY NOTES

COR: Jared Withers

14. ABSTRACT

The Federal Railroad Administration (FRA) sponsored a project, performed by Transportation Technology Center, Inc. (TTCI), to research the 

feasibility of an Onboard Broken Rail Detection (OBRD) concept. A parallel long term track impedance characterization effort was undertaken 

with the objective of understanding and modelling the track as an electrical transmission line under varying environmental conditions. Between 

October 2019 and November 2021, TTCI carried out a series of laboratory and field experiments of the concept in two configurations over 

6,000-feet and 12,000-feet sections of track.

15. SUBJECT TERMS

Alternative broken rail and rollout detection, ABRRD, full-moving block, FMB, Head-of-Train-Alternative Broken Rail and Rollout Detection, 

HOT-ABRRD, Onboard Broken Rail Detection, OBRD, Positive Train Control, PTC

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT 

18. NUMBER 

OF 

PAGES

158

19a. NAME OF RESPONSIBLE PERSON

a. REPORT David Khasenye, Principal Investigator

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified 19b. TELEPHONE NUMBER (Include area code)

719-585-1851

Standard Form 298 (Rev. 8/98)

Prescribed by ANSI Std. Z39.18
iii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in) 

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in) 

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft) 

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd) 

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter 

(cm2

) 

= 0.16 square inch (sq in, in2

) 

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2) 

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2) 

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters 

(m2

) 

= 1 hectare (ha) = 2.5 acres 

1 acre = 0.4 hectare (he) = 4,000 square meters (m2) 

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz) 

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds (lb) = 0.9 tonne (t) 1 tonne (t) = 

= 

1,000 kilograms (kg) 

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt) 

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt) 

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal) 

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l) 

1 gallon (gal) = 3.8 liters (l) 

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3) 

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

 

C 

 

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iv

Acknowledgements

The authors would like to acknowledge the members of the Onboard Broken Rail Detection 

research and development Technical Advisory Group (TAG). 
v 

Contents

Executive Summary ........................................................................................................................ 1

1. Introduction ............................................................................................................................ 3

1.1 Background ................................................................................................................... 3

1.2 Objectives ..................................................................................................................... 5

1.3 Overall Approach .......................................................................................................... 5

1.4 Scope ............................................................................................................................. 7

1.5 Organization of the Report ............................................................................................ 7

2. Research Review .................................................................................................................... 9

2.1 Background ................................................................................................................... 9

2.2 Tx and Rx Coils .......................................................................................................... 10

2.3 Track Impedance ......................................................................................................... 13

2.4 Transmission Line Model ........................................................................................... 15

2.5 Summary ..................................................................................................................... 17

3. Track Impedance Characterization ...................................................................................... 18

3.1 Setup ........................................................................................................................... 18

3.2 Equipment ................................................................................................................... 19

3.3 Data Collection ........................................................................................................... 21

3.4 Approach ..................................................................................................................... 25

3.5 Results and Analysis ................................................................................................... 25

3.6 Conclusion .................................................................................................................. 36

4. Evaluation of Tx and Rx Coils ............................................................................................. 38

4.1 Lab Testing ................................................................................................................. 38

4.2 Field Testing – Static and Dynamic ............................................................................ 53

5. Model Development ............................................................................................................. 98

5.1 Track Impedance Model ............................................................................................. 98

5.2 Signal Propagation Model ......................................................................................... 101

5.3 Proposed System Model ........................................................................................... 102

5.4 Transfer Function Model .......................................................................................... 103

5.5 Summary ................................................................................................................... 105

6. Preliminary Development and Migration Plan .................................................................. 107

6.1 OBRD Development Plan ......................................................................................... 107

6.2 Deployment Migration Plan ...................................................................................... 108
vi 

6.3 HOT OBRD Migration Plan ..................................................................................... 108

7. Conclusion ......................................................................................................................... 110

8. References .......................................................................................................................... 112

Appendix A. Resonance Signal Generator Equipment Setup Instructions ................................. 113

Appendix B. Tx Coil Specifications ........................................................................................... 117

Appendix C. Rx Coil Specifications ........................................................................................... 119

Appendix D. Supplementary Tx Coil Test Data ......................................................................... 121

Appendix E. Insulated Joints Measurements .............................................................................. 124

Appendix F. Measurement Equipment ....................................................................................... 127

Appendix G. Characteristic Impedance Calculations from Sample Track Impedance Data ...... 128

Appendix H. Portable Cab Signal Tester .................................................................................... 133
vii 

Illustrations

Figure 1. Illustration of the OBRD Concept ................................................................................... 4

Figure 2. Project Work Breakdown Structure ................................................................................. 6

Figure 3. Functional Representation of a Tx or Rx Coil ............................................................... 11

Figure 4. Functional Flow of OBRD System................................................................................ 12

Figure 5. Transmission Line ......................................................................................................... 15

Figure 6. Transmission Line Distributed-Element Model ............................................................ 16

Figure 7. PTT Track Impedance Data Collection Zone ................................................................ 18

Figure 8. Weather Station and Trailer that Holds Desktop Node Equipment at Post P64 of the 

PTT ....................................................................................................................................... 19

Figure 9. Track Impedance Data Collection and Measurement Setup ......................................... 20

Figure 10. External Data Collection Hardware ............................................................................. 21

Figure 11. Sample of Time Log File Raw Data ............................................................................ 23

Figure 12. Sample of Sensor Log File Raw Data ......................................................................... 23

Figure 13. Sample of LCR Meter Measurement File Raw Data ................................................... 23

Figure 14. Sample of Part of a Weather Data File ........................................................................ 24

Figure 15. Number of Data Points Recorded per Day by Each Measurement Source ................. 24

Figure 16. Flow Diagram of Measured Track Impedance Data of Data Analysis Process .......... 25

Figure 17. Weather and Rail Temperatures for All Data During 24 Hours of the Day ................ 26

Figure 18. Weather and Rail Temperatures for a Sample of Summer Days ................................. 27

Figure 19. Weather and Rail Temperatures for a Sample of Winter Days ................................... 27

Figure 20. Weather and Rail Temperatures for a Sample of Fall Days ........................................ 28

Figure 21. Track Impedance Variables (RLCG) vs. Frequency for 1 Day ................................... 29

Figure 22. Track Impedance Variables (RLCG) vs. Frequency for 9 Months ............................. 30

Figure 23. Track Resistance vs. Rail Temperature ....................................................................... 31

Figure 24. Time Series for Rail Temperature, Ballast Moisture, RLCG and Open Circuit 

Impedance ............................................................................................................................. 32

Figure 25. Characteristic Impedance vs. Frequency ..................................................................... 33

Figure 26. Time Series for Rail Temperature, Ballast Moisture, and Characteristic Impedance 

Magnitude, Phase Angle, Real and Imaginary Components ................................................ 34

Figure 27. Estimated Input Impedance vs. Distances and for Different Frequencies ................... 36

Figure 28. Diagram of Tx Coil and its Drivers ............................................................................. 39

Figure 29. RNB Testing Setup ...................................................................................................... 40
viii

Figure 30. Resonance Signal Generation Equipment ................................................................... 41

Figure 31. Tx Coil Setup One ....................................................................................................... 45

Figure 32. Tx Coil Setup Two ...................................................................................................... 45

Figure 33. Track Impedance Model Used for Lab Testing ........................................................... 46

Figure 34. Lab Track Impedance Model Measurement Setup ...................................................... 46

Figure 35. Image Simulated Track Circuit ................................................................................... 47

Figure 36. Gamma Voltage Measurements from 345–400 Hz ..................................................... 48

Figure 37. Gamma Current Measurements from 345–400 Hz ..................................................... 48

Figure 38. Omega Current Measurements from 345 Hz–400 Hz ................................................. 49

Figure 39. Portable Cab Signal Tester-Rx Coils Setup ................................................................. 50

Figure 40. Signal Generator-Rx Coils Setup ................................................................................ 50

Figure 41. Gaussmeter Testing Orientation .................................................................................. 51

Figure 42. TTT Testing Zone ........................................................................................................ 54

Figure 43. Track Resistance Measurement Setup ......................................................................... 56

Figure 44. Tx Coil Setup for Static Testing .................................................................................. 57

Figure 45. Test Setup for Static Testing ....................................................................................... 57

Figure 46. 6,000-foot Block Configuration for Static Testing ...................................................... 58

Figure 47. 12,000-foot Block Configuration for Static Testing .................................................... 58

Figure 48. 18,000-foot Block Configuration for Static Testing .................................................... 59

Figure 49. Comparison of Induced Currents at Far and Source Ends at Various Tx Coil Heights 

Above Rail and Distances from Far-End Shunt for Static Tests .......................................... 62

Figure 50. Comparison of Induced Current at Far and Source Ends at 12,000 feet vs. Tx Coil 

Height at Different Frequencies ............................................................................................ 62

Figure 51. Comparison of Induced Current at 568 Hz to Distance from Source .......................... 63

Figure 52. Comparison of Induced Current at Far and Source Ends for Closed (Shunt) and Open 

(No Shunt) Track Circuit at Different Tx Coil Heights and Different Frequencies ............. 64

Figure 53. Tx Coil Setups ............................................................................................................. 66

Figure 54. Rx Coil Setup .............................................................................................................. 67

Figure 55. Test Case 1 Setup with Rx Coil on Locomotive ......................................................... 67

Figure 56. Test Case 2 Setup with Rx Coil Located 30 feet from Locomotive ............................ 68

Figure 57. Rx Coil Setup .............................................................................................................. 71

Figure 58. Case 1 Shielding Orientations ..................................................................................... 72

Figure 59. Detected Cross Talk RMS Voltage Across Rx Coil for Various Shields.................... 73
ix

Figure 60. Skin Effect Depth Variance with Frequency for Various Materials ........................... 74

Figure 61. Images of Shielded Tx and Rx Coils ........................................................................... 75

Figure 62. Evolution of Tx Coil Shielding ................................................................................... 75

Figure 63. Evolution of Rx Coil Shielding ................................................................................... 76

Figure 64. Locomotive, Tx and Rx Coil Configurations for Dynamic Test Cases 4, 5, 6, 7, 8, and 

9............................................................................................................................................. 78

Figure 65. TTT Section and Track Connection Diagram for 12,000-foot Block Tests ................ 81

Figure 66. Test Track Section and Track Connection Diagram for 6,000-foot Block Tests ........ 82

Figure 67. Illustration of Tx Coil Setup When Attached to Locomotive ..................................... 83

Figure 68. Electrical and Measurement Configuration of Tx and Rx Coil for Configuration A ..... 83

Figure 69. Rx Coil Configurations and Setup ............................................................................... 84

Figure 70. Shunt Current at T33.5 for Dynamic Test Cases 4 and 5 vs. Locomotive Location ... 86

Figure 71. Rx Coil Signal Amplitude for Dynamic Test Cases 4 and 5 vs. Locomotive Location

............................................................................................................................................... 87

Figure 72. Shunt Current at T33.5 for Dynamic Test Case 6 vs. Locomotive Location .............. 88

Figure 73. Rx Coil Amplitude for Dynamic Test Case 6 vs. Locomotive Location .................... 88

Figure 74. Shunt Current at T39.5 for Combined Dynamic Test Cases 7, 8, and 9 vs. Locomotive 

Location ................................................................................................................................ 89

Figure 75. Rx Coil Amplitude for Combined Dynamic Test Cases 7, 8, and 9 vs. Locomotive 

Location ................................................................................................................................ 90

Figure 76. Phase Difference Between Tx and Rx Coils for Combined Dynamic Test Cases 7, 8, 

and 9 vs. Locomotive Location ............................................................................................. 90

Figure 77. Dynamic Test Cases 11 Showing Effects of Wet Ballast on Induced Signal vs. 

Locomotive Location ............................................................................................................ 91

Figure 78. Dynamic Test Cases 11 and 5 Comparison Showing Effects of Wet Ballast on 

Induced Signal vs. Locomotive Location ............................................................................. 91

Figure 79. Dynamic Test Case 12: Phase Difference Between Signal Generator and Tx Coil vs. 

Locomotive Location ............................................................................................................ 92

Figure 80. Dynamic Test Cases 7, 8, and 9 Tx and Rx Overlay vs. Locomotive Location from 

T27–T40 ................................................................................................................................ 93

Figure 81. Dynamic Test Cases 7, 8, and 9 Tx and Rx Overlay vs. Locomotive Location from 

T27–T33.5 ............................................................................................................................. 94

Figure 82. Dynamic Test Case 6 Tx and Rx Overlay vs. Locomotive Location .......................... 95

Figure 83. Sample Closed Loop Track Input Impedances at Different Frequencies and Distance 

to a Shunt .............................................................................................................................. 99

Figure 84. Sample Open Loop Track Input Impedances at Different Frequencies .................... 100
x 

Figure 85. Functional Block Diagram of System Model ............................................................ 102

Figure 86. Development Phases of the OBRD Concept ............................................................. 107

Figure 87. HOT-ABRRD Migration path ................................................................................... 109
xi 

Tables

Table 1. Relationships Between Input Signal Frequency and Track Impedance Variables ......... 35

Table 2. Relationships Between Track Condition and Track Impedance Variables .................... 35

Table 3. RNB Vendor Defined Jumper Settings ........................................................................... 39

Table 4. Induced Signal Measurement with One Amplifier ......................................................... 42

Table 5. Induced Signal Measurements with Two Amplifiers ..................................................... 43

Table 6. Updated RNB Resonant Frequency Jumper Settings ..................................................... 43

Table 7. Gaussmeter Measurements ............................................................................................. 52

Table 8. Rx Coil Readings at 0 Inch from Test Loop ................................................................... 52

Table 9. Rx Coil Current Measurements at 8 Inches from the Test Loop .................................... 53

Table 10. Resistances of Three Test Track Blocks ....................................................................... 60

Table 11. Summary of Executed Tests ......................................................................................... 61

Table 12. Static Test Measurements with Tx Coil at Various Heights from Rail and Distances 

from Far End Shunt ............................................................................................................... 61

Table 13. Shunt at 30 feet from Tx Coil Under Test Setup 1 ....................................................... 68

Table 14. Shunt at 6,000 feet from Tx Coil Under Test Setup 1 .................................................. 68

Table 15. Tx Coil Strap Mounted with Rx Coil at Various Distances from Tx Coil ................... 69

Table 16. Maximum RNB Voltage with Tx Strap Mount Configuration ..................................... 69

Table 17. Detected Crosstalk Voltage at Rx Coil for Various Shields ......................................... 72

Table 18. Summary of Pre-Dynamic Test Results ........................................................................ 77

Table 19. Other Devices, Equipment, and Tools .......................................................................... 80

Table 20. List of Test Dynamic Testing Test Cases ..................................................................... 84

Table 21. List of Conducted Dynamic Test Cases ........................................................................ 85

Table 22. Summary of Proposed Models .................................................................................... 105
1 

Executive Summary

From October 2019 to May 2022, the Federal Railroad Association (FRA) sponsored 

Transportation Technology Center, Inc. in investigating a concept for an Onboard Broken Rail 

Detection (OBRD) system capable of detecting the presence of broken rails and occupancies (or 

lack thereof) in advance of a moving train through a series of lab and field tests at the 

Transportation Technology Center (TTC) in Pueblo, CO. The investigation concluded that the 

OBRD concept is practicable, but also noted that certain issues, such as improved receiver 

sensitivity and an extended detection range, are yet to be resolved. The primary application for 

the OBRD concept is the support of Full Moving Block (FMB) train control because the 

predominant broken rail and occupancy detection method (conventional track circuits) does not 

support the headway and capacity improvements attainable with FMB. The OBRD system 

analyzed and tested during this project also has the potential to reduce the life cycle cost of 

broken rail and occupancy detection since the system does not require any active wayside 

equipment and does not require insulated joints (IJs). 

In the OBRD concept, alternating current (AC) electrical signals generated on board a 

locomotive are sent and received through the track via electromagnetic induction. This process

allows a current to flow through a circuit comprised of the two running rails, the ballast, the 

wheels and axles of the train, and a series of passive, tuned shunts placed along the track. 

Electromagnetic coils attached to the locomotive just above the rail induce and pick up the 

signals from the rail. This method 1) provides a clear track indication from the train to the 

location of the tuned shunt associated with each received frequency and 2) detects occupancies 

and distinguishes them from rail breaks.

The detection range of such a system should be great enough to allow the train to come to a 

complete stop before it arrives at the location of the broken rail. To advance the understanding of 

the OBRD concept, two parallel research efforts, one on track impedance characterization and 

another on testing the feasibility of the concept, were undertaken. Key challenges identified from 

previous research included (Transportation Technology Center, Inc., 2013): 

• A strong mutual inductance between the transmit (Tx) and receive (Rx) coils

• A weak mutual inductance between the rail and the induction coils 

• The track impedance variability

During the investigation and analysis of these issues, significant progress was made regarding 

the ability of the system to induce a signal with a usable range. The transmission-coil-generated 

signal had a consistent detectable range of at least 12,000 feet. Under the conditions established, 

test results indicated that an induced signal of higher magnitude could achieve a range beyond 

18,000 feet. The detectable range is a function of a combination of 1) the ability of the 

transmission (Tx) coil to induce a large enough signal, 2) the track impedance variability, and 3) 

the ability of the receiving coil to detect enough of the signal from the rail to discern the state of 

the track in advance of the locomotive. Variable track impedance data was collected, together 

with the testing of a receiver (Rx) coil, were used to help quantify the feasibility. 

It took approximately 9 months to collect track impedance data. The following data were 

collected from a 650-foot section of track:
2 

• Ambient weather

• Rail temperature

• Ballast temperature and moisture

• Resistance (R)

• Capacitance (C)

• Inductance (L)

• Conductance (G) 

• Open loop impedance 

• Closed loop impedance 

This report details the following: 1) the processes used to collect and analyze the track 

impedance data and 2) the parallel lab and static testing of the transmit and receive coils that 

culminated in the dynamic testing of the OBRD concept in two configurations. The dynamic 

testing analysis indicates that non-trivial issues, such as improved receiver sensitivity and a more 

extended range to accommodate longer braking distances of heavy trains or trains going down a 

grade, need to be addressed to move the concept up the Technology Readiness Level (TRL) 

scale. The test results suggest that, as conceived, the OBRD concept is practicable.
3 

1. Introduction

From October 2019 to May 2022, the Federal Railroad Association (FRA) sponsored 

Transportation Technology Center, Inc. in investigating a concept for an Onboard Broken Rail 

Detection (OBRD) system capable of detecting the presence of broken rails and occupancies (or 

lack thereof) in advance of a moving train through a series of lab and field tests at the 

Transportation Technology Center (TTC) in Pueblo, CO. 

Continued interest in improved methods of train control drives a need to develop alternative 

methods of broken rail detection from conventional track circuit technology. Advancements in 

moving block and other train control methods can significantly increase traffic capacity while 

maintaining safe following train distances. However, a new broken rail detection method is 

needed to achieve Full Moving Block (FMB) capacity because conventional methods of train 

control use fixed block track circuits that impose excess train spacing. 

There are potential advantages to onboard methods of detecting rail breaks as compared with 

wayside-based methods, particularly in terms of eliminating the need for extensive active track 

circuit hardware that is expensive to install, power, and maintain along with eliminating 

insulated joints (IJs). A suitable onboard approach is not yet available for use with FMB train 

control. This OBRD research and development (R&D) project aims to advance the knowledge 

and understanding of how such a system would function. 

1.1 Background

From approximately 2008 to 2015, the team researched a concept for an OBRD system that 

sends and receives alternate current (AC) electrical signals generated on board a locomotive 

through the track via electromagnetic induction (Transportation Technology Center, Inc., 2013). 

In this system, a current flows through a circuit comprised of the two running rails, the ballast, 

the wheels and axles of the train, and a series of passive tuned shunts placed along the track. 

Electromagnetic coils attached to the locomotive just above the rail induce and pick up the 

signals from the rail. This method 1) provides an indication of clear track from the train to the 

location of the tuned shunt associated with each frequency received, and 2) detects occupancies 

and distinguishes them from rail breaks. The method is similar to cab signaling except that one 

onboard coil induces the signal while the other coil acts as a receiver. Figure 1 shows an 

illustration of the OBRD system and concept. 
4 

Figure 1. Illustration of the OBRD Concept 

1. The transmit (Tx) coil transmits at Frequency A, onto Frequen

and Frequency D (D is not used in any shunt), and keeps repe

This system, as shown in Figure 1, functions as follows: 

cy B, then Frequency C

ating this cycle.

2. The OBRD determines how far ahead track is clear based on which signal frequencies

it receives.

3. If one or more signals is not received, then the OBRD system will assume that there is

a rail break between the locomotive and the nearest shunt of that frequency ahead of

the train.

4. If all frequencies are detected at the receive (Rx) coil (including D), then the OBRD

system will determine that there is an occupancy ahead.

5. The locations of the shunts and their expected tuned frequencies will be stored in an

onboard track database, so that the OBRD system will be able to determine which shunts

and associated frequencies to expect.

This concepts ability to induce a signal in the rail and detect it was proven early on with static 

demonstrations using electromagnetic coils mounted above the track. Subsequently, patents were

filed and granted by the United States Patent and Trademark Office (USPTO).1

Follow-on research was conducted to further the development of the concept. This research 

identified three fundamental challenges:

1. Strong mutual inductance between the transmit and receive coils: Due to the proximity of

the transmit and receive coils on the locomotive (both placed in front of the first axle),

some of the strong magnetic field generated by the transmit coil passes through the

1 See US Patent 9,162,691 for a more detailed description of the concept. 
5 

receive coil and induces a current in the receive coil that can mask the desired signal 

received through the rail. 

2. Weak mutual inductance between the rail and the induction coils: To be useful for broken

rail detection applications, the current induced by the system on board the locomotive

must be strong enough to flow through the desired length of track and be reliably

detected by the receive coil, requiring a strong magnetic field to be generated by the

system.

3. Track impedance variability: Track impedance is heavily influenced by track

infrastructure and ambient conditions, both of which significantly affect the system’s

ability to function, as revealed in previous experimentation. Track infrastructure and

ambient conditions can vary significantly with time, location, and type of construction, so

the system must be able to operate over a wide range of resulting track impedances.

These fundamental challenges need to be addressed to advance the concept. In addition, it is 

possible that variant or alternative solutions exist for an OBRD system that could bypass these 

challenges. These alternatives need to be explored. 

The focus of the work primarily regards the use of OBRD at the front of a train to protect the

train from rail breaks or occupancies on the track ahead of it. However, the OBRD concept can 

also be applied at the rear of a train to protect a following train, in which case, the detection 

range does not need to be nearly as long as the range for a front-of-train based OBRD

implementation.

1.2 Objectives

This research focused on the results from tests in the reduction of the scientific uncertainty of the 

OBRD concept, and the development of a transmission line track model to further the development 

and design of a functional OBRD system.

1.3 Overall Approach

Figure 2 shows the project work breakdown structure. 
6 

Figure 2. Project Work Breakdown Structure

The team performed a thorough review of previous research on this topic. This review was 

followed by the parallel track impedance characterization task that was then used, in part, to 

develop a transmission line model of the track. The Tx and Rx coil optimization and evaluation 

were done concurrently with the track impedance data collection. Potential alternate solutions to 

fundamental challenges, particularly the “crosstalk” issue between the Tx and Rx coils, were also 

investigated. 

After track impedance was characterized, the findings were incorporated into the development of 

a transmission line model of the track. Once a working concept was developed and dynamically 
7 

tested, work was performed to identify preferred design parameters that would optimize and 

deconflict a system of this nature in the current field test environment. 

The project was executed using an iterative approach, starting with lab testing and culminating 

with dynamic field testing of the Tx and Rx coils on the same locomotive. The findings from 

previous testing were considered in developing the subsequent tests. The laboratory and field 

tests followed the sequence listed below: 

• Evaluation of Tx and Rx Coils

o Lab Testing

 Resonant Network Box (RNB) Testing

 Tx Coil Testing

 Rx Coil Testing

o Field Testing

 Static Tx Coil

 Static Tx and Rx Coil on Locomotive

 Shielding Testing

 Shielding Testing II

 Dynamic Testing

1.4 Scope

This research is a continuation of prior OBRD-related internal R&D. The objective of the current 

project is to advance a viable working concept for an OBRD system through the major tasks 

outlined in Section 1.3. The project scope involved developing the OBRD system concept with a 

focus on the following: 

• Showing 1) that an induced signal can be propagated for a distance commensurate with

the train stopping distance under various track conditions, and 2) that the differences in

the received signal can be detected (i.e., clear track versus broken rail versus occupancy)

• Addressing known key challenges

• Developing models that can be used to refine the design

1.5 Organization of the Report

The report is organized into eight major sections:

• Section 1 introduces the importance of the work performed and provides a brief

background of the OBRD R&D project.

• Section 2 provides an overview of the research review task.

• Section 3 includes the overview, analysis, and outcomes of the track impedance

characterization task.

• Section 4 consists of the overview, analysis, and outcomes of the coil evaluation task.
8 

• Section 5 presents the overview, analysis, and outcomes of the model development task.

• Section 6 provides the overview, analysis, and outcomes of the migration

implementation task.

• Section 7 includes the project summary, recommendations, and conclusions.

• Appendix A gives RNB and Tx coil signal generation setup instructions.

• Appendix B consists of Tx coil specifications.

• Appendix C provides Rx coil specifications.

• Appendix D offers supplementary Tx coil testing data.

• Appendix E contains insulated joint measurements.

• Appendix F gives information on the measurement equipment used.

• Appendix H contains information on the portable cab signal tester.
9 

2. Research Review

The team performed extensive research on OBRD concepts and track impedance prior to this 

project (Transportation Technology Center, Inc., 2013). In 2014, a preliminary data collection 

and modeling effort was conducted to quantify the potential impact of track impedance and the 

variability of track impedance on the proposed OBRD system (Transportation Technology 

Center, Inc., 2013). The result of earlier efforts provided insight into the factors that affect track 

impedance, including precipitation, relative humidity, track/ballast structure, and soil conditions. 

In addition, research was carried out on the Tx and Rx coils. The review of the Tx and Rx coils

focused on understanding the fundamental laws of electromagnetics and their application to the 

OBRD concept.

2.1 Background

A railroad track has similar physical characteristics to a power transmission line and can be 

characterized and modeled as a transmission line as they are defined by their characteristic 

impedance, represented as Z0. The characteristic impedance is a complex value with a real and 

imaginary part. This complex value requires magnitude and phase to fully define the 

transmission line impedance. 

A track impedance measurement system (TIMS) was developed to measure impedance on tracks 

at the TTC. The TIMS was characterized with both resistive and reactive loads, and the results 

were compared to a Simulation Program with Integrated Circuit Emphasis (SPICE) model. 

Important insights, highlighted later in this section, were gained from the TIMS data collected.

A series of track impedance measurements were taken in varying weather conditions on two 

different tracks, the Railroad Test Track (RTT) and the Precision Test Track (PTT), with 

different characteristics. Three tests were conducted on each track:

• Ballast resistance (track conductance)–Conductance (G) in the transmission line model

(direct current [DC] measurement)

• Track Resistance–Resistance (R) in the transmission line model (DC measurement)

• Track Impedance–Magnitude of Impedance (Z) (AC measurement)

The test results revealed that precipitation heavily influences track impedance, which, in turn, 

has a dramatic effect on the ballast resistance (track conductance). The correlation between track 

impedance and relative humidity was also apparent (Transportation Technology Center, Inc., 

2013).A comparison between the RTT and PTT results indicates the physical characteristics of 

the track (e.g., tie material, tie fasteners, soil condition, and ballast depth) can also significantly 

affect the ballast resistance (track conductance) and, as a result, the track impedance.

The track impedance results from the RTT tests were used to develop a SPICE model to 

characterize the track as a transmission line. The model results suggested that the OBRD

system will be impacted less by track impedance and ambient conditions at frequencies at or 

below 500 Hz.

In addition to the RTT tests, a long-term track impedance measurement effort was conducted on 

a track block approximately 1,740 feet long (PTT). The data from these tests were analyzed for 

trends during different seasons. This analysis confirmed the relationship between the following:
10 

• Track impedance and precipitation

• The recovery of track impedance after a precipitation period and the soil condition

o Saturated soil recovered more slowly than dry soil

o Frozen ground recovered even more slowly

These results 1) provide important insights and general trends between track impedance, 

frequency, and weather conditions, and 2) refined the test conditions for the prototype 

electromagnet and determined its viability in the OBRD system concept. However, the analysis 

was limited because the TIMS did not measure phase. It was recommended that should the 

OBRD system prove viable, a more detailed track impedance analysis should be conducted, to

include the R, L, C, G, Z, and phase measurements over a more extended time period and in a 

wider variety of track conditions. This analysis will require additional instrumentation and a far 

more detailed effort to move the prototype system to a full production system. The above

recommendations were considered in implementing the TIMS effort for this project. A full 

description of this effort is found in Section 3. 

The Tx and Rx coils focused on 1) understanding how the Tx and Rx coils function and 2) 

applying the laws and theories of electromagnetism (Maxwell’s equations, Lenz law, Faradays 

law and Biot-Savart law (Dorf, R. C., 2000)) to the OBRD concept. In addition, the transmit coil 

design specifications were reviewed to better understand how the coil functions. The results of 

the review can be found in Appendix B. The same approach was taken with the research review 

of the Rx coil, the results of which can be found in Appendix C. 

2.2 Tx and Rx Coils

The Tx coil is a core component of the OBRD concept. The development of this concept is 

anchored in the source patent (US Patent 9,162,691). The system relies on an electromotive force 

(emf) signal induced by the transmit coil. Electrical loops were terminated by the tuned shunts 

segment the track and provided paths for the signal to return to the locomotive, where a Rx coil 

picks it up and passes it on to a signal processor for conditioning and analysis before passing it 

on to the train control system for use in determining the state of the track up to each tuned shunt 

(up to the braking/warning distance at a minimum) in advance of the locomotive. The states of 

concern are clear track, broken rail, and track occupancy in advance of the train. 

The primary function of the transmit coil for the OBRD is to induce a sufficient signal that can 

propagate at least 2 miles down the track and be detectable by a Rx coil. Because there are many 

possible ways to implement the sinusoid signal generators required for OBRD, this research 

focuses on the magnitude of the generated emf, a function of the magnetic field generated by the 

Tx coil and the distance of the magnetic field from the rail.

To induce a signal in the rail, the Tx coil used in this research applies fundamental laws of 

electromagnetic theory (Maxwell’s equations, Faraday’s law of electromagnetic induction and 

Lenz’s law (Dorf, R. C., 2000)). These laws explain the relationship between a time-varying 

magnetic flux and the induction of an emf in a nearby conductor. The time-varying magnetic flux 

can happen as a result of the following: 

• A changing magnetic field within a stationary circuit

• A circuit moving through a steady magnetic field


13 

circuit ahead of a train. To provide a shunt at all test frequencies, all shunts used for testing were 

wires or cables. 

The generated signals at the Tx coil and received signals at the Rx coil are intermediated by the 

characteristic track impedance, affecting the quality and propagation of a signal through the 

(tuned) shunt loops.

2.3 Track Impedance

Conventional railroad signaling track circuits are normally constructed using a length (“block”) 

of railroad track that has been electrically isolated from the rest of the railroad by two pairs of 

IJs, with one pair of IJs installed at each end of the track circuit (i.e., one IJ per rail at each end of 

the track circuit). A pulsed DC or AC voltage is then applied through a track resistor to limit the 

current to the two rails at one end of the track circuit (the transmitter), and this signal is detected 

at the opposite end (the receiver) when there is no occupancy or rail break within the block. The 

rails of the track serve to complete the circuit between the transmitter and receiver.

A break that occurs in either rail or the conductive axles of a train being present within the 

boundaries of the track circuit, thereby shunting the rails to prevent the transmitted signal from 

reaching the receiver. This method allows conventional track circuits to detect broken rails and 

the presence of trains within their boundaries. 

If railroad rails were perfectly insulated from the earth with no trains present, the entire current 

from the transmitter at one end of the track circuit would pass through the receiver at the 

opposite end. However, any conductive substances within or underneath the track will typically 

cause a portion of the track circuit’s transmitted current to flow directly from one rail to the other 

without reaching or passing through the receiver at the opposite end of the track circuit. 

This unwanted form of conduction normally occurs when otherwise dry ionic solids beneath the 

rails, such as naturally occurring minerals, road salts (particularly at grade crossings in colder 

climates), spilled lading, and other soil contaminants are dissolved (partially or completely) by 

moisture from environmental sources to form conductive electrolytes. The presence of these 

electrolytes, both on and within railroad ties, ballast rock, soils, and other subgrade materials, 

increases the electrical conductivity between the rails of the track circuit.

The various leakage paths that divert the current away from a track circuit’s receiver are 

collectively referred to as “ballast resistance.” Unwanted “leakage” conduction between the rails 

of a railroad track also occur via other paths and processes, including gauge plates, gauge rods, 

ties, tie pads, spikes, screws, and other track hardware, especially when the insulation built into 

these devices becomes degraded. In properly maintained track, the rail-to-rail conduction 

through these “leakage” paths is minimal, and conduction through the ballast itself is the 

dominant factor that diverts or “shunts” some of the track circuit’s transmitted current away from 

its receiver.

Generally of a much lower magnitude, the “shunting” of a track circuit’s transmitted current 

through ballast resistance is similar in effect to the shunting action of a train’s axles. However, in 

severe cases of low resistance ballast, the excessively low-resistance ballast may shunt enough 

current away from the track circuit’s receiver to cause the track circuits to fail either 

intermittently or continuously.
14 

The adverse effects of low track ballast resistance are not limited to conventional track circuits 

where electrical signals are transmitted from one end of a track circuit and received at the other

end. Motion sensors and constant warning time crossing signal equipment can also be adversely 

affected, even though track circuit transmitters and receivers are located at the same end of their 

approach track circuits. Very low ballast resistance can prevent these types of crossing signal 

equipment from properly seeing a change in the electrical impedance of the track when a train 

enters the far end of an approach to a railroad grade crossing, resulting in shortened warning 

times at the grade crossing. 

As the track circuit created by the OBRD system is electrically similar in many ways to those 

used by motion sensors and constant warning time crossing signal equipment, it is currently 

presumed that the OBRD system will be similarly affected by low track ballast resistance.

Therefore, the research team’s track electrical impedance model will need to be validated over a 

wide range of ballast resistance conditions.

Most railroad tracks experience a range of ballast resistance conditions that varies based on the 

amount of water present in the ballast. Short of sprinkling the track with copious amounts of 

water from a wayside water truck or an on-rail tank car, the amount of water in the ballast and 

subgrade materials of a railroad track at any given time is otherwise difficult to control.

The Pueblo, CO, area receives an average of approximately 12 inches of precipitation in a typical 

year, which is much less than many areas of North America that have railroad lines (National 

Weather Service Weather Forecast Office, 2021). Some of Pueblo’s precipitation is also 

delivered in the form of snow that may sublimate into the atmosphere without ever melting into 

the ballast and subgrade. During some of the colder parts of the year, some of the moisture 

present in the ties, ballast, and superficially subgrade materials of the test tracks at the TTC 

facility exist in the form of ice, which is largely non-conducting. All these factors are expected to 

combine to create a relatively low availability of liquid water in and around the test tracks at the 

TTC, meaning the average ballast resistance conditions at the TTC should be expected to be 

relatively high. 

Fortunately, the expected high ballast resistance of the track at the TTC should be favorable in 

this instance because it is easier to lower the electrical ballast resistance of the test track 

artificially than to raise it artificially. Lowering the electrical ballast resistance of a railroad track 

circuit can be done by adding several non-inductive resistors connected across the test track at 

regular intervals along its length.

Adding resistors connected from rail to rail within a track circuit to simulate the effects of 

reduced ballast resistance works well for most types of track circuit testing. However, the 

polarization and “track storage effects” afflicting DC track circuits are notable exceptions. Given 

a sufficient electrolyte concentration and composition and enough moisture, the metal rails of a 

track circuit can serve as “plates,” and these de facto battery components can combine to form a 

crude electrolytic cell (track battery). This “track battery” can generate, accept, and deliver 

electrical energy, which can adversely affect DC track circuits, and, to a lesser degree, pulsed 

DC track circuits. In extreme cases, this “track battery” may even be capable of providing 

enough energy to keep the track relay (i.e., the “receiver”) of a simple DC track circuit energized 

without the transmitting source at the other end of the circuit being connected. 

In addition to the above, there are polarization effects caused by the presence of these same 

electrolytic solutions in the ballast and subgrade materials that can interfere with the proper 
15 

measurement of ballast resistance. Such polarization effects are most noticeable when the rails 

are energized with DC, as in basic DC track circuits. However, polarization effects are greatly 

diminished when using either pulsed track circuits with pulses of alternating polarity or track 

circuits with AC of adequately high frequency (i.e., several Hz or higher). 

As the proposed OBRD system does not use DC currents, unipolar low-frequency DC pulses or 

extremely low-frequency AC currents, polarization and track storage effects are not significantly 

affected. Consequently, the measurements of track impedance characteristics were made using AC 

frequencies across the full spectrum of possible frequencies used by the OBRD system.

2.4 Transmission Line Model

Track impedance characterization aims to understand the characteristics of a track modeled as a 

lossy electrical transmission line under varying environmental conditions. The derived track 

characteristic impedance would then support future system design and feasibility analysis of the

proposed system which requires an AC signal to propagate for relatively long distances of 

approximately 2 miles or more. Signal leakage through the ties, ballast, and ground can reduce 

the signal’s ability to propagate over a distance with weather also being a significant factor, 

necessitating a method to quantify the induced the transmitted and received signal. 

As shown in Figure 5, when modeled as a transmission line, the track has a characteristic 

impedance Zo. VS is the driving signal, and ZS and ZL are the source and load impedances, 

respectively.

Figure 5. Transmission Line

An elemental length of transmission line can be expressed as a distributed-element model

consisting of the following parameters (Figure 6):

• Series Resistance, R (Rail Resistivity)

• Series Inductance, L (Track Inductance) 

• Shunt Capacitance, C (Track Capacitance)

• Shunt Conductance, G (Ballast Conductance) 


18 

3. Track Impedance Characterization

The OBRD project focuses on the development of an onboard electronic system capable of 

detecting the presence of broken rails in advance of a moving train. The detection range of such a 

system must be far enough to allow the train to come to a complete stop before arriving at the 

broken rail. To help determine the feasibility of this goal, the authors concentrated on modeling

the electrical impedance characteristics of modern railroad tracks. This model was validated via a 

long-term study of the impedance characteristics of actual test tracks at the TTC facilities 

including portions of the PTT and TTT. Given the often-dry and sometimes-frozen ballast 

conditions prevalent at the TTC, most of the long-term test data is expected to have been 

collected under high ballast resistance conditions. Therefore, validating the developmental track 

circuit electrical model under significantly lower ballast resistance conditions required 

researchers to use artificial means to lower the ballast resistance of the test track(s).

3.1 Setup

A track impedance data collection system was set up on the PTT track. The test area covered 

P62–P59, consisting of 115-pound rail and wood ties spaced approximately 19 inches apart

interspaced by relatively clean ballast. The section of track was left unoccupied for most of the

data collection time. The test segment of about 650 feet (~0.1 miles) is highlighted (in dark blue) 

in Figure 7. 

Figure 7. PTT Track Impedance Data Collection Zone 
19 

3.2 Equipment

The track impedance characterization involved building a measurement system that collects data 

about the track impedance variables as well as track and environmental conditions. Long-term 

data collection was completed over a period of 9 months (June 2021–February 2022) on the PTT

using data collection equipment was set up at different nodes between P64 and P63 and covering 

a distance of approximately 650 feet. 

The measurement system consisted of three nodes: the desktop node, the measurement node, and 

the relay node. The desktop node includes the desktop computer that receives and stores the 

measurements taken and the Inductance (L), Capacitance (C), and Resistance (R) (LCR) meter 

that sends the electrical signal and takes the measurements for the track impedance variables. To 

protect the equipment, the desktop and the LCR meter were located inside a trailer next to post 

P64 on the PTT, as seen in Figure 8. The computer controlled the two remote nodes as well as 

the LCR meter, and it collected data from the weather station shown in Figure 8. The weather 

station measured different variables such as temperature, humidity, wind direction, and UV and 

solar radiation. 

Figure 8. Weather Station and Trailer that Holds 

Desktop Node Equipment at Post P64 of the PTT

The measurement node was located 363 feet from the desktop node and 287 feet from the relay 

node. The measurement node included a microcontroller and several sensors that took 

temperature and moisture readings. The relay node was 650 feet from the desktop node and 

includes a relay that opens and closes the circuit while taking the different measurements, and it 

also has another set of microcontroller sensors that take temperature and moisture readings. 

Figure 9 shows the configuration of the track impedance data collection system. 

The system uses single board computers to facilitate communication between nodes that require 

AC power to be run to each node. Ethernet wires, ethernet extender kits, and switches were used 

to establish the communication between the nodes and to avoid crosstalk. 
20 

Figure 9. Track Impedance Data Collection and Measurement Setup

A single board computer was connected to the microcontroller through a serial connection to 

receive the measurements from the sensors. The microcontroller has three thermocouples that 

measure the temperatures of the rail, tie, and ballast and a moisture sensor to measure the 

moisture in the ballast. Information for the moisture sensor and thermocouple used are shown in 

Figure 10. The relay node has similar equipment with the addition of the relay switch that 

connects to both sides of the track to establish open and closed circuits. Figure 9 shows the 

organization of the measurement and the nodes, respectively. The ethernet cable was shielded 

and buried with the AC lines at various distances.

The use of AC power eliminated the need to work with and charge batteries. Ethernet interfaces 

are reliable and eliminate communication issues. The single board computers, i.e., Raspberry Pi 

boards, were used to facilitate communication between nodes and allow remote access and 

remote programming of the microcontroller Arduino. The single board computer also powered 

the relay using the 40 pin General Purpose Input/Output (GPIO) header, as shown in Figure 10. 

There are two 3.3 V-pins to power the relay, 8 ground lines, and 26 GPIO pins that can be 

configured to control the signal line. Because the thermocouples and moisture sensor require 

analog pins to take measurements, the Arduino was used to take measurements while 

transmitting data via a serial connection. Communication between remote nodes and the desktop 

node was done by sending XML packets via ethernet. A python script generates, sends, receives, 
21 

and parses messages. Pelican cases housing the Raspberry Pi, Arduino, and other equipment 

were used to protect the equipment, as shown in Figure 10. 

Figure 10. External Data Collection Hardware 

3.3 Data Collection

To fully characterize the track impedance under varying environmental conditions, several 

types of data needed to be measured over a long period of time. This data serves as the 

foundation for determining the dominating factors that affect the track impedance and, 

consequently, the signal of the OBRD system. Additionally, the data can be used as a basis to 

construct a model intended to estimate the electrical properties of the track. Three types of data 

were measured as described below:

Electrical Track Impedance Data

• Open circuit impedance magnitude and phase angle 

• Short circuit impedance magnitude and phase angle 

• Rail resistance, R

• Rail inductance, L 

• Track conductance, G

• Track capacitance, C

• Input signal frequency (30 frequencies varying between 20 Hz to 1.7 kHz)

Track Condition Data 

• Rail temperature (at both relay node and measurement nodes)
22 

• Ballast temperature (at both relay node and measurement nodes)

• Tie temperature (at both relay node and measurement nodes) 

• Ballast moisture (at both relay node and measurement nodes)

Environmental 

• Ambient temperature

• Relative humidity

• Precipitation

• Barometric pressure

• Wind speed and direction 

• UV and solar radiation 

The LCR meter was used to measure impedance magnitude, |Z|, and the phase angle, θ, of a 

selected section of electrically isolated track at predefined frequencies (i.e., 30 frequencies 

between 20 Hz and 1.7 kHz) as shown in Figure 13. Additionally, the LCR meter was also used 

to measure R, L, C, and G of the track directly. These frequencies were chosen based upon 

known frequencies used in track circuits today. 

The measurements of the impedance magnitude and phase angle (|Z| and θ) were taken twice at 

each frequency, once when the track circuit was shorted/shunted and once when the track 

circuit was open. It is important to take these measurements with as little time as possible 

between them to minimize the effects that changing environmental conditions like weather 

may have on the data. When measuring R, L, C, and G directly, R and L need to be measured 

in a closed-circuit state while C and G are measured in an open circuit state. These 

measurements are repeated throughout the data collection period. The measurement process 

has the following sequence of events:

1. The switch is open

2. Measurements of |Z| and θ are taken for all frequencies 

3. The switch is closed

4. Measurements of |Z| and θ are taken for all frequencies 

5. Measurements of R are taken for all frequencies

6. Measurements of L are taken for all frequencies

7. The switch is open

8. Measurements of C are taken for all frequencies

9. Measurements of G are taken for all frequencies

10. Repeat

While measuring the LCR meter measurements, sensor log, time log, and weather data, dour 

different files are generated. Samples of raw data files are shown in Figure 11 through Figure 14. 
23 

The sensor log includes an extra variable at each node that monitors the case inner temperature 

that was added in the summer days to check when the equipment could overheat. 

Figure 11. Sample of Time Log File Raw Data

Figure 12. Sample of Sensor Log File Raw Data 

Figure 13. Sample of LCR Meter Measurement File Raw Data
24 

Figure 14. Sample of Part of a Weather Data File 

Weather data is taken every minute while the other files take around 10 minutes on average to 

complete the impedance measurements as well as the sensor readings in the measurement and relay 

nodes. The number of data points from each measurement source is shown in Figure 15 where:

• Freq_Measurement denotes the number of data points recorded from the track 

impedance data

• Freq_Weather denotes the number of data points recorded from the weather station 

• Freq_Sensor denotes the number of data points recorded from the temperature and 

moisture sensors at the relay and measurement nodes

Figure 15. Number of Data Points Recorded per Day by Each Measurement Source

The collected data was saved on the desktop computer at the desktop node as well as uploaded 

periodically to a database on a server belonging to the researchers. The database serves as a 

backup for the desktop computer, and it allows analyses to be performed on the acquired 

26 

conditions. In addition, an estimation of the input impedance of the track based on different track 

distances was demonstrated and compared at different frequencies.

3.5.1 Exploratory Data Analysis

Figure 17 indicates that weather temperature affected the rail temperature, but, because there are 

other parameters that can affect rail temperature, this relationship is not linear. Figure 17 further 

shows an aggregate for all weather and rail temperature data, and Figure 18 focuses on summer 

days where the rail temperature readings increase reach 130 °F compared to a maximum weather 

temperature of approximately 100 °F. The rail temperature increase can be attributed to the fact 

that rail steel takes time to heat up and, as metal, can retain more heat. On fall and winter days, 

the rail temperature still has higher peaks compared to weather temperature, but there is almost 

no lag between rail and weather temperatures, as shown in Figure 19 and Figure 20, respectively. 

The lag between rail and weather temperatures occurred on summer days where sun exposure is 

longer, and temperatures are higher. A model that predicts the rail temperature based on weather 

temperature was developed on previous FRA research and shows a similar pattern (Al-Nazer, L., 

2008). 

Figure 17. Weather and Rail Temperatures for All Data During 24 Hours of the Day 
27 

Figure 18. Weather and Rail Temperatures for a Sample of Summer Days 

Figure 19. Weather and Rail Temperatures for a Sample of Winter Days 
28 

Figure 20. Weather and Rail Temperatures for a Sample of Fall Days 

For the observations mentioned above, the rail temperature was used for further analysis instead 

of the weather temperature because the rail temperature more accurately reflects the track 

condition. A model can be used to estimate the track temperature based on the weather 

temperature as stated in Al-Nazer (2008). 

The track impedance variables were measured at 30 different frequencies between 20 Hz and 

1.7 kHz. The graph in Figure 21 shows the RLCG variables across the frequency range for 1 day 

while Figure 22 shows the RLCG variables trends for all the data. The thick lines around the C 

and G plots indicate the 95 percent confidence interval range the measurements fall within. In the 

case of R and L, the confidence interval range lines are very close to the fitted line for the R and 

L, and therefore, are not visible in the plots.

As shown in Figure 21, on a regular day, track resistance increases as the frequency increases 

while G between rails decreases. The same resistance pattern across all data is shown in Figure 

22 where the resistance is still collectively increasing by the frequency. The conductance across 

all data measurements shows a similar pattern where it is first decreasing and then slightly 

increasing at 1.5 kHz.

The L and C values show an increase at low frequencies but are not affected much as the 

frequency increases to higher values. However, it is well known that their characteristics affect

the circuit due to the frequency dependent component of the reactance (B&K Precision, 2020). 

Inductance and capacitance readings both have negative values that might be due to the circuit 

having both capacitance and inductance components. Due to the limitations of the LCR 

measurement equipment, the inductance measurement can have a negative value at low 

frequencies when the circuit contains a capacitance component while having positive readings at 

high frequencies (B&K Precision, 2020). Some of the readings had a positive inductance reading 

at relatively high frequencies around 1.5 kHz. The same effect happens for the capacitance 

readings when inductance exists in the circuit and causes the capacitance measurements to be 

negative at low frequencies.
29 

Figure 21. Track Impedance Variables (RLCG) vs. Frequency for 1 Day
30 

Figure 22. Track Impedance Variables (RLCG) vs. Frequency for 9 Months

High resistance readings correspond to high temperatures on some days, but the readings are out 

of the reasonable range for how much the resistance over 650 feet of track. According to Figure 

22, the fitted line and 95 percent confidence interval for the resistance values for all data show 

resistances of up to 0.35 ohms while the data having higher resistance values are minimal 
31 

compared to the rest of the data acquired. However, over the days in different months, the 

resistance seemed to increase at lower rail temperatures as seen in Figure 23. 

Figure 23. Track Resistance vs. Rail Temperature

Due to the test track receiving limited ballast moisture readings with little precipitation, a tank 

car was used to dump approximately 11,000 gallons of water on the track to simulate higher 

precipitation conditions and a wetter ballast. As expected, the conductance in the ballast 

increased after wetting the track, with a corresponding decrease in the open loop impedance. 

This decrease can be seen in Figure 24 that shows where the track wetting simulation took place 

on January 12. It should be noted that a lower reading on the moisture sensor in the second plot 

in Figure 24 corresponds to more moisture in the ballast. The moisture sensor reading did not go 

very low (indicating high moisture content in the ballast) because the moisture sensor was placed 

outside the gauge right next to the rail, as seen in Figure 9 and as opposed to Figure 10 where the 

moisture sensor is buried next to the orange case enclosure while the water was dumped in the 

middle of the gauge. 
32 

Figure 24. Time Series for Rail Temperature, Ballast Moisture, RLCG and Open Circuit 

Impedance

3.5.2 Data Analysis of Characteristic and Input Impedance of the Track

The characteristic impedance was calculated based on the transmission line theory and the 

RLCG data collected. The characteristic impedance magnitude, phase angle, and real and 

imaginary components were calculated for the same range of frequencies as the input signal and 

are shown in Figure 25. Refer to Appendix H for examples of the calculations of the 

characteristic and input impedance with observations of the results obtained.
33 

The characteristic impedance magnitude increases as the frequency increases to a frequency of 

942 Hz then it starts decreasing to 1.5 kHz before increasing again. A similar behavior can be 

observed for the real component of the characteristic impedance. The imaginary component has a 

positive correlation with the frequency where this component increases as the frequency of the 

input signal increases, suggesting that using relatively lower frequencies for the input signal will 

decrease the impedance seen by the signal and would allow the signal to propagate for longer 

track distances.

Figure 25. Characteristic Impedance vs. Frequency

After using a tank car to dump water on the track to simulate higher precipitation conditions and 

a wetter ballast, on January 12, the characteristic impedance magnitude and real component 

decreased as shown in Figure 26. The moisture sensor readings decreased on January 12 

(indicating higher moisture in the ballast), and lower magnitude and real component values of 

the characteristic impedance can be seen following the wetting of the ballast. The impedance 

values after wetting the ballast were approximately half the previous measurement values. The 

moisture sensor reading did not go very low (indicating high moisture content in the ballast) 

because the moisture sensor was placed outside the gauge right next to the rail. 
34 

Figure 26. Time Series for Rail Temperature, Ballast Moisture, and Characteristic 

Impedance Magnitude, Phase Angle, Real and Imaginary Components

Table 1 summarizes the relationship between the input signal frequency and the track measured 

impedance variables as well as the characteristic impedance. Table 2 summarizes the relationship

between track condition variables and the track measured impedance variables as well as the 

characteristic impedance. Per Table 1, the characteristic impedance showed an increase with the 

frequency with some ranges showing some decrease. Therefore, the relation is denoted with (in 

general) to indicate that large increase in frequency will cause increase in the characteristic 

impedance.
35 

Table 1. Relationships Between Input Signal Frequency and Track Impedance Variables

Track Condition/Frequency Impedance Variables Relationship

Frequency Resistance Proportional

Frequency Conductance Inversely Proportional

(In general) 

Frequency Characteristic Impedance 

Magnitude 

Proportional

(In general) 

Frequency Characteristic Impedance 

Imaginary Component Proportional 

Table 2. Relationships Between Track Condition and Track Impedance Variables

Track Condition/Frequency Impedance Variables Relationship

Rail Temperature Resistance Inversely Proportional

Rail Temperature Characteristic Impedance 

Magnitude Inversely Proportional 

Rail Temperature Characteristic Impedance Real 

Component Inversely Proportional 

Rail Temperature Characteristic Impedance 

Imaginary Component Inversely Proportional 

Wet Ballast Conductance Directly Proportional

Wet Ballast Open Loop Impedance Inversely Proportional

Wet Ballast Characteristic Impedance 

Magnitude Inversely Proportional 

Wet Ballast Characteristic Impedance Real 

Component Inversely Proportional 

The input impedance was calculated at different track lengths based on the transmission line 

theory. Since the frequency of the input signal affects the impedance, three different frequencies 

were selected to show the input impedance change with distance as the frequency changes. 

Figure 27 shows the input impedance versus track distance for frequencies of 20.3, 594, and 

1,494 Hz. The graphs show that as the distance increases, the input impedance increases as well. 

On the other hand, as the frequency of the input signal increases (i.e., 1,494 Hz), the input 

impedance imaginary component (Zin_Img) increases with distance, causing a decrease in the 

corresponding phase angle (Zin_Phase). For the cases of the lower frequencies (20.3 and 594 Hz), 

the input impedance imaginary components decrease with distance, causing an increase in the 

corresponding phase angle. 

The input impedance phase angle 95 percent confidence interval range for each frequency may be 

used to define a tolerable range for how much the phase of the received signal changes from the 

phase angle of the input signal (i.e., induced signal in the track from the Tx coil), based on the 
36 

distance from the load (i.e., shunt). Based on the data in Figure 27, using an input signal frequency 

of 20.3 Hz, if the signal at the receiving coil has a phase angle change between 52–57 degrees from 

the input induced signal phase, could indicate that there is a shunt at a distance range of 8,000–

10,000 feet. These ranges can also be set based on the magnitude of the input impedance and how 

much the factor of the input signal magnitude the receiver is seeing. This approach needs further 

analysis to define those ranges both clearly and reliably.

Figure 27. Estimated Input Impedance vs. Distances and for Different Frequencies

3.6 Conclusion

A track impedance measurement system was installed on the PTT to collect the following over a 

period of 9 months: 

• Track impedance variables

• Track temperature variables

• Moisture variables

• Weather variables

The system measured the impedance variables (i.e., resistance, inductance, conductance, 

capacitance, open circuit impedance and phase angle, and the short circuit impedance and phase 

angle) for 30 frequencies ranging from 20 Hz to 1.7 kHz. As the frequency increases, the resistance 

increases while the conductance decreases. There was a correlation between the temperature of the 

rail with the weather temperature, but the rail temperature was lagging with higher peaks compared 

to the weather temperatures. After using a tank car to dump water on the track to simulate higher 

precipitation conditions, the conductance of the ballast showed an increase.
37 

Applying the transmission line theory using the impedance variables measured calculates the 

characteristic impedance and the propagation constant. The characteristic impedance showed an 

increase with the frequency of the input signal except within the range of approximately 1–1.5 

kHz where it decreased slightly before increasing again, suggesting an input signal with low 

frequencies would allow better propagation of the signal through the tracks. An optimization of 

usable frequencies that allows sufficient input voltage at the Tx coil to induce higher currents in

the rail while also decreasing the input impedance of the rail is needed. With acquiring an 

accurate estimation of the input impedance of the track at a specific frequency, a tolerable range 

of the change in the phase angle of the received signal compared to the phase angle of the input 

signal (i.e., induced signal in the track from the Tx coil) may be defined to infer the distance 

from the load (i.e., shunt). 

The results of this data analysis provide good insight about characterizing rail track impedance 

and highlight opportunities for further analysis that can benefit OBRD technologies. Further 

analyses and test experiments need to be conducted to achieve those goals. It is recommended 

that similar data collection and data analysis be performed over a section of track that 

corresponds to braking distance of trains in revenue service (e.g., at least 12,000 feet) to verify 

the track impedance data for such track lengths and the estimations done using the transmission 

line theory model.
38 

4. Evaluation of Tx and Rx Coils

Several test cases were carried out in both environments to characterize the Tx and Rx coils. The 

testing culminated in testing the Tx and Rx coil on a moving locomotive. The selected 

locomotive did not have a running engine and was pushed by an active locomotive to keep the 

electromagnetic noise generated by the motor at a minimum to avoid corrupting the 

measurements of desired signal data being collected (Liu, C., Yang, S., Cui, Y., et al., 2020). The 

effects of engine noise (if any) will need to be determined and accounted for in the final OBRD

system design. 

4.1 Lab Testing

The research team performed lab testing in the Component Test Lab at the TTC. The laboratory

test cases, designed to test how the Tx coil, including the RNB, were used to develop a baseline 

approach to the subsequent field testing. The laboratory test cases included: 

• RNB

• Tx coil

• Rx coil

• Power supply amplifiers

• Signal generator

• Various loads

The testing moved to the field environment after determining the baseline testing, functionality, 

and parameters.

4.1.1 Lab Testing – RNB

The coil relies on a RNB to 1) increase the signal voltage going to the coil and 2) set the resonant

frequency of the coil. The RNB is tuned to four specific frequencies that can be adjusted to a 

limited extent. The actual resonance point of each frequency varies based upon the objects

located within the magnetic field produced by the coil. The RNB box testing provided a baseline

of RNB functionality prior to the in-lab Tx coil testing. 

4.1.1.1 Signal Generation: Theory of Operation

The core principle behind the OBRD concept is the induction of an emf in the rail that

propagates the current through the rail and is detected by a Rx coil. A sufficiently large magnetic

field needs to be generated by the Tx coil to generate a useful signal. The creation of such a field 

is accomplished by using a RNB that comprises a capacitor network and two symmetrical

outputs that use the principle of resonance to increase the voltage applied to the Tx coil,

generating a magnetic field proportional to the driving current. The magnetic coil is designed to

work at four resonant frequencies, as shown in Table 3, whose resonance points are determined 

by the configuration of jumpers in the RNB. The RNB consists of two equivalent circuits, each

with an input and output to provide power to the two physical coils that reside inside the red Tx

coil housing box. A standard signal generator provides the input signal to two amplifiers. The 

signal generation setup consists of (Figure 28): 
39 

• One signal generator: This component generates the driving signal, typically set at about

2–5 peak volts (V) as this puts the amplifiers into saturation.

• Two Kepco bipolar 400 W power supply amplifiers: This component amplifies the output

of the signal generator to serve as the input to the RNB.

• A resonant network box: This component further increases the twin resonant signals to

drive the Tx coil.

• A Tx coil: This custom component generates a magnetic field and induces an emf in a

conductor (e.g., rail) within its magnetic field.

Figure 28. Diagram of Tx Coil and its Drivers

Table 3 shows the nominal resonance frequencies, jumper settings, and RNB output terminal 

currents. 

Table 3. RNB Vendor Defined Jumper Settings

Resonance Frequency (Hz) Jumper Settings Current at A and B Terminals

(rms)

1,420 All Jumpers Open 18 A

707 J2A J2B J4A J4B Jumped 30 A

419 J3A J3B J4A J4B Jumped 42 A

373 All Jumpers Jumped 

(Default)

48 A

The Tx coil generates a detectable magnetic field at a given resonance frequency setting.

4.1.1.2 Setup

The equipment was set up as depicted in Figure 29 following the setup instructions for the Power 

Supply, Resonant Network, and Tx coil.
40 

Figure 29. RNB Testing Setup

Power Supply Setup 

• Connect both power supplies to 120 VAC sources. 

• Each power amplifier must receive the same 3 V peak signal from the signal generator to 

ensure that each coil current is in phase with the other. Connect the signal generator 

across both “Voltage Programming Inputs.” 

• Connect “Common” to “Ground” to ensure everything is grounded at this point. 

• Connect voltage or current diagnostics tool (e.g., multimeter, oscilloscope, etc.) to 

monitor the power supply output. 

Resonant Network Setup 

• Connect the RNB to 120 VAC source. This only serves to power the fans to cool the 

capacitors that are switched on at the connector. The RNB electronics are passive. The 

fans should always be on during operation. 

• On the back of the RNB, connect the “A” terminal to the “Output” of one of the power 

supplies. Connect the “B” terminal to the “Output” of the other power supply. 

• On the back of the RNB, connect the “Common” from both power supplies to the 

“GND” terminal.

• Ensure that the wires used to connect the power supplies to the RNB are rated for at least 

20 A/20 V.
41 

The signal generator’s output is split into the input of both power amplifiers to ensure the phase 

of the output of both amplifiers is in sync. One of the power amplifiers drives the “A” side of the 

RNB, and the other drives the “B” side of the RNB, as shown in Figure 30. 

Figure 30. Resonance Signal Generation Equipment

The “A-” and “B-” side outputs are connected to the four inputs of the Tx coil.

Tx Coil Setup

• The polarity of the connections is important. If the polarity is incorrect, the magnetic 

fields will buck, the circuit will not work, and no field will be generated. 

• From the front of the RNB, the “A+” terminal should be wired to the “A+” terminal on 

the magnet. Likewise, the “AGND” terminal should be wired to the “A−” terminal.

• From the front of the RNB, the “B+” terminal should be wired to the “B+” terminal on 

the magnet. Likewise, the “BGND” terminal should be wired to the “B−” terminal.

• If a wire extension needs to be made, ensure that the extension used is rated 100 A/2,000 

V at the utilized frequency. Note that, electrically, these terminals are the most 

electrically dangerous of the circuit.

Appendix B contains the specifications and images of the Tx coil showing the terminals. 

According to the Tx coil simulation, the magnetic field generated with an at 80 A input per coil, 

at a point in the center of the magnet plane located 3 inches from the magnet is 300 Gauss. 
42 

4.1.1.3 Approach

The equipment setup instructions described above were followed to carry out the testing. The 

frequencies varied around the resonant point, and the data was recorded for all Jumper settings. 

The same signal generator was used as the input for each amplifier to ensure the signals had the 

same phase. The rail was used to measure the current induced by the coil. 

4.1.1.4 Results and Analysis

The tests were first completed with one amplifier to verify that a current was induced. These 

tests were then followed up by a test with both amplifiers. Table 4 and Table 5 recorded and 

tabulated the results.

Table 4. Induced Signal Measurement with One Amplifier

Resonance 

Frequency (Hz)

Signal Generator 

Peak Voltage (V) 

Amplifier 1 RMS 

Voltage (V)

Induced Rail 

Current (mA)

1,420 2 23.8 19 

" 4 29.1 36 

" 8 29 70 

" 10 28 85 

707 2 27.4 21 

" 4 28 38 

" 8 27.4 68 

" 10 29.3 83 

419 2 25 2 

" 4 25 2 

" 8 25 3 

" 10 25 4 

373 2 23.8 15 

" 4 23.6 27 

" 8 23 48 

" 10 21 56 
43 

Table 5. Induced Signal Measurements with Two Amplifiers

Resonance 

Frequency 

(Hz)

Signal 

Generator Peak 

Voltage (V) 

Amplifier 1 

RMS Voltage 

(V)

Amplifier 2 

RMS Voltage 

(V)

Induced Rail 

Current (mA)

1,420 2 27.1 32 142

" 3 26.8 32.3 211

" 5 25.6 31 341

" 7 24.7 29.4 458

707 2 31.4 37.3 168

" 3 31.4 36.7 265

" 5 30.4 37.9 440

" 7 29.1 35.6 590

373 2 25.6 3.02 198

" 3 25.3 4.35 293

" 5 25 7 464

" 7 24.8 9.8 613

Initially, the configuration for 419 Hz produced negligible voltage, as it was nowhere near its 

resonance point (as seen in Table 4). However, after stepping through frequencies and measuring 

the voltage at the output of the RNB, it was determined that the resonance point for the 419 Hz

configuration was around 574 Hz. As evidenced by observing the measured output of the RNB at

419 Hz was at 1.7 V while at 574 Hz, the voltage was 180 V, indicating that the resonance 

frequency for that setting was closer to 574 Hz. Both measurements used the same 2 V Peak 

input signal from the signal generator. 

4.1.1.5 Conclusions

The measurements yielded frequencies that closely match the original designed resonance points. 

The frequency table was updated, as shown in Table 6. 

Table 6. Updated RNB Resonant Frequency Jumper Settings

Resonance Frequency (Hz) Jumper Settings

1,420 All Jumpers Open

707 J2A J2B J4A J4B Jumped

560–580 J3A J3B J4A J4B Jumped

373 All Jumpers Jumped (Default)

The resonance frequency ranges in Table 6 were used for all subsequent testing.
44 

4.1.2 Laboratory Testing – Tx Coil

The in-laboratory coil testing was performed to provide a baseline for the coil field testing. The 

in-lab test used a circuit consisting of inductors and resistors to simulate 2 miles of track. The 

coil relies on the RNB to amplify the voltage going to the coil and the set resonant frequency of 

the coil. The RNB can be adjusted around four specific frequencies. The actual point of 

resonance varies based upon the objects in the magnetic field produced by the coil, and from 

prior testing, which were found to be around 373, 560, 707, and 1,420 Hz. 

4.1.2.1 Setup

The lab equipment and tools consisted of: 

• One signal generator 

• Two Kepco bipolar 400W power supply amplifiers

• RNB

• Tx coil 

• Oscilloscope

• Multimeters

• National Instrument A/D, a data acquisition (DAQ) bucket with voltage measuring cards 

• Resistors, capacitors, and inductors of various ratings 

• Breadboard 

Resonance Signal Generation Equipment Setup:

The amplified signal provided by the RNB powers the coil that operates as described in

Appendix A. 

Tx Coil Setup:

The Tx coil was set up in two orientations as described below and shown in Figure 31 and Figure 

32: 

• Tx coil setup 1: Coil and rail on a table at distances of 1, 3, and 8 inches from the base of 

the coil to the top of the rail head. 

• Tx coil setup 2: Coil in an aluminum stand at distances of 1, 3, and 8 inches from the 

base of the coil to the top of the rail head.
45 

Figure 31. Tx Coil Setup One

Figure 32. Tx Coil Setup Two

Simulated Track Setup:

A circuit consisting of inductors and resistors was constructed on a breadboard to simulate the 

electrical properties of 2 miles of track. All resistors used were 1 percent tolerance, and inductors 

were un-shielded. The circuit layout and component values are shown in Figure 33 through 

Figure 35 shows the simulated track circuit built on a breadboard. The inherent series resistance 

of the inductors was comparable to the value of the resistance of the rail, so the series resisters 

were not used. 
46 

Figure 33. Track Impedance Model Used for Lab Testing

Figure 34. Lab Track Impedance Model Measurement Setup
47 

Figure 35. Image Simulated Track Circuit

4.1.2.2 Approach

The equipment setup instructions were followed in accordance with Appendix A. The 

frequencies were varied around resonant points, and the data was recorded for all coil setups.

A DAQ bucket with voltage measuring cards and DAQ software were used to acquire data. 

Voltage measurements were taken at the output of each power amplifier and at the A- and B-side 

outputs of the RNB. Current measurements were made at the output of the A and B sides of the 

RNB. Measurements on the simulated track circuit breadboard were taken using a multimeter.

As referenced in the Figure 34, the following measurements were taken:

• Alpha measurements: Voltage readings between the signal generator and signal amplifiers

• Beta measurements: Voltage and current readings between the amplifiers and Tx coil 

• Gamma measurements: Voltage and current readings of the first simulated track section

• Omega measurements: Voltage and current readings of the last simulated track section

4.1.2.3 Results and Analysis

Measurements were taken at the resonance point for each frequency setup and two frequencies 

above and below resonance for a total of five measurements at each frequency setup. These 

measurements provide insight into the loss of power as the input signal frequency strays from the 
48 

resonance point of the system. Each frequency was tested with a short and an open circuit at the 

load. A sample graph of gamma and omega measurements around a nominal resonant 

frequency of 345–400 Hz are shown for various heights above the rail at the table and the stand

(Figure 36). 

Figure 36. Gamma Voltage Measurements from 345–400 Hz 

Figure 37. Gamma Current Measurements from 345–400 Hz 
49 

Figure 38. Omega Current Measurements from 345 Hz–400 Hz 

Supplemental numerical values for test results and graphs with additional data can be found in 

Appendix D. 

The collected data was analyzed and these observations were made: 

Resonance Shifts: As expected, the system’s resonant frequency varies based upon what the 

magnetic field encompasses. During the “Table” testing, the resonant point for each system 

configuration was about 3 percent lower than the resonance points for the “Stand” testing.

RNB Configuration: In all four frequency configurations, the current was detected on the level 

of tens of millivolts at the end of 2 miles of simulated track built on a breadboard. The 560 Hz 

configuration seemed to outperform the other configurations for each test.

4.1.2.4 Conclusion

The success of the in-lab testing was quantified by detecting a reasonable amount of current at 

the end of 2 miles of simulated track in all frequency and test setup configurations. 

It was noted that the current induced into the circuit drops off quickly as one strays off the 

resonance set point. In general, the induced current varied as follows: 

• ~60 percent of current induced when 2 percent off-resonant frequency 

• ~40 percent of current induced when 4 percent off-resonant frequency 

The in-lab testing provided insight into how the system works and promising results to carry into 

field testing. This insight was used in designing the scenarios for static and dynamic testing. 

4.1.3 Lab Testing – Rx Coil

In-lab tests were conducted to test a locomotive cab signal Rx coil and a handmade Rx coil. A 

portable cab signal (PCS) tester was used to test common cab signal frequencies, and the signal 

generator setup was used to test the frequencies that aligned with the resonant frequencies of the 
50 

transmit coil. This test was carried out to characterize and compare the performance of the Rx 

coils. Tests were conducted at varying frequencies and heights to determine the amount of signal 

induced from the test circuits into the coil.

4.1.3.1 Setup

A signal generator and amplifier were used to supply the test signal with an ammeter in series to 

measure the detected current. The PCS tester includes a display showing input current (see 

Appendix H). The Cab Signal Tester and signal generator setups are shown in Figure 39 and 

Figure 40, respectively.

Figure 39. Portable Cab Signal Tester-Rx Coils Setup

Figure 40. Signal Generator-Rx Coils Setup
51 

4.1.3.2 Approach

Tests were conducted using two different setups. First, the 60 and 100 Hz tests were conducted 

using a PCS receiver tester. The signal generator setup was used for 373, 560, 707, and 1,420 

Hz. The wires used to connect both input configurations (PCS tester and signal generator/RNB 

setup) and the PVC test loop had a resistance of 0.8 Ω. 

Two types of coils were tested:

• The cab signaling coil used is an Alstom Automatic Train Protection (ATP) Rx coil.

• The handmade coil was constructed using braided aluminum wire wrapped about 65 turns 

around a 3 inch diameter iron metal pipe.

4.1.3.3 Results and Analysis

A baseline of the induced magnetic field was measured using a gaussmeter at 1 inch above the 

test loop. Testing with the gaussmeter directly measures the background magnetic field and 

background magnetic fields in the X, Y, and Z directions. The orientations of the gaussmeter are 

shown in Figure 41. 

Figure 41. Gaussmeter Testing Orientation

The gaussmeter measurement results are tabulated in Table 7. 
52 

Table 7. Gaussmeter Measurements

Frequency

(Hz)

Loop Current 

Input (mA)

Perpendicular to 

Pipe “X” (G)

Along the 

Pipe “Y” (G)

Into Pipe “Z” 

(G)

Background 

(G)

60 1,400 0.071 0.004 0.061 0.003 

100 1,400 0.075 0.004 0.062 0.003 

373 516 0.023 0.004 0.021 0.003 

560 510 0.026 0.004 0.02 0.003 

707 504 0.028 0.004 0.022 0.003 

1,420 465 0.014 0.004 0.013 0.003 

Testing was conducted at 0 inch (coils in contact with the test loop) and 8 inches above the loop. 

The 0-inch test provides the best-case scenario as the magnetic field generated by the test loop is 

the strongest at the core of the test loop. The 8-inch test shows the worst-case scenario as the 

magnetic field generated by the test loop is at the furthest coil placement height defined for this 

project. The results were tabulated in Table 8 and Table 9. 

Table 8. Rx Coil Readings at 0 Inch from Test Loop 
53 

Table 9. Rx Coil Current Measurements at 8 Inches from the Test Loop

4.1.3.4 Conclusion

The handmade coil was able to detect current at 0 and 8 inches, but it did not perform as well as 

the cab signaling coil. A significant amount of improvement can be made to the handmade coil, 

including designing a pickup coil optimized for use with the Tx coil. However, further coil 

optimization was halted due to time constraints, and the ATP/cab signaling coil was selected for 

subsequent static and dynamic tests.

4.2 Field Testing – Static and Dynamic

Static and dynamic tests were both carried out on the TTT. The TTT consists of 119 pound/yard 

jointed rail up to T33 that transitions to welded rail with a mix of wood and concrete ties spaced 

approximately 19 inches apart interspaced by clean ballast. The test area varied from T21–T39 

for different tests, an area that is divided by IJs into three blocks that segment the track every 

6,000 feet (~1.1 miles). Figure 42 illustrates the TTT test areas (in red) with key test locations 

highlighted (in green). 
54 

Figure 42. TTT Testing Zone

Test cases were carried out both clockwise (increasing milepost direction) and counterclockwise 

(decreasing milepost direction). The IJs were located across from the signal houses and were 

shunted or open depending on the testing being carried out. Prior to the OBRD tests, the IJs were 

tested using both a Rogowski loop and multimeters to ensure their functionality. IJ readings were 

then recorded and rechecked prior to every cycle of testing (Appendix E).

The TTT test area with key points highlighted are listed below: 

• Signal house 4 – T210+00 (T21.0) 

• Insulated joint 21 – T210+00 (T21.0) 

• Signal house 5 – T278+00 (T27.8) 

• Insulated joint 27 – T278+00 (T27.8) 

• Signal house 6 – T335+00 (T33.5) 

• Insulated joint 33 – T335+00 (T33.5) 

• Switch 709 – T335+06 (T33.6) 

• Switch 710 – T38 +70 (T38.7) 

• Signal house 7 – T395+50 (T39.5) 
55 

• Insulated joint 39 – T395+50 (T39.5) 

Depending on the dynamic test case being carried out, the switches were either lined for normal 

movement or reverse movement on the main track. In addition, some grounding and shield tests 

were carried out in the siding between Switch 709 (T33.6) and Switch 710 (T38.7). The 

connections from the bungalows to the track are made via insulated underground 50-foot 

6-gauge cables. 

4.2.1 Static Testing – Tx Coil

This section provides the setup, results, and analysis of the OBRD static testing, including testing 

the Tx coil over three (6,000 feet) block lengths on the TTT. The analysis covers an assessment 

of the electrical signals induced, propagated, and detected in the rail tracks and the field testbed 

variables that affected the results obtained.

The static test with both the Tx and Rx coils was carried out to determine the induced signal 

propagation range and detectability. The field coil test was performed on the TTT track from

T39 to T21 (Figure 42). Three scenarios were performed for each set of test distances:

• No signal 

• Occupancy with signal

• No occupancy/Broken Rail (BR) with signal 

The Tx coil was placed on a stand across the rail.

4.2.1.1 Setup

The static tests included testing the Tx coil over three block lengths on the TTT using the 

following equipment.

• One Signal generator 

• Two Kepco bipolar 400W power supply amplifiers

• The resonant network box (see Section 4.1.1 for explanation of the RNB) 

• The Tx coil 

• Ohmmeter/Ammeter

• Test shunts – 6 gage cables2

The field and equipment setup included the following: 

• Location: TTT

o Track location: TTT MP T21–T39

2 Since the focus of this research was to determine if a sufficiently useful signal can be induced/detected and how far 

it can propagate under baseline conditions, broadband (wire) shunts were used in the testing rather than tuned shunts.

This was done to avoid creating undesired variable effects upon rail impedance that could be caused by reactive shunts. 
56 

o Type of ties: Concrete, wood 

o Ballast condition: Dry

o Ballast resistance: Various (see tests)

o Rail type: Welded 

• Coil heights from rail:

o Tx coil: 3–8 inches

o Tx coil: Mounted on a fixed metal frame mount (not on a locomotive)

• Tx coil electrical settings:

o Signal generator: 3 V peak

o RNB output: Various

o Frequency: Various

Pretest Setup

The pretest setup consisted of the track circuit shunted on one end with a multimeter set to 

measure resistance (ohms). The test track for measuring the track resistance was setup as shown 

in Figure 43. The shunt was progressively moved from T33 to T21 with the IJs in the middle of 

the test block were shunted to increase the measured block length. 

Figure 43. Track Resistance Measurement Setup

Tx Coil Setup

The Tx coil was mounted on a metal frame mount at varying heights of 3–8 inches above the rail 

(not attached to a locomotive). A stationary locomotive that housed the signal generation 

equipment was placed just before the insulated joint of the test block to avoid shunting the track 

and to allow for enough clearance for the Tx coil to be inside the test block. Figure 44 and Figure 

45 illustrate the respective setups.
57 

Figure 44. Tx Coil Setup for Static Testing

Figure 45. Test Setup for Static Testing

Three block lengths were selected for testing. The connections were made through the 

Association of American Railroads (AAR) terminals at the respective bungalows. The test block 

lengths were 6,000, 8,000, and 12,000 feet. The AAR terminals are connected to the track via 

insulated 50-foot, 6-gauge cables. The field setup for each block length is shown in Figure 46

through Figure 48, respectively.
58 

Figure 46. 6,000-foot Block Configuration for Static Testing

The total resistance of the 6,000-foot track block as measured at T39 with a shunt at T33 was

0.4 ohms. 

Figure 47. 12,000-foot Block Configuration for Static Testing
59 

Based on the ohmmeter reading, the total resistance of the 12,000-foot circuit loop was 3.3 

ohms. Two sets of tests were performed, each with a different height and each height with four 

different frequencies. 

Figure 48. 18,000-foot Block Configuration for Static Testing

The 18,000-foot test was carried out to prove that an induced signal may be able to propagate 

beyond 2 miles. Due to a higher-than-expected impedance observed at T27, the total resistance 

of the 18,000-foot track was 19.5 ohms. 

4.2.1.2 Approach

Prior to the testing, the track resistances were measured for various block lengths. The 

resistances of the various blocks were measured using an ohmmeter across the track at one end 

and a shunt across the track on the far end to complete the circuit. The shunt was set at T33 

(6,000-foot block), T27 (12,000-foot block) and T21 (18,000-foot block), and ohmmeter 

readings were measured and recorded at each location. To get the longer block lengths of 12,000 

feet and 18,000 feet, the IJs at T33 and T27 were shorted, respectively. An “X”-foot-long block 

of measured track implies a track circuit of “2X” feet.

The track resistance measurements were followed by the Tx coil testing. The first phase of static 

tests included testing the Tx coil over three block lengths on the TTT. The Tx coil equipment 

setup instructions as described in Appendix A were followed. The frequencies were varied 

around the nominal resonant frequency. Distances of the Tx coil from the shunt and Tx coil 

heights above the rail were varied, and the data was recorded. Testing at one coil height

(1–8 inches) with one frequency setting (nominal frequencies of 373, 560, 707, and 1,402 Hz) 

was performed, and the measured signal data recorded. Frequencies were varied from the 

nominal frequency because the coupling with the rail slightly shifted the peak resonant 

frequency. 
60 

4.2.1.3 Pretest Track Resistance Measurement Results and Analysis

The block lengths and the resistance measured for each block for the setup in Figure 43 are 

shown in Table 10. 

Table 10. Resistances of Three Test Track Blocks

Block Block Length (ft) Resistance (ohms)

T39–T33 6,000 0.4

T39–T27 12,000 3.3

T39–T21 18,000 19.5

Observations on the resistance of the test blocks include:

• The 6,000-foot block has values in the expected range since typical track resistance is 

approximately 0.02 ohm/1,000 feet and track cables are 0.1–0.2 ohms. 

• The 12,000-foot block shows higher resistance than expected track resistance values for a 

nominal 12,000-foot section of railroad track, which could cause the detected induced 

current signal to be lower than nominal values. 

• The 18,000-foot block shows much higher resistance than the expected values, which 

would significantly affect an induced current signal. 

• The high resistances may have been a result of the 50-foot cables between the track and 

the bungalows or the bad conditions of the jointed track sections between T33 and T21. 

The results of the detected signal clearly show the effect of the high resistance blocks on 

the detected induced current signal as shown in Figure 51. Typically, the resistance of 

these blocks should be much lower, resulting in a higher detected signal. 

4.2.1.4 Tx Coil Tests Results and Analysis 

Table 11 summarizes the test data from the executed tests, where the red check marks indicate 

combinations of tests performed. Table 12 summarizes the data collected for the 6,000-foot, 

12,000-foot, and 18,000-foot track lengths. 
61 

Table 11. Summary of Executed Tests

The data for each length of the test track and coil height combination is shown in Table 12

followed by an analysis of the tabulated data. Table 12 also shows the output voltage of the RNB 

and the open-circuit voltage at the shunt at different frequencies. The Resonant Frequency 

column shows the actual setting the signal generator was set to so as to achieve optimal Tx coil 

resonance. The table is followed by various graphic illustrations of the data. Figure 47 shows a 

plot of results for each Frequency/Height Set defined in Table 12. 

Table 12. Static Test Measurements with Tx Coil at Various Heights from Rail and 

Distances from Far End Shunt
62 

Figure 49. Comparison of Induced Currents at Far and Source Ends at Various Tx Coil 

Heights Above Rail and Distances from Far-End Shunt for Static Tests

From Figure 49, note that the induced signal measured at the far end of the rail can be discerned 

from the noise floor for all signal frequency heights. 

Figure 50. Comparison of Induced Current at Far and Source Ends at 12,000 feet vs. Tx 

Coil Height at Different Frequencies

From Figure 50, see that the height of the coil above the rail has an impact on the induced signal. 

This is expected as the magnitude of the induced current due to the magnetic field crossing the 

rail is inversely proportional to the distance between coil and rail. 
63 

Figure 51. Comparison of Induced Current at 568 Hz to Distance from Source

Based on Figure 51, observe that distance (or track resistance, as the resistance increases with the 

length of the track) affects the signal. It should be noted that, due to a higher-than-expected 

resistance between the 12,000-foot and 18,000-foot section, the measurement at 18,000 feet may 

contain some error. However, it displays the relationship between the track block length and 

signal, showing the signal strength is inversely proportional to the distance from the source. 

Additionally, it shows the possibility of propagating the induced signal beyond 12,000 feet. 
64 

Figure 52. Comparison of Induced Current at Far and Source Ends for Closed (Shunt) and 

Open (No Shunt) Track Circuit at Different Tx Coil Heights and Different Frequencies

The following can be inferred from the data above: 

• The test results in Table 12 show the Tx coil can induce a distinguishable signal from the 

noise floor or open shunt in which the signals are measured. The frequencies affect the 

magnitudes of the voltages and therefore, the current induced in the rails.

• As shown in Figure 49, the cases that use a nominal signal frequency of 560 Hz where 

the Tx coil is mounted at heights of 3 and 8 inches perform best.

• In all cases, the induced closed loop current in the track is significantly higher than the 

noise floor, while the open-circuit current is larger than the closed shunt signal in a few 

cases, as shown in Figure 52, where the test signal frequency is set at 1,420 Hz. 

• From Figure 52, it can also be observed that the ballast will complete the circuit when 

there is no shunt. For some frequencies, the difference in rail impedance may not be large

enough to distinguish between a shunted (occupancy) state versus the open (broken rail) 

state of the track circuit (due to current flowing through the ballast). However, if the clear 

track state (no rail break and no occupancy) is distinguishable from the non-clear state 

(rail break and/or occupancy), the system will be able to determine the state of the track.

• The 12,000-foot block and the 18,000-foot block have a much higher rail resistance than 

the expected values at normal rail conditions with 3.3 Ω and 19.5 Ω, respectively. This 

resistance is a major reason for low induced-current values in the tests done on those 

blocks. The Tx coil should perform better if tested with track sections that have more 

typical resistance values. 

• The detected current with an open loop track circuit could be higher if tested under wet 

ballast conditions. Therefore, the induced signal in shunted scenarios may not be 
65 

distinguishable from non-shunt scenarios for some cases that showed positive results in 

this test. 

4.2.1.5 Conclusions 

Occupancy detection:

By comparing the track circuit loop measurements with the ballast loop measurements, a 

significant difference between closed-circuit loop current versus ballast loop current can be 

confirmed for certain frequencies, so it is possible to design a function to detect a shunt (for 

detecting train occupancy). 

Broken rail/roll-out detection: 

By comparing the track circuit loop measurements with the ballast loop measurements, the 

difference between a good track circuit loop and a broken rail/no occupancy loop, which can 

detect a rail break between two trains, can be identified. Rail break detection is an initial design 

prerequisite for an alternative broken rail and rollout detection (ABRRD) system that will meet 

the needs of FMB. 

For real-world operations, the system would require tuned shunts to act as band-pass filters to 

enable the detection of a rail break at different intermediate distances in advance of a train, up to 

at least the train’s braking distance. Use of tuned shunts will also allow the system to distinguish 

an occupancy ahead versus clear track or a rail break.

Closest shunt detection:

This field test proved that this system could induce a sufficient track signal that could be detected 

at distances up to at least 18,000 feet from the Tx coil. This test result provides the basis to support 

conducting further analysis that focuses on performance and functionality possibilities. 

All the above insights were used in designing further static testing scenarios. 

4.2.2 Static Testing – Tx Coil and Rx Coil – Locomotive

A locomotive with the Tx coil attached with an aluminum frame (Figure 54, left-hand side) was 

introduced into the field testing, and this configuration is referred to as the “original setup.” 

Subsequently, an alternative configuration using non-conductive straps to suspend the Tx coil 

from the locomotive and referred to as the “strap setup” was used and is shown in the right-hand 

side of Figure 54. 

Testing was conducted to determine the impact of the aluminum frame being used in the original 

setup to brace the bottom of the Tx coil and the extent of the “crosstalk” between the Tx and Rx

coils with both attached to the front of the same locomotive. All tests in this configuration were 

conducted at a signal frequency of 578 Hz and the Tx and Rx coils mounted 8 inches on a 

locomotive above the rail. To avoid interference from the electrical equipment while the test 

measurements were taken, the locomotive was never self-powered. 
66 

4.2.2.1 Setup

The signal generation setup consisted of: 

• One signal generator 

• Two Kepco bipolar 400 W power supply amplifiers

• One RNB

• One Tx coil 

Tx Coil Setup

The Tx coil was set up in two orientations as described below and shown in Figure 53: 

• Tx coil setup 1: Coil mounted on aluminum frame

• Tx coil setup 2: Coil mounted using non-conductive straps

Figure 53. Tx Coil Setups

Rx Coil Setup

The Rx coil is composed of two coil sections separated by a nonconductive composite material. 

The larger coil (Rx Coil A) and the smaller coil (Rx Coil B) each have a positive and negative 

lead and can detect an electromagnetic field incident on the coils. The Rx coil was connected for 

measurement as shown in Figure 54. 
67 

Figure 54. Rx Coil Setup

4.2.2.2 Approach

The equipment setup instructions described in Appendix A were followed. The frequency was 

set at 578 Hz, and the data was recorded. The following two test cases were carried out: 

Test Case 1: The tests under this case were conducted with the Tx and Rx coils mounted to the 

locomotive just ahead of the leading axle with the distance to the shunt varied as shown in 

Figure 55. 

Figure 55. Test Case 1 Setup with Rx Coil on Locomotive 

Test Case 2: The test carried out under this case was conducted with the Tx coil mounted to the 

locomotive and the Rx coil placed 8 inches above the rail and at varying distances in front of the 

locomotive (30 feet, 1,000 feet, 6,000 feet). This process was carried out to ensure there is no 
68 

possibility of the Rx coil being in the range of the magnetic field created by the Tx coil as shown 

in Figure 56. 

Figure 56. Test Case 2 Setup with Rx Coil Located 30 feet from Locomotive

An additional test of the difference in the results between the two cases was used to 

quantify crosstalk.

4.2.2.3 Results and Analysis

Test Setup 1: Tabulated test results of the tests carried out under Test Setup 1 are shown in 

Table 13 and Table 14. 

Table 13. Shunt at 30 feet from Tx Coil Under Test Setup 1

Tx Coil 

Mount

RNB 

Output 

Peak 

Voltage 

(V)

Small Rx 

Coil RMS 

Voltage 

(mV) 

Large Rx 

Coil RMS 

Voltage (mV)

Small Rx Coil 

RMS Voltage 

(mV) 

(Tx Coil Off)

Large Rx Coil 

RMS Voltage 

(mV) 

(Tx Coil Off)

Small Rx Coil 

RMS Voltage 

(mV) 

(No Shunt)

Large Rx 

Coil RMS 

Voltage (V) 

(No Shunt)

Current 

Through 

Shunt 

(mA) 

Aluminum

“original” 350.1 144.4 37.89 4.2 5.8 147.4 38.6 219

Plastic

Strap

351.3 160.4 42.4 4.2 5.8 165 42.8 240.8

Table 14. Shunt at 6,000 feet from Tx Coil Under Test Setup 1

Tx Coil 

Mount

RNB 

Output 

Peak 

Voltage 

(V)

Smaller Rx 

Coil RMS 

Voltage 

(mV) 

Large Rx 

Coil RMS 

Voltage 

(mV) 

Smaller Rx Coil 

RMS Voltage 

(mV) 

(Tx Coil Off)

Large Rx Coil 

RMS 

Voltage(mV) 

(Tx Coil Off)

Small Rx 

RMS Voltage 

(mV) 

(No Shunt)

Large Rx 

RMS Voltage 

(V)

(No Shunt)

Current 

Through 

Shunt

(mA) 

Aluminum

“original” 350 144.2 37.96 4.2 5.8 147.4 38.6 3 

Plastic 

Strap 351.3 159 41.4 4.2 5.8 157 40.95 61
69 

Table 15. Tx Coil Strap Mounted with Rx Coil at Various Distances from Tx Coil

Tx Coil 

Mount

Distance of 

Rx Coil 

from 

Locomotive 

(ft.) 

RNB 

Output 

Peak 

Voltage 

(V)

Small 

Rx Coil 

RMS 

Voltage 

(mV) 

Large Rx 

Coil RMS 

Voltage 

(mV) 

Small Rx Coil 

RMS Voltage 

(mV) 

(Tx Coil Off)

Large Rx Coil 

RMS Voltage 

(mV) 

(Tx Coil Off)

Small Rx Coil 

RMS Voltage 

(mV) 

(No Shunt)

Large Rx 

Coil RMS 

Voltage (V) 

(No Shunt)

Current 

Through 

Shunt (mA)

Plastic 

Strap 30 351.3 4 341 V 4 20 61 4 257

Plastic 

Strap 1,000 351.3 4 175 4 20 61 4 140

Plastic 

Strap 6,000 351.3 4 31 4 20 61 4 45

Test Setup 2: Tabulated test results for the tests carried out under Test Setup 2 are shown in 

Table 15. 

The test results show that the aluminum frame under the coil’s base does affect the strength of 

the signal induced into the rail. Table 14 and Table 15 show the 6,000-foot tests for the original 

setup and the strap setup. In the original configuration with the aluminum frame under the coil, 

the measurable current at the shunt was 3 mA. The strap configuration measured a current of 61

mA at the shunt at 6,000 feet. The strapped configuration closely matched the values measured 

from the non-locomotive static tests (Section 4.2.1).

Table 16 shows the Rx coil voltages with the RNB output at 580 V under the strap configuration. 

The maximum RNB output voltage achievable in the original configuration was around 350 V. 

The measurements in the table were taken to show the maximum voltage output variation 

between the two setups. However, all other tests were done with similar RNB output voltages to 

accurately compare the test configurations. 

Table 16. Maximum RNB Voltage with Tx Strap Mount Configuration

Tx Coil 

Mount

RNB Output 

Peak Voltage 

(V)

Smaller Rx

RMS Coil 

Voltage (mV)

Large Rx Coil 

RMS Voltage

(V)

Large Rx Coil 

RMS Voltage (V)

(No Shunt)

Smaller Rx Coil 

RMS Voltage (mV)

(No Shunt)

Plastic 

Strap 580 263.8 70 70 263.8 

4.2.2.4 Conclusion

These results show that the current induced into the rail is lower when the aluminum frame is 

under the coil than when using the zip tie configuration. Therefore, the coil is thought to induce 

the current into the aluminum frame and ground out through the locomotive. Additionally, the 

crosstalk was noted to be more significant with the coil at the locomotive than when 30 feet from 

the locomotive. 

These insights led to the replacement of the aluminum frame with the plastic strap for all 

subsequent tests. Additionally, the testing provided insight regarding the effects of crosstalk and 

noise that led to testing and researching to mitigate crosstalk.
70 

4.2.3 Shielding Testing – Locomotive

Prior to the dynamic testing of the coils, several tests were conducted to establish the effects of 

electromagnetic noise and coupling on the system. The results of the previous test indicated 

enough “crosstalk” from the Tx coil to mask the Rx coil’s ability to detect the induced signal in 

rail. Therefore, several methods were proposed to mitigate the effects of noise and coupling 

between the coils. The mitigations included shielding the coils using a material with low 

magnetic permeability, increased air gap, and grounding. The investigative testing regarding the

efficacy of the proposed solutions proceeded as follows:

4.2.3.1 Setup

The field test setup and equipment setup included: 

• Locations: TTT

o Track location: TTT MP 39

o Type of ties: Concrete, wood

o Ballast condition: Dry

o Ballast resistance, measured over “X” ft: 7 K Ohms at 135 feet

o Rail Type: Welded

• Coil Heights from Rail

o Tx Coil: 3–8 Inches

o Rx Coil: 3–8 Inches

o Tx Coil: On Locomotive

o Rx Coil: Various Locations

• Tx Coil Electrical Settings:

o Signal generator: 3 V peak

o RNB Output: 364 V and 22.4 Amps

o Frequency: 568 Hz

• Oscilloscope:

o Channel 1: Rx Coil

o Channel 4: Tx Coil (at RNB Terminal)

The Tx coil equipment setup followed instructions described in Appendix A. 

The Rx coil was connected for measurements as shown in Figure 57. 
71 

Figure 57. Rx Coil Setup 

4.2.3.2 Approach

The Tx coil system was powered up, and different materials were placed in various orientations 

around the respective coils or between the coils. The test cases included the following: 

• Case I: Rx coil at mount (Figure 58)

1. No Shielding

2. Aluminum foil over cardboard partition between the Tx and Rx coils

3. Aluminum metal enclosure around Rx coil

4. Aluminum foil over cardboard partition behind Tx coil and aluminum metal enclosure 

at Rx coil

5. Aluminum foil over cardboard partition between the Tx and Rx coils and aluminum 

metal enclosure at Rx coil

6. Aluminum foil over cardboard partition at the Tx coil and aluminum metal enclosure 

at Rx coil

• Case II: Rx coil at Cow Catcher - Air Gap

• Case III: Rx coil at 20 feet from Cow Catcher ahead of locomotive - Air Gap

• Case IV: Rx coil at 135 feet from Cow Catcher ahead of locomotive - Air Gap

Figure 58 illustrates the various shielding orientations for Case 1. 
72 

Figure 58. Case 1 Shielding Orientations 

The aluminum foil over cardboard partition had four layers of 25-micron heavy duty foil, and the 

aluminum metal was 1/8-inch gauge. The Rx coil voltages across the larger Rx coil due to crosstalk 

from the Tx coil were recorded. No shunt was placed across the track for the 6,000-foot block that 

was terminated by IJs on both rails. The measured data was recorded and compared. 

4.2.3.3 Results and Analysis

Table 17 recorded and tabulated the measurement results for each test case of different shields. 

Table 17. Detected Crosstalk Voltage at Rx Coil for Various Shields

Test Case Frequency

(Hz)

Large Rx Coil 

RMS 

Voltage(mV)

(Tx signal off)

Large Rx Coil 

RMS Voltage(V)

(No Shunt)

Case I – Rx coil at mount (A) 568 1.4 60 

Case I – Rx coil at mount (B) 568 1.4 58 

Case I – Rx coil at mount (C) 568 1.4 45 

Case I – Rx coil at mount (D) 568 0.0014 40 

Case I – Rx coil at mount (E) 568 0.0014 39 

Case I – Rx coil at mount (F) 568 0.0014 36.5 

Case II – Rx coil at cow catcher 568 0.0014 0.5 
73 

Test Case Frequency

(Hz)

Large Rx Coil 

RMS 

Voltage(mV)

(Tx signal off)

Large Rx Coil 

RMS Voltage(V)

(No Shunt)

Case III – Rx coil at 20 ft. from cow catcher 568 0.0014 0.2 

Case IV – Rx coil at 135 ft. from cow 

catcher 568 0.0014 0.003 

Figure 59 shows the tabulated data as a graph.

Figure 59. Detected Cross Talk RMS Voltage Across Rx Coil for Various Shields

4.2.3.4 Conclusion

As expected, the distance between the Tx and Rx coils had the most significant effect in reducing 

crosstalk due to coupling. However, the shielding with the enclosure did show some promise, 

and further analysis was carried out to identify a more suitable material to enclose the coils.

Potential materials and thicknesses were analyzed for future testing using the collected data and 

the skin depth equation (δ), which defines the depth at which the current density induced on the 

surface of material falls to about 37 percent (Dorf, R. C., 2000). A graph of the skin depth for 

several materials was developed and used to determine the most appropriate material and 

material thickness needed to provide adequate shielding for follow-on testing (Figure 60 shows

the skin depth equation as given by: 
74 

(10) 

Where:

Ρ = resistivity of the conductor

ω = angular frequency of current 

μ = permeability of the conductor 

The skin effect versus frequency variance graph shown in Figure 60 for different materials was 

developed using the skin depth equation. 

Figure 60. Skin Effect Depth Variance with Frequency for Various Materials

Using both the equation and graph, 1/8-inch steel gauge (3.175 mm) was identified as an 

adequate shielding material for the range of frequencies (20–1500 Hz) used, i.e., using this 

shielding material could reduce the effect of the electromagnetic coupling between the Tx and 

Rx coil by approximately 66 percent. Shield enclosures for the Tx and Rx coils were fashioned 

and used for subsequent testing. 

The Tx coil shield was open on both the top and bottom, with the bottom section of the shield 

sitting parallel to the bottom section of the Tx coil. Each side of the coil was 2.5 inches 

equidistant from each side of the Tx coil. The Tx coil and shield are shown in Figure 61. 

The Rx coil shield was open at the bottom and fully enclosed on all other sides. The Rx coil was 

placed inside the enclosure with the bottom of the coil sitting parallel to the bottom of the Rx coil 

shield enclosure. The Rx coil and shield are shown in Figure 61. 
75 

Figure 61. Images of Shielded Tx and Rx Coils

4.2.4 Shielding Phase II Testing – Locomotive

Prior to the dynamic testing of the coils, several tests were performed to establish the effects of 

electromagnetic noise and coupling on the system. Several methods for mitigating the effects of 

noise and coupling between the coils were investigated. Signal generation, propagation, and 

detection data were collected and analyzed with the goal of finding the most optimal orientation 

of the Tx and Rx coils to mitigate the issues of magnetic coupling and electrical background 

noise. The Tx and Rx coil shielding methods evolved over several iterations, with final shields 

being fashioned out of 1/8-inch gauge steel. The images in Figure 62 show the evolution of the 

Tx coil shielding, and Figure 63 shows the evolution of the Rx coil shielding. 

Figure 62. Evolution of Tx Coil Shielding
76 

Figure 63. Evolution of Rx Coil Shielding

With the updated shielding and understanding of the system behavior determined prior testing, 

the following pre-dynamic static testing was carried out and the results were used to select the 

configuration used in dynamic testing, i.e., the coils are on the same locomotive, or the Rx coil is 

set at the far end of the test block. 

4.2.4.1 Setup

The field test setup and equipment setup included: 

• Locations: PTT Track

• Coil Heights from Rail:

o Tx Coil: 3–8 Inches

o Rx Coil: 3–8 Inches

• Tx Coil Electrical Settings:

o Signal generator: 3 V peak

o RNB Output: 248 V and 10 Amps

• Oscilloscope:

o Channel 1: Rx Coil

o Channel 4: Tx Coil (at RNB Terminals)

The Tx coil equipment setup followed the instructions described in Appendix A. 
77 

4.2.4.2 Approach

As with the static testing, data was collected with shunts placed at various locations ahead of the 

locomotive, the shunt current and detected signal at the coils were recorded, and the recorded 

data included the screenshot of the oscilloscope readings. 

4.2.4.3 Results and Analysis

The measured data was collected and tabulated as shown in Table 18. 

Table 18. Summary of Pre-Dynamic Test Results

Measured data 

Open 

track/No 

Shunt

Signal with 

shunt at10 ft. 

ahead of the 

locomotive

Signal with 

shunt at 300 

ft. ahead of 

the locomotive

Signal with 

Shunt at 650 

ft. ahead of 

the locomotive

Frequency (Channel 1; Rx coil) 568 Hz 568 Hz 568 Hz 568 Hz

Phase difference (CH1-CH4; 

Rx Coil - Tx coil) 91.35° 109.96° 92.78° 92.11° 

Amplitude (CH1; Rx coil) 700 mV 1,440 mV 800 mV 720 mV

RMS (CH1; Rx coil) 254 mV 514.43 mV 286.96 mV 266 mV

Current through shunt 0 A - 0.9 A 0.4 A

The signal detected by the Rx coil with a shunt at 650 feet was 5 percentage points above the 

crosstalk baseline of 254 mA. This indicates that the detected signal would not be discernible 

from the crosstalk signal when trying to detect the difference between a shunted and an open 

track section at large distances from the locomotive. 

4.2.4.4 Conclusion

Although the signal detected was largely masked by the crosstalk and did not meet the 

benchmark objective of reducing the coupling signal from a root means square (RMS) value of 

254 mA to less than 50 mA, it was decided that both configurations of the Rx coil, i.e., on the 

locomotive and at the far end of the test block, would be tested under dynamic conditions 1) to 

prove the concept of OBRD and 2) to collect empirical data that could be used to develop a 

model that could be used to further development an optimal OBRD system. A crosstalk 

mitigation is necessary and recommended for the development of a future project.

4.2.5 Dynamic Testing – Locomotive

The field testing culminated in the dynamic testing of the system with the primary purposes of 1) 

proving the proposed OBRD concept under different system configurations and 2) generating 

empirical field data under various track conditions for use in developing a system model and for 

future refinement of the concept. The dynamic field testing focused on two system 

configurations (“A” and “B”) that were based on previous static tests of Tx and Rx coils, 

grounding, and shielding tests. 
78 

4.2.5.1 Test Equipment and Setup

The Tx and Rx coil test configurations included: 

• System configuration A: The Tx and Rx coils are located on the same locomotive. 

• System configuration B: The Tx coil is located on the locomotive, and the Rx coil is located 

at the far end of the track test block. 

Occupancy by another train was simulated by a shunt connected in series with an ammeter to 

record the current through the shunt at the far end of the test block (e.g., at T39). The 

configurations for dynamic testing are illustrated in Figure 64. 

Figure 64. Locomotive, Tx and Rx Coil Configurations for

Dynamic Test Cases 4, 5, 6, 7, 8, and 9 

Distance “X” in Figure 64 is the starting point for each dynamic test and is equal to 6,000 feet 

(T27.8 (IJ) to T33.5 (IJ)) or 12,000 feet (T27.8 (IJ) to T39.5 (IJ)). Table 20 shows the test case 

matrix. Test cases 7, 8, 9, and 12 used system configuration A while test cases 4, 5, 6, and 11 

used system configuration B. 

Locomotives and Rail Cars 

Two locomotives were used in the series of dynamic tests. Locomotive A (ID: AAR 2000) was 

the platform where most of the test equipment was mounted. This locomotive has no engine 

power and was pushed by a powered locomotive, referred to as Locomotive B, for the duration 

of the dynamic testing. Care was taken not to use dynamic braking during the test, keeping the 
79 

potential engine electromagnetic noise from the locomotives to a minimum. The locomotive 

speeds were maintained at an average speed of 20 mph (±4) during each test. To simulate wet 

track conditions prior to the wet ballast dynamic testing, a tank car filled with 11,000 gallons of 

water was towed by Locomotive B and was used to wet the track. 

Tx and Rx Coils 

The Tx coil for this test and all tests is a custom-designed coil described and shown in Appendix 

B. The Rx coil used for testing was an Alstom cab signal coil (ATP Rx coil assembly). An 

illustration of the Rx coil is shown in Appendix C. This Rx coil was used for all on-track tests.

The Rx coil has two separate windings, one large, the other small. Each Rx coil winding had a 

1 K resistor connected across its terminals during all tests, to simulate the loading it was 

designed to experience.

Power Supplies 

Multiple power sources were used based on different test scenarios. Two power generators were 

mounted in the front nose of Locomotive A to provide the necessary power supply for test 

equipment. Bungalows at T27, T33, and T39 also had mainline power. 

Measurement Equipment 

• Clamp meter: A clamp meter provided the non-contact measurement of current and 

voltage for some scenarios. The clamp meter used in this test is branded as Bluetooth 

(BT) Meter BT-570C, allowing a wireless connection for data monitoring via BT. 

• Multimeter: Based on test scenarios, several fluke multimeters were used in this test as 

ohmmeter, voltmeter, and ammeter. 

• Oscilloscope: The Rx coil voltage and other related data were measured by oscilloscope 

and verified by the multimeter. The oscilloscope allows data to be saved to a Universal 

Serial Bus (USB) in real-time. The oscilloscope was used for the following reasons: 

o To measure the signals of the connected device (i.e., Tx and Rx coils, and signal 

generator) 

o To compare the relative amplitude and relative phase between the Tx and Rx signals, 

primarily to assess how relative amplitude and phase vary with differing test 

conditions, e.g., shunt present, shunt absent, rail break present, changes in the 

distance among transmitter, receiver, shunts, and rail breaks

o To verify that the signals being measured were the desired signals without additional 

extraneous signals 

• Global Positioning System (GPS) receiver: A mountable GPS receiver was placed at the 

top front of Locomotive A to provide speed and location data that was logged for posttest analysis. 

Other Devices, Equipment, and Tools 

Table 19 lists the other tools and equipment that were used during testing. 
80 

Table 19. Other Devices, Equipment, and Tools 

Equipment/Tool Amount Brand/Model

Portable cab signal tester 1 GE

1-ohm resistor 1 N/A

Jumper wires 6 N/A

Clip wire 4 N/A

Knife switch 1 N/A

Field Setup 

The field equipment setup for dynamic testing was as follows:

• Location: TTT

• Coil heights from rail for both configurations:

o Tx coil: 3 inches

o Rx coil: 3 inches

• Tx coil electrical settings:

o Signal generator: 3 V–3.19 V peak

o RNB output per channel: 180 V–248 V and 9–10 amps

• Oscilloscope:

o Channel 1: Rx coil (large coil)

o Channel 2: Rx coil (small coil)

o Channel 3: Tx coil (at RNB Terminal B)

o Channel 4: Tx coil (at RNB Terminal A)

The Tx coil equipment setup followed the instructions described in Appendix A. 

Test Track

The test block used for dynamic testing was 12,000 feet long to simulate a typical field track 

circuit block. As with the previous testing, the blocks between T27 to T39 of the TTT provided 

the desired length of at least 12,000 feet and were used for the dynamic field test. The IJs are 

located on both rails at T27.8, T33.5, and T39. Switch sections (turnouts) are located at T33.6 

and T38.7. Both switches were locked to normal during the test for 12,000 feet. During the 

6,000-foot tests (T27–T33.5), the switches were locked in reverse to break the track continuity 

for the section of track between T33.5 and T39. Figure 65 and Figure 66 illustrate the 12,000-

foot and 6,000-foot test track sections, respectively, as well as the high-level wiring and the 

bungalow locations with each bungalow having the track wires connected to the bungalow AAR 

terminal. 
81 

For most test cases, wires A and C were connected to each other, and wires B and D were 

connected to each other through the AAR terminal to short each IJ. To simulate a changing 

broken rail scenario in the test block, Terminals B and D at the T33.5 IJ were periodically 

connected to jumper a shunt across the IJ and disconnected approximately every 30 seconds to 

simulate a rail break when disconnected. A recorded change in the voltage of the terminals was 

used to indicate when the terminals were connected or disconnected to indicate whether there 

was a broken rail condition between T27.8 and T39.5 at T33.5. 

Figure 65. TTT Section and Track Connection Diagram for 12,000-foot Block Tests
82 

Figure 66. Test Track Section and Track Connection Diagram for 6,000-foot Block Tests

4.2.5.2 Transmit and Receive Coils Set Up

Tx Coil Set Up

The Tx coil was mounted and located under the front of Locomotive A. The bottom of the Tx 

coil was 3 inches above the rail (not including the shield). A steel shield was used to attenuate 

the crosstalk between the Tx coil and the Rx coil. The metal connection with Locomotive A 

grounded the shield to the locomotive chassis. 
83 

Figure 67. Illustration of Tx Coil Setup When Attached to Locomotive

Figure 68 shows the electrical configuration associated with the Tx coil for Configuration A. For 

the duration of testing, the signal generator was set at a frequency of 568 Hz and an amplitude 

setting of 3 ±0.2 volts. The cables between the locomotive cab and coil mounts had an American 

Wire Gauge (AWG) rating of 12 gauge or lower. 

Figure 68. Electrical and Measurement Configuration of Tx and Rx Coil for Configuration A

A second oscilloscope monitored the Rx coil when the system was set up in Configuration B. 

Rx Coil Set Up

Two Rx coil system configurations were tested as shown in Figure 69. They were: 

• Rx coil Configuration A: The steel cage shielding the Rx coil was mounted on Locomotive 

A, parallel to the Tx coil. The bottom of the Rx coil was 3 inches above the rail. The metal

connection with Locomotive A grounded the shield. 
84 

• Rx coil Configuration B: The steel cage shielding the Rx coil was positioned at the far end 

of the test block and was mounted on cinder block bases (not on a locomotive), 3 inches 

above the rail. Shielding was grounded via a cable and a ground rod. 

Figure 69. Rx Coil Configurations and Setup

4.2.5.3 Approach

Several test cases were carried out over 2 days with the goal of determining the signal behavior 

under dynamic conditions for both Configuration A and Configuration B. Table 20 lists all the 

test cases that were run.

Table 20. List of Test Dynamic Testing Test Cases

Case No. Name Rx coil configuration 

1 Track integrity verification Pretest

2 Test box verification Pretest

3 Static test box test, Rx coil at the far end Pretest

4 Static system test, Rx coil at the far end B 

5 Dynamic system test, Rx coil at the far end B 

6 Dynamic system test, Rx coil at the far end, with rail break B 

7 Static system test, Rx coil on the same locomotive A 

8 Dynamic system test, Rx coil on the same locomotive A 

9 Dynamic system test, Rx coil on the same locomotive, 

with rail break

A 

10 Wet track preparation Pretest

11 Dynamic system test, Rx coil at the far end, Wet B 

12 Tx coil phase changes with track conditions A 
85 

4.2.5.4 Results and Analysis

All testing was performed using test cases that were covered by one run combined as shown in 

Table 20. Test cases 7, 8, and 9 were combined into one locomotive test run from T27–T39.5 as 

this run provided the coverage for test cases 7 (Static system test, Rx coil on the same 

locomotive), 8 (Dynamic system test, Rx coil on the same locomotive), and 9 (Dynamic system 

test, Rx coil on the same location, with rail break). Similarly, test cases 4 (Static system test, Rx 

coil at the far end) and 5 (Dynamic system test, Rx coil at the far end) were combined into one 

locomotive test run from T27–T33.5 since the run provided coverage for test case 4.

In addition, the track was wetted in the last few test cases to simulate the rainy weather 

conditions. Test cases performed on day 1 used a 12,000-foot block, from post 27 to post 39, that 

focused mainly on Configuration A (Tx and Rx coils on the same locomotive). Test cases 

performed on day 2 used a 6,000-foot block, from post 27 to post 33, that focused mainly on 

Configuration B (Rx coil on the far end of the test block). The test section was shortened because 

some track sections were out of service and not usable as test track during this testing period. 

The data was monitored by the devices described in the test plan. All dynamic tests began with 

the locomotive at post 27 and moved in the direction of increasing posts at a constant speed 20 

mph (±4 mph). Measurement and video records for each test case were saved and organized for 

further analysis and research.

Table 21. List of Conducted Dynamic Test Cases 

Day Case No. Rx Coil Configuration Block Length Comments

1 7, 8, 9 A 12,000 ft. (27.8 (IJ)–T39.5 (IJ)) Combined Tests

1 12 A 12,000 ft. (27.8 (IJ)–T39.5 (IJ))

2 4, 5 B 6,000 ft. (T27.8 (IJ)–T33.5 (IJ)) Combined Tests

2 6 B 6,000 ft. (T27.8 (IJ)–T33.5 (IJ))

2 11 B 6,000 ft. (T27.8 (IJ)–T33.5 (IJ))

The track integrity checks at the time of the tests indicated the resistance of the track blocks for 

6,000-foot and 12,000-foot test sections to be 1.5 and 3.3 ohms, respectively (Figure 43). The 

track resistance measurements were carried out with a shunt on one end of the track block and 

the ohm meter reading taken on the other end of the track block. 

Prior to the start of testing with the Rx coil in Configuration B at the T33.5 (IJ), the PCS tester 

was used to test the Rx coil. The PCS was connected to the track at the bungalow at T27.8 (C 

and D terminals) and set to a frequency of 60 Hz. The output current was set at 1 amp and 1.5 

amps. The Rx amplitude was captured as 200 mV (RMS) and 320 mV (RMS). Testing resumed 

after receiving confirmation that the Rx coil worked in this configuration. 

In Rx coil Configuration A, the locomotive went past T39.5 (IJ), while in Rx coil Configuration 

B, the locomotive stopped approximately 100 feet from the Rx coil placed about 10 feet from 

T33.5 (IJ). 
86 

4.2.5.5 Combined Test Cases 4 and 5 with Rx Coil Configuration B

The purpose of test cases 4 and 5 was to analyze the system performance when the Rx coil uses 

Configuration B (i.e., Tx coil and Rx coil at different locations). The test was performed on day 

2 over a 6,000-foot block. The data for the shunt current and the Rx coil amplitude were 

measured by the oscilloscope and are shown in Figure 70 and Figure 71, respectively. A twodata-points moving average trendline was added to the Rx coil amplitude data in Figure 71 to 

show the Rx amplitude trend. 

Figure 70. Shunt Current at T33.5 for Dynamic Test Cases 4 and 5 

vs. Locomotive Location 
87 

Figure 71. Rx Coil Signal Amplitude for Dynamic Test Cases 4 and 5 

vs. Locomotive Location 

Test Case 6 with Rx Coil Configuration B 

The purpose of test case 6 was to analyze the system performance when the Rx coil uses 

Configuration B (i.e., Tx and Rx coils at different locations) with and without a broken rail 

condition. The broken rail was located at the T33.5 IJ, with a shunt at about 2 feet from the IJ at 

T33.5 (Figure 66). The rail break was simulated by removing a shunt across the T33.5 IJ. To

easily compare the results with a rail break versus without a rail break, the shunt was applied for 

30 seconds and then removed for the next 30 seconds. This cycle was repeated as the train 

moved from T27 to the other end of the block at a constant speed. 

The test was performed on day 2 over the 6,000–foot block section. The shunt current at T33.5 

and Rx coil amplitude are shown in Figure 72 and Figure 73, respectively. A two-data-point 

moving average trendline was added to the Rx coil amplitude to show the Rx amplitude trend

(Figure 73). 
88 

Figure 72. Shunt Current at T33.5 for Dynamic Test Case 6 vs. Locomotive Location 

Figure 73. Rx Coil Amplitude for Dynamic Test Case 6 vs. Locomotive Location 
89 

4.2.5.6 Combined Test Cases 7, 8 and 9 with Rx Coil Configuration A 

The purpose of test cases 7, 8, and 9 was to analyze the system performance when the Rx coil 

uses Configuration A (i.e., the Tx and Rx coils at same location, mounted to Locomotive A) with 

a broken rail condition at T33.5 and clear track from T33.5 to T39.5. The test was performed on 

day 1 over a 12,000–foot block. The shunt current at T39.5, the broken rail condition at T33.5, 

and the amplitude of the signal received at the Rx coil were monitored and recorded. The 

measurements of the shunt current, Rx coil amplitude, and phase difference between the Tx and 

Rx coils are shown in Figure 74 through Figure 76, respectively. 

Figure 74. Shunt Current at T39.5 for Combined Dynamic Test Cases 7, 8, and 9 vs. 

Locomotive Location 
90 

Figure 75. Rx Coil Amplitude for Combined Dynamic Test Cases 7, 8, and 9 vs. Locomotive 

Location 

Figure 76. Phase Difference Between Tx and Rx Coils for Combined Dynamic Test Cases 7, 

8, and 9 vs. Locomotive Location 
91 

4.2.5.7 Test Case 11 with Rx Coil Configuration B 

The purpose of test case 11 was to analyze the system performance under altered track impedance 

conditions due to wet ballast. The test track section was wetted with approximately 11,000 gallons 

of water while the Rx coil used Configuration B, and the test was performed over the 6,000-foot 

block. The measured shunt current for test case 11 is shown in Figure 77. The shunt current was 

normalized and compared to the normalized shunt current from test case 5. The results are shown 

in Figure 78. 

Figure 77. Dynamic Test Cases 11 Showing Effects of Wet Ballast on Induced Signal vs. 

Locomotive Location 

Figure 78. Dynamic Test Cases 11 and 5 Comparison Showing Effects of Wet Ballast on 

Induced Signal vs. Locomotive Location 
92 

4.2.5.8 Test Case 12 Configuration A 

The purpose of test case 12 was to provide an indication of the extent to which Tx coil 

impedance is affected by track conditions by monitoring the phase change between the signal 

generator output that drives the amplifiers and the amplifier outputs into the Tx coil. The test was 

performed on day 1 over a 12,000-foot block and Tx and Rx coils on the same locomotive. The 

phase difference between Tx and the function generator was consistent at 60 degrees (±1 

degrees). The results are shown in Figure 79. 

Figure 79. Dynamic Test Case 12: Phase Difference Between Signal Generator and Tx Coil 

vs. Locomotive Location 

4.2.5.9 Analysis 

The overall purpose of the field dynamic test was to simulate a scenario similar to actual 

operations by using the Tx and Rx coils tested during this phase to determine feasibility of the 

concept and to help determine the direction for the future development of the OBRD system. 

According to the test results, the system can identify the different track conditions presented, and 

the signals received for both Configuration A and Configuration B can be distinguished from the 

noise or clear track conditions. The difference in system configuration affects some 

characteristics of Rx coil measurements, such as amplitude. This difference is due to the Tx coil 

affecting the Rx coil signal (crosstalk) when both coils are co-located on the same locomotive. 
93 

The analysis is broken down into the following topics: 

• Operational scenarios

• Transmit range 

• Signal reception

• System performance with wet ballast

Operational Scenarios 

The data from test cases 7, 8, and 9 (Rx coil Configuration A), test cases 4, 5, and 6 (Rx coil 

Configuration B), and other test cases indicate that this system can induce a clearly detectable 

current in a shunt far in advance of the train and that signal increases as the locomotive approaches 

the shunt. This is a very important finding because it proves an induced signal can propagate over 

an appreciable length of track without being mostly dissipated through ballast leakage.

Figure 80 shows an overlay of the induced shunt current and the peak Rx coil voltage amplitude 

for the combined test cases 7, 8, and 9. Figure 81 shows the same data up to T33.5. 

Figure 80. Dynamic Test Cases 7, 8, and 9 Tx and Rx Overlay vs. Locomotive Location 

from T27–T40
94 

Figure 81. Dynamic Test Cases 7, 8, and 9 Tx and Rx Overlay vs. Locomotive Location 

from T27–T33.5 

The induced shunt currents at the end of the test block for test cases 7, 8, and 9 (Configuration 

A) and test cases 4, 5, and 6 (Configuration B) were observed to behave as follows. The current 

increases noticeably from the noise floor/open shunt current (5–7 mA) as the train enters the test 

track at T27.8 with a shunt at the far end. As the train traverses the track section from T27.8 to 

T33.5 and gets closer to the shunt, the decrease in track resistance and the increase in ballast 

resistance within the loop led to the increases in the detected current at the shunt. The current 

appeared to increase logarithmically as it approached the shunt. For instances where the rail was 

broken, the induced signal dropped to the noise floor/open shunt value (5–7 mA). When the train 

stopped 100 feet from IJ at T33.5, the induced current leveled off at the peak. For tests where the 

locomotive went past the IJ at T39.5, the induced signal dropped off to the noise floor/open loop 

current (5–7 mA). 

The measured Rx coil current shows a very slight monotonic increase as the train moves most of 

the way from T27 toward the T39 shunt. This increase is slight because the desired signal is 

being masked by crosstalk from the Tx coil on the same locomotive. Due to the resistance of the 

jumpers across the IJs at T33 no longer being in the circuit, a noticeable increase in the Rx coil 

current is seen when the train reaches this location. The other noticeable increase in the Rx coil 

current is seen when the train is very close to T39, where the desired signal detected becomes 

large enough to overcome the crosstalk masking. 

Test cases 6 and 9 show the system can induce a signal from which a broken rail within a 

shunted track is discernable. Figure 82 shows an overlay of the induced shunt current and the Rx 

amplitude for test case 6.
95 

Figure 82. Dynamic Test Case 6 Tx and Rx Overlay vs. Locomotive Location 

As the train enters the track section at T27.8, the current starts to rise as the train approaches the 

shunt. A rail break is simulated by removing the shunt from the IJ terminals at T33. After 

approximately 30 seconds, the shunt is reapplied. This cycle is repeated every 60 seconds (i.e., 

shunted for 30 seconds, then not shunted for 30 seconds) so that the difference in signal levels 

can be seen between the simulated cases of intact rail versus broken rail. The induced shunt 

current has been seen to drop and increase as the simulated rail break is made and removed. A 

similar behavior is observed with the Rx coil amplitude at approximately 3,000 feet from the 

shunt. Around this point, the induced signal in the rail increases in magnitude to the Rx coil 

signal pick up threshold with the approaching locomotive. 

By comparing the similar data between test cases 5 and 6, a distinct difference between detected 

normal and broken rail status can be observed. This difference can be used to set the system to 

trigger a broken rail warning to the train control system on board the locomotive. 

As soon as the simulated rail break condition was initiated, the detected shunt current decayed 

with a time constant before settling at the electrical noise floor (6 mA). The signal decay time 

constant on rail breaking decreased as the locomotive moved closer to the broken rail section 

and shunt.

4.2.5.10 Transmit Range 

In test case 9, it was observed that the detected current at the shunt at T33.5 increases from the 

noise floor (6 mA) to approximately 12 mA when the train enters the shunted test block at T27.8 
96 

with the shunt. This result indicates an induced signal can be detected up to at least 12,000 feet in 

advance of the locomotive. 

4.2.5.11 Signal Reception

By analyzing the recorded data, the signal received by the Rx coil was observed to have different 

characteristics with different system configurations. When the Tx and Rx coils are located on the 

same locomotive (test cases 8 and 9), the Rx coil signal amplitude remains relatively steady for 

Configuration A and slowly increases as the train gets closer to the shunt because the signal 

detected by the Rx coil is dominated by crosstalk from the nearby Tx coil. Because the desired 

signal is much smaller, it only has a small effect on the total signal level at the Rx coil.

The Rx coil is more effective at detecting the desired signal (not overwhelmed by crosstalk)

when the Rx coil is located at the far end of the track block (Configuration B), particularly when 

the locomotive is within approximately 3,000 feet from the shunt. As the train approaches the 

shunt, the Rx signal amplitude noticeably decreases on initiation of a broken rail event (test cases 

5, 6, and 11). In Configuration A, the level of coupling (Tx-to-Rx coil crosstalk) is evident 

during the dynamic testing with the Rx coil signal ranging between 248 and 300 mV. In 

contrast, the Rx amplitude in Configuration B ranged from 14 to 60 mV when the rail had no 

break. 

4.2.5.12 System Performance with Wet Ballast 

Test case 11 shows the system performance under wet track conditions. When comparing the data 

from test cases 5 and 11 (Figure 80), the system shows similar induced-current propagation 

characteristics. The detected signal is attenuated but not to a significant extent. Therefore, this 

system, as currently configured, continues to display an acceptable performance when the ballast is 

moderately wet, albeit with a slightly attenuated signal that can be picked up by an appropriate Rx. 

However, under heavy rain conditions, the results may be less acceptable. Further testing or

modeling with ballast conditions representative of heavy rain as well as snow is recommended. 

4.2.5.13 Conclusions

The following conclusions can be made from the dynamic test results: 

• The test system can induce a signal that varies between normal clear track, broken rail, 

and occupied track. However, with the Tx and Rx coils collocated on the same 

locomotive, the signal picked up at the Rx coil is masked due to electromagnetic coupling 

with the nearby Tx coil and other environmental electrical noise. To meet the objectives 

of a production OBRD system, a method to mitigate the crosstalk will need to be devised, 

e.g., during a follow-on project. 

• The Rx signal characteristics are affected by different system configurations, especially 

when the Tx and Rx coils are located at different locations, with the separation distance 

between coils in Configuration B highlighting the importance of reducing the coupling 

between Tx and Rx coils. 

• At the tested settings, the current system has a well detectable signal propagation range of 

more than 12,000 feet.

• There was no significant induced signal attenuation from the wet track and ballast 
97 

conditions. However, applying more water and/or a longer period between track 

wetting and testing to allow the water to sufficiently foul the ballast and create real 

world heavy rain conditions (or modeling thereof) may be needed to observe significant 

signal attenuation. 

To determine its viability, the described baseline OBRD system will need to induce, propagate, 

and detect a usable signal via a receiver on the same locomotive. The detected signal levels must 

be sufficiently different from each other to be distinguished by the system and ensure a clear, 

occupied, and broken rail track status. The signal induction and propagation from the dynamic 

test results have shown the system to be viable if the crosstalk problem can be solved. The 

research indicates that induction functionality is viable, but crosstalk mitigation is a lagging 

factor that will need to be further addressed for better system signal reception. Based on the field 

testing, analysis, and conclusions stated in this section, several research topics present 

themselves for further investigation to not only mitigate crosstalk but to enhance the overall 

OBRD system (Section 7). 
98 

5. Model Development

To assist with the development and testing of an optimal OBRD system, a helpful tool for further 

research would be models that incorporate empirical data to simulate the system’s performance 

when certain track and environmental variables are changed. The data collected from the track 

characterization and dynamic testing data aided in the development of models that can be used to 

predict how the track characteristic impedance varies with changing weather conditions and track 

length, as well as how these variations would in turn affect the OBRD system transfer function 

and signal propagation capabilities. These models will be instrumental in defining the 

operational envelope parameters of a fully functional OBRD system.

The proposed models presented included: 

• Track Impedance Model

o Variation with length

o Variation with temperature

o Variation with moisture

• Signal Propagation Model

• OBRD system transfer function

5.1 Track Impedance Model

The OBRD system can be modeled as a Tx and Rx coil affected by track characteristic impedance. 

The input impedance for any length of track section can vary up to the track characteristic

impedance, and the component parameters are affected by weather conditions, subsequently 

affecting the magnitude and phase of the input impedance. The following two models from 

Equations (12) and (13) can be derived by taking the empirical data and the transmission line 

equation into account: 

• Variation with length

• Variation with temperature

• Variation with moisture

5.1.1 Impedance Variation with Length

The frequency-dependent maximum and minimum track characteristic impedance can be used to

develop the operational envelope for the OBRD system. The data collected from the track

impedance characterization effort described in Section 3 provided a framework for determining

the edges of the operational system boundary. The proposed model used the standard 

transmission line from Equation (5) as shown Equation (11) (Section 2.4): 

(11) 

Using the data from the track impedance characterization effort and applying the standard Tx 

line from Equation (5), a sample family (Appendix H) of 30 input impedances over the range 

of 30 frequencies, and the distance is shown in Figure 83.



102 

The current propagation is the reciprocal of the input impedance that can be given by the 

reciprocal of the input impedance and varies accordingly with the propagation constant as shown 

in Equation (20). 

(20) 

The above Equation (20) can be enhanced to account for dynamic changes in impedance due 

to temperature and moisture by using as opposed to .

5.3 Proposed System Model

The proposed system model is derived from an ideal transformer model where the transformer 

coil intermediates between the input and output signals. The model replaces the primary input 

coil of the transformer with the Tx coil and the secondary output coil with the Rx coil. The 

transformer core is replaced with a characteristic impedance in the track circuit loop. Figure 85

illustrates the functional diagram of the system model.

Figure 85. Functional Block Diagram of System Model

The functional diagram shows the system model signal flow from initial signal generation, then 

propagation, and finally detection. Each block diagram part can be mathematically or electrically 

represented to produce a highly generalized model. The signal flow and interaction with each 

section can be explained as follows: 

• Input signal: A signal generator creates the AC input signal that is then amplified to drive

the Tx coil. The model is not concerned with how the magnetic field is generated but

with how the magnetic field is used to induce a voltage and resultant current in the rail.

• Input Tx coil: The Tx coil produces a changing magnetic field that induces an emf in the

rail. The equation to determine the induced emf can be found in Section 2.2.

• Characteristic impedance: The characteristic impedance determines the magnitude and

phase of the resultant current induced by the emf. The propagation characteristics of the

signal at a given distance are a function of the characteristic impedance and propagation

constant of the transmission line model. The relationship between the voltage and current

is given by ohms law.

• Output Rx coil: The output Rx coil detects the changing magnetic field due to the

induced current in the rail and generates voltage in the Rx coil. The characteristics of the

coil will determine the output voltage.
103 

• Output signal: The output signal is an AC voltage that drives a signal detection circuit.

The detection circuit could present a high input impedance to a signal

detection/processing unit.

• Magnetic coupling: Magnetic coupling over the air will occur due to the interplay of the

magnetic field generation function of the Tx coil and the magnetic detection function of

the Rx coil. This coupling is defined by the same equation that defines emf induction, but

it could also be reduced to a coupling constant that would vary with the strength of the

magnetic field.

• Electromagnetic noise: There are several sources of both internal and external

electromagnetic noise. These sources include, but are not limited to, the system selfinduced noise, particularly from the RNB, locomotive electric motor noise, overhead

electric power lines, catenary power lines, etc. The noise can be reduced to a signal

constant for simplicity.

• Transfer function: The functional block equations combine all the identified flows that

are then used to develop a transfer function for the system. The transfer function can then

be used to simulate the expected performance of a system given certain variable inputs.

5.4 Transfer Function Model

A transformer offers an analogy (i.e., two coils intermediated by a circuit) for developing the 

system model transfer function with the Tx coil modeled as the primary coil, the Rx coil 

modeled as the secondary coil, and the track modeled as the transformer core. Using a 

transformer analogy as the starting point, a transfer function can be developed based on the input 

(at the Tx coil) and output (at the Rx coil) magnetic fields.

The transfer function can be used to simulate the propagation characteristics of an induced signal 

given certain track conditions represented by the input impedance of the track circuit at a given 

distance. A transfer function that relates the input magnetic field from the Tx coil in the rail (Btx) 

and the induced magnetic field at the Rx coil (Brx) can be derived as follows.

Where:

Btx = Generated magnetic flux at Tx coil (Wb/m2) 

Brx = Induced magnetic flux at Rx coil due to current in the rail (Wb/m2) 

Ir = Current in Rail due to Induced emf and track Impedance Loop (A) 

r = Distance of Rx coil from rail (m)

S= Cross section areal of active area (m2

) 

emf = Induced electromotive force in rail due to Btx (V)

x = Distance from shunt (unit distance) 

Zin (x) = Input impedance as a function of distance from a shunt (ohms/unit distance) 

f = Frequency of Btx (Hz)

μ = Permeability of a medium (H/m) 

μo = Permeability of free space = 4π × 10−7 (H/m) 

105 

The transfer function is only concerned with the properties of the generated signal (i.e., 

magnitude, phase, amplitude, and frequency) and does not consider how the inducing magnetic 

field is generated by the Tx coil nor how the magnetic field is picked up by the Rx coil. These 

functions would be design specific to the respective coils. However, the equation can be used to 

determine 1) the desired design magnetic field generation of the Tx coil and 2) the desired signal 

pick-up sensitivity of an Rx coil for a given signal under certain track conditions. 

The transfer function presented is a highly generalized ideal function, but this function does not 

limit its usefulness. For example, this function can be used to estimate initial system behavior 

and can be improved upon to accommodate the impact of noise, “crosstalk,” and design 

characteristics of different types of Tx and Rx coils.

5.5 Summary

At the core of each model is the track input impedance at distance “x” from the shunt that is 

bound by the shunt impedance and the characteristic track impedance. The input impedance will 

vary with characteristic track impedance, changes in environmental conditions and track 

conditions, both of which will subsequently affect the OBRD system performance. Table 22

provides a summary of the models. 

Table 22. Summary of Proposed Models
106 

Although anchored in theorical and empirical data, the proposed foundational models will need 

to be continuously back tested under various scenarios and assumptions that capture as many of 

the real-world variances as possible. It is expected that the models will continue to evolve and 

incorporate more variables, such as noise due to the locomotive electric motor and other noise, 

the addition of tuned shunts, etc., to become more robust as further research on the topic is 

carried out. 

In addition, although a function-based approach in developing the model is presented, there is an 

opportunity for the collected track impedance data to be used in further research with a big data, 

model-based approach. 
107 

6. Preliminary Development and Migration Plan

The OBRD research project focuses on adopting and incorporating the technology into an 

enhanced version of the Overlay-Positive Train Control (O-PTC)/Quasi-Moving Block (QMB) 

train control system to enable the adoption of FMB operations. Since the project concept is still 

in the early stages of development, a preliminary development and subsequent migration plan are 

presented. Therefore, this section is divided into two main categories:

1. A development plan for transforming the research into a fully functional viable

technology capable of integrating with a train control system

2. The migration plan for the wide-scale deployment of the system in support of FMB

operation

6.1 OBRD Development Plan

Several phases would be expected to evolve the system into a highly reliable OBRD system that 

would replace conventional track circuits and enable FMB operations. Figure 86 illustrates the 

proposed subsequent phases of the OBRD development with this research project as Phase 1. 

Figure 86. Development Phases of the OBRD Concept

The objectives of Phase 2 include: 

• Demonstrating the OBRD concept as a complete breadboard design

• Evaluating using the models developed in this project, analyzing and comparing other

potential alternative architectures and configurations to potentially improve 

performance

• Identifying issues with the potential solution(s) and proposing practical mitigations

The scope of Phase 2 consists of:

• Using the models developed in Phase 1 to analyze and compare other potential alternative

variants, architectures, and configurations that could improve system performance
108 

• Developing a minimum viable, functional breadboard design that incorporates the

identified mitigations

• Evaluating and testing the breadboard in the lab and field environments

• Developing technical specifications for the proposed solution

Phase 3 will be the development of a form/fit/function demonstrator system capable of 

interfacing with O-PTC/QMB in support of a FMB that will be the final step in the development 

of the OBRD concept. After developing a functional demonstrator prototype with definitive 

specifications for use by vendors to design fully operational OBRD systems, the following 

proposed deployment migration plan can be initiated. 

6.2 Deployment Migration Plan

Once integrated with O-PTC, the OBRD concept will set the stage for the widescale adoption 

and deployment of FMB. Therefore, changes must be made to the functionality of O-PTC to 

accommodate interfacing with the OBRD concept. The required changes have been captured in 

the FMB concept of operations (ConOps) and companion system and segment requirements 

developed in a parallel FMB (TTCI, Pending) project. In addition to the ConOps and required 

specifications, a migration plan for several alternatives of the Alternative Broken Rail and 

Rollout Detection/Alternative Broken Rail Detection (ABRRD/ABRD) was developed, and this 

plan details the proposed deployment approach. The FMB ConOps details the three alternative 

ABBRD/ABRD variants as follows: 

• Head-of-Train (HOT)-ABRRD: Onboard broken rail and rollout detection interrogates

the track ahead of the train

• End-of-Train (EOT) ABRD: Onboard broken rail detection interrogates the track

behind the train

• Wayside ABRRD: Alternative wayside broken rail and rollout detection, i.e., waysidebased but without the limitations of fixed block track circuit-based detection

Since the OBRD system detailed in this project falls primarily under the category of a HOTABRRD, this section will summarize only the proposed migration path for the HOTABRRD/ABRD.

6.3 HOT OBRD Migration Plan

The FMB Migration Consideration document describes migration considerations, including cost 

drivers, potential implementation paths, and steps for the FMB train control method and 

ABRRD/ABRD alternatives. In addition, this document provides a high-level cost driver 

analysis for each path.

The FMB migration plan for the HOT-ABRRD technologies is shown in Figure 87. This plan 

consists of 3 initial territory stages and 10 potential paths to FMB implementation. The three 

stages include: 

• Stage a: FMB active with all track circuits and Wayside Status Messages (WSMs)

• Stage b: FMB active without conventional track circuits. This stage has two possibilities

depending on the infrastructure at two control points.
109 

o Field interlocking (b.1) 

o Switches status awareness (b.2) 

• Stage c: FMB with alternative IXL

Figure 87. HOT-ABRRD Migration path

Further enumeration on the identified paths, cost drivers, and high-level migration steps is 

beyond this project’s scope but can be found in the FMB Migration Considerations document 

(TTCI, Pending). 
110 

7. Conclusion

From October 2019 to May 2022, the team researched a concept for an OBRD system that sends 

and receives AC electrical signals generated on board the locomotive transmitted to the rail via 

electromagnetic induction with the resultant current propagating through a track section, and 

back to the locomotive via (tuned) shunts. This research used the long-term data collection of 

track electrical parameters for use in track impedance characterization. The collected data was 

used to 1) determine the relationships between track impedance and weather conditions (e.g., 

temperature, ballast moisture content, etc.), 2) develop foundational models to further research, 

and 3) develop an OBRD system and framework OBRD operational envelope. The three 

fundamental challenges included: 

1. Strong mutual inductance between the Tx and Rx coils

2. Weak mutual inductance between the rail and the induction coils

3. Track impedance variability

Through the R&D efforts, significant progress was made in the area of inducing a usable signal 

in the track and reliably propagating the signal over a range up to 2 miles (4 miles round trip). 

However, there still remains many railroad scenarios where propagation needs to be greater than 

that (e.g., a heavy train on a downgrade). In addition, the dynamic testing was carried out using 

one frequency (568 Hz) and track condition. Therefore, the performance reliability will have to 

be investigated under different frequencies and various track conditions to ascertain a signal can 

be reliably induced, propagated, and detected at ranges of 2 miles or more for multiple signal 

frequencies and various track conditions (i.e., weather and types of ballast).

The induced signal also varied appreciably with a change in track state (i.e., broken rail, shunted 

rail or open rail) indicating a suitable Rx coil would be able to detect these changes in the return 

signal. Although using passive means (shielding) reduced its effect, crosstalk still masked Rx 

coil detection sensitivity. The noise and crosstalk detected by the receiver made discerning the 

induced signal state uncertain, requiring the need for more work in active crosstalk mitigation 

and signal detection. 

The track impedance data collection effort collected several million data points at the rate of 2

MB per day of RLCG, Open Loop Impedance, Closed Loop Impedance, weather, and sensor 

data per day. This data was used to 1) understand the relationships between track impedance and 

weather conditions and 2) develop track impedance-based signal propagation models. These 

models will be useful in developing theoretically plausible signal propagation outcomes due to 

variable track impedance conditions and improving the overall system performance.

The result of this research confirms the possibility of the general concept of an OBRD system

based on an induced signal generated by an onboard transceiver and propagated through the rail 

with the return signal picked up by the same onboard transceiver. Making the system more 

reliable in picking up and inferring the signal and integrating it to an onboard train control (i.e., 

PTC) system would be the final step in enabling FMB functionality.

Recommendations for further improvement of the results of this project and the enhancements of 

the concept are:

• Interference canceling techniques: Signal canceling technology has been in use for
111 

decades to attenuate interferers based on the direction of arrival or recognizable signal 

characteristics. This technique involves producing a signal identical to the received 

interference but 180 degrees out of phase. This signal, when added to the received signal, 

cancels the interference. In situations where the interferer does not have significant 

frequency separation from the desired signal, interference cancelers provide far greater 

attenuation (e.g., 60 dB) than is achievable by filtering. OBRD is particularly well suited 

for interference canceling since the interfering signal is readily available onboard for 

subtraction from the received signal.

• Tx and Rx coil R&D to explore different types of Tx and Rx coils and configurations:

This research focused primarily on the use of cab signal pick up coils. Other magnetic

field detection receivers could be used but have not been tested (e.g., a Transceiver coil)

(i.e., a Tx and Rx coil on the same coil).
112 

8. References

Al-Nazer, L. (2008). Development of Rail Temperature Prediction Model. Research Results No.

RR08-06, Washington, DC: U.S. Department of Transportation, Federal Railroad 

Administration.

B&K Precision. (2020). B&K Precision LCR Meter Guide. Yorba Linda, CA: B&K Precision. 

Dorf, R. C. (2000). The Electrical Engineering Handbook. In C. Dorf Richard, The Electrical 

Engineering Handbook (pp. 803–879). Boca Raton, FL: CRC Press Inc. 

Ellingson, S. W. (2018). Electromagnetics, Vol. 1. In E. S. W, Electromagnetics, Vol. 1.

Blacksburg, VA, Blacksburg, VA: Virginia Tech University Libraries. 

Liu, C., Yang, S., Cui, Y., et al. (2020). Quantitative analysis on coupling of traction current into 

cab signaling in electrified railways. Railway Engineering Science, 28, pp. 275–289. 

National Weather Service Weather Forecast Office. (2021). Climatological Report (Annual) 

Pueblo, CO. Retrieved from NWS. 

Parsons, R. L., Rahman, A. J., Han, J., Glavinich, T. E. (2014). Track Ballast Fouling and 

Permeability Characterization by Using Resistivity. Transportation Research Record: 

Journal of the Transportation Research Board, 2448(-1), 133–141. 

The Association of American Railroads, (AAR). (n.d.). AAR standard S-9101, Locomotive 

Electronics System Architecture. Locomotive Electronics System Architecture. 

Transportation Technology Center, I., Polivka, A. L., Malone, J. J., Smith, B. E., & Renfrow, S. 

M. (2013). USA Patent No. 9,162,691.

Transportation Technology Center, Inc. (2013). Internal Research and Development Report: 

Track Impedance Research for Onboard Broken Rail Detection Project. Pueblo, CO: 

TTCI.

Transportation Technology Center, Inc., Malone, Jr., J. L., & Polivka, A. L. (2013). USA Patent 

No. 9,102,341.

Transportation Technology Center, Inc. (Pending). Full Moving Block Requirements for 

Railroad Operations. Washington, DC: Federal Railroad Administration (FRA).

Zhang, Y. J., Clemenzi, J., Kesler, K. & Lee, S. (2007). Real Time Prediction of Rail 

Temperature. Proceedings of the AREMA 2007 Annual Conference. Chicago, IL: 

American Railway Engineering and Maintenance-of-Way Association.
113 

Appendix A. 

Resonance Signal Generator Equipment Setup Instructions

Purpose:

This guide is designed to familiarize the user of the magnet system with setting up and using the 

high-power magnet system safely and effectively.

Safety Concerns:

The resonant capacitor network can produce above 2,000 V even with a low input voltage. 

Therefore, no modifications can be made to the jumpers or connections while the network is in

operation, but the capacitor network can hold several seconds of charge after power has been

removed.

Before modifications are made to the system, both high-voltage terminals should be shorted to 

ground. The transmission (Tx) coil electromagnet can produce high fields and high temperatures. 

Care should be taken to monitor the magnet’s temperature with a temperature sensor when

operating at high fields. The hot spots of the magnet are the two faces closest to the target. The 

Resonant Network Box (RNB) box can produce four resonant frequencies set by selecting 

jumpers. The RNB and jumper locations are shown in Figure A1. 

Figure A1. RNB Showing Jumper Locations 

Figure A2 shows the circuit diagram showing the amplifier, Resonant Network, and Tx coil. 
114 

Figure A2. RNB Circuit Diagram

The manufacturer expected resonance frequencies, jumper settings, and RNB output 

terminal currents that are shown in Table A1. 

Table A1. RNB Vendor Defined Jumper Settings

Resonance Frequency (Hz) Jumper Settings Current at A and B Terminals

1,420 All Jumpers Open 18 A 

707 J2A J2B J4A J4B Jumped 30 A 

419 J3A J3B J4A J4B Jumped 42 A 

373 All Jumpers Jumped 

(Default)

48 A 

The Tx coil generates a magnetic field at a given resonance frequency setting.

Setup 

The signal generation setup block diagram is shown in Figure A3. 

Figure A3. Flow Diagram of RNB Setup 
115 

Power Supply Setup

• Connect both power supplies to 120 V AC sources

• Each power supply must receive the same 10 V peak signal from the signal generator to

ensure that each coil current is in phase with the other. Connect this across both “Voltage

Programming Inputs.”

• Connect “Common” to “Ground” to ensure everything is grounded at this point

• Connect any voltage or current diagnostics to monitor the power supply output

Resonant Network Setup

• Connect the RNB to 120 V AC. This only serves to power the fans to cool the capacitors

that are switched on at the connector. The fans should always be on during operation.

• On the back of the RNB, connect from the “A” terminal to the “Output” of one of the

supplies. Connect the “B” terminal to the “Output” of the other supply. Both power

supplies “Common” will connect to the “GND” terminal on the back of the RNB.

• On the back of the RNB, both power supplies “Common” will connect to the “GND”

terminal.

• Ensure that the wires used to connect the power supplies to the RNB are rated for at least

20A/20 V.

The signal generator’s output is split into the input of both power supply amplifiers to ensure the 

phase of the output of both amplifiers is in sync. One of the power supply amplifiers goes to the 

“A” side of the RNB, and the other goes to the “B” side of the RNB. The “A” side and “B” side 

outputs are connected to the four inputs of the Tx coil.

Tx Coil Setup

1. The polarity of the connections is important. If the polarity is incorrect, then the magnetic

fields will buck, the circuit will not work, and no field will be output.

2. From the front of the RNB, the “A+” terminal on the RNB Front Panel should be wired

to the “A+” terminal on the magnet. Likewise, the “AGND” terminal on the RNB Front

Panel should be wired to the “A-” terminal on the magnet.

3. From the front of the RNB, the “B+” terminal on the RNB Front Panel should be wired to

the “B+” terminal on the magnet. Likewise, the “BGND” terminal on the RNB Front

Panel should be wired to the “B-” terminal on the magnet.

4. If a wire extension needs to be made, ensure that the extension used is rated

100A/2,000 V at the utilized frequency. Keep in mind that these terminals are the most

electrically dangerous of the circuit.

Energizing the Signal Generation Setup

The following steps are to be carried out to configure and energize the resonant signal generator 

equipment setup. 

• Configure RNB jumpers to the desired test frequency: The RNB operates at high

voltages. Be sure to short each capacitor bank to ground across a resistor prior to
116 

touching anything in the RNB. 

• Power on the signal generator, both power supplies, and the fans on the RNB.

• Select the desired frequency and input voltage on the signal generator: All tests were run

with 3 V ±0.5 output from a signal generator to ensure consistent power to the amplifiers.

• Close the A and B side switches on the RNB: The system is fully energized at this point. 

Do not touch the RNB, the coil, or any other part of the system.

• Using the High Voltage A and High Voltage B values, find the resonant frequency for the

system: The highest value corresponds to the resonant point, and resonant points vary

based upon test setup.

• Vary frequencies around resonant points as needed and record the desired data.

• Open the A and B side switches on the RNB.

• Turn off the signal generator, amplifiers, and fans on the RNB.
117 

Appendix B. 

Tx Coil Specifications

Throughout OBRD testing, the Tx coil is a custom-designed coil procured from Stangenes®

shown in Figure B1. 

Figure B1. Profiles of Tx Coil

Specifications

• Frequency range: 373 Hz–2,000 Hz

• Number of coils: Two coils (A and B)

• Cross section dimensions of each coil: 1.77 inches x 3.5 inches

• Total core dimensions: 1.77 inches x 7.08 inches

• Core material: Nanocrystalline

Tx Coil external dimensions

• 12 inches x 15 inches x 8.5 inches

119 

Appendix C. 

Rx Coil Specifications

The Rx coil used for testing was an Alstom Automatic Train Protection (ATP) Rx coil 

(Figure C1) with the specifications listed below. The receiver has two coils, the larger of 

which is predominantly used for testing shown in Figure C2. 

Figure C1. Rx Coil Assembly

Specifications

Electrical Specifications of Large Coil 

• Resistance = 226 Ohms (DC)

• Inductance = 19.3 Henries

• Q = 9.4 at1,000 Hz

• Serial number: 23727AH069

Dimensions

• Length of Rx coil: 24 Inches

• Large coil: 11 inches

• Small coil: 4 inches

• Diameter(s) of coil(s): 6 inches
120 

Figure C2. Illustration of Rx Coil Dimensions

Theory of Operation 

The ATP Rx coil is mounted on the locomotive between 3 and 8 inches above the rail. The 

receiver detects an AC signal that is transmitted through the rail. Upon detection, the coil 

converts the detected signal to an AC voltage. 
121 

Appendix D. 

Supplementary Tx Coil Test Data

Figure D1. Tx Coil Measurements 1
122 

Figure D2. Tx Coil Test Measurements 2
123 

Figure D3. Graphs of Tx Coil Measurements
124 

Appendix E. 

Insulated Joints Measurements

Tables E1 through E2 include the insulated joint (IJ) measurements on the Transit Test 

Track (TTT) test areas prior to field testing. 

Table E1. TTT IJ Measurements from September 2020

Location Test Type Rail Voltage Amps Ohms

T27.5 AC Inside 7.46 0.022 339.0909091 

T27.5 AC Outside 7.46 0.029 257.2413793 

T29.5 AC Inside 7.58 0.01 758 

T29.5 AC Outside 7.58 0.004 1,895 

T33.5 AC Inside 7.14 0.09 79.33333333 

T33.5 SMU/DC Inside 7.6 0.085 89.41176471 

T33.5 AC Outside 7.49 0.023 325.6521739 

T33.5 SMU/DC Outside 7.6 0.019 400 

T39.5 AC Inside 7.56 0.009 840 

T39.5 SMU/DC Inside 7.6 0.005 1,520 

T39.5 AC Outside 7.6 0.005 1,520 

T39.5 SMU/DC Outside 7.6 0.00003 253333.3333 

T45 AC Inside 7.58 0.06 126.3333333 

T45 SMU/DC Inside 7.6 0.004 1,900 

T45 AC Outside 7.56 0.005 1,512 

T45 SMU/DC Outside 7.6 0.002 3,800 

T51 AC Inside 7.57 0.009 841.1111111 

T51 SMU/DC Inside 7.57 0.001 7,570 

T51 AC Outside 7.59 0.008 948.75 

T51 SMU/DC Outside 7.59 0.0019 3994.736842 
125 

Table E2. TTT IJ Measurements from September 2021 

Location Test Type Rail Voltage Amps Ohms

T33.5 AC Inside 6.87 0.077 89.2207792

T33.5 DC Inside 7.08 0 ∞

T33.5 AC Outside 6.14 0.175 35.0857143

T33.5 DC Outside 7.25 0.003 2416.66667

T39.5 AC Inside 7.12 0.031 229.677419

T39.5 DC Inside 6.87 0.003 2290

T39.5 AC Outside 7.26 0 ∞

T39.5 DC Outside 6.14 0 ∞

Precision Test Track (PTT) Track Impedance Measurements

Measurements with the negative probe on A and positive probe on B are labeled AB, while 

measurements labeled BA have the negative probe on the south side and the positive probe on 

the north, shown in Table E3. All measurements were made using a Fluke multimeter. All 

pictures were taken for the joint bars and insulated joints as is. Ballast/sand was removed from

underneath the joint prior to measurements being taken. 
126 

Table E3. PTT IJ and Bond Wire Measurements from April 2021 
127 

Appendix F. 

Measurement Equipment

The following recording and measurement tools were used in the course of this research:

• Multimeters

o Fluke® 87/89 with true RMS AC voltmeter with an input impedance greater than

100 K Ohms

o BT Clamp Meters BT Meter BT-570C

• 5100 Series Meggit® Gauss METERS

• B&K precision 891 LCR Meter

• Oscilloscopes

o SIGLENT SDS1000X-E®

o Compocket Minis® Portable Oscilloscope

• Rogowski Loop

• Garmin® GPS Receiver

• Data Collection Computers

• National Instruments® Data Acquisition System (DAQ)

• DEWEsoft® software

• Portable Cab Signal Tester

• Raspberry Pi® Single board computer

• Arduino® Microcontroller
128 

Appendix G. 

Characteristic Impedance Calculations from Sample Track Impedance 

Data

According to the Transmission Line Model equations in Section 2.4, the characteristic 

impedance can be measured using two ways. One way is to use the Resistance, Inductance, 

Capacitance and Conductance (RLCG) variables to calculate the characteristic impedance and

propagation constant. Another way is to use the closed and open loop circuit impedance 

magnitude and phase angle as shown by Equation (7). In this section, an example for calculating

the characteristic impedance and propagation constant is shown as well as the input impedance at

a given track length. 

Table G1 shows a sample of measurement values for the impedance variables used to calculate

the corresponding characteristic impedance, propagation constant, and the input impedance with 

a shunt at a distance of 198 meters. Tables G1 and G2 show the results of the characteristic and 

input impedances using the following two methods, respectively: 

• The first method uses RLCG variables.

• The second method uses open and closed loop impedance measurements.

Table G1. Sample of Measurements for Track Impedance Variables at 20 Hz

Frequency

(Hz) R (ohm) L (H) C (F) G (S) |CL-Z| (ohm)

CL-Z Phase

(deg)

|OL-Z| 

(ohm)

OL-Z 

Phase 

(deg)

20.3 2.31E-01-9.50E-03-8.99E-06 2.99E-03 1.23 -78.9 308 20.9 

Method 1 

1. Applying the characteristic impedance Equation (4) from Section 2.4 to RLCG

measurements at the measured frequency to obtain the circuit characteristic impedance

2. Using the RLCG measurements at the measured frequency as inputs, the propagation

constant is calculated by applying the propagation constant from Equation (6) from

Section 2.4.

3. The propagation constant is normalized to per meter unit by dividing the results from step

2 by the unit measurement distance in meters (198 meters/~650 feet).

4. Using the obtained characteristic impedances as propagation constants and applying the

input impedance Equation (5) from Section 2.4, the input impedance with the load

(shunting axle of 0.06 ohm) is calculated at a specific distance (e.g., 190 meters) from the

source. The sample data results for each frequency data are tabulated in Table G1.

The calculations show that the estimated impedance seen from a source that includes track 

impedance and train shunt has a magnitude of 1.24 ohms. Comparing this value to the impedance 

measured with a short circuit condition (closed loop impedance) shows credibility in the results 

where the closed loop impedance has a magnitude of 1.23 ohms, a magnitude that is slightly 

lower than when the circuit has a shunt. 
129 

Table G2. Characteristic and Input Impedance Calculations for

RLCG Sample Measurements

Frequency 

(Hz) R (Ω) L (H) C (F) G (S) |Z0| (Ω) Z0 Phase (degrees)

Zin

(198) 

(Ω)

Zin (198) 

Phase 

(degrees)

CL_Z

(Ω)

CL_Z 

Phase 

(degrees)

20.3 0.21 -0.01029 -1E-05 0.0033 19.47 -29.8 1.34 -78.2 1.25 -80.3

23.7 0.21 -0.00868 -8E-06 0.0033 19.31 -30.0 1.32 -78.0 1.25 -79.9

27.6 0.21 -0.00750 -7E-06 0.0033 19.40 -30.1 1.33 -78.1 1.24 -80.4

32.2 0.21 -0.00608 -6E-06 0.0033 18.88 -29.9 1.26 -77.6 1.24 -79.9

37.5 0.21 -0.00526 -6E-06 0.0033 18.76 -28.6 1.27 -77.8 1.24 -79.7

43.8 0.21 -0.00426 -6E-06 0.0033 18.01 -26.5 1.20 -76.7 1.24 -79.5

51.0 0.22 -0.00392 -6E-06 0.0033 18.36 -25.2 1.29 -77.5 1.23 -79.7

59.5 0.24 -0.00373 -5E-06 0.0033 19.42 -25.5 1.43 -77.7 1.23 -79.3

69.3 0.18 -0.00308 -5E-06 0.0033 18.67 -25.0 1.36 -79.9 1.22 -78.5

80.9 0.22 -0.00239 -5E-06 0.0033 17.42 -21.5 1.25 -76.8 1.22 -79.4

94.3 0.23 -0.00220 -5E-06 0.0033 17.46 -19.7 1.33 -77.5 1.23 -79.3

109.9 0.24 -0.00185 -5E-06 0.0033 16.73 -17.1 1.32 -76.7 1.24 -79.2

128.1 0.24 -0.00165 -5E-06 0.0033 16.37 -15.2 1.37 -77.3 1.26 -79.0

149.4 0.24 -0.00150 -5E-06 0.0033 16.17 -13.6 1.44 -77.7 1.27 -78.6

174.2 0.26 -0.00128 -5E-06 0.0033 15.51 -11.6 1.44 -77.2 1.28 -78.5

203.1 0.26 -0.00109 -4E-06 0.0033 15.00 -10.6 1.43 -77.1 1.32 -78.7

236.8 0.26 -0.00090 -1E-06 0.0033 19.12 -25.2 1.38 -76.4 1.32 -78.5

276.1 0.27 -0.00081 -1E-06 0.0031 19.70 -23.8 1.44 -76.7 1.33 -78.3

321.9 0.27 -0.00067 -9E-07 0.0030 19.83 -23.5 1.39 -76.1 1.34 -78.2

375.3 0.28 -0.00059 -8E-07 0.0029 20.22 -22.9 1.44 -76.3 1.34 -77.9

437.6 0.29 -0.00054 -7E-07 0.0028 21.12 -22.5 1.54 -76.6 1.52 -78.5

510.1 0.30 -0.00048 -7E-07 0.0027 21.29 -20.3 1.59 -76.8 1.53 -78.5

594.8 0.30 -0.00043 -6E-07 0.0025 22.54 -20.0 1.66 -77.3 1.58 -78.5

693.5 0.31 -0.00038 -4E-07 0.0024 23.30 -20.5 1.69 -77.1 1.65 -75.8

808.5 0.33 -0.00031 -3E-07 0.0023 23.83 -20.4 1.64 -76.2 1.85 -67.9

942.7 0.33 -0.00024 -3E-07 0.0022 23.26 -20.3 1.46 -74.3 2.00 -54.9

1,099.1 0.36 -0.00015 -2E-07 0.0021 21.04 -18.4 1.13 -68.3 2.17 -36.8

1,281.4 0.37 -0.00006 -2E-07 0.0020 15.74 -9.0 0.63 -47.4 2.41 -13.5

1,494.0 0.38 0.00005 -1E-07 0.0019 15.84 42.1 0.63 45.6 2.70 14.9

1,741.9 0.40 0.00016 -1E-07 0.0018 27.98 58.3 1.84 75.6 3.06 48.5
130 

The calculations for the second method of figuring the characteristic impedance using closed and 

open loop values are shown below. 

Method 2

1. Applying the characteristic impedance Equation (7) from Section 2.4 to open loop (OL-Z) 

and closed loop (CL-Z) measurements at the measured frequency to obtain the circuit

characteristic impedance.

2. The propagation constant at different measurements is derived using the open loop (OLZ) and closed loop (CL-Z) measurements at the measured frequency as inputs for the

propagation constant Equation (8).

3. The propagation constant is normalized to per meter unit by dividing the results from step

2 above by the unit measurement distance in meters (198 meters/~650 feet).

4. Using the obtained characteristic impedance propagation constants and applying the input

impedance Equation (5) from Section 2.4, the input impedance is calculated with the load

(shunting axle of 0.06 ohm) at a specific distance (e.g., 190 meters) from the source. The

results for each frequency from the sample data are tabulated in Table G3.

Table G3. Characteristic and Input Impedance Calculations for Closed and Open Loop 

Impedance Sample Measurements

Frequency 

(Hz) R (Ω) L (H) C (F) G (S) |Z0| (Ω) Z0 Phase (degrees) Zin (198) (Ω) Zin (198) Phase (degrees)

20.3 1.25 -80.3 280.0 20.0 18.68 -30.1 1.26 -77.6

23.7 1.25 -79.9 280.9 19.8 18.71 -30.1 1.26 -77.2

27.6 1.24 -80.4 279.0 19.8 18.64 -30.3 1.26 -77.7

32.2 1.24 -79.9 276.4 19.7 18.53 -30.1 1.25 -77.2

37.5 1.24 -79.7 276.4 19.5 18.52 -30.1 1.25 -77.0

43.8 1.24 -79.5 276.8 19.5 18.51 -30.0 1.25 -76.8

51.0 1.23 -79.7 276.8 19.6 18.48 -30.1 1.25 -77.0

59.5 1.23 -79.3 276.9 19.8 18.46 -29.8 1.24 -76.5

69.3 1.22 -78.5 277.0 19.7 18.40 -29.4 1.24 -75.8

80.9 1.22 -79.4 277.1 19.6 18.39 -29.9 1.23 -76.6

94.3 1.23 -79.3 277.3 19.6 18.43 -29.9 1.24 -76.6

109.9 1.24 -79.2 277.6 19.6 18.56 -29.8 1.25 -76.5

128.1 1.26 -79.0 277.9 19.6 18.68 -29.7 1.27 -76.3

149.4 1.27 -78.6 278.2 19.8 18.77 -29.4 1.28 -76.0

174.2 1.28 -78.5 278.6 21.3 18.86 -28.6 1.29 -75.9

203.1 1.32 -78.7 278.7 21.4 19.16 -28.7 1.33 -76.2

236.8 1.32 -78.5 274.9 25.4 19.02 -26.5 1.33 -76.0

276.1 1.33 -78.3 273.6 30.7 19.05 -23.8 1.34 -75.8

321.9 1.34 -78.2 284.4 29.7 19.53 -24.2 1.36 -75.7

375.3 1.34 -77.9 285.5 32.5 19.56 -22.7 1.35 -75.4

437.6 1.52 -78.5 289.4 33.7 20.95 -22.4 1.53 -76.3
131 

Frequency 

(Hz) R (Ω) L (H) C (F) G (S) |Z0| (Ω) Z0 Phase (degrees) Zin (198) (Ω) Zin (198) Phase (degrees)

510.1 1.53 -78.5 283.9 36.9 20.86 -20.8 1.55 -76.3

594.8 1.58 -78.5 303.3 38.4 21.88 -20.1 1.59 -76.4

693.5 1.65 -75.8 313.8 39.7 22.75 -18.0 1.66 -73.8

808.5 1.85 -67.9 329.7 40.0 24.72 -14.0 1.88 -66.2

942.7 2.00 -54.9 324.4 40.7 25.44 -7.1 2.03 -53.5

1,099.1 2.17 -36.8 338.5 42.1 27.10 2.7 2.22 -35.8

1,281.4 2.41 -13.5 343.8 44.4 28.76 15.5 2.46 -13.2

1,494.0 2.70 14.9 361.8 47.5 31.26 31.2 2.76 14.6

1,741.9 3.06 48.5 366.6 51.3 33.48 49.9 3.10 47.7

The input impedance results in Table G3, where the characteristic impedance calculations were 

based on the second method (i.e., using the closed and open loop impedance measurements), 

show good estimation of the impedance seen by the source that includes track and train shunt 

impedances. How the estimation closely matches the closed loop impedance can be observed by 

comparing the input impedance magnitude measurements with the closed loop impedance 

magnitude measurements. However, the comparison of the input impedance results between 

Tables G2 and G3 show mismatches at some frequencies. These mismatches can be seen in 

Figure G1 where the percentage difference between the results of the two methods for 

calculating the characteristic impedance (Zo), propagation constant (Gamma), and input 

impedance (Zin) at a distance of 198 meters are shown above. The percentage difference curve in

each graph indicates the average percentage difference at each frequency while the wider curves 

show the standard deviation of the average percentage difference. The results of checking the 

real and imaginary components of the closed loop impedance measurements and comparing them 

to the corresponding resistance and inductance measurements showed that those values do not 

align at the frequency entries that mismatch with the input impedance calculations. These results 

give an indication that the input values for these entries have a margin of error either in the 

closed loop circuit measurement or the resistance and inductance measurements, while the 

general impedance trend and impedance are closely matched. It should be noted that component 

RLCG measurements are prone to parasitic interference that can cause some data points to vary

between 4 percent at lower frequencies to up to 10 percent at higher frequencies when compared 

to the open loop/closed loop method (B&K Precision, 2020). 
132 

Figure G1. Percentage Difference and the Corresponding Standard Deviation Between

the Results of the Two Methods of Calculating Zo, Gamma, and Zin with

the Transmission Line Equations
133 

Appendix H. 

Portable Cab Signal Tester

The portable cab signal tester (model number: D3005H15-A01) is a microprocessor-based test 

system designed to test cab signal equipment in railroad locomotives and cars. This tester

generates signals to drive the on-board signal receivers and speed detection equipment to test 

for proper receiver operation. The main function of the portable cab signal tester is to generate 

CAB and SPEED signals as required to test the functionality and sensitivity of the on-board 

receiver equipment. 

Figure H1. Image of Portable Cabs Signal Tester Utilized

System Components

• Portable cab signal tester

• 0.8 Ohm wire loop (housed in a PVC) pipe and connector

• DC Power Input Cable

Quick Instructions Guide

• Connect the power cable to the POWER input connector

• Connect the portable cab tester and turn the unit “ON”

• Connect the test loop to the “LOOP OUTPUT”

• Select the test frequency and adjust “LOOP CURRENT” to the desired setting
134 

Abbreviations and Acronyms

ACRONYM EXPLANATION

A GND A Ground Terminal on RNB

ABRRD Alternative Broken Rail and Rollout Detection

ABRD Alternative Broken Rail Detection

AC Alternating Current

AWG American Wire Gauge

AAR Association of American Railroads

ATP Automatic Train Protection

B GND B Ground Terminal on RNB

BT Bluetooth

CBTC Communications-Based Train Control

DAQ Data Acquisition

DC Direct Current

emf Electromotive Force

EOT End-of-Train

XML Extensible Markup Language

FRA Federal Railroad Administration

FMB Full Moving Block

GPIO General Purpose Input/Output

GPS Global Positioning System

GND Ground

HOT Head-of-Train

LCR Inductance (L), Capacitance (C), and Resistance (R)

IJ Insulated Joint

OBRD Onboard Broken Rail Detection

O-PTC Overlay-Positive Train Control

PVC Polyvinyl Chloride

PTC Positive Train Control

PTT Precision Test Track

QMB Quasi Moving Block

RTT Railroad Test Track
135 

ACRONYM EXPLANATION

Rx Receiver Coil

R&D Research and Development

RLCG Resistance (R), Inductance (L), Capacitance (C), Conductance (G) 

RNB Resonant Network Box 

RMS Root Mean Square

SPICE Simulation Program with Integrated Circuit Emphasis

SMU Source Measure Unit 

TRL Technology Readiness Level

TIMS Track Impedance Measurement System

TTT Transit Test Track

Tx Transmit (transmission) Coil

TTC Transportation Technology Center 

TTCI Transportation Technology Center Inc. 

UV Ultraviolet

USPTO United States Patent and Trademark Office

V Volts