NTIA Report 04-413 

POTENTIAL INTERFERENCE FROM 

BROADBAND OVER POWER LINE (BPL) 

SYSTEMS TO FEDERAL GOVERNMENT 

RADIOCOMMUNICATIONS AT 1.7 - 80 MHz 

Phase 1 Study 

VOLUME I 

technical report 

U.S. DEPARTMENT OF COMMERCE  National Telecommunications and Information Administration
 

NTIA Report 04-413 

POTENTIAL INTERFERENCE FROM BROADBAND OVER 

POWER LINE (BPL) SYSTEMS TO FEDERAL GOVERNMENT 

RADIOCOMMUNICATIONS AT 1.7 - 80 MHz 

Phase 1 Study 

VOLUME I 

U.S. Department of Commerce 

Donald Evans, Secretary 

Michael D Gallagher, Acting Assistant Secretary 

For Communications and Information 

APRIL 2004
iii

ACKNOWLEDGEMENTS 

 The measurements and studies underlying this report were performed by NTIA’s 

Spectrum Engineering and Analysis Division (SEAD) and Institute for Telecommunications 

Science (ITS). The following NTIA personnel contributed substantially to this report and the 

underlying studies: 

Brent Bedford (ITS lead) ITS Gary Patrick SEAD 

Ernesto Cerezo SEAD Alakananda Paul (tech. lead) SEAD 

Nick DeMinco ITS James Richards (admin. lead) SEAD 

Ed Drocella SEAD Robert Sole SEAD 

Phil Gawthrop SEAD Thomas Sullivan SEAD 

Randall Hoffman ITS Clement Townsend SEAD 

Gerald Hurt SEAD Cecilia Tucker SEAD 

Bernard Joiner SEAD Cou-Way Wang SEAD 

Yeh Lo ITS Jonathan Williams SEAD 

Norman Maisel SEAD Robert Wilson SEAD 

 NTIA is grateful for the cooperation provided by the BPL parties whose systems were 

subject to measurement. NTIA also greatly appreciates the equipment, special radio network 

access and radio operator support provided by the Department of Homeland Security for NTIA’s 

testing of BPL interference. 

Finally, NTIA would like to thank the Interdepartment Radio Advisory Committee (IRAC) for 

its review of this report and the inputs it provided. 
iv 

PREFACE 

 This Report contains two Volumes. Volume I presents the main text and Volume 

II contains appendixes that provide additional detail and backup information that is fully 

summarized in Volume I. 
v 

EXECUTIVE SUMMARY 

On April 23, 2003, the Federal Communications Commission (Commission or 

FCC) adopted a Notice of Inquiry (NOI) seeking information on potential interference 

from Broadband over Power Line (BPL) systems and associated changes that may be 

needed to accommodate BPL systems in Part 15 of the Commission's rules.1

 As 

described in the NOI, “access” BPL systems transmit Internet and other data at radio 

frequencies over neighborhood power lines and use electrical outlets in BPL users’ 

premises as data ports for computers and other devices. “In-house” BPL systems use 

indoor wiring for networking within the user’s premises. 

In its response to the NOI, the National Telecommunications and Information 

Administration (NTIA) described Federal Government usage of the 1.7-80 MHz 

frequency range, identified associated interference concerns, and outlined the studies it 

planned to conduct to address those concerns.2

 NTIA reviewed relevant studies and 

regulations in order to help refine the scope and priorities for its studies. NTIA parsed its 

planned studies into two time phases, first addressing technical issues of the most 

immediate importance. As reported herein, Phase 1 defines interference risks to radio 

reception in the immediate vicinity of overhead power lines used by “access” BPL 

systems. It also suggests means for reducing these risks and identifies techniques for 

mitigating local interference should it occur. Phase 2 of NTIA’s studies will evaluate the 

effectiveness of NTIA’s Phase 1 recommendations and address potential interference via 

ionospheric propagation of BPL emissions from mature large-scale deployments of BPL 

networks. 

NTIA reviewed the comments submitted in response to the NOI in order to 

characterize existing and potential future BPL systems and deployments. Simple BPL 

deployment models were addressed in the Phase 1 interference risk analyses. NTIA also 

developed more sophisticated deployment models for use in future studies. 

NTIA summarized technical and operating parameters of over fifty-nine-thousand 

(59,000) Federal Government frequency assignments in the 1.7-80 MHz frequency range. 

This information may help operators of BPL systems in development of BPL frequency 

plans. NTIA then defined representative radio systems for consideration in interference 

analyses: (1) a land vehicular receiver; (2) a shipborne receiver; (3) a receiver using a 

rooftop antenna (e.g., a base or fixed-service station); and (4) an aircraft receiver in flight. 

Federal communications require exceptional protection on frequencies amounting to 

about 5.4% of the 1.7-80 MHz frequency range. NTIA will address the associated 

protection requirements in on-going studies. 

 

1 Inquiry Regarding Carrier Current Systems, including Broadband over Power Line Systems, Notice of 

Inquiry, ET Docket No. 03-104, April 28, 2003 (“BPL Inquiry”). 

2

 Comments of the National Telecommunications and Information Administration, BPL Inquiry, August 

13, 2003. 
vi 

NTIA executed three two-week measurement campaigns and used Numerical 

Electromagnetic Code (NEC) software to characterize BPL signal radiation and 

propagation. These efforts revealed that BPL systems generate the highest electric field 

strength near the BPL device for horizontal-parallel polarized signals. However, these 

systems generate peak vertically-polarized field strength under and adjacent to the power 

lines and at impedance discontinuities at substantial distances from the BPL device. BPL 

systems generate peak field strength having horizontal-perpendicular polarization at 

small distances (e.g., less than 30 meters) from both the BPL device and power lines. 

Thus, measurements intending to demonstrate compliance with the Part 15 field strength 

limits should not focus solely on the BPL device. 

 Using NEC, NTIA evaluated interference risks in terms of the geographic extent 

of locations where interference may occur to radio reception at four frequencies used by 

outdoor, overhead BPL systems conforming to existing Part 15 rules. Interference to 

land vehicle, boat, and fixed stations receiving moderate-to-strong radio signals is likely 

in areas extending to 30 meters, 55 meters, and 230 meters, respectively, from one BPL 

device and the power lines to which it is connected. With low-to-moderate desired signal 

levels, interference is likely at these receivers within areas extending to 75 meters, 100 

meters and 460 meters from the power lines. Assuming that co-frequency BPL devices 

are deployed at a density of one per km2

 within a circular area of 10 km radius, 

interference to aircraft reception of moderate-to-strong radio signals is likely to occur 

below 6 km altitude within 12 km of the center of the BPL deployment. Interference 

likely would occur to aircraft reception of weak-to-moderate radio signals within 40 km 

of the center of the BPL deployment area. However, at two of the four BPL frequencies 

considered with the assumed power lines, NTIA predicted smaller areas over which 

interference is likely. 

 Critical review of the assumptions underlying these analyses revealed that 

application of existing Part 15 compliance measurement procedures for BPL systems 

results in a significant underestimation of peak field strength. Underestimation of the 

actual peak field strength is the leading contributor to high interference risks. As applied 

in current practice to BPL systems, Part 15 measurement guidelines do not address 

unique physical and electromagnetic characteristics of BPL radiated emissions. Refining 

compliance measurement procedures for BPL systems will not impede implementation of 

BPL technology because BPL networks reportedly can be successfully implemented 

under existing field strength limits.3

 Accordingly, NTIA does not recommend that the 

FCC relax Part 15 field strength limits for BPL systems. Further based on studies to date, 

NTIA recommends several “access” BPL compliance measurement provisions that derive 

from existing Part 15 measurement guidelines. Among these are requirements to: use 

measurement antenna heights near the height of power lines; measure at a uniform 

distance of ten (10) meters from the BPL device and power lines; and measure using a 

calibrated rod antenna or a loop antenna in connection with appropriate factors relating 

magnetic and electric field strength levels at frequencies below 30 MHz. 

 

3

 Comments of PowerWAN, Inc., BPL Inquiry, July 3, 2003 at 8-9; Comments of Amperion, Inc., BPL 

Inquiry, July 7, 2003 at ¶4.8; Reply Comments of PowerComm Systems, Inc., BPL Inquiry, August 20, 

2003 at ¶40. 
vii 

 NTIA suggested several means by which BPL interference can be prevented or 

eliminated should it occur. Mandatory registration of certain parameters of planned and 

deployed BPL systems would enable radio operators to advise BPL operators of 

anticipated interference problems and suspected actual interference; thus, registration 

could substantially facilitate prevention and mitigation of interference. BPL devices 

should be capable of frequency agility (notching and/or retuning) and power reduction for 

elimination of interference. NTIA further recommends that BPL developers consider 

several interference prevention and mitigation measures, including: routine use of the 

minimum output power needed from each BPL device; avoidance of locally used radio 

frequencies; differential-mode signal injection oriented to minimize radiation; use of 

filters and terminations to extinguish BPL signals on power lines where they are not 

needed; and judicious choice of BPL signal frequencies to decrease radiation. 
viii 

 TABLE OF CONTENTS 

 

VOLUME I 

ACKNOWLEDGEMENTS ................................................................... iii 

PREFACE ....................................................................................... iv 

EXECUTIVE SUMMARY .................................................................... v 

TABLE OF CONTENTS ...................................................................... viii 

GLOSSARY .................................................................................... xiii 

 

SECTION 1 INTRODUCTION 

 1.1 Background ............................................................... 1-1 

 1.2 Objectives ................................................................. 1-1 

 1.3 Approach .................................................................. 1-2 

 1.4 Scope ...................................................................... 1-2 

 

SECTION 2 TECHNICAL DESCRIPTION OF BPL SYSTEMS 

 2.1 Introduction ............................................................... 2-1 

 2.2 BPL System Architectures ............................................. 2-2 

 2.2.1 BPL System #1 .......................................................... 2-2 

 2.2.2 BPL System #2 .......................................................... 2-3 

 2.2.3 BPL System #3 ............................................................ 2-4 

 2.3 Potential Future Systems ................................................ 2-5 

 2.4 Summary ................................................................... 2-7 

 

SECTION 3 BPL RELATED STUDIES AND REGULATIONS 

 3.1 Introduction ............................................................... 3-1 

 3.2 Regulations ............................................................... 3-1 

 3.2.1 Part 15 of the Commission’s Rules .................................... 3-1 

 3.2.2 Foreign Regulations ...................................................... 3-2 

 3.3 Studies ..................................................................... 3-6 

 3.3.1 Analyses of Interference from BPL Filed Under the FCC NOI ... 3-6 

 3.3.2 International Telecommunications Union (ITU) Activities ........ 3-10 

 3.3.3 Other Technical Literature ............................................. 3-12 

 3.4 Conclusion ............................................................... 3-12 

 

SECTION 4 CHRACTERIZATION OF FEDERAL GOVERNMENT 

RADIO SYSTEMS AND SPECTRUM USAGE 

 4.1 Introduction ............................................................... 4-1 

 4.2 Allocations Overview ................................................... 4-2 

 4.3 Overview of Federal Government Spectrum Use ................... 4-4 

 4.4 Summary of the Representative Federal Government Systems in 

the 1.7-80 MHz Band ................................................... 4-6 

 4.5 Representative Technical Characteristics of Federal Equipment . 4-7 

 4.6 Sensitive or Protected Frequencies in the 1.7-80 MHz Band ...... 4-8 
ix 

 4.7 Conclusion ............................................................... 4-13 

 

SECTION 5 CHARACTERIZING BPL EMISSIONS THROUGH 

COMPUTER MODELING AND MEASUREMENTS 

 5.1 Introduction ............................................................... 5-1 

 5.2 Theory ..................................................................... 5-1 

 5.2.1 Relevant Radiation Theory ............................................. 5-1 

 5.2.2 Propagation Modes ...................................................... 5-2 

 5.3 BPL Measurements ...................................................... 5-3 

 5.3.1 Approach ................................................................. 5-3 

 5.3.2 Identification and Characterization of BPL Signals ................ 5-4 

 5.3.3 BPL Signal Power Along an Energized Power Line ............... 5-4 

 5.3.4 BPL Signal Power Away from the Energized Power Line ......... 5-5 

 5.3.5 Measurement of BPL Using Various Detectors ..................... 5-5 

 5.3.6 Measurement of BPL Using Different Antenna Heights ........... 5-6 

 5.3.7 Measurements of BPL Amplitude Probability Distributions 

(APDs) .................................................................... 5-6 

 5.4 Analytical Models of Power Line Radiation ........................ 5-7 

 5.4.1 Numerical Electromagnetics Code (NEC) ........................... 5-7 

 5.4.2 Modeling of Power Lines by NEC .................................... 5-8 

 5.4.3 Effects of a Neutral Line ................................................ 5-10 

 5.4.4 Environmental Noise ................................................... 5-11 

 5.5 Conclusion ............................................................... 5-15 

 

SECTION 6 ANALYSIS OF INTERFERENCE POTENTIAL TO 

VARIOUS SERVICES 

 6.1 Introduction ............................................................... 6-1 

 6.2 Methodology ............................................................. 6-1 

 6.3 Risk Evaluation Criteria ................................................ 6-2 

 6.3.1 Interfering Signal Thresholds .......................................... 6-2 

 6.3.2 Noise Calculations ...................................................... 6-5 

 6.4 Interference Models ..................................................... 6-5 

 6.4.1 Receiving Systems ...................................................... 6-5 

 6.4.2 Power Line Model ....................................................... 6-7 

 6.5 Interference Calculations ............................................... 6-7 

 6.5.1 Scaling Output Power to Meet FCC Part 15 Limits ................ 6-7 

 6.5.2 Analysis Methodology for Land-mobile, Fixed and Maritime 

Services ................................................................... 6-8 

 6.5.3 Analysis Methodology for Aeronautical Service .................... 6-9 

 6.6 Results of Interference Calculations .................................. 6-11 

 6.6.1 Land – Mobile Service .................................................. 6-11 

 6.6.2 Fixed Service ............................................................ 6-15 

 6.6.3 Maritime Service ......................................................... 6-15 

 6.6.4 Aeronautical Service .................................................... 6-20 

 6.7 Conclusion ................................................................ 6-23 

 
x 

SECTION 7 BPL COMPLIANCE MEASUREMENT PROCEDURES 

 7.1 Background ............................................................... 7-1 

 7.2 Measurements Must Address Radiation from Power Lines to 

Which BPL Devices are Connected ................................... 7-2 

 7.3 Measurements Should Address Aggregated Emissions for the 

Fully Deployed BPL Network ......................................... 7-2 

 7.4 Measurement Antenna Heights Should Address All Important 

Directions of BPL Signal Radiation .................................. 7-3 

 7.5 A Single Measurement Distance Should Be Used For Overhead 

Power Lines and BPL Devices ........................................ 7-4 

 7.6 A Modified Distance Extrapolation Factor is Needed for BPL ... 7-5 

 7.7 BPL Frequency Agility and Power Line Frequency Selective 

Effects Must Be Addressed in the Measurement Procedures ...... 7-5 

 7.8 Near Field Measurement Errors Must be Mitigated ................ 7-5 

 7.9 Appropriate Choice of Power Lines Used for BPL 

Measurements Will Reduce Statistical Sampling Uncertainties ... 7-6 

 7.10 BPL Device Output Power Should Be Reduced as Needed for 

Compliance with Radiated Emission Limits ......................... 7-7 

 7.11 The Results of Radiated Emission Measurements Should Be 

Properly Recorded in Measurement Reports and Applied in BPL 

Operations ................................................................ 7-7 

 7.12 Conclusion ............................................................... 7-8 

 

SECTION 8 INTERFERENCE PREVENTION AND MITIGATION 

TECHNIQUES 

 8.1 Introduction ............................................................... 8-1 

 8.2 Power Level .............................................................. 8-1 

 8.3 Avoidance of Locally Used Frequencies ............................. 8-1 

 8.4 Differential-mode Signal Injection .................................... 8-2 

 8.5 Filters and Signal Terminations ....................................... 8-3 

 8.6 Implementation of a “one active device per area” rule ............. 8-3 

 8.7 Judicious Signal Carrier Choice ....................................... 8-4 

 8.8 Maintenance of a Single Point of Control ............................ 8-4 

 8.9 Web-based Access to Radio License Information .................. 8-4 

 8.10 BPL Installation and Equipment Registration ....................... 8-5 

 8.11 Conclusion ............................................................... 8-5 

 

SECTION 9 SUMMARY OF RESULTS 

 9.1 Introduction .............................................................. 9-1 

 9.2 Preliminary Investigations ............................................. 9-1 

 9.2.1 Description of BPL Systems ............................................ 9-1 

 9.2.2 Studies and Relevant Regulations ......................................... 9-1 

 9.2.3 Federal Government Radio Systems and Spectrum Usage ........ 9-2 

 9.2.4 Characterization of BPL Emissions ................................... 9-2 

 9.3 Phase 1 Analyses ........................................................ 9-4 

 9.3.1 Evaluation of Potential Interference Risks ........................... 9-4 
xi 

 9.3.2 Risk Reduction Through Compliance Measurement Procedures . 9-6 

 9.3.3 Techniques for Prevention and Mitigation of Interference ........ 9-7 

 9.4 Topics for Further Study ................................................ 9-9 

 

VOLUME II 

TABLE OF CONTENTS ...................................................................... iii 

GLOSSARY .................................................................................... viii 

 

APPENDIX A RELEVANT PART 15 PROVISIONS 

 A.1 Provisions Regarding Field Strength Limits ......................... A-1 

 A.2 Provisions Specifying Compliance Measurements .................. A-2 

 

APPENDIX B SUMMARY OF FOREIGN TECHNICAL REPORTS 

 B.1 Introduction .............................................................. B-1 

 B.2 Implementation Reports ................................................ B-1 

 B.3 Measurement Reports ................................................... B-2 

 B.4 Modeling and Analysis Reports ....................................... B-8 

 

APPENDIX C CHARACTERIZATION OF FEDERAL GOVERNMENT 

SPECTRUM USAGE AND OPERATIONS, 

REPRESENTATIVE SYSTEMS AND TYPICAL 

PARAMETERS 

 C.1 Introduction ............................................................... C-1 

 C.2 Services And Example Systems ........................................... C-1 

 C.2.1 Fixed Service (1.7-29.7 MHz) ......................................... C-1 

 C.2.2 Fixed Service (29.7-80 MHz) .......................................... C-3 

 C.2.3 Mobile Service ........................................................... C-4 

 C.2.4 Land Mobile Service .................................................... C-7 

 C.2.5 Maritime Mobile Service ............................................... C-8 

 C.2.6 Broadcasting Service ................................................... C-11 

 C.2.7 Aeronautical Mobile Service .......................................... C-12 

 C.2.8 Standard Frequency and Time Signal ................................. C-16 

 C.2.9 Aeronautical Radionavigation ...................................................... C-17 

 C.2.10 Radiolocation Service ................................................... C-18 

 C.2.11 Amateur and Amateur-Satellite Services ............................. C-19 

 C.3 Federal Government Special Operations ............................. C-21 

 C.3.1 Automatic Link Establishment (ALE) Systems ..................... C-21 

 C.3.2 Sounders .................................................................. C-21 

 C.3.3 Over the Horizon (OTH) Radars ....................................... C-22 

 C.4 Special Operational Considerations ................................... C-24 

 C.4.1 Operational Requirements for Access to Several Frequency 

Assignments Within an Allocation .................................... C-24 

 C.4.2 Federal Government Use of Radio Frequencies Below 30 MHz 

for Domestic Fixed Service ............................................ C-25 
xii 

 C.4.3 Summary of the Emergency Use of Federal Government HF 

Frequencies for the Shares Program .................................. C-26 

 C.4.4 National Criteria Established Jointly by NTIA and FCC on the 

Use of Frequencies from Appendix 27 Allotment Plan ............ C-26 

 

APPENDIX D BROADBAND OVER POWER LINE EMISSION 

MEASUREMENTS 

 D.1 Introduction ............................................................... D-1 

 D.2 The Measurement System .............................................. D-1 

 D.3 BPL Measurements ...................................................... D-3 

 D.3.1 Background on BPL Emissions Measurements ..................... D-3 

 D.3.2 Measurements of BPL Along the Energized Power Line .......... D-10 

 D.3.3 Measurements of BPL Away From the Energized Power Line ... D-23 

 D.3.4 Measurements of BPL Using Various Detectors .................... D-37 

 D.3.5 Measurements of BPL Varying Antenna Height .................... D-41 

 D.3.6 Measurements of BPL APDs .......................................... D-47 

 D.4 Background on Amplitude Probability Distributions ............... D-50 

 D.5 Gain and Noise Figure Calibration Using a Noise Diode .......... D-59 

 

APPENDIX E BPL MODELING OUTPUT 

 E.1 Introduction ............................................................... E-1 

 E.2 Tables and NEC plots ................................................... E-1 

 

APPENDIX F NTIA PHASE 2 STUDY BPL DEPLOYMENT MODELS 

 F.1 Introduction ............................................................... F-1 

 F.2 Neighborhood Deployment Model .................................... F-1 

 F.3 Antenna Coverage Area Deployment Model ........................ F-3 

 F.4 Regional Deployment Model .......................................... F-4 

 F.4.1 Regional Deployment Model Description ........................... F-5 

 F.4.2 Density and Distribution of Households .............................. F-5 

 F.4.3 Density and Distribution of BPL Devices ........................... F-6 

 F.4.4 Other Factors ............................................................. F-6 

 F.4.5 Regional Model Output ................................................. F-9 

 
xiii 

 GLOSSARY 

 

 

AC Alternating Current 

ACA Australian Communications Authority 

AERO-SAR Aeronautical Search and Rescue 

ALE Automatic Link Establishment 

AM Amplitude Modulation 

ANSI American National Standards Institute 

APD Amplitude Probability Distribution 

ARRL Amateur Radio Relay League 

AWG American Wire Gauge 

BBC British Broadcasting Corporation 

BBG Broadcasting Board of Governors 

BPL Broadband over Power Line(s) 

BW Bandwidth 

CA Collision Avoidance 

CB Citizens Band 

CCS Carrier Current System 

CD Collision Detection 

CEPT European Conference of Postal and Telecommunications Administrations 

CISPR International Special Committee on Radio Interference 

CONUS Continental United States 

COTHEN Customs Over The Horizon Enforcement Network 

CSMA Carrier Sense Multiple Access 

CW Carrier Wave 

dB Decibel 

dBi Decibel referenced to an isotropic radiator 

dBm Decibel referenced to 1 milliWatt 

dBW Decibels above 1 Watt 

DHS Department of Homeland Security 

DOA Department of Agriculture 

DOC Department of Commerce 

DOD Department of Defense 

DOE Department of Energy 

DOI Department of the Interior 

DOJ Department of Justice 

DRM Digital Radio Mondiale 

DSC Digital Selective Calling 

DSL Digital Subscriber Line 

DSSS Direct Sequence Spread Spectrum 

DUT Device Under Test 

E Electric 

EBU European Broadcasting Union 

ECC Electronics Communications Committee 

EFIE Electric Field Integral Equation 
xiv 

EM Electromagnetic 

EMC Electromagnetic Compatibility 

EN European Norm (Standard) 

EUT Equipment Under Test 

FAA Federal Aviation Administration 

FCC Federal Communications Commission 

FEMA Federal Emergency Management Agency 

FICORA Finnish Communications Regulatory Authority 

FM Frequency Modulation 

FNRCS FEMA National Radio Communication System 

ft Feet 

GHz Gigahertz 

GMDSS Global Maritime Distress and Safety System 

GMF Government Master File 

GPS Global Positioning System 

GRWAVE Ground Wave Propagation Program 

H Magnetic 

HF High Frequency 

HPA HomePlug Powerline Alliance 

Hz Hertz 

I Interference Power 

ICAO International Civil Aviation Organization 

IEC International Electrotechnical Commission 

ILS Instrumentation Landing System 

IMO International Maritime Organization 

IRAC Interdepartment Radio Advisory Committee 

ITS Institute for Telecommunication Sciences 

ITU International Telecommunications Union 

ITU-R International Telecommunication Union Radiocommunication Sector 

ITU-T International Telecommunication Union Telecommunication 

Standardization Sector 

JARL Japan Amateur Radio League 

kHz Kilohertz 

km Kilometer 

LAN Local Area Network 

LF Low Frequency 

LORAN Long Range Aid to Navigation 

LV Low Voltage 

m Meter 

MARS Military Affiliate Radio System 

Mbps Megabits per second 

MF Medium Frequency 

MFIE Magnetic Field Integral Equation 

MHz Megahertz 

MPHPT Ministry of Public Management Home Affaires, Post and 

Telecommunications of Japan 
xv 

MPT Ministry of Posts and Telecommunications 

mS Siemens/meter 

ms Millisecond 

MSI-HF Marine Safety Information – High Frequency 

MV Medium Voltage 

MWARA Major World Air Route Areas 

N Noise Power 

NATO North Atlantic Treaty Organization 

NB30 Usage Provision 30 

NBDP-COM Narrow-Band Direct Printing - Communications 

NEC Numerical Electromagnetics Code 

NIST National Institute of Standards and Technology 

NOI Notice of Inquiry 

NPRM Notice of Proposed Rulemaking 

NRCS National Radio Communication System 

NSEP National Security Emergency Preparedness 

NTIA National Telecommunications and Information Administration 

OATS Open Air Test Site 

OFCOM Swiss Federal Office of Communications 

OFDM Orthogonal Frequency Division Multiplexing 

OR Off-Route 

OTH Over the Horizon 

PLC Power Line Communications 

PLT Power Line Telecommunications 

PSD Power Spectral Density 

QAM Quadrature Amplitude Modulation 

R Route 

RA Radio Communications Agency of UK 

RAM Random Access Memory 

RBW Resolution Bandwidth 

RDARA Regional and Domestic Air Route Areas 

RF Radio Frequency 

rms Root Mean Square 

RR Radio Regulations 

RSGB Radio Society of Great Britain 

RSMS Radio Spectrum Measurement System 

RTP-COM Radio Telephony - Communications 

S/N Signal-to-Noise Ratio 

SF&TS Standard Frequency and Time Signal 

SHARES Shared Resources network 

SINAD Signal to Interference and Noise Ratio 

SINCGARS Single-Channel Ground and Airborne Radio System 

SNR Signal-to-Noise Ratio 

SOLAS Safety of Life at Sea 

SSB Single Sideband 

TEM Transverse Electromagnetic Mode 
xvi 

TV Television 

TVA Tennessee Valley Authority 

UHF Ultra High Frequency 

UK United Kingdom 

US&P United States and Possessions 

USCG United States Coast Guard 

USGS United States Geological Survey 

UTC Coordinated Universal Time 

VDSL Very high-speed Digital Subscriber Line 

VHF Very High Frequency 

VOA Voice of America 

VOACAP Voice of America Coverage Analysis Program 

VOLMET Meteorological Information for Aircraft in Flight 

WiFi Wireless Fidelity 

xDSL Various types of Digital Subscriber Lines 

μA Microampere 

μV Microvolt 
1-1 

SECTION 1 

INTRODUCTION

1.1 BACKGROUND 

On April 23, 2003, the Federal Communications Commission (Commission or FCC) 

adopted a Notice of Inquiry (NOI) seeking information on several aspects of Broadband over 

Power Line (BPL) systems as well as associated changes that may be needed to accommodate 

BPL systems in Part 15 of the Commission's rules.1 The NOI described "access" BPL systems as 

a backbone network of devices that use low and medium voltage electrical power lines for 

transmission of broadband data to, from, and within the geographic area of BPL network users.2

 

"In-house" BPL systems were described as using low voltage wiring and electric power outlets 

for networking within the user’s premises, and for connecting end-user devices to the access 

BPL network. Because BPL systems unintentionally radiate emissions at radio frequencies, the 

NOI focused several questions on Part 15 provisions that control the risk of interference to radio 

reception. In its comments to the Commission, the National Telecommunications and 

Information Administration (NTIA) summarized Federal Government usage of the 1.7-80 MHz 

frequencies of prime interest to BPL developers, identified associated interference concerns, and 

outlined the studies it planned to conduct to address those concerns.3

 

Over five-thousand comments and replies were filed with the Commission in response to 

the NOI. These comments provided substantial technical details of BPL system design and 

operating features as well as analyses of potential interference and the underlying factors that 

may cause interference. Working independently of, but in coordination with the Commission’s 

Office of Engineering and Technology (OET), NTIA designed its study approach to add 

substantially to the information filed in response to the NOI. Considerations and findings of 

Phase 1 of NTIA’s study are reported herein. Phase 2 of NTIA’s study will evaluate potential 

interference from mature deployments of BPL systems via ionosperic signal propagation and 

further assess risks of local interference under various candidate BPL rules, including rules 

suggested in NTIA’s Phase 1 study. 

1.2 OBJECTIVES 

The objectives of this technical study are to define interference risks from operation of 

BPL systems under field strength limits and associated compliance measurement procedures 

specified in Part 15 of the Commissions rules, identify interference risk mitigation techniques 

 

1 Inquiry Regarding Carrier Current Systems, including Broadband over Power Line Systems, Notice of Inquiry, ET 

Docket No. 03-104, April 28, 2003 (“BPL Inquiry”). 

2 The Commission further expanded the definition of access BPL to include high voltage electrical power lines 

carrying greater than 40,000 Volts. See Amendment of Part 15 regarding new requirements and measurement 

guidelines for Access Broadband over Power Line Systems, Notice of Proposed Rule Making, ET Docket No. 04-37, 

February 23, 2004 (“BPL NPRM”), at ¶32. 

3

 Comments of the National Telecommunications and Information Administration, BPL Inquiry, August 13, 2003. 
1-2 

that may be employed by BPL manufacturers and system operators and, if appropriate, 

recommend modifications to Part 15 provisions that will reduce the interference risks. 

1.3 APPROACH 

Phase 1 of NTIA’s study addresses issues deemed most important to formulation of a 

regulatory framework that would limit risks of local interference from outdoor elements of BPL 

systems. NTIA reviewed publications and comments submitted in response to the FCC NOI to 

characterize existing and potential future BPL systems and deployments (Section 2). NTIA also 

reviewed relevant domestic and foreign studies and regulations to help refine NTIA's analysis 

approach and to prevent unneeded redundancy (Section 3). Technical and operating parameters 

of potentially affected Federal Government radiocommunications systems were compiled and 

representative systems were identified for consideration in the analyses (Section 4). NTIA 

analyzed BPL signal radiation and propagation and summarized key findings from NTIA's 

measurement and computer modeling efforts to date (Section 5). The report discusses 

environmental Radio Frequency (RF) noise levels insofar as ambient noise is an important factor 

in the evaluation of interference. Recognizing these considerations and assuming that BPL 

systems comply with existing Part 15 provisions, NTIA evaluated the risks of interference to 

representative Federal Government systems (Section 6). NTIA then developed 

recommendations for clarification and modification of existing Part 15 compliance measurement 

procedures to reduce the potential for underestimating the peak field strength (Section 7). NTIA 

identified techniques for preventing and mitigating BPL interference (Section 8). NTIA applied 

the results of these studies in recommendations regarding the Part 15 field strength limits and 

compliance measurements relevant to BPL systems, identified areas where further investigation 

by BPL proponents may lead to means for reducing interference risks and facilitating rapid 

elimination of interference, and outlined the focal points for NTIA’s Phase 2 studies (Section 9). 

1.4 SCOPE 

This study considers BPL systems utilizing fundamental frequencies in the 1.7 - 80 MHz 

frequency range.4 In this Phase 1 study, NTIA defines risks of interference from BPL systems to 

local radio reception assuming BPL systems comply with existing Part 15 field strength limits 

and compliance measurement procedures. Issues not addressed in Phase 1 include the following: 

• Regulatory framework, including the suitability of Part 15 for accommodation of BPL. 

• Aggregation of interfering signals from BPL systems via ionospheric propagation. 

This is of concern insofar as skyward emissions from hundreds of co-frequency BPL 

systems deployed over a large area theoretically could produce a significant composite 

interfering signal level at a very distant receiver. This phenomenon would not be 

possible until BPL technology is widely deployed. 

 

4

 The BPL Inquiry identified the 1.7-80 MHz frequency range to be of principal interest for BPL operations. BPL 

Inquiry at ¶15. 
1-3 

• Potential BPL emissions at frequencies other than the fundamental frequencies 

employed by the BPL system. In other words, BPL out-of-band emissions and 

intermodulation products were not a focal point. 

• Radio systems typically used by non-federal entities, except to the extent that their 

technical and operating parameters are similar to those of Federal Government systems. 

• BPL transmission over indoor low voltage wiring, noting that this is a focal point of the 

Commission's studies.5

• Potential interference or damage to BPL systems from local radio transmissions. 

NTIA’s Phase 2 study will assess the interference risks due to aggregation and ionospheric 

propagation of interfering signals from BPL systems. NTIA has developed BPL 

deployment models in the Phase 1 study to support the analysis of BPL signal aggregation 

and propagation (Appendix F); however, these models will be refined and applied in the 

Phase 2 Study. In its Phase 2 study, NTIA will also evaluate the effectiveness of proposed 

Part 15 measurement refinements and provide additional clarifications as appropriate. 

 

5

 Comments of the Office of Engineering and Technology (Initial results of FCC tests related to in-house Power 

Line Communications (PLC)), BPL Inquiry, September 16, 2003. 
2-1 

SECTION 2 

TECHNICAL DESCRIPTION OF BPL SYSTEMS 

2.1 INTRODUCTION 

Access BPL equipment consists of injectors (also known as concentrators), 

repeaters, and extractors. BPL injectors are tied to the Internet backbone via fiber or T1 

lines and interface to the Medium Voltage (MV) power lines feeding the BPL service 

area.6 MV power lines may be overhead on utility poles or underground in buried 

conduit. Overhead wiring is attached to utility poles that are typically 10 meters above 

the ground. Three phase wiring generally comprises an MV distribution circuit running 

from a substation, and these wires may be physically oriented on the utility pole in a 

number of configurations (e.g., horizontal, vertical, or triangular). This physical 

orientation may change from one pole to the next. One or more phase lines may branch 

out from the three phase lines to serve a number of customers. A grounded neutral 

conductor is generally located below the phase conductors and runs between distribution 

transformers that provide Low Voltage (LV) electric power for customer use. In theory, 

BPL signals may be injected onto MV power lines between two phase conductors, 

between a phase conductor and the neutral conductor, or onto a single phase or neutral 

conductor. 

Extractors provide the interface between the MV power lines carrying BPL 

signals and the households within the service area. BPL extractors are usually located at 

each LV distribution transformer feeding a group of homes. Some extractors boost BPL 

signal strength sufficiently to allow transmission through LV transformers and others 

relay the BPL signal around the transformers via couplers on the proximate MV and LV 

power lines. Other kinds of extractors interface with non-BPL devices (e.g., WiFiTM) that 

extend the BPL network to the customers’ premises. 

For long runs of MV power lines, signal attenuation or distortion through the 

power line may lead BPL service providers to employ repeaters to maintain the required 

BPL signal strength and fidelity. Figure 2-1 illustrates the basic BPL system, which can 

be deployed in cell-like fashion over a large area served by existing MV power lines. 

 

6

 MV lines, typically carrying 1,000 to 40,000 volts, bring power from an electrical substation to a 

residential neighborhood. Low Voltage distribution transformers step down the line voltage to 220/110 

volts for residential use. See BPL Inquiry at ¶ 13. 
2-2 

Figure 2-1: Basic BPL System 

2.2 BPL System Architectures 

NTIA identified three different network architectures used by BPL equipment 

vendors. These architectures are described below. 

2.2.1 System #1 

System #1 (see Figure 2-2) employs Orthogonal Frequency Division Multiplexing 

(OFDM) to distribute the BPL signal over a wide bandwidth using many narrow-band 

sub-carriers. At the BPL injector, data from the Internet backbone is converted into the 

OFDM signal format and is then coupled onto one phase of the MV power line. An 

injector also converts BPL signals on the MV power lines to the format used at the 

Internet backbone connection. The two-way data are transferred to and from the LV 

lines, each feeding a cluster of homes, using BPL extractors to bypass the LV distribution 

transformers. The extractor routes data and converts between access and in-house BPL 

signal formats. The subscribers access this BPL signal using in-house BPL devices. To 

span large distances between a BPL injector and the extractors it serves, repeaters may be 

employed. 

Subscriber’s

In-House BPL

Modem + PC

Internet

Distribution

Transformer

Low Voltage

Medium Voltage

Power Lines

Fiber / T1

BPL

Repeater

BPL

Injector

BPL

Extractor

Access

BPL
2-3 

Figure 2-2: BPL System #1

The System #1 injector and extractors share a common frequency band (F1) on 

the MV power lines, different than the frequency band (F2) used on the LV lines by the 

subscriber’s in-house BPL devices. In order to minimize contention for the channel, 

Carrier Sense Multiple Access (CSMA) is used with Collision Avoidance (CA) 

extensions. This type of system is designed to accept some amount of co-channel 

interference between quasi-independent BPL cells without the use of isolation filters on 

the power lines, as all devices on the MV lines operate over the same frequency band. 

The BPL signal may be sufficiently tolerant of co-channel BPL interference to enable 

implementation of two or three of these systems independently on adjacent MV power 

lines.7

 System #1 couples BPL signals into one phase line. 

2.2.2 System #2 

System #2 also uses OFDM as its modulation scheme, but differs from System #1 

in the way it delivers the BPL signal to the subscribers’ homes. Instead of using a device 

that uses LV power lines, System #2 extracts the BPL signal from the MV power line and 

converts it into an IEEE 802.11b WiFiTM signal for a wireless interface to subscribers’ 

home computers as well as local portable computers (see Figure 2-3). Technologies other 

than WiFiTM might also be used to interface to subscribers’ devices with the BPL 

network, the important point being that BPL is not used on LV power lines in System #2. 

 

7

 A degree of coupling occurs between BPL signals on adjacent phases. 

Subscriber’s

In-House BPL

Modem + PC

Internet

Distribution

Transformer

LV

Power

Lines

MV

Power Lines

Fiber / T1

BPL

Injector

BPL

Extractor

F1

F2

Access

BPL
2-4 

Figure 2-3: BPL System #2 

This system uses different radio frequency bands to separate upstream (from the 

user) and downstream (to the user) BPL signals, and to minimize co-channel interference 

with other nearby access BPL devices. To span large distances between a BPL injector 

and the extractors it serves, repeaters may be employed. Like the injectors, BPL 

repeaters transmit and receive on different frequencies, and they use different frequencies 

from those used by the injector and other nearby repeaters. System #2 repeaters may also 

provide the capabilities of an extractor when outfitted with a WiFiTM transceiver. System 

#2 couples BPL signals onto one phase of the MV power line. 

2.2.3 System #3 

System #3 uses Direct Sequence Spread Spectrum (DSSS) to transmit the BPL 

data over the MV power lines. All users within a BPL cell share a common frequency 

band. In order to minimize contention for the channel, Carrier Sense Multiple Access 

(CSMA) is used. Like System #1, this type of system is designed to accept some amount 

of co-channel interference between cells, as all devices operate over the same frequency 

band. At one trial deployment of the System #3 architecture, the BPL service provider 

independently implements two phases of the same run of three phase power lines. 

Each cell in System #3 (see Figure 2-4) is comprised of a concentrator (injector) 

that provides an interface to a T1 or fiber link to the Internet backbone, a number of 

repeaters (extractors) to make up for signal losses in the electric power line and through 

the distribution transformers feeding clusters of dwellings, and customer premises BPL 

equipment, used to bridge between the user’s computer and the electrical wiring carrying 

the BPL signal. Adjacent cells typically overlap and the customers’ BPL terminals and 

Subscriber’s

PC + WiFiTM

Transceiver

Internet

Distribution

Transformer

Low Voltage

Medium Voltage

Power Lines

Fiber / T1

BPL

Repeater

BPL

Injector

BPL

Extractor

WiFiTM

F1

F3

F2

F4

Access

BPL
2-5 

repeaters are able to communicate with the concentrator that affords the best 

communication path at any time. 

Figure 2-4: BPL System #3 

System #3 couples the BPL signal onto the power line using a pair of couplers on 

a phase and neutral line. 

2.3 POTENTIAL FUTURE SYSTEMS 

BPL manufacturers and service providers anticipate a wide range of applications 

that may be offered to their subscribers. High quality, multi-channel video, audio, voice 

over Internet Protocol (VoIP), and on-line gaming applications are expected to rapidly 

increase the demand for additional bandwidth.8

 To support the typical subscriber at 1 

Mbps, BPL systems are expected to operate at speeds of 100 Mbps or more on the MV 

power lines in the near future. A number of comments filed in response to the NOI 

indicate that the BPL industry is already preparing for this growth.9

A number of BPL vendors have suggested use of frequencies up to 50 MHz.10 At 

least one vendor is considering use of 4 MHz to 130 MHz, while excluding frequencies 

 

8 Comments of HomePlug Powerline Alliance, BPL Inquiry, July 7, 2003 (“HPA Comments”) at 3-5.

9 Comments of PowerWAN, Inc., BPL Inquiry, July 3, 2003, (“PowerWAN Comments”) at 2; Comments 

of Main.net Communications, Ltd., BPL Inquiry, July 7, 2003 (“Main.net Comments”) at 3. 

10 PowerWAN Comments at 2; Comments of Amperion, Inc., BPL Inquiry, July 7, 2003, (“Amperion 

Comments”) at 4. 

Subscriber’s

In-House BPL

Modem + PC

Internet

Distribution

Transformer

LV

Power

Lines

MV

Power Lines

Fiber / T1

BPL

Concentrator

(Injector)

BPL

Repeater

(Extractor)

F1

F1

Neutral

Access

BPL
2-6 

that are actively in use by certain licensed services.11 One solution put forward in an 

attempt to mitigate interference with licensed services is to attenuate or “notch” BPL 

signals in frequency bands where licensed services are in nearby use.12 Future BPL 

systems may be able to accomplish this automatically without system operator 

intervention. To implement this solution while simultaneously maximizing the useable 

bandwidth, BPL systems are expected to use new modulations that can support more subcarriers that are more finely spaced.13

As data rates and bandwidth requirements grow, the BPL systems may require 

operation at greater transmitted power levels but not necessarily with higher power 

density than is used today. BPL vendors may employ techniques to dynamically adjust 

the power level to maintain a minimum signal-to-noise ratio (SNR) over the entire BPL 

spectrum, while limiting emissions to levels compliant with Part 15. One vendor has 

proposed such a solution for adjusting transmitted power to maintain a constant SNR 

across the BPL spectrum, with a hard limit based on Part 15 rules.14 The challenge will 

be to develop the control mechanism that can maximize transmitted power while 

simultaneously limiting the radiated emissions, perhaps in conjunction with frequency 

agility. 

Nortel has developed and patented a filter that blocks BPL signals while 

concurrently passing medium-voltage AC power. The judicious use of such blocking 

filters will enable optimal segmentation of BPL networks into cells of various sizes 

having low conducted co-channel interference from neighboring cells. This will enable a 

greater level of frequency reuse than what is currently available.15

Another BPL technology utilizes the 2.4 GHz and 5.8 GHz unlicensed bands.16 

An implementation using multiple IEEE 802.11b/g WiFiTM chips sets has been used to 

demonstrate the concept of carrying data over medium-voltage power lines at rates 

exceeding 200 Mbps. However, no party filed comments contending that this technology 

and these frequencies should be considered in the BPL proceedings. 

 

11 Reply Comments of PowerComm Systems, Inc., BPL Inquiry, August 20, 2003, (“PowerComm Reply 

Comments”) at 14. 

12 Main.Net Comments at 7; Comments of Ambient Corporation, BPL Inquiry, July 7, 2003, (“Ambient 

Comments”) at 8; PowerWAN Comments at 3. 

13 PowerComm Reply Comments at 17. 

14 Ambient Comments at 6-7. 

15 System, device, and method for isolating signaling environments in a power line communication system, 

United States Patent No. 6,590,493, Rasimas, et al., July 8, 2003. 

16 Corridor Systems Announces Breakthrough Technology For Broadband Over Powerlines (BPL), 

Demonstrates 216Mbps over PG&E’s Medium-Voltage Grid, Santa Rosa, CA, September 22, 2003 

http://www.corridor.biz/0309-corridor-pr.pdf. 
2-7 

2.4 SUMMARY 

Three architectures for access BPL networks were identified: (1) BPL systems using 

different frequencies on medium- and low-voltage power lines for networking within a 

neighborhood and extensions to users’ premises, respectively; (2) BPL use of only 

medium voltage lines for networking within a neighborhood, with other technologies 

being used for network extensions to users’ premises; and (3) BPL use of the same 

frequencies on medium- and low-voltage power lines for networking in a neighborhood 

and extensions to users’ premises. BPL systems currently provide data rates ranging 

from 1 Mbps to 10 Mbps, and operate at frequencies between 2 MHz and 50 MHz. In the 

future, BPL systems will operate at data rates exceeding 100 Mbps, utilizing greater 

bandwidth and/or advanced modulation schemes. BPL equipment vendors may employ 

additional signal processing techniques to optimize performance while simultaneously 

limiting emissions to Part 15 levels. 
3-1 

SECTION 3 

BPL RELATED STUDIES AND REGULATIONS 

3.1 INTRODUCTION 

This section describes regulations applicable to BPL systems and studies conducted by 

various parties to investigate the characteristics of BPL emissions. The regulations 

include both the established and proposed radiation limits applicable to BPL systems. 

3.2 REGULATIONS 

3.2.1 Part 15 of the Commission's Rules

 Appendix A of this report delineates key field strength and compliance 

measurement provisions of Part 15 applicable to BPL systems. The Part 15 field strength 

limits are shown in Table 3-1, below. BPL systems fall under the Part 15 definition of 

carrier current systems.17 BPL systems are designed to transmit RF energy over the 

power line wiring by conduction; therefore, these systems are treated as unintentional 

radiators and the restricted bands of operation defined in 47 C.F.R. §15.205 do not apply. 

Although Part 15 emission limits are intended to limit the risk of harmful 

interference to licensed services, compliance measurement procedures are equally 

important to the risk of interference because measurement uncertainty may ultimately 

result in BPL operation at field strength levels that are significantly higher or lower than 

the limits. 

 

17 See 47 C.F.R. §15.3(f). Carrier current system. A system, or part of a system, that transmits radio 

frequency energy by conduction over the electric power lines. A carrier current system can be designed 

such that the signals are received by conduction directly from connection to the electric power lines 

(unintentional radiator)... 
3-2 

Table 3-1: FCC Part 15 Radiated Emission Limits Relevant to BPL 

Usage Frequency 

(MHz) 

Field 

Strength 

(μV/meter)

Measurement 

Distance 

(meters) 

Measurement 

Bandwidth 

(kHz) 

Detector Source 

Carrier 

Current 

Systems 

1.705-30.0 30 30 9 quasipeak 15.209 

Class A, in 

commercial, 

business, and 

industrial 

areas 

30-88 90 10 120 quasipeak 15.109 

Class B, 

marketed for 

use in 

residential 

areas 

30-88 100 3 120 quasipeak 15.109 

3.2.2 Foreign Regulations 

Some administrations have established rules or regulations for BPL 

implementation or have deferred BPL implementation pending the results of on-going 

studies. BPL has been successfully implemented in some countries, while other 

administrations have postponed BPL implementation while further interference studies 

are being conducted. Still others have implemented BPL, experienced interference 

problems, and then prohibited BPL operation at least for the time being. Regionally, 

emission rules have been proposed for evaluation. Some of these are presented here. 

Note that information collected here is not comprehensive and may not be current in light 

of the rapid pace of BPL studies and development. In the summaries presented in this 

section, the acronyms BPL (for Broadband on Power Line), PLC (for Power Line 

Communications), and PLT (for Power Line Telecommunications or Technologies) will 

be used in accordance with each original report. 

3.2.2.1 Administrative Rulings on BPL 

As summarized in Table 3-2, several administrations reportedly have already 

established rules applicable to BPL implementations. 
3-3 

Table 3-2: Countries and Their Rulings on BPL Implementations 

Country Ruling or Ruling Rationale Source of Information 

Australia ACA has no mandatory standards for BPL 

equipment for frequencies above 525 kHz. 

http://www.aca.gov.au/c

onsumer_info/fact_sheets

/industry_fact_sheets/fsi2

3.pdf 

Austria The Ministry of Traffic has terminated pilot 

projects on PLC. It concluded that the 

interference caused by PLC to communications in 

the frequency range 2 - 30 MHz could not be 

reduced to acceptable levels. 

http://futurezone.orf.at/fu

turezone.orf?read=detail

&id=205693&tmp=4659 

Finland FICORA Annual Report 2001: From 

measurement results, it decided that PLC 

technology can be accommodated only after 

interference and security problems have been 

solved and when the technology complies with 

official requirements. Favors compliance with 

NB30 until a pan-European norm is specified. 

http://www.ficora.fi/2001

/VV_vsk2001.pdf 

Germany NB30 (see Table 3-3) http://www.darc.de/refer

ate/emv/plc/c3.4-rev1-

PLC5RPRT.pdf 

Japan The MPHPT of Japan has determined that at this 

stage, increasing the bandwidth to be used for 

power line communications would be difficult. 

Proposed feasibility tests promoting modem 

research and development. 

http://www.soumu.go.jp/

joho_tsusin/eng/Releases

/Telecommunications/ne

ws020809_3.html 

U.K. No official position yet for the range 1.6 MHz to 

30 MHz. 

http://www.radio.gov.uk/

publication/mpt/mpt_pdf/

mpt1570.pdf 

ACA: Australian Communications Authority 

BBC: British Broadcasting Corporation 

DARC: Deutscher Amateur-Radio-Club 

EN: European Standard NF 

FICORA: Finnish Communications Regulatory Authority 

IEC: International Electrotechnical Commission 

MPHPT: Ministry of Public Management Home Affaires, Post and Telecommunications of Japan 

NB30: Usage Provision 30, issued by German RegTP in January 1999. It contains a limiting curve for the 

radiation of telecommunications services in and alongside of cables (including Cable TV, xDSL, and PLC) 

for the frequency range from 9 kHz to 3 GHz. 

RA: Radiocommunications Agency of U.K. 

RegTP: The Regulating Administration for Telecommunications and Posts of Germany
3-4 

Table 3-3: German NB30 Limits 

Frequency Range (MHz) Limit of Peak Field Strength at 3 

meters (dBμV/meter) 

Measuring 

Bandwidth 

Detector 

>1 to 30 40 – 8.8 * log10 (fMHz) 9 kHz peak 

>30 to 1000 27 (equivalent to radiated power of 

20 dBpW) 

not 

specified 

peak 

3.2.2.2 Proposed New Regulations 

Several proposals have been presented on a regional basis for consideration to 

regulate emissions from cable and BPL equipment, and the parts of these proposals 

relevant to BPL systems operating in the frequency band of 1.7 – 80 MHz are listed 

below.18 The first proposal, from Germany and taken from NB30, is shown in Table 3-4. 

Table 3-4: German Regional Proposal 

Frequency Range (MHz) Limit of Peak Field Strength at 3 

meters (dBμV/meter) 

Measuring 

Bandwidth 

Detector 

 >1 to 30 40 – 8.8 * log10 (fMHz) 9 kHz peak 

The limit is given in terms of the electric field strength. Below 30 MHz the limit applies for the 

magnetic field strength, assuming an intrinsic impedance of 377 Ω. This proposal is supported 

by Austria, Finland, France, Germany, Romania and Switzerland. 

A second proposal, from Norway, is shown in Table 3-5. 

Table 3-5: Norwegian Proposal 

Frequency Range (MHz) Limit of Peak Field Strength 

at 3 meters (dBμV/meter) 

Measuring 

Bandwidth 

Detector 

 >1 to 30 20 – 7.7 * log10 (fMHz) 9 kHz peak 

Magnetic field data, in dBμA/meter, are measured with a loop antenna. The equivalent 

E-field data are converted from the H-field data by the factor of 51.5 dB which 

corresponds to the free space impedance of 120π Ω. This proposal is supported by 

Ireland. 

A third proposal, from BBC of U.K. and NATO, is shown in Table 3-6. 

Table 3-6: Proposal from BBC and NATO 

Frequency Range 

(MHz) 

Limit of Peak Field Strength at 1 

meter 

Measuring 

Bandwidth 

Detector 

 3 – 30 Hpeak = – 29.7 – 8.15 Log10 (fMHz), 9 kHz peak 

 

18 European Conference of Postal and Telecommunications Administrations (CEPT) Electronic 

Communications Committee (ECC) Report 24, “PLT, DSL, Cable Communications (Including Cable TV), 

LANs and Their Effect on Radio Services,” Section 7. 
3-5 

(dBμA/meter, measured) 

 3 – 30 Epeak = 21.8 – 8.15 Log10 (f MHz), 

(dBμV/meter, calculated from Hpeak) 

9 kHz peak 

The H-field data are measured with a loop antenna, and the E-field data are converted 

from the H-field data by the factor of 51.5 dB. This limit is derived with the reference 

noise level from ITU-R Rec. P 372-7 and the protection distance of 10 meters where the 

sensitivity of a victim receiver degraded by less than 0.5 dB. It is supported by the radio 

users (military, broadcasting, civil aviation, amateur, etc.) of the LF, MF and HF bands. 

A fourth proposal, from BPL manufacturers and utility industries and taken from 

the FCC Part 15 limits, is shown in Table 3-7. 

Table 3-7: Proposal by Certain BPL Proponents 

Frequency (MHz) Field Strength at 30 meters 

(μV/meter) 

Measuring 

Bandwidth 

Detector 

1.705 - 30.0 30 9 kHz quasi-peak 

A comparison of these four proposals is shown in Figure 3-1. In this figure, the 

data are scaled to a 10 meter measurement distance according to §15.31 (f)(2) guidelines 

for measurement distance extrapolation under 30 MHz. 

Figure 3-1: Comparison of Proposals for Regulating BPL Emissions 

-40

-30

-20

-10

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Frequency (MHz)

Electtric Field Strength (dBuV/meter)

BPL proponents, FCC Part 15

Germany NB 30 

BBC and NATO

Norwegian
3-6 

3.3 STUDIES 

3.3.1 Analyses of Interference from BPL Filed Under the FCC NOI 

Proponents and opponents of the Commission’s NOI regarding Broadband over 

Power Lines submitted relevant technical information and analyses of the implications 

BPL will have on existing licensed services between 1.7 – 80 MHz. Some of their key 

points are summarized in the following paragraphs.19

3.3.1.1 Power Lines as Unintentional Radiators of BPL Signals 

Ameren Energy Communications, Inc. (Ameren) analyzed the Medium Voltage 

(MV) power line with respect to its ability to act as an unintentional antenna for 

frequencies below 30 MHz.20 In their analysis, Ameren stated that a two-conductor 

power line segment, driven differentially (e.g., an "aerial" mode21), supports mostly 

transverse electromagnetic modes (TEM) of propagation and acts like a wave guide. This 

line radiates only at points of discontinuity, such as at line terminations, junctions with 

other lines, sharp line turns, and at power distribution equipment such as transformers 

and capacitors. They further state that reflections at the receiving end of the power line 

cause the formation of two opposite traveling waves, with radiation at both ends of the 

line. 

Ameren noted that when calculating the radiation efficiency and gain of the power 

line, the source impedance at the BPL transmitter should be fixed and the load impedance 

should be allowed to vary. This contrasts with a line operating as a traveling wave 

antenna in that load impedance should be matched to the line’s characteristic impedance 

(between 350 to 420 Ω for frequencies between 1 and 30 MHz). Their calculations show 

that as the line termination varies, not only does the line’s radiation efficiency and gain 

change, the ability of the fixed source to couple power onto the power line decreases with 

the load mismatch. Ameren indicated that a single line is expected to be an inefficient 

radiator. Further, Ameren calculated the array factor for two conductors and show a 17% 

increase in radiation over the single conductor case. Ameren believes that transmission 

lines carrying TEM waves should not be compared with linear array elements as their 

radiation mechanisms are different. 

 

19 Inclusion or exclusion of any analysis in this section has no significance; NTIA reviewed all filings under 

the BPL Inquiry. 

20 See Reply Comments of Ameren Energy Communications Inc., BPL Inquiry, August 20, 2003, 

(“Ameren Reply Comments”). 

21 As described in Ameren Reply Comments, "aerial modes" direct their peak radiation skyward. 
3-7 

Ameren also discussed the case of interconnected segments of MV power 

distribution line and pointed out that the radiation pattern is determined by the current 

distribution in the lines running in different directions, and the radiation is likely to be 

more isotropic. This, they believe, will result in lower gains and increased attenuation of 

signals as they divide amongst each interconnected segment and reflects at 

discontinuities. Ameren concludes that the strongest radiation will be at the source and 

that is the critical part of the system for determining radiation of BPL signals. 

The ARRL submitted a paper presenting calculated antenna gains and patterns as 

a function of frequency for a simple power line model.22 Their results indicated that as 

frequency increases, the power line acts more like an antenna, with a complex and highly 

directive radiation pattern. 

In another paper, ARRL described their model of a MV distribution power line 

and compared the following three methods of injecting the BPL signal into the model23: 

• Differential feed between two phases, with the feed at one end of the power line; 

• One phase to Earth ground, with the feed in the center of the line; 

• Single phase fed differentially; with one conductor grounded to a relatively poor 

RF ground and the ungrounded phase feed point was offset from center. 

Based on their model, ARRL presented results for the antenna gain of the power 

line, with the single phase – differential feed with one conductor grounded as being the 

worst case. This case resulted in higher antenna gain for the modeled power line, and 

greater coupling to the simulated amateur radio antennas included in their model. ARRL 

noted that the calculated gain for this power line at 14 MHz rivaled many amateur HF 

antennas. A final observation was made that the radiated emission patterns for this model 

were very complex and that the peak radiation at 3.5 MHz is skyward. 

3.3.1.2 Existing Part 15 Rules Regarding BPL Signals 

Ameren questioned the validity of using a loop antenna to measure magnetic field 

strength.24 Ameren pointed out that power lines act as “large radiators” and 

measurements close to power lines (e.g. 30 meters) are in the near field where the value 

of free space impedance typically used in the far field, 377 Ω (51.42 dB), is no longer 

valid. They presented graphs of electric (E) and Magnetic (H) fields, and H field + 51.42 

dB to make the case that the far field value of free space impedance is incorrect in the 

near field. 

 

22 See Power Lines as Antenna From 100 kHz to 50 MHz, Ed Hare, Exhibit A to Comments of ARRL, BPL 

Inquiry, July 7, 2003, (“ARRL Comments”).

23 See Methods of Feeding Overhead Electrical Power-Line Distribution Lines With BPL Signals and the 

Relationship of These Methods to the Radiated Emissions of the Conductors, Ed Hare, Exhibit B to ARRL 

Comments.

24 See Use of Loop Antennae near Large Radiators, Appendix to Ameren Reply Comments.
3-8 

Ameren stated that the estimation error from the use of a loop antenna could be as 

high as 10 dBμV/m for measurements made along the power line, and as high as 20 

dBμV/m moving away from the power line, even as far out as 700 meters. The model 

used for this analysis showed that the peak field strength is above the horizon, at an 

elevation angle of 12°. Ameren concluded that the loop introduces significant 

measurement errors near power lines and recommended use of a monopole antenna for 

BPL measurements. 

In another paper, ARRL calculated the conducted emissions power levels based 

on several BPL manufacturers submissions to the Commission in response to the NOI.25 

ARRL stated that their calculations show a resultant level of conducted emissions 

exceeding 47 C.F.R. §15.107(a). ARRL further stated that, based on its understanding of 

how BPL couplers function, the typical losses for these couplers would lead to 

widespread radiated or conducted emissions. 

ARRL addressed the possibility that inaccuracies may occur in measured results 

when following current Part 15 rules.26 ARRL stated that from their model of power 

lines, BPL radiation patterns are complex and it would be difficult to predict where to 

make measurements to obtain the peak value of the electrical field. Another potential 

source of error may arise in arriving at an extrapolation factor, as they indicated that the 

HF electric field does not fall off at a 40 dB/decade inside 30 meters. Using the results 

from their power line model, ARRL noted that the power line field strength is greater 

above the power lines; therefore, measurements made near ground (1m) will typically 

underestimate the peak field strength. 

To maximize the likelihood that measured results accurately characterize the BPL 

field strength, ARRL recommended in-situ testing at closely spaced distance intervals 

above, below, and to the sides of BPL system installations. The practice of using 3 

“typical” installations to characterize emissions is considered by ARRL to be unrealistic 

and will result in measurements unrepresentative of the emissions in a real installation. 

Finally, ARRL noted that there are definitely standing waves in the simulation results for 

the power line modeled. 

Using their power line model, ARRL calculated the received signal level from 

BPL emissions in the vicinity of an amateur radio antenna and the expected increase in 

noise floor. The BPL transmitted power spectral density was estimated and, from this, 

ARRL calculated that the radiated field strength will exceed Part 15 limits.27 ARRL 

assumed ideal (high) coupling between the power line and the amateur radio antenna, and 

 

25 See Broadband Over Power Line Devices and Conducted Emissions, Ed Hare, Exhibit B to Reply 

Comments of ARRL, BPL Inquiry, August 20, 2003, (“ARRL Reply Comments”).

26 See Electric and Magnetic Fields Near Physically Large Radiators, Ed Hare, Exhibit D to ARRL 

Comments.

27 See Calculated Levels from Broadband Over Power Line Systems and their Impact on Amateur Radio 

Communications Circuits, Ed Hare, Exhibit C to ARRL Comments.
3-9 

that the antenna is located in a direction where the BPL signal’s radiated emissions are at 

their peak. In addition, ARRL used the results of their model of the power lines to 

estimate power line "antenna gain." ARRL further described potential measurement 

errors that can mistakenly lead BPL vendors to believe that they are meeting Part 15 

limits. 

In a paper by the BBC, various proposals were considered for limits on emissions 

that are under review in CEPT SE35 (a European technical committee) and evaluated the 

amount of protection that these limits would provide to broadcast receivers near cabling 

carrying xDSL and PLT (BPL) signals.28 The author concluded that none of the 

proposed limits adequately protect broadcast reception and that a proposal limiting the 

increase in noise floor appears to offer the most promise. 

3.3.1.3 BPL Impact on Existing Licensed HF Communications Services 

The ARRL modeled the reliability of HF communications for various noise floor 

levels.29 Their modeling used noise floor levels for a quiet residential environment, the 

ITU-R Recommendation P.372.8 (2003) for median noise level in a residential 

environment, the ITR-R Recommendation level +10 dB, and the noise plus BPL signal 

level calculated by ARRL for a wide-scale BPL deployment where these devices operate 

at the maximum field strength allowed under Part 15. ARRL modeled these conditions at 

5 MHz and 14 MHz using the VOACAP inverse-area coverage program. 

A number of plots of HF link availability were provided in this ARRL report. 

The results indicated that the reliability of HF communications is already degraded when 

operating a receiver in the presence of the ITU-R median level noise, and if BPL use 

increased the noise floor by 10 dB, or to the level ARRL says will result from widespread 

BPL deployment at Part 15 limits, ARRL concludes that worldwide HF communications 

will be severely degraded. 

In another paper, the BBC analyzed the cumulative effects of wide-scale 

deployment of xDSL and BPL. The BBC considered the skywave propagation effects on 

aircraft receivers and distant ground-based receivers due.30 The author concluded from 

his analysis that the extent of skywave interference to aircraft and ground-based receivers 

from widespread xDSL/PLT system deployment may not be negligible. The author 

suggests that the relevant competent authorities should further investigate this 

interference potential. 

 

28 See AM Broadcasting and Emissions from xDSL/PLT/etc., J. H. Stott, BBC R&D White Paper WHP-012, 

Attachment to Comments of David A. Lewis, BPL Inquiry, June 23, 2003, (“David Lewis Comments”).

29 See Impact of Man-Made Noise From Broadband Over Power Line Systems Operating at the FCC Part15 Radiated Emissions Limits on Worldwide HF Communications, Ed Hare, Exhibit of ARRL, BPL 

Inquiry, August 20, 2003, (“ARRL Exhibit”).

30 See Cumulative effects of distributed interferers, J. H. Stott, BBC R&D White Paper WHP-004, 

Attachment to David Lewis Comments.
3-10 

3.3.2 International Telecommunications Union (ITU) Activities 

 At least two of the three ITU Sectors have addressed BPL: the 

Telecommunications Standards Sector (ITU-T) and the Radiocommunications Sector 

(ITU-R). Working documents of the Study Groups in both of these sectors are not freely 

available to the public, so descriptions of current documentation and activities are 

presented in this section without comprehensive citations.31

3.3.2.1 ITU-T Study Group 5 

In mid-2003, ITU-T Study Group 5 approved Recommendation K.60, which 

addresses "Emission Limits and Test Methods for Telecommunication Networks". 

Specifically, its intended application is for investigation of complaints of radio 

interference and its scope includes all telecommunications networks using LV AC 

electrical power lines and frequencies between 9 kHz and 400 GHz. The recommended 

"target" field strength limits for the 1.7-80 MHz frequency range are listed in Table 3-8. 

Associated measurement and administrative procedures are specified in the 

Recommendation. The procedures feature a number of interference mitigation steps that 

should be taken by the parties directly involved before consideration is given to filing an 

interference complaint with government authorities. 

Table 3-8: Target Electric Field Strength Limits of ITU-T Rec. K.60

Frequency Field Strength (dBμV/m) Measurement Measurement 

Range (MHz) Peak Quasi-Peak Distance Bandwidth 

1 to 30 52 - 40 log (f) 40 - 20 log (f) 3 m 9 kHz 

30 to 230 52 - 8.8 log (f) 40 - 8.8 log (f) 3 m 120 kHz 

NOTES: f = frequency (MHz); below 30 MHz, 377 Ω impedance is assumed in 

estimating electric field strength from measured magnetic field strength; only the quasipeak limit applies if background noise is too high for a peak measurement. 

3.3.2.2 ITU-R Study Group 1 

Working Parties 1A (Spectrum Engineering) and 1C (Monitoring) met in 

November 2003 and examined BPL studies in response to Questions 221/1 and 218/1.32 

France presented an extensive, non-conclusory European study of potential interference 

from BPL and other wire-bound telecommunications systems. The United States 

(represented by ARRL) presented a paper outlining BPL interference measurement and 

 

31 Information on obtaining access to ITU documents, e.g., via corporate membership, is provided at 

www.itu.int. 

32 The texts of Question 221/1, "Compatibility between radiocommunication systems and high data rate 

telecommunication systems using electricity power supply or telephone distribution wiring," and Question 

218/1, "Techniques for measurement of radiation from high data rate telecommunication systems using 

electrical power supply or telephone distribution wiring," are freely available at www.itu.int. 
3-11 

analysis considerations consistent with the Commission's open BPL proceeding. Korea 

presented a paper describing an approach for measuring BPL emissions in a laboratory 

environment. A Liaison Statement presenting relevant Study Group 6 (broadcasting 

service) studies was reviewed. Insofar as Working Party 1A is the lead ITU-R group for 

development of recommendations regarding potential interference from BPL systems, it 

requested information from all other Working Parties responsible for signal propagation 

models and analysis and matters affecting specific radio services. Working Parties 1A 

and 1C both expect to complete their BPL studies in 2005. 

3.3.2.3 ITU-R Study Group 3 

The November 2003 meetings of Study Group 3, Working Parties 3J, 3K, 3L and 

3M, generated extensive discussions on propagation aspects of Power Line 

Telecommunication (PLT) systems. The Study Group 3 Chairman declared this to be one 

of the three most important topics for these meetings. Subgroups 3K-1 and 3L-2 spent 

appreciable time discussing PLT systems and Subgroup 3J-C contributed relevant 

information regarding environmental noise. Working parties 3J, 3K and 3L jointly 

drafted a liaison statement to Working Party 1A, identifying concerns and suggesting 

methods of estimation of PLT signal radiation levels. 

The concerns expressed included: the unbalanced nature and diverse 

characteristics of power lines; the possibility of both point and line sources of radiation; 

power aggregation of emissions from multiple sources; and the presence of both ground 

and sky waves. It was noted that in developing criteria for acceptable PLT use of radio 

frequencies, measurements of both electric and magnetic fields must be considered 

because of the unknown relationship between these fields in the near-field. It was 

suggested that: a model such as NEC be used for estimation of radiation; either ITU-R 

Rec. P. 368 or the software GRWAVE be used for evaluating ground wave propagation 

of PLT emissions; and ITU-R Rec. P. 533 be used for evaluating PLT propagation via 

sky wave. It was also suggested that ITU-R Rec. P. 372 be used for estimating levels of 

noise. 

In addition to the Liaison Statement, Working Party 3L drafted a new question 

and formed a new Correspondence Group to work on the PLT Communications. The 

draft new question focused on prediction methods and models applicable to PLT systems. 

Defined studies were also given high priority. The defined studies address radiation 

mechanisms of PLT systems, modeling techniques, effects of local ground planes and 

conductors, methods of aggregation, propagation models for calculation of interference 

and measurement of radiated fields in the near field. The Correspondence Group will 

exchange ideas and communicate outputs of various studies under progress for review by 

the international group. 

3.3.2.4 ITU-R Study Group 6 

In ITU WP 6E, the European Broadcasting Union (EBU) submitted a document 

recommending revision of PLT field strength limits and measurement distance identified 
3-12 

in an earlier study. This contribution suggested three shortcomings in the earlier study. 

First, digital broadcasting transmission, not Amplitude Modulation transmission, should 

be used to derive the allowable PLT signal strength. Second, the required signal-to-noise 

level should not support only a relatively interference-tolerant channel operating in a 

rugged mode with restricted capacity. Third, the 3-meter measurement distance specified 

in the NB30 limit (Table 3-3) is unrealistically large for indoor reception. Therefore 

EBU concluded that the NB30 limits were unacceptably lax by a large margin and 

proposed that: (1) the maximum allowable PLT interference should be at least 10-20 dB 

lower; and (2) reception at 1-meter and larger distances from the PLT emission source 

should be protected. 

3.3.3 Other Technical Literature 

Appendix B summarizes additional technical literature that was not filed in 

response to the BPL Inquiry. 

3.4 SUMMARY 

 Studies performed by other parties and applicable FCC and foreign regulations 

were reviewed to ensure that NTIA’s studies would address important interference 

mechanisms and factors as well as potential means for effectively accommodating BPL 

and radio systems. NTIA noted that BPL has been implemented with success in some 

countries, while other countries have postponed implementation of BPL systems until 

further interference studies are being conducted. Still others have withdrawn their 

approval for operation of BPL systems after experiencing interference problems. Several 

emission limits have been adopted or proposed for evaluation on international, national 

and regional bases. Most studies have been oriented to determine whether interference 

will occur at the variously proposed limits. In contrast, NTIA has oriented its study to 

find a solution that accommodates BPL systems while appropriately managing the risk of 

interference to radio systems. 

 Technical information and analyses submitted in response to the FCC NOI 

included several relevant observations. BPL signals unintentionally radiate from power 

lines, although there is substantial disagreement as to the strength of the emissions and 

their potential for causing interference to licensed radio services. Analyses indicate that 

the peak field strength due to unintentional BPL radiation occurs above the physical 

horizon of power lines. Current Part 15 measurement techniques may significantly 

underestimate the peak field strength generated by BPL systems as a result of using a 

loop antenna in the near field; performing measurements with an antenna situated near 

ground level (e.g., 1 meter); and measuring emissions in the vicinity of BPL devices 

without also considering emissions from the power lines. 
4-1 

SECTION 4 

CHARACTERIZATION OF FEDERAL GOVERNMENT RADIO 

SYSTEMS AND SPECTRUM USAGE 

4.1 INTRODUCTION

 The 1.7-80 MHz frequency range encompasses the high end of the medium frequency 

band (MF, 1.7-3.0 MHz), the high frequency band (HF, 3-30 MHz), and the low end of the very 

high frequency band (VHF, 30-80 MHz) portion of the spectrum. At HF frequencies and below, 

communications can be made possible over a very long distance (i.e., thousands of miles) using 

skywave, ionospheric propagation. A significant feature of communications using the HF bands 

is the great variability in radio propagation and ambient radio noise levels. These variations as a 

function of time of day, season, year, and geographic location have been extensively studied and 

are well understood. Modern technology, especially automatic link establishment (ALE), has 

reestablished HF as an important, reliable mode of communications. At VHF frequencies, 

communications are more local, generally limited to tens of miles. 

 The 1.7-80 MHz band supports a variety of radio services that are adapted to the 

propagation characteristics inherent in this range. In all, thirteen radio services are supported in 

the 1.7-80 MHz band (Table 4-1). Most of these radio services are used by federal agencies and 

are instrumental to the Federal Government in meeting its various radiocommunications 

requirements and responsibilities. 

 

Table 4-1: Radio Services in the 1.7-80 MHz Bands

Fixed 

Mobile 

Land Mobile 

Maritime Mobile 

Aeronautical Mobile (R) 

Aeronautical Mobile (OR) 

Radiolocation 

Amateur 

Amateur-satellite 

Radio Astronomy 

Broadcasting 

Aeronautical Radionavigation 

Standard Frequency and Time 

signal 

 
4-2 

4.2 ALLOCATIONS OVERVIEW 

 In the United States, the 1.7-80 MHz range is made up of 157 frequency bands. In 

accordance with the National Table of Frequency Allocations, each of these bands is designated 

for either exclusive federal use, exclusive non-federal use, or shared. The spectrum allocations 

in this band include many cases of band-sharing between the federal and non-federal users, and 

between different radio services. A total of 110 bands are shared by federal and non-federal 

users. Only 12 bands are allocated exclusively to the Federal Government for fixed and mobile 

services (Table 4-2). In comparison, 34 bands are allocated for non-federal use on an exclusive 

basis for various radio services including: amateur, amateur-satellite, fixed, land mobile, and 

broadcasting (Table 4-3). Over 50 footnotes to the allocation tables are associated with these 

bands, providing for additional spectrum sharing or constraints on operations. 

Table 4-2: Frequency Bands Allocated Exclusively to the Federal Government 

25330-25550 kHz 30-30.56 MHz 38.25-39 MHz 

26480-26950 kHz 32-33 MHz 40-42 MHz 

27540-28000 kHz 34-35 MHz 46.6-47 MHz 

29.89-29.91 MHz 36-37 MHz 49.6-50 MHz 

Table 4-3: Frequency Bands Allocated Exclusively to Non-Federal Use33

1800-1900 kHz 28–29.89 MHz 

3500-4000 kHz 29.91-30 MHz 

7000-7300 kHz 30.56-32 MHz 

10100-10150 kHz 33-34 MHz 

14000-14350 kHz 35-36 MHz 

18068-18168 kHz 37-37.5 MHz 

21000-21450 kHz 39-40 MHz 

24890-24990 kHz 42-46.6 MHz 

25005-25010 kHz 47-49.6 MHz 

25210-25330 kHz 50-73 MHz 

26175-26480 kHz 75.4-88 MHz 

26950-27540 kHz 

 The allocations to radio services in the 1.7-80 MHz band can be broadly grouped into 

four overall categories as shown in Table 4-4. 

 

33 Some bands are grouped together. 
4-3 

Table 4-4: Frequency Allocations in the 1.7 – 80 MHz Band by Service Category34

Service Category Bandwidth Percent of Total 

1.7 – 80 MHz Band 

Fixed & Mobile 

Communications 

40.9 MHz 52% 

Broadcasting (including 

shortwave & TV) 

25.7 MHz 33% 

Amateur/Amateur-Satellite 10.4 MHz 13% 

Other 3.1 MHz 4% 

The largest category, fixed and mobile communications, includes a number of specific 

allocations for various land, air and sea communications services. For purposes of this summary, 

the “Other” category is comprised of the aeronautical radionavigation, radio astronomy, 

radiolocation, and standard frequency and time signal. Table 4-5 shows the breakdown of the 

total number of bands allocated to all the radio services, including their respective total 

bandwidths. This Phase 1 study focused largely on fixed and mobile communications systems. 

The NTIA Phase 2 effort will further explore other services. 

 Further discussion on these radio services and spectrum use are presented in Appendix C. 

Table 4-5: Summary of Bands Allocated to the Radio Services (1.7-80 MHz Band) 

Radio Service No. of Bands 

(Fed. Gov’t) 

Total Bandwidth 

(kHz) 

No. of Bands 

(Non-Federal) 

Total Bandwidth 

(kHz) 

Aeronautical Mobile (R) 11 1331 11 1331 

Aeronautical Mobile (OR) 10 845 10 845 

Aeronautical 

Radionavigation 

1 400 1 400 

Amateur -- -- 12 7650 

Amateur-Satellite -- -- 6 2700 

Broadcasting 18 3720 20 25720 

Fixed 58 19810 55 18235 

Land Mobile -- -- 17 14064 

Maritime Mobile 15 4857 15 4857 

Mobile 42 17560 19 5531 

Radiolocation 3 365 3 365 

Radio Astronomy 4 2270 4 2270 

Standard Frequency & 

Time Signal 

13 90 13 90 

 

34 Note that the combined percentage of spectrum for all the radio services exceeds 100 % of the total spectrum in 

the band. This is because a band could be allocated to two or more radio services. 
4-4 

4.3 OVERVIEW OF FEDERAL GOVERNMENT SPECTRUM USE

 The Federal Government agencies use the 1.7-80 MHz band, specifically the HF band, 

extensively for emergency services, including communications support for the Department of 

Defense (DoD); Coast Guard operations for distress, digital selective calling, search and rescue, 

and other safety of life operations; Department of Interior (DOI) and Department of Agriculture 

(DOA) for the management, maintenance, and preservation of our natural resources; Department 

of Justice (DOJ) and Department of Homeland Security (DHS) for law enforcement activities, 

and backup or emergency uses of the other federal agencies. Backup systems play a crucial role 

in times of national security emergency preparedness (NSEP) emergencies, when regular 

communications links are disrupted, inadequate or non-operational. In an emergency situation, 

the Federal Government has a program for the use of government HF frequencies for the shared 

resources (SHARES) network. The SHARES network intends to provide backup capability to 

exchange critical information among federal entities by HF radio in crisis situations. 

 Federal agencies, especially the DoD and law enforcement community, utilizing this 

portion of the radio spectrum employ over the horizon and encrypted radios that may utilize ALE 

which samples channels periodically to determine channel availability. All these systems could 

be a part of the emergency communications network. As indicated earlier, the 1.7-80 MHz band, 

for the most part, is shared by the federal and non-federal users and is extensively used by both 

communities for numerous radio applications. 

 There are more than 59,000 Federal Government frequency assignments authorized in the 

1.7-80 MHz band.35 Table 4-6 shows the number of frequency assignments by radio service and 

by entity. These assignments support the numerous federal activities and requirements in the 

1.7-80 MHz band (see Appendix C). 

 

35 Statistics on frequency assignments are current as of October 2003. 
4-5 

Table 4-6: Federal and Non-Federal Frequency Assignments by Radio Service in the 1.7-80 MHz band

Entity Aero. 

Mobile 

Radionav. BC Fixed Land 

Mobile 

Mar. 

Mobile 

Mobile Radio -

location 

SF & 

TS 

Others Total by 

Entity 

A 76 1 753 188 175 1193 

AF 2491 18 1112 844 323 217 23 103 5131 

AR 192 142 1 5521 2350 433 1844 20 30 10533 

BBG 469 146 3 618 

C 130 644 625 512 31 1 12 32 1987 

CG 888 3 554 9 7034 15 8503 

DHS 40 1118 33 72 1263 

E 232 252 301 17 86 2 4 894 

EPA 90 30 10 130 

FAA 293 1564 1506 129 24 1 3517 

FCC 459 484 943 

HHS 571 32 25 628 

I 124 3 317 421 145 330 1340 

J 2 1890 295 16 167 2370 

N 2433 2950 2525 5346 2663 26 56 15999 

NASA 16 72 41 62 26 6 223 

NG 399 119 1158 1191 1252 646 144 1135 6044 

S 118 3 10 131 

SI 1 7 106 114 

T 149 56 199 8 708 1120 

TRAN 137 9 6 3 155 

TVA 22 82 2 144 2 252 

VA 107 52 159 

Others 5 8 1366 145 106 383 17 2030 

Total Assignments 65,277 

Legend: Aero = Aeronautical, Nav = Navigation, BC = Broadcasting, SF&TS = Standard Frequency and Time Signal, 

Mar = Maritime, A =Agriculture, AF = Air Force, AR = Army, BBG = Broadcasting Board of Governors, C = Commerce, 

CG = Coast Guard, DHS = Homeland Security, E = Energy, EPA = Environmental Protection Agency, FAA = Federal Aviation 

Administration, FCC = Federal Communications Commission, I = Interior, J = Justice, L= Labor, N = Navy, 

NASA = National Aeronautics and Space Administration, NG = Non-Government, NS = National Security Agency, 

NSF = National Science Foundation, S = State, SI = Smithsonian Institution, T = Treasury, TRAN = Transportation, 

TVA = Tennessee Valley Authority, VA = Veterans Administration 
4-6 

4.4 SUMMARY OF REPRESENTATIVE FEDERAL GOVERNMENT 

SYSTEMS IN THE 1.7-80 MHz BAND

Federal agencies employ a number of radiocommunication systems that have a 

significant presence in the 1.7 – 80 MHz band. These systems, summarized in Table 4-7, are 

presented as the representative systems for certain radio services because they are prevalent (e.g., 

the number of frequency assignments supporting these systems overwhelm the others) and their 

uses are widespread in the band. The functions and operations of these systems are described in 

Appendix C, as appropriate. 

Table 4-7: Summary of Representative Federal Government Radio Systems in the 1.7-80 MHz Band 

Radio Service Freq. 

Band 

(MHz) 

Federal Entity Representative System 

Many federal agencies HF Shared Resources (SHARES) 

DHS/FEMA FEMA National Radio System (FNRC) 

Army/Corps of Engineers HF Emergency Operations Net Fixed 2-30 

FAA National Radio Communications System 

(NRCS) 

Fixed 30-50 Many federal agencies Base Stations (Repeaters) 

Land Mobile 2-30 DHS/US Customs Custom’s Over the Horizon Enforcement 

Network (COTHEN) 

Land Mobile 30-50 DoD Single-Channel Ground and Airborne 

Radio System (SINCGARS) 

Maritime Mobile 2-30 DHS/USCG Global Maritime Distress and Safety 

System (GMDSS) 

Aeronautical 

Mobile (R) 2-30 FAA Air Traffic Control (VOLMET) 

Aeronautical 

Mobile (OR) 2-30 DoD Tactical Radios (AN/ARC Series) 

Radionavigation 74.8-75.2 FAA Marker Beacons 

Radiolocation 2-3.4 DoD Over the Horizon Radars (OTHR) 

Broadcasting 2-30 BBG Voice of America (VOA) 

Standard Freq. & 

Time Signal 2-30 DOC/NIST WWV & WWVH Stations 
4-7 

4.5 REPRESENTATIVE TECHNICAL CHARACTERISTICS OF 

FEDERAL EQUIPMENT

The technical characteristics of equipment in the 1.7-80 MHz band can be largely 

grouped into uses below and above 30 MHz, with considerable consistency within these two 

frequency bands. Table 4-8 summarizes representative technical characteristics of federal radio 

equipment in the 1.7-80 MHz band. Appendix C provides a more in-depth presentation of these 

technical characteristics. 

Table 4-8: Representative Technical Characteristics of Receivers in the 1.7-80 MHz Band 

Radio Service Station 

Type 

Freq. Band 

(MHz) 

BW 

(kHz) 

Antenna 

Gain (dBi)

Antenna 

Height (ft) 

Antenna 

Type/Pol 

Modulation 

Type 

Fixed Fixed 2-30 2.8 0-2 30-140 Dipole/V&H J3E, simplex 

operation 

Fixed Fixed 30-50 16 0-3 10-400 Whip/V F3E, simplex and 

half duplex 

Land Mobile Base 2-30 2.8 0 30-100 Whip/V&H J3E, simplex 

operation 

Land Mobile Land Mobile 2-30 2.8-3 0-2 6-32 Whip/V&H J3E, simplex 

operation 

Land Mobile Base 29.7-50 16 3 30-400 Whip/V J3E, simplex and 

half duplex 

Land Mobile Land Mobile 29.7-50 16 0 6-32 Whip/V J3E, simplex and 

half duplex 

Aeronautical 

Mobile (AM(R)S) 

Aeronautical 

(Ground) 

2-30 2.8 0 unknown Various/V J3E, simplex 

operation 

Aeronautical 

Mobile (AM(R)S) 

Aircraft 2-30 2.8 0 18000-40000 Conformal/V J3E, simplex 

operation 

Aeronautical 

Fixed (NRCS) 

Fixed 

(Ground) 

2-30 6 0 unknown Whip/V J3E, simplex 

operation 

Aeronautical 

Mobile 

Aircraft 30-50 16 0 18000-40000 Blade/V J3E, simplex 

operation 

Maritime Mobile Ship & Coast 2-30 2.8 0-2 unknown Whip/V J3E, simplex 

operation 

Maritime Mobile Ship & Coast 30-50 16 2 30-100 Whip/V J3E, simplex 

operation 

Aeronautical 

Radionavigation 

Services (ARNS) 

Aircraft 74.8-75.2 0.8-6 -2.5 - 2 0-3000 Blade/H A2A 

Standard Freq. & 

Time Signal 

In-home 2-30 0 6-30 Whip/V A2 

Radio Astronomy Fixed 13.36-13.41 

37.5-38, 73-74.6 

 23 100 Parabolic Receive Only 

Legend: Freq. = Frequency, Pol. = Polarization, V = Vertical, H = Horizontal 

J3E = Single sideband with suppressed carrier, using a single channel containing an analog signal for telephony 

F3E = Frequency modulated, using a single channel containing an analog signal for telephony 

N0N or P0N = No modulating signal and no information transmitted 

A2A = Double sideband using a single channel containing a quantized or digital signal with modulating subcarrier 
4-8 

4.6 SENSITIVE OR PROTECTED FREQUENCIES IN THE 1.7-80 MHz 

 BAND

 All spectrum regulatory organizations, including the FCC, NTIA, and the ITU, have long 

recognized that certain frequencies or bands in the radio spectrum, including the 1.7-80 MHz 

range, require special protection because of the critical or sensitive functions they support. Some 

of these functions include: distress and safety, standard frequency and time signal, radio 

astronomy, and radionavigation. 

 Three parts of the FCC Rules and Regulations, Parts 15, 80 and 87, provide specific lists 

of protected frequencies in this range. While all three impose limitations on licensed services or 

unlicensed intentional radiation devices in these bands, the concept may be relevant as well to 

the unintentional radiation from BPL systems because of the interference risks. The ITU Radio 

Regulations, Appendices 13 and 15, provide similar lists of protected frequencies. Table 4-9 

summarizes and compares these lists of protected frequencies adopted by the FCC and ITU, 

showing the various functions being protected. 

 Based on these FCC and ITU sources, NTIA proposes a candidate list of 41 protected 

frequencies for BPL systems. This candidate list, shown in Table 4-9, comprises a total of less 

than 6% of the spectrum in the 1.7-30 MHz range and about 5.5% of the spectrum in the 30-80 

MHz range. Operations supported by these frequencies are vital to certain federal 

communications requirements such as safety of life and property, disaster communications, 

reception of weak galactic signals by the radio astronomy community, and safety of flight. In 

some cases, these frequencies or frequency bands provide for essential communications incident 

to or in connection with disasters or other incidents that involve loss of communication facilities 

normally available or that require the temporary establishment of communication facilities 

beyond those normally available. 

 The applicability of these candidate sensitive frequencies or others with respect to BPL 

systems will be examined further in the NTIA Phase 2 effort. 
4-9 

Table 4-9: Lists of Protected Frequencies Recognized by the FCC and ITU in the 1.7-80 MHz Band 

FCC 

15.205

FCC 

87.149 80.229

ITU-R 

 App15 

(GMDSS)36

ITU-R 

 App 13 

(Non-GMDSS)

ITU-R 

 App 27 

AM(R) S 

FUNCTION CAND

PROTECT

 2091 2173.5-2190.5 2174.5, 

2182, 2187.5 

2174.5 2182 2187.5 

2174.5 2182 2187.5 

 NBDP-COM 

RTP-COM DSC 

2173.5-2190

 2500 SF&TS 2495-2505  2850-3025 ATC 2850-3025  3023 3023 3023 AERO-SAR 3023-3026  3400-3500 ATC 3400-3500  4000 4125-4128 4125-4128 4125 4125 RTP-COM 4125-4128 4177.25-4177.75 4177.5 4177.5 4177.5 NBDP-COM 4177.25-417 4188 4207.25-4207.75 4207.5 4207.5 4207.5 DSC 4207.25-420 4650-4700 ATC 4650-4700  5000 SF&TS 4995-5005  5167.5  5450-5480 ATC 5450-5480 

36 ITU RR AP13-8 “... any emission capable of causing harmful interference to distress, alarm, urgency or safety communications [on t

prohibited.” 
4-10 

FCC 

15.205

FCC 

87.149 80.229

ITU-R 

 App15 

(GMDSS)36

ITU-R 

 App 13 

(Non-GMDSS)

ITU-R 

 App 27 

AM(R) S 

FUNCTION CAND

PROTECT

 5480-5680 ATC 5480-5680  5680 5680 5680 AERO-SAR 5680-5683 6215-6218 6215 6215 6215 RTP-COM 6215-6218 6267.75-6268.25 6268 6268 6268 NBDP-COM 6267.75-626 6282 6311.75-6312.25 6312 6312 6312 DSC 6311.75-631 6314 MSI-HF  6525-6685 ATC 6525-6685  8257 8291-8294 8291 8291 8291 RTP-COM 8291-8294  8357.5 8362-8366 8364 8364 Survival Craft 8361-8367 8376.25-8386.75 8375, 8376.25-

8386.75 

8376.5 8376.5 NBDP-COM 8376.25-838

8414.25-8414.75 8414 8414.5 8414.5 DSC 8414.25-841 8416.5 MSI-HF  8815-8965 ATC 8815-8965  10000 SF&TS 9995-10005  10005-10100 ATC 10005-1010 11275-11400 ATC 11275-1140
4-11 

FCC 

15.205

FCC 

87.149 80.229

ITU-R 

 App15 

(GMDSS)36

ITU-R 

 App 13 

(Non-GMDSS)

ITU-R 

 App 27 

AM(R) S 

FUNCTION CAND

PROTECT

12290-12293 12290 12290 12290 RTP-COM 12290-1229 12392 12519.75-12520.25 12520 12520 12520 NBDP-COM 12519.75-12 12563 12576.75-12577.25 12577 12577 12577 DSC 12576.75-12 12579 MSI-HF  13260-13360 ATC 13260-133613360-13410 13360-13410 Radio Astronomy 13360-1341 15000 SF&TS 14990-1501 16000 16420-16423 16420 16420 16420 RTP-COM 16420-1642 16522 16694.75-16695.25 16695 16695 16695 NBDP-COM 16694.75-16 16750 16804.25-16804.75 16804 16804.5 16804.5 DSC 16804.25-16 16806.5 MSI-HF  17900-17970 ATC 17900-1797 19680.5 MSI-HF  20000 SF&TS 19990-2001
4-12 

FCC 

15.205

FCC 

87.149 80.229

ITU-R 

 App15 

(GMDSS)36

ITU-R 

 App 13 

(Non-GMDSS)

ITU-R 

 App 27 

AM(R) S 

FUNCTION CAND

PROTECT

 21924-22000 ATC 21924-2200 22376 MSI-HF  25000 SF&TS (Not 

Currently Used) 

25500-25670 25500-25670 Radio Astronomy 25500-2567 26100.5 MSI-HF 37.5-38.25 MHz Radio Astronomy 37.5-38.25 M73-74.6 MHz Radio Astronomy 73.0-74.6 M74.8-75.2 MHz Aeronautical – 

Instrument Landing System Marker Beacons 

74.8-75.2 M

Legend: AERO-SAR = Aeronautical Search and Rescue ATC = Air Traffic Control DSC = Digital Selective Calling MSI-HF = Marine Safety Information – High Frequency NBDP-COM = Narrow Band Direct Printing – Communications RTP-COM = Radio Telephony – Communications SF&TS = Standard Frequency and Time Signal 
4-13 

4.7 CONCLUSION

Frequencies between 1.7 MHz and 80 MHz are allocated to a total of 13 radio 

services, with the Federal Government using all but two, in varying degrees, to satisfy 

various mandated mission requirements. Federal agencies currently have over 59,000 

frequency assignments in this frequency range. Allocations for the fixed and mobile 

services accommodate communications for homeland security, distress and safety, and 

other critical functions. These communications occupy over one-half of the frequency 

range and were chosen as the focus of this Phase 1 study. Characteristics of fixed and 

mobile equipment can largely be grouped into uses below 30 MHz and above 30 MHz 

and the equipment characteristics show considerable consistency within these two 

categories. 

Both NTIA and FCC have long recognized that certain frequencies or bands in 

the radio spectrum require special protection from interference because of the critical 

or sensitive functions they support, including distress and safety, radio astronomy, 

radionavigation, and others. NTIA identified forty-one (41) such frequency bands 

between 1.7 MHz and 80 MHz, totaling approximately 4.2 MHz (5.4% of the total 

spectrum under study), and proposes that they receive special protection from 

interference by licensed and/or unlicensed transmitters. 
5-1 

SECTION 5

CHARACTERIZING BPL EMISSIONS THROUGH COMPUTER 

MODELING AND MEASUREMENTS 

5.1 INTRODUCTION 

This section explains theoretical factors in BPL signal radiation and propagation 

and summarizes key findings from NTIA's measurement and modeling efforts to date 

(Appendix D and E). Environmental RF noise levels are discussed insofar as ambient 

noise is an important factor in the evaluation of interference. These considerations are 

applied in Section 6 in evaluations of risks of interference to representative Federal 

Government systems. 

5.2 THEORY 

5.2.1 Relevant Radiation Theory 

 In the subject range of frequencies, 1.7 – 80 MHz, BPL devices and the power 

lines that carry BPL signals have the potential to act as unintentional radiators. The 

amount of radiation depends on the symmetry of the network at radio frequencies. 

Symmetry is defined in terms of impedance between conductors and ground. If for a two 

wire line, the impedance between each conductor and ground is equal, the line is 

symmetrical or balanced. A lack of symmetry leads to an unwanted, common mode 

signal. Common mode currents flow in parallel in both conductors, while return portions 

flow through ground. Balanced lines are necessary for differential mode transmission in 

which currents are equal in magnitude and flow in opposite directions on the signal 

conductors. The fields radiating from these conductors tend to cancel each other in the 

far field area. On parallel or nearly parallel, non-concentric conductors, common mode 

currents at radio frequencies produce more radiation than differential mode currents.37 

 Any impedance discontinuity in a transmission line, which may arise from a BPL 

coupling device, a transformer, branch or a change in the direction of the line, may 

produce radiation directly or by reflections of signals forming standing waves that are 

radiated from the conductors. Even if the RF energy is injected into one of two or more 

conductors, the remaining wires generally act as parasitic radiators and, therefore, the 

lines can act as an array of antenna elements at certain frequencies. Radiation may come 

from one or more point radiators corresponding to the coupling devices as well as one or 

more power lines. Numerical Electromagnetics Code (NEC), as discussed later in this 

section, and similar method of moments models, as used with realistic physical 

arrangements and impedances of the power lines, have been applied to simulate the 

 

37 See e.g., Physical and Regulatory Constraints for Communication over the Power Supply Grid, M. 

Gebhardt, F. Weinman and K. Dostert, IEEE Communications Magazine, May 2003, pp. 84-90. 
5-2 

current distribution on the power lines and the radiated fields. Modeling results shown in 

Appendix E and discussed in this section indicate that, depending on radio antenna 

polarization, standing waves generated by an impedance discontinuity will produce 

radiation at numerous points along the power lines. 

 The space surrounding a radiator can be divided into three regions: the reactive 

near-field, the radiating near field and the far field. The boundaries of the radiating near 

field are often given as ( ) λ λ 3 2 0.62 ⋅ D < r < 2 ⋅ D , where “D” is the largest linear 

dimension of the radiator, “r” is the distance from the radiator, λ is the wavelength, and 

these dimensions and wavelength are expressed in common units (typically meters). In 

the near-field region, also called Fresnel region, the field pattern is a function of the 

radial distance. Also, it should be remembered that the criteria for defining these field 

boundaries are not rigid and the field spatial distributions change very gradually as the 

boundaries are crossed.38 Of course, “D” depends on the extent of the line responsible 

for most of the radiation. For most BPL applications, the victim receivers will be in the 

radiating near field. However, for interference through sky waves, and at distances seen 

by aircraft receivers, far fields are important. 

5.2.2 Propagation Modes 

 The dominant, relevant propagation modes in the 1.7 – 80 MHz frequency range 

are ground wave, space wave and sky wave. The ground wave signal can be a composite 

of a direct wave, a ground reflected wave and/or a surface wave. For a direct wave from 

a point source (i.e., infinitesimal D, yield essentially no near field), the received power is 

inversely proportional to the square of distance (r2

). If the radiator is located several 

wavelengths above ground, the direct wave and the ground reflected waves are 

considered as separate rays and the peak combined received power is inversely 

proportional to r4

. If the radiator is close to ground in terms of wavelength (e.g., BPL 

below 40 MHz), it is no longer appropriate to consider separate rays. A surface wave 

propagates close to ground by inducing currents which flow in the ground and support (or 

potentially interfere with) short range communications. However, horizontally polarized 

surface waves are heavily attenuated, and, for any polarization, surface wave propagation 

exhibits substantially higher rates of attenuation with distance than the direct wave, 

especially at VHF frequencies (i.e., above 30 MHz). In general, sky or ionospheric 

waves are important up to about 30 MHz, above which propagation is sporadic. Sky 

wave propagation may be represented by rays which are refracted and reflected from the 

ionosphere and is responsible for signal transmission to distances ranging from hundreds 

to thousands of kilometers, depending on elevation angle of the radiated field, frequency 

and variability of the ionosphere. The ionosphere, which ranges from about 60 to 600 km 

in height, acts as a low-conductivity dielectric.39 

 

38 See e.g., Antenna Theory, Analysis and Design, C. A. Balanis, John Wiley, 1982. 

39 See e.g., Propagation of Radiowaves, Edited by M. P.M Hall, L. W. Barclay and M. T. Hewitt , IEE, 

London, 1996. 
5-3 

 Space wave propagation occurs on line-of-sight signal paths above the height of 

the power lines where surface and reflected waves are received at magnitudes much less 

than the direct wave magnitude. Friis, or free-space loss typically is assumed for these 

paths although in most cases, reflected waves (multipath effects) can yield a degree of 

location variability of the received signal magnitude. 

 To summarize, propagation mechanisms of concern for BPL emissions toward or 

below the power line horizon will be by ground waves. For emissions in directions above 

the power line horizon, the propagation may be either by space and ground waves for 

shorter distances or by sky waves for larger distances. 

 Sky waves suffer large losses mainly due to ionospheric absorption and 

polarization coupling losses. In a dense deployment of BPL systems, there may be 

aggregation of co-frequency BPL emissions toward the ionosphere. Emissions in 

directions above the power lines may aggregate via sky wave or via ground wave and 

space wave, and emissions toward or below the power lines generally may aggregate via 

ground wave. Preliminary modeling of power lines (Appendix E) suggests that there is 

relatively strong radiation in directions above the power line horizon (i.e., higher than 

radiation toward directions below the power lines), and so, aggregation of BPL signals at 

locations above power lines may be more significant than at lower heights where BPL 

signal propagation is less efficient. 

5.3 BPL MEASUREMENTS 

5.3.1 Approach 

 During the period August to November 2003, NTIA performed measurements 

with a goal of quantifying key aspects of BPL signals. The measurements were 

conducted at three sites where BPL systems are currently deployed for testing and are 

serving customers. All three of the sites had BPL signals on the MV wires and two of the 

sites also used BPL on the LV wires. The types of measurements of fundamental 

emission, as detailed in Appendix D, consisted of the following: 

1. Identification and characterization of BPL signals. 

2. BPL signal power at locations along and near an energized line. 

3. BPL signal power at various distances away from an energized line. 

4. BPL signal power comparisons using peak, average and quasi-peak detectors. 

5. BPL signal power at different receiving antenna heights and polarization orientations. 

6. Amplitude probability distributions (APDs) of the BPL signal. 

 These measurements were made using NTIA’s instrumented measurement vehicle 

and either an antenna positioned 10 meters above the ground on a telescopic mast, or 2 

meters above the ground on a wooden tripod. Four types of antennas were used. A small 

discone antenna over a small ground plane was used to measure the electric fields above 

30 MHz. Below 30 MHz, small shielded loops were used to measure the magnetic fields, 
5-4 

and a rod antenna over a small ground plane was used for measuring the electric fields. 

To measure the received power that would be seen by a mobile unit, an off-the-shelf 2.1 

meter base-loaded whip antenna was mounted on the roof of a vehicle at an approximate 

height of 1.5 meters. The whip antennas were narrow-banded so several of them were 

used to cover the measurement frequencies. 

5.3.2 Identification and Characterization of BPL Signals 

 All measurements were preceded by system calibration as described in Appendix 

D. At the three BPL deployments, the BPL signals were identified and analyzed by 

looking at the spectrum and temporal characteristics of the BPL transmission as described 

in the Section D.3.1. 

5.3.3 BPL Signal Power Along an Energized Power Line 

 The measurement results for BPL signal power along an energized power line are 

given in Section D.3.2. The peak received power due to the electric field generated by 

BPL signals was measured with a rod antenna at a height of 2 meters at various points 

along a power line. Three mutually orthogonal components of the electric field were 

measured. These measurements indicate that there is a strong BPL electric field (relative 

to noise) along and near the BPL power line and in general, the field does not measurably 

decay with distance from the device (along the power lines). In at least one case, the 

electric field actually increased with increasing distance from the BPL device. This is 

thought to be due to BPL signal reflection by one or more impedance discontinuities and 

the generation of standing waves. In general, the location variability in the field is 

thought to be due to the presence of standing waves in the current distribution along the 

power line. 

 The magnetic field using a loop antenna at 2 meters height was not measurable 

along the power line at most locations as indicated in Section D.3.2. 

 The peak received power due to the electric field was measured with the whip 

antenna mounted on the top of a vehicle at various distances along the power lines. The 

results are similar to those obtained from the electric field measurements using the rod 

antenna. 

 The measurements at one site at a frequency of 32.70 MHz and at a height of 10 

meters indicate that after an initial decrease of received power with increasing distance 

from the BPL device along the power line, the power remains at about the same level 

with increasing distance along the power line. 
5-5 

5.3.4 BPL Signal Power Away from the Energized Power Line 

 The measurement results for BPL signal power away from an energized power 

line are given in Section D.3.3. The peak received power due to the magnetic field was 

measured at one site with a loop antenna directly under the power line at a height of 2 

meters and a weak BPL magnetic field was detected on four frequencies (4.4 MHz, 8.8 

MHz, 23.8 MHz, and 28.8 MHz). At a distance of approximately 50 meters 

perpendicular to the power line, BPL signals were received at only 28.8 MHz. The peak 

received power due to the electric field away from the power line was also measured with 

the vertically polarized whip antenna at 4.26 MHz, 7.30 MHz and 28.78 MHz. The 

results indicate that there is a decrease in received power with an increase in distance 

from the BPL device and power line, but the decrease was not monotonic at 28.78 MHz. 

The received power and the manner in which it decreased with increasing distance varied 

substantially at different frequencies. 

At the same site, the peak received power due to the vertical electric field was 

measured with the whip antenna on a different path at various distances from the power 

line. Even though the received power generally decreases with increasing distance, there 

are some amplitude oscillations. This non-monotonic behavior is thought to be mainly 

due to near-field effects and not ground reflections; however, underground power lines 

that branched from the BPL transmission line were noted to run across the measurement 

path in the vicinity of a local peak measured signal power level. 

 The whip antenna was used to measure peak received power due to the vertical 

electric field at two other sites. At one site, the signal decreased to an immeasurable level 

within 600 feet. At the second site, comprising a complex arrangement of power lines 

with many turns and BPL devices, the signal power significantly exceeded the noise 

power beyond 1,500 feet (approx. 500 m). 

 Measurements were also conducted using a discone antenna with vertical 

polarization at a height of 3.4 meters above ground in another power line configuration. 

Pulse power measurements were made at three different frequencies (35.05 MHz, 39.93 

MHz and 45.40 MHz) at various distances from the power line. In this case, the results 

indicate that the received power decreases as distance from the power line (r) increases at 

a rate lower than would be predicted by 1/r2

 (space wave loss). 

5.3.5 Measurement of BPL Using Various Detectors 

Two sets of measurements were made to compare effects of using three different 

detectors: peak, average and quasi-peak. The results are provided in Table 5-1. 
5-6 

Table 5-1: Measured peak, average and quasi-peak levels 

Frequency Peak Average Quasi-Peak 

22.96 MHz -74 dBm -81 dBm -76 dBm 

28.30 MHz -60 dBm -65 dBm -65 dBm 

5.3.6 Measurement of BPL Using Different Antenna Heights 

 

Measurements of BPL emissions from MV lines were performed using two 

different antenna heights. The results show that in general, the measured power levels 

were substantially higher at the greater antenna height. For example, the 100% duty 

cycle power measured at a frequency of 32.70 MHz and at a 10 meter antenna height was 

4.8 to 10.7 dB greater than at 2 meters. The pulse power at a 10 meter antenna height for 

this same frequency was 8.2 to 15.1 dB higher than at 2 meters. 

 Measurements were also made of emissions from a LV power line carrying BPL 

signals from a LV coupler near a pole-mounted transformer to a house (Section D.3.5). 

The phase lines were twisted about the neutral line. A loop antenna was oriented to 

maximize the reception of the horizontal magnetic field. The antenna was located at 8.7 

meters from the utility pole near the midpoint of the LV line and measurements were 

made at antenna heights of 2 meters and 10 meters at frequencies of 5 MHz, 6.43 MHz, 

10.74 MHz and 18.38 MHz, each with resolution bandwidths of 3 kHz, 10 kHz and 30 

kHz. The results indicate that measured power at a 10 meter height is always larger than 

the power measured at 2 meter height (by 3-9 dBm). Table 5-2 summarizes results from 

both these measurements for 100% duty cycle power where meaningful comparisons 

could be made. 

Table 5-2: Measured 100% Duty Cycle Power at Two Different Antenna Heights 

Frequency Bandwidth 2 meter 

height 

10 meter 

height 

Difference 

6.43 MHz 3 kHz -113.3 dBm -108.7 dBm 4.6 dB 

6.43 MHz 10 kHz -109.1 dBm -106.4 dBm 2.7 dB 

18.38 MHz 3 kHz -115.3 dBm -106.6 dBm 8.7 dB 

32.70 MHz 30 kHz -101.1 dBm -96.3 dBm 4.8 dB 

32.70 MHz 10 kHz -111.4 dBm -100.7 dBm 10.7 dB 

5.3.7 Measurements of BPL Amplitude Probability Distributions (APDs) 

Several APDs were measured at two of the three BPL deployment sites and the 

results are given in Section D.3.6. At one site, APD measurements were conducted at 

two frequencies, 32.70 MHz and 42.47 MHz, at three different resolution bandwidths: 

200 kHz, 30 kHz and 10 kHz. A discone antenna with vertical polarization located at 10 

meters above the ground and 11.6 meters from the power line was used to measure the 

APDs and the 100% duty cycle power levels were derived from the APDs. The results 
5-7 

show that the 100% duty cycle power is higher for higher resolution bandwidth for the 

same frequency, and that the power levels are proportional to bandwidth (confirming that 

100% equivalent power was accurately estimated from APDs). 

 With BPL loaded on the power lines, pulse-power measurements and APDs were 

conducted at 32.70 MHz with two different resolution bandwidths (30 kHz, and 10 kHz) 

and four different antenna orientations. A discone antenna was located at various direct 

distances from the power lines and backhaul point (x and y respectively) and set at a 

vertical height from the ground of 2 meters. The results indicate that the measured power 

for all four antenna orientations was at similar levels for the same location. A long wire 

antenna is linearly polarized, but the direction of the linear polarization is not the same in 

all parts of the pattern.40 Therefore, in this case, similar power was measured for one set 

of coordinates, whereas, for another set of coordinates, the measured power for vertical 

polarization was larger than that for horizontal polarization. 

 The occasional sampling of environmental noise power levels shown in APDs 

with the BPL system turned off were lower than the levels predicted by ITU-R 

Recommendation P.372-8. Thus, the sites for these measurements have relatively low 

noise power levels and use of the higher noise power levels predicted by ITU-R 

Recommendation P.372-8 in our analyses may bias results toward underestimation of 

interference levels. 

5.4 ANALYTICAL MODELS OF POWER LINE RADIATION 

5.4.1 Numerical Electromagnetics Code (NEC) 

NEC is a computer program for analyzing the electromagnetic response of 

antennas and scatterers.41 The code is based on the numerical solution of integral 

equations by the method of moments. An electric field integral equation (EFIE) is used 

for modeling thin wires and a magnetic field integral equation (MFIE) is used for closed 

conducting surfaces. This form of simulation breaks the structure of interest down into 

moments or line segments (for solid structures, a wire mesh is used). The current in each 

segment is calculated and the resulting electromagnetic fields are derived. 

NEC 4.1 is the latest version of the NEC, which has been developed and 

improved over the years at Lawrence Livermore National Laboratory. NEC codes offer 

features, which include excitation by voltage sources or plane waves, lumped or 

distributed loading, and networks or transmission lines. The code output includes current 

distributions, impedances, power input, dissipation, efficiency, radiation patterns, gains 

and scattering cross section. Among other output, it can be used to produce far-field 

 

40 See e.g., Antenna Theory, Analysis and Design, C. A. Balanis, John Wiley, 1982, Chapter 9. 

41Numerical Electromagnetics Code – NEC-4 Method of Moments, Part I: User’s Manual, Part II: NEC 

Program Description - Theory, Part III: NEC Program description – Code, Gerald J. Burke, January 1992. 
5-8 

(power gain) antenna patterns, near-field electric and magnetic field strength, groundwave field strengths at different distances from an antenna, antenna input impedance and 

total radiated power. NEC-4.1 can be used to model structures over a ground surface 

with a wide range of characteristics, insulated wires, impedance and conductivity in loads 

and wires, and various forms of electromagnetic excitation in a structure, and structures 

in dielectric media other than air. However, it is important to design and input the 

physical model correctly, precisely portraying parameters such as segment length, 

diameter, and wire spacing, insofar as these parameters greatly influence results in many 

cases. It is important that segment length be small enough that the model is well-behaved 

(converges) and results change little despite further shortening of the segments. 

The most relevant limitation of NEC simulation for the purposes of studying BPL 

is the computer Random Access Memory (RAM) and computational time necessary to 

simulate very large structures. Computer memory needed to simulate a structure is 

directly proportional to the square of the number of line segments used in the structure 

model, as the calculations are run in a matrix. Because segment length is dictated in part 

by the frequency of interest, the number of line segments needed to simulate a part of a 

power grid can be very large. The time required to fill and factor the matrix can also 

become very large, depending upon the number of segments. Additionally, running a 

NEC simulation can become prohibitively time-consuming if the size of the matrix 

becomes so large that the computer’s core memory is insufficient, and disk swapping 

occurs. 

5.4.2 Modeling of Power Lines by NEC 

Extensive work was done at NTIA’s Institute for Telecommunication Sciences 

(ITS) on a typical arrangement of three phase MV power lines.42 The modeled power 

lines consisted of three horizontal parallel copper wires 8.5 meters (27.9 feet) above a 

ground with average characteristics (conductivity σ = .005 mS, relative permittivity εr = 

15). Each wire had a diameter of 0.01 meter (approximating AWG gauge 4/0) and the 

wires were separated in the horizontal plane by 0.60 meter. The feed point was at the 

center of one of the wires, which ran parallel to the x axis (y = 0). The equivalent of a 

BPL coupler was placed on the center segment of the wire and was modeled as a voltage 

source of 1 volt in series with a resistor that represented the source impedance. The other 

two phase wires ran parallel to the x axis at y = 0.6 and y = 1.2 meters. 

All three orthonormal components of electric and magnetic field intensities (Ex, 

Ey, Ez in dBμV/m, Hx, Hy and Hz in dBμA/m) in the near field were plotted in a plane 

two meters above the ground at frequencies of 2 MHz, 10 MHz, and 40 MHz. Three 

different line lengths of 100 m, 200 m and 340 m were used with four different 

impedance conditions for the source and loads. The impedance conditions were as 

follows: source impedance of 150 Ω with load impedance of 50 Ω and 575 Ω, and 

 

42 See The Lineman’s and Cableman’s Handbook, E. B. Kurtz and T. M. Shoemaker, Fifth Edition, 

McGraw Hill, 1976. 
5-9 

source impedance of 575 Ω with 50 Ω and 575 Ω load impedances. The field strengths 

were plotted as contours in 5 dB increments for four different ranges of x and y 

coordinates, i.e., 0 to 20 m, 0 to 200 m, 0 to 1000 m and 0 to 18000 m. The far field 

radiation patterns were also plotted at several azimuth angles. 

Several representative far field radiation patterns and near field plots for three 

components of the electric field Ex, Ey and Ez are presented in Appendix E for various 

combinations of line length, frequency, source impedance and load impedance. The 

complete results of the above simulation work are available at NTIA. 

The far field patterns indicate that there are more lobes in the radiation pattern as 

the ratio of line length to wavelength (L/λ) increases. Varying source and load 

impedances have minor effects. The transmission line analyzed here has a characteristic 

impedance of approximately 575 Ω, therefore, when the load and source impedance are 

both 575 Ω, the line acts as a traveling wave antenna. The highest radiation was 

generally associated with the combination of source impedance of 150 Ω and load 

impedance of 50 Ω which corresponds to the largest mismatch among the cases 

considered here. In the azimuth angle of 0o, i.e., along the direction of the power lines, 

the elevation pattern has several lobes and the largest lobe is generally around 30o or 

lower elevation above the horizontal plane containing the power lines. The larger the 

L/λ ratio, the lower is this main elevation angle. However, as the azimuth angle increases 

to 90o, there are fewer lobes and the maximum gain is in or near the vertical direction. 

Tables E-1, E-2 and E-3 summarize the results of the near field plots at 2 meters 

above the ground for three components of the electric field for various combinations of 

input parameters. Several general trends can be seen from the near field plots at 2 meters 

from ground near a typical power line configuration. Table E-1 summarizes the 

characteristics of the vertically polarized electric field, Ez. For the vertical electric field 

Ez, the peak field is never at the BPL source; instead, 2 to 20 local peaks occur near and 

under the power lines. The first peak occurs at approximately λ/4 down the wire from the 

device. Several peaks of slightly higher strength occur down the wire at λ/2 intervals. 

The number of peaks depends on the L/λ ratio. As frequency increases, the peak 

decreases, but the number of local peaks along the line increases. The peaks gradually 

diminish down the line because of RF attenuation and radiative losses. As mentioned 

earlier, varying source and load impedances has only a minor effect on peak field 

strength (less than 5 dB min-max variation), and peaks generally decrease as the source 

& load impedances are changed as follows (in decreasing order of peak vertical electric 

field strength): 150 & 50 Ω, 150 & 575 Ω, 575 & 50 Ω, 575 & 575 Ω. 

 

Tables E-2 and E-3 summarize characteristics of horizontally polarized electric 

fields Ex and Ey. The peak horizontally polarized field is never at the BPL source for the 

perpendicular case (as was the case for vertical polarization); instead, 2 to 24 local peaks 

occur at various distances from the BPL source with the first peak occurring at 

approximately 0.75λ and subsequent peaks occurring at approximately λ/2 intervals 

occurring at about λ/4 on either side of the wire. In contrast, the peak field is always at 
5-10 

the BPL source for the parallel case with additional peaks down the line of equal or lower 

field strengths. 

The far field patterns, the near field surface plots and measurements along power 

lines indicate that there are standing waves along the power line. Various other 

representative power line configurations need to be studied with sensitivity analysis with 

respect to line length, position of the source, position of other conductors in the vicinity, 

source and load impedances and frequency need to be done. Electric fields at other 

heights have to be calculated. Limited measurements have indicated that the electric 

fields at 10 meter high antenna are much higher than that at 2 meter high antenna. To 

facilitate further investigations, NTIA is developing software for statistical analysis of the 

spatial distribution of electric field strength. 

5.4.3 Effects of a Neutral Line 

In the case of power line simulation for a BPL system, the most obvious 

consideration is the addition of parallel wires, such as a neutral (assuming the three-phase 

lines are arranged in a “wye” configuration) and telephone and cable wires, which are 

typically found under the neutral. To determine the effects of a neutral line on the model 

considered above, sample simulations with and without a neutral wire were run and the 

resulting outputs compared to one another. 

As can be seen in Figure 5-1 for a frequency of 4 MHz, the addition of a grounded 

neutral line does have an impact on the model output. This impact is dependent upon 

frequency, and primarily manifests itself in amount of gain found in the main lobes of the 

far-field radiation pattern. The change in gain is less than 2 dB, and the overall shape of 

the radiation pattern remains the about the same. The comparisons for frequencies 15 

MHz, 25 MHz and 40 MHz are given in Appendix E, showing that the change in gain 

becomes less at higher frequencies. Equally importantly, at all of the frequencies 

examined, the addition of a neutral tended to increase, not decrease, the overall gain of 

the power line radiation. Additional computations of electric field magnitude also 

demonstrated an increased electric field around the modeled power line in the presence of 

a multi-grounded neutral. This would seem to indicate that the omission of a grounded 

neutral from the NEC power line model would tend to produce a more conservative 

result, i.e., produce less radiation. 
5-11 

Figure 5-1: Comparison of NEC model with and without a parasitic 

multi-grounded neutral at 4 MHz. 

5.4.4 Environmental Noise 

The standard reference for radio-frequency noise is the ITU-R Rec. P.372-8. It 

includes detailed formulas and charts for predicting median ambient noise at any 

geographic point due to atmospheric, man-made and galactic noise sources as well as 

temporal variability. The noise at any given location varies hourly, daily, and seasonally, 

and predicted levels depend upon frequency, time of day, time of year and the local 

environment (ranging from industrial to quiet rural conditions). 
5-12 

Noise is especially at issue on lower frequencies in the 1.7 – 80 MHz range, 

because total ambient noise generally increases as the frequency decreases. In general, 

the level of ambient noise (the “noise floor”) determines the strength of the received 

signal necessary to carry out communications in the absence of interfering signals. 

Substantial noise can make HF communications difficult or even impossible, depending 

upon the strength of the received signal. 

The causes of HF radio noise are broadly categorized into man-made, 

atmospheric, and galactic sources. Each contributes to the overall noise level, and the 

relative contribution of each source of noise is dependent upon several factors. 

Man-made noise is generally produced by electrical devices, ranging from 

overhead power lines to automobile ignition and household appliances. The level of 

man-made noise, as statistically characterized, is mainly a function of the area. Industrial 

areas, for example, tend to have much higher levels of man-made noise than remote rural 

areas. ITU-R Rec. P.372-8 specifically categorizes areas as business, residential, rural 

and quiet rural noise environments, in order of decreasing median noise levels. Manmade noise tends to have greater levels at higher frequencies in the 1.7 – 80 MHz range 

(e.g., typically, above 20 MHz), although this is not always the case for all environments. 

Atmospheric noise is primarily produced by lightning. Trends in this form of 

noise are heavily dependent upon geographic location, time of day and time of year. 

Areas in the Midwestern United States, for example, tend to see much higher atmospheric 

noise levels in the afternoon during spring and summer than do other parts of the country. 

Atmospheric noise tends to account for the bulk of noise at lower HF frequencies. 

Galactic noise is radio noise produced by emission from celestial bodies (e.g., 

stars) in our own galaxy, and tends to become a factor only at higher frequencies and 

low-noise locales. Galactic noise can serve as an effective “best case” noise level for 

low-noise conditions, as its level is fairly constant at a given frequency and substantial in 

relation to relatively low median levels of atmospheric and man-made noise. 

The data in ITU-R Rec. P.372-8 is incorporated into software available from the 

ITU web site; that software was used in this report to obtain ambient background noise 

values for use in interference analyses.43

Noise levels have high location (spatial) variability in addition to temporal variability. 

For example, a business location in the Midwest United States during a summer 

afternoon can experience relatively high levels of noise, but a rural locale in Alaska on a 

winter morning can see low noise levels approaching that of the galactic background 

noise (Figure 5-2). 

 

43 NTIA’s NOISEDAT program is available from the ITU web site, URL: http://www.itu.int/ITUR/software/study-groups/rsg3/databanks/ionosph/index.html. 
5-13 

Figure 5-2: Example calculated median background noise levels. Left: industrial environment 

during the height of thunderstorm season in the Midwest United States. Right: rural Alaskan 

environment during the winter. 

It is instructive to examine typical median noise values in relation to signals 

meeting FCC Part 15 limits. For the 1.7 - 80 MHz frequency range, Figure 5-3 and 

Figure 5-4 show typical median levels of receiver system noise power as well as Part 15 

field strength limits at the specified measurement distance. For this figure, the noise 

levels were calculated for 450 locations around the United States assuming a residential 

environment, and the median of these values for midday in spring were selected. Several 

geographic points had calculated median noise values that were very close to the overall 

medians for each frequency; the noise levels for one such point (Kansas City, MO) were 

used for further calculations in Section 6. 

The levels have been translated into electric field strength levels, and both the 

noise and the Part 15-limit electric field strength levels are presented, assuming they are 

received by a short vertical monopole antenna. Noise levels shown also include a 12 dB 

receiver noise factor, referenced to the electric field at the antenna, which (for the most 

part) is insignificant in relation to the ambient noise levels in question. As can be seen by 

the figures, signals received at Part 15 limits are 15 dB to 25 dB above the median noise 

levels. 

-190

-180

-170

-160

-150

-140

-130

-120

-110

-100

1 10 100

Frequency (MHz)

Noise Power (dBW/Hz)

Atmospheric

Galactic

Manmade

Total

-190

-180

-170

-160

-150

-140

-130

-120

-110

-100

1 10 100

Frequency (MHz)

Noise Power (dBW/Hz)

Atmospheric

Galactic

Manmade

Total
5-14 

0

5

10

15

20

25

30

35

1 10 100

Frequency, MHz

Field Strength, dB( μ V/m)

Typical Total

Receiver System

Noise

Part 15 Limits

 

Figure 5-3: Typical median noise field strength and FCC Part 15 limits at 30 meters, 

1.705 MHz to 30 MHz, 9 kHz bandwidth. 

-5

0

5

10

15

20

25

10 100

Frequency, MHz

Field Strength, dB( μ V/m)

Typical Total Receiver

System Noise

Part 15 limits, 20 Log(d /d)

Part 15 limits, 40 Log(d /d)

ref

ref

 

Figure 5-4: Typical median noise field strength and FCC Part 15 limits at 3 meters 
5-15 

5.5 CONCLUSION 

Numerous textbooks explain the electromagnetic theory behind wires serving as 

transmission lines or antennas. For unshielded wires such as power lines, the magnitude 

of radiation is largely affected by the degree of balance between radio frequency currents 

in adjacent wires and the spacing of those wires. Common mode currents (traveling in 

the same direction) in parallel wires generally produce mode radiation than differential 

currents (traveling in opposite directions) because for differential currents, the fields 

generated by each wire tend to cancel if the wires are closely spaced (e.g., twisted pair 

used for telephone lines). Impedance discontinuities can occur on power lines at 

transformers, branches and turns, and can produce radiation directly or cause signal 

reflections in the power lines that produce standing waves and associated radiation along 

the line. The fields generated by radio frequency currents have different types of spatial 

distributions in three successively more distant areas around a radiator: the reactive- and 

radiative-near-field and far-field regions. The distances over which reactive and radiative 

near-field regions extend increase with the size of the radiator and frequency. In the far 

field region, which could start several kilometers away from a radiating power line, the 

radiation patterns are independent of distance and field strength in free space generally 

decreases in proportion to increasing distance. 

 The dominant signal propagation modes in the 1.7 – 80 MHz frequency range are 

ground wave, space wave and sky wave. The ground wave signal can consist of a direct 

wave, ground reflected wave and/or a surface wave, each of which exhibit a different 

characteristic relationship between signal loss and distance. The direct wave signal 

power from a point source (i.e., very small in relation to wavelength) is inversely 

proportional to the square of the distance and when combined with a strong groundreflected wave from a radiator several wavelengths above the ground, the composite 

signal power is inversely proportional to distance to the fourth power. The latter high 

rate of attenuation does not occur for radiators closer to the ground. A surface wave 

propagates close to the ground and exhibits substantially higher rates of attenuation than 

the direct wave. Thus, groundwave propagation is pertinent on BPL signal paths below 

the power line horizon. Space wave propagation involves only a direct wave and occurs 

over elevated signal paths, e.g., on signal paths above the power line horizon. Sky wave 

propagation also occurs above the power line horizon and most consistently at 

frequencies between 1.7 MHz and 30 MHz. Skywave signal paths are represented as rays 

that are refracted and reflected by the ionosphere and can extend to distances of 

thousands of kilometers depending on the signal elevation angle and frequency as well as 

parameters of the ionosphere that exhibit temporal and spatial variability. 

 

 As a part of its study, NTIA modeled an overhead, three-phase MV power line 

using the NEC software program. The far field patterns of the electric field indicate that 

there are more local peaks in the radiation pattern as the ratio of line length to BPL signal 

wavelength increases. Varying the source and load impedances have a minor effect, 

although the highest radiation was generally associated with the largest impedance 

mismatch between source and load. The far field radiation patterns and radiating near-
5-16 

fields at a height of two meters both indicate that BPL signal reflections from impedance 

discontinuities can generate standing waves that cause radiation from power lines. Along 

the direction of the power lines, the peak field strength in the far field occurs above the 

horizontal plane containing the power lines. In the near field, the peak level of the 

vertical electric field is never at the BPL source; instead, multiple local peaks occur near 

and under the power lines. Similarly, the peak horizontally polarized field in the 

direction perpendicular to the power lines is never at the BPL source; instead, peaks 

occur at various distances away from the BPL source and power lines. Based on the 

models considered to date, only in the case of the horizontally polarized electric field in 

the direction parallel to the power lines does the peak field occur at the BPL device. 

NTIA’s modeling showed that inclusion of a neutral line with three phase medium 

voltage wiring tended to increase the overall radiation. Thus, models omitting the neutral 

wire tend to predict lower field strength. The implications of these modeling results are 

that compliance measurements taken only around a BPL device and at heights below the 

power lines, may significantly underestimate the peak electric field. 

 NTIA performed measurements at three different BPL deployment sites in order 

to characterize the BPL fundamental emissions. Measurements indicate that the BPL 

electric field does not generally decay monotonically with distance from the BPL source 

as the measurement antenna was positioned near to and moving along the length of the 

power line. As the measurement antenna was moved away from the BPL energized 

power line, the radiated power decreased with increasing distance, but the decrease was 

not always monotonic and a number of local peaks were observed at some locations. In 

some cases, the BPL signal was observed to decay with distance away from the power 

line at a rate slower than would be predicted by space wave loss from a point source. At 

one measurement location where a large number of BPL devices were deployed on 

multiple three-phase and single-phase MV power lines, appreciable BPL signal levels 

(i.e., at least 5 dB higher than ambient noise) were observed beyond 500 meters from the 

nearest BPL energized power lines. Finally, NTIA’s measurements show that the 

radiated power from the BPL energized power lines was consistently higher when the 

measurement antenna was placed at a greater height (e.g., 10 meter vs. 2 meter). These 

results indicate a need to refine the Part 15 compliance measurement guidelines to ensure 

that the peak field strength of any unintentional BPL emissions is measured. 
6-1 

SECTION 6 

ANALYSIS OF INTERFERENCE POTENTIAL 

TO VARIOUS SERVICES 

6.1 INTRODUCTION 

 The potential impact of a single access BPL device to representative groundbased federal receivers is examined in this section, as is the impact of multiple cofrequency BPL devices on in-flight aeronautical receivers. Because of the wide range of 

federal systems that are of concern, representative systems in the fixed, land-mobile, 

maritime and aeronautical services were chosen for analysis.44 The criteria for evaluating 

the risk of interference are defined in terms equivalent to moderate and high potential risk 

levels. 

6.2 METHODOLOGY 

 It was assumed that the BPL systems conform to Part 15 field strength limits 

using existing BPL compliance measurement practices. Analyses of potential 

interference to fixed, land-mobile and maritime mobile services used the same 

methodology. For distances less than one kilometer, a NEC-4.1 model of a three-phase 

power line driven with a single source was used to estimate electric field strengths, from 

which received BPL interfering signal power was derived. Analyses of potential 

interference to aeronautical systems followed a somewhat different approach. An 

analytical model was developed using a Matlab software shell. In this time simulation, 

an aircraft operating an aeronautical mobile receiver was flown over and near a BPL 

deployment area. BPL signal levels were calculated with the aircraft either approaching 

or directly above the service area. 

 For all services, the calculated received BPL signal power was used with median 

background noise values to determine expected (I+N)/N characteristics at the potential 

radio receiver sites. This parameter was used to illustrate the effective increases in the 

radio receiver noise power level due to the combination of BPL interfering signals and 

noise. Calculations were performed at 4 MHz, 15 MHz, 25 MHz and 40 MHz using the 

same type of BPL system and power line configuration, but in the case of potential 

interference to aircraft radios, the power lines were randomly oriented. 

 In these interference calculations, it was recognized that the Part 15 field strength 

limits are defined in terms of quasi-peak and, as used in interference analyses, the power 

 

44 Maritime and aeronautical services also have ground-based receivers. Although not specifically 

addressed in NTIA’s modeling, these stations are expected to be impacted similarly to the fixed service 

case modeled by NTIA. 
6-2 

levels for noise are root mean square (rms) values. Consequently, to compute a valid 

ratio of the two, or more specifically the power ratio (interference-plus-noise)-to-noise, 

(I + N)/N, a quasi-peak-to-rms conversion factor should be applied to the interfering 

signal power levels so that I and N both are specified as rms values. From a theoretical 

standpoint, the conversion factor for a pure sinusoidal signal is zero dB, whereas for a 

non-frequency-agile pulse-like signal having a uniform pulse repetition rate, quasi-peak 

levels can exceed rms by about 10 dB. BPL signals are expected to fall between these 

two extremes depending on their duty cycle. Limited measurements documented in 

Appendix D (See Section D.3.4) for a system employing OFDM modulation, show the 

conversion factor from quasi-peak to rms to be in the range of 0 to 5 dB. For this 

preliminary study, quasi-peak values were assumed to exceed rms values by 5 dB. 

Further study of this factor is needed. 

6.3 RISK EVALUATION CRITERIA 

6.3.1 Interfering Signal Thresholds 

 A given level of unwanted (interfering) signal power may cause interference 

ranging from barely perceptible to harmful levels depending on the magnitude of 

environmental and equipment noise, the desired signal level, as well as the temporal 

variability of each of these parameters.45 Because these and several underlying 

parameters may vary substantially among locations and over time, the level of 

interference caused by BPL systems is both temporally and spatially stochastic. Other 

important considerations are whether the radio system is operating continuously or only 

occasionally (e.g., as a back-up means of communications) and the speed with which 

harmful interference can be eliminated should it occur. These considerations relate to 

risk tolerance. 

 If the received desired signal is consistently very much more powerful than the 

noise and unwanted BPL signals, interference will not occur and receiver performance is 

dictated by the ratio of desired signal to noise power. Likewise, if the received unwanted 

BPL signal is very weak in relation to environmental noise power, it is unlikely to cause 

interference and receiver performance is dictated by desired signal and noise power 

levels. It is instructive to consider both permutations of variables for evaluation of BPL 

interference risks, namely, the ratio of received BPL signal power to noise power under 

conditions of strong and weak desired signal levels. As shown in Equations 6-1 through 

6-3, below, this interference-to-noise power ratio (I/N) relates directly to an increase in 

the receiver noise floor or a reduction in the ratio of desired signal-to-total noise (i.e., the 

ratio (N+I)/N or -∆S/N). 

 

45 "Interference" is defined in 47 C.F.R., §2.1. “Parties responsible for equipment compliance should note 

that the limits specified in this part will not prevent harmful interference under all circumstances.” 47 

C.F.R. §15.15(c). 
6-3 

∆S/N = -(N+I)/N = -10log(100.1(I/N) + 1) (6-1) 

 ∆S/N ≈ -(I/N), for I/N > 6 dB (6-2) 

I/N ≈ Fu - Fam, Fam >> receiver system noise figure (6-3) 

where: 

∆S/N is the change in signal-to-noise power ratio (dB) caused by the unwanted 

 signal (always a negative number corresponding to a reduction of S/N); 

I/N is the ratio of unwanted signal power to total receiver system noise power 

 (dB), with power levels measured in the same reference bandwidth; 

Fu is the field strength of the BPL signal (dB(μV/m)); and 

Fam is the total field strength of all environment radio noise (dB(μV/m)). 

 In order to minimize potential interference and promote efficient reuse of 

assigned and adjacent frequencies, by treaty, radio transmission systems should not 

radiate substantially more power than what is needed to fulfill communications 

requirements.46 For most frequency sharing situations, it is well established in 

international and domestic spectrum management practices to generally limit interfering 

signal levels in a manner that preserves good control over radio system performance by 

designers and operators (e.g., (I+N)/N = 0.5 or 1 dB). However, for the interference risk 

evaluation herein, the focus is on risks under the most typical situations (i.e., the 

statistical mode of possible scenarios). Less favorable situations are not considered, e.g., 

where desired signals are near the minimum levels needed to fulfill performance 

objectives. Thus, in general, it is assumed herein that substantial and perhaps harmful 

interference will occur in a high percentage of cases if the (I+N)/N ratio exceeds 10 dB (a 

factor of 10). It is assumed that substantial interference will occur in a smaller but still 

significant percentage of cases if (I+N)/N is 3 dB (a factor of 2, or a doubling of the 

"noise floor" of the receiver). There is still a small probability that interference will 

occur with (I+N)/I of 1 dB or less (I/N of -6 dB or less) and, at the least, unwanted 

signals at these levels manifest interference during signal fading (i.e., reductions in 

communications availability). In this phase of study, the extent of geographic areas 

associated with various levels of (I+N)/N are determined. Levels of (I+N)/N of 3 dB and 

10 dB are considered as important interference risk thresholds because these levels relate 

to moderate and high likelihood of interference, respectively, for unknown levels of 

desired signal power. 

 To put the 3 dB and 10 dB (I+N)/N levels (S/N reductions) in perspective, Figure 

6-1 illustrates the S/N reduction caused by an unwanted signal at the Part 15 limit level. 

Figure 6-1 shows that in an environment having the typical median noise power level of a 

residential environment (Kansas City, MO), field strength at the Part 15 limit would 

reduce the S/N by over 15 dB. 

 

46 See e.g., ITU Radio regulation Nos. 3.3, 4.3, 4.11, and especially 15.2 ("Transmitting stations shall 

radiate only as much power as is necessary to ensure a satisfactory service.") 
6-4 

-30

-25

-20

-15

-10

1 10 100

Frequency, MHz

∆S/N, d

B

Figure 6-1: Change in Receiver Signal-to-Noise Power Ratio Caused By Unintentional Emissions at 

the Part 15 Limit47

 To illustrate the extent of area in which (I+N)/N is greater than or equal to 3 dB, 

Figure 6-2 depicts the range of separation distances generally needed between a receiving 

antenna and one Part 15 device acting as a single-point source and radiating power 

toward the antenna at a level that exactly complies with the Part 15 field strength limit. 

As noted above, actual BPL system radiating characteristics will be considered in the 

interference risk analysis, and so, radiation at the level of the present Part 15 limits would 

occur only in the direction(s) of peak radiation. 

0

100

200

300

400

500

600

1 10 100

Frequency, MHz

Distance, meters

40 Log(d /d)

20 Log(d /d)

ref

ref

Figure 6-2: Distance at which external noise levels equal FCC Part 15 

radiated emission limits (Class B)48

 

47 Above 30 MHz, the limit and bandwidth for Class B devices is assumed in Figure 6-1. Noise levels used 

are median for Kansas City, MO. 

48 Figure 6 assumes that Fam = Fu (see equation 6-3). The “40 Log...” curve is representative for a point 

source radiating toward a radio antenna located at most a few meters above the ground. The “20 Log...” 

curve pertains to a radio antenna located well above ground level (e.g., >10 meters). 
6-5 

6.3.2 Noise Calculations 

 For the purposes of this study, ambient background noise was calculated using the 

Institute for Telecommunication Science’s NOISEDAT computer program.49 This 

program implements the data contained in the ITU-R Rec. P.372-8 discussed in section 

5.4.4. Noise was calculated for a centrally-located geographic point (Kansas City, 

Kansas.) for all times of the day and seasons of the year under residential conditions. 

From this data, the median noise levels at each frequency of interest were used as 

background noise for (I+N)/N calculations. The one exception to this regime for the 

noise power levels used for off-shore ship station calculations, for which noise data at a 

location off the Atlantic coast near Wallops Flight Facility in Virginia under “quiet rural” 

conditions was used. 

 After adjusting for a single-sideband (SSB) receiver noise bandwidth of 2.8 kHz 

for frequencies less than 30 MHz and a bandwidth of 16 kHz for frequencies greater than 

30 MHz, the noise power levels listed in Table 6-1 were used. 

Table 6-1: Noise power values for (I+N)/N calculations. 

Service Location and Noise Power, dBW (NdBW) 

Conditions 4 MHz 15 MHz 25 MHz 40 MHz 

Land Stations50 39.12 N, 

94.62 W, 

Residential 

-111.3 -128.8 -135.6 -134.3 

Ship Stations 37.69 N, 

75.25 W, 

Quiet Rural 

-119.3 -136.9 -150.0 -147.5 

6.4 INTERFERENCE MODELS 

NEC modeling for this report was used to derive electric field strength and far-field 

radiation patterns due to a power line energized by a single BPL device. Electric field 

strength levels generated by the simulated BPL system in areas where the representative 

ground-based receivers typically operate were evaluated statistically. 

6.4.1 Receiving Systems 

Representative systems from the land-mobile, fixed, maritime and aeronautical 

services were chosen, and system characteristics were subsequently used in interference 

calculations. Various parameters from all the chosen systems are listed in Table 6-2. 

 

49 NOISEDAT is available from the ITU Website, URL: http://www.itu.int/ITU-R/software/studygroups/rsg3/databanks/ionosph/index.html. 

50 Land stations include land mobile, fixed, maritime coast and aeronautical stations. 
6-6 

Table 6-2: Receive system characteristics used in interference study. 

STATION TYPE 

Receiver Characteristics 

(2-30 MHz) Fixed and 

Land 

Land Mobile Maritime 

Mobile 

Aeronautical 

Bandwidth (kHz) 2.8 2.8 2.8 2.8 

Modulation J3E J3E J3E J3E 

Antenna Type Horizontal 

dipole 

Vertical whip Vertical whip Vertical whip 

Antenna Height (m) 42.7 2 9 6, 9, & 12 km 

Antenna Length (m) 24.4 3 4 3 

Polarization Horizontal Vertical Vertical Vertical or 

horizontal 

Noise Environment Residential Residential Quiet Rural Residential 

Antenna Gain (towards 

horizon) dBi 

0 -4.8 @ 4 MHz 

-0.9 @ 15 MHz 

0.3 @ 25 MHz 

0 0 

Horizontal distance from BPL 0-4 km from 

single BPL 

emitter 

0-4 km from 

single BPL 

emitter 

0-4 km from 

single BPL 

emitter 

0-50 km from 

center of BPL 

service area 

Interference Criteria (I+N)/N 3 & 10 dB 3 & 10 dB 3 & 10 dB 3 & 10 dB 

Receiver Characteristics 

(30-50 MHz)

Bandwidth (kHz) 16 16 16 16 

Modulation F3E J3E J3E J3E 

Antenna Type Vertical whip Vertical whip Vertical whip Vertical blade 

Antenna Height (m) 42.7 2 9 6, 9, & 12 km 

Antenna Length (m) 6 2 2 2 

Polarization Vertical Vertical Vertical Vertical 

Noise Environment Residential Residential Quiet Rural Residential 

Antenna Gain (towards 

horizon) dBi 

3 2 2 0 

Horizontal distance from BPL 0-4 km from 

single BPL 

emitter 

0-4 km from 

single BPL 

emitter 

0-4 km from 

single BPL 

emitter 

0-50 km from 

center of BPL 

service area 

Interference Criteria (I+N)/N 3 & 10 dB 3 & 10 dB 3 & 10 dB 3 & 10 dB 
6-7 

6.4.2 Power Line Model 

The NEC power line model used in these analyses consisted of three parallel 

straight wires, each 340 meters long, spaced in a horizontally parallel configuration 0.6 

meters apart. The three wires were given conductivity characteristics equal to copper 

wire and AWG 4/0 diameter. They were placed 8.5 meters above a “Sommerfeld” 

ground with average characteristics (relative permittivity εr = 15, conductivity σ = .005 

Siemens/meter) to simulate land-mobile and fixed service conditions, and above a 

Sommerfeld ground with saltwater characteristics (relative permittivity εr = 81, 

conductivity σ = 5 Siemens/meter) to simulate power lines along a coast line for maritime 

conditions. One of the outer power lines was center-fed using a voltage source to 

simulate the BPL coupler. The source was set to provide 1 volt. The source impedance 

(modeled by serially loading the segment upon which the source was placed) was given a 

real impedance of 150 Ω. 

The ends of the long wires were connected together at each end by inter-phase 

loads of 50 Ω each (wires 1 and 2 and wires 2 and 3 were connected in this manner) to 

simulate a degree of system loading and discontinuity. 

The wires used for this model were segmented following recommendations from 

Lawrence Livermore National Laboratories NEC documentation. Specifically, segment 

length was set to provide 20 segments per wavelength at the desired frequency, rounded 

up to an odd number of segments. This resulted in 340-meter-long wires consisting of 

91, 341, 567 and 907 segments each for 4 MHz, 15 MHz, 25 MHz and 40 MHz, 

respectively. Convergence testing (by increasing the number of segments for each 

frequency) and average gain testing indicated good model stability and behavior. 

6.5 INTERFERENCE CALCULATIONS 

6.5.1 Scaling Output Power to Meet FCC Part 15 Limits 

FCC Part 15 measurement procedures generally follow American National 

Standards Institute (ANSI) publication C63.4-1992, which specifies measurements with 

both vertical and horizontal polarization. To ensure the modeled radiation from the wires 

met FCC Part 15 limits consistent with existing BPL measurement practices, initial NEC 

runs were executed to find the expected electric field in the x-, y- and z-vector directions 

at a height of one meter above the ground, 30 meters away from the wire on which the 

voltage source was placed, for 4 MHz, 15 MHz and 25 MHz, and at a distance of 3 

meters away at 40 MHz. The rms values of the NEC-calculated electric field x, y and zvectors would be found in a straightforward manner, assuming a sinusoidal BPL test 

signal, as shown in the following equation. 
6-8 

(6-4) 

where 

Eox, Eoy, Eoz are the magnitudes of the NEC-calculated x-, y- and z-vector 

 electric-fields 

The calculated electric field values were then divided by the FCC Part 15 limits 

(30 μV for frequencies less than 30 MHz, 100 μV for frequencies greater than 30 MHz), 

and the maximum such value found along the line in any vector was used to scale all 

subsequent electric field calculations. Because measured quasi-peak values of field 

strength are expected to be near or slightly exceed the above rms values (see Appendix D, 

Section D.3.4), this scaling process may yield adjusted field strength values slightly in 

excess of values needed for compliance using a quasi-peak detector. The purpose of this 

exercise was to ensure the radiated signal complied with FCC Part 15 limits for each 

frequency. 

6.5.2 Analysis Methodology for Land-Mobile, Fixed and Maritime Services 

After the initial “scaling” runs, NEC simulations were performed to find the 

spatial distribution of electric field strength values. The calculations were made for a 

geographic grid of points with 5 meter spacing along and away from the line to a distance 

of 1 km, at heights of 2 meters, 42.7 meters and 9 meters to simulate land mobile vehicle, 

mobile-base/fixed and ship antennas, respectively. This grid included points lateral to the 

power lines and excluded points off the end of the modeled power line, as it was felt that 

the arbitrary ending of the power line at both ends of the power line layout would yield 

unrealistic radiation properties in nearby areas. The NEC simulations indicated 

substantial radiation off the ends of the line, and real-world power lines do indeed 

terminate at many points. 

Electric field values were calculated using NEC’s ground wave capability for 

distances greater than one kilometer from the line. These values were calculated in 

cylindrical coordinates, meaning values were found for a given distance and height in a 

circle around the power line model. Values were calculated in 5-degree increments at 

distance increments of 100 meters from 1 km to 4 km, at the same antenna heights used 

for near-field calculations. 

In addition to the above NEC runs, a “close-in” simulation was completed to 

gather fine detail along the line at land-mobile antenna height (two meters). This was 

done to determine the degree of potential interference expected to be found on streets 

next to power line runs. This “close-in” run was done using NEC’s near-field facility on 

a grid with 0.5 meter spacing out to a distance of 15 meters from the line. 

2, 2 , 2

z

z

y

y

x

x

E

E

E

E

E

E o o o = = =
6-9 

Once calculated, the electric field values were scaled and the relevant real field 

value (Ex for the vertical land mobile antenna, Ey and Ez for horizontal fixed and 

maritime antennas) was translated into received interfering signal power as follows: 

(6-5) 

where 

EV/m is the received signal strength in V/m 

FMHz is the measurement frequency in MHz 

G is the gain of the receiving antenna 

BW is the ratio of receiver to measurement bandwidth 

φ is the average duty cycle 

δ is a quasi-peak to rms measurement factor 

For the purposes of this study, the average duty cycle (φ) was taken to be 55%, 

which was midway between an always-on (100%) downstream signal and an intermittent 

(10%) upstream customer-to-internet signal. Additionally, to compensate for differences 

between ambient noise levels expressed in rms values and BPL signal radiation measured 

using quasi-peak detection, a measurement factor (δ) adjustment of -2 dB was applied to 

the calculated received BPL signal power. 

From the received signal power and the background noise, the (I+N)/N ratio was 

calculated at each point in the assumed receiver operating areas: 

(6-6) 

Once these calculations were complete, the percentages of locations for each 

distance value (near field and ground wave calculations) or in areas around the BPLenergized line (for close-in land-mobile situations) exceeding given (I+N)/N values were 

determined. 

6.5.3 Analysis Methodology for Aeronautical Service 

In order to calculate interference to an aircraft receiver, several parameters were 

defined: 

• BPL service area: circular area of 10 km radius (6.2 miles) 

( ) ( ) ( ) ( )

10 ( ) 10 ( ) 12.8

20 20

10 10

10 10

+ ⋅ + ⋅ + +

= ⋅ − ⋅ +

Log BW Log φ δ

PdBW Log EV m Log FMHz Gr dBi

( ) ( )





 



 = ⋅ + + −

10 10 10 1 10

PdBW NdBW

Log N

I N
6-10 

• Number and density of co-channel BPL transmitters: 1200, 300, and 75 

deployed over an area of 314 km2

, with approximately 0.5, 1, and 2 km 

separation between units, respectively 

• BPL unit radiated power: 

o For 4 MHz: -69.8dBW/2.8 kHz 

o For 15 MHz: -67.3dBW/2.8 kHz 

o For 25 MHz: -64.9dBW/2.8 kHz 

o For 40 MHz: -81.1dBW/16.0 kHz 

BPL device output power was derived from the NEC scaling runs. NECcalculated power line input power was scaled by the square of the scaling factor for each 

frequency, as well as by the ratio between the receiver and measurement bandwidths. 

Additionally, NEC was used to find the far-field directional gain pattern from the 

modeled power lines for all frequencies of interest. Simulations were run using the 

directional gain pattern in azimuthal directions both parallel and perpendicular to the 

main radiation lobe of the power line. The average directional gain levels for each 

elevation were found for the two patterns (Figure 6-3) used in the analysis. 

Average Directivity v. Elevation Angle

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

0 20 40 60 80

Elevation Angle (degrees)

Directional Radiation Pattern 

(dBi)

4 MHz 15 MHz

25 MHz 40 MHz

Figure 6-3: Average far field directional gain antenna patterns used for aeronautical interference 

calculations. 

As mentioned previously, a Matlab model was used to simulate an aircraft at 

various heights and horizontal distances from the centroid of a BPL deployment area. 

This model simulated the signal effects of multiple BPL devices in different deployment 

cells at the aircraft location. 
6-11 

As with interference calculations for the other services, several additional factors 

were taken into account. Two of these, duty cycle (φ) and quasi-peak to rms 

measurement factor (δ) were discussed in subsection 6.5.2, and the same values were 

used here (55% and -2 dB, respectively). An additional adjustment factor, polarization 

mismatch, was used with aeronautical service calculations. This factor was designed to 

compensate for the fact that the aeronautical service antenna used in this simulation was 

vertically polarized, whereas the BPL structure was horizontally polarized. Both 

structures interacted with radiation of the opposite polarization in NEC simulations. For 

example, the BPL structure produced significant (or even primary) radiation that was 

vertically polarized in most azimuthal directions. Further, over a significant number of 

azimuthal directions, the short aeronautical antenna could be expected to respond well to 

both horizontally- and vertically-polarized radiation. Nonetheless, for a small number of 

orientations a cross-polarization effect would likely reduce coupling between the BPL 

structure and the receiving antenna. In order to account for this effect, an overall 

decrease of 1 dB in the received BPL signal was assumed. 

6.6 RESULTS OF INTERFERENCE CALCULATIONS 

6.6.1 Land-Mobile Service 

Calculations of close-to-the-line interference potential for vehicular land-mobile 

receivers due to a BPL transmitter operating at FCC Part 15 limits show that there would 

be significant increases in the noise floor due to interference. As can be seen in 

Table 6-3, for frequencies less than 30 MHz, virtually all points close to the line would 

experience (I+N)/N levels greater than 10 dB. In other words, there would be at least a 

ten-fold increase in total receiver noise power on the street adjacent to the BPL device 

and power lines. At 40 MHz, a majority of the areas in a road along the power line 

would see this level of interference. 

Table 6-3: Percent of points exceeding specified interference level, by frequency, for land-mobile 

receiver system within 15 meters of a BPL-energized power line. Radiated power and noise are into 

a 2.8 kHz bandwidth for 4 MHz, 15 MHz and 25 MHz, and a 16 kHz bandwidth at 40 MHz. 

Frequency 

(MHz) 

Radiated 

Power 

(dBW) 

Noise 

(dBW) 

3 dB 

(I+N)/N 

10 dB 

(I+N)/N 

20 dB 

(I+N)/N 

30 dB 

(I+N)/N 

40 dB 

(I+N)/N 

50 dB 

(I+N)/N 

4 -69.8 -111.3 99.3% 93.2% 54.7% 6.2% 0.0% 0.0% 

15 -67.3 -128.8 99.8% 99.7% 95.7% 59.5% 4.3% 0.0% 

25 -64.9 -135.6 99.8% 99.0% 92.1% 58.5% 18.5% 0.0% 

40 -81.1 -134.3 87.9% 49.2% 10.0% 0.0% 0.0% 0.0% 

The increases in the noise floor a land-mobile system might encounter along a 

BPL-energized power line are further illustrated in Figure 6-4. In this figure, (I+N)/N 

values are depicted using colors from red to blue, with dark red representing 50 dB and 

dark blue representing zero. 
6-12 

It can be inferred from these calculations that a vehicle-mounted HF receiver 

operating in a residential environment on a roadway adjacent to a BPL-energized power 

line may experience harmful interference, depending upon the frequency, the distance 

along the line away from the BPL transmitter, the BPL transmitter duty cycle and the 

number of BPL devices on the line. 

Figure 6-4: (I+N)/N values around the modeled power line, to a distance of 15 meters. Colors 

 represent a range from zero dB (dark blue) to 50 dB (dark red). a) 4 MHz. b) 15 MHz. c) 25 MHz. 

d) 40 MHz. The BPL structure is denoted with a dark horizontal line in the center of each plot. 

Near-field calculations of interference levels stemming from a single BPL device, 

out to a distance of one kilometer from the power line, indicated a sharp falloff in the 

level of interference with distance. As shown in Figure 6-5, out to distances on the order 

of 120 meters from the power line, a land-mobile receiver operating in the modeled noise 

environment could experience interference. 

Ground wave calculations of interference levels at a distance from one to four 

kilometers were in good agreement with those for the near field. Results at a nominal 

one kilometer near-field/ground-wave juncture were well-matched. In no areas adjacent 

to, and more than 120 meters from the power lines would the modeled land-mobile 

system be likely to experience significant interference from a single BPL transmitter 

operating at FCC Part 15 limits. 

(a)

(b)

(c)

(d)
6-13 

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

Figure 6-5: Percent of near-field points, by distance, where a land-mobile receiver would see the 

specified (I+N)/N levels due to a BPL transmitter operating at Part 15 limits. a) 4 MHz. b) 15 MHz. 

(a)

(b)
6-14 

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

Figure 6-5 continued: c) 25 MHz. d) 40 MHz. 

(c)

(d)
6-15 

6.6.2 Fixed Service 

NEC interference calculations for an assumed fixed service or mobile base station 

receiving antenna found substantial (I+N)/N values at greater distances from the line than 

those found for land mobile receivers. This was especially true at 15 and 25 MHz. 

The near field results are depicted in Figure 6.6. As can be seen, at 15 MHz the 

potential for a 3dB (I+N)/N level exists beyond 500 meters away, and at 25 MHz some 

locations more than 700 meters away could see this level of interference. Additionally, 

locations past 300 and 400 meters from the BPL-energized line on 15 MHz and 25 MHz, 

respectively, could experience (I+N)/N levels in excess of 10 dB. 

The differences in potential interference found with different frequencies are 

partly due to the ambient noise floor decreases as the frequency is increased. However, 

the increased gain of the modeled antenna with frequency also plays a part, which means 

that higher gain antennas and lower-noise areas could face greater risks of interference at 

lower frequencies. Likewise, receivers with lower-gain antennas and high-noise 

environments would likely experience less degradation in the noise floor, but would 

likely also see a reduced S/N. This is true for all of the services modeled. 

6.6.3 Maritime Service 

As noted previously, the calculations for a ship receiver differed from the fixed 

and land-mobile services in two important respects: the use of lower ambient noise levels 

and the use of salt-water ground characteristics. This model assumed a power line 

running along the shoreline, and the ship receiver possibly in a bay or harbor. 

Results for the simulated maritime receiver were similar to those for the fixed 

service receiver. Substantial areas near the shore (near field) would likely see greater 

than 3 dB increases in the noise floor. As with the other services, this effect would be 

most pronounced at 25 MHz with the assumed power lines. According to the 

calculations, a single BPL device could S/N at 25 MHz by 3 dB for more than 50% of 

points within 100 meters of the shore (Figure 6-7). 

Despite the lower noise levels seen by the simulated system at distances greater 

than one kilometer from shore, calculations indicated that at no point would the simulated 

system experience (I+N)/N levels greater than 3 dB. 
6-16 

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 200 400 600 800 1000

Perpendicular Distance

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

Figure 6-6: Percent of near-field points, by distance, where a fixed receiver would see the specified 

(I+N)/N levels due to a BPL transmitter operating at FCC Part 15 limits. a) 4 MHz. b) 15 MHz. 

(a)

(b)
6-17 

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 200 400 600 800 1000

Perpendicular Distance

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

 

Figure 6.6 continued: c) 25 MHz. d) 40 MHz. 

(c)

(d)
6-18 

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

Figure 6-7: Percent of near-field points, by distance, where a maritime receiver would see the 

specified (I+N)/N levels due to a BPL transmitter operating at FCC Part 15 limits. a) 4 MHz. b) 15 

MHz. 

(a)

(b)
6-19 

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 50 100 150 200

Perpendicular Distance (m)

Percent Exceeding

3 dB (I+N)/N

10 dB (I+N)/N

Figure 6-7 continued: c) 25 MHz. d) 40 MHz. 

(c)

(d)
6-20 

6.6.4 Aeronautical Service 

The analysis of potential interference to aeronautical transceivers covered 

modeled deployments of 1200, 300, and 75 co-frequency BPL devices in an area of 10 

km radius. Results indicated that multiplying the number of BPL devices by a factor of 

four produced a straightforward 6 dB increase in aggregate interfering BPL signal power; 

therefore only the analysis with 300 units is presented. The calculated data is listed in 

Table 6-4 and shown graphically in Figure 6-8. 

Table 6-4: Calculated (I+N)/N values, in dB, for aircraft receiver at listed distance, frequency and 

height, with 300 BPL units visible to the receiver in a 314 km2

 area. 

 (I+N)/N (dB) 

4 MHz 

 (I+N)/N (dB) 

15 MHz 

(I+N)/N (dB) 

25 MHz 

 (I+N)/N (dB) 

40 MHz 

Height 

 Distance 6 km 9 km 12 km 6 km 9 km 12 km 6 km 9 km 12 km 6 km 9 km 12 km

0 km 0.8 0.5 0.4 12.2 8.9 6.4 8.9 6.3 5.7 0.3 0.1 0.0 

5 km 0.7 0.5 0.3 11.3 8.9 6.6 9.2 6.5 5.5 0.2 0.1 0.1 

10 km 0.5 0.4 0.2 10.7 8.6 6.7 9.6 6.2 4.5 0.2 0.1 0.1 

15 km 0.3 0.3 0.2 9.3 7.8 6.6 9.0 6.1 3.8 0.1 0.1 0.1 

20 km 0.2 0.2 0.1 7.8 6.9 5.9 8.4 6.7 4.3 0.1 0.0 0.0 

25 km 0.1 0.1 0.1 6.0 6.1 5.3 7.4 6.3 5.0 0.1 0.1 0.0 

30 km 0.1 0.1 0.1 4.1 5.4 4.6 6.4 5.6 5.0 0.1 0.1 0.0 

35 km 0.0 0.1 0.1 2.6 4.3 4.4 5.5 4.8 4.6 0.1 0.1 0.0 

40 km 0.0 0.0 0.0 1.7 3.1 3.8 4.6 4.4 3.9 0.1 0.1 0.0 

45 km 0.0 0.0 0.0 1.1 2.2 3.1 3.6 4.1 3.3 0.0 0.0 0.0 

50 km 0.0 0.0 0.0 0.7 1.6 2.4 2.8 3.6 3.1 0.0 0.0 0.0 

As the figures indicate, an aircraft traveling above or near the modeled BPL 

deployment area could see substantial S/N degradation. These calculations include parts 

of the far-field radiation pattern (off the ends of the power lines, or on-axis) that exhibited 

potentially elevated power gain levels. Further study is needed of representative power 

line gain levels in skyward directions. 
6-21 

0.0

0.5

1.0

0 10 20 30 40 50

Horizontal Distance from BPL Deployment Center (km)

(I+N)/N (dB)

6 km Height

9 km Height

12 km Height

2

4

6

8

10

12

0 10 20 30 40 50

Horizontal Distance from BPL Deployment Center (km)

(I+N)/N (dB)

6 km Height

9 km Height

12 km Height

Figure 6-8: Calculated (I+N)/N level for an aeronautical receiver at the specified distance and height 

from a BPL deployment, with 300 BPL devices visible to the receiver. (a) 4 MHz. (b) 15 MHz. 

(a)

(b)
6-22 

0

1

2

3

4

5

6

7

8

9

10

11

12

13

0 10 20 30 40 50

Horizontal Distance from BPL Deployment Center (km)

(I+N)/N (dB)

6 km Height

9 km Height

12 km Height

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50

Horizontal Distance from BPL Deployment Center (km)

(I+N)/N (dB)

6 km Height

9 km Height

12 km Height

Figure 6-8 continued: c) 25 MHz d) 40 MHz 

(c)

(d)
6-23 

6.7 CONCLUSION 

 Interference risks were estimated using NEC models for four representative types 

of federal radio stations operating in the fixed and mobile services: a land vehicular 

radio; shipborne radio; a fixed or mobile-base station with roof top antenna; and an 

aircraft radio in flight. These risks were gauged from the extent of geographic areas in 

which BPL emissions would reduce the ratio of desired radio signal power to ambient 

noise power by amounts associated with moderate and high probabilities of interference 

(i.e., 3 dB and 10 dB reductions in (S/N), respectively). Along with the four 

representative radio stations, a three-phase power line structure was modeled using NEC. 

Predicted nationwide, Springtime, median ambient noise power levels were assumed and 

analyses were performed at four frequencies between 1.7 – 80 MHz. The BPL device 

output was adjusted to produce emissions at the limits of Part 15 for unintentional 

radiators (Class B above 30 MHz), as generally determined by compliance measurement 

practices extant with the exception that measurement distances were applied with respect 

to the BPL device and power lines rather than only the BPL device. This exception 

generally results in compliance at BPL output power levels lower than output levels that 

yield compliance when distances are measured from the BPL device. For all of these 

analyses, the frequencies at which the lowest and highest reductions in S/N occur may 

change for different power line configurations. 

The results for the vehicular mobile receiver predict that the received BPL signal 

power near the Earth surface falls off rapidly with distance from the lines. For the two 

frequencies at which the highest BPL signal power levels were received (15 MHz and 25 

MHz), signal power from one co-frequency BPL system (one device) equaled noise 

power (3 dB reduction in S/N) at fifty percent of the locations within seventy and seventy 

five meters of the power lines. At these same frequencies, BPL signals reduced S/N by 

10 dB at fifty percent of locations within twenty-five and thirty meters of the power lines. 

The distances within which these thresholds were exceeded at fifty percent of locations 

were modestly smaller at a third frequency (4 MHz) and much smaller at the fourth 

frequency (40 MHz). In all land vehicular cases considered, reductions in S/N were less 

than 3 dB and 10 dB beyond one-hundred-and-twenty-five meters and fifty-five meters, 

respectively. 

The results for the fixed service (or mobile base station) receiver predict that the 

received BPL signal power falls off less rapidly with distance from the power lines than 

occurred for the land vehicle case. For the two frequencies at which the highest BPL 

signal power levels were received, signal power from one co-frequency BPL system (one 

device) equaled noise power (3 dB reduction in S/N) at fifty percent of the locations 

within three-hundred-and-ten and four-hundred meters of the power lines. At these same 

frequencies, BPL signals reduced S/N by 10 dB at fifty percent of locations within onehundred-and-seventy-five and two-hundred-and-thirty meters of the power lines. In all 

cases, reductions in S/N were less than 3 dB and 10 dB beyond seven-hundred-andseventy meters and four-hundred-and-fifty meters, respectively. 
6-24 

The results for the shipborne receiver predict that the received BPL signal power 

falls off rapidly with distance from the power lines, but less rapidly than for the land 

vehicle case. For the two frequencies at which the highest BPL signal power levels were 

received, signal power from one co-frequency BPL system (one device) equaled noise 

power (3 dB reduction in S/N) at fifty percent of the locations within one-hundred meters 

of the power lines. At these same frequencies, BPL signals reduced S/N by 10 dB at fifty 

percent of locations within fifty-five meters of the power lines. In all cases, reductions in 

S/N were less than 3 dB and 10 dB beyond one-hundred-and-thirty-five meters and 

eighty-five meters, respectively. 

 For the aircraft receiver, aggregate interference effects were considered for 

simultaneously active, co-frequency BPL systems deployed at a density of one per square 

kilometer over an area having ten (10) kilometers radius. The power lines were assumed 

to be randomly oriented and an average of the power line far-field gain levels were used 

in each direction under consideration. Aircraft were assumed to be operating at altitudes 

of 6 to 12 km at locations ranging from zero to fifty (50) kilometers from the center of the 

BPL deployment area. Results showed that aggregate interference levels to the aircraft 

could exceed average ambient RF noise levels at two frequencies (15 MHz and 25 MHz), 

at distances ranging from thirty-three kilometers (six kilometers altitude) to over fifty 

kilometers (altitudes between six and twelve kilometers). The S/N reduction exceeded 10 

dB at only one frequency, at six kilometers altitude within twelve kilometers of the center 

of the BPL deployment area. At the two frequencies where the assumed BPL systems 

produced the lowest interfering signal power levels (i.e., 4 MHz and 40 MHz), S/N 

reductions peaked at about 0.8 dB and 0.3 dB directly over the center of the BPL 

deployment area. Higher or lower densities of active co-frequency BPL units would raise 

or lower the predicted interference levels in direct proportion to the unit density. 
7-1 

SECTION 7 

BPL COMPLIANCE MEASUREMENT PROCEDURES 

7.1 INTRODUCTION 

 The BPL Inquiry states that Part 15 of the Commission’s rules do not specifically 

provide measurement procedures that apply to BPL systems and notes that the 

Commission has “...allowed measurements of radiated emissions at three installations 

that the operator deems as representative of typical installations.”51 This approach is 

allowed under Part 15 (§15.31(d)) when it is impractical to perform compliance 

measurements at Open Air Test Sites (OATS). Compliance measurements must be 

designed to be practical, but they should also be accurate with any composite 

measurement error biased toward overestimation of actual field strength.52

In Section 5.2, it was noted that peak levels of BPL field strength may arise from 

standing waves on the power lines that are generated by reflections of signals at 

impedance discontinuities along the power lines. It is essential that these standing wave 

conditions be addressed during compliance measurements. These radiation conditions 

have little to do with the BPL device itself; instead, they result from various features of 

power lines that cannot be readily emulated in a laboratory or at a conventional OATS. 

 NTIA has reviewed three proprietary reports of BPL measurements that were 

performed by contractors hired by BPL proponents to test compliance of trial BPL 

systems with Part 15 field strength limits. In all cases involving outdoor overhead power 

lines, measurements were performed using a one-meter high antenna on radials 

emanating from a power line pole to which a BPL access device was mounted. While 

consistent with §15.31(f)(5), this ad hoc measurement approach does not demonstrate 

compliance with the field strength limits because as shown by NTIA’s measurements and 

models, peak field strength levels are not centered at the BPL device and do not occur at 

a height of one-meter above the ground.53 Other sources of potential BPL measurement 

inaccuracies include: the measurement distance and extrapolation factor; frequencyselective radiation effects; estimation of electric fields using a loop antenna; and selection 

of representative BPL installations for testing. Potential solutions to most of these 

measurement challenges are at hand within existing Part 15 measurement procedures, as 

discussed below (also see the listing of applicable Part 15 rules in Appendix A). 

 

51 BPL Notice of Inquiry, at ¶2 and 21-23. 

52 See e.g., Information technology equipment – Radio disturbance characteristics – Limits and methods of 

measurement, CISPR 22:2003, (“CISPR 22”), Section 7.1.2. “The significance of the limits for equipment 

shall be that, on a statistical basis, at least 80% of the mass-produced equipment complies with the limits 

with at least 80% confidence.” 

53 See Potential Interference from Broadband over Power Line (BPL) Systems to Federal Government 

Radiocommunications at 1.7 – 80 MHz, NTIA Report 04-413, (“NTIA BPL Report”),Volume I, Section 

5.2. 
7-2 

7.2 MEASUREMENTS MUST ADDRESS RADIATION FROM 

POWER LINES TO WHICH BPL DEVICES ARE 

CONNECTED 

Part 15 already clearly specifies that compliance measurements must address the 

device under test (DUT, also referred to as equipment under test or EUT) while it is 

connected to all cables, wires and companion devices normally used with the DUT.54 

The measurement distances are specified to be relative to an imaginary, ground-based 

boundary around the DUT and the interconnected cables, wires and companion devices. 

Nonetheless, because BPL measurement contractors have applied measurement distances 

with respect to only the BPL DUT, the Commission should consider clarifications to the 

provisions that apply to BPL systems. 

When applying measurement distances relative to the BPL DUT, the peak field 

strength may be substantially overestimated or underestimated. As shown in NEC 

models of BPL radiation (see Appendix E), vertical electric field strength varies 

substantially over small distances along radials from the BPL DUT and, depending on 

geometric and electrical factors, the measurement location may coincide with a local field 

strength peak or trough. There is no apparent need to measure local field peaks under 

power lines because radio receivers operating in the subject frequency range inherently 

should not be located directly under power lines in order to avoid degradation from 

ambient local power line noise. 

7.3 MEASUREMENTS SHOULD ADDRESS AGGREGATED 

EMISSIONS FOR THE FULLY DEPLOYED BPL NETWORK 

Part 15 specifies that the aggregate emissions from a composite system must satisfy 

the field strength limits applicable for a single device.55 As BPL networks are 

substantially deployed in a community, the aggregated BPL emissions for the overall 

network are expected to increase above the levels generated by a single BPL device. This 

aggregation has already been observed by NTIA at one of the trial BPL systems where 

multiple simultaneous transmissions occur.56 

 

54 See 47 C.F.R. §15.31(g)-(k). 

55 See 47 C.F.R. §15.31(h)-(k) 

56 See NTIA BPL Report, Volume II, Appendix D, § D.1 
7-3 

7.4 MEASUREMENT ANTENNA HEIGHTS SHOULD ADDRESS 

ALL IMPORTANT DIRECTIONS OF BPL SIGNAL 

RADIATION 

 Part 15 measurement procedures for testing at OATS require measurement of 

emissions radiated in all directions and identification of the direction of maximum 

radiation intensity.57 This is accomplished using: a turntable on which the DUT and 

interconnection cables, wires and companion devices are rotated; a reflecting ground 

plane in conjunction with predetermined normalized site attenuation; and measurement 

antenna heights varied between 1 meter and 4 meters in order to facilitate determination 

of the height of maximum radiation. Although these OATS provisions are not practicable 

when measuring at a BPL installation site, the underlying principles remain critical to 

measurement accuracy and control of interference risks. Specifically, it is essential that 

BPL compliance measurements be made in directions where emissions may propagate to 

radio receivers. 

In the case of outdoor BPL systems, radio receivers can be located in any 

direction around the BPL device and the power lines to which the BPL device is 

connected. Receiving antennas on masts or buildings near the power lines or on aircraft 

flying over power lines can be at high elevation angles from the DUT and power lines, 

whereas land mobile antennas will typically be at low (including negative) elevation 

angles. The lowest receiver antenna heights typically will be of the order of two (2) 

meters. Thus, since BPL measurements at an OATS are not practicable (where a one (1) 

meter antenna height should be considered), there is no need to measure BPL emissions 

at a height less than two (2) meters. However, to adequately address emissions at high 

elevation angles, it is necessary to measure BPL emissions at heights comparable to the 

power line height. 

Conceptually, this can be accomplished either through direct measurement at 

various heights and directions or by application of a standard two-meter or higher 

measurement antenna height with an adjustment factor that accounts for other heights. 

The direct measurement approach may require more measurement samples but is favored 

by NTIA because the logistically simpler adjustment factor approach introduces 

uncertainty and electric utilities generally have access to bucket-trucks ("cherry pickers") 

needed to safely perform measurements at and above the heights on MV and LV power 

lines. In the alternative, NTIA's measurement results to date (see Appendix D, §D.5) 

indicate that electric field strength generated within tens of feet of the power lines at two 

(2) meters above ground level generally are 3 dB to 15 dB lower than values generated at 

a height of ten (10) meters (i.e., typically one (1) meter above the height of power lines). 

This indicates that at heights above a BPL energized power line, a height adjustment 

factor would be needed to properly estimate the peak field strength based on 

measurements made at a two (2) meter height. In light of the large range of potentially 

 

57 See e.g., 47 C.F.R. §15.31(f)(5) and ANSI C63.4-2001, clause 8.3.1.2. When measurements are made at 

an installation site, ANSI C63.4-2001, clause 8.3.2 requires identification of the radial of maximum 

emissions. 
7-4 

required adjustment factors and the need for high certainty of compliance in directions 

where emissions may propagate to radio receivers, the adjustment factor approach 

necessarily would have substantial bias toward overestimation of field strength. 

To minimize the number of measurement samples associated with direct 

measurement, it appears feasible to apply only a single, high, standard measurement 

height, combined with a smaller adjustment factor, unless the measurement height 

coincides with peak field strength. For example, a 10 meter measurement height may be 

adequate with a small adjustment factor that accounts for higher field strength levels than 

could occur above the 10 meter height; however, further study is needed to identify the 

most practical but accurate approach. Measurement at a lower height may be superfluous 

since higher peak electric fields appear to consistently occur at heights above the power 

lines. NTIA plans to further address this potential measurement solution in its Phase 2 

studies. 

7.5 A SINGLE MEASUREMENT DISTANCE SHOULD BE USED 

FOR OVERHEAD POWER LINES AND BPL DEVICES 

Practical and technical considerations dictate that BPL compliance measurements 

be made in the near-field. NTIA's BPL measurements and NEC radiation models both 

manifest near-field behavior at large distances (e.g., over 300 meters) in many directions 

from BPL systems. In many cases, the field strength at large distances in the near-field is 

at levels too low for reliable measurement. Thus, avoidance of measurement in the nearfield is not practicable and the measurement distance must be based on other factors, such 

as: 

• The possible occurrence of local peak field strength levels at distances beyond the 

measurement distance, where these local peaks are near or exceed the measured 

peak level. If this were to occur, the BPL emissions may cause interference over 

an area much larger than implied by the limits and conventional point-source 

radiation. 

• The desire to not make measurements at multiple measurement distances 

associated with different frequency ranges. Use of two different measurement 

distances above and below 30 MHz almost doubles the time needed to conduct 

the measurements. 

• The measurements should be made at distances no closer than the minimum 

typical separation between power lines and radio receiver antennas. Otherwise, 

measurement uncertainties associated with any extrapolation are unnecessarily 

incurred. 

NTIA's measurements and radiation models, deployment of Federal Government 

radio receivers, and safety considerations indicate that a measurement distance of 
7-5 

10 meters from any BPL device and its connected power lines satisfies the above 

conditions. Thus, NTIA recommends that a standard measurement distance of 10 meters 

be used for BPL compliance measurements. 

7.6 A MODIFIED DISTANCE EXTRAPOLATION FACTOR IS 

NEEDED FOR BPL 

NTIA's measurements and radiation models indicate that at distances within 

several tens of meters of the power lines, BPL field strength does not decrease with 

increasing distance consistent with the existing Part 15 distance extrapolation factors of 

20 dB and 40 dB per decade above and below 30 MHz, respectively. In several cases not 

deemed to be anomalous, field strength diminishes at a lower rate and NTIA plans in its 

Phase 2 studies to further investigate this extrapolation factor for outdoor BPL systems. 

7.7 BPL FREQUENCY AGILITY AND POWER LINE 

FREQUENCY SELECTIVE EFFECTS MUST BE ADDRESSED 

IN THE MEASUREMENT PROCEDURES 

Many BPL devices feature frequency agility, where the band of frequencies used 

by each device can be remotely adjusted via network control software.58 Because the 

standing waves generated in any given power line depend on the BPL device frequency, 

it is necessary to perform compliance measurements with the BPL device sequentially 

tuned across the entire frequency range that it is capable of using. For example, a BPL 

device that occupies a 3 MHz bandwidth located anywhere in the 4 MHz to 22 MHz 

frequency range would have to be tuned to five (5) different center frequencies during 

successive measurements (e.g., 5.5 MHz, 8.5 MHz). The uncertainty in estimating the 

peak field strength stemming from measurement with the BPL device operating at only 

one of many possibly frequency settings could exceed tens of decibels. 

7.8 NEAR FIELD MEASUREMENT ERRORS MUST BE 

 MITIGATED 

At frequencies below 30 MHz, Part 15 measurement procedures dictate the use of 

loop antennas to estimate electric field strength.59 Loop antennas inherently respond to 

magnetic fields and are relatively insensitive to electric fields; yet Part 15 applies to 

limits on electric field strength. Hence, as noted in several comments in response to the 

BPL Inquiry, the magnetic field strength measured with a loop antenna must be converted 

to an estimated electric field strength assuming a certain ratio of electric-to-magnetic 

field strength. This ratio, which is related to wave impedance, is assumed to be 377Ω. 

 

58 Reply Comments of UPLC, BPL Inquiry, August 20, 2003, (“UPLC Reply Comments”), at 7; Ambient 

Comments at 8; Ameren Comments at 9-10. 

59 See 47 C.F.R. §15.31(a)(6) and ANSI C63.4-2001, clauses 4.1.5.1 and 4.1.5.2. 
7-6 

This is a reasonable assumption if not exact in the far field of the radiating structure. 

However, as noted above, BPL compliance measurements must be made in the near field 

where the impedance is highly variable and will be substantially higher than 377Ω in 

many locations. 

Loop antennas are used below 30 MHz at OATS in order to avoid effects of 

reflections that are more vagarious for electric than magnetic fields. In other words, loop 

antennas yield better repeatability of measurements, but such a goal is readily achievable 

only in a laboratory or at an OATS (rather than at a BPL installation site). Rather than 

derive impedance values for various BPL measurement heights, NTIA recommends 

consideration of BPL compliance testing below 30 MHz using a calibrated rod antenna. 

7.9 APPROPRIATE CHOICE OF POWER LINES USED FOR BPL 

MEASUREMENTS WILL REDUCE STATISTICAL 

SAMPLING UNCERTAINTIES 

One reason Part 15 requires measurement at three or more representative 

installation sites in cases where OATS are impractical is that there is a significant chance 

that one such installation site will not manifest the highest field strength levels that will 

occur in practice. This possibility exists even with three or more measurement sites 

unless the sites are selected (or established) to yield the highest field strength levels. 

Measurement venue notwithstanding, CISPR 22 requires use of an adjustment factor 

accounting for statistical sampling uncertainty.60 Rather than deal with these adjustment 

factors, which may lead to significant overestimation of BPL field strength, NTIA 

recommends that BPL installations be selected (or established) in a manner ensuring that 

the highest possible levels of BPL field strength will be generated. 

Conceptually, testing should be conducted using various lengths of power lines 

that include substantial impedance discontinuities at various distances from the BPL 

device that may result in the generation of standing waves that are associated with the 

highest possible levels of field strength. This is because the distance between the BPL 

device and the impedance discontinuity affects the distribution of standing waves (and 

spatial distribution of field strength) at a given frequency. Based on NTIA's 

measurements and modeling to date, and noting that further study is needed of the effects 

of power line branches and turns, the following types of test site selection criteria (or 

standard test facility design factors) are suggested for further consideration and 

refinement for the case of outdoor, overhead power lines: 

• The BPL device should be located near the center of a straight section of 

power lines at least 600 meters in length that is devoid of significant 

impedance discontinuities. This ensures that at the lower frequencies (longer 

wavelengths), at least four standing wave crests can be generated in the 

straight section of power lines in order to establish a minimally sufficient 

 

60 See CISPR 22, Section 7.2.2. Here, the error from statistical sampling uncertainties is biased in a manner 

“...which assures with 80% confidence that 80% of the [equipment] type is below the limit.” 
7-7 

number of radiating power line sections. Because BPL devices themselves 

may establish impedance discontinuities, the other BPL devices operating 

with the BPL DUT should be located beyond the nearest impedance 

discontinuity. 

• If a standard test facility is established and the power lines used for testing are 

not a segment of operational power lines that extend well beyond the test 

facility, the lines should be terminated in the characteristic impedance of the 

power lines as tested. This avoids inadvertent, unrealistic radiation caused by 

non-typical termination of the power lines. 

• A variety of representative MV power line configurations should be present in 

the test site (or standard BPL test facility). For example, the site should 

include single and three-phase power line segments, sharp turns in the power 

line, and risers that connect overhead lines to underground lines. 

7.10 BPL DEVICE OUTPUT POWER SHOULD BE REDUCED AS 

NEEDED FOR COMPLIANCE WITH RADIATED EMISSION 

LIMITS 

The measurements should be initially conducted while the BPL device is 

operating with maximum power output as required by §15.31(g). This may yield field 

strength values that exceed the limits, in which case the BPL device output power should 

be reduced to the extent necessary to obtain compliance with the limits. Because 

different limits are applied above and below 30 MHz, and because all possible power line 

configurations are not being measured, at most two different BPL output power levels 

may be determined for compliance with the limits (i.e., one above and one below 30 

MHz). 

In the event that an output power reduction is needed to achieve compliance, all 

measurements must be made at the reduced output level including any measurements 

preceding discovery of field strength in excess of the limiting value. 

7.11 THE RESULTS OF RADIATED EMISSION MEASUREMENTS 

 SHOULD BE PROPERLY RECORDED IN MEASUREMENT 

 REPORTS AND APPLIED IN BPL OPERATIONS 

The measurement report should record all measurements including those 

preceding any BPL output power reductions needed for compliance with the field 

strength limits. If a power reduction is needed for compliance, the amount of necessary 

reduction and the means by which it was achieved during testing should be recorded in 

the measurement report. As a condition for authorization, where BPL output power can 

be adjusted, the BPL power control software, firmware and hardware should be modified 

to prevent operation at output power levels higher than those yielding compliance with 

the field strength limits. In other cases where BPL device output power is not adjustable, 
7-8 

inclusion of a fixed attenuator or suitably lower-power output stage should be mandated 

in the authorization. In no case should BPL operators be equipped to exceed output 

power levels at which compliance is obtained. 

7.12 CONCLUSION 

 The Phase 1 analyses assumed that for outdoor overhead power lines, compliance 

measurements were performed using a one-meter high measurement antenna. This ad 

hoc measurement approach does not demonstrate compliance with the field strength 

limits because, as shown by NTIA’s measurements and models (Section 5), peak field 

strength levels are not necessarily centered at the BPL device and do not occur at a height 

of one-meter above the ground. Moreover, all of the receiving antennas assumed in the 

Phase 1 analyses were located at least two meters above the ground. Other potential 

sources of measurement underestimation of BPL field strength include: the measurement 

distance and extrapolation factor; frequency-selective radiation effects; estimation of 

electric fields using a loop antenna; and selection of representative BPL installations for 

testing. Solutions to most of these measurement challenges are at hand within existing 

Part 15 measurement guidelines. 

 In light of the above considerations and the high perceived interference risks, 

NTIA recommends that field strength limits for BPL systems not be relaxed and that 

measurement procedures be refined and clarified as described in this section to better 

ensure compliance. These risk reductions should be effected as quickly as possible in 

order to better protect radio communications. 
8-1 

SECTION 8 

INTERFERENCE PREVENTION AND MITIGATION 

TECHNIQUES 

8.1 INTRODUCTION 

The risk of harmful interference from any kind of radiator can usually be reduced 

through the use of various interference prevention measures, and the risk of sustained 

interference generally can be eliminated through various interference mitigation 

techniques. A number of possible means for the prevention and reduction of BPL 

interference to other services have been proposed and are presented and supplemented 

herein. Further study is needed of the potential effectiveness of these techniques. 

8.2 POWER LEVEL 

The single most effective method for reducing the potential for harmful 

interference from a BPL device may be to reduce the RF power it generates. As the FCC 

notes in §15.15 (c), “...the limits specified in this part will not prevent harmful 

interference under all circumstances. Since the operators of part 15 devices are required 

to cease operation should harmful interference occur to authorized users of the radio 

frequency spectrum, the parties responsible for equipment compliance are encouraged to 

employ the minimum field strength necessary for communications...” The minimum 

signal power necessary for BPL communications will obviously depend upon the system 

configuration used and the specific characteristics of the power line network. In some 

cases, reduction of BPL device output power may reduce data throughput. Throughput 

could be restored to the previous levels in existing BPL deployments by the addition of 

repeaters or in planned new deployments by reducing separation distances between 

devices. Consistent with §15.15(c), BPL systems should use the least power needed to 

carry out power line communications. 

8.3 AVOIDANCE OF LOCALLY USED FREQUENCIES 

Several access BPL systems make use of technology that can enable the avoidance 

of certain frequencies and frequency bands through capabilities for shifting BPL signal 

frequencies or notching or filtering out of BPL signals on those frequencies. Various 

FCC filings have indicated that this type of mitigation technique would not only be 

possible, but in fact has already been implemented to reduce BPL interference issues.61

 

61 PowerComm Reply Comments at 3; Comments of the IEEE Power System Relaying Committee, BPL 

Inquiry, July 1, 2003 at 1; Comments of Ameren Energy Communications Inc., BPL Inquiry, July 7, 2003, 

(“Ameren Comments”), at 9-10. 
8-2 

Another, more advanced method of frequency avoidance would be agile or 

adaptive filtering. Unlike fixed frequency notching, systems with agile frequency 

avoidance would monitor frequency bands and dynamically change their frequency usage 

to avoid radio channels on which strong signals were detected. This is a solution that 

might enable increased, interference-free use of the RF spectrum by BPL systems.62 

However, there is significant concern that such a system, even if it were to work 

instantaneously, would not reduce the interference potential to systems operating in 

duplex mode or local weak-signal reception.63 Interference to these operations may be 

discovered at the same time effective radio communications are needed most. Rather, 

this technique would protect only those radiocommunications using simplex mode and 

originating from a local radio transmitter. 

A more basic form of adaptive filtering should be considered as a requirement. 

Again, it must be recognized that BPL systems may be susceptible to disabling if 

subjected to signals from a powerful, nearby transmitter. To the extent that this 

vulnerability exists, which is a vulnerability commonly found in all kinds of electronic 

systems, BPL systems must inherently avoid operating at frequencies used by powerful, 

local radio transmitters. 

 

8.4 DIFFERENTIAL-MODE SIGNAL INJECTION 

The use of unshielded, twin-lead lines for achieving non-radiating signal 

transmission depends upon differential or balanced line driving (as well as fundamental 

balance in the lines themselves). In this conceptual mode of signal injection, a signal of 

equal magnitude and opposite phase is placed simultaneously on both wires, resulting in 

cancellation of radiation in the far-field. While balanced transmission lines are usually 

constructed with very small wire spacing relative to the wavelength of the signal, 

preliminary NTIA NEC modeling of long wires using power-line dimensions, typical 

loads to neutral lines, and various grounding configurations has shown a decrease of 

several decibels in RF radiation for balanced differential BPL signal injection as opposed 

to non-differential injection. At least one BPL manufacturer, in its comments to the FCC, 

indicated that differential-mode driving should reduce signal radiation as well.64 

It should be noted, however, that inherently unbalanced systems such as power lines 

(due to multiple grounds and transformer taps) will not act as true balanced transmission 

 

62 Some BPL proponents have indicated that during routine installation of BPL devices, existing noise 

sources on power lines will be repaired. See e.g., Ambient Comments at 9; Reply Comments of Southern 

Linc, Southern Telecom, Inc., and Southern Company Services, Inc., BPL Inquiry, August 20, 2003 at 15. 

Thus, it should not be necessary for BPL operators to select frequencies that also avoid relatively high 

noise power that is generated by the power lines themselves. 

63 Reply Comments of Current Technologies, LLC, BPL Inquiry, August 20, 2003, at 15, note 33. 

64 PowerComm Reply Comments at 4. 
8-3 

lines regardless of the method of signal injection. Thus, this method of interference 

mitigation is limited in impact by the power line configuration. 

Further reductions in radiated emissions may be possible using unbalanced driving 

of the unbalanced power and neutral lines, and there may exist ways to couple to all 

power lines in a manner that yields lower radiated emissions while achieving relatively 

high BPL signal currents and throughput. NTIA encourages further investigation of these 

possible solutions by BPL developers as appropriate. 

8.5 FILTERS AND SIGNAL TERMINATIONS 

Typical BPL signals will travel for at least several hundred meters along power 

lines before losses attenuate them to below useable levels. In many cases, conduction of 

BPL signals over these distances is unnecessary, as it means signals may continue far 

past the couplers, repeaters and customers for whom they are intended. Additionally, 

frequency re-use for BPL systems may be an issue for closely-spaced cells that renders 

conduction of BPL signals over extended distances undesirable. 

One way to prevent unnecessary signal conduction is to make use of terminations or 

blocking filters on the transmission line. Since BPL signals are much higher in frequency 

than the 60 Hz power carrier, such terminations might range from the very simple (a large 

ferrite bead placed around the power line) to complex (for example, a system that 

inductively retransmits the signal out-of-phase with the original in a manner that does not 

disrupt BPL signal reception). Ideally, such a filter would absorb, rather than reflect, the 

incoming signal. 

Additionally, the installation of filters on low-voltage distribution wiring before it 

enters a premises could help to prevent in-house interference to radio reception from BPL 

signal leakage. At least one relevant patent on such a filter was recently issued.65 

Although NTIA’s studies were focused on outdoor wiring and Federal Goverment 

radio systems, it should be recognized that in many cases filtering techniques may reduce 

interference to other radio receivers that may be vulnerable to interference from signals 

radiated by indoor LV wiring. 

8.6 IMPLEMENTATION OF A “ONE ACTIVE DEVICE PER 

AREA” RULE 

Several manufacturers have noted that BPL devices in a given area tend to 

transmit one at a time, and their signals therefore do not aggregate.66 Making such a 

 

65 System, device, and method for isolating signaling environments in a power line communication system, 

United States Patent No. 6,590,493, Rasimas, et al., July 8, 2003. 

66 See, for example, Ameren Reply Comments at 13. 
8-4 

configuration standard practice (i.e., only using one power line phase in a given area and 

only one signal injection point per wire) would help to ensure such were the case, at least 

for a local receiver. 

8.7 JUDICIOUS SIGNAL CARRIER CHOICE 

Due to the specific physical and electrical characteristics of a given section of 

power line, it is conceptually possible to find one or more frequency bands at which BPL 

signal radiation is relatively low. Specifically, on a case-by-case basis during installation 

or operation, it is theoretically possible to consistently preclude worst-case radiation 

conditions through avoidance of combinations of certain frequencies and coupler 

placement geometry (relative to power line impedance discontinuities) that yield worstcase radiation. NTIA’s studies have only partially addressed frequency selective 

characteristics of BPL radiation, but work to date indicates that less than 50% of possible 

operating frequencies will exhibit this low-radiation characteristic. 

 To implement this concept, detailed measurements may be needed at every 

installation site to reliably identify frequency and coupler placement combinations that 

should be avoided. It likely would be found that use of a substantial amount of 

bandwidth would be precluded at each segment of a BPL network. NTIA welcomes 

further investigation of this concept by BPL proponents because if practicable, BPL 

devices could operate at higher signal power levels while still complying with field 

strength limits. 

8.8 MAINTENANCE OF A SINGLE POINT OF CONTROL 

 

In order to improve the resolution of actual cases of harmful interference, it would 

be prudent to have one entity in a service area controlling all the devices in that area, as 

well as one contact point for that entity. This contact point should be capable of 

addressing cases of suspected interference and resolving actual harmful interference 

through any and all means available to the BPL provider, without government 

intervention. 

8.9 WEB-BASED ACCESS TO RADIO LICENSE INFORMATION 

Knowing what radio operations are located in their immediate environment 

should facilitate BPL operators in selecting frequencies, power and other technical 

parameters that minimize interference. The FCC and NTIA both maintain databases of 

licensed/authorized radio systems across the radio spectrum, including the 1.7-80 MHz 

frequency range. The possibility of making parts of the NTIA database available to 

appropriate persons via a web-based mechanism will be further investigated by NTIA. 

However, it should be recognized at the outset that such an approach could, at most, be 

only a partial solution due to the nature of such data bases. For example, many frequency 
8-5 

assignments are registered for nationwide use rather than use at a specific location. Also 

numerous uses are not publicly releasable. 

8.10 INSTALLATION AND EQUIPMENT REGISTRATION

By centrally registering their current and planned BPL deployment details in a 

central, publicly accessible data base, BPL operators will have equipped local radio users 

with information they need to alert the BPL operator of potential interference problems. 

Such a registry could assist local radio users in diagnosing suspected interference, which 

in turn may preclude unfounded complaints of BPL interference. Furthermore, in the 

event of actual interference that is believed to originate from a BPL system, the radio user 

could consult the registry to determine the cognizant point of contact with the 

organization of the BPL operator. By keeping potential requirements for filing of an 

interference complaint with the FCC to a minimum, the registry would expedite 

elimination of actual interference should it occur and avoid the buildup of an unfavorable 

track record at the Commission. Unfavorable track records could precipitate further 

Inquiry and Rulemaking actions that, in actual fact, may be unnecessary. NTIA will 

further study and recommend the BPL deployment parameters that should be included in 

the registrations. 

8.11 CONCLUSION

 NTIA suggested several means by which BPL interference can be eliminated; 

some of these and others may be used to reduce the risk of interference. Mandatory 

registration of certain parameters of planned and deployed BPL systems would enable 

radio operators to advise BPL operators of anticipated interference problems and 

suspected actual interference; thus, registration could substantially facilitate prevention 

and mitigation of interference. Consideration should be given to BPL frequency agility 

(notching and/or retuning) and power reduction for elimination of interference. NTIA 

further recommends consideration of the following interference prevention and 

mitigation measures: 

• Routine use of the minimum output power needed from each BPL device; 

• Avoidance of locally used radio frequencies; 

• Differential-mode signal injection oriented to minimize radiation; 

• Use of filters and terminations to extinguish BPL signals on power lines where 

they are not needed; 

• Use of one active device per frequency and area; 

• Judicious choice of BPL signal frequencies to avoid efficient radiation; 

• Maintenance of single points of contact and BPL network control; 

• Use of web-based access to radio license information to avoid locally used radio 

frequencies. 
9-1 

SECTION 9 

SUMMARY OF RESULTS 

9.1 INTRODUCTION 

 Section 9.2 summarizes the results of NTIA’s preliminary investigations (Sections 2 – 5). 

These investigations helped refine the scope and approach of NTIA’s analyses and established 

certain technical assumptions. Section 9.3 summarizes the results of NTIA’s Phase 1 analyses of 

interference risks (Section 6), measurement procedures (Section 7) and techniques for prevention 

and mitigation of interference (Section 8). Section 9.4 summarizes matters requiring further 

study. 

9.2 PRELIMINARY INVESTIGATIONS 

9.2.1 Descriptions of BPL Systems 

NTIA identified three architectures for access BPL networks (Section 2): (1) BPL 

systems using different frequencies on medium- and low-voltage power lines for networking 

within a neighborhood and extensions to users’ premises, respectively; (2) BPL use of only 

medium voltage lines for networking within a neighborhood, with other technologies being used 

for network extensions to users’ premises; and (3) BPL use of the same frequencies on mediumand low-voltage power lines for networking in a neighborhood and extensions to users’ premises. 

Responses of BPL manufacturers and operators to the FCC’s BPL NOI generally indicate that 

BPL systems will operate at or near the Part 15 field strength limits in order to achieve maximum 

throughput and distance separation between BPL devices. NTIA addressed simple BPL 

deployment models in the Phase 1 interference risk analyses (Section 6). Specifically, a single 

BPL device and associated power lines were considered for cases of potential interference to 

ground-based radio receivers and several co-frequency BPL devices were assumed to be 

deployed throughout the area covered by an aircraft receiver antenna. For future studies, NTIA 

developed preliminary BPL deployment models addressing three geographic scales (Appendix 

F): a “neighborhood” deployment model useful for analyses of interference to radio receivers 

having antennas at heights lower than power lines; an “antenna coverage area” model useful for 

consideration of radio antennas atop buildings and towers and on aircraft; and a “regional” 

deployment model for studies of potential interference via ionospheric signal propagation. 

9.2.2 Studies and Relevant Regulations 

 NTIA reviewed studies performed by other parties and applicable FCC and foreign 

regulations to ensure that NTIA’s studies would address important interference mechanisms and 

factors as well as potential means for effectively accommodating BPL and radio systems 

(Section 3). NTIA noted that BPL apparently has been implemented with success in some 

countries, while other countries have postponed implementation of BPL systems until further 

interference studies are being conducted. Still others have withdrawn their approval for 

operation of BPL systems after experiencing interference problems. Several emission limits 

have been adopted or proposed for evaluation on international, national and regional bases. Most 

studies have sought to determine whether interference will occur at the variously proposed limits. 
9-2 

In contrast, NTIA has oriented its study to appropriately manage the risk of interference to radio 

systems. 

 Technical information and analyses submitted in response to the FCC NOI included 

several relevant observations. BPL signals unintentionally radiate from power lines, although 

there is substantial disagreement as to the strength of the emissions and their potential for 

causing interference to licensed radio services. Analyses indicate that the peak field strength due 

to unintentional BPL radiation occurs above the physical horizon of power lines. Current ad hoc 

measurement techniques used in Part 15 compliance tests may significantly underestimate the 

peak field strength generated by BPL systems as a result of using a loop antenna in the near field; 

performing measurements with an antenna situated near ground level (e.g., 1 meter); and 

measuring emissions in the vicinity of BPL devices without also considering emissions from the 

power lines. 

9.2.3 Federal Government Radio Systems and Spectrum Usage 

Frequencies between 1.7 MHz and 80 MHz are allocated to a total of 13 radio services, 

with the Federal Government using most of these radio services to satisfy various mandated 

mission requirements (Section 4). Federal agencies currently have over 59,000 frequency 

assignments in this frequency range. Allocations for the fixed and mobile services accommodate 

communications for homeland security, distress and safety, and other critical functions. These 

communications occupy over one-half of the frequency range and NTIA chose them as the focus 

of this Phase 1 study. Characteristics of fixed and mobile equipment largely group into uses 

below 30 MHz and above 30 MHz and the equipment characteristics show considerable 

consistency within these two categories. 

 Both NTIA and FCC have long recognized that certain frequencies or bands in the radio 

spectrum require special protection from interference because of the critical or sensitive 

functions they support, including distress and safety, radio astronomy, radionavigation, and 

others. NTIA identified forty-one (41) such frequency bands between 1.7 MHz and 80 MHz, 

totaling approximately 4.2 MHz (5.4% of the total spectrum under study), that may warrant 

special protection from interference by licensed and/or unlicensed transmitters. NTIA will 

further review the appropriateness of applying geographic BPL restrictions or other special BPL 

provisions to these and other frequencies that warrant special protection in its Phase 2 study. 

9.2.4 Characterization of BPL Emissions 

Numerous textbooks explain the electromagnetic theory behind wires serving as 

transmission lines or antennas. For unshielded wires such as power lines, the magnitude of 

radiation is largely affected by the degree of balance between radio frequency currents in 

adjacent wires and the spacing of those wires. Common mode currents (traveling in the same 

direction) in parallel wires generally produce mode radiation than differential currents (traveling 

in opposite directions) because for differential currents, the fields generated by each wire tend to 

cancel if the wires are closely spaced (e.g., twisted pair used for telephone lines). Impedance 

discontinuities can occur on power lines at transformers, branches and turns, and can produce 

radiation directly or cause signal reflections in the power lines that produce standing waves and 
9-3 

associated radiation along the line. The fields generated by radio frequency currents have 

different types of spatial distributions in three successively more distant areas around a radiator: 

the reactive- and radiative-near-field and far-field regions. The distances over which reactive 

and radiative near-field regions extend increase with the size of the radiator and frequency. In 

the far field region, which could start several kilometers away from a radiating power line, the 

radiation patterns are independent of distance and field strength in free space generally decreases 

in proportion to increasing distance. 

 The relevant signal propagation modes in the 1.7 – 80 MHz frequency range are ground 

wave, space wave and sky wave. The ground wave signal can consist of a direct wave, ground 

reflected wave and/or a surface wave, each of which exhibit a different characteristic relationship 

between signal loss and distance. The direct wave signal power from a point source (i.e., very 

small in relation to wavelength) is inversely proportional to the square of the distance and when 

combined with a strong ground-reflected wave from a radiator several wavelengths above the 

ground, the composite signal power is inversely proportional to distance to the fourth power. 

The latter high rate of attenuation does not occur for radiators closer to the ground. A surface 

wave propagates close to the ground and exhibits substantially higher rates of attenuation than 

the direct wave. Thus, groundwave propagation is pertinent on BPL signal paths below the 

power line horizon. Space wave propagation involves only a direct wave and occurs over 

elevated signal paths, e.g., on signal paths above the power line horizon. Sky wave propagation 

also occurs above the power line horizon and most consistently at frequencies between 1.7 MHz 

and 30 MHz. Skywave signal paths are represented as rays that are refracted and reflected by the 

ionosphere and can extend to distances of thousands of kilometers depending on the signal 

elevation angle and frequency as well as parameters of the ionosphere that exhibit temporal and 

spatial variability. 

 

 As a part of its study, NTIA modeled an overhead, three-phase Medium Voltage power 

line using the NEC software program. The far field patterns of the electric field indicate that the 

number of local peaks in the radiation pattern increase as the ratio of line length to BPL signal 

wavelength increases. Varying the source and load impedances have a minor effect, although the 

highest radiation was generally associated with the largest impedance mismatch between source 

and load. The far field radiation patterns and radiating near-fields at a height of two meters both 

indicate that BPL signal reflections from impedance discontinuities can generate standing waves 

that cause radiation from power lines. Along the direction of the power lines, the peak field 

strength in the far field occurs above the horizontal plane containing the power lines. In the near 

field, the peak level of the vertical electric field never occurs at the BPL source; instead, multiple 

local peaks occur near and under the power lines. Similarly, the peak horizontally polarized field 

in the direction perpendicular to the power lines never occurs at the BPL source; instead, peaks 

occur at various distances away from the BPL source and power lines. Based on the models 

considered to date, only in the case of the horizontally polarized electric field in the direction 

parallel to the power lines does the peak field occur at the BPL device. NTIA’s modeling 

showed that inclusion of a neutral line with three phase medium voltage wiring tended to 

increase the overall radiation. Thus, models omitting the neutral wire tend to predict lower field 

strength. These modeling results imply that compliance measurements, taken only around a BPL 

device and at heights below the power lines, may significantly underestimate the peak electric 

field. 
9-4 

 NTIA performed measurements at three different BPL deployment sites in order to 

characterize the BPL fundamental emissions. Measurements indicate that the BPL electric field 

does not generally decay monotonically with distance from the BPL source as the measurement 

antenna was positioned near to and moving along the length of the power line. As the 

measurement antenna was moved away from the BPL energized power line, the radiated power 

decreased with increasing distance, but the decrease was not always monotonic and a number of 

local peaks were observed at some locations. In some cases, the BPL signal decayed with 

distance away from the power line at a rate slower than would be predicted by space wave loss 

from a point source. At one measurement location where a large number of BPL devices were 

deployed on multiple three-phase and single-phase MV power lines, appreciable BPL signal 

levels (i.e., at least 5 dB higher than ambient noise) were observed beyond 500 meters from the 

nearest BPL energized power lines. Finally, NTIA’s measurements show that the radiated power 

from the BPL energized power lines was consistently higher when the measurement antenna was 

placed at a greater height (e.g., 10 meter vs. 2 meter). These results indicate a need to refine the 

Part 15 compliance measurement guidelines to ensure that the peak field strength of any 

unintentional BPL emissions is measured. 

9.3 PHASE 1 ANALYSES 

9.3.1 Evaluation of Potential Interference Risks 

 NTIA evaluated interference risks using NEC models for four representative types of 

federal radio stations operating in the fixed and mobile services (Section 6): a land vehicular 

radio; shipborne radio; a fixed or mobile-base station with roof top antenna; and an aircraft radio 

in flight. These risks were gauged from the size of geographic areas in which BPL emissions 

would reduce the ratio of desired radio signal power to ambient noise power by amounts 

associated with moderate and high probabilities of interference (i.e., 3 dB and 10 dB reductions 

in (S/N), respectively). Predicted nationwide, Springtime, median ambient noise power levels 

were assumed and analyses were performed for frequencies of 4 MHz, 15 MHz, 25 MHz and 40 

MHz. Three-phase power lines were modeled as straight American Wire Gauge (AWG) 4/0 

copper wires, 340 meters in length, and horizontally spaced by 60 centimeters. No neutral line 

was included in the model in order to reduce NEC execution time; this benefit was in trade for 

underestimation of field strength by a few dB (Section 5.4.3). The three phase lines were 

assumed to be 8.5 meters above ground having typical electrical characteristics. The BPL device 

was assumed to present a source impedance of 150 Ω, coupled on an outer power line, halfway 

between the ends of the lines. The lines were terminated with 50 Ω loads to emulate an 

impedance discontinuity (e.g., transformer) and on-going power lines with additional loads; 

however, emissions beyond the ends of the lines were not considered because field strength 

levels may be non-typical and radio receivers would more typically be located adjacent to power 

lines. The BPL device output was adjusted to produce emissions at the limits of Part 15 for 

unintentional radiators (Class B above 30 MHz), as generally determined by compliance 

measurement practices extant with the exception that measurement distances were applied with 

respect to the BPL device and power lines rather than only the BPL device. This exception 

generally results in compliance at BPL output power levels lower than output levels that yield 

compliance when distances are measured from the BPL device. For all of these analyses, the 
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frequencies at which the lowest and highest reductions in S/N occur may change for different 

power line configurations. 

The results for the vehicular mobile receiver predict that the received BPL signal power 

near the Earth surface falls off rapidly with distance from the lines. For the two frequencies at 

which the highest BPL signal power levels were received (15 MHz and 25 MHz), signal power 

from one co-frequency BPL system (one device) equaled noise power (3 dB reduction in S/N) at 

50% of the locations within 70 and 75 meters of the power lines. At these same frequencies, 

BPL signals reduced S/N by 10 dB at 50% of locations within 25 and 30 meters of the power 

lines. The distances within which these thresholds were exceeded at 50% of locations were 

modestly smaller at a third frequency (4 MHz) and much smaller at the fourth frequency (40 

MHz). In all land vehicular cases considered, reductions in S/N were less than 3 dB and 10 dB 

beyond 125 meters and 55 meters, respectively. 

The results for the fixed service (or mobile base station) receiver predict that the received 

BPL signal power falls off less rapidly with distance from the power lines than occurred for the 

land vehicle case. For the two frequencies at which the highest BPL signal power levels were 

received, signal power from one co-frequency BPL system (one device) equaled noise power (3 

dB reduction in S/N) at 50% of the locations within 310 and 400 meters of the power lines. At 

these same frequencies, BPL signals reduced S/N by 10 dB at 50% of locations within 175 and 

230 meters of the power lines. In all cases, reductions in S/N were less than 3 dB and 10 dB 

beyond 770 meters and 450 meters, respectively. 

The results for the shipborne receiver predict that the received BPL signal power falls off 

rapidly with distance from the power lines, but less rapidly than for the land vehicle case. For 

the two frequencies at which the highest BPL signal power levels were received, signal power 

from one co-frequency BPL system (one device) equaled noise power (3 dB reduction in S/N) at 

50% of the locations within 100 meters of the power lines. At these same frequencies, BPL 

signals reduced S/N by 10 dB at 50% of locations within 55 meters of the power lines. In all 

cases, reductions in S/N were less than 3 dB and 10 dB beyond 135 meters and 85 meters, 

respectively. 

 For the aircraft receiver, aggregate interference effects were considered for 

simultaneously active, co-frequency BPL systems deployed at a density of one per square 

kilometer over an area having a 10 kilometers radius. The power lines were assumed to be 

randomly oriented and an average of the power line far-field gain levels were used in each 

direction under consideration. Aircraft were assumed to be operating at altitudes of 6 to 12 km at 

locations ranging from 0 to 50 kilometers from the center of the BPL deployment area. Results 

showed that aggregate interference levels to the aircraft could exceed average ambient RF noise 

levels at two frequencies (15 MHz and 25 MHz), at distances ranging from 33 kilometers (6 

kilometers altitude) to over 50 kilometers (altitudes between 6 and 12 kilometers). The S/N 

reduction exceeded 10 dB at only one frequency, at 6 kilometers altitude within 12 kilometers of 

the center of the BPL deployment area. At the two frequencies where the assumed BPL systems 

produced the lowest interfering signal power levels (i.e., 4 MHz and 40 MHz), S/N reductions 

peaked at about 0.8 dB and 0.3 dB directly over the center of the BPL deployment area. Higher 
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or lower densities of active co-frequency BPL units would raise or lower the predicted 

interference levels in direct proportion to the unit density. 

9.3.2 Risk Reduction Through Compliance Measurement Procedures 

 The Phase 1 analyses assumed that for outdoor overhead power lines, compliance 

measurements were performed using a one-meter high measurement antenna (Section 7). This 

ad hoc measurement approach does not demonstrate compliance with the field strength limits 

because, as shown by NTIA’s measurements and models (Section 5), peak field strength levels 

are not necessarily centered at the BPL device and do not occur at a height of 1-meter above the 

ground. Moreover, all of the receiving antennas assumed in the Phase 1 analyses were located at 

least 2 meters above the ground. Other potential sources of measurement underestimation of 

BPL field strength include: the measurement distance and extrapolation factor; frequencyselective radiation effects; estimation of electric fields using a loop antenna; and selection of 

representative BPL installations for testing. Solutions to most of these measurement challenges 

are at hand within existing Part 15 measurement guidelines. 

 In light of the above considerations and the high perceived interference risks, NTIA 

recommends that the FCC not relax field strength limits for BPL systems and that measurement 

procedures be refined and clarified to better ensure compliance. These recommendations should 

be effected as quickly as possible in order to better protect radio communications. Specifically, 

NTIA recommends the following BPL compliance measurement provisions. 

(a) Consistent with §15.31(f), (h), (j) and (k), BPL measurements should address the BPL 

devices and power lines to which they are connected. Measurement reports submitted by

contractors hired by BPL proponents to test compliance of trial BPL systems with Part 15 

field strength limits showed that measurements were performed on radials emanating 

from a power line pole to which a BPL access device was mounted. 

(b) BPL systems should be tested in situ using the maximum potential frequency reuse in 

accordance with §15.31(h) and (i). 

(c) Measurement antenna heights should address all directions of BPL signal radiation 

toward potential local radio antennas. NTIA's work to date indicates that a measurement 

antenna height of the order of the power line height may properly protect radio receivers 

having antennas at rooftop heights. In any case, measurements must identify the peak 

level of electric field strength consistent with §15.31(f)(5). 

(d) A ten (10) meter measurement distance should be used uniformly with respect to the 

BPL devices and power lines to which they are connected. A uniform measurement 

distance will greatly simplify compliance measurements. 

 

(e) A modified distance extrapolation factor should be applied for BPL systems that 

reflect realistic decay in field strength with increasing distance. The extrapolation factors 

assumed in Part 15 appear to be unrealistic for BPL systems (40 dB/decade and 20 
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dB/decade below and above 30 MHz, respectively (§§15.31(f)(1) and (2)). Further study 

is needed to determine the appropriate extrapolation factors. 

(f) Radiated emissions must be measured with the BPL devices operating at all 

frequencies at which they are capable of operating. This will require sequential tuning 

and measurements in each abutting frequency band within the tuning range of the BPL 

devices. Measurement with the BPL devices tuned to each possible operating frequency 

is required for consistency with §15.31(g). 

(g) Measurements below 30 MHz should be made with either a calibrated rod antenna 

(direct measurement of electric field) or a loop antenna in connection with adjustment 

factors that properly account for the ratio of BPL near-field electric and magnetic field 

strengths for vertical, horizontal-parallel, and horizontal-perpendicular polarization. 

NTIA's work to date indicates that in the near-field of BPL emissions, this ratio may 

differ significantly from the 377 Ω far-field value assumed in Part 15 for other devices. 

(h) Consistent with §15.31(d), power lines used for in situ testing of BPL devices should 

be carefully selected to be representative of deployments that produce the highest levels 

of field strength. Further study is needed of the power line features that should be 

included. 

(i) In the course of measurements, if it is determined that BPL device output power must 

be reduced in order to obtain compliance with field strength limits, the measurements 

preceding this discovery should be included in the measurement report and measurements 

should be repeated with the lower required output power. As required under §15.15(b), 

the equipment to be marketed should be constructed to prevent operation at field strength 

levels exceeding the limiting values. 

9.3.3 Techniques for Prevention and Mitigation of Interference 

 NTIA identified a number of currently employed techniques and other potential means to 

reduce the interference risks or facilitate mitigation of interference problems (Section 8): 

Minimize Power Level. The single most effective method for reducing the potential for 

interference may be to reduce BPL device output power. Consistent with §15.15(c), BPL system 

operators are encouraged to use the least power needed to carry out power line communications. 

The use of adaptive transmitter power control could be used to ensure that the furthest subscriber 

in the line has an adequate but not excessive conducted signal level. 

Avoidance of Locally Used Frequencies. Shifting or notching BPL signal frequencies to avoid 

interference to local radio receivers may be an effective interference prevention or mitigation 

technique. More advanced methods would include agile or adaptive filtering in real time, which 

may be very effective in reducing interference to simplex-mode communications originating in 

the local environment. These adaptive techniques are not expected to be effective in reducing 

interference to duplex-mode communications or simplex communications originating outside the 

local area, where the associated radio transmitter may be tens, hundreds, or even thousands of 
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miles away. NTIA further recommends consideration of excluding BPL use of certain narrow 

frequency bands, but further study is needed to determine whether these exclusions can be 

specified on a geographical basis. Generally, BPL systems should not operate in certain 

frequency bands in order to protect distress, alarm, urgency or safety communications in 

accordance with ITU Radio Regulations (RR No. 4.22). 

Differential-mode Signal Injection. Use of differential-mode injection of the RF signal onto 

two parallel power lines could potentially reduce radiated BPL emissions in a manner similar to 

unshielded twin-lead transmission lines used in communications systems. The generallyunbalanced nature of power line pairs will limit the effectiveness of this technique. 

Filters and Signal Terminations. The use of filters on the power lines that would absorb, rather 

than reflect, RF signals at impedance discontinuities or termination points beyond the last 

subscriber on the line could reduce unnecessary RF emissions from BPL energized power lines. 

Further, the use of absorbing filters on LV lines to prevent RF signals from entering the premises 

of non-subscribers may mitigate certain interference problems. 

Implementation of a “One Active Device per Frequency and Area” Rule. Several 

implementations of BPL systems use a technique whereby only one device in a local “cell” is 

active on the same frequency at any one time. Such techniques would reduce or eliminate the 

chance of any potential local, ground level aggregate BPL interference effects. However, in 

order to increase BPL network capacity or decrease network latency in a given area, it may be 

desirable to operate independent, co-frequency BPL devices on two or three phases of the same 

run of three-phase power lines. In any case, compliance measurements are to address radiated 

field strength due to all BPL devices operating co-frequency within the BPL network in 

accordance with §15.31(k). 

Judicious Signal Carrier Choice. Due to the frequency selectivity potentially established by 

various physical and electrical characteristics of a given section of power line, it is conceptually 

possible to identify frequency segments within the range 1.7-80 MHz that would allow higher 

levels of injected signal yet at the same time exhibiting lower radiation levels. 

Maintenance of a Single Point of Control. To facilitate rapid resolution of actual cases of 

interference without third-party intervention, a single point of control should be employed for 

each BPL service area and a BPL point of contact should be designated to address cases of 

suspected interference and resolving actual interference. 

Web-based Access to Radio License Information. Knowledge of what licensed radio systems 

may be located in the local environment of a BPL system could assist BPL operators in selecting 

frequency, power levels, and other technical parameters that minimize interference. NTIA will 

further investigate which elements, if any, of the federal frequency assignment data base might 

be made available via a web-based mechanism. The FCC assignment data base already is 

publicly available. 

BPL Installation and Equipment Registration. By registering their current and planned BPL 

deployment details in a central, publicly accessible data base, BPL operators will have equipped 
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local radio users with information they need to alert the BPL operator of potential interference 

problems. The database also could assist radio operators in diagnosing cases of suspected 

interference. NTIA will further study and recommend the BPL deployment parameters that 

should be included in the registration database. 

9.4 TOPICS FOR FURTHER STUDY 

(a) The appropriate measurement antenna height and need for a height-adjustment factor 

should be determined with a goal of identifying the minimum set of measurements that 

will ensure identification of peak BPL emissions in important directions of radiation. 

(b) Measurement distance extrapolation factors reflecting the realistic decay of BPL field 

strength with increasing distance should be determined. 

(c) To enable suitable estimation of electric field strength using a loop antenna below 30 

MHz, the appropriate ratio of electric to magnetic field strength should be determined for 

the recommended ten (10) meter measurement distance and measurement antenna 

heights. 

 (d) Quasi-peak to rms conversion factors should be further investigated for BPL systems. 

This will ensure that the levels due to a radiated BPL signal and noise can be specified in 

consistent terms for analysis purposes. 

 (e) Aggregation of emissions from BPL systems via ionospheric propagation and the 

associated BPL deployment models require further study. This is of concern in the longterm insofar as skyward emissions from many hundreds of BPL systems deployed over a 

large region might produce significant composite interfering signal levels at a very distant 

receiver. 

(f) The local interference risk reductions obtained from the proposed compliance 

measurement guidelines (Section 9.3.2 and item (a), above) should be determined to 

ensure that BPL systems will neither be unnecessarily constrained or pose unacceptably 

high interference risks. 

(g) Possibilities for issuing specific guidance on local Federal Government and other 

frequency usage should be explored in order to enable interference to be prevented. For 

example, special current versions of NTIA and FCC frequency assignment databases 

might be made available via a web site. 

(h) Potential new requirements should be identified for more frequent testing of Federal 

Government radio systems used for backup or emergency purposes in the vicinity of BPL 

systems.