**TECHNICAL APPENDIX**

**TO THE NTIA COMMENTS ON THE BPL NPRM**

**EXECUTIVE SUMMARY**

In response to the Federal Communication Commission's BPL Notice of
Proposed Rulemaking (NPRM), NTIA's Phase 1 study of Broadband over Power
Line (BPL) systems summarized Federal Government usage of the 1.7 -- 80
MHz frequency range, presented measurement and modeling results for BPL
emissions, defined interference risks to radio reception in the
immediate vicinity of overhead power lines used by Access BPL systems,
suggested refinements to measurement guidelines applicable to BPL
systems, and identified means for mitigating local interference should
it occur.[^1] NTIA identified a number of issues requiring further study
during its Phase 2 investigation of BPL. A number of these issues are
addressed in this technical appendix to NTIA's comments on the BPL NPRM:
the recommended antenna height for measuring emission levels; an
appropriate height correction factor for use with measurements performed
at a height of 1 meter; where to measure emissions relative to the BPL
device and the attached power lines; and the aggregation of BPL
emissions via ionospheric propagation.

Numerical Electromagnetic Code (NEC) models of a variety of power line
models show a substantial variability in the height at which the peak
field strength occurs. This variability can be seen over frequency and
power line topology. In all cases where the operating frequency is above
6 MHz, the peak field strength occurred at heights greater than 1 meter.
Analysis of the difference between peak field strength at any height and
the peak field strength at 1 meter, or "height correction factor,"
showed that 80% of the values are less than 4 to 6 dB. In light of these
results, NTIA recommends that measurements be performed at a height of 1
meter and a height correction factor of 5 dB be applied.

NTIA found from the NEC power line models that the locations all along
the length of the power line where the field strength is at its peak,
both at heights of 1 meter and overall, vary widely. For any given power
line configuration, at some frequencies the peak occurs adjacent to or
near the BPL device, while at other frequencies the peak occurs at
substantial distances from the BPL device at an impedance discontinuity.
There are also many frequencies where the field strength peaks at
various distances along the power line. Thus, NTIA recommends that field
strength measurements be performed at a 10 meter horizontal distance
from an Access BPL power line, at points all along key segments of the
power line where the maximum field strength from BPL emissions is
expected to occur. In its ongoing Phase 2 study, NTIA will continue to
investigate emissions along the power lines and recommend criteria for
choosing representative segments of power lines to measure.

NTIA's worst-case oriented analysis of ionospheric propagation and
aggregation of emissions from Access BPL systems indicates that
interference via this mechanism will not occur in the near term.
Considering realistically dispersed deployments of BPL systems, it would
take hundreds of thousands of Access BPL devices operating under
existing rules to cause a 1 dB increase in median noise. Under NTIA's
recommended rule elements, chiefly the 5 dB height correction factor and
power control, it would take millions of BPL devices to increase the
median noise by 1 dB. NTIA will continue to analyze the long-term
potential for interference due to aggregation via ionospheric
propagation in its ongoing Phase 2 study.

In its Phase 1 study, NTIA analyzed the interference risks in terms of
geographic locations where interference may occur to representative
federal radio receivers due to outdoor, overhead Access BPL systems
conforming to Part 15 rules for Class B digital devices above 30
MHz.[^2] NTIA extended the interference risk analysis to include
operation at Class A emissions limits above 30 MHz. Relative to
operation under the Class B limit, the results for Class A show an
increase of approximately 40 -- 50% in the distances at which receiver
operation at a given percentage of locations would experience a given
noise floor increase. NTIA evaluated the effectiveness of its
recommendations for a measurement height correction factor and found
that it only slightly reduces interference risks for nearby land-mobile
receivers. After applying the height correction factor, most locations
within 15 meters of an Access BPL power line will experience a noise
floor increase of 10 dB or more at operating frequencies between 1.7 MHz
and 30 MHz. To further protect land-mobile operations, other risk
reduction techniques should be employed, such as power control and
avoidance of use of mobile service frequencies in physically adjacent
Access BPL network elements. NTIA will further investigate these
recommendations in its ongoing Phase 2 study.

NTIA will continue to investigate these and other issues identified in
its Phase 1 report as requiring further study.[^3] These include:
determination of the equivalent field strength limits for the FCC's
proposed ten meter measurement distance that reflects realistic decay of
BPL signal strength with distance; the ratio of electric field to
magnetic field below 30 MHz for suitable estimation of the electric
field with a loop antenna in the near field; the protection requirements
for sensitive or critical frequencies used by the Federal Government;
and extending the interference risk analysis to include any resulting
recommendations to enhance the Commission's Part 15 rules applicable to
BPL systems.

**TABLE OF CONTENTS**

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

  **VOLUME I**                                                                                                                                        

                                                                                                                                                      

  EXECUTIVE SUMMARY                                                                                                                                   ii
  ............................................................\...\.....                                                                              

  TABLE OF CONTENTS                                                                                                                                   iv
  ...............................................................\...\....                                                                            

                                                                                                                                                      

  SECTION 1                                                                  INTRODUCTION                                                             

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

  1.2                                                                        Objectives                                                               1-2
                                                                             ............................................................\.....       

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

                                                                                                                                                      

  SECTION 2                                                                  ANALYSIS OF MEASUREMENT ANTENNA HEIGHT                                   

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

  2.2                                                                        Power Line Models                                                        2-1
                                                                             ....................................\...\...\...\...\...\...\.....       

  2.3                                                                        Height Corresponding to Peak Field Strength ......\..................    2-4

  2.4                                                                        Antenna Measurement Height Correction Factor ...................         2-18

  2.5                                                                        Conclusion                                                               2-28
                                                                             .........................................................\...\.....      

                                                                                                                                                      

  SECTION 3                                                                  MEASUREMENT DISTANCE ALONG POWER LINE AWAY FROM BPL DEVICES              

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

  3.2                                                                        Methodology                                                              3-1
                                                                             .........................................................\.....          

  3.3                                                                        Results                                                                  3-1
                                                                             .....................................................................    

  3.4                                                                        Conclusion                                                               3-11
                                                                             ...............................................................          

                                                                                                                                                      

  SECTION 4                                                                  IONOSPHERIC PROPAGATION OF BPL SIGNALS                                   

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

  4.2                                                                        Analytical Modeling of Skywave Propagation ..................\...        4-1

  4.3                                                                        Results                                                                  4-3
                                                                             ......\...............................................................   

  4.4                                                                        Conclusion                                                               4-4
                                                                             ...............................................................          

                                                                                                                                                      

  SECTION 5                                                                  INTERFERENCE RISK ANALYSIS                                               

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

  5.2                                                                        BPL Operations at Current Part 15 Rules Above 30 MHz \.........          5-1

  5.3                                                                        Antenna Height Correction Factor Applied to the Land-Mobile Receiver     5-5
                                                                             Case ...................................................\...\...\...\... 

  5.4                                                                        Conclusion                                                               5-5
                                                                             ...............................................................          

                                                                                                                                                      

                                                                                                                                                      

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

**SECTION 1**

**INTRODUCTION**

1.  **BACKGROUND**

NTIA's Phase 1 study of Broadband over Power Line (BPL) systems
summarized Federal Government use of the 1.7 -- 80 MHz frequency range,
presented measurement and modeling results for BPL emissions, defined
interference risks to radio reception in the immediate vicinity of
overhead power lines used by Access BPL systems, suggested refinements
to Part 15 measurement guidelines applicable to BPL systems, and
identified means for mitigating local interference should it occur.
Propagation and aggregation of emissions from BPL systems and the
associated BPL deployment models were suggested as issues requiring
further study.

Critical review of the assumptions underlying the BPL interference risk
analyses revealed that compliance measurement procedures rather than
field strength limits are the leading cause of high perceived
interference risks. As applied in current practice to BPL systems, Part
15 measurement guidelines do not fully address certain unique
characteristics of BPL radiated emissions. NTIA recommended the
following supplemental BPL compliance measurement guidelines that derive
from existing Part 15 measurement guidelines:

-   Measurement of emissions from both the BPL devices and power lines
    to which they are attached.

-   Measurement of BPL systems exhibiting the maximum potential
    frequency reuse.

-   Use of measurement antenna heights at or above the height of power
    lines, possibly in connection with an adjustment factor accounting
    for field strength levels at other heights.

-   Measurement at a distance of ten meters from the BPL device and
    power lines.

-   Application of a distance extrapolation factor that reflects the
    radiation characteristics of BPL systems.

-   Measurement of emissions with the BPL devices variously tuned to all
    frequencies at which it is capable of operating.

-   Below 30 MHz, measurement using a calibrated rod antenna or a loop
    antenna in connection with appropriate factors relating magnetic and
    electric field strength levels.

-   Careful selection of representative BPL installations that produce
    the highest levels of radiated emissions.

-   Controls available to the operator must not be capable of causing
    generation of field strength in excess of the limiting values.

NTIA suggested in its Phase 1 report to further study the effectiveness
of these recommended supplemental measurement guidelines.

1.  **OBJECTIVE**

The objectives of this technical appendix are to offer specific
recommendations to enhance Part 15 measurement guidelines applicable to
Access BPL systems, to expand upon the interference risk analysis
provided in NTIA's Phase 1 study report to include an assessment of the
effectiveness of NTIA's recommended height correction factor, and to
evaluate the potential impact on federal radiocommunications due to
ionospheric propagation and aggregation of BPL emissions.

2.  **APPROACH**

NTIA analyzed BPL field strength to determine the measurement height
corresponding to the peak field strength and a reasonable height
correction factor to employ when conducting measurements at the current
Part 15 measurement height guideline of 1 meter (Section 2). NTIA also
analyzed the locations corresponding to peak field strength along the
power line in response to the Commission's proposal in the BPL NPRM to
perform measurements only at specific locations (Section 3).[^4] NTIA
evaluated BPL signal aggregation and ionospheric propagation to provide
initial worst-case estimates of the potential increase in noise (Section
4). The interference risk analysis from NTIA's Phase 1 study was
expanded to include operation employing current Part 15 Class A digital
device emission limits for frequencies above 30 MHz and the risk
reduction from NTIA's recommended measurement height correction factor
(Section 5).

**SECTION 2**

**ANALYSIS OF MEASUREMENT ANTENNA HEIGHT**

1.  **INTRODUCTION**

Most federal radio receiver antennas are located at heights above 2
meters. The limited measurements from the Phase 1 study indicated that
the level of radiated emissions was greater at the height of the power
lines than at a 1 meter height. In NTIA's Phase 1 study, preliminary NEC
modeling yielded similar results, leading to a recommendation to measure
BPL emissions with an antenna situated near the height of the power
lines. As an alternative, NTIA recommended that measurements performed
at a height of 1 meter include a correction factor to account for the
greater field strength at greater heights.

2.  **POWER LINE MODELS**

A number of power line models were created using the NEC software to
gain a greater understanding of the effects various physical topologies
might have on the electric fields radiated by BPL signals on power
lines. The electric field strength results in any polarization, over a
range of heights and at any position along the length of the power line
model were then evaluated statistically.

NTIA evaluated nineteen different power line topologies to calculate
three-axis electric field values in a vertical grid located 10 meters
from the power line (FCC-proposed measurement distance in the BPL NPRM),
at heights ranging from 1 to 20 meters in one meter increments. These
calculations were made horizontally along the length of the modeled
power lines in one-meter increments, and at frequencies from 2 to 50 MHz
(in 2 MHz increments). Eighteen relatively simple power line topologies
are listed in Table 2-1. The orientation of power line conductors for
these topologies is depicted in Figure 2-1.

Table 2-1: Power line topologies used to model antenna measurement
height

+-------+--------+---------------------+----------------+------------+
| Model | Number | Wire                | Multi-grounded | Wire       |
| Name  | of     |                     | neutral with 3 |            |
|       | Wires  | Configuration       | transformers   | Spacing    |
+=======+========+=====================+================+============+
| tri26 | 2      | tr                  | not included   | 0.6 meters |
|       |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| t     | 2      | tr                  | not included   | 1.0 meters |
| ri210 |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| tri36 | 3      | tr                  | not included   | 0.6 meters |
|       |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| t     | 3      | tr                  | not included   | 1.0 meters |
| ri310 |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| t     | 2      | tr                  | included       | 0.6 meters |
| ri26n |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| tr    | 2      | tr                  | included       | 1.0 meters |
| i210n |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| t     | 3      | tr                  | included       | 0.6 meters |
| ri36n |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| tr    | 3      | tr                  | included       | 1.0 meters |
| i310n |        | iangular-horizontal |                |            |
+-------+--------+---------------------+----------------+------------+
| ver1  | 1      | vertical            | not included   | n/a        |
+-------+--------+---------------------+----------------+------------+
| ver26 | 2      | vertical            | not included   | 0.6 meters |
+-------+--------+---------------------+----------------+------------+
| v     | 2      | vertical            | not included   | 1.0 meters |
| er210 |        |                     |                |            |
+-------+--------+---------------------+----------------+------------+
| ver36 | 3      | vertical            | not included   | 0.6 meters |
+-------+--------+---------------------+----------------+------------+
| v     | 3      | vertical            | not included   | 1.0 meters |
| er310 |        |                     |                |            |
+-------+--------+---------------------+----------------+------------+
| ver1n | 1      | vertical            | included       | n/a        |
+-------+--------+---------------------+----------------+------------+
| v     | 2      | vertical            | included       | 0.6 meters |
| er26n |        |                     |                |            |
+-------+--------+---------------------+----------------+------------+
| ve    | 2      | vertical            | included       | 1.0 meters |
| r210n |        |                     |                |            |
+-------+--------+---------------------+----------------+------------+
| v     | 3      | vertical            | included       | 0.6 meters |
| er36n |        |                     |                |            |
+-------+--------+---------------------+----------------+------------+
| ve    | 3      | vertical            | included       | 1.0 meters |
| r310n |        |                     |                |            |
+-------+--------+---------------------+----------------+------------+

![](media/image1.png){width="4.614583333333333in"
height="3.7604166666666665in"}

**Figure 2-1: Power line topologies**

All modeled power lines were 340 meters in length, and consisted of
eight segments of catenary (hanging) wires (with catenary lengths of 43
meters each) between nine utility poles. The models were fed on a
segment next to the model axis on one of the outside wires. All wires
were assumed to be copper, and all models with neutral wires included
three simulated distribution transformers wired between one of the
phases and neutral, with 7.7 of real impedance.[^5] On the models with a
neutral wire, the neutral was connected to ground at each transformer
point (in the center of the model and at each end).

Vertical-alignment models were designed such that all wires (including
the neutral, if any) were arranged in a vertical line.
Triangular-horizontal models with three wires were designed with the
middle wire 0.25 meter higher than the outer two. The neutral wire (if
one was included) was centered under the phase wires.

NTIA also constructed an extensive NEC model based upon an actual MV
distribution branch in one of the BPL deployment areas where NTIA
conducted field measurements. This model was designed using power line
maps as well as actual observation (Figure 2-2).

![](media/image2.png){width="5.708333333333333in"
height="3.9791666666666665in"}

**Figure 2-2: NEC model of actual power line carrying BPL signals**

The model consisted of three-phase and multi-grounded neutral wiring.
Included in the model are "risers" (connections of all three phases to
underground wiring having a characteristic impedance of 30), wire
intersections, transformers and neutral grounds. Along most of the power
line, the wiring topology is vertical, but at one pole (at a riser) it
shifts to a horizontal-triangular configuration and then back to
vertical.

The model covered an area of some 240,000 square meters (600m 400m), and
was designed (segmented and tested) at 4.303 MHz, 8.192 MHz, 22.957 MHz
and 28.298 MHz (frequencies which corresponded with measurement
frequencies in the field).

3.  **HEIGHT CORRESPONDING TO PEAK FIELD STRENGTH**

Figures 2-3 through 2-20 show the heights where the peak electric field
strength occurred over the frequency range of 2 -- 50 MHz for the
various power line topologies described in Section 2.2.

> ![](media/image3.wmf){width="5.996527777777778in" height="3.65in"}

**Figure 2-3: Height corresponding to peak field strength, vs. frequency
-- tri36 topology**

![](media/image4.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-4: Height corresponding to peak field
strength, vs. frequency -- tri36n topology**

![](media/image5.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-5: Height corresponding to peak field
strength, vs. frequency -- tri310 topology**

![](media/image6.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-6: Height corresponding to peak field
strength, vs. frequency -- tri310n topology**

![](media/image7.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-7: Height corresponding to peak field
strength, vs. frequency -- ver36 topology**

![](media/image8.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-8: Height corresponding to peak field
strength, vs. frequency -- ver36n topology**

![](media/image9.wmf)**Figure 2-9: Height corresponding to peak field
strength, vs. frequency -- ver310 topology**

![](media/image10.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-10: Height corresponding to peak field
strength, vs. frequency -- ver310n topology**

![](media/image11.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-11: Height corresponding to peak field
strength, vs. frequency -- tri26 topology**

![](media/image12.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-12: Height corresponding to peak field
strength, vs. frequency -- tri26n topology**

![](media/image13.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-13: Height corresponding to peak field
strength, vs. frequency -- tri210 topology**

![](media/image14.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-14: Height corresponding to peak field
strength, vs. frequency -- tri210n topology**

![](media/image15.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-15: Height corresponding to peak field
strength, vs. frequency -- ver26 topology**

![](media/image16.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-16: Height corresponding to peak field
strength, vs. frequency -- ver26n topology**

![](media/image17.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-17: Height corresponding to peak field
strength, vs. frequency -- ver210 topology**

![](media/image18.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-18: Height corresponding to peak field
strength, vs. frequency -- ver210n topology**

![](media/image19.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-19: Height corresponding to peak field
strength, vs. frequency -- ver1 topology**

![](media/image20.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-20: Height corresponding to peak field
strength, vs. frequency -- ver1n topology**

For the model based upon an actual Access BPL power line structure
(Figure 2-2), electric field simulations were performed at heights of 1
meter and 2 to 20 meters (in two-meter increments) for the entire area
adjacent to the power line structure. The latter simulation was
completed using NEC's "Near Field Along a Line" command ("LE"), which
calculates electric fields for vectors along and perpendicular to a
line. This more accurately depicts real-world measurement conditions in
which measurements would be taken along these vectors. Figures 2-21
through 2-23 illustrate the variation in field strength in all three
polarizations at 1 meter and at the height of the power lines (12
meters). Figure 2-24 shows the height corresponding to the peak field
strength in any polarization at ten meters from the power line, for the
four frequencies evaluated with this model.

![](media/image21.jpeg){width="5.370138888888889in"
height="4.027777777777778in"}

![](media/image22.jpeg){width="5.370138888888889in"
height="4.027777777777778in"}

**Figure 2-21: X-axis electric field values surrounding power line
structure at 28.298 MHz. Top: 1 meter height. Bottom: 12 meter height.
Axis values in meters; relative electric field values in dB.**

![](media/image23.jpeg){width="5.370138888888889in"
height="4.027777777777778in"}

![](media/image24.jpeg){width="5.370138888888889in"
height="4.027777777777778in"}**Figure 2-22: Y-axis electric field values
surrounding power line structure at 28.298 MHz. Top: 1 meter height.
Bottom: 12 meter height.**

![](media/image25.jpeg){width="5.370138888888889in"
height="4.027777777777778in"}

![](media/image26.jpeg){width="5.370138888888889in"
height="4.027777777777778in"}**Figure 2-23: Z-axis electric field values
surrounding power line structure at 28.298 MHz. Top: 1 meter height.
Bottom: 12 meter height.**

> ![](media/image27.wmf){width="5.490277777777778in"
> height="3.107638888888889in"}**Figure 2-24: Height corresponding to
> peak field strength, vs. frequency for the power line model shown in
> Figure 2-2.**

4.  **ANTENNA MEASUREMENT HEIGHT CORRECTION FACTOR**

NTIA has found through measurements and simulations that existing Part
15 compliance measurements performed at an antenna height of 1 meter
will likely underestimate the overall peak electric field strength of
BPL emissions. Determination of peak field strength over all heights for
Part 15 compliance measurement purposes can be accomplished either
through direct measurement at various heights and directions, or by
application of a correction factor to measurements made with a standard
1 meter antenna height. NTIA evaluated the above power line
configurations using the NEC software to determine a suitable height
correction factor when field strength measurements are performed at a 1
meter height.

Calculations of peak field strength *vs.* height for the eighteen simple
power line models described earlier are shown in Figures 2-25 through
2-42. The peak electric field strength at each height was determined
from the 80^th^ percentile values of field strength along the length of
the power line. The 80^th^ percentile values eliminate the localized
peaks that are unlikely to be encountered by a radio receiver randomly
located in close proximity to an Access BPL power line. Use of the
80^th^ percentile value is consistent with international measurement
standards that seek 80% compliance with an 80% degree of confidence.[^6]

![](media/image28.wmf){width="5.996527777777778in"
height="3.6597222222222223in"}**Figure 2-25: Difference between peak
field strength at any height and the peak field strength at 1 meter,
based on 80^th^ percentile values; tri36 power line topology**

**Figure 2-26: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image29.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; tri36n power line topology**

**Figure 2-27: Difference between peak field strength at any height and
the peak field strength at 1**
![](media/image30.wmf){width="5.996527777777778in"
height="3.65in"}**meter, based on 80^th^ percentile values; tri310 power
line topology**

![](media/image31.wmf){width="5.996527777777778in" height="3.65in"}

**Figure 2-28: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on 80^th^ percentile values;
tri310n power line topology**

![](media/image32.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-29: Difference between peak field strength at
any height and the peak field strength at 1 meter, based on 80^th^
percentile values; ver36 power line topology**

![](media/image33.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-30: Difference between peak field strength at
any height and the peak field strength at 1 meter, based on 80^th^
percentile values; ver36n power line topology**

![](media/image34.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-31: Difference between peak field strength at
any height and the peak field strength at 1 meter, based on 80^th^
percentile values; ver310 power line topology**

![](media/image35.wmf){width="5.996527777777778in" height="3.65in"}

**Figure 2-32: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on 80^th^ percentile values;
ver310n power line topology**

**Figure 2-33: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image36.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; tri26 power line topology**

**Figure 2-34: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image37.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; tri26n power line topology**

**Figure 2-35: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image38.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; tri210 power line topology**

**Figure 2-36: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image39.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; tri210n power line topology**

**Figure 2-37: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image40.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; ver26 power line topology**

**Figure 2-38: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image41.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; ver26n power line topology**

**Figure 2-39: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image42.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; ver210 power line topology**

**Figure 2-40: Difference between peak field strength at any height and
the peak field strength at 1 meter, based on
80^th^**![](media/image43.wmf){width="5.996527777777778in"
height="3.65in"} **percentile values; ver210n power line topology**

![](media/image44.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-41: Difference between peak field strength at
any height and the peak field strength at 1 meter, based on 80^th^
percentile values; ver1 power line topology**

![](media/image45.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 2-42: Difference between peak field strength at
any height and the peak field strength at 1 meter, based on 80^th^
percentile values; ver1n power line topology**

5.  **CONCLUSION**

The figures in Section 2.3 show substantial variability of the height at
which the peak field strength occurs. This variability can be seen over
frequency and power line topology. In all cases where the operating
frequency is above 6 MHz, the peak field strength occurred at heights
greater than 1 meter. Below 6 MHz, the wavelengths are greater than four
times the modeled power line height (12 meters) and under such
conditions, it is expected that increased in-phase coupling between the
power line and ground will lead to the highest values of electric field
at or near ground level as explained below.

A long wire radiator is linearly polarized in the plane formed by the
wire and the radial vector from the center of the wire to the
observation point. Therefore, the direction of the linear polarization
changes from point to point. Near ground, the polarization is almost
vertical, especially when the height of the wire is small compared to
wavelength. This is evident from graphical depiction of the vertical
electric field in Figure 2-17 (p. 2-14) and comparison of this field
with the two horizontal fields at 1 meter, as shown in Figures 2-15 and
2-16 (p. 2-12 and p. 2-13).

The figures illustrating the height for peak field strength, and the
difference between the overall peak field strength and the peak at 1
meter show variability over the frequency range and also show
variability from one power line structure to the next. One reason for
this is that the ratio of the measurement height to wavelength changes
and another reason is that all calculations are performed at a distance
of 10 meters from the BPL energized power line. The figures in Section
2.4 show that the difference between peak field strength at any height
and the peak field strength at 1 meter tends to range from about 4 to 6
dB.

Calculations for the real-world power line model (*see* Figure 2-2)
produced results in substantial agreement with these findings. This
model consists of a topology most closely resembling that of the
"ver36n" model (over most of its extent, this model has a three-phase
vertical with neutral configuration). The 80^th^-percentile data for
this model levels off at just above 4 dB at higher frequencies, as does
the data for "ver36n."

In light of the variability of height where peak field strength occurs,
NTIA recommends that measurements be performed at a height of 1 meter
and use of a height correction factor of 5 dB. This will eliminate the
need for an exhaustive search for the peak field in the height
dimension, which could require considerable time and would not provide
any statistical easement.

**SECTION 3**

**MEASUREMENT DISTANCE ALONG POWER LINE AWAY FROM BPL DEVICES**

1.  **INTRODUCTION**

As noted in NTIA's Phase 1 report, compliance measurement testing
commissioned by BPL equipment vendors and service providers has
generally focused on radiated emissions measured on radials from the BPL
device under test. However, current FCC guidelines also state that the
Part 15 devices and all attached wiring should be considered when
measuring radiated emissions.[^7] In the Commission's BPL NPRM, the
proposed measurement guidelines specify the measurement locations along
the power line away from a BPL device.[^8] In this section, NTIA
evaluates the location along the length of the power line where the peak
field strength occurs and the likelihood of finding the peak level at
the prescribed locations.

2.  **METHODOLOGY**

Field strength predictions from the power line models described in
Section 2 were evaluated for the location of peak field strength along
the length of the power line. The data correspond to the location 10
meters from the power line where the field strength was at its peak at a
height of 1 meter and the location where the field strength was at its
overall peak.

3.  **RESULTS**

Figures 3-1 through 3-18 show the location where field strength is at
its peak level along the power line for a variety of simulated power
line configurations and over the frequency range of 2 to 50 MHz.
Distances are expressed in terms of wavelengths away from the BPL
device. The locations along the power line (10 meters from the power
line) where the overall peak and the peak at a measurement height of 1
meter occur are displayed in each figure.

![](media/image46.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-1: Location of peak field strength along the
power line -- tri36 topology**

**Figure 3-2: Location of peak field strength along the power line --
tri36n topology**

![](media/image48.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-3: Location of peak field strength along the
power line -- tr310 topology**

![](media/image49.wmf){width="5.996527777777778in" height="3.65in"}

**Figure 3-4: Location of peak field strength along the power line --
tri310n topology**

![](media/image50.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-5: Location of peak field strength along the
power line -- ver36 topology**

![](media/image51.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-6: Location of peak field strength along the
power line -- ver36n topology**

![](media/image52.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-7: Location of peak field strength along the
power line -- ver310 topology**

![](media/image53.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-8: Location of peak field strength along the
power line -- ver310n topology**

![](media/image54.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-9: Location of peak field strength along the
power line -- tri26 topology**

![](media/image55.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-10: Location of peak field strength along the
power line -- tri26n topology**

![](media/image56.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-11: Location of peak field strength along the
power line -- tri210 topology**

![](media/image57.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-12: Location of peak field strength along the
power line -- tri210n topology**

![](media/image58.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-13: Location of peak field strength along the
power line -- ver26 topology**

![](media/image59.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-14: Location of peak field strength along the
power line -- ver26n topology**

![](media/image60.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-15: Location of peak field strength along the
power line -- ver210 topology**

![](media/image61.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-16: Location of peak field strength along the
power line -- ver210n topology**

![](media/image62.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-17: Location of peak field strength along the
power line - ver1 topology**

![](media/image63.wmf){width="5.996527777777778in"
height="3.65in"}**Figure 3-18: Location of peak field strength along the
power line -- ver1n topology**

4.  **CONCLUSION**

From the figures in Section 3.3, the locations all along the length of
the power line where the field strength is at its peak, both at heights
of 1 meter and overall, vary widely. For any given power line
configuration, at some frequencies the peak occurs adjacent to or near
the BPL device, while at other frequencies the peak occurs at
substantial distances from the BPL device at an impedance discontinuity.
There are also many frequencies where the field strength peaks at
various distances along the power line. The variability of these results
from power line to power line is due to different degrees of asymmetry
in the power line structures and the fact that the electric field was
calculated at a fixed horizontal distance (10 meters) from the power
lines. The signal source was positioned on an outer conductor at a small
positive (x-axis) offset from the center of the power line structure.
The results are more asymmetric when a neutral wire is added to the
power line structure, due to introduction of additional asymmetry. These
results argue against use of the measurement locations proposed in the
Commission's BPL NPRM. NTIA recommends that field strength measurements
be performed at a 10 meter horizontal distance from an Access BPL power
line, at points all along key segments of the power line where the
maximum field strength from BPL emissions is expected to occur. In its
ongoing Phase 2 study, NTIA will continue to investigate emissions along
the power lines and recommend criteria for choosing representative
segments of power line to measure.

**SECTION 4**

> **IONOSPHERIC PROPAGATION OF BPL SIGNALS**

1.  **INTRODUCTION**

Sky wave ionospheric propagation may occur above the power line horizon
for frequencies between 1.7 MHz and 30 MHz, as discussed in NTIA's Phase
1 report. 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 parameters of the ionosphere that exhibit temporal and
spatial variability. The ionosphere, which ranges from about 60 to 600
km in height, acts as a low-conductivity dielectric.[^9] In general, sky
waves are reliable for radiocommunications up to about 30 MHz, above
which this mode of propagation is sporadic.

Sky waves suffer large losses mainly due to ionospheric absorption and
polarization coupling losses. In a widespread deployment of BPL systems,
there may be aggregation of co-frequency BPL emissions toward the
ionosphere. The modeling results in the Phase I report suggest 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.

2.  **ANALYTICAL MODELING OF SKY WAVE PROPAGATION**

The goal of this preliminary analysis of aggregation and ionospheric
propagation from widespread deployment of BPL systems was to gauge
whether it could lead to interference in the near-term (next few years).
Accordingly, the analysis has a worst-case orientation.

To make predictions regarding the large-scale effects of a widespread
BPL deployment, NTIA employed the VOACAP HF propagation software
developed at its Institute of Telecommunication Sciences (ITS).[^10]
NTIA modeled propagation under a range of times, months and frequencies
to determine potentially worst-case I/N conditions. In this process,
NTIA used VOACAP's "point-to-point" mode to find potential time,
seasonal and frequency combinations that produced the highest I/N levels
between several points around the nation. VOACAP's "area" mode was then
used to further refine these predictions by determining the geographic
coverage of relatively high I/N levels due to single transmitters placed
around the nation as propagation factors were varied.

Using these values, NTIA then ran VOACAP in its area mode to obtain
interfering signal and noise power values in a fixed 3131-point grid of
receiving points covering the United States and centered on Kansas City,
Missouri. For this step, NTIA placed BPL devices in the geographic
center of each county in the United States (including Alaska and
Hawaii). Each of the BPL transmitters (corresponding to a county) was
assigned a radiated power that would produce field strength at the level
of the Part 15 limit as measured using existing procedures. The total
radiated power of each BPL device is shown in Table 4-1. These power
levels were scaled by the number of active BPL devices expected to serve
the urban households in each county.[^11]

**Table 4-1: BPL Total Radiated** Power

  ----------------------------------- -----------------------------------
  **Frequency (MHz)**                 **Power (dBW/Hz)**

  4                                   -104.26

  15                                  -101.79

  25                                  -99.35

  40                                  -123.15
  ----------------------------------- -----------------------------------

Several other factors were taken into consideration when predicting the
interference-to-noise ratio. BPL devices will not all operate at the
Part 15 limit; therefore, the average field strength was assumed to be 4
dB below the Part 15 limit. The analysis was based on RMS values;
therefore an adjustment was made to convert the quasi-peak BPL signal
level to an RMS level. Finally, since the devices in the system do not
all operate at the same frequency, an allowance of 6 dB was given
(*i.e.*, 1 in 4 BPL injectors are assumed to be co-frequency). These
adjustment factors are listed in Table 4-2.

# Table 4-2: Adjustment Factors

  --------------------------------------------------- -------------------
  **Factor**                                          **Adjustment (dB)**

  Devices operating at levels below Part 15 limits    4

  Quasi-Peak to RMS S/N difference                    3

  Co-frequency distribution factor                    6

  Total                                               13
  --------------------------------------------------- -------------------

All simulated BPL transmitters were given an average antenna pattern
based upon the NTIA NEC far-field simulations of a complex power line
model (Figure 2-2). This model was based upon a real Medium Voltage (MV)
power line configuration at a test BPL deployment area. The NEC-derived
far-field patterns were arithmetically averaged over azimuth, assuming a
random distribution of power line orientations, which resulted in gain
patterns with variation in elevation only.

The VOACAP program's variable inputs for this analysis are listed in
Table 4-3.

Table 4-3: VOACAP Input Parameters

+--------------------------------+---------+---------------------------+
| **Variable**                   | #       | **Comment**               |
|                                | # Value |                           |
+--------------------------------+---------+---------------------------+
| Smoothed Sunspot Number (SSN)  | 150     | Yields efficient          |
|                                |         | propagation               |
+--------------------------------+---------+---------------------------+
| Month                          | D       | Yields good propagation   |
|                                | ecember | and low noise             |
+--------------------------------+---------+---------------------------+
| Time (UTC)                     | 18:00   |                           |
+--------------------------------+---------+---------------------------+
| Frequency (MHz)                | 23      |                           |
+--------------------------------+---------+---------------------------+
| Manmade Noise at 3 MHz         | -164    | Relatively low value      |
| (dBW/Hz)                       |         |                           |
+--------------------------------+---------+---------------------------+
| BPL Total Radiated Power       | -100    | Maximum coupled BPL power |
| (dBW/Hz)                       |         | for compliance with       |
|                                |         | limit[^12]                |
+--------------------------------+---------+---------------------------+

**4.3 RESULTS**

Aggregated output for a simulated nationwide deployment of over 700,000
Access BPL devices is depicted in Figure 4-1. The calculated hourly
median I/N (VOACAP refers to it as S/N) level under these circumstances
are greater than --17 dB over the continental United States, with hourly
median I/N levels through much of the central United States between -8.4
dB and -11 dB. Thus, the highest expected hourly median increase in
ambient noise due to the assumed extensive deployment of BPL devices
would be less than 1 dB.

![](media/image64.png){width="5.992361111111111in"
height="3.636111111111111in"}**Figure 4-1: Aggregated BPL I/N levels due
to ionospheric propagation\
(Existing Rules, Worst-Case Oriented Analysis)**

**4.4 CONCLUSION**

NTIA's worst-case oriented analysis of ionospheric propagation and
aggregation of emissions from Access BPL systems indicates that
interference via this mechanism will not occur in the near term.
Considering realistically dispersed deployments of BPL systems, it would
take hundreds of thousands of Access BPL devices operating under
existing rules to cause a 1 dB increase in median noise. Under NTIA's
recommended rule elements, chiefly the 5 dB height correction factor and
power control, it would take millions of BPL devices to increase the
median noise by 1 dB.

**SECTION 5**

**INTERFERENCE RISK ANALYSES**

1.  **INTRODUCTION**

In its Phase 1 study, NTIA analyzed the risk of interference to various
representative federal radio systems assuming BPL devices are operating
at Class B emissions limits above 30 MHz under the current Part 15
rules. The interference risks were evaluated for two interfering signal
thresholds: a doubling of receiver noise floor (I+N/N = 3 dB) that would
result in interference in a low percentage of cases, and a ten fold
increase in receiver noise floor (I+N/N = 10 dB) that would result in
interference in a moderate percentage of cases. This section extends the
Phase I study interference risk analyses to include operation of BPL
devices at current Part 15 limits for Class A digital devices. In
addition, the effect of NTIA's recommended 5 dB height correction factor
is evaluated for the case of a land-mobile receiver in close proximity
to an Access BPL power line.

2.  **BPL OPERATIONS AT CURRENT PART 15 RULES ABOVE 30 MHz**

NTIA analyzed four representative federal radio systems assuming
operation at Class A emissions limits above 30 MHz.[^13] Figures 5-1
through 5-3 show the percent of locations, by distance from the Access
BPL power lines, which could experience a noise floor increase of 3 or
10 dB. Both Class A and B results are plotted for land mobile, fixed and
maritime stations, respectively.

Figures 5-4 through 5-6 illustrate the noise floor increase that an
aeronautical receiver would experience at various altitudes and
horizontal distances from the centroid of an area where BPL systems are
deployed. As in the NTIA Phase 1 study, this deployment area has a 10
kilometer radius and the assumed density of co-frequency active BPL
devices was one per square kilometer. Both Class A and B results are
shown for the aeronautical receiver operating at an altitude of 6, 9 and
12 kilometers.

![](media/image65.wmf){width="5.991666666666666in"
height="3.417361111111111in"} **Figure 5-1: Percent of locations, by
distance, exceeding the specified (I+N/N) levels at 40 MHz --
Land-mobile receiver**

![](media/image66.wmf){width="5.995833333333334in"
height="3.4118055555555555in"} **Figure 5-2: Percent of locations, by
distance, exceeding the specified (I+N)/N levels at 40 MHz -- Fixed
receiver**

![](media/image67.wmf){width="5.991666666666666in"
height="3.417361111111111in"} **Figure 5-3: Percent of locations, by
distance, exceeding the specified (I+N)/N levels at 40 MHz -- Maritime
receiver**

![](media/image68.wmf){width="5.993055555555555in"
height="3.4868055555555557in"} **Figure 5-4: Calculated (I+N)/N level
for an aeronautical receiver at the specified distance and 6 km altitude
from a BPL deployment, with 300 BPL devices visible to the receiver**
**in a 314 km^2^ area -- 40 MHz**

![](media/image69.wmf){width="5.998611111111111in"
height="3.457638888888889in"} **Figure 5-5: Calculated (I+N)/N level for
an aeronautical receiver at the specified distance and 9 km altitude
from a BPL deployment, with 300 BPL devices visible to the receiver in a
314 km^2^ area -- 40 MHz**

![](media/image70.wmf){width="5.993055555555555in"
height="3.4069444444444446in"} **Figure 5-6: Calculated (I+N)/N level
for an aeronautical receiver at the specified distance and 12 km
altitude from a BPL deployment, with 300 BPL devices visible to the
receiver in a 314 km^2^ area -- 40 MHz**

3.  **ANTENNA HEIGHT CORRECTION FACTOR APPLIED TO THE LAND-MOBILE
    RECEIVER CASE**

NTIA recommendations for enhancements to the Commission's Part 15 rules
applicable to BPL systems are expected to yield significant reductions
in the interference risks to federal radiocommunications. In its Phase 1
study, NTIA showed that there exists a substantial risk of interference
to a land-mobile receiver due to a BPL transmitter operating at FCC Part
15 limits as measured using existing Part 15 measurement
procedures.[^14] For frequencies below 30 MHz, virtually all points
close to an Access BPL power line would experience noise floor increases
exceeding 10 dB. NTIA evaluated the probability that a land-mobile
receiver would experience various levels of increased noise due to BPL
interference, with the results shown in Table 5-1. Radiated power and
noise are referenced to a 2.8 kHz bandwidth below 30 MHz and a 16 kHz
bandwidth above 30 MHz. The table shows these probabilities with or
without applying NTIA's recommended 5 dB measurement height correction
factor. The results above 30 MHz in Table 5-1 are based on Access BPL
operating at the Class B limit.

Table 5-1: Percentage of locations exceeding the specified interference
level, by frequency, for a land-mobile receiver within 15 meters of an
Access BPL power line.

  --------------- -------------- ----------- ------------- -------- -------- -------- -------- -------
  **With Height                                                                                
  Adjustment**                                                                                 

  **Frequency**   **Radiated**   **Noise**   **(I+N)/N**                                       

  **(MHz)**       **Power        **(dBW)**   **3 dB**      **10     **20     **30     **40     **50
                  (dBW)**                                  dB**     dB**     dB**     dB**     dB**

  4               -74.79         -111.31     98.01%        81.54%   28.27%   0.00%    0.00%    0.00%

  15              -72.32         -128.83     99.83%        98.85%   83.00%   34.97%   0.00%    0.00%

  25              -69.88         -135.61     99.54%        97.52%   78.07%   39.32%   0.45%    0.00%

  40[^15]         -86.11         -134.27     66.05%        30.84%   0.00%    0.00%    0.00%    0.00%

                                                                                               

  **Without                                                                                    
  Height                                                                                       
  Adjustment**                                                                                 

  **Frequency**   **Radiated**   **Noise**   **(I+N)/N**                                       

  **(MHz)**       **Power        **(dBW)**   **3 dB**      **10     **20     **30     **40     **50
                  (dBW)**                                  dB**     dB**     dB**     dB**     dB**

  4               -69.79         -111.31     99.33%        93.17%   54.69%   6.16%    0.00%    0.00%

  15              -67.32         -128.83     99.85%        99.66%   95.69%   59.48%   4.28%    0.00%

  25              -64.88         -135.61     99.78%        98.97%   92.11%   58.53%   18.52%   0.00%

  40Error:        -81.11         -134.27     87.89%        49.15%   10.00%   0.00%    0.00%    0.00%
  Reference                                                                                    
  source not                                                                                   
  found                                                                                        
  --------------- -------------- ----------- ------------- -------- -------- -------- -------- -------

4.  **CONCLUSION**

Figures 5-1 through 5-6 show that the operation of BPL devices at the
Class A emissions limits, rather than Class B limits above 30 MHz, as
determined using existing Part 15 measurement procedures, increases the
distances at which a given percentage of locations experience a
specified increase in receiver noise floor. Relative to operation under
the Class B limit, the results for Class A show an increase of
approximately 40 -- 50% in the distances at which receiver operation at
a given percentage of locations would experience a given noise floor
increase.[^16]

NTIA evaluated the effectiveness of its recommendations for a
measurement height correction factor and found that it only slightly
reduces interference risks for nearby land-mobile receivers. After
applying the height correction factor, most locations within 15 meters
of an Access BPL power line will experience a noise floor increase of 10
dB or more at operating frequencies between 1.7 MHz and 30 MHz. To
further protect land-mobile operations, other risk reduction techniques
should be employed, such as power control and avoidance of use of mobile
service frequencies in physically adjacent Access BPL network elements.
Radio frequency noise on power lines can vary by upwards of 20 dB
throughout a day; therefore, adjustment of BPL signal power to the
minimum level needed for proper BPL device operation should result in an
overall lowering of interference risks. Precluding reuse of mobile
service frequencies in adjacent BPL devices lowers the probability that
a land-mobile receiver will be operating co-frequency with BPL network
elements within a large contiguous portion of the area served by Access
BPL.

[^1]: *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"); *Potential Interference from Broadband over Power Line (BPL)
    Systems to Federal Radiocommunications at 1.7 -- 80 MHz*, NTIA
    Report 04-413, BPL NPRM, April 28, 2004 ("NTIA Phase 1 Study").

[^2]: *See* NTIA Phase 1 Study, §6.

[^3]: *Id*. at §9.4.

[^4]: BPL NPRM, Appendix C, at ¶2.b.2.

[^5]: In actual systems, all transformer impedances vary widely, based
    upon varying loads in the system. However, preliminary calculations
    found that changing transformer impedances had little impact upon
    the results.

[^6]: *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."

[^7]: *See* 47 C.F.R. §15.31(g)-(k).

[^8]: *See* BPL NPRM, Appendix C at ¶2.b.2 -- "Testing shall be
    performed at distances of 0, ¼, ½, ¾, and 1 wavelength down the line
    from the BPL injection point on the power line. Wavelength spacing
    is based on the mid-band frequency..."

[^9]: *See e.g*., Propagation of Radio Waves, Edited by M. P.M Hall, L.
    W. Barclay and M. T. Hewitt, IEE, London, 1996.

[^10]: VOACAP is available from the NTIA Institute for Telecommunication
    Sciences, URL: http://elbert.its.bldrdoc.gov/hf.html.

[^11]: For this preliminary analysis, NTIA assumed that a BPL injector
    has the data handling capacity to support an average of 30
    customers, and 1 of 4 urban households is a BPL customer. In other
    words, one BPL injector was assumed per 120 urban households.

[^12]: ^\*^ The maximum coupled BPL power that yields compliance with
    field strength limits can vary substantially among different power
    lines.

[^13]: *See* NTIA Phase 1 Study, at §6.

[^14]: *See* NTIA Phase 1 Study, at §6.6.1.

[^15]: ^\*^ Analyzed assuming BPL device operating at the Part 15 Class
    B limit.

[^16]: *See* 47 C.F.R. 15.31(f)(1)