**Direct-Pickup Interference Tests of Three Consumer Digital Cable
Television Receivers\
Available in 2005**

**July 31, 2007**

**Technical Research Branch**

**Laboratory Division**

**Office of Engineering and Technology**

**Federal Communications Commission**

**OET Report Prepared by:**

**FCC/OET 07-TR-1005 Stephen R. Martin**

**TABLE OF CONTENTS**

[EXECUTIVE SUMMARY iii](#executive-summary)

[CHAPTER 1 INTRODUCTION 1](#introduction)

[Background and Objective 1](#background-and-objective)

[Overview 2](#overview)

[CHAPTER 2 TEST DESCRIPTION 2-1](#test-description)

[TV Samples 2-1](#tv-samples)

[Test Sites 2-1](#test-sites)

[Test Setup 2-10](#test-setup)

[Test Methodology 2-14](#test-methodology)

[CHAPTER 3 TEST RESULTS 3-1](#test-results)

[Overview of Measurements Under Common Conditions Across the Test Sites
3-1](#overview-of-measurements-under-common-conditions-across-the-test-sites)

[Detailed Results for All Measurement Conditions
3-2](#detailed-results-for-all-measurement-conditions)

[Variability of Direct Pickup Vulnerability
3-6](#variability-of-direct-pickup-vulnerability)

**ILLUSTRATIONS**

[Figure 2‑1. Test Site 0---No Wall 2-4](#__RefHeading___Toc173221988)

[Figure 2‑2. Test Site 1---Inside View of Exterior Wall
2-5](#__RefHeading___Toc173221989)

[Figure 2‑3. Test Site 1---Outside View of Exterior Wall
2-5](#__RefHeading___Toc173221990)

[Figure 2‑4. Test Site 2---View of Inter-Unit Townhouse Wall from
Townhouse A During Tests at 2 Meters Separation Distance
2-6](#__RefHeading___Toc173221991)

[Figure 2‑5. Test Site 2---Antenna Positioned for 2 Meters Separation
Distance 2-7](#__RefHeading___Toc173221992)

[Figure 2‑6. Test Site 2---Townhouse A with Antenna Positioned for 10
Meters Separation Distance (Inter-Unit Wall Is Behind and to the Left of
Camera) 2-7](#__RefHeading___Toc173221993)

[Figure 2‑7. Test Site 2---TV Positioned in Front of Common Wall in
Townhouse B for Tests at 2 Meters Separation Distance
2-8](#__RefHeading___Toc173221994)

[Figure 2‑8. Test Site 2---TV Positioned in Townhouse B for Tests at 10
Meters Separation Distance 2-8](#__RefHeading___Toc173221995)

[Figure 2‑9. Inter-Unit Wall of a Townhouse Under Construction
2-9](#__RefHeading___Toc173221996)

[Figure 2‑10. Close-Up View of Inter-Unit Wall of a Townhouse Under
Construction 2-9](#__RefHeading___Toc173221997)

[Figure 2‑11. Block Diagram of Test Setup
2-10](#__RefHeading___Toc173221998)

[Figure 2‑12. Test Equipment as Set Up at Site 1
2-11](#__RefHeading___Toc173221999)

[Figure 2‑13. Close-Up of Test Equipment
2-12](#__RefHeading___Toc173222000)

[Figure 2‑14. Spectrum of Cable TV Signal Measured at Site 1
2-13](#__RefHeading___Toc173222001)

[Figure 2‑15. Spectrum of OFDM Signal Used as Interferer
2-14](#__RefHeading___Toc173222002)

**TABLES**

[Table 2‑1. Wall Construction 2-2](#__RefHeading___Toc173222003)

[Table 2‑2. Test Configurations at Each Site
2-3](#__RefHeading___Toc173222004)

[Table 2‑3. Equipment List 2-11](#__RefHeading___Toc173222005)

[Table 3‑1. Minimum EIRP at TOV Across Two Antenna Heights and Two
Polarizations for Interference to TVs from the Rear
3-2](#__RefHeading___Toc173222006)

[Table 3‑2. Measurements at Site 0 With 2 Meters Separation
3-3](#__RefHeading___Toc173222007)

[Table 3‑3. Measurements at Site 1 With 2 Meters Separation
3-3](#__RefHeading___Toc173222008)

[Table 3‑4. Measurements at Site 1 With 10 Meters Separation
3-4](#__RefHeading___Toc173222009)

[Table 3‑5. Measurements at Site 2 With 2 Meters Separation
3-4](#__RefHeading___Toc173222010)

[Table 3‑6. Measurements at Site 2 With 10 Meters Separation
3-5](#__RefHeading___Toc173222011)

# EXECUTIVE SUMMARY

This report presents the results of *in situ* measurements of the
interference susceptibility of three digital television (DTV) receivers
to direct-pickup of emissions within the channel width of a digital
cable TV signal to which the receivers were tuned. The tests were
intended to identify the susceptibility of cable TV reception by a
digital cable TV receiver connected directly to the cable TV system
(without the use of a set-top box) to interference from devices that
might operate within the TV broadcast spectrum on locally unused
broadcast channels (TV white spaces) that overlap the frequencies of
channels used by the cable TV system. The Commission is currently
considering rules that would permit the use of such white-space devices.

The three DTV receivers were Digital Cable-Ready (DCR) models that were
on the market in 2005. The digital cable TV signal used in these tests
was a 256-quadrature amplitude modulation (256-QAM) signal adjusted to a
signal level near the minimum level specified by the "Digital Cable
Network Interface Standard"[^1] for the "input terminals of the first
device located on the subscriber's premises." Tests were performed on
EIA cable TV channel 70, which overlaps the spectrum of broadcast UHF TV
channel 19.

The interfering signal was a 4.8-MHz wide orthogonal frequency-division
multiplexing (OFDM) signal operating in the spectrum occupied by the
selected cable TV channel. This signal was radiated from an antenna
having near 0 dBi gain.

The tests were performed with the interfering signal source separated
from the DTV receiver by distances of 2 meters or 10 meters and, in most
cases, by one of two residential walls: an exterior wall of a
single-family house or a wall separating two townhouse units. The
interfering source was operated at two different heights at most
locations and at two different polarizations. Most measurements were
performed with the interferer located behind the TV receiver, but some
measurements were also performed with interference from the front of the
TV and a few measurements were performed at other aspect angles. A total
of 108 measurements were made.

The tests show that an OFDM source operating at an effective isotropic
radiated power (EIRP) as low as 6.3 dBm can cause interference to cable
DTV reception at a distance of 2 meters and that an EIRP as low as 15.3
dBm can cause interference at a distance of 10 meters. [^2] The TVs
exhibited less susceptibility to interference from the front than to
interference from the rear. For interference from the rear, the median
interference threshold EIRPs across the three tested receivers and all
antenna heights, polarizations, and lateral-offset positions were 16.9
dBm and 24.2 dBm for 2 and 10 meter distances, respectively. Median
thresholds for interference from the front were 21.2 dBm and \>25.1 dBm
at 2 and 10 meters, respectively. (We note that interference from a
device in a neighboring residential unit is unlikely to occur with the
front aspect at a distance of only 2 meters.)

Due to the limited scope of these tests (three TV sets, one cable-TV
channel, and two primary test sites), the results are not intended to
constitute a complete basis for defining criteria necessary to protect
cable TV viewers from interference by devices operating in the TV white
spaces. Nevertheless, the tests provide an empirical demonstration of
the potential for such interference at relatively low power levels, and,
as such, a useful input to the decision process.

# ** **INTRODUCTION

This report presents the results of *in situ* tests of the direct-pickup
co-channel interference susceptibility of Digital Cable-Ready (DCR) TV
receivers connected to a digital cable system delivering 256-quatdrature
amplitude modulation (256-QAM) signals. The interferer for these tests
was an orthogonal frequency-division multiplexing (OFDM) signal radiated
in the frequency band occupied by the digital cable signal to which the
"victim" TV receiver was tuned. The tests were intended to identify the
susceptibility of cable TV reception by a digital cable TV receiver
connected directly to the cable TV system (without the use of a set-top
box) to interference from devices that might operate within the TV
broadcast spectrum on locally unused broadcast channels (TV white
spaces) that overlap the frequencies of channels used by the cable TV
system. The Commission is currently considering rules that would permit
the use of such white-space devices.

The tests were limited to three TV sets, one cable-TV channel, and two
primary test sites---with limited comparative tests performed at an
additional outdoor site. Given the observed variability of interference
thresholds among the receivers and among the test sites and the expected
variability with frequency (*i.e.*, tuned channel), we recognize that
the limited testing reported herein is not sufficient to serve as the
sole basis for establishing emission limits to protect cable TV viewers
from interference by devices operating in the TV white spaces.
Nevertheless, the tests provide an empirical demonstration of the
potential for such interference at relatively low power levels, and, as
such, a useful input to the decision process.

## Background and Objective

Digital TV signals carried over consumer cable television networks in
United States use QAM modulation, which requires a different type of
demodulator than the ATSC 8-VSB signal format used for broadcast digital
TV in the U.S. Many digital TV receivers include QAM demodulators, in
addition to the required ATSC 8-VSB demodulators, in order to allow
reception of digital cable TV signals without the use of a set-top box
from the cable company. This provides a convenience to the consumer by
eliminating one device and one or more cables that must be connected and
by allowing the TV's remote control to be used for channel selection.

Digital TVs having QAM tuners can receive unencrypted digital cable TV
programming. TVs that are identified as "Digital Cable Ready" (DCR) have
the additional capability of tuning encrypted digital cable TV
programming to which the consumer subscribes. Decryption is provided by
means of a "Point of Deployment module" (POD) that can be rented from
the cable service provider and inserted into a slot in a DCR TV. The POD
is more commonly known by the term as CableCARD^TM^, a trademark of
Cable Television Laboratories Inc.

The FCC is considering rules that would allow unlicensed radio devices
to operate on locally-unused broadcast TV channels. This concept is
commonly known as use of the TV "white spaces." The cable TV industry
has expressed concern that such devices could cause interference to
television receivers connected directly to a digital cable TV service
without the use of a set-top box. The concern exists because the portion
of TV spectrum that is not used for TV broadcast in a given local area
is still likely to be used within the cable-TV transmission system;
*i.e.*, there may be few, if any, white spaces within the cable system,
even though there are white spaces in the local broadcast spectrum.
Depending on the effectiveness of shielding of a TV receiver's tuner,
emissions within a broadcast white space (*i.e.*, within an unused
broadcast channel) could potentially cause co-channel interference to a
TV receiver tuned to a digital cable channel that overlaps the spectrum
of the white-space device emission. (It is also plausible that
adjacent-channel interference could occur; however, based on conducted
measurements of TV interference rejection performance for ATSC 8-VSB
signals, adjacent-channel interference susceptibility is much less than
co-channel susceptibility. For first adjacent channels, this difference
is typically on the order of 54 dB.[^3]) This issue is less of a concern
for consumers that use cable-company-provided set-top boxes because
those are expected to be better shielded than typical DTV receivers.

The purpose of this study is to provide an initial set of empirical data
regarding the potential for such interference.

## Overview

Tests were performed to determine the susceptibility of three DCR DTV
receivers to interference on one digital cable TV channel. In each test,
the power of an OFDM signal applied to an antenna was adjusted to
determine the minimum level that caused interference to operation of a
TV connected to a digital cable system. In the tests, the interferer was
separated from the TV by a distance of 2 or 10 meters and, in most
tests, by a wall at one of two residential locations. Limited testing
was also performed outdoors with no wall separating the interferer from
the TV.

#  TEST DESCRIPTION

This chapter describes the selection of sample TVs, the test sites, the
test equipment configuration, and the methodology used for the tests.

## TV Samples

The tested TV samples were selected from among DTV receivers that were
used in a 2005 study by the Commission's laboratory of DTV reception
performance.[^4] Eight of the televisions in that study included QAM
tuners for digital cable reception---a requirement for this
direct-pickup study. The three of those that were most easily
transportable were selected for the field tests described herein. The
three are 2005-model flat-panel LCD digital TVs of different brand
names. All have the DCR logo, indicating that they are "Digital Cable
Ready." As such, all can accept a CableCARD^TM^ to allow premium digital
cable channels to be decrypted; however, no CableCARD^TM^ was used in
these tests, so testing was limited to unencrypted "clear QAM" channels.

In order to avoid revealing the performance of specific brands or models
of the samples, the TV sets are identified in this report by a letter
and number code assigned to each product. The receivers tested for this
report are designated D3, F3, and I1.[^5]

## Test Sites

In all tests, an interfering signal was radiated from a biconical
antenna placed at a distance of either 2 meters or 10 meters from the TV
receiver under test. One test site was outdoors, with no objects between
the antenna and the TV. Two test sites included a wall between the
antenna and the TV: in one case, an exterior wall of a single-family
home, and in the other, the wall separating two adjacent townhouses.
Table 2-1 describes the walls. Table 2-2 describes the test
configuration used at each site.

### Site 0: No Wall

Tests of one TV were performed with both the TV and the interfering
source located outdoors above an asphalt driveway. Figure 2-1 shows a
photo of the test setup. Note that in this and other photographs, the TV
receiver is obscured to prevent identification of brand and model. This
test was performed for comparison to the tests at site 1. The metal
garage door was in the open position during the tests, as shown in
Figure 2-1.

[]{#__RefHeading___Toc173222003 .anchor}Table 2‑1. Wall Construction

+----------+----------------------+------------------------------------+
|          | **Site 1: Exterior   | **Site 2: Townhouse**              |
|          | House**              |                                    |
+----------+----------------------+------------------------------------+
| **Descr  | Exterior garage wall | Wall between adjacent townhouse    |
| iption** | of single-family     | units                              |
|          | home                 |                                    |
+----------+----------------------+------------------------------------+
| **Constr | 1.  Drywall inside   | Probable construction based on     |
| uction** |                      | nearby townhouses under            |
|          | 2.  2x4 wood framing | construction:                      |
|          |     on 16-inch       |                                    |
|          |     centers          | 1.  2-inch thick gypsum firewall   |
|          |                      |     framed and joined with steel   |
|          | 3.  Energy-Brace     |     channels                       |
|          |     sheathing +      |                                    |
|          |     vinyl siding     | 2.  2x4 wood framing on 12-inch    |
|          |     outside          |     centers on each side of        |
|          |                      |     firewall                       |
|          | (Same as exterior of |                                    |
|          | 3 sides of house,    | 3.  Drywall for interior walls     |
|          | except for absence   |                                    |
|          | of insulation,       |                                    |
|          | electrical wiring,   |                                    |
|          | and windows.)        |                                    |
+----------+----------------------+------------------------------------+
| **Insu   | None, but fiberglass | Fiberglass                         |
| lation** | used in rest of      |                                    |
|          | house                |                                    |
+----------+----------------------+------------------------------------+
| **Vapor  | None, but clear      | Unknown                            |
| b        | plastic sheeting     |                                    |
| arrier** | used in rest of      |                                    |
|          | house                |                                    |
+----------+----------------------+------------------------------------+
| **       | Only nails and       | 1.  Electrical outlets adjacent to |
| Metallic | screws               |     test area                      |
| objects  |                      |                                    |
| in       |                      | 2.  Probable steel channels to     |
| wall**   |                      |     join and frame gypsum sheets   |
|          |                      |     for firewall:\                 |
|          |                      |     \--Horizontal piece at bottom  |
|          |                      |     and approximately 10-foot      |
|          |                      |     intervals vertically\          |
|          |                      |     \--Vertical pieces at 24-inch  |
|          |                      |     horizontal intervals           |
|          |                      |                                    |
|          |                      | 3.  Single diagonal metal          |
|          |                      |     T-channel in each wall         |
+----------+----------------------+------------------------------------+

Note: Townhouse wall construction was assumed to be the same as nearby
townhouses that were under construction (by a different builder) at the
time of the tests.

[]{#__RefHeading___Toc173222004 .anchor}**Table 2‑2. Test Configurations
at Each Site**

+---------+-------------------+-------------------+-------------------+
|         | **Site 0: No      | **Site 1:         | **Site 2:         |
|         | Wall**            | Exterior House    | Inter-Unit        |
|         |                   | Wall**            | Townhouse Wall**  |
+---------+-------------------+-------------------+-------------------+
| **T     |                   |                   |                   |
| ransmit |                   |                   |                   |
| Ant     |                   |                   |                   |
| enna:** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   | Outdoors          | Garage            | Townhouse A,      |
| Loc     |                   |                   | ground floor      |
| ation** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   | Wood/fiberglass   | Wood/fiberglass   | Wood tripod       |
| Mount** | mast              | mast              |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   | Asphalt driveway  | Concrete slab     | Carpeted concrete |
| Floor** |                   |                   | slab              |
+---------+-------------------+-------------------+-------------------+
| **\--   | 0.97 m and 1.47 m | 1.  0.97 m and    | 3.  0.88 m and    |
| Height  |                   |     1.47 m for    |     1.26 m at 2-m |
| (center |                   |     2-m distance  |     distance      |
| of      |                   |                   |                   |
| ant     |                   | 2.  0.97 m and    | 4.  0.88 m and    |
| enna)** |                   |     2.39 m for    |     1.45 m at     |
|         |                   |     10-m distance |     10-m distance |
+---------+-------------------+-------------------+-------------------+
| **TV:** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   | Outdoors          | Outdoors          | Townhouse B,      |
| Loc     |                   |                   | ground floor      |
| ation** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   | 0.85-m tall       | 0.85-m tall       | 0.85-m tall       |
| Mount** | plastic cart      | plastic cart      | plastic cart      |
+---------+-------------------+-------------------+-------------------+
| **\--   | Asphalt driveway  | 5.  Asphalt       | Carpeted concrete |
| Floor** |                   |     driveway      | slab              |
|         |                   |     extension at  |                   |
|         |                   |     2-m distance  |                   |
|         |                   |                   |                   |
|         |                   | 6.  Grass at 10-m |                   |
|         |                   |     distance      |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   | Front, rear,      | Front and rear    | Rear              |
| Aspect  | right side,       |                   |                   |
| Angle** | right-rear (\~45  |                   |                   |
|         | deg.)             |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\# of | One               | Three             | Three             |
| TVs     |                   |                   |                   |
| T       |                   |                   |                   |
| ested** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **Sep   | 2 m               | 2 m and 10 m      | 2 m and 10 m      |
| aration |                   |                   |                   |
| Dis     |                   |                   |                   |
| tance** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   |                   | 5.25 inches (0.13 | 12 inches (0.30   |
| Wall    |                   | m)                | m)                |
| thic    |                   |                   |                   |
| kness** |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| **\--   |                   | 7.  20 inches     | 9.  33 inches     |
| From    |                   |     (0.51 m) for  |     (0.85 m) for  |
| t       |                   |     2-m distance  |     2-m distance  |
| ransmit |                   |                   |                   |
| antenna |                   | 8.  162 inches    | 10. 191 inches    |
| to      |                   |     (4.11 m) for  |     (4.85 m) for  |
| wall**  |                   |     10-m distance |     10-m distance |
+---------+-------------------+-------------------+-------------------+
| **\--   |                   | 11. 53 inches     | 13. 33 inches     |
| From TV |                   |     (1.36 m) for  |     (0.85 m) for  |
| to      |                   |     2-m distance  |     2-m distance  |
| wall**  |                   |                   |                   |
|         |                   | 12. 226 inches    | 14. 191 inches    |
|         |                   |     (5.75 m) for  |     (4.85 m) for  |
|         |                   |     10-m distance |     10-m distance |
+---------+-------------------+-------------------+-------------------+
| **Cable | 8-way splitter    | 8-way splitter    | Cable wall outlet |
| Conne   | near cable        | near cable        | on far side of    |
| ction** | entrance \--\>    | entrance \--\>    | test room \--\>   |
|         | 6-foot RG-6 \--\> | 6-foot RG-6 \--\> | 6-foot RG-6 \--\> |
|         | step attenuator   | step attenuator   | step attenuator   |
|         | \--\> 100-foot    | \--\> 100-foot    | \--\> 50-foot     |
|         | "quad shielded"   | "quad shielded"   | RG-6 \--\> TV     |
|         | RG-6 \--\> TV     | RG-6 \--\> TV     |                   |
+---------+-------------------+-------------------+-------------------+

> Note: Aspect angle refers to the location of the interferer with
> respect to the TV receiver. For example, "rear" indicates that the
> transmit antenna was located behind the receiver.

![](media/image1.jpeg){width="6.498611111111111in"
height="4.319444444444445in"}

[]{#__RefHeading___Toc173221988 .anchor}Figure 2‑1. Test Site 0---No
Wall

### Site 1: Exterior House Wall

Three TVs were tested at a single-family house. The initial intent had
been to place the TV inside the residence and the transmitter outside.
The plan was to avoid windows in order to ensure that the interfering
emission propagated through a wall rather than through a window;
however, all potential test areas included either closely-spaced windows
or large metallic objects (air-conditioning units, metal gas fireplace,
or washer and dryer). Consequently, an exterior garage wall was selected
as the barrier between the transmitter and the TV receiver. It was more
convenient at this site to run the cable for TV operation outdoors than
into the garage; consequently, the TV was place outdoors for the tests
and the interfering source was placed inside the garage. Figures 2-2 and
2-3 show the test setup.[^6]

As was shown in Table 2-1 and the illustrations, the exterior garage
wall had the same type of construction as the back and side walls of the
house (wood frame with drywall inside and vinyl siding over sheathing on
the outside). The only elements missing from the garage wall relative to
the exterior residence walls were insulation and electrical wiring.
Because the insulation in the residence walls was fiberglass with a
clear plastic vapor barrier, it is not expected to contribute
significantly to wall attenuation; consequently, the absence of
insulation is not expected to influence the test results. While the
presence or absence of electrical wiring in a wall can affect
propagation, we note that, except where wall switches, overhead lights,
or feeds to the second floor exist, the first floor wiring on the
exterior walls extends above the floor level only to the height of the
outlets (16 inches), which are spaced at 12-foot intervals;
consequently, in at least some cases, its effect on propagation is
likely to be small.

![](media/image2.jpeg){width="6.499305555555556in"
height="4.059027777777778in"}

[]{#__RefHeading___Toc173221989 .anchor}Figure 2‑2. Test Site 1---Inside
View of Exterior Wall

![](media/image3.jpeg){width="6.498611111111111in"
height="4.319444444444445in"}

[]{#__RefHeading___Toc173221990 .anchor}Figure 2‑3. Test Site
1---Outside View of Exterior Wall

### Site 2: Inter-Unit Townhouse Wall

At site 2, the TV and the interfering source were placed in adjacent
townhouses, separated by a firewall. The tests were performed on the
ground floor of each townhouse in finished, carpeted rooms.

Figures 2-4 and 2-5 show the interferer test setup in the Townhouse A
for 2 meters separation distance. Figure 2-6 shows the configuration
with the antenna on the other side of the room for tests at 10 meters
distance. Figures 2-7 and 2-8 show the setup of a TV sample in Townhouse
B for 2 meters and 10 meters separation distances, respectively.

The townhouse site was expected to create more complex multipath
propagation between the interferer and the TV than that at the other two
sites. A wrought iron bookcase can be seen in the Figures 2-7 and 2-8,
37" to left of centerline between antenna and starting position of the
TV (to the right of the TV when viewed from the front of the TV). In
addition, the townhouse fire wall is believed to include metallic
components, based on observations of similar townhouses under
construction near site 2. Figures 2-9 and 2-10 show photographs of the
firewall in one of those townhouses. The gypsum firewall panels
(two-inches thick) are joined by vertical steel channels on 24-inch
centers, as described in Table 2-1; the firewall also includes
horizontal channels at about 10-foot intervals vertically and each wall
includes a diagonal metal strip.

![](media/image4.jpeg){width="6.498611111111111in"
height="4.319444444444445in"}

[]{#__RefHeading___Toc173221991 .anchor}Figure 2‑4. Test Site 2---View
of Inter-Unit Townhouse Wall from Townhouse A During Tests at 2 Meters
Separation Distance

![](media/image5.jpeg){width="6.4in" height="4.304861111111111in"}

[]{#__RefHeading___Toc173221992 .anchor}Figure 2‑5. Test Site
2---Antenna Positioned for 2 Meters Separation Distance

![](media/image6.jpeg){width="6.4006944444444445in"
height="4.429861111111111in"}

[]{#__RefHeading___Toc173221993 .anchor}Figure 2‑6. Test Site
2---Townhouse A with Antenna Positioned for 10 Meters Separation
Distance (Inter-Unit Wall Is Behind and to the Left of Camera)

![](media/image7.jpeg){width="6.402777777777778in"
height="4.261111111111111in"}

[]{#__RefHeading___Toc173221994 .anchor}Figure 2‑7. Test Site 2---TV
Positioned in Front of Common Wall in Townhouse B for Tests at 2 Meters
Separation Distance

![](media/image8.jpeg){width="6.402777777777778in"
height="4.261111111111111in"}

[]{#__RefHeading___Toc173221995 .anchor}Figure 2‑8. Test Site 2---TV
Positioned in Townhouse B for Tests at 10 Meters Separation Distance

![](media/image9.jpeg){width="6.501388888888889in"
height="4.004861111111111in"}

[]{#__RefHeading___Toc173221996 .anchor}Figure 2‑9. Inter-Unit Wall of a
Townhouse Under Construction

![](media/image10.jpeg){width="6.498611111111111in"
height="4.319444444444445in"}

[]{#__RefHeading___Toc173221997 .anchor}Figure 2‑10. Close-Up View of
Inter-Unit Wall of a Townhouse Under Construction

## Test Setup

Figure 2-11 shows a block diagram of the test setup for all tests. Table
2-3 identifies the equipment that was used. Figures 2-12 and 2-13 show
photographs of the signal generation and measurement equipment taken at
test site 1.

A vector signal generator[^7] was configured to generate a 4.8-MHz wide
DVB-H OFDM signal. That signal was amplified by an RF power amplifier
that drove a signal splitter, allowing the signal to be delivered to
both a spectrum analyzer and a calibrated UHF biconical antenna having
-1.1 dBi gain at 501 MHz. On-site measurements were performed to
calibrate the relative gains of the two signal paths, including the
effects of splitter imbalance and cable losses so that signal power
measurements on the spectrum analyzer could be converted into equivalent
power delivered to the antenna.[^8]

A cable TV source was connected through a step attenuator with 0.1 dB
steps at a location on the opposite side of the room (site 2) or at the
other end of the house (site 1) from the interfering source. The step
attenuator output was fed through a 50- or 100-foot long 75-ohm coaxial
cable to the RF input of the TV under test. The step attenuator was used
to adjust the signal level delivered to the TV by the cable TV system.

![](media/image11.wmf){width="5.998611111111111in"
height="3.6881944444444446in"}

[]{#__RefHeading___Toc173221998 .anchor}Figure 2‑11. Block Diagram of
Test Setup

[]{#__RefHeading___Toc173222005 .anchor}Table 2‑3. Equipment List

+--------------------------+-------------------------------------------+
| **Equipment**            | **Brand and Model**                       |
+--------------------------+-------------------------------------------+
| **Vector signal          | Agilent E4438C                            |
| generator**              |                                           |
+--------------------------+-------------------------------------------+
| **RF power amplifier**   | Amplifier Research 5W1000                 |
+--------------------------+-------------------------------------------+
| **Splitter**             | Mini-Circuits ZFSC-2-4-N                  |
+--------------------------+-------------------------------------------+
| **Spectrum Analyzer**    | Agilent E4440A                            |
+--------------------------+-------------------------------------------+
| **UHF Biconical          | Schwarzbeck Mess model VUBA 9117          |
| Antenna**                |                                           |
+--------------------------+-------------------------------------------+
| **50-ohm cables in       | Various double-shielded coaxial cables    |
| interferer test setup**  |                                           |
+--------------------------+-------------------------------------------+
| **75-ohm cables in CATV  | Identified in Table 2-2                   |
| setup**                  |                                           |
+--------------------------+-------------------------------------------+
| **Step Attenuator**      | Trilithic ZMT-57 75-to-50 ohm matching    |
|                          | transformer                               |
|                          |                                           |
|                          | \+                                        |
|                          |                                           |
|                          | Weinschel AF119A-99-33 50-ohm 1-dB step   |
|                          | attenuator                                |
|                          |                                           |
|                          | \+                                        |
|                          |                                           |
|                          | JFW Industries 50R-249 50-ohm 0.1-dB step |
|                          | attenuator                                |
|                          |                                           |
|                          | \+                                        |
|                          |                                           |
|                          | Trilithic ZMT-57 50-to-75 ohm matching    |
|                          | transformer                               |
+--------------------------+-------------------------------------------+
| **75 to 50-ohm           | Trilithic ZM-57                           |
| minimum-loss pad**       |                                           |
+--------------------------+-------------------------------------------+

![](media/image12.jpeg){width="6.495138888888889in"
height="4.329861111111111in"}

[]{#__RefHeading___Toc173221999 .anchor}Figure 2‑12. Test Equipment as
Set Up at Site 1

![](media/image13.jpeg){width="6.498611111111111in"
height="4.319444444444445in"}

[]{#__RefHeading___Toc173222000 .anchor}Figure 2‑13. Close-Up of Test
Equipment

### Cable TV Channel Selection and Signal Level

The cable TV signals for these tests came from Verizon FIOS
installations at the two residences. Verizon identifies the digital
cable signals as being 256-QAM.

The intent was to test at one or more cable TV channels that overlap
broadcast TV bands. Verizon provided a list of clear-QAM channels on
their FIOS system in terms of virtual channel numbers, but did not
provide a mapping to EIA RF cable channel numbers; consequently, the
availability of clear-QAM signals in terms of EIA channel numbers was
determined by "channel surfing".[^9]

Only two cable RF channels within the TV broadcast bands were found to
include clear-QAM programming---EIA channels 70 and 73; however, channel
73 was not successfully tuned on two of the receivers. Consequently, EIA
cable channel 70 was selected for testing. This RF channel is centered
at 501 MHz and overlaps broadcast channel 19, which is centered at 503
MHz. (Cable TV channels, like broadcast TV channels, have 6 MHz
bandwidth.) The cable channel included multiple standard-definition
program streams, but no high-definition programming.

In each residence, a step attenuator with 0.1-dB steps was inserted into
the cable TV signal path at the source end of the cable driving the TV
to allow signal level to be set. The "Digital Cable Network Interface
Standard"[^10] specifies that the carrier level at the "input terminals
of the first device located on the subscriber's premises" should be -12
to +15 dBmV (-60.8 to -33.8 dBm) for 256-QAM signals. The step
attenuator was adjusted so that the power delivered on EIA channel 70 to
the television's RF input terminal was -11 dBmV (-59.8 dBm), *i.e.*, 1
dB above the minimum specified level.[^11]

Figure 2-14 shows the measured spectrum of the signal delivered to the
TV for an 18-MHz span centered at EIA channel 70 at site 1. The spectrum
levels have been adjusted for loss of the impedance-matching pad used in
the measurement.

![](media/image14.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc173222001 .anchor}Figure 2‑14. Spectrum of Cable
TV Signal Measured at Site 1

### Interference Source

The interfering signal for these tests was an OFDM DVB-H signal
generated using a commercial software package for a vector signal
generator[^12] with parameters set for a 2k OFDM signal with 5-MHz
channel width and 64-QAM modulation. Measured bandwidths were 4.76 MHz
at the -3-dB points and 4.8 MHz at the -20-dB points.

Figure 2-15 shows the spectrum of the interfering signal, which was
centered on the [cable]{.underline} channel. The cable channel center is
2-MHz below the center of the nearest broadcast channel. Such an offset
exists for all cable channels that overlap UHF TV broadcast channels
under the standard and IRC cable channel plans; the offset is larger
under the HRC channel plan.[^13] In VHF, there is no offset between
broadcast and cable channel frequencies under the standard cable channel
plan and, for most channels, under the IRC plan.

![](media/image15.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

[]{#__RefHeading___Toc173222002 .anchor}Figure 2‑15. Spectrum of OFDM
Signal Used as Interferer

In an application involving white-space use of broadcast TV spectrum,
the transmit spectrum of the white-space device is likely to be centered
on a [broadcast]{.underline} channel rather than on the cable channel,
as was done here. In such a case, we anticipate that the interference
effect would depend on the amount of power that overlaps the cable
channel. If, for example, a device transmitted with a bandwidth of 2-MHz
or less, centered on broadcast channel 19, then all of the power would
fall within EIA cable channel 70 and the interference thresholds would
likely match those measured in this report. For greater bandwidths, a
portion of the transmit power would fall into another cable channel. For
example, a transmission with a rectangular signal spectrum having 4-MHz
bandwidth centered on broadcast channel 19 would extend from 501 to 505
MHz; since only 75% of the spectrum overlaps cable channel 70, the
interference effect on that channel would be reduced by about 1.25 dB.

## Test Methodology

### Determining the Interference Threshold

Sound from the TV receiver under test was monitored as a basis for
identifying interference. This enabled the tests to be performed by a
single engineer without moving from the interfering signal generation
location to the TV location multiple times per measurement. At sites 0
and 1, the sound was monitored directly by the test engineer. At site 2,
the sound was monitored through a 2.4 GHz wireless phone operating in
intercom mode. To confirm that the phone itself did not cause
interference, the cable TV signal level was reduced 5 dB below the level
used in the interference tests. The phone handset was then moved to
various locations in contact (plastic-to-plastic) with the case TV
receiver housing, with particular emphasis in regions near the location
of the RF input to the TV, while monitoring the TV picture and sound for
signs of interference. No interference effect was observed.

With the cable signal level returned to the level used for interference
testing, the OFDM transmit signal level was increased in one-dB steps
while monitoring the sound from the TV for about 4 seconds at each step.
If an audio dropout was observed, the sound was monitored for an
additional period of about 20 seconds. If dropouts were found to last
less than about 50 percent of the observation period, the interference
level was increased another 1 dB until a sound dropout exceeding 50
percent was observed. At that point, the transmit level was measured. In
most cases sound was present continuously during the 4 seconds of
monitoring for one amplitude step, but it dropped out completed (based
on about 20 seconds of monitoring) on the next step. In a few cases
sound dropped out and back in during the 20-second monitoring, but was
absent well over 50% of the time.

The interference amplitude at which greater than 50 percent loss of
sound occurred was then known to be between the measured level and the
previous step, 1 dB lower; consequently, 0.5 dB was subtracted from the
measured power to obtain the nominal threshold at which sound loss
exceeds 50 percent.

Interference threshold measurements based on loss of sound were
performed as a matter of convenience, though the actual parameter of
interest is the undesired signal level at the threshold of visibility
(TOV) of picture degradation. Because of the cliff effect that is
observed with DTV systems, the difference between the TOV level and the
level that causes complete loss of picture and sound was expected to be
relatively small. For ATSC 8-VSB systems, this difference is about 1
dB.[^14] Since the 256-QAM system used for the digital cable TV tests
could have exhibited a different slope to its cliff from that of the
8-VSB system, measurements were performed to determine the difference in
interference level at TOV versus that at loss of sound. The measurements
were performed using receiver I1 with the desired signal level specified
earlier in this chapter and with the interfering signal summed with the
desired signal by means of a signal combiner (*i.e.*, the test was
conducted rather than radiated). The undesired signal level was adjusted
in 0.1-dB steps to determine thresholds. Results were as follows:

1.  Interference level at 50 percent loss of sound is 0.9 dB above that
    at TOV;

2.  Interference level at complete loss of sound is 1.1 dB above that at
    TOV. The picture is also completely lost at this point.

Based on these results an additional 1 dB was subtracted from the
interference power levels to provide an estimate of the interference
level at the threshold of visibility (TOV) of picture degradation.

The level was then calibrated for splitter and cable attenuation
imbalance and for antenna gain (-1.1 dBi) to obtain an estimate of
effective isotropic radiated power (EIRP) at TOV.

### Test Conditions

At each site and separation distance, several measurements of
interference thresholds were performed while varying the parameters
described below.

#### Transmit Polarization {#transmit-polarization .unnumbered}

All tests were performed for two different polarizations of the transmit
antenna---vertical and horizontal.

#### Transmit Antenna Height {#transmit-antenna-height .unnumbered}

The reflection of the interfering signal from the ground can combine
with the direct-path signal in a way that either enhances or partially
cancels the direct signal depending on the phase shift occurring on
reflection from the ground and on the difference in path length between
the bounce path and the direct path, in wavelengths. Given sufficient
time, tests could be performed over a range of transmit antenna heights
to determine the minimum interference threshold that occurs as a
function of height; however, in order to reduce the number of
measurements to a manageable level while still attempting to ensure that
the measurements were not exclusively performed under conditions that
caused signal cancellation by the ground reflection, measurements were
performed at two antenna heights. The heights were selected so that the
path length difference between the direct and the ground-reflected paths
was approximately half-wavelength greater for the higher antenna height
as compared to the lower antenna height;[^15] however, for tests at site
2 (the townhouses) at a 10-meter separation distance, the tripod on
which the antenna was mounted was not tall enough to achieve this
condition.[^16] In that case, the higher antenna height resulted in only
a 0.2-wavelength increase in path length difference relative to the
lower antenna height.

#### TV Orientation {#tv-orientation .unnumbered}

For tests at site 2, the TV under test was oriented so that rear of the
TV faced the interfering source antenna. At site 1, two orientations
were used: rear facing the source and front facing the source. At
site 0, two additional orientations were tested.

#### Lateral Offset {#lateral-offset .unnumbered}

At site 2, the wall separating the interferer from the TV is believed to
have contained vertical metal channels and a diagonal metallic strip, as
described in Table 2-1. These conductive components can be expected to
affect propagation through the wall in ways that may vary with
horizontal positioning of the interfering source antenna and the TV. In
addition, the site included a wrought iron bookcase near the propagation
path.

To provide an indication of these effects, tests at that site with one
of the TVs were performed for several lateral offset positions (parallel
to the wall separating the interferer from the TV) of the antenna and of
the TV.

#  TEST RESULTS

A total of 108 measurements of interference thresholds were made. Each
was converted to an EIRP corresponding to the threshold of visibility
(TOV) of picture degradation, as described in the previous chapter. In
addition to other measurement tolerances, the reported values are
subject to a tolerance of\
+/-0.5 dB due to the 1-dB step size used in identifying thresholds.

## Overview of Measurements Under Common Conditions Across the Test Sites

At all three test sites, measurements were performed using two heights
and two polarizations of the transmit antenna, with the test TV oriented
so that the interfering emission was directed at the back of the
receiver. We will refer to the configurations for those
measurements---four at each separation distance tested at each site for
each TV---as the common conditions of the tests, though we note that the
pair of antenna heights tested differed among the sites, as was shown in
Table 2-2.

In addition to these common test conditions, tests were performed at
some sites using other conditions including other aspect angles for the
TV and lateral offsets of the TV and of the transmit antenna. In this
section we discuss only the measurements made under the "common"
conditions.

Table 3-1 summarizes the measurements corresponding to maximum
susceptibility (minimum threshold EIRP) across two antenna heights and
two polarizations with the interfering emission coming from the rear of
the TV receiver (*i.e.*, the common conditions).

Interference thresholds occurred at EIRPs as low as 6.3 dBm for the
two-meter separation distance and as low as 15.3 dBm for the ten-meter
separation distance.[^17]

> []{#__RefHeading___Toc173222006 .anchor}Table 3‑4. Minimum EIRP at TOV
> Across Two Antenna Heights and Two Polarizations for Interference to
> TVs from the Rear

  -------------- ------------- --------------- ----------------- ----------------
                               **Minimum EIRP                    
                               at TOV (dBm)                      
                               with Specified                    
                               Wall Between                      
                               the Interferer                    
                               and the TV                        
                               Receiver^A^**                     

  **Separation   **TV**        **Site 0 ---\   **Site 1 ---      **Site 2 ---\
  Distance (m)**               No Wall**       Exterior          Inter-Unit\
                                               Single-Family     Townhouse Wall**
                                               House Wall**      

  2              D3                            13.4              8.5

  2              F3                            9.4               14.4

  2              I1            6.3             6.3               16.4^B^

  **2**          **Minimum**                   **6.3**           **8.5**

  10             D3                            21.2              24.2

  10             F3                            15.3              15.4

  10             I1                            17.4              \>24.2

  **10**         **Minimum**                   **15.3**          **15.4**
  -------------- ------------- --------------- ----------------- ----------------

> Notes
>
> ^A^ In addition to other measurement tolerances, the EIRP values are
> subject to +/- 0.5 dB error due to 1-dB step size used in identifying
> thresholds.
>
> ^B^ The values in the table correspond to minimum threshold EIRP
> across two polarizations and two heights of the interferer for
> interference arriving directly from the rear of the TV receiver. In
> addition, measurements were performed on TV I1 at site 2 for 2 meters
> separation with two lateral offset positions for the transmit antenna
> and one lateral offset position of the TV receiver in order to observe
> the effects of metallic components of the wall construction and of the
> wrought-iron bookcase. Those measurements resulted in a 3-dB lower
> minimum threshold EIRP for receiver I1 than that shown in the table
> (*i.e.* greater susceptibility to interference).

## Detailed Results for All Measurement Conditions

Each of the measurements presented in the previous table corresponded to
the lowest of four measurements across two antenna heights and two
polarizations for interference from the rear of the TV receiver. The
tables that follow contain all of the EIRP measurements underlying those
results, as well as additional EIRP measurements corresponding to other
conditions that were not included in the previous table.

### Site 0: No Wall

Table 3-2 shows the results of all measurements performed at site 0. The
site-0 tests involved only one TV receiver and one separation distance.
The tests were performed after the site-1 measurements, outside of the
site-1 residence, as a basis for comparison. The measurements were
performed for four aspect angles of the TV: interference from the front
of the TV; interference from the back of the TV; TV rotated 45 degrees
counter-clockwise from the rearward aspect (*i.e.*, interference from
the right rear of the TV as viewed from the front); TV rotated 90
degrees counter-clockwise from the rearward aspect (*i.e.*, interference
from the right side of the TV). The tested TV had its RF input on the
right side, which suggests that the tuner was also on that side. The
rear aspect exhibited the greatest susceptibility to interference among
the aspects that were tested.

[]{#__RefHeading___Toc173222007 .anchor}Table 3‑5. Measurements at Site
0 With 2 Meters Separation

  ---------------- --------------- ---------- ---------- ---------- ---------- ----------
                                   **EIRP at                                   
                                   TOV                                         
                                   (dBm)**                                     

  **Tx Antenna                     **0.97**   **0.97**   **1.47**   **1.47**   
  Height (m)**                                                                 

  **Tx                             **H**      **V**      **H**      **V**      **Min**
  Polarization**                                                               

  **TV**           **Aspect**                                                  

  I1               Front           21.2       \>25.1     16.2       20.2       **16.2**

  I1               Rear            20.3       10.3       12.4       6.3        **6.3**

  I1               45deg CCW       11.3       10.3       7.4        8.4        **7.4**

  I1               90deg CCW       11.3       14.3       15.3       14.3       **11.3**

  **Overall Min**                                                              **6.3**
  ---------------- --------------- ---------- ---------- ---------- ---------- ----------

### Site 1: Single-Family Home Wall

Table 3-3 shows the results of all measurements at site 1 for two meters
separation between the transmit antenna and the TV receiver. The
measurements were performed on three TV receivers for front and rear
aspects of the TV. The individual threshold EIRP measurements at site 1
averaged 2.1 dB lower than those at site 0 for the seven measurements at
corresponding conditions. This result is unexpected, given that the wall
attenuation at site 1 was expected to result in higher threshold EIRP
values at site 1. We note, however, that differences in the multipath
environment, such as a possible difference in effective depth of the
ground planes could cause measurement differences at fixed antenna
heights. Though the individual measurements differed from most of the
corresponding measurements at site 0, the overall minimum threshold EIRP
(*i.e.*, maximum susceptibility to interference) at site 1 matched that
measured at site 0.

[]{#__RefHeading___Toc173222008 .anchor}Table 3‑6. Measurements at Site
1 With 2 Meters Separation

  ---------------- -------------- ---------- ---------- ---------- ---------- ------------
                                  **EIRP at                                   
                                  TOV                                         
                                  (dBm)**                                     

  **Tx Antenna                    **0.97**   **0.97**   **1.47**   **1.47**   
  Height (m)**                                                                

  **Tx                            **H**      **V**      **H**      **V**      **Min**
  Polarization**                                                              

  **TV**           **Aspect**                                                 

  D3               Front          \>25.1     \>25.1     \>25.1     \>25.1     **\>25.1**

  D3               Rear           \>25.1     13.4       19.3       13.4       **13.4**

  F3               Front          14.4       19.3       10.3       21.3       **10.3**

  F3               Rear           11.3       15.3       19.3       9.4        **9.4**

  I1               Front          16.3       \>25.1     15.3       25.1       **15.3**

  I1               Rear           14.3       7.4        7.4        6.3        **6.3**

  **Overall Min**                                                             **6.3**
  ---------------- -------------- ---------- ---------- ---------- ---------- ------------

Table 3-4 shows the results of all measurements at site 1 for ten meters
separation distance. The minimum threshold EIRP at this distance was
9-dB higher than that at two meters separation.

[]{#__RefHeading___Toc173222009 .anchor}Table 3‑7. Measurements at Site
1 With 10 Meters Separation

  ---------------- -------------- ---------- ---------- ---------- ---------- ------------
                                  **EIRP at                                   
                                  TOV                                         
                                  (dBm)**                                     

  **Tx Antenna                    **0.97**   **0.97**   **2.39**   **2.39**   
  Height (m)**                                                                

  **Tx                            **H**      **V**      **H**      **V**      **Min**
  Polarization**                                                              

  **TV**           **Aspect**                                                 

  D3               Front          \>25.1     \>25.1     \>25.1     \>25.1     **\>25.1**

  D3               Rear           \>25.1     25.1       21.2       22.2       **21.2**

  F3               Front          16.3       \>25.1     15.3       25.1       **15.3**

  F3               Rear           \>25.1     18.4       15.3       18.3       **15.3**

  I1               Front          \>25.1     \>25.1     \>25.1     25.1       **25.1**

  I1               Rear           17.4       25.1       20.3       24.2       **17.4**

  **Overall Min**                                                             **15.3**
  ---------------- -------------- ---------- ---------- ---------- ---------- ------------

### Site 2: Inter-Unit Townhouse Wall

Table 3-5 shows the results of all measurements at site 2 for two meters
separation between the transmit antenna and the TV receiver. The
measurements were performed on three TV receivers, but with only one
aspect angle---interference from the rear.

[]{#__RefHeading___Toc173222010 .anchor}Table 3‑8. Measurements at Site
2 With 2 Meters Separation

  ---------------- ------------ ---------- ---------- ---------- ---------- ---------- ------------- --------
                                **EIRP at                                                            
                                TOV                                                                  
                                (dBm)**                                                              

  **Tx Antenna                  **0.88**   **0.88**   **1.26**   **1.26**              **Lateral     
  Height (m)**                                                                         Offset        
                                                                                       (inches)**    

  **Tx                          **H**      **V**      **H**      **V**      **Min**                  
  Polarization**                                                                                     

  **TV**           **Aspect**                                                          **Antenna**   **TV**

  D3               Rear         10.4       12.5       9.4        8.5        **8.5**    0             0

  F3               Rear         20.3       17.4       14.4       15.4       **14.4**   0             0

  I1               Rear         \>24.2     24.2       17.4       16.4       **16.4**   0             0

  I1               Rear         \>24.2     22.3       13.4       18.4       **13.4**   32            0

  I1               Rear         \>24.2     16.4       19.4       \>24.2     **16.4**   -32           0

  I1               Rear         \>24.2     20.3       17.4       15.4       **15.4**   0             16

  I1               Rear         19.4       21.3       18.4       20.3       **18.4**   32            16

  **Overall Min**                                                           **8.5**                  
  ---------------- ------------ ---------- ---------- ---------- ---------- ---------- ------------- --------

Because of the vertical metal channels that are believed to be a part of
the construction of the firewall between the two townhouses and because
of the wrought iron bookcase near the television receiver, one receiver
was tested for combinations of lateral offsets of the antenna and of the
TV from the centerline used in the primary tests. The lateral offsets
shown in the table are specified in inches to the right of the
centerline from the antenna to the TV receiver in their initial
positions, as viewed from behind the antenna. Thus, the +16-inch offset
shown for the TV corresponds to a 16-inch offset to the right as viewed
from the antenna, but to the *[left]{.underline}* as viewed from the
front of the TV; this corresponds to a position farther from the
bookcase. Two of the four new offset combinations that were tested
yielded lower minimum interference thresholds than the zero-offset
results by amounts of 1 dB and 3 dB (*i.e.*, 15.4 and 13.4 dBm relative
to 16.4 dBm); one yielded a higher minimum offset by 2 dB.

The minimum threshold EIRP (corresponding to maximum susceptibility to
interference) measured at site 2 was about 2 dB higher than that
measured at site 1. This may suggest that the inter-unit townhouse wall
exhibited higher attenuation than the exterior house wall, although the
caveats presented in the next section should be observed. The townhouse
wall is believed to include 1.5 inches more gypsum drywall thickness
than the exterior house wall, as well as more closely-spaced studs (12
inches versus 16 inches), in addition to having metal channels that were
not present in the exterior house wall. The exterior house wall included
sheathing and vinyl siding not present in the townhouse wall.

Table 3-6 shows the results of all measurements at site 2 for ten meters
separation distance. At 10 meters distance, the higher of the two
transmit antenna heights was limited by the tripod height, which, in
turn, limited the change in direct-path versus ground-reflected path
between the two heights to only 0.2 wavelength instead of the
half-wavelength change that was desired and was achieved for the other
tests. This creates the possibility that, for a given TV, the
measurements at [both]{.underline} heights could have been in a region
of partial cancellation of the direct path by the bounce path signal.

[]{#__RefHeading___Toc173222011 .anchor}Table 3‑9. Measurements at Site
2 With 10 Meters Separation

  ---------------- -------------- ---------- ---------- ---------- ---------- ------------
                                  **EIRP at                                   
                                  TOV                                         
                                  (dBm)**                                     

  **Tx Antenna                    **0.88**   **0.88**   **1.26**   **1.26**   
  Height (m)**                                                                

  **Tx                            **H**      **V**      **H**      **V**      **Min**
  Polarization**                                                              

  **TV**           **Aspect**                                                 

  D3               Rear           \>24.2     24.2       \>24.2     \>24.2     **24.2**

  F3               Rear           20.3       15.4       \>24.2     21.3       **15.4**

  I1               Rear           \>24.2     \>24.2     \>24.2     \>24.2     **\>24.2**

  F3 Repeat        Rear           20.3       21.3       \>24.2     22.3       **20.3**

  **Overall Min**                                                             **15.4**
  ---------------- -------------- ---------- ---------- ---------- ---------- ------------

Based on the minimum measurements across the two antenna heights and two
polarizations, the interference threshold of receiver F3 was found to be
only 1 dB greater at 10 meters than at 2 meters. This difference was
unexpectedly small. After all other tests had been completed, the
10-meter tests of F3 were repeated. The second set of tests, shown in
Table 3-6 as "F3 Repeat", produced higher interference thresholds for
two of the test conditions than the corresponding thresholds in the
first set of measurements. It is assumed that the change is due to
slightly different positioning of the transmit antenna and of the TV,
because both the tripod and the TV cart had been moved to the 2-meter
separation distance between the two sets of 10-meter measurements on
receiver F3.

Across the three TVs, the minimum threshold EIRP at 10 meters was 7-dB
higher than that at two meters separation. The 10-meter minimum EIRP
thresholds at site 2 closely matched those at site 1.

### Median Results

Though median results are not generally of direct interest where
interference probabilities must be reduced to low levels, the median
measurement results are summarized here for completeness.

Measurements with interference arriving from the rear of the TV
comprised 72 of the 108 measurements performed in this study. Of the
rear aspect measurements, 44 were at 2 meters distance and 28 were at
10 meters distance. The rear aspect measurements were performed on only
one TV at site 0 and on all three TVs at sites 1 and 2. The median
interference threshold EIRP was 16.9 dBm at 2 meters and 24.2 dBm at
10 meters.

Front aspect measurements were performed on one TV at site 0, three TVs
at site 1, and none at site 2, for a total of 16 measurements at 2
meters distance and 12 measurements at 10 meters distance. Median
thresholds for interference from the front were 21.2 dBm and \>25.1 dBm
at 2 and 10 meters, respectively, though we note that interference at a
distance of 2 meters from a device in a neighboring residential unit is
unlikely to occur with the front aspect of the TV.

## Variability of Direct Pickup Vulnerability

The propagation loss between the antenna and the TV receiver point of
vulnerability (presumably the tuner module) is expected to be a function
of---among other things---the phase of the arriving ground-reflected
wave relative to the direct-path wave.[^18] This phase difference
depends on the horizontal separation distance as well as on the heights
of the transmit antenna and of the TV receiver point of vulnerability
above the effective ground plane.

In measuring *emission* levels of a device---as opposed to
susceptibility to interference---typical procedures call for varying the
height of the receive antenna to find the maximum response. In the
*interference susceptibility* tests presented here, the transmit antenna
height was varied, but only among two heights for each propagation
distance. As a result of testing at only two heights, we cannot know how
closely we achieved a propagation condition that maximized the
interference potential. Furthermore, the difference between the observed
interference levels and those corresponding to a true maximum
interference susceptibility across antenna heights can be expected to
vary: (1) among the TV receivers, since the height of the point of
interference vulnerability probably varies among the tested TVs; (2)
among the test sites, since antenna heights differed among some of the
sites and the depths of the effective ground plane may differ among the
sites; and, (3) among the separation distances, since the
bounce-versus-direct-path propagation path length difference varies with
separation distance. Additionally, each test site had its own other
sources of multipath reflections (such as the bookcase at the townhouse
location.). These variations should be recognized when comparing test
results to estimate differences in wall attenuation, differences in TV
susceptibilities, and differences in propagation loss for 10 meters
versus 2 meters separation distances.

We note, for example, that receiver D3 appears to be the *least*
susceptible to interference among the three TVs by a margin of about 4
dB based on tests at site 1 at both separation distances (Table 3-1);
however, in the two-meter separation tests at site 2, receiver D3
exhibited the *greatest* susceptibility to interference among the three
receivers---by a 5‑dB margin if all measurements are included, or by a
6-dB margin based on only the comparable measurements (*i.e.*,
measurements with zero lateral offset). This apparent relative increase
in susceptibility of receiver D3 may be a result of variations caused by
the effects discussed in the preceding paragraph. Alternatively, we note
that the wrought iron bookcase located to the right of the TV during the
two-meter tests at site 2 could have altered the effective arrival
direction of the interference to a direction from which that TV is more
susceptible to interference.

[^1]: Society of Cable Telecommunications Engineers, "Digital Cable
    Network Interface Standard", ANSI/SCTE 40-2004, p.1, 17.

[^2]: The Commission's *First Report and Order and Further Notice of
    Proposed Rule Making* (FCC 06-156), adopted October 12, 2006,
    proposed permitting [fixed]{.underline} white space devices to
    operate at EIRP levels up to 36 dBm (1 watt power with up to 6 dBi
    antenna gain). The earlier *Notice of Proposed Rule Making* (FCC
    04-113), adopted May 13, 2004, proposed a peak EIRP limit of 26 dBm
    (100 mW peak power with up to 6 dBi antenna gain) for
    [portable]{.underline} devices. Final power limits have not yet been
    determined.

[^3]: For 8-VSB signals, D/U rejection ratio for co-channel interference
    is about 15 dB. Median D/U rejection ratio for first-adjacent
    channel interference of 8 DTV receivers measured by the FCC
    Laboratory was about -39 dB---a difference of 54 dB. First-adjacent
    channel D/U ratio is from Appendix A of:\
    Stephen R. Martin, "Interference Rejection Thresholds of Consumer
    Digital Television Receivers Available in 2005 and 2006", Report
    FCC/OET 07-TR-1003, March 30, 2007.

[^4]: Stephen R. Martin, "Tests of ATSC 8-VSB Reception Performance of
    Consumer Digital Television Receivers Available in 2005", Report
    FCC/OET TR 05-1017, \<SHVERA Study\>, November 2, 2005.

[^5]: In the 2005 study, laboratory tests were performed to characterize
    the over-the-air DTV reception performance of 28 consumer receivers
    that were selected as representative of the products that were on
    the market in 2005. Since the tests involved 8-VSB signals (the DTV
    signal format used for broadcast in the United States) rather than
    QAM signals and did not include direct pickup interference, the
    results of that testing are not directly related to the work
    performed for the current report. Nevertheless, the relative
    performance in those earlier tests of the three receivers selected
    for the current study may be of interest as an indication of overall
    quality or level of technological advancement. In terms of
    multipath-handling capability the 28 receivers were found to fall
    primarily into two performance tiers; receivers D3 and I1 were among
    the ten receivers fell into the upper performance tier, while
    receiver F3 was among the majority that fell into the lower tier. In
    terms of ability to receive weak over-the-air DTV signals in UHF,
    receivers I1, F3, and D3 ranked 2^nd^, 5^th^, 22^nd^, respectively,
    among the 28 tested receivers, where first would represent the best
    performing receiver. The difference in sensitivity between the 2^nd^
    and 22^nd^ ranked receivers was 1.7 dB. Thus, the selected receivers
    represent a reasonable range of performance levels among the
    receivers tested in 2005.

[^6]: The metal garage door was in the open position during the tests,
    as shown in Figure 2-2.

[^7]: This device was an Agilent 4438C vector signal generator equipped
    with Signal Studio for DVB software.

[^8]: Calibration was performed by setting the vector signal generator
    to produce a CW signal at the center frequency to be used for the
    OFDM transmission; the signal level at the output of each cable from
    the splitter was measured while the other cable was terminated in 50
    ohms.

[^9]: Since no CableCARD was used in these tests, reception was limited
    to unencrypted (clear QAM) channels.

[^10]: Society of Cable Telecommunications Engineers, "Digital Cable
    Network Interface Standard", ANSI/SCTE 40-2004, p.1, 17.

[^11]: Power levels were measured by disconnecting the 75-ohm cable at
    the TV RF input and connecting it through a 75-ohm to 50-ohm
    impedance matching pad connected directly to a spectrum analyzer.
    Band power in the 6-MHz TV channel was measured after power
    averaging by the spectrum analyzer; the measurement was then
    corrected for loss of the impedance matching pad.

[^12]: Agilent Signal Studio for DVB software was used to create the
    waveform for an Agilent 4438C vector signal generator.

[^13]: Cable channel frequencies can be found in "Cable Television
    Channel Identification Plan", CEA Standard CEA-542-B, July 2003

[^14]: \<SHVERA Study\>, p.1-2 to 1-3.

[^15]: Ideally, the path-length difference would be computed based on
    heights of the center of the transmit antenna and the center of the
    point of interfering signal ingress into the TV receiver, and
    heights would be measured relative to the effective ground plane. In
    practice, the calculation was based on height of the center of the
    transmit antenna and the average height of the RF inputs of the
    three TVs (presumed to be near the average height of the tuners)
    above the floor surface (e.g., top of the carpet at site 2).

[^16]: Ceiling height was too low to accommodate the antenna mast that
    was used at sites 0 and 1.

[^17]: The Commission's *First Report and Order and Further Notice of
    Proposed Rule Making* (FCC 06-156), adopted October 12, 2006,
    proposed permitting fixed white space devices to operate at EIRP
    levels up to 36 dBm (1 watt power with up to 6 dBi antenna gain).
    The earlier *Notice of Proposed Rule Making* (FCC 04-113), adopted
    May 13, 2004, proposed a peak EIRP limit of 26 dBm (100 mW peak
    power with up to 6 dBi antenna gain) for portable devices. Final
    power limits have not yet been determined.

[^18]: This discussion is presented from the perspective that leakage
    into the TV receiver's tuner can be approximated as occurring at a
    single discrete location. In reality, the leakage may be more
    complex than that.