**Peer Review Panel Report**

**On**

**OET Report FCC/OET 07-TR-1005**

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

Peer Reviewers:

George Dillon, EB

James Higgins, EB/Columbia

Martin Liebman, WTB

Doug Miller, EB/Atlanta

Mary Shultz, WTB

**Background:**

This report contains the peer review of OET Report FCC/OET 07-TR-1005,
entitled "Direct-Pickup Interference Tests of Three Consumer Digital
Cable Television Receivers Available in 2005." This study presents the
results of *in situ* measurements of the interference susceptibility of
three Digital Cable Ready (DCR) TV receivers to direct pickup
interference when receiving digital cable service. The purpose of the
study was to assess the vulnerability of a very small sample of digital
cable ready TV receivers to direct pickup of undesired emissions within
the channel width of a digital cable signal to which the TV was tuned.
The study was undertaken to obtain some understanding of direct pickup
interference susceptibility of such receivers within the limited time
frame of the Commission's proceeding on unlicensed operation in the TV
broadcast bands, ET Docket NO. 04-186.

Peer review of the report was performed as required under the OMD
Information Improvement Act for influential scientific and engineering
studies. The review panel was made up of five engineers, three from the
Enforcement Bureau and two from the Wireless Telecommunications Bureau.
The review panel analyzed and discussed various subject areas in the OET
report, both independently and jointly. Specifically, as requested in
the OET memo, the review panel addressed the following:

1.  Whether the type of receivers chosen for the study was appropriate,
    given the limited scope of this test, and provides useful
    information in conjunction with other data submitted into the record
    to better understand the potential impact of direct-pickup
    interference to digital cable ready receivers available to consumers
    for reception of digital cable television signals;

2.  Whether the scope of testing in terms of the direct pickup
    interference conditions examined with respect to digital cable
    signals was appropriate; and,

3.  Whether the measurement methodologies used to examine the receivers'
    susceptibility to direct pickup of interference on digital cable
    channels were appropriate and the tests were properly conducted
    consistent with those methodologies.

The response of the review panel is presented below for each question
shown above:

**1) Whether the type of receivers chosen for the study was appropriate,
given the limited scope of this test, and provides useful information in
conjunction with other data submitted into the record to better
understand the potential impact of direct-pickup interference to digital
cable ready receivers available to consumers for reception of digital
cable television signals.**

The report, in the Executive Summary, acknowledges the limited scope of
the test. The review panel generally feels that the sample of TVs chosen
for the study, which included recent models from different
manufacturers, was appropriate, given the test's limited scope. The TV
samples tested were selected from among the DTV receivers that were used
in a 2005 study by the Commission's laboratory of DTV reception
performance. It would have been useful for the report to have given some
indication of where the three models tested ranked in those tests
(ideally, they would have represented the median range of tuner
performance). The three TVs were 2005-model flat-panel LCD digital TVs
of different brand names. All had the DCR logo, indicating that they
were "Digital Cable Ready." As such, all could accept a CableCARD^TM^ to
allow premium digital cable channels to be decrypted.

In the opinion of the review panel the televisions tested are
representative of a limited study and cross-section of the digital
televisions currently in use by consumers. The TVs are "Digital Cable
Ready" and have the capability of accepting a CableCARD^TM^ as would
many TVs in use by consumers today. Thus, given that the tests were
performed on newer models in a real-world environment, the panel feels
that the tests was able to provide some indication of the interfering
power levels at which current digital TV owners might detect direct
pickup interference.

The review panel recognizes that there were time constraints, which
prevented the acquisition and testing of newer TVs, but the panel
believes that if there had been more time to conduct the test, it would
have been beneficial to have tested newer TVs (i.e., 2006 and 2007
models could have contained improvements that might have made them less
vulnerable to interference). The review panel also thinks that if more
TVs could have been acquired, then it would have been beneficial if at
least one or two of the TVs were plasmas (instead of only LCD TVs).

**2) Whether the scope of testing in terms of the direct pickup
interference conditions examined with respect to digital cable signals
was appropriate.**

Given the study's time limitations, the review panel believes that the
scope of the testing was appropriate and yielded measurements of direct
pickup interference levels that could interfere with cable signals in a
real-world environment. The review panel also feels that the study can
provide some insight into the mitigating factors that might affect
direct pickup interference in that environment.

The tests were conducted on a single 256-quatdrature amplitude
modulation (256-QAM) digital cable TV signal. The review panel generally
agrees that testing a single unencrypted "clear QAM" channel provides
interference measurements that can cause a cable customer to experience
direct pick-up interference in some instances. However, the review panel
feels if there had been more time to conduct the study, then a more
complete picture of the affects of direct pickup interference on cable
viewing could have been made by, for example, testing on multiple cable
channels, on encrypted channels, and on high definition cable TV
signals.

For these tests, the cable TV signal was adjusted to a signal level near
the minimum level specified by the "Digital Cable Network Interface
Standard" for the "input terminals of the first device located on the
subscriber's premises." If there had been additional time for testing,
the review panel thinks that conducting the tests at one or more higher
signal levels would have provided a more complete picture of the
susceptibility of DCR TVs to direct pick-up interference (e.g., TVs
could have been tested at the median level prescribed by the standard,
which might have provided a more typical measure of the direct pickup
interference vulnerability of DCR TV receivers).

Measurements were performed at three test sites. 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. The review panel thinks that, given the limited
time available for this study, the test sites were appropriate to
represent a reasonable sample of the actual interference situations that
cable customers might experience. The tests were performed in complex
multipath propagation environments that mirror actual environments where
direct pickup interference would be experienced. However, the panel
believes that if additional time is available in the future,
measurements should be taken in an apartment/condo building -- whose
units (adjacent, above, and below) are likely to be separated by
building materials different than those found in a townhouse or a single
family house.

Although the sites were realistic, the review panel feels that more
thorough information on the interference environment would be helpful in
determining all of the mitigating factors that could affect the
measurements. For example, at test site 2, the report could include
information on the position of the large metallic garage door (up or
down) and note the location of metal tools and a garage door opener
since all of these items could affect the measurements. Also, because
the report acknowledges that the presence of electrical wiring and the
location of metal items in the walls can affect propagation, the review
panel feels that it's important to provide a clear basis for the make-up
of the walls. For example, the review panel thinks that verifying the
location of items within the wall by use of a stud sensor that can
detect metal or electrical wiring or some other method would be
beneficial.

The report states that one element missing from the garage wall relative
to the exterior residence wall was insulation. The reports maintains
that *"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."* The review
panel agrees that one would not normally expect insulation to be a
factor, but insulation can be foil-backed rather than kraft-backed
(paper). And so, in the opinion of the review panel, a better
description of the wall construction, including insulation, sheathing,
wiring, etc. would be useful, as well as a citation, if available,
confirming that such materials will not attenuate signals. Ideally, in a
larger study, actual testing of an insulated outside wall would be
conducted to provide certainty regarding the affect of insulation on
interference measurements.

In these tests, most measurements were performed with the interfering
device located behind the TV receiver, but some measurements were
performed with the interfering device located in front of the TV, and a
few measurements were performed at other aspect angles and at various
offsets with respect to the TV. The report indicates that the number of
measurements was limited to keep the study at a manageable level.
Considering the limited time that was available for this test, the
review panel feels that the number aspect angles and offsets tested were
sufficient, but in a larger study, the review panel thinks that it would
be useful to measure at least eight different angles around the
television to examine a greater number of possible spatial
relationships, which might exist between an interfering source and a TV.
Although the panel recognized the need to employ a plastic TV cart so as
not to introduce extraneous RF reflections into the TV, the panel
believes that in a larger study, tests could be done with the TV
situated on carts made of different materials (carts are available to
consumers today, which are made of various, different materials,
including metal).

In general, the review panel feels that, given the limitations of this
study, the scope of the study was appropriate to provide a basic
understanding of the vulnerability of DCR TV receivers to direct pick-up
interference and to determine if there are grounds for further study. To
obtain a more complete picture of DCR TV receiver susceptibility to such
interference, the panel believes that a larger study would be needed.
Ideally, the scope of a larger test would include a larger number of
measurements, with a larger number of TVs, at more aspect angles,
distances and antenna heights, and in various different types of
buildings, with rooms containing different types of furnishings. The
review panel thinks that by taking additional measurements on more TVs
and in more environments, the variety of conditions that exist in the
real world could be better explored. We suggest that if further testing
and measurements take place, that the initial measurements be made on a
test range or anechoic chamber, where multiple interference source
angles and distances can be more fully explored.

**3) Whether the measurement methodologies used to examine the
receivers' susceptibility to direct pickup of interference on digital
cable channels were appropriate and the tests were properly conducted
consistent with those methodologies.**

The review panel believes that the measurement methodologies used in the
test were appropriate and that the tests were properly conducted
consistent with those methodologies. However, the panel believes that in
a more expansive test, where more time would be available to gather and
analyze results, certain improvements could be made in the way that
measurements were made and analyzed.

During the tests, sound from the TV receiver under test was monitored as
a basis for identifying interference. The tests were performed by a
single engineer who directly monitored the sound at sites 0 and 1. At
site 2, the sound was monitored through a 2.4 GHz wireless phone
operating in intercom mode. The interfering transmit signal level was
increased in one-dB steps while monitoring the sound from the TV. If an
audio dropout was observed, the sound was monitored for an additional
period. 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.

The review panel has no reason to believe that the sound of an audio
dropout will not be the same for all observers, and any concerns about a
single observer's ability to distinguish a dropout are mitigated by the
fact that apparently sound was present continuously during the
monitoring period for one interfering signal step, but then dropped out
completely on the next step. However, the review panel thinks that in a
more extensive study, it would be beneficial to have multiple observers,
with the results averaged.

Ideally, the test would also be structured to eliminate the need for
observers to rely on a 2.4 GHz phone to hear the sound coming from the
TV. In the opinion of the review panel, this secondary sound source
could have potentially introduced audio noise, which could have affected
the listener's ability to distinguish or determine a dropout.

The test employed a 4.8 MHz OFDM signal centered at the mid-point of
Cable Channel 70, at 501 MHz, and measurements were made on the effect
of this signal on TV channel 19, which extends from 500 to 506 MHz. The
panel believes that in a more extensive study, interfering signals of
both smaller and wider bandwidths could be employed to determine the
effects of different-sized and partially and fully overlapping
interfering signals.

The report indicates that a limited number of measurements were taken to
keep testing to a manageable level so the study could be completed in a
timely manner. However, because unexpected results can sometimes occur
when measuring radio transmissions, the panel believes that in a more
exhaustive study, more than one measurement should be taken for each
condition at each location. Finally, the reported interfering signal
levels in the Executive Summary were the lowest interfering signal
levels from among all those measured at 2 meters and 10 meters (i.e.,
6.3 dBm for 2 meters and 15.3 dBm for 10 meters). In the opinion of the
review panel, it might have more informative to indicate the median
interfering signal level measured (perhaps along with standard
deviation) in addition to the lowest measured, interfering signal level
at each distance.