As shown in Figure 3, even with low levels of continuously
induced 60 Hz voltages on their digital subscriber
line (DSL) circuits that are used to provide the internet
and U-verse TV services, a broad range of induced power
harmonic noise frequencies could override on the induc-
tion to amplify other minor or severe impairments
causing severely detrimental video effects, such as
pixelation, freezing, high forward error correction (FEC)
counts, and reinitializations (REINITs) causing loss
of sync. Other internet and IPTV service providers
(e.g., Comcast, Charter Communications, CenturyLink)
might experience the same impairments per the U-verse
TV example.
It has been determined in tests made at Fluke Labs
that power influence (PI) levels exceeding 92 decibels
above reference noise with C-message weighting (dBrnC)
causes loss of sync between the IPTV video equipment
located at both ends of the circuit. It is also known that
excessive levels of impulse noise can cause pixelation and
picture freezing, which can force the length of the circuit
to be shortened to obtain acceptable service. However,
induced longitudinal voltages can cause gateway devices
and set top boxes (STBs) to “lock-up,” thereby requiring
rebooting or momentarily being unplugged in order to
release the surge of electricity that caused the problem.
Higher levels of induced currents/voltages can even
damage the video equipment ports, gateways, and STBs,
36 I ICT TODAY
Active Line Noise
BAN: 1022951525 Target RG: 290711056782
Frequency(kHZ)
Tone(Tone allocation:U0 6-32, D1 33-868, U1 869-1205, D2 1206-1971)
ALN — MASK(1% worst case 5-VDSL crosstalk)
0
-80
-90
-100
-110
-120
-130
-140
500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 7,000 7,500 8,000 8,500
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Noise (dBm/Hz)
FIGURE 3: Induced 60Hz/noise effects on VDSL circuits.
causing unnecessary outages, excessive technician
repair visits, and the additional expense of replacing
the units.
There are similar EMI issues of less magnitude in
the inside wiring from the gateway device to the STB/
DVR, especially due to the use of unshielded Cat 5
or Cat 6 cabling. Compact fluorescent lights (CFLs),
treadmills, light dimmer switches, and a host of other
harmonic-producing electrical loads can create highfrequency
electrical noise problems that can affect the
signal quality and customer QoE, leading to mysterious
circuit malfunctions that are frustrating to find
and troubleshoot.
This same phenomenon occurs in LANs, even though
the cable infrastructures are typically shorter in length
than what is found in DSL video streaming services and
are generally inside buildings. Buildings are notorious
locations for sources of EMI generation. It takes only one
antenna to pick up EMI, especially when most of the
cables used are unshielded twisted pair (UTP) as shown
in Figure 4. As the 100 meter (328 ft) maximum design
length of Ethernet circuits is approached, similar QoE
issues can start to occur with video streaming applications
and WLANS. Now that circuits are being allowed
to exceed these lengths due to the use of extenders, there
is a substantially higher risk of experiencing problems
from EMI.